Palaeontology (Greek: logos ton palaion onton), or the science of fossils, deals with extinct or primeval animals and plants. It treats of their characteristics, classification, life and habits, geographical distribution, and succession. It embraces also whatever deductions may be drawn from these investigations for the history of the organisms and of the earth. Palaeontology, therefore, is closely connected with geology, botany, zoology, comparative anatomy, and embryology, or ontogeny, which at the same time serve it as auxiliary sciences. The science of fossils is divided into palaeophytology (Greek: phuton, plant), also called phytopalaeontology, or palaeobotany (Greek: botane, herb), treating of fossil plants, and palaeozoology (Greek: zoon, animal), treating of extinct animals.
Historical Summary.—Even in antiquity fossil marine animals attracted the attention of a number of philosophers who, in some measure, explained them correctly, drawing the conclusion that at one time there had been a different distribution of sea and land. The earliest of these philosophers was Xenophanes of Colophon, the founder of the Eleatic school of philosophy (600 B.C.). After him came Strabo, Seneca etc.; the earliest Christian observers were Tertullian of Carthage (160-230), and Eusebius of Caesarea (about 270-339). In the Middle Ages little attention was paid to fossils, which were generally regarded as products of a creative force of the earth (vis plastica, or virtus formativa), though a few men like Albertus Magnus, and later Leonardo da Vinci (1452-1519) held correct views on the subject. In the sixteenth century the first engravings of fossils were published by the Swiss physician Conrad Gessner. It was not until a century later, however, that a few scholars, particularly the Englishmen, Robert Hooke, John Ray, and John Woodward, vigorously maintained the organic origin of fossils. The opinion was still universal that fossils represented life destroyed by the flood, a theory championed especially by Scheuchzer. William Smith (1769-1839) was the first to recognize the value of fossils for the historical investigation of the strata of the earth, his theory being introduced into France by Alexander Brongniart (1770-1847), who, with Cuvier (1769-1832), was the first to apply the principles of botany, zoology, and comparative anatomy to palaeontology, whereby the latter became a science. The designation “palaeontology”, however, was first given it by a pupil of Cuvier, Ducrotay de Blainville, and the zoologist Fischer of Waldheim. Since then about one hundred thousand species of extinct organisms have been described. Cuvier and his successors, as d’Orbigny, Agassiz, d’Archiac, and Barrande, however, maintained the catastrophic theory, that is, the doctrine that at the end of each geologic period the entire fauna was destroyed, and replaced by a new order of life. Darwin’s “The Origin of Species by Means of Natural Selection” (1859) proved a turning-point for these theories, for since that time the theory of descent was also applied to palaeontology, and today is generally accepted. We may especially mention the works on this subject by Kowalewsky, Rütimeyer, Gaudry, Cope, W. Waagen, Neumayr, and Zittel. The geological and palaeontological collections of universities serve for the study of palaeontology and instruction in this science, as do also similar collections in museums of natural history. The national geological collections and geological societies have the same object. There are only two purely palaeontological societies, the Swiss and the London; their object being the publication of palaeontological works. Palaeozoology is cultivated almost exclusively by geologists; it is only in exceptional cases that zoologists occupy themselves with this science, while phytopalaeontology is carried on mainly by botanists.
