PART II.

_ON THE DISTRIBUTION OF EXTINCT ANIMALS._

{107}CHAPTER VI.

THE EXTINCT MAMMALIA OF THE OLD WORLD.

Although it may seem somewhat out of place to begin the systematic treatment of our subject with extinct rather than with living animals, it is necessary to do so in order that we may see the meaning and trace the causes of the existing distribution of animal forms. It is true, that the animals found fossil in a country are very generally allied to those which still inhabit it; but this is by no means universally the case. If it were, the attempt to elucidate our subject by Palæontology would be hopeless, since the past would show us the same puzzling diversities of faunas and floras that now exist. We find however very numerous exceptions to this rule, and it is these exceptions which tell us of the past migrations of whole groups of animals. We are thus enabled to determine what portion of the existing races of animals in a country are descendants of its ancient fauna, and which are comparatively modern immigrants; and combining these movements of the forms of life with known or probable changes in the distribution of land and sea, we shall sometimes be able to trace approximately the long series of changes which have resulted in the actual state of things. To gain this knowledge is our object in studying the "Geographical Distribution of Animals," and our plan of study must be determined, mainly, by the facilities it affords us for attaining this object. In discussing the countless details of distribution we shall meet with in our survey of the zoological regions, we shall often find it useful to refer to the evidence we possess of the range of the group in question in {108}past times; and when we attempt to generalise the phenomena on a large scale, with the details fresh in our memory, we shall find a reference to the extinct faunas of various epochs to be absolutely necessary.

The degree of our knowledge of the Palæontology of various parts of the world is so unequal, that it will not be advisable to treat the subject under each of our six regions. Yet some subdivision must be made, and it seems best to consider separately the extinct animals of the Old and of the New Worlds. Those of Europe and Asia are intimately connected, and throw light on the past changes which have led to the establishment of the three great continental Old World regions, with their various subdivisions. The wonderful extinct fauna recently discovered in North America, with what was previously known from South temperate America, not only elucidates the past history of the whole continent, but also gives indications of the mutual relations of the eastern and western hemispheres.

The materials to be dealt with are enormous; and it will be necessary to confine ourselves to a general summary, with fuller details on those points which directly bear upon our special subject. The objects of most interest to the pure zoologist and to the geologist--those strange forms which are farthest removed from any now living--are of least interest to us, since we aim at tracing the local origin or birthplace of existing genera and families; and for this purpose animals whose affinities with living forms are altogether doubtful, are of no value whatever.

The great mass of the vertebrate fossils of the tertiary period consist of mammalia, and this is precisely the class which is of most value in the determination of zoological regions. The animals of the secondary period, though of the highest interest to the zoologist are of little importance to us; both because of their very uncertain affinities for any existing groups, and also because we can form no adequate notion of the distribution of land and sea in those remote epochs. Our great object is to trace back, step by step, the varying distribution of the chief forms of life; and to deduce, wherever possible, the physical changes which must have accompanied or caused such changes. {109}The natural division of our subject therefore is into geological periods. We first go back to the Post-Pliocene period, which includes that of the caves and gravels of Europe containing flint implements, and extends back to the deposit of the glacial drift in the concluding phase of the glacial epoch. Next we have the Pliocene period, divided into its later portion (the Newer Pliocene) which includes the Glacial epoch of the northern hemisphere; and its earlier portion (the Older Pliocene), represented by the red and coralline crag of England, and deposits of similar age in the continent. During this earlier epoch the climate was not very dissimilar from that which now prevails; but we next get evidence of a still earlier period, the Miocene, when a warmer climate prevailed in Europe, and the whole fauna and flora were very different. This is perhaps the most interesting portion of the tertiary deposits, and furnishes us with the most valuable materials for our present study. Further back still we have the Eocene period, with apparently an almost tropical climate in Europe; and here we find a clue to some of the most puzzling facts in the distribution of living animals. Our knowledge of this epoch is however very imperfect; and we wait for discoveries that will elucidate some of the mystery that still hangs over the origin and migrations of many important families. Beyond this there is a great chasm in the geological record as regards land animals; and we have to go so far back into the past, that when we again meet with mammalia, birds, and land-reptiles, they appear under such archaic forms that they cease to have any local or geographical significance, and we can only refer them to wide-spread classes and orders. For the purpose of elucidating geographical distribution, therefore, it is, in the present state of our knowledge, unnecessary to go back beyond the tertiary period of geology.

The remains of Mammalia being so much more numerous and important than those of other classes, we shall at first confine ourselves almost exclusively to these. What is known of the birds, reptiles, and fishes of the tertiary epoch will be best indicated by a brief connected sketch of their fossils in all parts of the globe, which we shall give in a subsequent chapter.

{110}_Historic Period._--In tracing back the history of the organic world we find, even within the limits of the historical period, that some animals have become extinct, while the distribution of others has been materially changed. The _Rytina_ of the North Pacific, the dodo of Mauritius, and the great auk of the North Atlantic coasts, have been exterminated almost in our own times. The kitchen-middens of Denmark contain remains of the capercailzie, the _Bos primigenius_, and the beaver. The first still abounds farther north, the second is extinct, and the third is becoming so in Europe. The great Irish elk, a huge-antlered deer, probably existed almost down to historic times.

_Pleistocene or Post-Pliocene Period._--We first meet with proofs of important changes in the character of the European fauna, in studying the remains found in the caverns of England and France, which have recently been so well explored. These cave-remains are probably all subsequent to the Glacial epoch, and they all come within the period of man's occupation of the country. Yet we find clear proofs of two distinct kinds of change in the forms of animal life. First we have a change clearly traceable to a difference of climate. We find such arctic forms as the rein-deer, the musk-sheep, the glutton, and the lemming, with the mammoth and the woolly rhinoceros of the Siberian ice-cliffs, inhabiting this country and even the south of France. This is held to be good proof that a sub-arctic climate prevailed over all Central Europe; and this climate, together with the continental condition of Britain, will sufficiently explain such a southward range of what are now arctic forms.

But together with this change we have another that seems at first sight to be in an exactly opposite direction. We meet with numerous animals which now only inhabit Africa, or South Europe, or the warmer parts of Asia. Such are, large felines--some closely related to the lion (_Felis spelæa_), others of altogether extinct type (_Machairodus_) and forming the extreme development of the feline race;--hyænas; horses of two or more species; and a hippopotamus. If we go a little further back, to the remains furnished by the gravels and brick-earths, we still find the same association of forms. The reindeer, the glutton, {111}the musk-sheep, and the woolly rhinoceros, are associated with several other species of rhinoceros and elephant; with numerous civets, now abundant only in warm countries; and with antelopes of several species. We also meet here with a great extension of range of forms now limited to small areas. The Saiga antelope of Eastern Europe occurs in France, where wild sheep and goats and the chamois were then found, together with several species of deer, of bear, and of hyæna. A few extinct genera even come down to this late period, such as the great sabre-toothed tiger, _Machairodus_; _Galeotherium_, a form of Viverridæ; _Palæospalax_, allied to the mole; and _Trogontherium_, a gigantic form of beaver,

We find then, that even at so early a stage of our inquiries we meet with a problem in distribution by no means easy to solve. How are we to explain the banishment from Europe in so short a space of time (geologically speaking) of so many forms of life now characteristic of warmer countries, and this too during a period when the climate of Central Europe was itself becoming warmer? Such a change must almost certainly have been due to changes of physical geography, which we shall be better able to understand when we have examined the preceding Pliocene period. We may here notice, however, that so far as we yet know, this great recent change in the character of the fauna is confined to the western part of the Palæarctic region. In caves in the Altai Mountains examined by Prof. Brandt, a great collection of fossil bones was discovered. These comprised the Siberian rhinoceros and mammoth, and the cave hyæna; but all the others, more than thirty distinct species, are now living in or near the same regions. We may perhaps impute this difference to the fact that the migration of Southern types into this part of Siberia was prevented by the great mountain and desert barrier of the Central Asiatic plateau; whereas in Europe there was at this time a land connection with Africa. Post-pliocene deposits and caverns in Algeria have yielded remains resembling the more southern European types of the Post-pliocene period, but without any admixture of Arctic forms; showing, as we might expect, that the glacial cold did not {112}extend so far south. We have here remains of _Equus_, _Bos_, _Antilope_, _Hippopotamus_, _Elephas_, _Rhinoceros_, _Ursus_, _Canis_, and _Hyæna_, together with _Phacochoerus_, an African type of swine which has not occurred in the European deposits.

It is perhaps to the earlier portion of this period that the _Merycotherium_ of the Siberian drift belongs. This was an animal related to the living camel, thus supporting the view that the _Camelidæ_ are essentially denizens of the extra-tropical zone.

PLIOCENE PERIOD.

_Primates._--We here first meet with evidence of the existence of monkeys in Central Europe. Species of _Macacus_ have left remains not only in the Newer Pliocene of the Val d'Arno in Italy, but in beds of the same age at Grays in Essex; while _Semnopithecus_ and _Cercopithecus_, genera now confined to the Oriental and Ethiopian regions respectively, have been found in the Pliocene deposits of the South of France and Italy.

_Carnivora._--Most of the genera which occurred in the Post-Pliocene are found here also, and many of the same species. Few new forms appear, except _Hyænarctos_, a large bear with characters approaching the hyænas, and _Pristiphoca_, a new form of seal, both from the Older Pliocene of France; and _Galecynus_, a fox-like animal intermediate between _Canis_ and _Viverra_, from the Pliocene of Oeninghen in Switzerland.

_Cetacea._--Species of _Balæna_, _Physeter_, and _Delphinus_ occur in the Older Pliocene of England and France, and with these the remains of many extinct forms, _Balænodon_ and _Hoplocetus_ (Balænidæ); _Belemnoziphius_ and _Choneziphius_ (Hyperoodontidæ), and _Halitherium_, an extinct form of the next order--Sirenia, now confined to the tropics, although the recently extinct _Rytina_ of the N. W. Pacific shows that it is also adapted for temperate climates.

_Ungulata._--The Pliocene deposits are not very rich in this order. The horses (_Equidæ_) are represented by the genus _Equus_; and here we first meet with _Hipparion_, in which small lateral toes appear. Both genera occur in British deposits of this age. {113}A more interesting fact for us is the occurrence of the genus _Tapirus_ in the Newer Pliocene of France and in the older beds of both France and England, since this genus is now isolated in the remotest parts of the eastern and western tropics. The genera _Rhinoceros_, _Hippopotamus_, and _Sus_, occur here as in the preceding epoch.

We next come to the deer genus (_Cervus_), which appears to have been at its maximum in this period, no less than eight species occurring in the Norwich Crag, and Forest-beds. Among the Bovidæ, the antelopes, ox, and bison, are the only forms represented here, as in the Post-Pliocene period. Passing on to the Proboscidea, we find three species of elephants and two of _Mastodon_ preserved in European beds of this period, all distinct from those of Post-Pliocene times.

_Rodentia._--In this order we find representatives of many living European forms; as _Cricetus_ (hamster), _Arvicola_ (vole), _Castor_ (beaver), _Arctomys_ (marmot), _Hystrix_ (porcupine), _Lepus_ (hare), and _Lagomys_ (pika); and a few that are extinct, the most important being _Chalicomys_, allied to the beaver; and _Issiodromys_, said to come nearest to the remarkable _Pedetes_ of South Africa, both found in the Pliocene formations of France.

_General Conclusions as to Pliocene and Post-Pliocene Faunas of Europe._--This completes the series of fossil forms of the Pliocene deposits of Europe. They show us that the presence of numerous large carnivora and ungulates (now almost wholly tropical) in the Post-Pliocene period, was due to no exceptional or temporary cause, but was the result of a natural succession from similar races which had inhabited the same countries for long preceding ages. In order to understand the vast periods of time covered by the Pliocene and Post-Pliocene formations, the works of Sir Charles Lyell must be studied. We shall then come to see, that the present condition of the fauna of Europe is wholly new and exceptional. For a long succession of ages, various forms of monkeys, hyænas, lions, horses, hipparions, tapirs, rhinoceroses, hippopotami, elephants, mastodons, deer, and antelopes, together {114}with almost all the forms now living, produced a rich and varied fauna such as we now see only in the open country of tropical Africa. During all this period we have no reason to believe that the climate or other physical conditions of Europe were more favourable to the existence of these animals than now. We must look upon them, therefore, as true indigenes of the country, and their comparatively recent extinction or banishment as a remarkable phenomenon for which there must have been some adequate cause. What this cause was we can only conjecture; but it seems most probable that it was due to the combined action of the Glacial period, and the subsidence of large areas of land once connecting Europe with Africa. The existence, in the small island of Malta, of no less than three extinct species of elephant (two of very small stature), of a gigantic dormouse, an extinct hippopotamus, and other mammalia, together with the occurrence of remains of hippopotamus in the caves of Gibraltar, indicate very clearly that during the Pliocene epoch, and perhaps during a considerable part of the Post-Pliocene, a connection existed between South Europe and North Africa in at least these two localities. At the same time we have every reason to believe that Britain was united to the Continent, what is now the German Ocean constituting a great river-valley. During the height of the Glacial epoch, these large animals would probably retire into this Mediterranean land and into North Africa, making annual migrations northwards during the summer. But as the connecting land sank and became narrower and narrower, the migrating herds would diminish, and at last cease altogether; and when the glacial cold had passed away would be altogether prevented from returning to their former haunts.

MIOCENE PERIOD.

We now come to a period which was wonderfully rich in all forms of life, and of which the geological record is exceptionally complete. Various lacustrine, estuarine, and other deposits in Europe, North India, and North America, have furnished such a {115}vast number of remains of extinct mammalia, as to solve many zoological problems, and to throw great light on the early distribution and centres of dispersal of various groups of animals. In order to show the bearing of these remains on our special subject, we will first give an account of the extinct fauna of Greece, of the Upper Miocene period; since this, being nearest to Africa and Asia, best exhibits the relations of the old European fauna to those countries. We shall then pass to the Miocene fauna of France and Central Europe; and conclude with the remarkable Siwalik and other Indian extinct faunas, which throw an additional light on the early history of the animal life of the great old-world continents.

_Extinct Animals of Greece._

These are from the Upper Miocene deposits at Pikermi, near Athens, and were collected by M. Gaudry a few years ago. They comprise ten living and eighteen extinct genera of mammalia, with a few birds and reptiles.

