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Originally appearing in Volume V20, Page 585 of the 1911 Encyclopedia Britannica.
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PALAEOLOGUS, a Byzantine family name which first appears in history about the middle of the 11th century, when George Palaeologus is mentioned among the prominent supporters of Nicephorus Botaniates, and afterwards as having helped to raise Alexius I. Comnenus to the throne in Io81; he is also noted for his brave defence of Durazzo against the Normans in that year. Michael Palaeologus, probably his son, was sent by Manuel II. Comnenus into Italy as ambassador to the court of Frederick I. in 1154; in the following year he took part in the campaign against William of Sicily, and died at Bari in 1155. A son or brother of Michael, named George, received from the emperor Manuel the title of Sebastos, and was entrusted with several important missions; it is uncertain whether he ought to be identified with the George Palaeologus who took part in the conspiracy which dethroned Isaac Angelus in favour of Alexius Angelus in 1195. Andronicus Palaeologus Comnenus was Great Domestic under Theodore Lascaris and John Vatatzes; his eldest son by Irene Palaeologina, Michael (q.v.), became the eighth emperor of that name in 126o, and was in turn followed by his son Andronicus II. (1282-1328). Michael, the son of Andronicus, and associated with him in the empire, died in 1320, but left a son, Andronicus III., who reigned from 1328 to 1341; John VI. (1355-1391), Manuel II. (1391-1425) and John VII. (1425-1448) then followed in lineal succession; Constantine XI. or XII., the last emperor of the East (1448-1453), was the younger brother of John VII. Other brothers were Demetrius, prince of the Morea until 146o, and Thomas, prince of Achaia, who died at Rome in 1465. A daughter of Thomas, Zoe by name, married Ivan III. of Russia. A younger branch of the Palaeologi held the principality of Monferrat from 1305 to 1533, when it became extinct. See ROMAN EMPIRE, LATER, and articles on the separate rulers. PALAEONTOLOGY (Gr. 7raXat6s, ancient, neut. pl. ilvra, beings, and Xoyia, discourse, science), the science of extinct forms of life. Like many other natural sciences, this study dawned among the Greeks. It was retarded and took false directions until the revival of learning in Italy. It became established as a distinct branch in the beginning of the 19th century, and some-what later received the appellation " palaeontology," which was given independently by De Blainville and by Fischer von Waldheim about 1834. In recent years the science of vegetable palaeontology has been given the distinct name of Palaeobotany (q.v.), so that " palaeontology " among biologists mainly refers to zoology; but historically the two cannot be disconnected. Palaeontology both borrows from and sheds light upon geology and other branches of the physical history of the earth, each of which, such as palaeogeography or palaeometeorology, is the more fascinating because of the large element of the unknown, the need for constructive imagination, the appeal to other branches of biological and physical investigation for supplementary evidence, and the necessity of constant comparison with the present aspects of nature. The task of the palaeontologist thus begins with the appearance of life on the globe, and ends in close relation to the studies of the archaeologist and historian as well as of the zoologist and botanist. That wealth of evidence which the zoologist enjoys, including environment in all its aspects and anatomy in its perfection of organs and tissues, the palaeontologist finds partially or wholly destroyed, and his highest art is that of complete restoration of both the past forms and past environments of life (see Plates I. and II.; figs. 1, 2, 3, 4, 5). The degree of accuracy in such anatomical and physiographic restorations from relatively imperfect evidence will always represent the state of the science and the degree of its approach toward being exact or complete. Progress in the science also depends upon the pursuit of palaeontology as zoology and not as geology, because it was a mere accident of birth which connected palaeontology so closely with geology. In order to illustrate the grateful services which palaeontology through restoration may render to the related earth sciences let us imagine a vast continent of the past wholly unknown in its physical features, elevation, climate, configuration, but richly represented by fossil remains. All the fossil plants and animals of every kind are brought from this continent into a great museum; the latitude, longitude and relative elevation of each specimen are precisely recorded; a corps of investigators, having the most exact and thorough training in zoology and botany, and gifted with imagination, will soon begin to restore the geographic and physiographic outlines of the continent, its fresh, brackish and salt-water confines, its seas, rivers and lakes, its forests, uplands, plains, meadows and swamps, also to a certain extent the cosmic relations of this continent, the amount and duration of its sunshine, as well as something of the chemical constitution of its atmosphere and the waters of its rivers and seas; they will trace the progressive changes which took place in the outlines of the continent and its surrounding oceans, following the invasions of the land by the sea and the re-emergence of the land and retreatal of the seashore; they will outline the shoals and deeps of its border seas, and trace the barriers which pre-vented intermingling of the inhabitants of the various provinces of the continent and the surrounding seas. From a study of remains of