254 GEOLOGY. 



muskrats, martens, civet cats, and various xiphodonts andanoplothcivs, 

 as well as extinct forms. 



The rhinoceros tribe had deployed into three notable branches, one 

 a true lowland form, ancestral in type to the existing family, another 

 aquatic {Metamynodon), and a third an upland, horse-like, running 

 form {Hyracodon) . The Metamynodon was massive and stocky, like 

 the modern rhinoceros, but hornless, while the Hyracodon was light- 

 limbed and equine in many features, re-asserting the ancestral alliance 



Fig. 439. — Titanotherium validum Marsh, photograph of a mounted specimen in the 

 Carnegie Museum, by Director Holland. 



of the horses and rhinoceroses. The tribe had a cosmopolitan range 

 and was well represented in Europe. 



The titanotheres were a massive erratic branch of the ocld-toed 

 ungulates which arose late in the Eocene, reached their climax in the 

 Oligocene (White River), and then suddenly disappeared. They were 

 intermediate in proportions between the rhinoceros and the elephant, 

 and were distinguished by a long, depressed skull armed with a pair of 

 horns near the extremity of the nose, as were their kin the rhinoceroses, 

 but placed transversely, as in the ox (Fig. 439). . They readied some 

 fourteen feet in length and ten in height. There were many variations 

 with age and sex, and several genera have been founded on these 