_Primates._--These are represented by _Mesopithecus_, a genus believed to be intermediate between the two Indian genera of monkeys, _Semnopithecus_ and _Macacus_.

_Carnivora._--These were abundant. Of _Felis_ there were four species, ranging from the size of a cat to that of a jaguar, a large _hyæna_, and a large weasel (_Mustela_). Besides these there were the huge _Machairodus_, larger than any existing lion or tiger, and with enormously developed canine teeth; _Hyænictis_ and _Lycæna_, extinct forms of Hyænidæ; _Thalassictis_=_Ictitherium_, an extinct genus of Viverridæ but with resemblances to the hyænas, represented by three species, some of which were larger than any existing Viverridæ; _Promephytis_, an extinct form of Mustelidæ, having resemblances to the European marten, to the otters, and to the S. African _Zorilla_; and lastly, _Simocyon_, an extraordinary carnivore of the size of a small panther, but having the canines of a cat, the molars of a dog, and the jaws shaped like those of a bear.

_Ungulata._--These are numerous and very _interesting_. The Equidæ are represented by the three-toed _Hipparion_, which {116}continued to exist till the Older Pliocene period. There are three large species of _Rhinoceros_, as well as a species of the extinct genus _Leptodon_ of smaller size. Remains of a very large wild boar (_Sus_) were found. Very interesting is the occurrence of a species of giraffe (_Camelopardalis_) as tall as the African species but more slender; and also an extinct genus _Helladotherium_, not quite so tall as the giraffe but much more robust, and showing some approach to the Antilopidæ in its dentition. Antelopes were abundant, ranging from the size of the gazelle to that of the largest living species. Three or four seem referable to living genera, but the majority are of extinct types, and are classed in the genera _Palæotragus_, _Palæoryx_, _Tragocerus_, and _Palæoreas_; while _Dremotherium_ is an ancient generalized form of _Cervidæ_ or deer.

_Proboscidea._--These are represented by two species of _Mastodon_, and two of _Dinotherium_, an extraordinary extinct form supposed to be, to some extent, intermediate between the elephants and the aquatic manatees (_Sirenia_.)

_Rodentia._--This order is represented by a species of _Hystrix_, larger than living porcupines.

_Edentata._--This order, now almost confined to South America, was represented in the Miocene period by several European species. _Ancylotherium_ and _Macrotherium_, belonging to an extinct family but remotely allied to the African ant-bear (_Orycteropus_), occur in Greece.

_Birds._--Species of _Phasianus_ and _Gallus_ were found; the latter especially interesting as being now confined to India.

_Reptiles._--These are few and unimportant, consisting of a tortoise (_Testudo_) and a large lizard allied to _Varanus_.

_Summary of the Miocene Fauna of Greece._--Although we cannot consider that the preceding enumeration gives us by any means a complete view of the actual inhabitants of this part of Europe during the later portion of the Miocene period, we yet obtain some important information. The resemblance that appeared in the Pliocene fauna of Europe, to that of the open country of tropical Africa, is now still more remarkable. We {117}not only find great felines, surpassing in size and destructive power the lions and leopards of Africa, with hyænas of a size and in a variety not to be equalled now, but also huge rhinoceroses and elephants, two forms of giraffes, and a host of antelopes, which, from the sample here obtained, were probably quite as numerous and varied as they now are in Africa. Joined with this abundance of antelopes we have the absence of deer, which probably indicates that the country was open and somewhat of a desert character, since there were deer in other parts of Europe at this epoch. The occurrence of but a single species of monkey is also favourable to this view, since a well-wooded country would most likely have supplied many forms of these animals.

_Miocene Fauna of Central and Western Europe._

We have now to consider the Miocene fauna of Europe generally, of which we have very full information from numerous deposits of this age in France, Switzerland, Italy, Germany, and Hungary.

_Primates._--Three distinct forms of monkeys have been found in Europe--in the South of France, in Switzerland, and Wurtemberg; one was very like _Colobus_ or _Semnopithecus_; the others--_Pliopithecus_ and _Dryopithecus_--were of higher type, and belonged to the anthropomorphous apes, being nearest to the genus _Hylobates_ or gibbons. Both have occurred in the South of France. The _Dryopithecus_ was a very large animal (equal to the gorilla), and M. Lartet considers that in the character of its dentition it approached nearer to man than any of the existing anthropoid apes.

_Insectivora._--These small animals are represented by numerous remains belonging to four families and a dozen genera. Of _Erinaceus_ (hedgehog) several species are found in the Upper Miocene; and in the Lower Miocene of Auvergne two extinct genera of the same family--_Amphechinus_ and _Tetracus_--have been discovered. Several species of _Talpa_ (mole) occur in the Upper Miocene of France, while the extinct _Dinylus_ is from Germany, and _Palæospalax_ from the Lower Miocene of the Isle of {118}Wight. The Malayan family Tupaiidæ or squirrel-shrews, is believed to be represented by _Oxygomphus_, a fossil discovered in South Germany (Wiesenau) by H. von Meyer. The Soricidæ or shrews, are represented by several extinct genera--_Plesiosorex_, _Mysarachne_ and _Galeospalax_; as well as by _Amphisorex_ and _Myogale_ still living. _Echinogale_, a genus of Centetidæ now confined to Madagascar, is said to occur in the Lower Miocene of Auvergne, a most interesting determination, if correct, as it would form a transition to the _Solenodon_ of the Antilles belonging to the same family; but I am informed by Prof. Flower that the affinities of the animals described under this name are very doubtful.

_Carnivora._--Besides _Felis_ and _Machairodus_, which extend back to the Upper Miocene, there are two other genera of Felidæ, _Pseudælurus_ in the Upper Miocene of France, and _Hyænodon_, which occurs in the Upper and Lower Miocene of France, named from some resemblance in its teeth to the hyænas, and considered by some Palæontologists to form a distinct family, Hyænodontidæ. The Viverridæ, or civets, were very numerous, consisting of the living genus _Viverra_, and three extinct forms--_Thalassictis_=_Ictitherium_, as large as a panther, and _Soricictis_, a smaller form, occurring both in France and Hungary. Of _Hyænidæ_, there was the living genus _Hyæna_, and the extinct _Hyænictis_, which has occurred in Hungary as well as in Greece. The Canidæ, or wolf and fox family, were represented by _Pseudocyon_, near to _Canis_; _Hemicyon_, intermediate between dogs and gluttons; and _Amphicyon_, of which several species occur in the Upper and Lower Miocene of France, some of them larger than a tiger. The Mustelidæ, or weasels, were represented by five genera, the existing genera _Lutra_ (otter) and _Mustela_ (weasel); _Potamotherium_, an extinct form of otter; _Taxodon_, allied to the badger and otter; _Palæomephitis_ in Germany, and the _Promephytis_ (already noticed) in Greece. The bears were represented only by _Hyænarctos_, which has been noticed as occurring in the Pliocene, and first appears in the Upper Miocene of France. Seals are represented by a form resembling the Antarctic _Otaria_, remains of which occur in the Upper Miocene of France.

{119}_Cetacea_ (whales).--These occur frequently in the Miocene deposits, four living, and five extinct genera having been described; but these marine forms are not of much importance for our purpose.

_Sirenia_ (sea-cows).--These are represented by two extinct genera, _Halitherium_ and _Trachytherium_. Several species of the former have been discovered, but the latter has occurred in France only, and its affinities are doubtful.

_Ungulata._--Horses are represented by _Hipparion_ and _Anchitherium_, the latter occurring in both Upper and Lower Miocene and Eocene; while _Hipparion_, which is more nearly allied to living horses, first appears in the Upper Miocene and continues in the Pliocene.

_Hippotherium_, in the Upper Miocene of the Vienna basin, forms a transition to _Paloplotherium_, an Eocene genus of Tapiridæ or Palæotheridæ. Tapirs, allied to living forms, occur in both Upper and Lower Miocene. Rhinoceroses are still found in the Upper Miocene, and here first appear the four-toed hornless rhinoceros, _Acerotherium_. The Suidæ (swine) are rather numerous. _Sus_ (wild boar) continued as far back as the Upper Miocene; but now there first appear a number of extinct forms which have been named _Hyotherium_, _Palæochoerus_, _Choeromorus_, all of a small or moderate size; _Hyopotamus_, nearly as large as a tapir; and _Anthracotherium_, nearly the size of a hippopotamus and, according to Dr. Leidy, the type of a distinct family. _Listriodon_, from the Upper Miocene of the Vienna basin, is sometimes classed with the tapirs.

We now come to a well-marked new family of Artiodactyle or even-toed Ungulata, the _Anoplotheriidæ_, which consisted of more slender long-tailed animals, allied to the swine but with indications of a transition towards the camels. The only genera that appear in the Miocene formation are, _Chalicotherium_, nearly as large as a rhinoceros, of which three species have been found in Germany and France; and _Synaphodus_, known only from its teeth, which differ somewhat from those of the _Anoplotherium_ which appears earlier in the Eocene formation. Another extinct family, _Amphimericidæ_ or _Xiphodontidæ_, is represented by two {120}genera, _Cainotherium_ and _Microtherium_, in the Miocene of France. They were of very small size, and are supposed to be intermediate between the Suidæ and Tragulidæ.

The Camelopardalidæ, or giraffes, were represented in Europe in Miocene times by the gigantic _Helladotherium_, which has been found in the south of France, and in Hungary, as well as in Greece. The chevrotains (Tragulidæ) are represented by the extinct genus _Hyomoschus_.

The Cervidæ do not seem to have appeared in Europe before the Upper Miocene epoch, when they were represented by _Dorcatherium_ and _Amphimoschus_, allied to _Moschus_, and also by true _Cervus_, as well as by small allied forms, _Dremotherium_, _Amphitragalus_ (in the Lower Miocene), _Micromeryx_, _Palæomeryx_, and _Dicrocerus_.

The Bovidæ, or hollow-horned ruminants, were not well represented in Central Europe in Miocene times. There were no sheep, goats, or oxen, and only a few antelopes of the genus _Tragocerus_, and one allied to _Hippotragus_; and these all lived in the Upper Miocene period, as did the more numerous forms of Greece.

_Proboscidea._--The true elephants do not extend back to the Miocene period, but they are represented by the Mastodons, which had less complex teeth. These first appear in the Upper Miocene of Europe, five species being known from France, Germany, Switzerland, and Greece. _Dinotherium_, already noticed as occurring in Greece, extended also to Germany and France, where remains of three species have been found.

_Rodentia._--A considerable number of generic forms of this order have been obtained from the Miocene strata. The principal genera are _Cricetodon_, allied to the hamsters, numerous in both the Upper and Lower Miocene period of France; _Myoxus_ (the dormice) in France, and an allied genus, _Brachymys_, in Germany. The beavers were represented by the still living genus _Castor_, and the extinct _Steneofiber_ in France. The squirrels by the existing _Scuirus_ and _Spermophilus_; and by extinct forms, _Lithomys_ and _Aulacodon_, in Germany, the latter resembling the African genus _Aulacodes_. The hares, by _Lagomys_ and an {121}extinct form _Titanomys_. Besides these, remains referred to the South American genera, _Cavia_ (cavy) and _Dasyprocta_ (agouti), have been found, the former in the Upper Miocene of Switzerland, the latter in the Lower Miocene of Auvergne. _Palæomys_, allied to the West Indian _Capromys_, has been found in the same deposits; as well as _Theridomys_, said by Gervais to be allied to _Anomalurus_ and _Echimys_, the former now living in W. Africa, the latter in S. America.

_Edentata._--These are only represented by the _Macrotherium_ and _Ancylotherium_ of the Grecian deposits, the former occurring also in France and Germany in Upper Miocene strata.

_Marsupials_.--These consist of numerous species related to the opossums (_Didelphys_), but separated by Gervais under the name _Peratherium_. They occur in both Upper and Lower Miocene beds.

_Upper Miocene Deposits of the Siwalik Hills and other Localities in N. W. India._

These remarkable fresh-water deposits form a range of hills at the foot of the Himalayas, a little south of Simla. They were investigated for many years by Sir P. Cautley and Dr. Falconer, and add greatly to our knowledge of the early fauna of the Old World continent.

_Primates_.--Remains of the genera _Semnopithecus_ and _Macacus_ were found, with other forms of intermediate character; and some teeth indicated animals allied to the orang-utan of Borneo, and of similar size.

_Carnivora_.--These consisted of species of _Felis_ and _Machairodus_ of large size; _Hyæna_, _Canis_, _Mellivora_, and an allied genus _Ursitaxus_; _Ursus_, in the deposits of the Nerbudda valley (of Pliocene age); _Hyænarctos_ as large as the cave bear; _Amphicyon_ of the size of a polar bear (in the deposits of the Indus valley, west of Cashmere); _Lutra_, and an extinct allied genus _Enhydrion_.

_Ungulata_.--These are very numerous, and constitute the most important feature of this ancient fauna. Horses are represented by a species of _Equus_ from the Siwalik Hills and the Irawaddy {122}deposits in Burmah, and by two others from the Pliocene of the Nerbudda Valley; while _Hippotherium_--a slender, antelope-like animal, found in the Siwalik Hills and in Europe--is supposed to form a transition from the Equidæ to the Tapiridæ. These latter are found in the Upper Indus deposits, where there is a species of _Tapirus_, and one of an extinct genus _Antelotherium_. Of _Rhinoceros_, five extinct species have been found--in the Siwalik Hills, in Perim Island, and one at an elevation of 16,000 feet in the deserts of Thibet. _Hippopotamus_ occurs in the Pliocene of the Nerbudda, and is represented in the older Miocene deposits by _Hexaprotodon_, of which three species have been found in various parts of India. Another remarkable genus, _Merycopotamus_, connects _Hippopotamus_ with _Anthracotherium_, one of the extinct European forms allied to the swine. These last are represented by several large species of _Sus_, and by the extinct European genus _Choerotherium_.

The extinct Anoplotheridæ are represented by a species of the European genus _Chalicotherium_, larger than a horse.

An extinct camel, larger than the living species, was found in the Siwalik Hills.

Three species of deer (_Cervus_) have been found in the Siwaliks, and one in the Nerbudda deposits.

A large and a small species of giraffe (_Camelopardalis_) were found in the Siwalik Hills and at Perim Island.