the mollusca, brachiopoda and other marine organisms they will determine the shallow water (littoral) and deep water (abyssal) regions of the surrounding oceans, and the clear or muddy, salt, brackish or fresh character of its inland and marginal seas; and even the physical conditions of the open sea at the time will be ascertained. In such manner Johannes Walther (Die Fauna der Solnhofener Flatten Kalke Bionomisch betrachtet. Festschrift zum 7oterl Geburtstage von Ernst Haeckel, 1904) has restored the conditions existing in the lagoons and atoll reefs of the Jurassic sea of Solnhofen in Bavaria; he has traced the process of gradual accumulation of the coral mud now constituting the fine litho-graphic stones in the inter-reef region, and has recognized the periodic laying bare of the mud surfaces thus formed; he has determined the winds which carried the dust particles from the not far distant land and brought the insects from the adjacent Jurassic forests. Finally the presence of the flying lizards (Pterydactylus, Rhamphorhynchus) and the ancient birds (Archaeopteryx) is determined from remains in a most wonderful state of preservation in these ancient deposits. Still another example of restoration, relating to the surface of a continent, may be cited. It has been discovered that at the beginning of the Eocene the lake of Rilly occupied a vast area east of the present site of Paris; a water-course fell there in cascades, and Munier-Chalmas has reconstructed all the details of that singular locality; plants which loved moist places, such as Marchantia, Asplenium, the covered banks overshadowed bylindens, laurels, magnolias and palms; there also were found the vine and the ivy; mosses (Fontinalisj and Chara sheltered the crayfish (Astacus); insects and even flowers have left their delicate impressions in the travertine which formed the borders of this lake. The Oligocene lake basin of Florissant, Colorado, has been reconstructed similarly by Samuel Hubbard Scudder and T. D. A. Cockerell, including the plants of its shores, the insects which lived upon them, the fluctuations of its level, and many other characteristics of this extinct water body, now in the heart of the arid region of the Rocky Mountains. Such restorations are possible because of the intimate fitness of animals and plants to their environment, and because such fitness has distinguished certain forms of life from the Cambrian to the present time; the species have altogether changed, but the laws governing the life of certain kinds of organisms have remained exactly the same for the whole period of time assigned to the duration of life; in fact, we read the conditions of the past in a mirror of adaptation, often sadly tarnished and incomplete owing to breaks in the palaeontological record, but constantly becoming more polished by discoveries which increase the understanding of life and its all-pervading relations to the non-life. Therefore adaptation is the central principle of modern palaeontology in its most comprehensive sense. This conception of the science and its possibilities is the result of very gradual advances since the beginning of the 19th century in what is known as the method of palaeontology. The history of this science, like that of all physical sciences, covers two parallel lines of development which have acted and reacted upon each other—namely, progress in exploration, research and discovery, and progress in philosophic interpretation. Progress in these two lines is by no means uniform; while, for example, palaeontology enjoyed a sudden advance early in the 19th century through the discoveries and researches of Cuvier, guided by his genius as a comparative anatomist, it was checked by his failure as a natural philosopher. The great philosophical impulse was that given by Darwin in 1859 through his demonstration of the theory of descent, which gave tremendous zest to the search for pedigrees (phylogeny) of the existing and extinct types of animal and plant life. In future the philosophic method of palaeontology must continue to advance step by step with exploration; it would be a reproach to later generations if they did not progress as far beyond the philosophic status of Cuvier, Owen and even of Huxley and Cope, as the new materials represent an advance upon the material opportunities which came to them through exploration. To set forth how best to do our thinking, rather than to follow the triumphs achieved in any particular line of exploration, and to present the point we have now reached in the method or principles of palaeontology, is the chief purpose of this article. The illustrations will be drawn both from vertebrate and invertebrate palaeontology. In the latter branch the author is wholly indebted to Professor Amadeus W. Grabau of Columbia University. The subject will be treated in its biological aspects, because the relations of palaeontology to historical and strati-graphic geology are more appropriately considered under the article GEOLOGY. See also, for botany, the article PALAEOBOTANY. We may first trace in outline the history of the birth of palaeontological ideas, from the time of their first adumbration. But for full details reference must be made to the treatises on the history of the science cited in the bibliography at the end of the article. I.-FIRST HISTORIC PERIOD The scientific recognition of fossils as connected with the past history of the earth, from Aristotle (384-322 B.C.) to the beginning of the 19th century, in connexion with the rise of comparative anatomy and geology.—The dawn of the science covers the first observation of facts and the rudiments of true interpretation. Among the Greeks, Aristotle (384-322 B.C.) Xenophon (430-357 B.C.) and Straho (63 B.C.