The object of palaeontological study is petrefactions (from Greek: petros, stone, and facere, to make), or fossils (fossilis, what is buried). Fossils are those remains or traces of plants and animals which before the beginning of the present geological era found their way into the strata of the earth and have been preserved there. Most of the species thus found are extinct, but the more recent the strata the greater the number of extant species it contains. As implied by the word petrefaction, most palaeontological remains have been transformed into stone, but leaves and bones completely incrusted in limestone, and therefore petrified, have been found which belong to the present geological era and are, therefore, not considered fossils, whereas the skeletons of the mammoth and rhinoceros frozen in the ice of Siberia, or the insects preserved in amber are. The fossilization of the remains of plants and animals could take place only under very unusual conditions, for in the normal process of decay. only the hard parts of the bodies of animals at the most, as bones, teeth, shells of molluscs, etc., are preserved. Even these hard parts gradually disappear by disintegration through atmospheric influences. One very important process of preservation for primeval organisms is carbonization, which affects plants particularly; it takes place under water, air being excluded. Most frequently, however, organic remains are completely penetrated by solutions of mineral matter and are thus in the literal sense mineralized or petrified. Generally the petrifying substance is carbonate of lime, but silicious earth, and more rarely brown clay iron-ore, red iron-ore, zinc-spar, sulphide of zinc, black lead ore etc., also contribute to produce fossils. The mineralization does not always destroy the original structure of the tissue, especially in case of silicatization. But there are still other means of preserving as fossils the remains of ancient organisms. Not infrequently such remains are covered by mineral waters with an envelope, the organic body itself was afterwards dissolved, leaving only an impression. On the other hand molluscs, echinoderms, corals, etc., have their hollow chambers filled with a mineral substance and afterwards the outer shell is chemically removed, so that only a cast of the inside or a hard kernel remains. Finally, the tracks of birds and reptiles, and traces of the trails of crustacea and worms which have been preserved as impressions are counted as fossils. These are often found with the remains of molluscs, as the well-known impressions of medusa in the lithographic slate of Bavaria. The study of palaeontological objects is often attended with great difficulties as for the most part the remains found are incomplete and their correct interpretation requires careful comparison with living organisms. Palaeontology, therefore, makes use of the methods of zoology and botany, but its task is a far more difficult one. In the fossils of animals all the fleshy parts are lacking, and even the hard parts are often enough only very imperfectly represented, and preserved in fragments. The blossoms of plants are completely wanting, while leaves, fruit, stem, and root are hardly ever found together. Consequently, palaeontologists have given special attention to the study of the comparative anatomy of the hard parts of organisms, and thus discovered important organic laws; among these should be especially mentioned Cuvier’s “law of correlation”. By this is meant the mutual dependence of the different parts of an organism, which enables us, e.g., from the teeth alone, to decide whether an animal was carnivorous or herbivorous etc. Furthermore, by the aid of palaeontology the material of the biological sciences was enlarged to an astonishing degree, and many gaps therein were filled. The problems of the development theory received much light from the same source. Finally palaeogeography is wholly dependent on this science, as the fossils indicate where there were continents and, oceans, where the animal life of the coast developed, where coral reefs grew, where lakes containing fresh water organisms existed, where the primeval tropical forests flourished, and where the tundras of the cold regions extended. This not only enables us to fill the outlines of ancient continents and oceans, but also furnishes the means of determining the geographical distribution of plants and animals, and the climatic conditions during the different geological eras.
Of special importance is the historical side of palaeontology. As has already been said, William Smith was the first to recognize the importance of fossils for the historical investigation of the earth’s strata. Before his day they were regarded as proofs of the Flood. The greater part of the surface of the earth consists of varying stratified rocks that have been deposited by the ocean, by brackish, and by fresh water. Geology studies the individual strata and infers their age from their succession. This can easily be done in a limited district, but if two districts somewhat distant from each other are compared, then it will prove impossible by geology alone to establish that the two strata are of the same age, for at the same time in one place limestone may have been deposited, in another sandstone, and in a third clay. Again, strata of an epoch which appear in one place may be wanting in another. In such cases the geologist may receive great assistance from palaeontology. For the stratified portion of the earth generally contains fossils which are found more or less frequently, which are so distributed that each group of strata corresponds to a definite collection of species that lived when these strata were deposited. In such a case palaeontology determines the chronological succession of the several fauna and flora and studies the mutual relations of the organic remains found at the different localities. By this means the contemporaneousness of the various strata may be recognized or the parallelism of the several strata established. In doing this, however, many obstacles have been overcome with considerable difficulty. Most strata have been deposited by the sea.