The Bovidæ are represented by numerous species of _Bos_, and by the extinct genera _Hemibos_ and _Amphibos_. There are also three species of antelopes, one of which is allied to the African _Alcephalus_.

We now come to an extraordinary group of extinct animals, probably forming a new family intermediate between the antelope and the giraffe. The _Sivatherium_ was an enormous four-horned ruminant, larger than a rhinoceros. It had a short trunk like a tapir, the lower horns on the forehead were simple, the upper pair palmated. The _Bramatherium_, an allied form from Perim Island, showed somewhat more affinity for the giraffe.

_Proboscidea._--No less than seven species of elephants and four {123}of mastodons ranged over India, their remains being found in all the deposits from the Siwalik Hills to Burmah. A large _Dinotherium_ has also been found at Perim Island.

_Reptiles._--Many remains of birds were found, but these have not been determined. Reptiles were numerous and interesting, the most remarkable being the huge tortoise, _Colossochelys_, whose shell was twelve feet long and head and neck eight feet more. Other small tortoises of the genera _Testudo_, _Emys_, _Trionyx_ and _Emydida_ were found, the Emys being a living species. There were three extinct and one living species of crocodile, and one of them was larger than any now living. The only other reptile of importance was a large lizard of the genus _Varanus_.

_General Observations on the Miocene faunas of Europe and Asia._--Comparing the three faunas of approximately the same period, and allowing for the necessarily imperfect record of each, we find a wonderful similarity of general type over the enormous area between France on the west and the Irawaddy river in Burmah on the east. We may even extend our comparison to Northern China, where remains of _Hyæna_, _Tapir_, _Rhinoceros_, _Chalicotherium_, and _Elephas_, have been recently found, closely resembling those from the Miocene or Pliocene deposits of Europe or India, and showing that the Palæarctic region had then the same great extent from west to east that it has now. Of about forty genera comprised in the Indian Miocene fauna, no less than twenty-seven inhabited Central and Western Europe during the same epoch. The Indian Miocene fossils are much what we should expect as the forerunners of the existing fauna, the giraffes and hippopotami being the only additions from the present Ethiopian fauna. The numerous forms of the restricted bovine type, show that these probably originated in India; while the monkeys appear to be altogether of Oriental types.

In Europe, however, we meet with a totally different assemblage of animals from those that form the existing fauna. We find apes and monkeys, many large Felidæ, numerous civets {124}and hyænas, tapirs, rhinoceros, hippopotamus, elephants, giraffes, and antelopes, such as now characterise the tropics of Africa and Asia. Along with these we meet with less familiar types, showing relations with the Centetidæ of Madagascar, the Tupaiidæ of the Malay Islands, the _Capromys_, of the West Indies, and the _Echimys_ of South America. And besides all these living types we have a host of extinct forms,--ten or twelve genera allied to swine; nine genera of tapir-like animals; four of horses; nine of wolves; with many distinct forms of the long-extinct families of Anoplotheridæ, Xiphodontidæ, and the edentate Macrotheridæ. It is almost certain that during the Miocene period Europe was not only far richer than it is now in the higher forms of life, but not improbably richer than any part of the globe now is, not excepting tropical Africa and tropical Asia.

EOCENE PERIOD.

The deposits of Eocene age are less numerous, and spread over a far more limited area, than those of the Miocene period, and only restricted portions of them furnish any remains of land animals. Our knowledge of the Eocene mammalian fauna is therefore very imperfect and will not occupy us long, as most of the new types it furnishes are of more interest to the zoologist than to the student of distribution. Some of the Eocene mammalia of Europe are, however, of interest in comparison with those of North America of the same age; while others show that ancestral types of groups now confined to Australia or to South America, then inhabited Europe.

_Primates._--The only undoubted Eocene examples of this order, are the _Cænopithecus lemuroides_ from the Jura, which has points of resemblance to the South American marmosets and howlers, and also to the Lemuridæ; and a cranium recently discovered in the Department of Lot (S.W. France), undoubtedly belonging to the Lemuridæ, and which most resembles that of the West African "Potto" (_Perodicticus_). This discovery has led to another, for it is now believed that remains formerly {125}referred to the Anoplotheridæ (_Adapis_ and _Aphelotherium_ from the Upper Eocene of Paris) were also Lemurs. Some remains from the Lower Eocene of Suffolk were at first supposed to be allied to _Macacus_, but were subsequently referred to the Ungulate, _Hyracotherium_. There is still, however, some doubt as to its true affinities.

_Chiroptera._--In the Upper Eocene of Paris remains of bats have been found, so closely resembling living forms as to be referred to the genus _Vespertilio_.

_Carnivora._--The only feline remains, are those of _Hyænodon_ in the Upper Eocene of Hampshire, and _Pterodon_, an allied form from beds of the same age in France; with _Ælurogale_, found in the South of France in deposits of phosphate of lime of uncertain age, but probably belonging to this period. Viverridæ (civets) are represented by two genera, _Tylodon_, the size of a glutton from the Upper Eocene, and _Palæonyctis_, allied to _Viverra_, from the Middle Eocene of France. The Canidæ (wolves and foxes) appear to have been the most ancient of the existing types of Carnivora, five genera being represented by Eocene remains. Of these, _Galethylax_ and _Cyotherium_ were small, and with the existing genus _Canis_ are found in the Upper Eocene of France. _Arctocyon_, about the size of a wolf, is a very ancient and generalised form of carnivore which can not be placed in any existing family. It is found in the Lower Eocene of France, and is thus the oldest known member of the Carnivora.

_Ungulata._--These are more numerous. Equidæ (horses) are represented by the Miocene _Anchitherium_ in the Lower, and by a more ancient form, _Anchilophus_, in the Middle Eocene of France. Tapiridæ and Palæotheridæ were very numerous. _Palæotherium_ and the allied genus _Paloplotherium_, were abundant in France and England in Upper Eocene times. They somewhat resembled the tapir, with affinities for the horse and rhinoceros. A new genus, _Cadurcotherium_, allied to the rhinoceros and equally large, has been found in the same deposits of phosphate of lime as the lemur and _Ælurogale_. In the Middle Eocene of both England and France are found _Lophiodon_ allied to the tapir, {126}but in some of the species reaching a larger size; _Propalæotherium_ and _Pachynolophus_ of smaller size and having affinities for the other genera named; and _Plagiolophus_, a small, slender animal which Professor Huxley thinks may have been a direct ancestor of the horse. In the Lower Eocene we meet with _Coryphodon_, much larger than the tapir, and armed with large canine teeth; _Pliolophus_, a generalised type, allied to the tapir and horse; and _Hyracotherium_, a small animal from the Lower Eocene of England, remotely allied to the tapir.

Among the Artiodactyla, or even-toed ungulates, the swine are represented by several extinct genera, of moderate or small size--_Acotherium_, _Choeropotamus_, _Cebochoerus_ and _Dichobune_, all from the Upper and the last also from the Middle Eocene of France; but _Eutelodon_, from the phosphate of lime deposits is large. The _Dichobune_ was the most generalised type, presenting the characters of many of the other genera combined, and was believed by Dr. Falconer to approach the musk-deer. The _Cainotherium_ of the Miocene also occurs here, and an allied genus _Plesiomeryx_ from the same deposits as _Euteledon_.

The Eocene Anoplotheridæ were numerous. The _Anoplotherium_ was a two-toed, long-tailed Pachyderm, ranging from the size of a hog to that of an ass; the allied _Eurytherium_ was four-toed; and there are one or two others of doubtful affinity. All are from the Upper Eocene of France and England.

_Rodentia._--Remains referred to the genera _Myoxus_ (dormouse) and _Sciurus_ (squirrel) have been found in the Upper Eocene of France; as well as _Plesiarctomys_, an extinct genus between the marmots and squirrels. The Miocene _Theridomys_ is also found here.

_Marsupials._--The _Didelphys_ (opossum) of Cuvier, now referred to an extinct genus _Peratherium_, is found in the Upper Eocene of France and England.

_General Considerations on the Extinct Mammalian Fauna of Europe._--It is a curious fact that no family, and hardly a genus, of European mammalia occurs in the Pliocene deposits, without extending back also into those of Miocene age. There are, {127}however, a few groups which, seem to be late developments or recent importations into the Palæarctic region, as they occur only in Post-Pliocene deposits. The most important of these are the badger, glutton, elk, reindeer, chamois, goat, and sheep, which only occur in caves and other deposits of Post-Pliocene age. Camels only occur in the Post-Pliocene of Siberia (_Merycotherium_), although a true _Camelus_ of large size appears to have inhabited some part of Central Asia in the Upper Miocene period, being found in the Siwalik beds. The only exclusively Pliocene genera in Europe are _Ursus_, _Equus_, _Hippopotamus_, _Bos_, _Elephas_, _Arvicola_, _Trogontherium_, _Arctomys_, _Hystrix_ and _Lepus_; but of these _Equus_, _Hippopotamus_, _Bos_, and _Elephas_ are found in the Miocene deposits of India. Owing, no doubt, in part to the superior productiveness of the various Miocene beds, large numbers of groups appear to have their origin or earliest appearance here. Such are Insectivora, Felidæ, Hyænidæ, Mustelidæ, _Ursus_, Equidæ, _Tapirus_, Rhinocerotidæ, Hippopotamidæ, Anthracotheridæ (extinct), _Sus_, Camelopardidæ, Tragulidæ, Cervidæ, Bovidæ, Elephantidæ, and Edentata.

Groups which go back to the Eocene period, are, Primates allied to South American monkeys, as well as some of the Lemuridæ; bats of the living genus _Vespertilio_; Hyænodontidæ, an ancestral form of Carnivore; Viverridæ; Canidæ (to the Upper Eocene), and the ancestral Arctocyonidæ to the Lower Eocene; _Hyænarctos_, an ancestral type of bears and hyænas; Anchitheridæ, ancestral horses, to the Middle Eocene; Palæotheridæ, comprising numerous generalised forms, ancestors of the rhinoceros, horse, and tapir; Suidæ, with numerous generalised forms, to the Middle Eocene; Anoplotheridæ and Xiphodontidæ, ancestral families of even-toed Ungulates, connecting the ruminants with the swine; and lastly, several groups of Rodents, and a Marsupial, in the Upper Eocene. We thus find all the great types of Mammalia well developed in the earliest portion of the tertiary period; and the occurrence of Quadrumana, of the highly specialized bats (_Vespertilio_), of various forms of Carnivora, and of Ungulates, clearly differentiated into the odd and even-toed series, associated with such lower forms as {128}Lemurs and Marsupials--proves, that we have here hardly made an approach towards the epoch when the mammalian type itself began to diverge into its various modifications. Some of the Carnivora and Ungulates do, indeed, exhibit a less specialised structure than later forms; yet so far back as the Upper Miocene the most specialised of all carnivora, the great sabre-toothed _Machairodus_, makes its appearance.

The Miocene is, for our special study, the most valuable and instructive of the Tertiary periods, both on account of its superior richness, and because we here meet with many types now confined to separate regions. Such facts as the occurrence in Europe during this period of hippopotami, tapirs, giraffes, Tragulidæ, Edentata, and Marsupials--will assist us in solving many of the problems we shall meet with in reviewing the actual distribution of living forms of those groups. Still more light will, however, be thrown on the subject by the fossil forms of the American continent, which we will now proceed to examine.

{129}CHAPTER VII.

EXTINCT MAMMALIA OF THE NEW WORLD.

The discoveries of very rich deposits of mammalian remains in various parts of the United States have thrown great light on the relations of the faunas of very distant regions. North America now makes a near approach to Europe in the number and variety of its extinct mammalia, and in no part of the world have such perfect specimens been discovered. In what are called the "Mauvaises terres" of Nebraska (the dried-up mud of an ancient lake), thousands of entire crania and some almost entire skeletons of ancient animals have been found, their teeth absolutely perfect, and altogether more resembling the preparations of the anatomist, than time-worn fossils such as we are accustomed to see in the museums of Europe. Other deposits have been discovered in Oregon, California, Virginia, South Carolina, Texas, and Utah, ranging over all the Tertiary epochs, from Post-Pliocene to Eocene, and furnishing a remarkable picture of the numerous strange mammalia which inhabited the ancient North American continent.

NORTH AMERICA--POST-PLIOCENE PERIOD.

_Insectivora._--The only indications of this order yet discovered, consists of a single tooth of some insectivorous animal found in Illinois, but which cannot be referred to any known group.

_Carnivora._--These are fairly represented. Two species of _Felis_ as large as a lion; the equally large extinct _Trucifelis_, found only in Texas; four species of _Canis_, some of them larger {130}than wolves; two species of _Galera_, a genus now confined to the Neotropical region; two bears, and an extinct genus, _Arctodus_; an extinct species of racoon (_Procyon_), and an allied extinct genus, _Myxophagus_--show, that at a very recent period North America was better supplied with Carnivora than it is now. Remains of the walrus (_Trichechus_) have also been found as far south as Virginia.

_Cetacea._--Three species of dolphins belonging to existing genera, have been found in the Eastern States; and two species of _Manatus_, or sea-cow, in Florida and South Carolina.

_Ungulata._--Six extinct horses (_Equus_), and one _Hipparion_; the living South American tapir, and a larger extinct species; a _Dicotyles_, or peccary, and an allied genus, _Platygonus_; a species of the South American llamas (_Auchenia_), and one of a kind of camel, _Procamelus_; two extinct bisons; a sheep, and two musk-sheep (_Ovibos_); with three living and one extinct deer (_Cervus_), show an important increase in its Herbivora.

_Proboscidea._--Two elephants and two mastodons, added to this remarkable assemblage of large vegetable-feeding quadrupeds.

_Rodentia._--These consist mainly of genera and species still living in North America; the only important exceptions being a species of the South American capybara (_Hydrochoerus_) in South Carolina; and _Praotherium_, an extinct form of hare, found in a bone cave in Pennsylvania.

_Edentata._--Here we meet with a wonderful assemblage, of six species belonging to four extinct genera, mostly of gigantic size. A species of _Megatherium_, three of _Megalonyx_, and one of _Mylodon_--huge terrestrial sloths as large as the rhinoceros or even as the largest elephants--ranged over the Southern States to Pennsylvania, the latter (_Mylodon_) going as far as the great lakes and Oregon. Another form, _Ereptodon_, has been found in the Mississippi Valley.