-A.D. 24) knew of the existence of fossils and surmised in a crude way their relation to earth history. Similar prophetic views are found among certain Roman writers. The pioneers of the science in the 16th and r 7th centuries put forth anticipations of some of the well-known modern principles, often followed by recantations, through deference to prevailing religious or traditional beliefs. There were the retarding influences of the Mosaic account of sudden creation, and the belief that fossils represented relics of a universal deluge. There were crude medieval notions that fossils were " freaks " or " sports " of nature (lusus naturae), or that they represented failures of a creative force within the earth (a notion of Greek and Arabic origin), or that larger and smaller fossils represented the remains of races of giants or of pygmies (the mythical idea). As early as the middle of the 15th century Leonardo da Vinci (1452–1519) recognized in seashells as well as in the teeth of marine fishes proofs of ancient sea-levels on what are now the summits of the Apennines. Successive observers in Italy, notably Fracastoro (1483–1553), Fabio Colonna (1567–1640 or 165o) and Nicolaus Steno (1638–c. 1687), a Danish anatomist, professor in Padua, advanced the still embryonic science and set forth the principle of comparison of fossil with living forms. Near the end of the 17th century Martin Lister (1638–1712), examining the Mesozoic shell types of England, recognized the great similarity as well as the differences between these and modern species, and insisted on the need of close comparison of fossil and living shells, yet he clung to the old view that fossils were sports of nature. In Italy, where shells of the sub-Apennine formations were discovered in the extensive quarrying for the fortifications of cities, the close similarity between these Tertiary and the modern species soon led to the established recognition of their organic origin. In England Robert Hooke (1635–1703) held to the theory of extinction of fossil forms, and advanced the two most fertile ideas of deriving from fossils a chronology, or series of time intervals in the earth's history, and of primary changes of climate, to account for the former existence of tropical species in England. The 18th century witnessed the development of these suggestions and the birth of many additional theories. Sir A. Geikie assigns high rank to Jean Etienne Guettard (1715–1786) for his treatises on fossils, although admitting that he had no clear idea of the sequence of formations. The theory of successive formations was soundly developing in the treatises of John Woodward (1665–1728) in England, of Antonio Vallisnieri (1661–1730) in Italy, and of Johann Gottlob Lehmann (d. 1767) in Germany, who distinguished between the primary, or unfossiliferous, and secondary or fossiliferous, formations. The beginnings of palaeogeography followed those of palaeometeorology. The Italian geologist Soldani distinguished (1758) between the fossil fauna of the deep sea and of the shore-lines. In the same year Johann Gesner (1709–1790) set forth the theory of a great period of time, which he estimated at 8o,000 years, for the elevation of the shell-bearing levels of the Apennines to their present height above the sea. The brilliant French naturalist Georges Louis Leclerc, comte de Buffon (1707–1788), in Les Epoques de la nature, included in his vast speculations the theory of alternate submergence and emergence of the continents. Abraham Gottlob Werner (1750-1817), the famous exponent of the aqueous theory of earth formation, observed in successive geological formations the gradual approach to the forms of existing species. II.—SECOND HISTORIC PERIOD Invertebrate palaeontology founded by Lamarck, vertebrate palaeontology by Cuvier. Palaeontology connected with comparative anatomy by Cuvier. Invertebrate fossils employed for the definite division of all the great periods of time.—Although pre-evolutionary, this was the heroic period of the science, extending from the close of the 18th century to the publication of Darwin's Origin of Species in 1859. Among the pioneers of this period were the vertebrate zoologists and comparative anatomists Peter Simon Pallas, Pieter Camper and Johann Friedrich Blumenbach. Pallas (1741–1811) in his great journey (1768–1774) through Siberia discovered the vast deposits of extinct mammoths and rhinoceroses. Camper (1722–1789) contrasted (1777) the Pleistocene and recent species of elephants and Blumenbach (1752–1840) separated (178o) the mammoth from the existing species as Elephas primigenius. In 1793 Thomas Pennant (1726–1798) distinguished the American mastodon as Elephas americanus. Political troubles and the dominating influence of Werner's speculations checked palaeontology in Germany, while under the leadership of Lamarck and Cuvier France came to the fore. J. B. Lamarck (1744–1829) was the founder of invertebrate palaeontology. The treatise which laid the foundation for all subsequent invertebrate palaeontology was his memoir, Sur les fossiles des environs de Paris . . . (1802–1806). Beginning in 1793 he boldly advocated evolution, and further elaborated five great principles--namely, the method of comparison of extinct and existing forms, the broad sequence of formations and succession of epochs, the correlation of geological horizons by means of fossils, the climatic or environmental changes as influencing the development of species, the inheritance of the bodily modifications caused by change of habit and habitat. As a natural philosopher he radically opposed Cuvier and was distinctly a precursor of uniformitarianism, advocating the hypothesis of slow changes and variations, both