Palæontology (Gr., 'study of ancient life'), the science or study of fossil organic remains—whether of animal or plant life. The study of fossil animals is sometimes termed palæozoology, and that of fossil plants palæophytology. The aim of palæontology is to attain a knowledge of all the various plants and animals which have successively appeared and disappeared in the course of geological ages. But as the geological record is highly imperfect, and myriads of species must have lived and died without leaving any trace behind them, it is obvious that our knowledge, no matter how enlarged it may become, can never possibly be complete. The history is full of gaps, some of which may eventually be bridged over, but, however that may be, it is nevertheless certain that our knowledge must always bear but a small proportion to our ignorance. Nevertheless, the study of palæontology has been fruitful in results. It has greatly influenced zoology and botany—and that not merely by adding to the number of subjects with which those sciences deal, but especially by the light which it has thrown on the evolution and mutual relations of existing forms of life. Fossil organic remains consist chiefly of the harder parts—such as bones, scales, teeth, shells, crusts, spines, &c.—of animals, and the ligneous tissues of plants (see FOSSILS). In attempting to interpret the evidence supplied by such remains, palæontologists were early led to study, for purposes of comparison, the structures of existing plants and animals. By applying the results of these comparisons to the restoration of extinct forms of life, Cuvier was enabled to establish the law of the 'correlation of organs;' and thus the palæontologist, who has to deal principally with fragmentary remains, is not in such a helpless case as might have been supposed. 'Stated in its most general form, the law of the correlation of organs is the law that all the parts of an organism stand in some relation to one another, the form and characters of each part being more or less closely dependent on, and connected with, the form and characters of all the rest. In other words, an organism is not a fortuitous collocation of unrelated parts, but is composed of mutually adapted and related organs; the possession of any given organ, therefore, implying the possession of other "correlated" parts' (Nicholson and Lydekker). Hence the palæontologist can often infer from an isolated organ or structure the essential characters of the remainder of the organism. But, while the biological sciences have greatly benefited, it is geology which has been most advanced by palæontological research. Without the help of fossils the geologist would be unable to reconstruct the past. By their aid he is able to identify and correlate the various formations which constitute his systems. It is from them that he infers former climatic and geographical changes—that he is able to distinguish between fresh-water and marine, shallow-water and deep-sea conditions, &c. But for the general relations of palæontology to geological research the reader is referred to the article GEOLOGY. Some account of the palæontology of the stratified or fossiliferous rocks will be found in the articles that deal with the various geological systems. Here all that need be done is to summarise the characteristic features of the Palæozoic, Mesozoic, Cainozoic, and Quaternary or Post-Tertiary faunas and floras.
Palæozoic Life.—The most prominent types of Palæozoic times were Graptolites, Rugose corals, Brachiopods, Crinoids, Pteropods, Nautilid Cephalopods, Trilobites, Eurypterids, and Heteroceral Ganoids. Graptolites ranged from the Cambrian into the Lower Old Red Sandstone, but attained their maximum in Lower Silurian times. Rugose corals, unknown in the Cambrian, swarmed in Silurian, Devonian, and Carboniferous seas, but were much less numerous in those of the Permian. Crinoids first appear in the Cambrian, are numerous in Silurian and Devonian rocks, but more abundant still in the Carboniferous. After this they begin to decline. Brachiopods, commencing in the Cambrian, abounded all through Palæozoic times, but culminated in the Upper Silurian period. They were still numerous in Devonian and Carboniferous seas, but less abundant in those of the Permian period. Pteropods were more common in Upper Cambrian and Silurian than during Devonian and Carboniferous times. Nautilid Cephalopods first appear in the Upper Cambrian, and seem to culminate in the Silurian, but they continued to abound in the Devonian and Carboniferous seas, becoming reduced in those of the Permian period. Trilobites appear first in the Cambrian, reach a maximum in the Silurian, wane in the Devonian and Carboniferous, and die out in the Permian. They are therefore essentially and characteristically Palæozoic forms. So likewise are the Eurypterids, which, culminating apparently in the Upper Silurian and Old Red Sandstone, became extinct in Carboniferous times. Ganoids with heteroceral tails first appear in Upper Silurian strata, and reach their maximum in the Old Red Sandstone. The great order of Sharks and Rays likewise dates back to Upper Silurian times. Such are the more prominent types in Palæozoic strata. Many other forms, however, are met with, amongst which may be noted starfishes (Asteroidea), brittle-stars (Ophiuroidea), sea-urchins (Echinoidea), and the wholly extinct and characteristic Palæozoic types, Cystoidea and Blastoidea. Amongst the crustacea were cirripedes, ostracods, phyllopods, king-crabs, amphipods, isopods, long-tailed decapods, and stomapods. Arachnids were represented by scorpions and other forms; myriapods and insects by a number of ancestral types. All the great classes of molluscan life were present—Cephalopods appearing first in the Upper Cambrian; Pteropods in Lower Cambrian; Gasteropods in Lower Silurian; and Lamellibranchs in Upper Cambrian. The fishes have been already mentioned. Amphibians, represented by Labyrinthodonts and Salamandroids, appear first in Carboniferous strata.