At the same time, however, deposits were formed by lakes; on land forests grew and land animals lived, in warm seas there were luxurious growths of coral. Naturally each of these regions produced organisms utterly different; consequently some lucky discovery such as that of shells which found their way into deposits of plants, or that of the bone of a mammal imbedded in the sea-sand is required, in order to be able to decide whether the deposits are contemporaneous. From what has been said it is clear that all fossils are not equally important and useful in determining the age of strata. Thus, all remains of land and fresh-water organisms are of less importance, because most strata were deposited by the ocean. Even the marine fossils are not all equally important. The most important are those combining the most rapid changes in character with the most extensive geographical distribution. The most important task of palaeontology is the investigation of the history of the development of life, for it is the only science which furnishes means and in the fossils offers documents to elucidate this problem. Only in this way is it possible to learn whether the past and present organisms form a continuous whole, or whether the fauna and flora of the various periods in the earth’s history were destroyed by catastrophes and were replaced by a new creation. There are two fundamental characteristics of all organisms: heredity and variation. It is, at the same time, interesting to prove that the conception of mutation and with it of the evolution of living beings is older than the knowledge of its capacity of persistence. Aristotle believed that eels sprang from mud, Theophrastus accepted the belief that the tubers of a number of plants were formed from the earth, and even Goethe maintained the opinion that plant-lice were developed from parts of the plants. With Linnaeus began the perception of the great importance in physical law of the capacity of persistence in organisms, which makes it possible for the naturalist to organize the whole of the great kingdom of living beings into genera and species. Darwin was as the opponent of Linnaeus, in that he once more brought the capacity for mutation of all organisms into the focus of natural philosophy.
According to the theory of the evolutionist all life issued from several cells, or according to some from a single cell. Of this cell, of course, no fossilized traces can have been preserved. Yet according to this theory we should expect the most ancient strata to be filled with the remains of animals and plants of the lowest type capable of preservation. This, however, is not the case. In the Cambrian, the oldest stratified formation, which has yielded somewhat abundant fossils, all families of the animal kingdom are found, with exception of the vertebrates; all plants are likewise missing. These two groups first appear in the Silurian formation. The organisms found in the Cambrian formation are not the lowest of their kind, the brachiopods, for instance, and the trilobites are as highly-organized as the present representatives of their species. In the same manner, vertebrates are represented in the Silurian formation by the trunk-fish or ostraciidoe, and the oldest known plants are the algoe and the highly-organized ferns. Consequently the lowest classes are not the earliest. When by the discovery of older remains the limits of life were traced further back, here also remains of higher organisms were found, so that even here we are very far removed from the beginnings of life. In attempting to find traces of the simplest organisms the Eozoon canadense played a great rôle until it was seen that in the remains in question crystals of olivin or chrysolite, that had been converted into serpentine, had produced the illusion of an organic structure. Great importance was also attached to the appearance of graphite in the earliest of strata, until Weinschenk proved, at least for many of them, that they owed their existence to volcanic action. Equally inconclusive are the earliest limestones, now that we know that these are still being produced chemically in the ocean. In short, palaeontology tells us nothing about the origin of life; the whole series of organisms, from the simplest protoplasmic masses to the differentiated forms found in the Cambrian rocks is missing.
If we survey the fossils so far known in historical order, the following facts are ascertained: The earliest or primary period of the earth is the era of the Pteridophyta, the ferns, horsetails, and club-mosses; in the Triassic and Jurassic periods the gymnosperms prevail, and beginning with the cretaceous period the angiosperms. The history of the animal kingdom is similar. Of the articulata, only the crustacea appear in the earliest formations, insects and spiders are not found until the Upper Carboniferous. The first vertebrates are found in the Upper Silurian, these are some trunk-fish or ostraciidae, which reached their most flourishing period in the Upper Devonian. The first vertebrates living on land appear in the Carboniferous period; these were amphibians represented by the stegocephala, and the first reptiles. The Triassic also yields the first small mammals, which, however, do not become important until the Old Tertiary period, while true birds are already known in the Jurassic. Man, who appears in the Quaternary, concludes the series. Thus, starting from geological antiquity, the fossils of which still in part seem strange to us, although in almost all cases they can be inserted without difficulty in the existing orders and classes of the animal and vegetable kingdoms, there is found a progressive approximation to the organisms now existing which is completed by the gradual and unbroken succession of beings more and more highly differentiated. At the first glance this seems to be a brilliant confirmation of the theory of development, but when more closely examined it is seen that the guiding-thread, which should lead from one point to another, is continually broken and the loose ends cannot readily be connected. Vertebrates first appear in the Silurian and angiosperms in the cretaceous, but there are no organisms leading up to these groups. Thus we are met by the broad fact that both vertebrates and flowering plants with covered seed appear without intermediate links. The same thing is true of each one of the classes in the animal and vegetable kingdoms. We see them, indeed, appear one after another in time, but we always miss the intervening links which would indicate genetic relations among the several orders. It is true that at times animal remains are found which, it is believed, may rightly be claimed as the missing links. The best known of these is probably the aboriginal bird, the archaeopteryx, which ranks midway between reptile and bird. Its plumage, its bird-like foot, and the closed capsule of its skull characterize it as a bird, while the structure of the vertebra, the teeth, and the long, lizard-like tail point to the reptiles. Since, however, it has been found that these reptile-like peculiarities also appear in embryonic birds, there is no longer any doubt that the species under consideration are real birds, the highly-differentiated last link of an extinct class of birds. In the same way the opinion that the theromorpha, a kind of reptile, are the aboriginal form of vertebrates, has not proved tenable. At the same time we now and then find in the record of successive geological strata forms that may be regarded as the common starting point of two or of several orders. We know, for instance, the connecting links between the four-branched and six-branched corals, or between the ganoids, and the teleosts (bony fish), also between the two great groups of carnivorous and insectivorous marsupials on the one side and the herbivorous marsupials on the other. At the base of the placental mammalia are found forms which unite the characteristics of hoofed animals, beasts of prey, and insectivorous animals. Such collective types as they are called, however, are very rare, whereas according to the theory of descent they should be found in large numbers.
