INTEODUCTION TO MAMMALIAN PALEONTOLOGY 



11 



competed with members of two archaic orders, the 

 Amblypoda, typified by Coryphodon, and the Condy- 

 larthra, typified by Phenacodus. The titanotheres 

 survived both these archaic orders. They came 

 into competition with members of several other 

 families of the Perissodactyla and rapidly outstripped 

 them in evolution. The period of the extinction of 

 the titanotheres, at the end of lower Oligocene time, 

 marked also the decline of several other of the great 



rhinoceroses are the only odd-toed ungulates that 

 outlived the titanotheres and survived to the present 

 time. The fourth order of quadrupeds that competed 

 with the titanotheres were the Artiodactyla, the dimin- 

 utive ancestors of the even-toed ungulates, including 

 the ruminants, which entered a great era of expansion 

 soon after the titanotheres became extinct. 



The earliest known types of titanothere evolution, 

 Lambdotherium and Eotitanops, which were contem- 



FiGUEE 11. — Amblypoda: Skeletons and restorations of an ancestral form (A) and a specialized form (B) 



A, Pantolamida of the basal Eocene Torrejon formation; B, Coryphodon of the Wasatch formation, persisting throughout five life zones of 

 lower Eocene time, contemporaneous in its later stages of development with Eotitanops and Lambdothtriiim, ancestral titanotheres. 



families of perissodactyls, especially the aquatic 

 rhinoceroses (amynodonts), the cursorial rhinoceroses 

 (hyracodonts), and the fleet lophiodonts (Colodon), 

 all of which became extinct soon after the titanotheres 

 disappeared. The aberrant perissodactyl chalico- 

 theres, which are in many respects similar to the titan- 

 otheres, survived, perhaps because they retreated, 

 like the okapi of the Congo region of Africa, into the 

 recesses of the forests. The tapirs, horses, and true 



poraneous, appear in the fourth Coryphodon life zone. 

 Coryphodon is a clumsy but powerful mammal of very 

 archaic type, heavily armed with great canine tusks. 

 It is descended from Pantolamhda of the basal Eocene. 

 As Coryphodon appears in the far distant region of 

 the Sparnacian of France as the companion of a giant 

 bird (Gastornis) and of a primitive horse {Hyracothe- 

 rium) similar to the American Eohippus, France and 

 western America are brought close together in their 