Amongst plants the prominent Palæozoic types are cryptogams—Lepidodendroids, Sigillarioids, and Calamites being exclusively Palæozoic, but conifers were also present.
It may be noted that many of the characteristic life-forms of Palæozoic times were what are termed synthetic or comprehensive types, that is to say, types which while belonging fundamentally to some particular division or group of the animal kingdom, yet present in their structure characteristics of one or more contemporaneous, or as yet non-existing types. Among such intermediate or comprehensive forms may be mentioned the Labyrinthodonts, which were urodele amphibians with many piscine and reptilian characteristics. Examples are also furnished by the Ganoids, the Trilobites, the Brachiopods, the insects, &c. Amongst plants the Lepidodendroids exhibit similar peculiarities, for they combine characteristics of club-mosses and conifers. Again, many Palæozoic forms attained a larger size than the corresponding forms that belong to later times. Thus, some of the ptero- pod, cephalopods, ostracods, phyllopods, and insects were larger than any corresponding forms of our own day. The amphibians likewise exceeded in size any living representatives of their class.
Innumerable Palæozoic genera died out before Mesozoic times, while not a few lived on, and some have even persisted to the present day. These persistent forms are met with chiefly among the lower types of animal life, as foraminifers, brachiopods, and molluscs. See CAMBRIAN, SILURIAN, OLD RED SANDSTONE, CARBONIFEROUS, and PERMIAN SYSTEMS.
Mesozoic Life.—The life of Mesozoic times is in many respects strongly contrasted with that of the Palæozoic era. In place of Sigillarioids and Lepidodendroids, the prevalent forms of plant-life up to the close of the Cretaceous period were arborescent and herbaceous ferns, conifers, and cycads, while in late Cretaceous times the earliest angiosperms appeared. Corals, which were plentiful in Mesozoic seas, consisted almost exclusively of modern types—the rugose corals having waned almost to extinction. Echinoids and starfishes abounded, but Crinoids, so prevalent in Palæozoic seas, were now much reduced in numbers. Some of the higher grades of the crustacea, which are hardly known in Palæozoic rocks, were plentiful in Mesozoic times, and the same was the case with insects. Brachiopods ceased now to be dominant forms; while amongst molluscs the Cephalopods take the lead, and reach their culmination in swarms of Ammonitidæ and Belemnitidæ. Gasteropods and Lamellibranchs are well represented, and include a number of modern genera, which increased towards the close of the era. Ganoids were still numerous, mostly with symmetrical tails. Chimæroids, true sharks, and rays were all represented, while Teleosteans or bony fishes made their first appearance. Labyrinthodonts, which in Triassic times attained a great size, soon died out, making way for the advent of a prodigious reptilian fauna, in which all orders, save the Ophidians, were represented. There were swimming reptiles (Ichthyosaurus, q.v., Plesiosaurus, q.v.), flying reptiles (Pterodactylus, q.v.), snake-like reptiles (Dinosaurs, see DINOSAURIA), crocodiles, and chelonians. This reptilian life was specially abundant in Jurassic times. Birds probably were numerous, some of the forms being toothed, while others may have approximated to modern types. Mammals were represented by only the inferior grade of marsupials, and were all of small size. All the remarkable reptiles referred to became extinct before the beginning of the Cainozoic era. So it was with the characteristic Mesozoic molluscan families of Ammonitidæ, Belemnitidæ, and Hippuritidæ. Putting aside the lowly organised Protozoa, it may be said that hardly one Cretaceous species has been met with in Cainozoic or Tertiary strata. See TRIASSIC, JURASSIC, and CRETACEOUS SYSTEMS.