In the smallest classified case of minute systematic units it is true palaeontological series of descent may be recognized, for here individual species by imperceptible mutations lead to new species. The best known line of descent of this kind is probably the ancestral tree of the horse, published long ago by Huxley; but this very case illustrates the difficulties of such problems, for just now it is very doubtful if some of the links should be inserted in the series. Moreover, such proofs always contain hypothetical elements. Besides, connecting links are often lacking or parts separately found, such as teeth or bones, are the only means of completing a line of ancestral descent. A special obstacle to the recognition of true relationship is the phenomenon called convergence. By convergence is meant the fact that, in consequence of similar conditions of life, uniformity of organs or even of the entire structure can be developed by animals far apart in systematic classification. Thus, for example, a mollusc of the cretaceous period, a brachiopod of the Carboniferous, and a coral of the Devonian externally are much alike. Or, again, in Mesozoic times the reptilia prevailed in water, air, and on land. There existed in this period beasts of prey, along with herbivorous and insectivorous animals, cheiroptera in the air, and fish-like carnivora in the ocean. In the latest geological periods the mammals took the lead, and placental mammals took possession of all three elements. Alongside of these there existed carnivorous, insectivorous, and rodent marsupials.
If we study the fossils of successive strata we will notice along with the forms which are gradually changed, numerous new forms unconnected with previously-existing forms. There is, therefore, a gap which cannot be filled up by means of small, inappreciable changes, as the Darwinian theory of descent demands, because there is not time enough for numerous intermediate members of the series. Häckel, therefore, assumes a process of change which he calls metakinesis, by this he understands “an almost violent and always far-reaching change in the forms, which certainly cannot take place in the adult form of the organism, but only in its earlier younger stages when the individual organs are not yet histologically specialized and therefore possess a more or less independent plasticity”. In the shortest space of time such metakinetic processes can completely change the appearance of the entire fauna and flora, and in the history of life periods of relative constancy alternate with those of violent change and new formation. Under these conditions the individual genera act very differently. Many genera of the brachiopods, the foraminifera, the echinoderms, gasteropods, as well as the mollusca, the cephalopods, and the crustacea extend almost without change from geological antiquity up into the present time. Other genera, on the contrary, have only a life of very brief duration. In these latter is perceived, at times, a very gradual remodeling by mutations, mutations which being separated into fragments by a violent metakinetic break-up, afterwards give rise to a large number of species; thus the vital energy of the genera is soon exhausted. This phenomenon brings us, therefore, face to face with a new problem, commonly called the “extinction of species”.
