. An introduction to the study of mammals living and extinct. Mammals. 292 UNGULATA Extinct Transitional Artiodactyles. In this place it will be convenient to notice briefly a few of the extinct types of Tertiary Artiodactyles which connect the existing bunodont Suina with the more specialised selenodont groups mentioned below so closely as to show that in a strictly palseontological classification such groups cannot be maintained. It should be mentioned that while some of these extinct forms were in all probability actual ancestral links between the bun- odonts and selenodonts, others, like t
. An introduction to the study of mammals living and extinct. Mammals. 292 UNGULATA Extinct Transitional Artiodactyles. In this place it will be convenient to notice briefly a few of the extinct types of Tertiary Artiodactyles which connect the existing bunodont Suina with the more specialised selenodont groups mentioned below so closely as to show that in a strictly palseontological classification such groups cannot be maintained. It should be mentioned that while some of these extinct forms were in all probability actual ancestral links between the bun- odonts and selenodonts, others, like the Anoplotheres, died out entirely without giving rise to any more specialised descendants. Chmropotamidce.—In this family the molars are intermediate in structure between those of the Suidce and the next family. The upper ones have very broad crowns, with the five columns arranged as in Anthracotheriitm ; while the premolars are not secant, and may be very large. The best known forms are the small Gebochmrus of the Phosphorites of Central France; Chceropotamus of the Upper Eocene, the type species of which was of the size of a large Pig, with the dental formula if, c \, p ^, m f, and no distinctly selenodont structure in the molars; the much larger Elotlieriwm, from the Upper Eocene and Lower Miocene of both the Old and New Worlds, which presents the very rare feature of the absence of a third lobe to the last lower molar; and the equally large Teiracoiwdon of the Pliocene of India, in which this third lobe was present and the premolars were of enormous size. The remarkable North American Eocene genus AcJicenodon should perhaps also be placed here. Anthracotheriidce.—The genera Anthracotherium and Syopotamus, of the upper Eocene and Miocene, have the typical Eutherian dental for- mula; the upper molars (Pig. Ill) carrying three columns on the anterior and two on the posterior half of the crown, all of which are of a more or less decidedly selenodont structure. The mandible
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