_Marsupialia._--The living American genus of opossums, _Didelphys_, has been found in deposits of this age in South Carolina.

_Remarks on the Post-Pliocene fauna of North America._--The assemblage of animals proved, by these remains, to have {131}inhabited North America at a comparatively recent epoch, is most remarkable. In Europe, we found a striking change in the fauna at the same period; but that consisted almost wholly in the presence of animals now inhabiting countries immediately to the north or south. Here we have the appearance of two new assemblages of animals, the one now confined to the Old World--horses, camels, and elephants; the other exclusively of South American type--llamas, tapirs, capybaras, _Galera_, and gigantic Edentata. The age of the various deposits in which these remains are found is somewhat uncertain, and probably extends over a considerable period of time, inclusive of the Glacial epoch, and perhaps both anterior and subsequent to it. We have here, as in Europe, the presence and apparent co-existence in the same area, of Arctic and Southern forms--the walrus and the manatee--the musk-sheep and the gigantic sloths. Unfortunately, as we shall see, the immediately preceding Pliocene deposits of North America are rather poor in organic remains; yet it can hardly be owing to the imperfection of the record of this period, that _not one_ of the South American types above numerated occurs there, while a considerable number of Old World forms are represented. Neither in the preceding wonderfully rich Miocene or Eocene periods, does any _one_ of these forms occur; or, with the exception of _Morotherium_, from Pliocene deposits _west_ of the Rocky Mountains, any apparent ancestor of them! We have here unmistakable evidence of an extensive immigration from South into North America, not very long before the beginning of the Glacial epoch. It was an immigration of types altogether new to the country, which spread over all the southern and central portions of it, and established themselves sufficiently to leave abundance of remains in the few detached localities where they have been discovered. How such large yet defenceless animals as tapirs and great terrestrial sloths, could have made their way into a country abounding in large felines equal in size and destructiveness to the lion and the tiger, with numerous wolves and bears of the largest size, is a great mystery. But it is nevertheless certain that they did so; and the fact that no such {132}migration had occurred for countless preceding ages, proves that some great barrier to the entrance of terrestrial mammalia which had previously existed, must for a time have been removed. We must defer further discussion of this subject till we have examined the relations of the existing faunas of North and South America.

TERTIARY PERIOD.

When we get to remains of the Tertiary age, especially those of the Miocene and Eocene epochs, we meet with so many interesting and connected types, and such curious relations with living forms in Europe, that it will be clearer to trace the history of each order and family throughout the Tertiary period, instead of considering each of the subdivisions of that period separately.

It will be well however first to note the few American Post-Pliocene or living genera that are found in the Pliocene beds. These consist of several species of _Canis_, from the size of a fox to that of a large wolf; a _Felis_ as large as a tiger; an Otter (_Lutra_); several species of _Hipparion_; a peccary (_Dicotyles_); a deer (_Cervus_); several species of _Procamelus_; a mastodon; an elephant; and a beaver (_Castor_). It thus appears that out of nearly forty genera found in the Post-Pliocene deposits, only ten are found in the preceding Pliocene period. About twelve additional genera, however, appear there, as we shall see in going over the various orders.

_Primates._--Among the vast number of extinct mammalia discovered in the Tertiary deposits of North America, no example of this order had been recognized up to 1872, when the discovery of more perfect remains showed, that a number of small animals of obscure affinities from the Lower Eocene of Wyoming, were really allied to the lemurs and perhaps also to the marmosets, the lowest form of American monkeys, but having a larger number of teeth than either. A number of other remains of small animals from the same formation, previously supposed to be allied to the Ungulata, are now shown to {133}belong to the Primates; so that no less than twelve genera of these animals are recognized by Mr. Marsh, who classes them in two families--Limnotheridæ, comprising the genera _Limnotherium_, (which had larger canine teeth), _Thinolestes_, _Telmatolestes_, _Mesacodon_, _Bathrodon_, and _Antiacodon_ of Marsh, with _Notharctos_, _Hipposyus_, _Microsyops_, and _Palæacodon_ previously described by Leidy;--and Lemuravidæ, consisting of the genera _Lemuravus_ (Marsh) and _Hyopsodus_ (Leidy). The animals of the latter family were most allied to existing lemurs, but were a more generalized form, _Lemuravus_ having forty-four teeth, the greatest number known in the order. These numerous forms ranged from the size of a small squirrel to that of a racoon. It is especially interesting to find these peculiar lemuroid forms in America, just when a lemur has been discovered of about the same age in Europe; and as the American forms are said to show an affinity with the South American marmosets, while the European animal is most allied to a West African group, we have evidently not yet got back far enough to find the primeval or ancestral type from which all the Primates sprang.

About the same time, in the succeeding Miocene formation, true monkeys were discovered. Mr. Marsh describes _Laopithecus_ as an animal nearly the size of the largest South American monkeys, and allied both to the Cebidæ and the Eocene Limnotheridæ. Mr. Cope has described _Menotherium_ from the Miocene of Colorado, as a lemuroid animal, the size of a cat, and perhaps allied to _Limnotherium_. More Miocene remains will, no doubt, be discovered, by which we shall be enabled to trace the origin of some of the existing forms of South American monkeys; and perhaps help to decide the question (now in dispute among anatomists) whether the lemurs are really Primates, or form an altogether distinct and isolated order of mammalia.

_Insectivora._--This order is represented by comparatively few forms in the tertiary beds, and these are all very different from existing types. In the Upper Miocene of Dakota are found remains indicating two extinct genera, _Lepictis_ and _Ictops_. In the Miocene of Colorado, Professor Cope has recently discovered four new genera, _Isacis_; allied to the preceding, but as large as a {134}_Mephitis_ or skunk; _Herpetotherium_, near the moles; _Embasis_, more allied to the shrews; and _Dommina_, of uncertain affinities. Two others have been found in the Eocene of Wyoming; _Amomys_, having some resemblance to hedgehogs and to the Eastern _Tupaia_; and _Washakius_, of doubtful affinities.

Far back in the Triassic coal of North Carolina has been found the jaw of a small mammal (_Dromotherium_), the teeth of which somewhat resemble those of the Australian _Myrmecobius_, and may belong either to the Insectivora or Marsupials; if indeed, at that early period these orders were differentiated.

_Carnivora._--The most ancient forms of this order are some remains found in the Middle Eocene of Wyoming, and others recently described by Professor Cope (1875) from the Eocene of New Mexico, of perhaps earlier date. The former consist of three genera, _Patriofelis_, _Uintacyon_, and _Sinopa_,--animals of large size but which cannot be classed in any existing family; and two others, _Mesonyx_ and _Synoplotherium_, believed by Mr. Cope to be allied to _Hyænodon_. The latter consist of four genera,-- _Oxyæna_, consisting of several species, some as large as a jaguar, was allied to _Hyænodon_ and _Pterodon_; _Pachyæna_, allied to the last; _Prototomus_, allied to _Amphicyon_ and the Viverridæ; and _Limnocyon_, a civet-like carnivore with resemblances to the Canidæ.

In the Miocene formations we find the Feline type well developed. The wonderful _Machairodus_, which in Europe lived down to Post-Pliocene times, is found in the Upper Miocene of Dakota; and perfect crania have been discovered, showing that the chin was lengthened downwards to receive and protect the enormous canines. _Dinyctis_ was allied both to _Machairodus_ and to the weasels. Three new genera have been lately described by Professor Cope from the Miocene of Colorado,--_Bunælurus_, with characters of both cats and weasels; _Daptophilus_, allied to _Dinyctis_; and _Hoplophoneus_, more allied to _Machairodus_. The Canidæ are represented by _Amphicyon_, which occurs in deposits of the same age in Europe; and by _Canis_, four species of which genus are recorded by Professor Cope from the Miocene of Colorado, and it also occurs in the Pliocene. The _Hyænodon_ is represented by three species in the Miocene of Dakota and Colorado. It occurs {135}also in the European Miocene and Upper Eocene formations, and constitutes a distinct family Hyænodontidæ, allied, according to Dr. Leidy, to wolves, cats, hyænas and weasels. The Ursidæ are represented by only one species of an extinct genus, _Leptarchus_, from the Pliocene of Nebraska. From the Pliocene of Colorado, Prof. Cope has recently described _Tomarctos_, as a "short-faced type of dog;" well as species of _Canis_ and _Martes_.

_Ungulata._--The animals belonging to this order being usually of large size and accustomed to feed and travel in herds, are liable to wholesale destruction by floods, bogs, precipices, drought or hunger. It is for these reasons, probably, that their remains are almost always more numerous than those of other orders of mammalia. In America they are especially abundant; and the number of new and intermediate types about whose position there is much difference of opinion among Palæontologists, renders it very difficult to give a connected summary of them with any approach to systematic accuracy.

Beginning with the Perissodactyla, or odd-toed ungulates, we find the Equine animals remarkably numerous and interesting. The true horses of the genus _Equus_, so abundant in the Post-Pliocene formations, are represented in the Pliocene by several ancestral forms. The most nearly allied to _Equus_ is _Pliohippus_, consisting of animals about the size of an ass, with the lateral toes not externally developed, but with some differences of dentition. Next come _Protohippus_ and _Hipparion_, in which the lateral toes are developed but are small and functionless. Then we have the allied genera, _Anchippus_, _Merychippus_, and _Hyohippus_, related to the European _Hippotherium_, which were all still smaller animals, _Protohippus_ being only 2½ feet high. In the older deposits we come to a series of forms, still unmistakably equine, but with three or more toes used for locomotion and with numerous differentiations in form, proportions, and dentition. These constitute the family Anchitheridæ. In the Miocene we have the genera _Anchitherium_ (found also in the European Miocene), _Miohippus_ and _Mesohippus_, all with three toes on each foot, and about the size of a sheep or large goat. In the Eocene of {136}Utah and Wyoming, we get a step further back, several species having been discovered about the size of a fox with four toes in front and three behind. These form the genus _Orohippus_, and are the oldest ancestral horse known. Prof. Marsh points out the remarkably perfect series of forms in America, which, beginning with this minute ancient type, is gradually modified by gaining increased size, increased speed by concentration of the limb-bones, elongation of the head and neck, the canine teeth decreased in size, the molars becoming longer and being coated with cement--till we at last come to animals hardly distinguishable, specifically, from the living horse.

Allied to these, are a series of forms showing a transition to the tapirs, and to the _Palæotherium_ of the European Eocene. In the Pliocene we have _Parahippus_; in the Miocene _Lophiodon_, found in the same formation and in the Eocene of Europe, and allied to the tapir; and in the Eocene, _Palæosyops_, as large as a rhinoceros, which had large canines and was allied to the tapir and _Palæotherium_; _Limnohyus_, forming the type of a family Limnohyidæ, which included the last genus and some others mentioned further on; and _Hyrachyus_, allied to _Lophiodon_, and to _Hyracodon_ an extinct form of rhinoceros. Besides these we have _Lophiotherium_ (also from the Eocene of Europe); _Diplacodon_ allied to _Limnohyus_, but with affinities to modern Perissodactyla and nearly as large as a rhinoceros; and _Colonoceras_, also belonging to the Limnohyidæ, an animal which was the size of a sheep, and had divergent protuberances or horns on its nose. A remarkable genus, _Bathmodon_, lately described by Professor Cope, and of which five species have been found in the Eocene of New Mexico and Wyoming, is believed to form the type of a new family, having some affinity to _Palæosyops_ and to the extinct Brontotheridæ. It had large canine tusks but no horns.

The Rhinocerotidæ are represented in America by the genus _Rhinoceros_ in the Pliocene and Miocene, and by _Aceratherium_ and _Hyracodon_ in the Miocene. Both the latter were hornless, and _Hyracodon_ was allied to the Eocene _Hyrachyus_, one of the Lophiodontidæ. In the Eocene and Miocene deposits of Utah, and Oregon, several remarkable extinct rhinoceroses have been {137}recently discovered, forming the genus _Diceratherium_. These had a pair of nasal horns placed side by side on the snout, not behind each other as in existing two-horned rhinoceroses, the rest of their skeleton resembling the hornless _Aceratherium_. They were of rather small size.

Next to these extinct rhinoceroses come the Brontotheridæ, an extraordinary family of large mammalia, some of which exceeded in bulk the largest living rhinoceros. They had four toes to the front and three to the hind feet, with a pair of large divergent horns on the front of the head, in both sexes. Professor Marsh and Dr. Leidy have described four genera, _Brontotherium_, _Titanotheium_, _Megacerops_, and _Anisacodon_, distinguished by peculiarities of dentition. Though most nearly allied to the rhinoceroses, they show some affinity for the gigantic Dinocerata of the Eocene to be noticed further on. Professor Cope has since described another genus, _Symborodon_, from the Miocene of Colorado, with no less than seven species, one nearly the size of an elephant. He thinks they had a short tapir-like proboscis. The species differ greatly in the form of the cranium and development of the horn-bearing processes.

We commence the Artiodactyla, or even-toed Ungulates, with the hog tribe. These are represented by species of peccaries, (_Dicotyles_) from the Pliocene of Nebraska and Oregon; and by an allied form _Thinohyus_, very like _Dicotyles_, but having an additional premolar tooth and a much smaller brain-cavity. From the Miocene are three allied genera, _Nanohyus_, _Leptochoerus_, and _Perchoerus_. Professor Cope, however, thinks _Leptochoerus_ may be Lemuroid, and allied to _Menotherium_. The Anthracotheridæ, a family which connects the Hippopotamidæ and Ruminants, and which occurs in the Miocene of Europe and India, are represented in America by the genus _Hyopotamus_ from the Miocene of Dakota, and _Elotherium_ from the Miocene of Oregon and the Eocene of Wyoming; the latter genus being sometimes classed with the preceding family, and lately placed by Professor Marsh, in the new order, Tillodontia. Professor Cope has since described three other genera from the Eocene of New {138}Mexico: _Meniscotherium_, having resemblances to _Palæosyops_, _Hyopotamus_, and the Limnotheridæ; _Phenacodus_, the size of a hog, of doubtful position, but perhaps near _Elotherium_; and _Achænodon_, as large as a cow, but more hog-like than the preceding. Another new genus from the Miocene of Colorado--_Pelonax_--is said by Professor Cope to come between _Elotherium_ and _Hippopotamus_.