One circumstance must, however, still be pointed out, namely that the variability of the form groups does not appear to be unlimited in all directions, but that this variability in different families frequently moves independently in the same direction. For instance, there was a tendency toward bilateral symmetry in the animal kingdom at a fairly early period, and individual echinoderms attained it; but it was not general until the era of the worms. One family of worms already had gills, yet it was only upon the appearance of the molluscoidea that such organs for breathing were always present. In the same manner the crocodiles, alone of the reptilia, have a heart divided into two ante-chambers and two main chambers, a form of heart which is found, once more, without exception among birds and mammals. This agreement among various groups, however, cannot be based upon a close relationship, but, strictly speaking, comes also under the conception of convergence If we survey extinct organisms, there are without doubt many important considerations which tell for the theory of development. However, the theory of development in its extreme, monistic sense, signifies that all life, both animal and plant, springs from a single root. For this many proofs are still lacking, even if we set aside the fact that the oldest organisms of every family (except the vertebrates and plants) are highly organized, inasmuch as their oldest progenitors may have been made unrecognizable by the metamorphosis of the earliest rocks and thus withdrawn from our observation; and even if the enormous length of time required for the development of forms so highly specialized as the trilobite, does not seem to be sufficiently represented in the eozoic sediments. But in the later formations also the entire family of vertebrates appear without any preparation; among the plants to name only a few, the flowering cretaceous angiosperms appear without any precursors, and the Older Tertiary brings without warning us, all ten orders of the mammalia; even among these ten orders a closer relationship can be conjectured in only a few cases. In the pedigree of organic beings, therefore, we meet with chasms which cannot be bridged over even with the help of Häckel’s metakinesis. In view of this fact it is hardly possible any longer to maintain the opinion that all life has sprung from a single root (monophyletic). It appears much more probable that the different genera of animals and plants originate in various roots (polyphyletic). The advocates of the monophyletic theory, it is true, declare that the experience of animal breeders and florists shows that new variations appear for the first time in few examples only, and that in view of the fragmentary character of palaeontological records these first examples may have perished. If we were to accept this explanation we should deceive ourselves as to the difficulties of the problem of development. For in every case a whole series of intermediate links is missing, and it would, therefore, be strange that none of these should have been transmitted to us. It would be still more startling if the transition-links had regularly perished in all the larger units of classification.
We infer therefore that the facts presented to us by the known fossils compel us to accept a polyphyletic descent. It is, therefore, interesting that zoologists like E. von Beer, Fleischmann, and Th. Boveri, and a number of botanists like A. von Kerner, who work in a different field, have also gradually adopted a polyphyletic line of descent.
Finally, if we examine more closely the individual groups of forms, we see their mutual relations in a new and peculiar light. For the studies in question show that the extinct animals and plants, while differing more or less in structure from those now living, did not fall below them in the perfection of their organization, that, on the contrary, in many cases indeed, a decline is manifested. All the great orders begin at once with highly differentiated forms, so that, with Koken, we can only speak of a “modification of limited systematic divisions”.
Development may, therefore, take place without progress in organizations, for all forms which have been classified as belonging to the same genus or the same family stand upon the same level of organization. The difference consists essentially in a strong differentiation and specialization of peculiarities, which are subject now to an increase and again to a decrease. By means of this metamorphosis new species, new genera, and even new families may easily arise. This may exemplify for us progressive development, which, however, should be strictly distinguished from ascending development. The new forms produced today in the breeding of animals or in floriculture, belong entirely to the domain of progressive evolution. Hither to unquestioned proofs of ascending development have been lacking in palaeontology, nor does experiment supply the deficiency. We may therefore say that the organisms of the geological ages are connected by descent, and that there is good reason for accepting progressive development in the several lines of descent down to the present time. But if we go beyond this and set up a divergent line of descent for the whole world of organisms, or seek to trace all organisms back to a single cell, we abandon the foundation of fact. If, therefore, we infer that a general development cannot be established by the facts, we are still within the lines of the theory of descent, for the essential conception of this theory is that the systematic species of zoology and botany are not rigid and unchangeable, but have developed from ancestors unlike themselves, and may likewise develop into differently formed descendants. It is the business of the theory of development to investigate the facts and causes which underlie the series of organic forms, at the head of which stand existing species. Consequently, it is no essential part of its aim to prove that development is ascending or that it supposes a single original progenitor.
