Identifier: geology00cham (find matches)
Title: Geology
Year: 1907 (1900s)
Authors: Chamberlin, Thomas C. (Thomas Chrowder), 1843-1928 Salisbury, Rollin D., 1859- joint author
Subjects: Geology
Publisher: New York, H. Holt and co.
Contributing Library: Internet Archive
Digitizing Sponsor: Internet Archive

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withthese bird tracks, it is supposed that they and their relatives wereresponsible for them, which is made the more probable by the occa-sional imprint of the fourth toe and of the fore foot. Most of thebird-like characters of the dinosaurs are more probably due to parallelevolution than to any immediate ancestral relationship to birds; moreremotely, birds and dinosaurs probably arose from a common stock.The dinosaurs will claim much further attention in the followingperiods. Even as early as the Triassic, they had a wide and signifi-cant distribution, appearing in the Rocky Mountains, North Carolina,Pennsylvania, Connecticut, Prince Edwards Island, England, Scotland,France, Germany, India, and South Africa. The advanced differentiation of the chelonians.—The turtle tribe II (JE0L0Q1 was represented in the record by Proganochelys (Psammockelys), ahighly specialized form belonging to the Pleurodira, from the UpperTrias of Europe, as well as by others (Chelyzoon) of true cryptodiran
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Fig. 340.—A Triassic dinosaur of the Connecticut valley, Anchisaurus colurus, restoredby Marsh, one-thirtieth of natural size. affinities from the middle Trias,1 indicating, by their divergence andspecialization, a much earlier origin of the chelonian order. The advent of the non-placental mammals. —Of peculiar interestis the appearance of early forms of non-placental mammals. Theywere small, and so primitive in type, that it is not altogether certainthat they were not mammal-like theromorphs. They are regarded,however, as prototherian mammals, allied to the monotremes andmarsupials. The remains are fragmentary, teeth being the mostsignificant portions preserved. These show relations to the theco-donts, and perhaps point to them as the source of descent, thoughthis is far from certain. Two genera are recognized in America 1 Recently described by von Huene. THE TRIASS1C PERIOD. 45 (Dromotherium and Microconodon) and one in Europe (Microlestes).This early appearance of the mammals,

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