in living forms and in their environment. His speculations on phylogeny, or the descent of invertebrates and vertebrates, were, however, most fantastic and bore no relation to palaeontological evidence. It is most interesting to note that William Smith (1769–1839), now known as the " father of historical geology," was born in the same year as Cuvier. Observing for himself (1794–18co) the stratigraphic value of fossils, he began to distinguish the great Mesozoic formations of England (18or). Cuvier (1769–1832) is famous as the founder of vertebrate palaeontology, and with Alexandre Brongniart (177o–1847) as the author of the first exact contribution to stratigraphic geology. Early trained as a comparative anatomist, the discovery of Upper Eocene mammals in the gypsum quarries of Montmartre found him fully prepared (1798), and in 1812 appeared his Recherches sur les ossemens fossiles, brilliantly written and constituting the foundation of the modern study of the extinct vertebrates. Invulnerable in exact anatomical description and comparison, he failed in all his philosophical generalizations, even in those strictly within the domain of anatomy. His famous " law of correlation;" which by its apparent brilliancy added enormously to his prestige, is not supported by modern philosophical anatomy, and his services to stratigraphy were diminished by his generalizations as to a succession of sudden extinctions and renovations of life. His joint memoirs with Brongniart, Essai sur la geographie mineralogique des environs de Paris aver une carte geognostique et des coupes de terrain (18o8) and Description geologique des environs de Paris (1835) were based on the wonderful succession of Tertiary faunas in the rocks of the Paris basin. In Cuvier's defence Charles Deperet maintains that the extreme theory of successive extinctions followed by a succession of creations is attributable to Cuvier's followers rather than to the master himself. Deperet points also that we owe to Cuvier the first clear expression of the idea of the increasing organic perfection of all forms of life from the lower to the higher horizons, and that, while he believed that extinctions were due to sudden revolutions on the surface of the earth, he also set forth the pregnant ideas that the renewals of animal life were by migration from other regions unknown, and that these migrations were favoured by alternate elevations and depressions which formed various land routes between great continents and islands. Thus Cuvier, following Buffon, clearly anticipated the modern doctrine of faunal migrations. His reactionary and retarding ideas as a special creationist and his advocacy of the cataclysmic theory of change exerted a baneful influence until overthrown by the uniformitarianism of James Hutton (1726–1797) and Charles Lyell (1797–1875) and the evolutionism of Darwin. The chief contributions of Cuvier's great philosophical opponent, Etienne Geoffroy St Hilaire (1772–1844), are to be found in his maintenance with Lamarck of the doctrine of the mutability of species. In this connexion he developed his special theory of saltations, or of sudden modifications of structure through changes of environment, especially through the direct influences of temperature and atmosphere. He clearly set forth also the phenomena of analogous or parallel adaptation. It was Alcide Dessalines d'Orbigny (1802—1857) who pushed to an extreme Cuvier's ideas of the fixity of species and of successive extinctions, and finally developed the wild hypothesis of twenty-seven distinct Creations. While these views were current in France, exaggerating and surpassing the thought of Cuvier, they were strongly opposed in Germany by such authors as Ernst Friedrich von Schlotheim (1764—1832) and Heinrich Georg Bronn (18o0—1862); and the latter demonstrated that certain species actually pass from one formation to another. In the meantime the foundations of palaeobotany were being laid (1804) by Ernst Friedrich von Schlotheim (1764—1832), (1811) by Kaspar Maria Sternberg (1761—1838) and (1838) by Theophile Brongniart (180x—1876). Following Cuvier's Recherches sur les ossemens fossiles, the rich succession of Tertiary mammalian life was gradually revealed to France through the explorations and descriptions of such authors as Croizet, Jobert, de Christol, Eymar, Pomel and Lartet, during a period of rather dry, systematic work, which included, however, the broader generalizations of Henri Marie Ducrotay de Blainville (1778—1850), and culminated in the comprehensive treatises on Tertiary palaeontology of Paul Gervais (1816—1879). Extending the knowledge of the extinct mammals of Germany, the principal contributors were Georg August Goldfuss (1782—1848), Georg Friedrich von Jaegar (1785—1866), Felix F. Plieninger (1807—1873) and Johann Jacob Kaup (1803—1873). As Cuvier founded the palaeontology of mammals and reptiles, so Louis Agassiz's epoch-making works Recherches sur les poissons fossiles (1833—1845) laid the secure foundations of palaeichthyology, and were followed by Christian Heinrich Pander's (1794—1865) classic memoirs on the fossil fishes of Russia. In philosophy Agassiz was distinctly a disciple of Cuvier and supporter of the doctrine of special creation, and to a more limited extent of cataclysmic extinctions. Animals of the next higher order, the amphibians of the coal measures and the Permian, were first comprehensively treated in the masterly memoirs of Christian Erich Hermann von Meyer (18or—1869) beginning in 1829, especially in his Beitrtige zur Petrefactenkunde (1829—1830) and his Zur Fauna der Vorwelt (4 vols., 1845—186o). Successive discoveries gradually revealed the world of extinct Reptilia; in 182 r Charles Konig (1784—1851), the first keeper of the mineralogical collection in the British Museum, described Ichthyosaurus from the Jurassic; in the same year William Daniel Conybeare (1787—1857) described Plesiosaurus; and a year later (1822) Mosasaurus; in 1824 William Buckland described the great carnivorous dinosaur Megalosaurus; while Gideon Algernon Mantell (1790—1852) in 1848 announced the discovery of Iguanodon. Some of the fossil Reptilia of France were made known through St Hilaire's researches on the Crocodilia (1831), and those of J. A. Deslongchamps (1794—1867) and his son on the teleosaurs, or long-snouted crocodiles. Materials accumulated far more rapidly, however, than the power of generalization and classification. Able as von Meyer was, his classification of the Reptilia failed because based upon the single adaptive characters of foot structure. The reptiles awaited a great classifier, and such a one appeared in England in the person of Sir Richard Owen (1804—1892), the direct successor of Cuvier and a comparative anatomist of the first rank. Non-committal as regards evolution, he vastly broadened the field of vertebrate palaeontology by his descriptions of the extinct fauna of England, of South America (including especially the great edentates revealed by the voyage of the " Beagle "), of Australia (the ancient and modern marsupials) and of New Zealand (the great struthious birds). His contributions on the Mesozoic reptiles of Great Britain culminated in his complete rearrangement and classification of this group, one of his greatest services to palaeontology. Meanwhile the researches of Hugh Falconer (18o8—1865) and of Proby Thomas Cautley (18o2—1875) in the sub-Himalayasbrought to light the marvellous fauna of the Siwalik hills of India, published in Fauna antiqua Sivalensis (London, 1845) and in the volumes of Falconer's individual researches. The ancient life of the Atlantic border of North America was also becoming known through the work of the pioneer vertebrate palaeontologists Thomas Jefferson (1743—1826), Richard Harlan (1796—1843), Jeffries Wyman (1814—1874) and Joseph Leidy (1823—1891). This was followed by the revelation of the vast ancient life of the western half of the American continent, which was destined to revolutionize the science. The master works of Joseph Leidy began with the first-fruits of western exploration in 1847 and extended through a series of grand memoirs, culminating in 1874. Leidy adhered strictly to Cuvier's exact descriptive methods, and while an evolutionist and recognizing clearly the genetic relationships of the horses and other groups, he never indulged in speculation. The history of invertebrate palaeontology during the second period is more closely connected with the rise of historic geology and stratigraphy, especially with the settlement of the great and minor time divisions of the earth's history. The path-breaking works of Lamarck were soon followed by the monumental treatise of Gerard Paul Deshayes (1795—1875) entitled Descriptions des coquilles fossiles des environs de Paris (1824—1837), the first of a series of great contributions by this and other authors. These and other early monographs on the Tertiary shells of the Paris basin, of the environs of Bordeaux, and of the sub-Apennine formations of Italy, brought out the striking distinctness of these faunas from each other and from other molluscan faunas. Recognition of this threefold character led Deshayes to establish a threefold division of the Tertiary based on the percentage of molluscs belonging to types now living found in each. To these divisions Lyell gave in 1833 the names Eocene, Miocene and Pliocene. James Hutton (1726—1797) had set forth (1788) the principle that during all geological time there has been no essential change in the character of events, and that uniformity of law is perfectly consistent with mutability in the results. Lyell marshalled all the observations he could collect in support of this principle, teaching that the present is the key to the past, and arraying all obtainable evidence against the cataclysmic theories of Cuvier. He thus exerted a potent influence on palaeontology through his persistent advocacy of uniformitarianism, a doctrine with which Lamarck should also be credited. As among the vertebrates, materials were accumulating rapidly for the great generalizations which were to follow in the third period. De Blainville added to the knowledge of the shells of the Paris basin; Giovanni Battista Brocchi (1772—1826) in 1814, and Luigi Bellardi (1818—1889) and Giovanni Michelotti (born 1812) in 184o, described the Pliocene molluscs of the sub-Apennine formation of Italy; from Germany and Austria appeared the epoch-making works of Heinrich Ernst Beyrich (1815—1896) and of Moritz Hoernes (1815—1868). We shall pass over here the labours of Adam Sedgwick (1785—1873) and Sir Roderick Murchison (1792—1871) in the Palaeozoic of England, which because of their close relation to stratigraphy more properly concern geology; but must mention the grand contributions of Joachim Barrande (1799—1883), published in his Systeme silurien du centre de la Bakelite, the first volume of which appeared in 1852. While establishing the historic divisions of the Silurian in Bohemia, Barrande also propounded his famous theory of " colonies," by which he attempted to explain the aberrant occurrence of strata containing animals of a more advanced stage among strata containing earlier and more primitive faunas; his assumption was that the second fauna had migrated from an unknown neighbouring region. It is proved that the specific instances on which Barrande's generalizations were founded were due to his misinterpretation of the overturned and