CHAPTER XV

THE SCIENCE OF FOSSIL LIFE

It gradually dawned on the minds of men that the crust of the earth is like a gigantic mausoleum, containing within it the remains of numerous and varied forms of life that formerly existed upon the surface of the earth. The evidence is clear that untold generations of living forms, now preserved as fossils, inhabited the earth, disported themselves, and passed away long before the advent of man. The knowledge of this fossil life, on account of its great diversity, is an essential part of biology, and all the more so from the circumstance that many forms of life, remains of which are exhibited in the rocks, have long since become extinct. No history of biology would be complete without an account of the rise and progress of that department of biology which deals with fossil life.

It has been determined by collecting and systematically studying the remains of this ancient life that they bear testimony to a long, unbroken history in which the forms of both animals and plants have been greatly altered. The more ancient remains are simple in structure, and form with the later ones, a series that exhibits a gradually increasing complexity of structure. The study of the fossil series has brought about a very great extension of our knowledge regarding the age of the world and of the conditions under which life was evolved.

Strange Views Regarding Fossils.--But this state of our knowledge was a long time coming, and in the development of the subject we can recognize several distinct epochs, "well-marked by prominent features, but like all stages of intellectual growth, without definite boundaries." Fossils were known to the ancients, and by some of the foremost philosophers of Greece were understood to be the remains of animals and plants. After the revival of learning, however, lively controversies arose as to their nature and their meaning.

Some of the fantastic ideas that were entertained regarding the nature of fossil remains may be indicated. The fossils were declared by many to be freaks of nature; others maintained that they were the results of spontaneous generation, and were produced by the plastic forces of nature within the rocks in which they were found embedded. Another opinion expressed was that they were generated by fermentations. As the history of intellectual development shows, the mind has ever seemed benumbed in the face of phenomena that are completely misconceived; mystical explanations have accordingly been devised to account for them. Some of the pious persons of that period declared that fossils had been made and distributed by the Creator in pursuance of a plan beyond our comprehension. Another droll opinion expressed was that the Creator in His wisdom had introduced fossil forms into the rocks in order that they should be a source of confusion to the race of geologists that was later to arise.

And still another fantastic conception suggested that the fossils were the original molds used by the Creator in forming different varieties of animals and plants, some of which had been used and others discarded. It was supposed that in preparing for the creation of life He experimented and discarded some of His earliest attempts; and that fossils represented these discarded molds and also, perhaps, some that had been used in fashioning the created forms.

When large bones, as of fossil elephants, began to be exhumed, they became for the most part the objects of stupid wonder. The passage in the Scriptures was pointed out, that "there were giants in those days," and the bones were taken to be evidences of the former existence of giants. The opinions expressed regarding the fossil bones were varied and fantastic, "some saying that they were rained from Heaven, others saying that they were the gigantic limbs of the ancient patriarchs, men who were believed to be tall because they were known to be old." Following out this idea, "Henrion in 1718 published a work in which he assigned to Adam a height of 123 feet 9 inches, Noah being 20 feet shorter, and so on."

Determination of the Nature of Fossils.--In due course it came to be recognized that fossils were the remains of forms that had been alive during earlier periods of time; but in reaching this position there was continual controversy. Objections were especially vigorous from theological quarters, since such a conclusion was deemed to be contradictory to the Scriptures. The true nature of fossils had been clearly perceived by Leonardo da Vinci (1452-1519) and certain others in the sixteenth century.

The work, however, that approached more nearly to scientific demonstration was that of Steno (1638-1686), a Dane who migrated to Italy and became the court physician to the dukes of Tuscany. He was a versatile man who had laid fast hold upon the new learning of his day. Eminent as anatomist, physiologist, and physician, with his ever active mind he undertook to encompass all learning. It is interesting that Steno--or Stensen--after being passionately devoted to science, became equally devoted to religion and theology, and, forsaking all scientific pursuits, took orders and returned to his native country with the title of bishop. Here he worked in the service of humanity and religion to the end of his life.