The Camelidæ are very abundant, and form one of the most striking features of the ancient fauna of America. _Procamelus_, _Homocamelus_, and _Megalomeryx_, are extinct genera found in the Pliocene formation; the first very closely allied to the Old World camel, the last smaller and more sheep-like. In the Miocene two other genera occur, _Poebrotherium_ and _Protomeryx_, the former allied to both the camel and the llama.

Deer are represented by a single species of _Cervus_ in the Pliocene, while two extinct genera, _Leptomeryx_ and _Merycodus_, are found in the Miocene deposits, the latter indicating a transition between camels and deer. Two other genera, _Hypisodus_ and _Hypertragulus_, of very small size, are said by Professor Cope to be allied to the Tragulidæ and to _Leptomeryx_.

The Bovidæ, or hollow-horned ruminants, are only represented in the Newer Pliocene by a single species of an extinct genus, _Casoryx_, said to be intermediate between antelopes and deer.

We now come to an exclusively American family, the _Oreodontidæ_, which consisted of small animals termed by Dr. Leidy, "ruminating hogs," and which had some general structural resemblances to deer and camels. They abounded in North America during the Pliocene, and especially during the Miocene epoch, no less than six genera and twenty species having been discovered. _Merychus_ contains the Pliocene forms; while _Oreodon_, _Eporeodon_, _Merychochoerus_, _Leptauchenia_, and _Agriochoerus_ are Miocene. The last genus extends back into the Eocene period, and shows affinity to the European Anoplotheridæ of the same epoch.

_Proboscidea._--The Elephantidæ are only represented in America by one species of _Mastodon_ and one of _Elephas_, in the Newer Pliocene deposits. In the Older Pliocene, Miocene, {139}and Upper Eocene, no remains of this order have been found; and in 1869, Dr. Leidy remarked on the small average size of the extinct North American mammalia, which were almost all smaller than their living analogues. Since then, however, wonderful discoveries have been made in deposits of Middle Eocene age in Wyoming and Colorado, of a group of huge animals not only rivalling the elephants in size, but of so remarkable and peculiar a structure as to require the formation of a new order of mammals--Dinocerata--for their reception.

This order consists of animals with generalised Ungulate and Proboscidean affinities. The lower jaw resembles that of the hippopotamus; they had five toes on the anterior feet and four on the posterior; three pairs of horns, the first pair on the top of the head, large and perhaps palmated, the second pair above the eyes, while the third and smallest stood out sideways on the snout. They had enormous upper canines, of which the roots entered the middle horn cores, no upper incisors, and small molars. Professor Marsh believes that they had no trunk. The remains discovered indicate four genera, _Dinoceras_ (3 sp.), _Tinoceras_ (2 sp.), _Uintatherium_ (1 sp.), and _Eobasileus_ (2 sp.). Many other names have been given to fragments of these animals, and even those here given may not be all distinct.

Another new order, Tillodontia, recently established by Professor Marsh, is perhaps yet more remarkable in a zoological point of view, since it combines the characters of Carnivora, Ungulata, and Rodents. These animals have been formed into two families, Tillotheridæ and Stylinodontidæ; and three genera, _Tillotherium_, _Anchippodus_, and _Stylinodontia_. All are from the Eocene of Wyoming and New Jersey. Perhaps to these must be added _Elotherium_ from the Miocene of Dakota, the other forms being all Eocene. They were mostly animals of small size, between that of the capybara and tapir. The skull resembled in form that of a bear; the molar teeth were of Ungulate type, and the incisors like those of a Rodent; but the skeleton was more that of the Ursidæ, the feet being plantigrade. Professor Cope has since described three new genera from the Eocene of New Mexico, _Ectoganus_, _Calamodon_, and _Esthonyx_, comprising {140}seven species allied to _Tillotherium_ and _Anchippodus_, and having also relations, as Professor Cope believes, with the South American Toxodontidæ.

_Rodentia._--This order is represented in the Pliocene by a beaver, a porcupine, and an American mouse (_Hesperomys_), all extinct species of living genera, the _Hystrix_ being an Old World type; and Professor Cope has recently described _Panolax_, a new genus of hares from the Pliocene of New Mexico. The Miocene deposits have furnished an extinct genus allied to the hares--_Palæolagus_; one of the squirrel family--_Ischyromys_; a small extinct form of beaver--_Palæocastor_; and an extinct mouse--_Eumys_. The Eocene strata of Wyoming have lately furnished two extinct forms of squirrel, _Paramys_ and _Sciuravus_; and another of the Muridæ (or mouse family), _Mysops_.

_Cetacea._--Numerous remains of dolphins and whales, belonging to no less than twelve genera, mostly extinct, have been found in the Miocene deposits of the Atlantic and Gulf States, from New Jersey to South Carolina and Louisiana; while seven genera of the extinct family, Zeuglodontidæ, have been found in Miocene and Eocene beds of the same districts. Some remains associated with these are doubtfully referred to the Seal family (Phocidæ) among the Carnivora.

_Edentata._--Till quite recently no remains of this order have occurred in any North American deposits below the Post-Pliocene; but in 1874 Prof. Marsh described some remains allied to _Megalonyx_ and _Mylodon_, from the Pliocene beds of California and Idaho, and forming a new genus, _Morotherium_. As these remains have only occurred to the west of the Rocky Mountains, and in Pliocene deposits whose exact age is not ascertained, they hardly affect the remarkable absence of this group from the whole of the exceedingly rich Tertiary deposits in all other parts of North America.

_General Relations of the extinct Tertiary Mammalia of North America and Europe._--Having now given a sketch of the extinct Mammalia which inhabited Europe and North America during the Tertiary period, we are enabled by comparing them, {141}to ascertain their relations to each other, and to see how far they elucidate the problem of the birth-place and subsequent migrations of the several families and genera. We have already pointed out the remarkable features of the Quaternary (or Post-Pliocene) fauna of North America, and now proceed to discuss that of the various Tertiary periods, which is closely connected with the extinct fauna of Europe.

The Tertiary Mammalia of North America at present described belong to from eighty to one hundred genera, while those of Europe are nearly double that number; yet only eighteen genera are common to the two faunas, and of these eight are living and belong chiefly to the Pliocene period. Taking first, the genera which in America do not go back beyond the Pliocene period (ten in number), we find that eight of them in Europe go back to the Upper Miocene. These are _Felis_, _Pseudælurus_, _Hipparion_, _Cervus_, _Mastodon_, _Elephas_ (in India), _Castor_ and _Hystrix_; while another, _Canis_, goes back to the Upper Eocene and the tenth, _Equus_, confined to the newer Pliocene or perhaps to the Post-Pliocene in America, extends back to the older Pliocene in Europe. Of the seven European genera which are confined to the Miocene period in America, three, _Hyænodon_, _Anchitherium_, and _Lophiodon_ go back to the Eocene in Europe; three others, _Machairodus_, _Rhinoceros_, and _Aceratherium_, are also of Miocene age in Europe; _Amphicyon_ goes back to the Lower Miocene of Europe. _Lophiotherium_ belongs to the Eocene of both countries.

If we turn now to families instead of genera, we find that the same general rule prevails. Mustelidæ (weasels), Ursidæ (bears), true Equidæ (horses), and Bovidæ (oxen &c.), go no further back in America than the Pliocene, while they all go back to the Miocene in Europe. Suidæ (swine) and Anoplotheridæ (extinct) are found in the American Miocene and in the European Eocene. Anchitheridæ (extinct) reach the Upper Eocene in America, while in Europe they range through Upper, Middle, and Lower Eocene. Cervidæ (deer) alone are Miocene in both countries. There remain two families in which America has the preeminence. Camelidæ (camels) were wonderfully developed in {142}the American Pliocene and Miocene periods, abounding in genera and species; whereas in Europe the group only exists in the Post-Pliocene or Lower Pliocene, with one Upper Miocene species of _Camelus_ in N. India. The Anthracotheridæ (extinct), found only in the Upper Miocene of France and India, reach even the Lower Eocene in America.

These facts may be due, in part, to a want of strict co-ordination between the Tertiary deposits of Europe and North America,--in part to the imperfection of the record in the latter country. Yet it does not seem probable that they are altogether due South America and well marked differences to imperfect knowledge; yet we find such important families as the Civets, Hyænas, Giraffes, and Hippopotami absent from America, with the Weasels, and Antelopes almost so; while America possesses almost all the Camelidæ, two peculiar orders, Dinocerata and Tillodontia, and four remarkably peculiar families, Limnotheridæ, Lemuravidæ, Oreodontidæ and Brontotheridæ. If then the facts at present known represent approximately the real time-relations of the groups in question on the two continents, they render it probable that weasels, bears, true horses, swine, oxen, sheep and antelopes, originated on the Old World continent, and were transmitted to America during some part of the Miocene period; while camels originated in the New World, and somewhere about the same time passed over to Europe. Of the extinct families common to the two hemispheres, the Anthracotheridæ alone seem to have had an American origin. Of the genera common to the two countries, almost all seem to have had a European origin, the only genera of equal date being the two rhinoceroses and three Anchitheridæ; but if the Brontotheridæ are allied to the Rhinocerotidæ, these latter may have originated in America, although now an exclusively Old World type. These conclusions are not improbable when we consider the much greater size of the Old World continents, extending far into the tropics and probably {143}always more or less united to the tropical areas; while the evidence of the extinct mammalia themselves shows, that South America has been for the most part isolated from the northern continent, and did not take part in the development of its characteristic Tertiary fauna.

Before speculating further on this subject, it will be well to lay before our readers a summary of South American palæontology, after which we shall be in a better position to draw correct inferences from the whole body of the evidence.

SOUTH AMERICA.

Unfortunately, our knowledge of the interesting fossil fauna of this continent, is almost wholly confined to the Post-Pliocene and Pliocene periods. A few remains have been discovered in deposits believed to be of Eocene age, but nothing whatever representing the vast intervening period, so rich in peculiar forms of animal life both in North America and Europe.

_Fauna of the Brazilian caves._--What we know of the Post-Pliocene period is chiefly due to the long-continued researches of Dr. Lund in the caves of Central Brazil, mostly situated in a district near the head waters of the San Francisco river in the Province of Minas Geraes. The caves are formed in limestone rocks, and are so numerous that Dr. Lund visited thousands, but only sixty contained bones in any quantity. These caves have a floor of reddish earth, often crowded with bones. In one experiment, half a cubic foot of this earth contained jaws of 400 opossums, 2,000 mice, besides remains of bats, porcupines and small birds. In another trial, the whole of the earth in a cavern was carried out for examination, amounting to 6,552 firkins; and, from a calculation made by measured samples, it was estimated to contain nearly seven millions of jaw-bones of cavies, opossums, porcupines, and mice, besides small birds, lizards, and frogs. This immense accumulation is believed to have been formed from the bodies of animals brought into the cavern by owls; and, as these are unsocial birds, the quantity found implies an {144}immense lapse of time, probably some thousands of years. More than 100 species of Mammalia, in all, were obtained in these caves. Some were living species or closely allied to such; but the majority were extinct, and a considerable number, about one-fourth, belonged to extinct genera, or genera not now inhabiting South America. Stone implements and human remains were found in several of the caves with extinct animals. The following enumeration of these remains is from the corrected list of M. Gervais.

_Primates._--Extinct species of _Cebus_, _Callithrix_, and _Jacchus_--South American genera of monkeys; with an extinct genus, _Protopithecus_--an animal of large size but belonging to the American family Cebidæ.

_Chiroptera._--Species belonging to the South American Phyllostomidæ, and to two South American genera of other families.

_Carnivora._--Five species of _Felis_, some allied to living animals, others extinct; a species of the widespread extinct genus _Machairodus_; and a small species referred to _Cynælurus_, the genus containing the hunting leopard now found only in Africa and India. Canidæ are represented by _Canis_ and _Icticyon_ (a living Brazilian species of the latter genus), and the extinct genus _Speothos_. Mustelidæ are represented by extinct species of the South American genera _Mephitis_ and _Galictis_. Procyonidæ, by a species of _Nasua_. Ursidæ, by _Arctotherium_, a genus closely resembling, if not identical with, that containing the "spectacled bear" of Chili.

_Ungulata._--_Equus_, _Tapirus_, _Dicotyles_, _Auchenia_, _Cervus_, _Leptotherium_, and _Antilope_, are the cave-genera of this order. _Equus_ and _Antelope_ are particularly interesting, as representing groups forming no part of existing South American zoology; while the presence also of _Leptotherium_, an extinct genus of antelopes, shows that the group was fairly represented in South America at this comparatively recent period.

_Proboscidea._--A species of _Mastodon_, found also in the Pliocene of La Plata, represents this order.

_Rodentia._--These abound. _Dasyprocta_, _Cælogenys_, _Cavia_, _Kerodon_, all living genera of Caviidæ, are represented by {145}extinct species. _Cercolabes_, the 'tree porcupine' (Cercolabidæ) has two species, one as large as a peccary; _Myopotamus_, _Loncheres_, _Carterodon_, are existing genera of spiny rats (Echimyidæ); and there are two extinct genera of the same family, _Lonchophorus_ and _Phyllomys_. _Lagostomus_ (Chinchillidæ), the viscacha of the Pampas, is represented by an extinct species. There is also an extinct species of _Lepus_; several species of _Hesperomys_ and _Oxymycterus_; and a large _Arvicola_, a genus not living in South America.

_Edentata._--These, which constitute the great feature of the existing South American fauna, were still more abundant and varied in the Cave period, and it is remarkable that most of them are extinct _genera_. The armadillos are alone represented by living forms, _Dasypus_, and _Xenurus_; _Eurydon_ and _Heterodon_, are extinct genera of the same family, as well as _Chlamydotherium_--huge armadillos the size of a tapir or rhinoceros, and _Pachytherium_, which was nearly as large. The ant-eaters are represented only by _Glossotherium_, an extinct form allied to _Myrmecophaga_ and _Manis_. The sloths were more numerous, being represented by the extinct genera _Cælodon_, _Sphenodon_ and _Ochotherium_, the last of large size. The huge terrestrial sloths--Megatheridæ, also abounded; there being species of _Megatherium_ and _Megalonyx_, as well as the allied _Scelidotherium_, supposed to have some affinity for the African _Orycteropus_.

_Marsupials._--No new forms of these appear, but numerous species of _Didelphys_, all closely allied to opossums still living in South America.