faulted strata, but his conception of the simultaneous existence of two faunas, one of more ancient and one of more modern type, and of their alternation in a given area, was based on sound philosophical principles and has been confirmed by more recent work. The greatest generalization of this second period, however, was that partly prepared for by d'Orbigny, as will be more fully explained later in this article, and clearly expressed by Agassiz —namely, the law of repetition of ancestral stages of life in the course of the successive stages of individual development. This law of recapitulation, subsequently termed the " biogenetic law " by Ernest Haeckel, was the greatest philosophic contribution of this period, and proved to be not only one of the bulwarks of the evolution theory but one of the most important principles in the method of palaeontology. On the whole, as in the case of vertebrate palaeontology, the pre-Darwinian period of invertebrate palaeontology was one of rather dry systematic description, in which, however, the applications of the science gradually extended to many regions of the world and to all divisions of the kingdom of invertebrates. Beginning with the publication of Darwin's great works, " Narrative of the Surveying Voyages of H.M.S. `Adventure' and ` Beagle' " (1839), and " On the Origin of Species by Means of Natural Selection" (1859).—A review of the two first classic works of Charles Robert Darwin (1809-1882) and of their influence proves that he was the founder of modern palaeontology. Principles of descent and other applications of uniformitarianism which had been struggling for expression in the writings of Lamarck, St Hilaire and de Blainville here found their true interpretation, because the geological succession, the rise, the migrations, the extinctions, were all connected with the grand central idea of evolution from primordial forms. A close study of the exact modes of evolution and of the philosophy of evolution is the distinguishing feature of this period. It appears from comparison of the work in the two great divisions of vertebrate and invertebrate palaeontology made for the first time in this article that in accuracy of observation and in close philosophical analysis of facts the students of invertebrate palaeontology led the way. This was due to the much greater completeness and abundance of material afforded among invertebrate fossils, and it was manifested in the demonstration of two great principles or laws: first, the law of recapitulation, which is found in its most ideal expression in the shells of invertebrates; second, in the law of direct genetic succession through very gradual modification. It is singular that the second law is still ignored by many zoologists. Both laws were of paramount importance, as direct evidence of Darwin's theory of descent, which, it will ne remembered, was at the time regarded merely as an hypothesis. Nevertheless, the tracing of phylogeny, or direct lines of descent, suddenly began to attract far more interest than the naming and description of species. The Law of Recapitulation. Acceleration. Retardation.—This law, that in the stages of growth of individual development (ontogeny), an animal repeats the stages of its ancestral evolution (phylogeny) was, as we have stated, anticipated by d'Orbigny. He recognized the fact that the shells of molluscs, which grow by successive additions, preserve unchanged the whole series of stages of their individual development, 3o that each shell of a Cretaceous ammonite, for example, represents five stages of progressive modification as follows: the first is the periode embryonnaire, during which the shell is smooth; the second and third represent periods of elaboration and ornamentation; the fourth is a period of initial degeneration; the fifth and last a period of degeneration when ornamentation becomes obsolete and the exterior smooth again, as in the young. D'Orbigny, being a special creationist, failed to recognize the bearing of these individual stages on evolution. Alpheus Hyatt (1838-1902) was the first to discover (1866) that these changes in the form of the ammonite shell agreed closely with those which had been passed through in the ancestral history of the ammonites. In an epoch-making essay, On the Parallelism between the Different stages of Life in the individual and those in the entire group of the Molluscous Order Tetrabranchiata (1866), and in a number of subsequent memoirs, among which Genesis of the Arietidae (1889)583 and Phylogeny of an Acquired Characteristic (1894) should be mentioned, he laid the foundations, by methods of the most exact analysis, for all future recapitulation work of invertebrate palaeontologists. He showed that from each individual shell of an ammonite the entire ancestral series may be reconstructed, and that, while the earlier shell-whorls retain the characters of the adults of preceding members of the series, a shell in its own adult stage adds a new character, which in turn becomes the pre-adult character of the types which will succeed it; finally, that this comparison between the revolutions of the life of an individual and the life of the entire order of ammonites is wonder= fully harmonious and precise. Moreover, the last stages of individual life are prophetic not only of future rising and progressing derivatives, but in the case of senile individuals of future declining and degradational series. Thus the recapitulation law, which had been built up independently from the observations and speculations on vertebrates by Lorenz Olen (1779-1851), Johann Friedrich Meckel (1781-1833), St Hilaire, Karl Ernst von Baer (1792-1876) and others, and had been applied (1842-1843) by Karl Vogt (1817-1895) and Agassiz, in their respective fields of observation, to comparison of individual stages with the adults of the same group in preceding geological periods, furnished the key to the determination of the ancestry of the invertebrates generally. Hyatt went further and demonstrated that ancestral characters are passed through by successive descendants at a more and more accelerated rate in each generation, thus giving time for the appearance of new characters in the adult. His " law of acceleration " together with the complementary " law of retardation," or the slowing up in the development of certain characters (first propounded by E. D. Cope), was also a philo- ..1d 2e 2b 3b--1 -ie.