In reference to his work in geology, his conclusions regarding fossils (1669) were based on the dissection of the head of a shark, by which means he showed an almost exact correspondence between certain glossy fossils and the teeth of living sharks. He applied his reasoning, that like effects imply like causes, to all manner of fossils, and clearly established the point that they should be regarded as the remains of animals and plants. The method of investigation practiced by Steno was that "which has consciously or unconsciously guided the researches of palæontologists ever since."

Although his conclusions were well supported, they did not completely overthrow the opposing views, and become a fixed basis in geology. When, at the close of the eighteenth century and the beginning of the nineteenth, fossil remains were being exhumed in great quantities in the Paris basin, Cuvier, the great French naturalist, reëstablished the doctrine that fossils are the remains of ancient life. An account of this will be given presently, and in the mean time we shall go on with the consideration of a question raised by the conclusions of Steno.

Fossil Deposits Ascribed to the Flood.--After it began to be reluctantly conceded that fossils might possibly be the remains of former generations of animals and plants, there followed a period characterized by the general belief that these entombed forms had been deposited at the time of the Mosaic deluge. This was the prevailing view in the eighteenth century. As observation increased and the extent and variety of fossil life became known, as well as the positions in which fossils were found, it became more difficult to hold this view with any appearance of reason. Large forms were found on the tops of mountains, and also lighter forms were found near the bottom. Miles upon miles of superimposed rocks were discovered, all of them bearing quantities of animal forms, and the interpretation that these had been killed and distributed by a deluge became very strained. But to the reasoners who gave free play to their fancies the facts of observation afforded little difficulty. Some declared that the entire surface of the earth had been reduced to the condition of a pasty mass, and that the animals drowned by the Deluge had been deposited within this pasty mass which, on the receding of the waters, hardened into rocks.

The belief that fossil deposits were due to the Deluge sensibly declined, however, near the close of the eighteenth century, but was still warmly debated in the early part of the nineteenth century. Fossil bones of large tropical animals having been discovered about 1821, embedded in the stalagmite-covered floor of a cavern in Yorkshire, England, some of the ingenious supporters of the flood-theory maintained that caves were produced by gases proceeding from the bodies of decaying animals of large size; that they were like large bubbles in the crust of the earth, and, furthermore, that bones found in caverns were either those from the decayed carcasses or others that had been deposited during the occurrence of the Flood.

Even the utterances of Cuvier, in his theory of catastrophism to which we shall presently return, gave countenance to the conclusion that the Deluge was of universal extent. As late as 1823, William Buckland, reader in geology in Oxford, and later canon (1825) of Christ Church, and dean (1845) of Westminster, published his _Reliquiæ Diluvianæ_, or _Observations on the Organic Remains Attesting the Action of a Universal Deluge_.

The theory that the Mosaic deluge had any part in the deposit of organic fossils was finally surrendered through the advance of knowledge, owing mainly to the labors of Lyell and his followers.

The Comparison of Fossil and Living Animals.--The very great interest connected with the reëstablishment of the conclusion of Steno, that fossils were once alive, leads us to speak more at length of the discoveries upon which Cuvier passed his opinion. In the gypsum rocks about Paris the workmen had been turning up to the light bones of enormous size. While the workmen could recognize that they were bones of some monsters, they were entirely at loss to imagine to what kind of animals they had belonged, but the opinion was frequently expressed that they were the bones of human giants.

Cuvier, with his extensive preparation in comparative anatomy, was the best fitted man perhaps in all the world to pass judgment upon these particular bones. He went to the quarries and, after observing the remains, he saw very clearly that they were different from the bones of any animals now existing. His great knowledge of comparative anatomy was founded on a comprehensive study of the bony system as well as the other structures of all classes of living animals. He was familiar with the anatomy of elephants, and when he examined the large bones brought to light in the quarries of Montmartre, he saw that he was confronted with the bones of elephant-like animals, but animals differing in their anatomy from those at present living on the earth.

The great feature of Cuvier's investigations was that he instituted comparisons on a broad scale between fossil remains and living animals. It was not merely that he followed the method of investigation employed by Steno; he went much further and reached a new conclusion of great importance. Not only was the nature of fossil remains determined, but by comparing their structure with that of living animals the astounding inference was drawn that the fossil remains examined belonged to forms that were truly extinct. This discovery marks an epoch in the development of the knowledge of extinct animals.