Cainozoic Life.—The plants of early Cainozoic times, although differing specifically and often generically from living forms, yet approach on the whole to existing types. Palms were a common feature of the floras from Eocene into Pliocene times. Indo-Australian types were common in Europe during the early Eocene, but later on forms characteristic of the warmer latitudes of North America began to abound. A commingling of Indo-Australian and American types also marked the Oligocene period, but the American forms gradually increased until in Miocene times they preponderated over all the others. The Pliocene flora of central Europe had a prevalent Mediterranean character. With regard to the lower forms of animal life, all that need be noted here is the general fact that these have a modern aspect, the number of existing genera and species becoming greater as we advance from the lower to the higher stages. The foraminifers attained now their maximum development, and are characteristically represented by the large coin-shaped nummulites. Amongst molluscs the Cephalopods are no longer dominant forms—the most abundant groups being Lamellibranchs and Gasteropods. But the most striking and leading Cainozoic forms were the mammals. In Eocene times the mammals were greatly developed—many of the forms attaining a large size. Among the more notable types of the early European Tertiary are Palæotherium (q.v.), Anoplotherium (q.v.), along with which were carnivores, rodents, insectivores, and bats, and also the earliest representatives of the horse and the monkey tribe. The later Tertiaries are marked by the appearance of Dinotheres, Mastodons, true elephants, rhinoceroses, hippopotamus, deer, antelope, gazelles, various carnivores, such as Machairodus, bears, cats, wolves, &c., and apes. No certain or unequivocal evidence of man is yet forthcoming from Tertiary strata.
While it is true that the general aspect of the plant and animal life of the Cainozoic era approaches to that of the present, yet this is truer for the less highly organised types than it is for those which are higher in the scale of being. Amongst the higher vertebrates of early Tertiary times not a few possessed characters which are now met with only in widely separated forms. Some, for example, were intermediate in character between tapirs and horses; in others (Tillodonts) we meet with a combination of structures now seen in ungulates, rodents, and carnivores; while many of the carnivores had decided marsupial affinities. Other remarkable composite forms were the Dino-cerata (q.v.).
Quaternary or Post-Tertiary Life.—The animals and plants of Quaternary age belong for the most part to existing species; a number of the higher vertebrates, however, are extinct. Among these latter, in Europe, were the Mammoth and various other elephants, several rhinoceroses, a dwarf form of hippopotamus, and Machairodus. In North America the fauna also included various extinct species, such as Mastodon, an elephant, and several gigantic members of the Sloth family (Megatherium, Mylodon, Megalonyx). These last seem to have abounded in South America, where they were associated with great armadillos (Glyptodon). The Quaternary period was characterised by marked oscillations of climate, and consequently by secular migrations of flora and fauna. Thus numerous forms which had survived from the Tertiary era eventually became extinct, and a still larger number were banished from the areas which they had occupied in Pliocene times. It is in the deposits of the Pleistocene that we meet with the first unquestioned relics and remains of man. See PLEISTOCENE SYSTEM, POSTGLACIAL AND RECENT SYSTEM; works cited at GEOLOGY; and the special handbooks of Palæontology, as by Nicholson (new ed. 1889), Seeley (1885), Steinmann and Döderlein (1888), Zittel (i.-iii. 1879-90), &c.