VERTEBRATE PALEONTOLOGY 245 



especially among reptiles and mammals, have come to 

 light as the fruits of American discovery. But aside 

 from the dry cataloguing of such groups, the American 

 systematists have worked out some very remarkable phy- 

 logenies and have thus clarified our vision of animal 

 relationships in a way which the recent zoologist could 

 never have done. In this connection, the Permian ver- 

 tebrates, which have been collected and studied with 

 amazing success, principally by Williston and Case, 

 should be mentioned, although the work is yet incom- 

 plete. Some of these forms are amphibian, others rep- 

 tilian, yet others of such character as to link the two 

 classes as transitional forms. Of the Mesozoic reptiles, 

 a very remarkable assemblage has come to light, in a 

 degree of perfection unknown elsewhere. These are dino- 

 saurs, of which several phyla are now known ; carnivores 

 both great and small, some of the latter being actually 

 toothless; Sauropoda, whose perfection and dimensions 

 are incomparable except for those found in East Africa ; 

 and predentates, armored, unarmored, and horned, the 

 last exclusively American. The unarmored trachodonts 

 are now known in their entirety, for not only has our 

 West produced articulated skeletons but mummified car- 

 casses whose skin and other portions of their soft 

 anatomy are represented, and which are thus far without 

 a parallel elsewhere in the world. Other reptilian 

 groups are well known, notably the Triassic ichthyosaurs, 

 and the mosasaurs and plesiosaurs of the Kansas chalk. 

 The last formation has also produced toothed birds, 

 Hesperornis and Ichfhyornis, which again are absolutely 

 unique. 



But it is in the mammalian class that the phylogenies 

 become so highly complete and of such great importance 

 as evolutionary evidences, for nowhere else than in our 

 own West have such series been found as the Dinocerata 

 and creodonts among archaic forms, the primitive 

 primates from the Eocene, the carnivores such as the 

 dogs and cats and mustellids, but especially the hoofed 

 orders such as the horses. Of these hoofed orders, the 

 classic American series of horses is complete, that of 

 the camels probably no less so, while much is known of 

 the deer and oreodonts, the last showing several parallel 