Cuvier the Founder of Vertebrate Palæontology.--The interesting discovery that the fossil relics in the Eocene rocks about Paris embraced extinct species was announced to the Institute by Cuvier in January, 1796; and thereafter he continued for a quarter of a century to devote much attention to the systematic study of collections made in that district. These observations were, however, shared with other labors upon comparative anatomy and zoölogy, which indicates the prodigious industry for which he was notable. In 1812-1813 he published a monumental work, profusely illustrated, under the title _Ossemens Fossiles_. This standard publication entitles him to recognition as the founder of vertebrate palæontology.

In examining the records of fossil life, Cuvier and others saw that the evidence indicated a succession of animal populations that had become extinct, and also that myriads of new forms of life appeared in the rocks of succeeding ages. Here Cuvier, who believed that species were fixed and unalterable, was confronted with a puzzling problem. In attempting to account for the extinction of life, and what seemed to him the creation of new forms, he could see no way out consistent with his theoretical views except to assume that the earth had periodically been the scene of great catastrophes, of which the Mosaic deluge was the most recent, but possibly not the last. He supposed that these cataclysms of nature resulted in the extinction of all life, and that after each catastrophe the salubrious condition of the earth was restored, and that it was re-peopled by a new creation of living beings. This conception, known as the theory of catastrophism, was an obstacle to the progress of science. It is to be regretted that Cuvier was not able to accept the views of his illustrious contemporary Lamarck, who believed that the variations in fossil life, as well as those of living forms, were owing to gradual transformations.

Lamarck Founds Invertebrate Palæontology.--The credit of founding the science of palæontology does not belong exclusively to Cuvier. Associated with his name as co-founders are those of Lamarck and William Smith. Lamarck, that quiet, forceful thinker who for so many years worked by the side of Cuvier, founded the science of invertebrate palæontology. The large bones with which Cuvier worked were more easy to be recognized as unique or as belonging to extinct animals than the shells which occurred in abundance in the rocks about Paris. The latter were more difficult to place in their true position because the number of forms of life in the sea is very extended and very diverse. Just as Cuvier was a complete master of knowledge regarding vertebrate organization, so Lamarck was equally a master of that vast domain of animal forms which are of a lower grade of organization--the invertebrates. From his study of the collections of shells and other invertebrate forms from the rocks, Lamarck created invertebrate palæontology and this, coupled with the work of Cuvier, formed the foundations of the entire field.

Lamarck's study of the extinct invertebrates led him to conclusions widely at variance with those of Cuvier. Instead of thinking of a series of catastrophes, he saw that not all of the forms of life belonging to one geological period became extinct, but that some of them were continued into the succeeding period. He saw, therefore, that the succession of life in the rocks bore testimony to a long series of gradual changes upon the earth's surface, and did not in any way indicate the occurrence of catastrophes. The changes, according to the views of Lamarck, were all knit together into a continuous process, and his conception of the origin of life upon the earth grew and expanded until it culminated in the elaboration of the first consistent theory of evolution.

These two men, Lamarck and Cuvier, form a contrast as to the favors distributed by fortune: Cuvier, picturesque, highly honored, the favorite of princes, advanced to the highest places of recognition in the government, acclaimed as the Jove of natural science; Lamarck, hard-working, harassed by poverty, insufficiently recognized, and, although more gifted than his confrère, overlooked by the scientific men of the time. The judgment of the relative position of these two men in natural science is now being reversed, and on the basis of intellectual supremacy Lamarck is coming into general recognition as the better man of the two. In the chapters dealing with organic evolution some events in the life of this remarkable man will be given.

The Arrangement of Fossils in Strata.--The other name associated with Lamarck and Cuvier is that of William Smith, the English surveyor. Both Lamarck and Cuvier were men of extended scientific training, but William Smith had a moderate education as a surveyor. While the two former were able to express scientific opinions upon the nature of the fossil forms discovered, William Smith went at his task as an observer with a clear and unprejudiced mind, an observer who walked about over the fields, noticing the conditions of rocks and of fossil forms embedded therein. He noted that the organic remains were distributed in strata, and that particular forms of fossil life characterized particular strata and occupied the same relative position to one another. He found, for illustration, that certain particular forms would be found underlying certain other forms in one mass of rocks in a certain part of the country. Wherever he traveled, and whatever rocks he examined, he found these forms occupying the same relative positions, and thus he came to the conclusion that the living forms within the rocks constitute a stratified series, having definite and unvarying arrangement with reference to one another.

