Part 9

The food of _Pontia Freyeri_ is doubtful. All the living species of the genus so far as known, feed upon Cruciferæ; within this family they do not seem to be at all particular, making use of a large number of genera, but in only a single instance are they known to attack the leaves of a genus (Reseda) belonging to an adjoining family. Cruciferæ, however, are excessively rare in the tertiaries of Europe, two species only being recorded, and this from the comparatively recent beds of Œningen. This is unquestionably due simply to the nature of the plants themselves, which scarcely could leave any trace of their existence; the almost complete absence of the herbaceous families of plants, even in the later tertiaries, is doubtless due to this fact. The plants nearest related to the Cruciferæ found near the horizon of _Pontia Freyeri_ are a species of Nelumbium from Günzbourg in the Mayencian, and of Terminalia (_T. radobojensis_ Ung.)—one of the Calycifloræ, from Radoboj itself. Perhaps in the absence of better evidence we may provisionally consider the latter to have been the food plant of _P. Freyeri_.

A single Radoboj species remains, _Eugonia atava_. The recent species of Eugonia feed particularly on Salix, Populus and Betula; also upon Ulmus, and occasionally on Ribes, and even on Hippophae. The first three seem however to be their proper food; and since the tertiaries of Radoboj contain fossils of all these genera, we need look no farther. There are specified: _Salix apollinis_ Ung., sp., _Populus latior_ Br., _P. mutabilis_ Heer., _P. Heliadum_ Ung., _Betula Dryadum_ Brongn. and _B. prisca_ Ett. Three species of Ulmus are also recorded from the same place.

Excepting in a single case, there is then no difficulty in finding, in the very hods in which the butterflies occur, remains of plants, which in all probability served them as food during the larval stage; and even in this single instance, a plant not far removed from those upon which species of the genus now feed, occurs in the same strata.

PRESENT DISTRIBUTION OF BUTTERFLIES MOST NEARLY ALLIED TO FOSSIL SPECIES.

To discuss this question properly we must consider the butterflies of each geological horizon separately.

BUTTERFLIES OF THE LIGURIAN (Upper Eocene).

The nearest living ally of _Neorinopis sepulta_ is, with little doubt, _Neorina Lowi_, which, like the other members of the genus, is found in the Indo-Malayan region. The same is strictly true of the species of Zophoessa, Debis and Lethe, with which we have been obliged to compare this fossil. Cœlites has also been used in comparison, and most of the species of this group belong to the same region, although one is described by Felder from Celebes on the confines of the Austro-Malayan region. We have also pointed out (as Butler has done, but in incorrect points) its relation to Antirrhæa, a Brazilian genus, but this is too distant to be given much weight. The closest allies of _N. sepulta_ are to be found in the Indo-Malayan region.

The same is true, but not to so striking a degree, of _Lethites Reynesii_. We have compared this also to Debis, Lethe and Neorina, and especially to the two former; and all three of these genera, which are certainly its nearest allies, are strictly confined to the Indo-Malayan region. It is, however, also related, but in a secondary degree, to Enodia, Cercyonis and Maniola, which are genera appertaining to the north temperate zone of both hemispheres.

_Coliates Proserpina_ finds its nearest living representatives in the genus Delias, which also is strictly confined to the Indo-Malayan region. Thyca and Prioneris are closely related, the latter of which is limited to the same district and the former to the Indo-Malayan and Austro-Malayan regions.

_Thaites Ruminiana_ is represented in recent times by the genus Thais, which is confined to the Mediterranean district, within which Aix lies. An allied genus, Archon, is also restricted to the same region. Sericinus, however, and Eurycus, with which we have been obliged to compare it in many points, are found only in the East, the former in China, the latter in Australia; while on the other hand, Parnassius, a genus it quite as much resembles, is limited to alpine and subarctic regions of the northern hemisphere.