`--2o I 8p I 4c--I - 1d~-2d--f—3d 4d I 5d--) - 1eI--2e-~--3e--f—4e—•—I-- 5e— 6e---I - 1f --f - 2f 3t ----~---- 4f — ~-- 6f -{— 6f —J-- 7f —I - 1 g-..2g..f_ 3g --I-- 4g —I 5g I--6g-l---- 7g. ----~ -lb-f.2h-'--31i—~-4h 7b--~ -11 -~ 21 -r-- 3i --{-- 4 i - 71----F—8i--1 (From the American Naturalist.) sophic contribution of the first importance (see fig. 6 and Plate III., fig. 7). In the same year, 1866, Franz Martin Hilgendorf (1839- ) studied the shells of Planorbis from the Miocene lake basin underlying the present village of Steinheim in Wurttemberg, and introduced the method of examination of large numbers of individual specimens, a method which has become of prime importance in the science. He discovered the actual transmutations in direct genetic series of species on the successive deposition levels of the old lake basin. This study of direct genetic series marked another great advance, and became possible in invertebrate palaeontology long before it was introduced among the vertebrates. Hyatt, in a re-examination of the Steinheim deposits, proved that successive modifications occur at the same level as well as in vertical succession. Melchior Neumayr (1845-1890) and C. M. Paul similarly demonstrated genetic series of Paludina (Vivipara) in the Pliocene lakes of Slavonia (1875). The Mutations of Waagen. Orthogenesis.—In 1869 Wilhelm Heinrich Waagen (1841-1900) entered the field with the study of Ammonites subradiatus. He proposed the term "mutations " for the minute progressive changes of single characters in definite directions as observed in successive stratigraphic levels. Even when seen in minute features only he recognized them as constant progressive characters or " chronologic varieties " in contrast with contemporaneous or " geographic varieties," which he considered inconstant and of slight systematic value. More recent analysis has shown, however, that certain modifications observed within the same stratigraphic level are really grades of mutations which show divergences comparable to those found in successive levels. The collective term " mutation," as now employed by palaeontologists, signifies a type modified to a slight degree in one or more of its characters along a progressive or definite line of phyletic development. The term " mutation " also applies to a single new character and for distinction' may be known as " the mutation of Waagen." This definitely directed evolution, or development in a few determinable directions, has since been termed " orthogenetic evolution," and is recognized by all workers in invertebrate palaeontology and phylogeny as fundamental because the facts of invertebrate palaeontology admit of no other interpretation. Among the many who followed the method of attack first outlined by Hyatt, or who independently discovered his method, only a few can be mentioned here—namely, Waagen (1869), Neumayr (1871), Wurttemberger (188o), Branco (188o), Mojsisovics (1882), Buckman (1887), Karpinsky (1889), Jackson (1890), Beecher (189o), Perrin-Smith (1897), Clarke (1898) and Grabau (19o4). Melchior Neumayr, the great Austrian palaeontologist, especially extended the philosophic foundations of modern invertebrate palaeontology, and traced a number of continuous genetic series (formenreihe) in successive horizons. He also demonstrated that mutations have this special or distinctive character, that they repeat in the same direction without oscillation or retrogression. He expressed great reserve as to the causes of these mutations. He was the first to attempt a comprehensive treatment of all invertebrates from the genetic point of view; but unfortunately his great work, entitled Die Stamme des Thierreichs (Vienna and Prague, 1889), was uncompleted. The absolute agreement in the results independently obtained by these various investigators, the interpretation of individual development as the guide to phyletic development, the demonstration of continuous genetic series, each mutation falling into its proper place and all showing a definite direction, constitute contributions to biological philosophy of the first importance, which have been little known or appreciated by zoologists because of their publication in monographs of very . special character. Vertebrate Palaeontology after Darwin.