In short, the work of these three men--Cuvier, Lamarck, and William Smith--placed the new science of palæontology upon a secure basis at the beginning of the nineteenth century.

Summary.--The chief steps up to this time in the growth of the science of fossil life may now be set forth in categories, though we must remember that the advances proceeded concurrently and were much intermingled, so that, whatever arrangement we may adopt, it does not represent a strict chronological order of events:

I. The determination of the nature of fossils. Owing to the labors of Da Vinci, Steno, and Cuvier, the truth was established that fossils are the remains of former generations of animals and plants.

II. The comparison of organic fossils with living forms that was instituted on a broad scale by Cuvier resulted in the conclusion that some of the fossils belong to extinct races. The belief of Cuvier that entire populations became extinct simultaneously, led him to the theory of catastrophism. The observations of Lamarck, that, while some species disappear, others are continued and pass through transmutations, were contrary to that theory.

III. The recognition that the stratified rocks in which fossils are distributed are sedimentary deposits of gradual formation. This observation and the following took the ground from under the theory that fossils had been deposited during the Mosaic deluge.

IV. The discovery by William Smith that the arrangement of fossils within rocks is always the same, and the relative age of rocks may be determined by an examination of their fossil contents.

Upon the basis of the foregoing, we come to the next advance, _viz._:

V. The application of this knowledge to the determination of the history of the earth.

Fossil Remains as an Index to the Past History of the Earth.--The most advanced and enlightened position that had been taken in reference to the fossil series during the first third of the nineteenth century was that taken by Lamarck, he being the first to read in the series the history of life upon the globe, weaving it into a connected story, and establishing thereon a doctrine of organic evolution. It was not until after 1859, however, that the truth of this conclusion was generally admitted, and when it was accepted it was not through the earlier publications of Lamarck, but through the arguments of later observers, founded primarily upon the hypothesis set forth by Darwin. There were several gradations of scientific opinion in the period, short as it was, between the time of Cuvier and of Darwin; and this intermediate period was one of contention and warfare between the theologians and the geologists. Cuvier had championed the theory of a succession of catastrophes, and since this hypothesis did not come into such marked conflict with the prevailing theological opinion as did the views of Lamarck, the theologians were ready to accept the notion of Cuvier, and to point with considerable satisfaction to his unique position as an authority.

Lyell.--In 1830 there was published an epoch-making work in geology by Charles Lyell (Fig. 97), afterward Sir Charles, one of the most brilliant geologists of all the world. This British leader of scientific thought showed the prevalence of a uniform law of development in reference to the earth's surface. He pointed out the fact that had been maintained by Hutton, that changes in the past were to be interpreted in the light of what is occurring in the present. By making a careful study of the work performed by the waters in cutting down the continents and in transferring the eroded material to other places, and distributing it in the form of deltas; by observing also the action of frost and wind and wave; by noting, furthermore, the conditions under which animals die and are subsequently covered up in the matrix of detritus--by all this he showed evidences of a series of slow, continuous changes that have occurred in the past and have molded the earth's crust into its present condition.

He showed, further, that organic fossils are no exception to this law of uniform change. He pointed to the evidences that ages of time had been required for the formation of the rocks bearing fossils; and that the regular succession of animal forms indicates a continual process of development of animal life; and that the disappearance of some forms, that is, their becoming extinct, was not owing to sudden changes, but to gradual changes. When this view was accepted, it overthrew the theory of catastrophism and replaced it by one designated uniformatism, based on the prevalence of uniform natural laws.

This new conception, with all of its logical inferences, was scouted by those of theological bias, but it won its way in the scientific world and became an important feature in preparing for the reception of Darwin's great book upon the descent of animal life.