The relations of _Pamphilites abdita_ are very different. I have searched carefully for very closely allied forms among East Indian Urbicolæ; but, while it doubtless is not far removed from some of them, its more intimate relationships are certainly with insects from tropical America and especially with Pansydia and Carystus.

Three out of the five Aix butterflies, therefore, find their nearest living allies in the Indo-Malayan region, one is most closely related to forms now found in tropical America and one is at home in its own resting place.

BUTTERFLIES OF THE AQUITANIAN (Lower Miocene).

_Thanatites vetula_ is the only butterfly yet found from this horizon, and this is closely related to Thanaos, a genus belonging to the north temperate zones of both hemispheres, but vastly more developed in the new world, which has at least four times as many species as the old, some of them extending into the subtropical regions. The genera adjacent to Thanaos are purely American, although tropical or subtropical, and therefore the Aquitanian butterfly looks toward subtropical North America for its relatives of the present day.

BUTTERFLIES OF THE MAYENCIAN (Middle Miocene).

Only a single one of these butterflies, _Mylothrites Pluto_, belongs to an extinct genus. Its nearest living representatives are to be looked for in the genera Mylothris and Hebomoia, the former of which finds its highest development in torrid Africa, while the latter is confined to the Indo-Malayan and Austro-Malayan regions.

The other two belong to modern genera, Eugonia (_E. atava_) and Pontia (_P. Freyeri_). These two genera are very similar in their distribution, spreading, like Thanaos, above referred to, over the north temperate regions of both hemispheres. Eugonia, however, is represented equally in Europe and America, while Pontia is considerably richer in species in the Old World than in the New; yet when we look into the distribution of the neighboring genera we shall find a result somewhat similar to the case of Thanaos. Taking into consideration, in the one case, the present distribution of the genera Hypanartia, Polygonia, Papilio and Hamadryas,[AQ] and on the other of Neophasia, Tatocheila and Leptophobia, we shall find that the largest development of these groups of genera has been in the New World rather than in the Old, but in those parts of the New World which lie on the tropical confines of the temperate zone.

Two of the more recent species of fossil butterflies are therefore at home where they are found, although the present development of the group of genera to which they belong finds its fullest expression in America; while the third species follows most of those from the lower tertiaries in seeking its allies of to-day in the tropics of the old world.

* * * * *

Undoubtedly the material at our disposal is, as we have already remarked, far too meagre to present any generalities of importance, so long as they are unsupported by external proof. This aid we can claim in considering the facts we have presented concerning the present distribution of the genera of butterflies most nearly allied to those once living in the neighborhood of Aix. The careful researches of Count Saporta upon the rich flora of this region at the same epoch, points to very nearly the same results as are here indicated. In his _Examen des flores tertiaires de Provence_,[AR] when writing of the characteristics of the Aix flora, Count Saporta says (page 150) that about one-fifth of the families represented in it are now strangers to Europe; that fifty-one genera have an exotic and more or less tropical aspect, and that forty out of seventy-four, or about one-half, if not exclusively tropical, inhabit the warmer parts of southern regions, or, in small numbers, temperate extra-European countries. The result is still more striking, if species are considered, of which there are at least eighty whose individual analogy with living species is sufficiently clear to yield results of great probability. “De ces espèces,” to use his own words, “12 seulement correspondent à des espèces de l’Europe moyenne, 6 à des espèces de l’Europe méridionale, 18 en tout. Les espèces correspondant à des formes de l’Amérique septentrionale ou des régions élevées de l’Amérique tropicale, sont au nombre de 10; celles qui répondent à des formes de l’Amérique tropicale s’élèvent à 9 …; 3 correspondent à des espèces du Cap et 2 à des espèces des îles Atlantiques et de la Barbarie; 14 représentent des formes particulières aux Indes ou aux îles de l’Archipel indien et 30, enfin, correspondent à des formes australiennes. Le groupe australien est donc le plus considérable, si on les prend isolement. En les réunnissant, on voit que sur les 80 et quelques espèces, 28 à 30 seulement correspondent à des formes habitant aujourd’hui l’Europe et l’Amérique du Nord, en y comprenant même les parties méridionales de ces continents; tandis que 57 au moins, soit 60 en nombre rond, représentent des formes tropicales ou subtropicales, et dans ce nombre 40 au moins, c’est-a-dire la moitié du nombre total se rapportent au Cap, aux [151] Indes orientales où à l’Australie; de sorte que le caractère dominant de cette flore est encore Austro-indien, quoique dans une proportion déjà décroissante par rapport à l’âge précédant.”