—The impulse which Darwin gave to vertebrate palaeontology was immediate and unbounded, finding expression especially in the writings of Thomas Henry Huxley (1825-1895) in England, of Jean Albert Gaudry (b. 1827) in France, in America of Edward Drinker Cope (184o-1897) and Othniel Charles Marsh (1831-1899). Fine examples of the spirit of the period as applied to extinct Mammalia are Gaudry's Animaux fossiles et geologie de 1'Attique (1862) on the Upper Miocene fauna of Pikermi near Athens, and the remarkable memoirs of Vladimir Onufrievich Kowalevsky (1842-1883), published in 1873. These works swept aside the dry traditional fossil lore which had been accumulating in France and Germany. They breathed the new spirit of the recognition of adaptation and descent. In 1867-1872 Milne Edwards published his memoirs on the Miocene birds of central France. Huxley's development of the method of palaeontology should be studied in his collected memoirs (Scientific Memoirs of Thomas Henry Huxley, 4 vols., 1898). In Kowalevsky's Versuch einer natiirlichen Classification der Fossilen Hufthiere (1873) we find a model union of detailed inductive study with theory and working hypothesis. All these writers attacked the problem of descent, and published preliminary phylogenies of such animals as the horse, rhinoceros and elephant, which time has proved to be of only general value and not at all comparable to the exact phylogenetic series which were being established by invertebrate palaeontologists. Phyletic gaps began to be filled in this general way, however, by discovery, especially through remarkable ' The Dutch botanist, De Vries, has employed the term in another sense, to mean a slight jump or saltation.discoveries in North America by Leidy, Cope and Marsh, and the ensuing phylogenies gave enormous prestige to palaeontology. Cope's philosophic contributions to palaeontology began in 1868 (see essays in The Origin of the Fittest, New York, 1887, and The Primary Factors of Organic Evolution, Chicago, 1896) with the independent discovery and demonstration among vertebrates of the laws of acceleration and retardation. To the law of " recapitulation " he unfortunately applied Hyatt's term " parallelism," a term which is used now in another sense. He especially pointed out the laws of the " extinction of the specialized " and " survival of the non-specialized " forms of life, and challenged Darwin's principle of selection as an explanation of the origin of adaptations by saying that the " survival of the fittest " does not explain the " origin of the fittest." He personally sought to demonstrate such origin, first, in the existence of a specific internal growth force, which he termed bathmic force, and second in the direct inheritance of acquired mechanical modifications of the teeth and feet. He thus revived Lamarck's views and helped to found the so-called neo-Lamarckian school in America. To this school A. Hyatt, W. H. Dail and many other invertebrate palaeontologists subscribed. History of Discovery. Vertebrates.—In discovery the theatre of interest has shifted from continent to continent, often in a sensational manner. After a long period of gradual revelation of the ancient life of Europe, extending eastward to Greece, eastern Asia and to Australia, attention became centred on North America, especially on Rocky Mountain exploration. New and unheard-of orders of amphibians, reptiles and mammals came to the surface of knowledge, revolutionizing thought, demonstrating the evolution theory, and solving some of the most important problems of descent. Especially noteworthy was the discovery of birds with teeth both in Europe (Archaeopteryx) and in North America (Hesperornis), of Eocene stages in the history of the horse, and of the giant drnosauria of the Jurassic and Cretaceous in North America. Then the stage of novelty suddenly shifted to South America, where after the pioneer labours of Darwin, Owen and Burmeister, the field of our knowledge was suddenly and vastly extended by explorations by the brothers Ameghino (Carlos and Florentino). We were in the midst of more thorough examination of the ancient world of Patagonia, of the Pampean region and of its submerged sister continent Antarctica, when the scene shifted to North Africa through the discoveries of Hugh J. L. Beadnell and Charles W. Andrews. These latter discoveries supply us with the ancestry of the elephants and many other forms. They round out our knowledge of Tertiary history, but leave the .problems of the Cretaceous mammals and of their relations to Tertiary mammals still unsolved. Similarly, the Mesozoic reptiles have been traced successively to various parts of the world from France, Germany, England, to North America and South America, to Australia and New Zealand and to northern Russia, from Cretaceous times back into the Permian, and by latest reports into the Carboniferous. Discovery of Invertebrates.—The most striking feature of exploration for invertebrates, next to the world-wide extent to which exploration has been carried on and results applied, is the early appearance of life. Until comparatively recent times the molluscs were considered as appearing on the limits of the Cambrian and Ordovician; but Charles D. Walcott has described a tiny lamellibranch (Modioloides) from the inferior Cambrian, and he reports the gastropod (?) genus Chuaria from the pre-Cambrian. Cephalopod molluscs have been traced back to the straight-shelled nautiloids of the genus Volborthella, while true ammonites have been found in the inferior Permian of the Continent and by American palaeontologists in the true coal measures. Similarly, early forms of the crustacean sub-class Merostomata have been traced to the pre-Cambrian of North America. Recent discoveries of vertebrates are of the same significance, the most primitive fishes being traced to the Ordovician or base of the Silurian,2 which proves that we shall discover more Professor Bashford Dean doubts the fish characters of these Ordovic Rocky Mountain forms. Frech admits their fish character but considers the rocks infaulted Devonic. ancient chordates in the Cambrian or even pre-Cambrian. Thus all recent discovery tends to carry the centres of origin and of dispersal of all animal types farther and farther back in geological time. IV.-RELATIONS OF PALAEONTOLOGY TO OTHER PHYSICAL
End of Article: PALAEOLOGUS
PALAEOLITHIC (Gr. iraXates, old, and )tWBor, stone)...

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