The preceding sketch of the wonderful cave fauna of Central Brazil, is sufficient to show that it represents, in the main, a period of great antiquity. Not only are almost the whole of the species extinct, but there are twenty extinct genera, and three others not now inhabitants of South America. The fact that so few remains of the living animals of the country are found in these caves, indicates that some change of physical conditions has occurred since they were the receptacles of so many of the larger animals; and the presence of many extinct genera of {146}large size, especially among the Edentata and American families of Rodents, are additional proofs of a very high antiquity. Yet many of these cave animals are closely allied to those which are found in North America in the Post-Pliocene deposits only, so that we have no reason to suppose the cave-fauna to be of much earlier date. But the great amount of organic change it implies, must give us an enlarged idea of the vast periods of time, as measured by years, which are included in this, the most recent of all geological epochs.

_Pliocene Period of Temperate South America._--We have now to consider the numerous remains of extinct animals found in various deposits in the Pampas, and in Patagonia, and a few in Bolivia. The age of these is uncertain; but as they are very similar to the cave-fauna, though containing a somewhat larger proportion of extinct genera and some very remarkable new forms, they cannot be _very_ much older, and are perhaps best referred at present to the newer portion of the Pliocene formation.

_Carnivora._--The genus _Machairodus_ or sabre-toothed tigers, represents the Felidæ. There are several species of wolves (_Canis_); a weasel (_Mustela_); two bears of the Brazilian cave-genus _Arctotherium_; and the extinct European genus _Hyænarctos_.

_Ungulata._--There are two species of _Equus_, found in the Pampas, Chili, and Bolivia; two of _Macrauchenia_, an extraordinary extinct group allied to the tapir and _Palæotherium_, but with the long neck, and general size of a camel. A second species found on the highlands of Bolivia is much smaller.

A more recent discovery, in Patagonia, is the almost perfect series of teeth of a large animal named _Homalodontotherium_; and which is believed by Professor Flower, who has described it, to have been allied to _Rhinoceros_, and still more to the Miocene _Hyracodon_ from North America; and also to present some resemblances to _Macrauchenia_, and though much more remotely, to the curious genus _Nesodon_ mentioned further on.

The Artiodactyla, or even-toed Ungulates, are represented by a species of _Dicotyles_, or peccary, found in the deposits of the {147}Pampas; by _Auchenia_, or llama, of which three extinct species inhabited Bolivia, in which country two allied but extinct genera, _Palæolama_ and _Camelotherium_, have also been found. Three species of deer (_Cervus_), from the Pampas deposits, complete the list of Pliocene Ungulates.

_Proboscidea._--The cave species of _Mastodon_ is found also in the Pampas deposits, and another in the Andes of Chili and Bolivia.

_Rodents._--These are not so numerous as in the caves. There are species of the existing genera, _Kerodon_ and _Cavia_ (Caviidæ); _Lagostomus_ (Chinchillidæ); _Ctenomys_ (Octodontidæ); _Lepus_ (hare); _Hesperomys_ and _Oxymycterus_ (Muridæ); _Arvicola_, a genus not living in South America; and an extinct genus, _Cardiodus_. There is also a remarkable extinct form, _Typotherium_, larger than the capybara, and having affinities to Edentates and Ungulates. Three species have been found in the Pampas deposits.

_Edentata._--These are as abundant and remarkable as in the cave deposits. _Scelidotherium_, _Megatherium_, _Megalonyx_, _Glossotherium_ and _Dasypus_, have already been noticed as from the Brazilian caves. We have here, in addition, the huge _Mylodon_ allied to the _Megatherium_, and the allied genera--_Gnathopsis_ and _Lestodon_. We then come to the huge extinct armadillos, _Glyptodon_ and _Schistopleurum_, the former consisting of numerous species, some of which were as large as an elephant. Another genus, _Eutatus_, is allied to the living three-banded armadillos; and a species of the existing genus _Euphractus_ has been found in Bolivia.

_Toxodontidæ._--There remain a number of huge animals rivalling the Megatherium in size, and forming the genera _Toxodon_ and _Nesodon_, but whose position is doubtful. Several species have been found in the deposits of the Pampas and Patagonia. They are allied at once to Ungulates, Rodents, Edentates, and the aquatic Sirenia, in so puzzling a manner that it is impossible to determine to what order they belong, or whether they require a new order to be formed for their reception. Some are believed to date back to the Miocene period, and they indicate what strange forms may still be discovered, should any {148}productive deposits be found in South America of middle Tertiary age.

_Pliocene Mammalia of the Antilles._--These may be noticed here, as they are of special interest, proving the connection of the larger West Indian Islands with the Continent some time in the later Tertiary period. They consist of remains of two large animals belonging to the South American Chinchillidæ, found in cave deposits in the island of Anguilla, and forming two new genera, _Amblyrhiza_ and _Loxomylus_; and remain allied to _Megalonyx_ from Cuba, which have been named _Megalocnus_ and _Myomorphus_.

_Eocene fauna of South America._--The few remains yet discovered in the Tertiary deposits of the Pampas which are believed to be of Eocene age, are exceedingly interesting, because they show us another change in the scenery of the great drama of life; there being apparently a considerable resemblance, at this epoch, between South America and Europe. They consist of a large extinct feline animal, _Eutemnodus_; of _Palæotherium_ and _Anoplotherium_, the well-known extinct Ungulates of the European Tertiaries, and which have never been found in North America; and of three genera of Rodents,--_Theridromys_, allied to _Echimys_, and found also in the Eocene and Miocene of France; _Megamys_, allied to the living _Capromys_ of the Antilles, and also to _Palæomys_, an extinct form of the French Miocene; and a very large animal referred to _Arvicola_, a genus found also in the Pliocene deposits of South America, and abundant in the northern hemisphere. No Edentates have been found.

The resemblances of this fauna to that of Europe rather than to any part of America, are so strong, that they can hardly be accidental. We greatly want, however, more information on this point, as well as some corresponding evidences as to the condition of West and South Africa about the same epoch, before we can venture to speculate on their bearing as regards the early migrations of organic forms.

_General Remarks on the Extinct Mammalian Fauna of the Old {149}and New Worlds._--Leaving the more special applications of palæontological evidence to be made after discussing the relations of the existing fauna of the several regions, we propose here to indicate briefly, some of the more general deductions from the evidence which has now been laid before our readers.

The first, and perhaps the most startling fact brought out by our systematic review, is the very recent and almost universal change that has taken place in the character of the fauna, over all the areas we have been considering; a change which seems to be altogether unprecedented in the past history of the same countries as revealed by the geological record. In Europe, in North America, and in South America, we have evidence that a very similar change occurred about the same time. In all three we find, in the most recent deposits--cave-earths, peat-bogs, and gravels--the remains of a whole series of large animals, which have since become wholly extinct or only survive in far-distant lands. In Europe, the great Irish elk, the _Machairodus_ and cave-lion, the rhinoceros, hippopotamus, and elephant;--in North America, equally large felines, horses and tapirs larger than any now living, a llama as large as a camel, great mastodons and elephants, and abundance of huge megatheroid animals of almost equal size;--in South America these same megatheroids in greater variety, numerous huge armadillos, a mastodon, large horses and tapirs, large porcupines, two forms of antelope, numerous bears and felines, including a _Machairodus_, and a large monkey,--have all become extinct since the deposition of the most recent of the fossil-bearing strata. This is certainly not a great while ago, geologically; and it is _almost_ certain that this great organic revolution, implying physical changes of such vast proportions that they must have been due to causes of adequate intensity and proportionate range, has taken place since man lived on the earth. This is proved to have been the case in Europe, and is supported by much evidence both as regards North and South America.

It is clear that so complete and sudden a change in the higher forms of life, does not represent the normal state of things. Species and genera have not, at all times, become so rapidly extinct. The time occupied by the "Recent period," that is the {150}time _since_ these changes took place is, geologically, minute. The time of the whole of the Post-Pliocene period, as measured by the amount of physical and _general_ organic change known to have taken place, is exceedingly small when compared with the duration of the Pliocene period, and still smaller, probably, as compared with the Miocene. Yet during these two periods we meet with no such break in the continuity of the forms of life, no such radical change in the _character_ of the fauna (though the number of specific and generic changes may be as great) as we find in passing from the Post-Pliocene to recent times. For example, in Central Europe numerous hyænas, rhinoceroses, and antelopes, with the great _Machairodus_, continued from Miocene all through Pliocene into Post-Pliocene times; while hippopotami and elephants continued to live through a good part of the Pliocene and Post-Pliocene periods,--and then all suddenly became extinct or left the country. In North America there has been more movement of the fauna in all the periods; but we have similar great felines, horses, mastodons, and elephants, in the Pliocene and Post-Pliocene periods, while _Rhinoceros_ is common to the Miocene and Pliocene, and camels range continuously from Miocene, through Pliocene, to Post-Pliocene times;--when all alike became extinct. Even in South America the evidence is, as far as it goes, all the same way. We find _Machairodus_, _Equus_, _Mastodon_, _Megatherium_, _Scelidotherium_, _Megalonyx_, and numerous gigantic armadillos, alike in the caves and in the stratified tertiary deposits of the Pampas;--yet all have since passed away.

It is clear, therefore, that we are now in an altogether exceptional period of the earth's history. We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared; and it is, no doubt, a much better world for us now they have gone. Yet it is surely a marvellous fact, and one that has hardly been sufficiently dwelt upon, this sudden dying out of so many large mammalia, not in one place only but over half the land surface of the globe. We cannot but believe that there must have been some physical cause for this great change; and it must have been a cause capable of acting almost simultaneously over large {151}portions of the earth's surface, and one which, as far as the Tertiary period at least is concerned, was of an exceptional character. Such a cause exists in the great and recent physical change known as "the Glacial epoch." We have proof in both Europe and North America, that just about the time these large animals were disappearing, all the northern parts of these continents were wrapped in a mantle of ice; and we have every reason to believe that the presence of this large quantity of ice (known to have been thousands of feet if not some miles in thickness) must have acted in various ways to have produced alterations of level of the ocean as well as vast local floods, which would have combined with the excessive cold to destroy animal life. There is great difference of opinion among geologists and physicists as to the extent, nature, and duration of the Glacial epoch. Some believe it to have prevailed alternately in the northern and southern hemispheres; others that it was simultaneous in both. Some think there was a succession of cold periods, each lasting many thousands of years, but with intercalated warm periods of equal duration; others deny that there is any evidence of such changes, and maintain that the Glacial epoch was one continuous period of arctic conditions in the temperate zones, with some fluctuations perhaps but with no regular alternations of warm periods. Some believe in a huge ice-cap covering the whole northern hemisphere from the pole to near 50° north latitude in the eastern, and 40° in the western hemisphere; while others impute the observed effects either to glaciers from local centres, or to floating icebergs of vast size passing over the surface during a period of submersion.

Without venturing to decide which of these various theories will be ultimately proved to be correct, we may state, that there is an increasing belief among geologists in the long duration of this ice-period, and the vast extent and great thickness attained by the ice-sheet. One of the most recent, and not the least able, of the writers on this question (Mr. Belt) shows strong reasons for adopting the view that the ice-period was simultaneous in both hemispheres; and he calculates that the vast amount of water abstracted from the ocean and locked up {152}in mountains of ice around the two poles, would lower the general level of the ocean about 2,000 feet. This would be equivalent to a general elevation of the land to the same amount, and would thus tend to intensify the cold; and this elevation may enable us to understand the recent discoveries of signs of glacial action at moderate elevations in Central America and Brazil, far within the tropics. At the same time, the weight of ice piled up in the north would cause the land surface to sink there, perhaps unequally, according to the varying nature of the interior crust of the earth; and since the weight has been removed land would rise again, still somewhat irregularly; and thus the phenomena of raised beds of arctic shells in temperate latitudes, are explained.

Now, it is evident, that the phenomena we have been considering--of the recent changes of the mammalian fauna in Europe, North America, South Temperate America, and the highlands of Brazil--are such as might be explained by the most extreme views as to the extent and vastness of the ice-sheet, and especially as to its simultaneous occurrence in the northern and southern hemispheres; and where two such completely independent sets of facts are found to combine harmoniously, and supplement each other on a particular hypothesis, the evidence in favour of that hypothesis is greatly strengthened. An objection that will occur to zoologists, may here be noticed. If the Glacial epoch extended over so much of the temperate and even parts of the tropical zone, and led to the extinction of so many forms of life even within the tropics, how is it that so much of the purely tropical fauna of South America has maintained itself, and that there are still such a vast number of forms, both of mammalia, birds, reptiles, and insects, that seem organized for an exclusive existence in tropical forests? Now Mr. Belt's theory, of the subsidence of the ocean to the extent of about 2,000 feet, supplies an answer to this objection; for we should thus have a tract of lowland of an average width of some hundreds of miles, added to the whole east coast of Central and South America. This tract would, no doubt, become covered with forests as it was slowly formed, would enjoy a perfectly {153}tropical climate, and would thus afford an ample area for the continued existence and development of the typical South American fauna; even had glaciers descended in places so low as what is now the level of the sea, which, however, there is no reason to believe they ever did. It is probable too, that this low tract, which all round the Gulf of Mexico would be of considerable width, offered that passage for intermigration between North and South America, which led to the sudden appearance in the former country in Post-Pliocene times, of the huge Megatheroids from the latter; a migration which took place in opposite directions as we shall presently show.

_The birth-place and migrations of some mammalian families and genera._--We have now to consider a few of those cases in which the evidence already at our command, is sufficiently definite and complete, to enable us to pronounce with some confidence as to the last movements of several important groups of mammalia.

_Primates._--The occurrence in North America of numerous forms of Lemuroidea, forming two extinct families, which are believed by American palæontologists to present generalized features of both Lemuridæ and Hapalidæ, while in Europe only Lemurine forms allied to those of Africa have occurred in deposits of the same age (Eocene), renders it possible that the Primates may have originated in America, and sent one branch to South America to form the Hapalidæ and Cebidæ, and another to the Old World, giving rise to the lemurs and true apes. But the fact that apes of a high degree of organization occur in the European Miocene, while in the Eocene, a monkey believed to have relations to the Lemuroids and Cebidæ has also been discovered, make it more probable that the ancestral forms of this order originated in the Old World at a still earlier period. The absence of any early tertiary remains from the tropical parts of the two hemispheres, renders it impossible to arrive at any definite conclusions as to the origin of groups which were, no doubt, always best developed in tropical regions.