This was published in 1861, and would accord entirely with what we know of the butterflies of Aix and their nearest allies. But eleven years later, after studying the great amount of material which had meanwhile accumulated, Saporta seems to have reached different conclusions, for in his _Revision de la Flore des Gypses d’Aix_ he states that the affinities of the eocene vegetation of Aix are with southeastern Asia and with Africa, and lists of analogous species are given, showing that twenty-two Aix species are to be compared with similar types in Asia, and forty with those of Africa. So that African forms much surpass the Asiatic in the eocene flora of Aix. This is particularly true, he says, with reference to the region of Africa between Abyssinia and the Cape of Good Hope. “C’est là évidemment le pays qui nous offre le tableau le plus ressemblant de ce que devait être le midi de la France, et c’est aussi vers ce même pays, ne l’oublions pas, que nous avons été ramenés par l’examen des autres élémens de la flore, spécialement par la proportion relative des deux grandes classes et des familles prédominantes.”[AS] The African element seems to be almost altogether wanting in the eocene butterflies, while the Asiatic predominates. In a chart accompanying Count Saporta’s paper, however, he represents the present limits of the _principal genera_ noticed in the flora of the gypsum of Aix by means of colored lines. These lines cluster remarkably along the southern borders of Asia and extend over a large part of Africa and across the ocean to America, and particularly toward the southern United States and the Antilles. Based on the distribution of these principal genera alone, the flora of the southern border of Asia would show a closer affinity to that of eocene Aix than would that of any equivalent belt in Africa; and if we may suppose that our relics of butterflies represent the principal genera then existing, we should trace a somewhat similar chart, but for the entire absence of African types; for subtropical American types mingle with those of the Mediterranean district and especially with those of the Indo-Malayan region. Count Saporta shows in his memoir just quoted, as before, that the relations of the eocene flora of Aix to that of the present Mediterranean basin were more restricted than its relations to exotic types, but in a letter to me he writes: “Ces affinités [les affinités présumées de la flore d’Aix] sont d’une part avec la région Méditerranéen, de l’autre avec l’Afrique et les Indes orientales. Les affinités miocènes avec l’Amérique sont postérieures.” These later American affinities are, however, foreshadowed among the plants and also, as we have seen, in the Pamphilites of eocene Aix. They appear again, and very decidedly, when we reach the miocene itself, for the affinities of the butterfly from Rott, and two of the later butterflies from Radoboj (where first we meet with truly modern types), are certainly with America in the first instance, and secondarily with the whole north temperate zone. While the last of the Radoboj butterflies shows still the remains of the earlier affinities of the Aix flora in finding its nearer existing types in Africa and southeastern Asia. The results we reach in considering the Aix butterflies are not, however, in accordance with those drawn from the insects of the same locality by Professor Heer. He writes:[AT]—

“A Radoboj, … on rencontre une plus forte proportion de formes tropicales [than at Œningen].…

Cette faune des insectes s’harmonise parfaitement avec le flore de Radoboj qui, ainsi que nous l’avons prouvé précédemment, a un caractère plus méridional que celle d’Œningen; ce qui s’expliquerait par sa plus grande ancienneté.