One of the questions involved in this problem is that of the descent of man, which will be touched on here because it has aroused the greatest interest. We may begin by stating that palaeontology has, indeed, made known to us an older race of men with very beetling brows and an almost total absence of chin, but that up to now no ape-like progenitors of men have been discovered. Wherever fossil remains of man have been found—and hitherto they have been found only in the Quaternary period, for all reports of Tertiary man have so far been proved unreliable—man always appears as a true man. So far only a relatively small number of remains of Quaternary man are known (e.g. the skulls of Spy, Neandertal, and Krapina, and the lower jaws of Schipka, La Naulette, and Ochos). There is, moreover, the Pithecanthropus erectus, parts of the skeleton of which were found by the Dutch military surgeon Eugen Dubois in 1891 on the island of Java. Since its discovery it has been industriously brought forward by certain supporters of the theory of development as the long-sought missing link between ape and man. At present, however, it is agreed that this Pithecanthropus is only a large gibbon, an ape, although there is no doubt that, as regards the size of brain, he should be placed between the largest man-ape now known and man. One more fact must be emphasized. Volz and Elbert have lately investigated the locality in Java where the Pithecanthropus was found, and they have proved incontestably that the strata in which these remains were discovered belong to the Quaternary period, that therefore the Pithecanthropus erectus was a contemporary of man and could not be his ancestor.
When we look at Häckel’s “Stammbaum der Primaten” (Descent of the Primates), the pedigree seems somewhat fuller. In this work the ancestors of man are arranged in the following order: Archiprimas, from which are descended the Pachylemures, including the Lemuravidoe, from which in turn the necrolemures are descended; and these are the direct ancestors of the apes. Starting with the ape the descent is continued as follows: Archipithecus, the primeval ape: Prothylobates, the primeval gibbon; Pithecanthropus alalus, the speechless man-ape; Homo stupidus, the stupid man; and finally Homo sapiens. It will not be uninteresting to examine this line of descent a little more closely. Both the Pachylemures and the Necrolemures are conceived quite indefinitely. The specially indicated forms: Archiprimas, Archipithecus, Prothylobates, Pithecanthropus alalus, are pure inventions, not even the smallest bone belonging to them is known, in fact there is nothing to them but their imposing names. Nevertheless, as Klaatsch asserts, it cannot be doubted that there are a sufficient number of facts to lead every thinking man to the inexorable conclusion that man has sprung from the same source of life as the animal kingdom. The only question is: whether, from the similarity of two beings in structure and function of body, in spite of what we know of the phenomena of convergence, we not only may, but, as Klaatsch says, logically must, infer their genetic connection in the sense of a blood relationship or of descent from the same basic form? Klaatsch answers this question in the affirmative, but we rather agree with Kathariner, whose answer is: “At this point our views diverge, and all the more as it is impossible to reach a completely satisfactory conclusion on the origin of man-kind if we base it solely on morphology and ignore man’s spiritual side. A discussion of this question based on palaeontological data is fruitless, as the decision is too greatly influenced by the conception which men have of creation as a whole and of its need of a first cause, of their views on the theory of cognition, and of other subjective considerations.” Consequently, neither palaeontology nor morphology can say anything positive concerning the physical origin of man.
When we review the facts of palaeontology, we recognize that this science, while offering probable arguments for a progressive evolution of the organic world, can only to a limited degree—even with the aid of fossil fauna and flora—explain the process of development, and that certain phenomena, such as the complete disappearance of entire large groups, cannot at present be satisfactorily explained. The question of the efficient causes of the changes in the organic world has already begotten many theories, to decide the merits of which palaeontology sometimes assists us. Darwin’s theory has exceedingly few adherents among palaeontologists. On the other hand, Lamarck’s teaching, developed by Cope as neo-Lamarckism, meets with continually increasing acceptance. It teaches that the development of organisms rests mainly on hereditary changes, produced by the use or non-use of the organs, as well as by correlation and direct transforming influences, while selection has only a slight, if any, importance. Nevertheless, we must confess, with Diener, that “in our attempts to explain the changes of the present forms of life, which are the results of purely mechanical causes still acting before our eyes, we constantly meet with the action of factors, which we cannot directly understand with the aid of physical science alone. The knowledge of the phenomena of adaptation is a matter of experience, but the explanation, how such an adaptation of the cell-groups of a complicated body is possible, belongs to the do-main of metaphysics. Whether we speak of new creations, in the sense of A. d’Orbigny, or of the modification of the fauna, in both cases we formulate biological phenomena which are not clear to us in their nature, and the explanation of which by a mechanical method does not satisfy our need of causality.”
LUKAS WAAGEN