_Carnivora._--This is a very ancient and wide-spread group, the families and genera of which had an extensive range in very {154}early times. The true bears (_Ursus_) are almost the only important genus that seems to have recently migrated. In Europe it dates back to the Older Pliocene, while in North America it is Post-Pliocene only. Bears, therefore, seem to have passed into America from the Palæarctic region in the latter part of the Pliocene period. They probably came in on the north-west, and passed down the Andes into South America, where one isolated species still exists.

_Ungulata._--Horses are very interesting. In Europe they date back under various forms to the Miocene period, and true _Equus_ to the Older Pliocene. In North America they are chiefly Pliocene, true _Equus_ being Post-Pliocene, with perhaps one or two species Newer Pliocene; but numerous ancestral forms date back to the Miocene and Eocene, giving a more perfect "pedigree of the horse" than the European forms, and going back to a more primitive type--_Orohippus_. In South America, _Equus_ is the only genus, and is Post-Pliocene or at most Newer Pliocene. While, therefore, the ancient progenitors of the Equidæ were common to North America and Europe, in Miocene and even Eocene times, true horses appear to have arisen in the Palæarctic region, to have passed into North America in the latter part of the Pliocene period, and thence to have spread over all suitable districts in South America. They were not, however, able to maintain themselves permanently in their new territory, and all became extinct; while in their birth-place, the Old World, they continue to exist under several varied forms.

True tapirs are an Old World group. They go back to the Lower Miocene in Europe, while in both North and South America they are exclusively Post-Pliocene. They occur in France down to the Newer Pliocene, and must, about that time, have entered America. The land connection by which this and so many other animals passed between the Old and New Worlds in late Tertiary times, was almost certainly in the North Pacific, south of Behring's Straits, where, as will be seen by our general map, there is a large expanse of shallow water, which a moderate elevation would convert into dry land, in a sufficiently temperate latitude.

{155}The peccary (_Dicotyles_), now a characteristic South American genus, is a recent immigrant from North America, where it appears to have been developed from ancestral forms of swine dating back to the Miocene period.

Antelopes are an Old World type, but a few of them appear to have entered North, and reached South America in late Pliocene times. Camels, strange to say, are a special North American type, since they abounded in that continent under various ancient forms in the Miocene period. Towards the end of that period they appear to have entered eastern Asia, and developed into the Siberian _Merycotherium_ and the North Indian _Camelus_, while in the Pliocene age the ancestral llamas entered South America.

_Cervidæ_ are a wide-spread northern type in their generalized form, but true deer (_Cervus_) are Palæarctic. They abounded in Europe in Miocene times, but only appear in North and South America in the later Pliocene and Post-Pliocene periods.

True oxen (_Bovinæ_) seem to be an Oriental type (Miocene), while they appear in Europe only late in the Pliocene period, and in America are confined to the Post-Pliocene.

Elephants (_Elephantidæ_) are an Old World type, abounding in the Miocene period in Europe and India, and first appearing in America in Post-Pliocene or later Pliocene times. Ancestral forms, doubtfully Proboscidean (_Dinocerata_), existed in North America in the Eocene period, but these became extinct without leaving any direct descendants, unless the _Brontotheridæ_ and rhinoceroses may be so considered.

Marsupials are almost certainly a recent introduction into South and North America from Asia. They existed in Europe in Eocene and Miocene times, and presumably over a considerable part of the Old World; but no trace of them appears in North or South America before the Post-Pliocene period.

_Edentata._--These offer a most curious and difficult problem. In South America they abound, and were so much more numerous and varied in the Post-Pliocene and Pliocene, that we may be sure they lived also in the preceding Miocene period. A few living Edentates are scattered over Africa and Asia, and {156}they flourished in Europe during the Miocene age--animals as large (in some species) as a rhinoceros, and most allied to living African forms. In North America no trace of Edentata has been found earlier than the Post-Pliocene period, or perhaps the Newer Pliocene on the west coast. Neither is there any trace of them in South America in the Eocene formations; but this may well be owing to our very imperfect knowledge of the forms of that epoch. Their absence from North America is, however, probably real; and we have to account for their presence in the Old World and in South America. Their antiquity is no doubt very great, and the point of divergence of the Old World and South American groups, may take us back to early Eocene, or even to Pre-Eocene times. The distribution of land and sea may then have been very different from what it is now; and to those who would create a continent to account for the migrations of a beetle, nothing would seem more probable than that a South Atlantic continent, then united parts of what are now Africa and South America. There is, however, so much evidence for the general permanence of what are now the great continents and deep oceans, that Professor Huxley's supposition of a considerable extension of land round the borders of the North Pacific Ocean in Mesozoic times, best indicates the probable area in which the Edentate type originated, and thence spread over much of the Old World and South America. But while in the latter country it flourished and increased with little check, in the other great continents it was soon overcome by the competition of higher forms, only leaving a few small-sized representatives in Africa and Asia.

{157}CHAPTER VIII.

VARIOUS EXTINCT ANIMALS;--AND ON THE ANTIQUITY OF THE GENERA OF INSECTS AND LAND MOLLUSCA.

EXTINCT MAMMALIA OF AUSTRALIA.

These have all been obtained from caves and late Tertiary or Post-Tertiary deposits, and consist of a large number of extinct forms, some of gigantic size, but all marsupials and allied to the existing fauna. There are numerous forms of kangaroos, some larger than any living species; and among these are two genera, _Protemnodon_ and _Sthenurus_, which Professor Garrod has lately shown to have been allied, not to any Australian forms, but to the _Dendrolagi_ or tree-kangaroos of New Guinea. We have also remains of _Thylacinus_ and _Dasyurus_, which now only exist in Tasmania; and extinct species of _Hypsiprymnus_ and _Phascolomys_, the latter as large as a tapir. Among the more remarkable extinct genera are _Diprotodon_, a huge thick-limbed animal allied to the kangaroos, but nearly as large as an elephant; _Nototherium_, having characters of _Macropus_ and _Phascolarctos_ combined, and as large as a rhinoceros; and _Thylacoleo_, a phalanger-like marsupial nearly as large as a lion, and supposed by Professor Owen to have been of carnivorous habits, though this opinion is not held by other naturalists.

Here then we find the same phenomena as in the other countries we have already discussed,--the very recent disappearance of a large number of peculiar forms, many of them far surpassing in size any that continue to exist. It hardly seems probable that in this case their disappearance can have been due to the direct effects of the Glacial epoch, since no very extensive {158}glaciation could have occurred in a country like Australia; but if the ocean sank 2,000 feet, the great eastern mountain range might have given rise to local glaciers. It is, however, almost certain that during late Tertiary times Australia must have been much more extensive than it is now. This is necessary to allow of the development of its peculiar and extensive fauna, especially as we see that that fauna comprised animals rivalling in bulk those of the great continents. It is further indicated by the relations with New Guinea, already alluded to, and by the general character of the various faunas which compose the Australian region, details of which will be found in the succeeding part of this work. The lowering of the ocean during the Glacial period would be favourable to the still further development of the fauna of such a country; and it is to the unfavourable conditions produced by its subsequent rising--equivalent to a depression of the land to the amount of two thousand feet--that we must impute the extinction of so many remarkable groups of animals. It is not improbable, that the disappearance of the ice and the consequent (apparent) subsidence of the land, might have been rapid as compared with the rate at which large animals can become modified to meet new conditions. Extensive tracts of fertile land might have been submerged, and the consequent crowding of large numbers of species and individuals on limited areas would have led to a struggle for existence in which the less adapted and less easily modifiable, not the physically weaker, would succumb.

There is, however, another cause for the extinction of large rather than small animals whenever an important change of conditions occurs, which has been suggested to me by a correspondent,[4] but which has not, I believe, been adduced by Mr. Darwin or by any other writer on the subject. It is dependent on the fact, that large animals as compared with small ones are almost invariably slow breeders, and as they also necessarily exist in much smaller numbers in a given area, they offer far less materials for favourable variations than do smaller animals. In such an extreme case as that of the rabbit and elephant, the {159}young born each year in the world are probably as some millions to one; and it is very easily conceivable that in a thousand years the former might, under pressure of rapidly changing conditions, become modified into a distinct species, while the latter, not offering enough favourable variations to effect a suitable adaptation, would become extinct. We must also remember the extreme specialization of many of the large animals that have become extinct--a specialization which would necessarily render modification in any new direction difficult, since the inherited tendency of variation would probably be to increase the specialization in the same directions which had heretofore been beneficial. If to these two causes we add the difficulty of obtaining sufficient food for such large animals, and perhaps the injurious effects of changes of climate, we shall not find it difficult to understand how such a vast physical revolution as the Glacial epoch, with its attendant phenomena of elevations and subsidences, icy winds, and sudden floods by the bursting of lake barriers, might have led to the total extinction of a vast number of the most bulky forms of mammalia, while the less bulky were able to survive, either by greater hardiness of constitution or by becoming more or less modified. The result is apparent in the comparatively small or moderate size of the species constituting the temperate fauna, in all parts of the globe.

It is much to be regretted that no mammalian remains of earlier date have been found in Australia, as we should then see if it is really the case that marsupials have always formed its highest type of mammalian life. At present its fossil fauna is chiefly interesting to the zoologist, but throws little light on the past relations of this isolated country with other parts of the globe.

MAMMALIAN REMAINS IN THE SECONDARY FORMATIONS.

In the oldest Tertiary beds of Europe and North America, we have (even with our present imperfect record) a rich and varied mammalian fauna. As compared with our living or recent highly specialized forms, it may be said to consist of generalised types; but as compared with any primeval mammalian type, it must be pronounced highly specialised. Not only are such diversified {160}groups as Carnivora, Perrissodactyle and Artiodactyle Ungulates, Primates, Chiroptera, Rodents, and Marsupials already well marked, but in many of these there is a differentiation into numerous families and genera of diverse character. It is impossible therefore to doubt, that many peculiar forms of mammalia must have lived long anterior to the Eocene period; but there is unfortunately a great gap in the record between the Eocene and Cretaceous beds, and these latter being for the most part marine continue the gap as regards mammals over an enormous lapse of time. Yet far beyond both these chasms in the Upper Oolitic strata, remains of small mammalia have been found; again, in the Stonesfield slate, a member of the Lower Oolite, other forms appear. Then comes the marine Lias formation with another huge gap; but beyond this again in the Upper Trias, the oldest of the secondary formations, mammalian teeth have been discovered in both England and Germany, and these are, as nearly as can be ascertained, of the same age as the _Dromatherium_ already noticed, from North America. They have been named _Microlestes_, and show some resemblance to those of the West Australian _Myrmecobius_. In the Oolitic strata numerous small jawbones have been found, which have served to characterise eight genera, all of which are believed to have been Marsupials, and in some of them a resemblance can be traced to some of the smaller living Australian species. These, however, are mere indications of the number of mammalia that must have lived in the secondary period, so long thought to be exclusively "the age of reptiles;" and the fact that the few yet found are at all comparable with such specialised forms as still exist, must convince us, that we shall have to seek far beyond even the earliest of these remains, for the first appearance of the mammalian type of vertebrata.

EXTINCT BIRDS.

Compared with those of mammalia, the remains of birds are exceedingly scarce in Europe and America; and from the wandering habits of so many of this class, they are of much less value {161}as indications of past changes in physical geography. A large proportion of the remains belong to aquatic or wading types, and as these have now often a world-wide range, the occurrence of extinct forms can have little bearing on our present inquiry. There are, however, a few interesting cases of extinct land-birds belonging to groups now quite strangers to the country in which they are found; and others scarcely less interesting, in which groups now peculiar to certain areas are shown to have been preceded by allied species or genera of gigantic size.

_Palæarctic Region and N. India._--In the caves and other Post-Pliocene deposits of these countries, the remains of birds almost all belong to genera now inhabiting the same districts. Almost the only exceptions are, the great auk and the capercailzie, already mentioned as being found in the Danish mounds; the latter bird, with _Tetrao albus_, in Italian caverns; and a species of pheasant (_Phasianus_) said to have occurred in the Post-Pliocene of France, considerably west of the existing range of the genus in a wild state.

In the preceding Pliocene deposits, but few remains have been found, and all of existing genera but one, a gallinaceous bird (_Gallus bravardi_) allied to the domestic fowl and peacock.

The Miocene beds of France and Central Europe have produced many more remains of birds, but these, too, are mostly of existing European genera, though there are some notable exceptions. Along with forms undistinguishable from crows (_Corvus_), shrikes (_Lanius_), wagtails (_Motacilla_), and woodpeckers (_Picus_), are found remains allied to the Oriental edible-nest swift (_Collocalia_) and _Trogon_; a parrot resembling the African genus _Psittacus_; an extinct form _Necrornis_, perhaps allied to the plantain-eaters (_Musophaga_); _Homalophus_, doubtfully allied to woodpeckers, and _Limnatornis_ to the hoopoes. The gallinaceous birds are represented by three species of pheasants, some very close to the domesticated species; _Palæoperdix_ allied to the partridges; and _Palæortyx_, small birds allied to the American genus _Ortyx_, but with larger wings. There are also species of _Pterocles_ allied to living birds, and a small pigeon. There are numerous living genera of Accipitres; such as eagle (_Aquila_), {162}kite (_Milvus_), eagle-owl (_Bubo_), and screech-owl (_Strix_); with the African secretary-bird (_Serpentarius_), and some extinct forms, as _Palæocercus_, _Palæohierix_ and _Palæetus_.

Aquatic and wading birds were abundant, including numerous rails, bustards, herons, sandpipers, gulls, divers, and pelicans. There were also many ducks, some allied to the genus _Dendrocygna_; the Oriental genus of storks, _Leptoptilus_; _Ibidipodia_, a remarkable form allied to _Ibis_ and _Ciconia_; _Elornis_, near _Limosa_; _Pelagornis_, a large bird allied to gannets and pelicans; _Hydrornis_, allied to the ducks and petrels; _Dolichopterus_, allied to plovers. Perhaps the most interesting of these extinct birds are, however, the flamingoes, represented by forms hardly distinguishable from living species, and by one extinct genus _Palælodus_, which had very long toes, and probably walked on aquatic plants like the tropical jacanas.