Comme il résulte des recherches de M. G. de Saporta qu’Aix appartient à l’étage ligurien, on devrait s’attendre à y rencontrer encore plus de formes tropicales qu’à Radoboj. C’est tout le contraire, si bien qu’en m’appuyant sur la faune et en voyant que Aix avait 10 espèces en commun avec Radoboj et 4 avec Œningen, j’avais rapporté précédemment les terrains d’Aix à la même époque que ceux de Radobo; et je les avais rangés dans le Mayencien. Quatre genres ont disparu.… Tous les autres genres vivent encore dans la Provence, mais ce sont, comme à Œningen, presque tous des genres qui occupent une aire géographique très vaste.… On ne peut pas dire que la faune des insectes d’Aix contredise positivement l’idée que cette localité avait un climat sous-tropical, cas presque tous les genres que l’on y a observés jusqu’à présent s’étendent jusque dans la zône sous-tropicale, néanmoins cette faune ne fournit que bien peu de preuves positives, tandis que, comme M. de Saporta l’a démontré, la flore est riche en formes méridionales.”

It should be remarked, however, that the insect fauna of Aix is as yet little known; that these observations of the learned Zurich Professor were founded upon a material exceedingly meagre, in comparison with the present vast accumulations of the museums of Marseilles, Paris and Aix; we may hope soon to become familiar with them through the careful researches of M. Oustalet; and these will show that the beds of Aix are, perhaps, even richer in fossil insects than those of Œningen.

The American affinities of the Rott butterfly are in entire harmony with what is known of the other insects of the lignites of the Rhine, where, says Professor Heer:[AU]—“On retrouve également des types américains, qui appertiennent à l’Amérique tropicale et sous-tropicale.”

As to the flora of Radoboj, Professor Heer writes in the work just quoted (p. 96): “Les plantes de la zône tempérée sont représentées plus fortement qu’à Sotzka,” and of the latter place he says (p. 95), after speaking of types of the temperate zone: “Cependant ces espèces se trouvent fort à l’arrière-plan en comparison des formes tropicales et subtropicales, parmi lesquelles prédominent … les formes indo-australiens; néanmoins les formes américains, loin d’y faire défaut, sont représentées par des types assez nombreux et nettement accusés.” As a whole, therefore, the affinities of the tertiary butterflies seem to be precisely what we should have anticipated from a study of the vegetation of the period.

We close this portion of our subject with a tabular view of the results we have reached in considering the affinities of the tertiary butterflies with living types, in which the countries, where the living allies of the fossil forms are now found, are placed in the right-hand columns according to the degree of affinity of their inhabitants to the tertiary species against which they are placed.

+--------+------------+------------------------------------------------+ | | | DEGREE OF AFFINITIES. | | |NAMES OF +--------------+------------+----------+---------+ | |BUTTERFLIES.| FIRST | SECOND | THIRD | FOURTH | | | | DEGREE. | DEGREE. | DEGREE. | DEGREE. | | +------------+--------------+------------+----------+---------+ | |Neorinopis |Indo-Malayan. | Austro- | |S. | | |sepulta. | | Malayan. | |American.| | +------------+--------------+------------+----------+---------+ | Aix— |Lethites |Indo-Malayan. | | |North | | Upper |Reynesii. | | | |temperate| |Eocene. | | | | |Zone. | | +------------+--------------+------------+----------+---------+ | |Coliates |Indo-Malayan. | |Austro- | | | |Proserpina. | | |Malayan. | | | +------------+--------------+------------+----------+---------+ | |Thaites |Mediterranean.|Chinese and Australian,| | | |Ruminiana. | | Subarctic and Alpine. | | | +------------+--------------+------------+----------+---------+ | |Pamphilites | Tropical | | |Indo- | | |abdita. | America. | | |Malayan. | +========+============+==============+============+==========+=========+ | | | | | | | | Rott— |Thanatites | Subtropical | North | | | | lower |vetula. | North | temperate | | | |miocene.| | America. | Zone. | | | | | | | | | | +========+============+==============+============+==========+=========+ | | | Subtropical | North | | | | |Eugonia | temperate | temperate | | | | |atava. | America. | Zone. | | | | +------------+--------------+------------+----------+---------+ |Radoboj—| | Subtropical | North | | | | middle |Pontia | temperate | temperate | | | |miocene.|Freyeri. | America. | Zone. | | | | +------------+--------------+------------+----------+---------+ | | | | Indo- | | | | |Mylothrites | African. | Malayan. | | | | |Pluto. | | Austro- | | | | | | | Malayan. | | | +--------+------------+--------------+------------+----------+---------+

GENERAL RESUME, WITH NOTICES OF UNDETERMINED FORMS.