We step forward now to the year 1859, to consider the effect upon the science of palæontology of the publication of Darwin's _Origin of Species_. Its influence was tremendous. The geological theories that had provoked so much controversy were concerned not merely with the disappearance of organic forms, but also with the introduction of new species. The _Origin of Species_ made it clear that the only rational point of view in reference to fossil life was that it had been gradually developed, that it gave us a picture of the conditions of life upon the globe in past ages, that the succession of forms within the rocks represented in outline the successive steps in the formation of different kinds of animals and plants.

Owen.--Both before and after Darwin's hypothesis was given to science, notable anatomists, a few of whom must be mentioned, gave attention to fossil remains. Richard Owen (1804-1892) had his interest in fossil life stimulated by a visit to Cuvier in 1831, and for more than forty years thereafter he published studies on the structure of fossil animals. His studies on the fossil remains of Australia and New Zealand brought to light some interesting forms. The extinct giant bird of New Zealand (Fig. 98) was a spectacular demonstration of the enormous size to which birds had attained during the Eocene period. Owen's monograph (1879) on the oldest known bird--the archæopteryx--described an interesting form uniting both bird-like and reptilian characteristics.

Agassiz.--Louis Agassiz (1807-1873) (Fig. 99) also came into close personal contact with Cuvier, and produced his first great work partly under the stimulus of the latter. When Agassiz visited Paris, Cuvier placed his collections at Agassiz's disposal, together with numerous drawings of fossil fishes. The profusely illustrated monograph of Agassiz on the fossil fishes (1833-1844) began to appear in 1833, the year after Cuvier's death, and was carried on eleven years before it was completed.

Agassiz, with his extensive knowledge of the developmental stages of animals, came to see a marked parallelism between the stages in development of the embryo and the successive forms in the geological series. This remarkable parallelism between the fossil forms of life and the stages in the development of higher forms of recent animals is very interesting and very significant, and helps materially in elucidating the idea that the fossil series represent roughly the successive stages through which animal forms have passed in their upward course of development from the simplest to the highest, through long ages of time. Curiously enough, however, Agassiz failed to grasp the meaning of the principle that he had worked out. After illustrating so nicely the process of organic evolution, he remained to the end of his life an opponent of that theory.

Huxley.--Thomas Henry Huxley (1825-1895) was led to study fossil life on an extended scale, and he shed light in this province as in others upon which he touched. With critical analysis and impartial mind he applied the principles of evolution to the study of fossil remains. His first conclusion was that the evidence of evolution derived from palæontology was negative, but with the advances in discovery he grew gradually to recognize that palæontologists, in bringing to light complete evolutionary series, had supplied some of the strongest supporting evidence of organic evolution. By many geologists fossils have been used as time-markers for the determination of the age of various deposits; but, with Huxley, the study of them was always biological. It is to the latter point of view that palæontology owes its great importance and its great development. The statement of Huxley, that the only difference between a fossil and a recent animal is that one has been dead longer than the other, represents the spirit in which the study is being carried forward.

With the establishment of the doctrine of organic evolution palæontology entered upon its modern phase of growth; upon this basis there is being reared a worthy structure through the efforts of the recent votaries to the science. It is neither essential nor desirable that the present history of the subject should be followed here in detail. The collections of material upon which palæontologists are working have been enormously increased, and there is perhaps no place where activity has been greater than in the United States. The rocks of the Western States and Territories embrace a very rich collection of fossil forms, and, through the generosity of several wealthy men, exploring parties have been provided for and immense collections have been brought back to be preserved in the museums, especially of New Haven, Conn., and in the American Museum of Natural History in New York City.

Leidy, Cope, and Marsh.--Among the early explorers of the fossils of the West must be named Joseph Leidy, E.D. Cope (Fig. 100), and O.C. Marsh. These gentlemen all had access to rich material, and all of them made notable contributions to the science of palæontology. The work of Cope (1840-1897) is very noteworthy. He was a comparative anatomist equal to Cuvier in the extent of his knowledge, and of larger philosophical views. His extended publications under the direction of the United States Government have very greatly extended the knowledge of fossil vertebrate life in America.