The Miocene beds of North India have furnished few birds; the only one of geographical interest being an extinct species of ostrich, not very different from that now inhabiting Arabia.

On the whole, the birds of Europe at this period were very like those now living, with the addition of a few tropical forms. These latter were, however, perhaps more numerous and important than they appear to be, as they belong to inland and forest-haunting types, which would not be so frequently preserved as the marsh and lake-dwelling species. Taking this into consideration, the assemblage of Miocene birds accords well with what we know of the mammalian fauna. We have the same indications of a luxuriant vegetation and subtropical climate, and the same appearance of Oriental and especially of African types. _Trogon_ is perhaps the most interesting of all the forms yet discovered, since it furnishes us with a central point whence the living trogons of Asia, Africa, and South America might have diverged.

In the Eocene we find ourselves almost wholly among extinct forms of birds. The earliest known Passerine bird is here met with, in _Protornis_, somewhat similar to a lark, found in the Lower Eocene of Switzerland; while another Passerine form, _Palægithalus_, and one allied to the nuthatch (_Sitta_), have been {163}discovered in the Upper Eocene of Paris. Picariæ of equal antiquity are found. _Cryptornis_, from the Paris Eocene, and _Halcyornis_ from the Lower Eocene of the Isle of Sheppey, were both allied to kingfishers; while a form allied to _Centropus_ a genus of cuckoos, or, as Milne-Edwards thinks, to the Madagascar _Leptosomus_, has been found in the Upper Eocene of France. Several _Accipitres_ of somewhat doubtful affinities have been found in the same country; while _Lithornis_, from the Lower Eocene of the Isle of Sheppey, was a small vulturine bird supposed to be allied to the American group, _Cathartes_. Among the waders, some extinct forms of plovers have been found, and a genus (_Agnopterus_), allied to the flamingoes; while there are many swimming birds, such as pelicans, divers, and several extinct types of doubtful affinities. Most intersting of all is a portion of a cranium discovered in the Lower Eocene of Sheppey, and lately pronounced by Professor Owen to belong to a large Struthious bird, allied to the New Zealand _Dinornis_ and also perhaps to the ostrich. Another gigantic bird is the _Gastornis_, from the Lower Eocene of Paris, which was as large as an ostrich, but which is believed to have been a generalised type, allied to wading and swimming birds as well as to the Struthiones.

Beyond this epoch we have no remains of birds in European strata till we come to the wonderful _Archæopteryx_ from the Upper Oolite of Bavaria; a bird of a totally new type, with a bony tail, longer than the body, each vertebra of which carried a pair of diverging feathers.

_North America._--A number of bird-remains have lately been found in the rich Tertiary and Cretaceous deposits of the United States; but here, too, comparatively few are terrestrial forms. No Passerine bird has yet been found. The Picariæ are represented by _Uintornis_, an extinct form allied to woodpeckers, from the Eocene of Wyoming. Species of turkey (_Meleagris_) occur in the Post-Pliocene and as far back as the Miocene strata, showing that this interesting type is a true denizen of temperate North America. The other birds are, _Accipitres_; waders and aquatics of existing genera; and a number of extinct forms of the two latter orders--such as, _Aletornis_ an Eocene wader; {164}_Palæotringa_, allied to the sandpipers, and _Telmatobius_ to the rails, both Cretaceous; with _Graculavus_, allied to _Graculus_; _Laornis_ allied to the swans; _Hesperornis_ a gigantic diver; and _Icthyornis_ a very low form, with biconcave vertebra, such as are only found in fishes and some reptiles--also from Cretaceous deposits.

_South America._--The caverns of Brazil produced thirty-four species of birds, most of them referable to Brazilian genera, and many to still existing species. The most interesting were two species of American ostrich (_Rhea_), one larger than either of the living species; a large turkey-buzzard (_Cathartes_); a new species of the very isolated South American genus _Opisthocomus_; and a _Cariama_, or allied new genus.

_Madagascar and the Mascarene Islands._--We have here only evidence of birds that have become extinct in the historical period or very little earlier. First we have a group of birds incapable of flight, allied to pigeons, but forming a separate family, _Dididæ_; and which, so far as we yet know, inhabited Mauritius, Rodriguez, and probably Bourbon. _Aphanapteryx_, an extinct genus of rails, inhabited Mauritius; and another genus, (_Erythromachus_), Rodriguez. A large parrot, said by Prof. Milne Edwards to be allied to _Ara_ and _Microglossus_, also inhabited Mauritius; and another allied to _Eclectus_, the island of Rodriguez. None of these have been found in Madagascar; but a gigantic Struthious bird, _Æpyornis_, forming a peculiar family distinct both from the ostriches of Africa and the _Dinornis_ of New Zealand inhabited that island; and there is reason to believe that this may have lived less than 200 years ago.

_New Zealand._--A number of extinct Struthious birds, forming two families, _Dinornithidæ_ and _Palapterygidæ_, have been found in New Zealand. Some were of gigantic size. They seem allied both to the living _Apteryx_ of New Zealand and the emu of Australia. They are quite recent, and some of them have probably lived within the last few centuries. Remains of _Dinornis_ have also been found in a Post-Pliocene deposit in Queensland, N. E. Australia[5]--a very important discovery, as it {165}gives support to the theory of a great eastward extension of Australia in Tertiary times.

EXTINCT TERTIARY REPTILES.

These will not occupy us long, as no very great number are known, and most of them belong to a few principal forms of comparatively little geographical interest.

Tortoises are perhaps the most abundant of the Tertiary reptiles. They are numerous in the Eocene and Miocene formations both in Europe and North America. The genera _Emys_ and _Trionyx_ abound in both countries, as well as in the Miocene of India. Land tortoises occur in the Eocene of North America and in the Miocene of Europe and India, where the huge _Colossochelys_, twelve feet long, has been found. In the Pliocene deposits of Switzerland the living American genus _Chelydra_ has been met with. These facts, together with the occurrence of a living _species_ in the Miocene of India, show that this order of reptiles is of great antiquity, and that most of the genera once had a wider range than now.

Crocodiles, allied to the three forms now characteristic of India, Africa, and America, have been found in the Eocene of our own country, and several species of _Crocodilus_ have occurred in beds of the same age in North America.

Lizards are very ancient, many small terrestrial forms occurring in all the Tertiary deposits. A species of the genus _Chamæleo_ is recorded from the Eocene of North America, together with several extinct genera.

Snakes were well developed in the Eocene period, where remains of several have been found which must have been from twelve to twenty feet long. An extinct species of true viper has occurred in the Miocene of France, and one of the Pythonidæ in the Miocene brown coal of Germany.

Batrachia occur but sparingly in a fossil state in the Tertiary deposits. The most remarkable is the large Salamander (_Andreas_) from the Upper Miocene of Switzerland, which {166}is allied to the _Menopoma_ living in North America. Species of frog (_Rana_), and _Palæophryus_ an extinct genus of toads, have been found in the Miocene deposits of Germany and Switzerland.

Fresh water fish are almost unknown in the Tertiary deposits of Europe, although most of the families and some genera of living marine fish are represented from the Eocene downwards.

ANTIQUITY OF THE GENERA OF INSECTS.

Fossil insects are far too rarely found, to aid us in our determination of difficult questions of geographical distribution; but in discussing these questions it will be important to know, whether we are to look upon the existing generic forms of insects as of great or small antiquity, compared with the higher vertebrates; and to decide this question the materials at our command are ample.

The conditions requisite for the preservation of insects in a fossil state are no doubt very local and peculiar; the result being, that it is only at long intervals in the geological record that we meet with remains of insects in a recognisable condition. None appear to have been found in the Pliocene formation; but in the Upper Miocene of Oeninghen in Switzerland, associated with the wonderfully rich fossil flora, are found immense quantities of insects. Prof. Heer examined more than 5,000 specimens belonging to over 800 species, and many have been found in other localities in Switzerland; so that more than 1,300 species of Miocene insects have now been determined. Most of the orders are represented, but the beetles (Coleoptera) are far the most abundant. Almost all belong to existing genera, and the majority of these genera now inhabit Europe, only three or four being exclusively Indian, African, or American.

In the Lower Miocene of Croatia there is another rich deposit of insects, somewhat more tropical in character, comprising large white-ants and dragon-flies differently marked from any {167}now inhabiting Europe. A butterfly is also well preserved, with all the markings of the wings; and it seems to be a _Junonia_, a tropical genus, though it may be a _Vanessa_, which is European, but the fossil most resembles Indian species of _Junonia_.

The Eocene formations seem to have produced no insect remains; but they occur again in the Upper Cretaceous at Aix-la-Chapelle, where two butterflies have been found, _Cyllo sepulta_ and _Satyrites Reynesii_, both belonging to the Satyridæ, and the former to a genus now spread over Africa, India, and Australia.

A little earlier, in the Wealden formation of our own country, numerous insects have been found, principally dragon flies (_Libellula_, _Æshna_); aquatic Hemiptera (_Velia Hydrometra_); crickets, cockroaches, and cicadas, of familiar types.

Further back in the Upper Oolite of Bavaria--which produced the wonderful long-tailed bird, _Archæopteryx_--insects of all orders have been found, including a moth referred to the existing genus _Sphinx_.

In the Lower Oolite of Oxfordshire many fossil beetles have been found whose affinities are shown by their names:--_Buprestidium_, _Curculionidium_, _Blapsidium_, _Melolonthidium_, and _Prionidium_; a wing of a butterfly has also been found, allied to the Brassolidæ now confined to tropical America, and named _Palæontina oolitica_.

Still more remote are the insects of the Lias of Gloucestershire, yet they too can be referred to well-known family types--Carabidæ, Melolonthidæ, Telephoridæ, Elateridæ, and Curculionidæ, among beetles; Gryllidæ and Blattidæ among Orthoptera; with _Libellula_, _Agrion_, _Æshna_, _Ephemera_, and some extinct genera. When we consider that almost the only vertebrata of this period were huge Saurian reptiles like the _Icthyosaurus_, _Plesiosaurus_, and _Dinosaurus_, with the flying Pterodactyles; and that the great mass of our existing genera, and even families, of fish and reptiles had almost certainly not come into existence, we see at once that types of insect-form are, proportionately, far more ancient. At this remote epoch we find the chief family types (the _genera_ of the time of Linnæus) perfectly differentiated {168}and recognisable. It is only when we go further back still, into the Palæozoic formations, that the insect forms begin to show that generalization of type which renders it impossible to classify them in any existing groups. Yet even in the coal formation of Nova Scotia and Durham, the fossil insects are said by competent entomologists to be "allied to _Ephemera_," "near _Blatta_," "near _Phasmidæ_;" and in deposits of the same age at Saarbrück near Trèves, a well-preserved wing of a grasshopper or locust has been found, as well as a beetle referred to the Scarabeidæ. More remarkable, however, is the recent discovery in the carboniferous shales of Belgium, of the clearly-defined wing of a large moth (_Breyeria borinensis_), closely resembling some of the Saturniidæ; so that we have now all the chief orders of Insects--including those supposed to be the most highly developed and the most recent--well represented at this very remote epoch. Even the oldest insects, from the Devonian rocks of North America, can mostly be classed as Neuroptera or Myriapoda, but appear to form new families.

We may consider it, therefore, as proved, that many of the larger and more important genera of insects date back to the beginning of the Tertiary period, or perhaps beyond it; but the family types are far older, and must have been differentiated very early in the Secondary period, while some of them perhaps go back to Palæozoic times. The great comparative antiquity of the _genera_ is however the important fact for us, and we shall have occasion often to refer to it, in endeavouring to ascertain the true bearing of the facts of insect distribution, as elucidating or invalidating the conclusions arrived at from a study of the distribution of the higher animals.

ANTIQUITY OF THE GENERA OF LAND AND FRESH-WATER SHELLS.

The remains of land and fresh-water shells are not much more frequent than those of insects. Like them, too, their forms are very stable, continuing unchanged through several geological {169}periods. In the Pliocene and Miocene formations, most of the shells are very similar to living species, and some are quite identical. In the Eocene we meet with ordinary forms of the genera _Helix_, _Clausilia_, _Pupa_, _Bulimus_, _Glandina_, _Cyclostoma_, _Megalostoma_, _Planorbis_, _Paludina_ and _Limnæa_, some resembling European species, others more like tropical forms. A British Eocene species of _Helix_ is still living in Texas; and in the South of France are found species of the Brazilian sub-genera _Megaspira_ and _Anastoma_. In the secondary formation no true land shells have been found, but fresh water shells are tolerably abundant, and almost all are still of living forms. In the Wealden (Lower Cretaceous) and Purbeck (Upper Oolite) are found _Unio_, _Melania_, _Paludina_, _Planorbis_, and _Limnæa_; while the last named genus occurs even in the Lias.

The notion that land shells were really not in existence during the secondary period is, however, proved to be erroneous by the startling discovery, in the Palæozoic coal measures of Nova Scotia, of two species of Helicidæ, both of living genera--_Pupa vetusta_, and _Zonites priscus_. They have been found in the hollow trunk of a _Sigillaria_, and in great quantities in a bed full of Stigmarian rootlets. The most minute examination detects no important differences of form or of microscopic structure, between these shells and living species of the same genera! These mollusca were the contemporaries of Labyrinthodonts and strange Ganoid fishes, which formed almost the whole vertebrate fauna. This unexpected discovery renders it almost certain, that numbers of other existing genera, of which we have found no traces, lived with these two through the whole secondary period; and we are thus obliged to assume as a probability, that any particular genus has lived through a long succession of geological ages. In estimating the importance of any peculiarities or anomalies in the geographical distribution of land shells as compared with the higher vertebrates, we shall, therefore, have to keep this possible, and even probable high antiquity, constantly in mind.

We have now concluded our sketch of Tertiary Palæontology as a preparation for the intelligent study of the Geographical {170}Distribution of Land Animals; and however imperfectly the task has been performed, the reader will at all events have been convinced that some such preliminary investigation is an essential and most important part of our work. So much of palæontology is at present tentative and conjectural, that in combining the information derived from numerous writers, many errors of detail must have been made. The main conclusions have, however, been drawn from as large a basis of facts as possible; and although fresh discoveries may show that our views as to the past history of some of the less important genera or families are erroneous, they can hardly invalidate our results to any important degree, either as regards the intercommunications between separate regions in the various geological epochs, or as to the centres from which some of the more important groups have been dispersed.