INTRODUCTION TO MAMMALIAN PALEONTOLOGY 



13 



TTie eleven orders of Tertiary ungulates 



I. Archaic ungulates: 



I America and Eurasia. Originating in Cretaceous time and contemporaneous 

 in Eocene time (Coryphodon) witli the titanotheres, becoming extinct in late 

 Eocene time {Uintatherium and Eobasileus). 

 I America, Eurasia, and possibly South America. For a short period contempo- 

 raneous with the titanotheres, becoming extinct in the lower Eocene (Phena- 

 codontidae) . 



II. Modernized ungulates: 



A. Primarily North American and north Eurasian: 



..,,,, . , , , f America, Eurasia, and subsequently South America. First appearing in early 



,' „ . , ^ , „ i.j_^_ _I,'""7 ~ I Eocene time. The Perissodactyla gradually gave way to the Artiodactj^la. 



The chalicotheres were in part contemporaneous with the titanotheres near 

 the end of their Ufe period. 



4. Perissodactyla (horses, titanotheres, 

 tapirs, rhinoceroses). 



B. Originally African-Asiatic ungulates: 



„ -H rv, ^ [First appearing on the African continent; subsequently, in part, entering 



„■ „ , ., , , , _ ~j ----------- 1 southern Eurasia and North America. None of these orders is known to 



Proboscidea (elephants and masto- 

 dons). 



7. Sirenia (sirenians') . 



have been contemporaneous (in Europe) with the titanotheres or to have 



[ entered into competition with them. 



[Aquatic mammals, first known in Africa, possibly related to the same ancestors 



' I as the Proboscidea; believed to have sprung from ungulate ancestors. 



8. Embrithopoda (arsinoitheres) Known solely on the African continent; Oligocene. 



C. Distinctively South American ungulates: 



Q p iv^ . / .i.- j_N [Exclusively South American in history and evolution.'' None of these orders 



in T rl +• f f l'\ J entered into competition with the titanotheres. Part of them (Litopterna) 



,,'-i X , \- J.N I imitated the other orders of ungulates, and part (Toxodontia) evolved into 



11. Litopterna (extmct) ■ , & > f ^ 



[ unique forms. 



* A single jaw attributed to one of the aberrant Southi American ungulates has been found in the Eohippus- Corypho 

 Basin, Wyo. 



I lite zone, "Sand Coulee beds" of Clark Fork 



Only three of the eleven ungulate orders shown 

 in the table were living in the Rocky Mountain 

 region when the titanotheres arrived — (1) the archaic 

 Amblypoda, represented, as we have seen, by Cory- 

 phodon, extremely smaU-brained, of very clumsy 

 build, heavy-footed, in general proportions somewhat 

 like the African rhinoceroses, RTiinoceros (Cerato- 

 therium) simus and R. (Opsiceros) iicornis; (2) the 

 Condylarthra, represented by a diminutive Phena- 

 codus, also extremely small-brained, contrasting with 

 Coryphodon in its small size and cursorial build, 

 formerly but no longer believed to be ancestral to the 

 higher ungulates; (3) the modernized Perissodactyla, 

 including the ancestors of the horses {Eohippus), 

 tapirs (Systemodon) , and lophiodonts (Heptodon). 



The newly arriving perissodactyl titanotheres 

 equaled in size and resembled in their general cursorial 

 limb structure the condylarths as well as the horses, 

 tapirs, and lophiodonts. They were greatly surpassed 

 in size by members of the Coryphodon family, some 

 species of which were quadruple the size of the earliest 

 known titanotheres. However, certain of the titano- 

 theres of this stage (Eofitanops) exceeded the condy- 

 larths (Phenacodus) in size. 



It is noteworthy that the archaic Condylarthra 

 (Phenacodus) were numerically preponderant in the 

 Phenacodus zone, just prior to the arrival of the 

 earliest perissodactyl horses. There was doubtless an 

 incessant competition between all these modernized, 

 alert, large-brained perissodactyl ungulates and the 

 archaic, small-brained ungulates {Coryphodon and 

 Phenacodus), which were especially inferior in the 



mechanics of their foot structure. When, in the 

 upper Eocene, the clumsily built Amblypoda reached 

 the final phase of their evolution in the gigantic 

 Uintatherium and Eohasileus, they apparently became 

 suddenly extinct, and at the same time the titanotheres 

 suddenly began to develop into more formidable 

 animals. At no time in the Tertiary period was the 

 earth populated in the same region with more than 

 one type of very large quadruped. In the Northern 

 Hemisphere the dominance of the amblypods (in the 

 Eohasileus- Coryphodon epoch) was succeeded by the 

 dominance of the titanotheres (in the closing titano- 

 there epoch), and the titanotheres in turn, when 

 they had reached their largest development, suddenly 

 became extinct with no trace of a preliminary stage of 

 decline. 



OID AND NEW SYSTEMS OF CLASSIFICATION 

 OLD TERMINOLOGY RETAINED 



The studies for this monograph were begun by 

 Professor Marsh under the old ideas of classification 

 in mammalogy, derived from Linnaeus and his suc- 

 cessors. These studies were continued by Osborn on 

 the same old lines, as shown in his first paper on the 

 titanotheres. (Osborn, 1896.107.) The discovery 

 of adaptive radiation and of polyphyletic evolution, 

 which was one result of the researches made for this 

 monograph, has developed a new phyletic system of 

 classification. Yet even in this new system it is 

 necessary to adhere to the old Linnaean terminology, 

 for the reason that Linnaean methods have been used 

 during the long period of systematic description in 