O.C. Marsh (Fig. 101) is noteworthy for similar explorations; his discovery of toothed birds in the Western rocks and his collection of fossil horses, until recently the most complete one in existence, are all very well known. Throughout his long life he contributed from his own private fortune, and intellectually through his indefatigable labors, to the progress of palæontology.

Zittel.--The name most widely known in palæontology is that of the late Karl von Zittel (1839-1904), who devoted all his working life to the advancement of the science of fossils. In his great work, _Handbuch der Palaeontologie_ (1876-1893), he brought under one view the entire range of fossils from the protozoa up to the mammals. Osborn says: "It is probably not an exaggeration to say that he did more for the promotion and diffusion of palæontology than any other single man who lived during the nineteenth century. While not gifted with genius, he possessed extraordinary judgment, critical capacity, and untiring industry." His portrait (Fig. 102) shows a face "full of keen intelligence and enthusiasm."

Zittel's influence was exerted not only through his writings, but also through his lectures and the stimulus imparted to the large number of young men who were attracted to Munich to study under his direction. These disciples are now distributed in various universities in Europe and the United States, and are there carrying forward the work begun by Zittel. The great collection of fossils which he left at Munich contains illustrations of the whole story of the evolution of life through geological ages.

Recent Developments.--The greatest advance now being made in the study of fossil vertebrate life consists in establishing the lineage of families, orders, and classes. Investigators have been especially fortunate in working out the direct line of descent of a number of living mammals. Fossils have been collected which supply a panoramic view of the line of descent of horses, of camels, of rhinoceroses, and of other animals. The most fruitful worker in this field at the present time is perhaps Henry F. Osborn, of the American Museum of Natural History, New York City. His profound and important investigations in the ancestry of animal life are now nearing the time of their publication in elaborated form.

Palæontology, by treating fossil life and recent life in the same category, has come to be one of the important lines of investigation in biology. It is, of course, especially rich in giving us a knowledge of the hard parts of animals, but by ingenious methods we can arrive at an idea of some of the soft parts that have completely disappeared. Molds of the interior of the cranium can be made, and thus one may form a notion of the relative size and development of the brain in different vertebrated animals. This method of making molds and studying them has shown that one characteristic of the geological time of the tertiary period was a marked development in regard to the brain size of the different animals. There was apparently, just prior to the quaternary epoch, a need on the part of animals to have an increased brain-growth; and one can not doubt that this feature which is demonstrated by fossil life had a great influence in the development of higher animal forms.

The methods of collecting fossils in the field have been greatly developed. By means of spreading mucilage and tissue paper over delicate bones that crumble on exposure to the air, and of wrapping fossils in plaster casts for transportation, it has been made possible to uncover and preserve many structures which with a rougher method of handling would have been lost to science.

Fossil Man.--One extremely interesting section of palæontology deals with the fossil remains of the supposed ancestors of the present human race. Geological evidence establishes the great antiquity of man, but up to the present time little systematic exploration has been carried on with a view to discover all possible traces of fossil man. From time to time since 1840 there have been discovered in caverns and river-gravels bones which, taken together, constitute an interesting series. The parts of the skull are of especial importance in this kind of study, and there now exists in different collections a series containing the Neanderthal skull, the skulls of Spy and Engis, and the Java skull described in 1894 by Dubois. There have also been found recently (November, 1906) in deposits near Lincoln, Neb., some fossil human remains that occupy an intermediate position between the Neanderthal skull and the skulls of the lower representatives of living races of mankind. We shall have occasion to revert to this question in considering the evidences of organic evolution. (See page 364.)

The name palæontology was brought into use about 1830. The science affords, in some particulars, the most interesting field for biological research, and the feature of the reconstruction of ancient life and the determination of the lineage of living forms has taken a strong hold on the popular imagination. According to Osborn, the most important palæontological event of recent times was the discovery, in 1900, of fossil beds of mammals in the Fayûm lake-province of Egypt, about forty-seven miles south of Cairo. Here are embedded fossil forms, some of which have been already described in a volume by Charles W. Andrews, which Osborn says "marks a turning-point in the history of mammalia of the world." It is now established that "Africa was a very important center in the evolution of mammalian life." It is expected that the lineage of several orders of mammalia will be cleared up through the further study of fossils from this district.