Nine well authenticated fossil butterflies are now known, all from the European Tertiaries; five of these have been found in the gypsum beds of Aix in Provence, southern France, belonging to the Ligurian, a division of the upper eocene; one in the lignites of Rott in the Rhenish Provinces of Prussia, belonging to the Aquitanian, or lower miocene; and three in the marls of Radoboj in Croatia, Austria, appertaining to the Mayencian or middle miocene. Our present knowledge, then, places the apparition of butterflies towards the end of the lower tertiaries.

As a general rule the specimens thus far discovered are in a fair state of preservation, and especially are those parts preserved which enable us, with considerable confidence, to determine their exact affinities. Three of these insects belong to the highest family of butterflies, Nymphales, four to the Papilionidæ, and two only to the Urbicolæ. If it be considered probable that the lowest of these families was the oldest, we can reasonably account for the scarcity of its members in the tertiary strata by the fact that their almost universally robust and muscular frame enables them to maintain flight when they have lost all but the merest stubs of wings. They would thus seldom meet their end by falling into pools of water, or if at last they did, it would be with fragments of wings whose affinities could not be traced. This supposition would be strengthened on noticing that one of the two fossil forms classed here, _Thanatites vetula_, belongs to a group of genera which comprises the very feeblest flyers in the family; and by the further consideration that two of the three fossil Nymphalids belong to the weak-winged Oreades. Eugonia, as well as Pamphilites, were doubtless strong and bold flyers; while the genera of Papilionidæ were moderately endowed. To proceed further in the analysis of their structural relations, two of the three Nymphales belong, as we have said, to the highest group of butterflies, the Oreades, represented now by the dark brown butterflies of our meadows; the remaining one to the Præfecti, a group of gaily attired butterflies with angulated wings like our common thistle butterfly, the cosmopolite. Of the four Papilionidæ, three belong to the Danai; two of these three to the group Fugacia, represented by our common yellow brimstone butterflies; the third to the Voracia, or white butterflies of the garden, so destructive to cabbages and other cruciferous plants. The fourth Papilionid belongs to the lower subfamily Papilionides; not, however, to that group which contains our swallow-tailed butterflies, but rather to an allied tribe, represented in America only by the Parnasii of the Rocky Mountain region. The two Urbicolæ are divided between the Hesperides and Astyci, the former closely related to the dingy, sylvan hesperians of early spring, seldom seen but by the naturalist; the latter to the tawny, brisk little skippers busy around the flowers in June.

But a single family of butterflies, then, is unknown in a fossil state,—that of Rurales; and since this comprises, in the main, insects of exceedingly delicate structure and of small size, their absence is by no means unaccountable. Yet, as we shall see further on, there are intimations of the presence of some of their caterpillars in amber, and an obscure and doubtful reference to a fossil Polyommatus from the beds of Aix.

If we enquire where the allies of these nine fossil butterflies are now living, we must seek for those of four of them in the East Indies; for those of three of them in America, and especially in that part lying on the confines of the tropical and north temperate zones; for those of one of them in the north temperate zone of both Europe-Asia and America; and for those of one in the Mediterranean district; for those of two only, therefore, out of the nine, or less than one-fourth, in the region where the fossils were discovered. Analyzing this point still further, we notice that three out of the four species whose living allies are to be sought in the East Indies come from the older deposits of Aix, and that only one of the two remaining Aix species shows special affinities to American types; we thus find here, as among other insects and among the plants, a growing likeness to American types as we pass upward through the European tertiaries.