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VERTEBRATA. 99 VERTEBRATA. liorse (see IIorse. Fossil) ; that of the camel stands next in c-ompletencss ; and less oomplete series represent the aneestry of many of the liiglier ruminants, of the elephants, rhin<X'eroses. tapirs, dogs, and many other animals. Indeed, it may be said that there are eomparatively few land mammals of which some aneestnil types are not Unown; and these ancestral forms in- varialily present primitive characters linkinji; the modern representative to the common ancestor of tlic mammals, altliou^h they often ciimliine these jirimitivc characters with peculiar specializations which show that they are not in the ilirect line of descent. And these primitive characters are more |)ronounccd in the more ancient forms. We have, however, very little positive knowl- edge of the ancestry of the marine mammals, the seals, cetaceans (whales, dolphins, and porpoises, etc.), and sirenians (dugongs and manatees). Setting aside these, with a few rare an<l peculiar land niannnals whose history is unknown, and the Australian mammals (marsupials aiul mul- tituberculates) which probably diverged from the conunon stock at an earlier date, we can infer with a high degree of probability from these known lines of descent a common ancestor to the modern mammals, which lived during -the C'relaccois period and whose descendants at the begiiniing of the Tertiary period had diverged comparatively little in characters. This conunon ancestor was of small size, of a low order of in- telligence for a maunnal, the legs short, five toes on each foot and claws on the toes, and a long heavy tail. Its teeth were 44 in number. 11 on each side of each jaw-, consisting of three incisors, a canine, four premolars, and three molars. The molars had each three sharp cusps arranged in the form of a triangle; the remaining teeth had but one cusp, but the canine was larger tlian the rest. The animal walked on the sole of the foot, and there are some reasons for thinking that it was at least partly arboreal. Its food was prob- ably chiefly insects or other small animals. Only a few fragments of jaws and teeth of Cretaceous mannnals have been found; but some of them cor- respond, as far as they go, to the characters of the hypothetical type, while others represent more ancient otTshoots from the central stock. The oldest Tertiary mammals preserve nearly all the above characters of their supposed ances- tor, but show the early steps of the divergence which led into the various types of the present day. Some were becoming herbivorous, develop- ing hoofs instead of claws, lengthening the limbs and losing one or more Of the side toes on each foot to increase the speed, and changing the character of the teeth to fit them better for a vegetarian diet. Others were becoming more strictly carnivorous, adapting the teeth to cut and tear flesh; while others again were arboreal and frugivorous as judged from the characters of their limbs and teeth. In the succeeding stages of the Tertiary the characters of each line become more marked, some lines leading up into modern animals, others into side-branches which liave died out. Several of these side-branches ended in clumsy monstrous races of huge size and peculiar form, occupying the same place in the various Tertiary faunas that the elephants, rhinoceroses, and hippopotami do in that of to-day. Such were the Coryphoflon and Uinta- therium of the Eocene, the Titanotherium and Elotherium of the Oligocene, the Chalicotherium of the Miocene, and various peculiar extinct rhinoceroses in America and Europe. Evolution of Man. Of animals which can be considered as in or near the line of ancestry of man, the remains are very few and very fragmentary in the Tertiary, and are foiuid only in the Old World. It must be supposed that the evolution of man during this period took place in a region which has not been thor- oughly explored, or in which the Tertiary strata arc not well exjiosed. But early in the Quater- nary period remains and indications of iniin are found fossil in all ))arts of the world, along with animals identical or closely allied witii, those of modern time as well as others which have become extinct, such as the mammoth and the mastodon in the northern world, the mega- therium in South America, and the diprotodon in Australia. For the extinction of these and for the rarity of most other large animals at the present time, man is, no doubt, largely re- sponsible, directly as a hunter, or indirectly by depriving them of their food and range. He has become cosmopolitan and dcnninant in a sense that no animal ever was in previous ages, and it may almost be said that all other animals exist only by his suflFeranee or to be exploited for his benefit. ilrsEUMS AND Collecting Grounds. The col- lections of fossil vertebrates are practically con- fined to the large museums of Euro])c and the I'nited States, the best being in New York, Lon- don, and Paris. With the Paris Museum is especially connected the name of Cuvier (q.v.). In the middle of the last century Owen and Huxley in England were the most prominent investigators, while in its latter years Ameri- can students, especially Leidy. Cope, and ilarsh, were in the front rank. In recent years Ameri- can museums and collectors have been in the lead, the arid Western States containing the richest fossil-fields yet known. While in Europe the best collecting grounds have been quarries worked primarily for building-stone, slate, or phosphate rock, or bone-beds of limited area, the Western fossil-fields are the extensive areas of Mesozoie or Tertiary rocks laid bare in the 'bad lands.' and while the fossils are widely scattered, they are remarkably Well preserved. The appended table shows the characteristic vertebrate animals found in the difi'erent geo- logical periods as understood at the present time. BiBLioGEAPHT. LucES, Animals of the Past (Xew York. 1001), is a popular book on verte- brate fossils, entertainingly written, but very incomplete. A later book, 'Animals Before Man in Noi-th' America, by the same author, partly fills the gaps of the earlier work. Hutchinson, Extinct Monsters (London and New Y'ork, 1802), contains very good accounts of the more re- markable extinct types known up to the date of their publications, but does not include more recent American advances in the subject. A. Smith Woodward, Oiiflines of Vertebrate Paleontolofij/ for Students of Zoolof/ii (Cambridge, 180S). is the best English textbook on the subject, and it contains a well-selected bibliographic list. Zittel, Uandhnch der PaUionlologic, vols. iii. and iv. (Munich, 1S87-93), is the most complete ref- erence book for advanced students, and his