ENVIEONMENT OF THE TITANOTHEEES 



69 



rodents, artiodactyls, and perissodactyls. Of the 

 Perissodactyla only one family occurs, the Equidae, 

 represented by a prhnitive specific form of EoJiippus 

 (E. horealis). There are two or possibly three species 

 of Eohippus in these "Sand Coulee beds," which are 

 not yet separable from the species found in the "Gray 

 Bull" horizon above. Here also occurs Palaeanodon, 

 an ancestral armadillo, which left descendants in lower 

 and middle Eocene time. 



This lower Eocene horizon, described by Granger 

 (1914.1, p. 205), appears to constitute the beginning 

 of Sparnacian time in the Rocky Mountain region. It 

 contains the oldest known modernized fauna (perisso- 

 dactyls, artiodactyls, rodents, etc.) found in America. 

 The antiquity of these beds is indicated by the last 

 recorded appearance of the primitive order Multi- 

 tuberculata, as represented by remains of Ptilodusf sp. 

 The horizon is also distinguished by the absence of 

 tapirs (Systemodon) . Here occur the first known 

 species of the primitive lemuroid Notharctidae (Pely- 

 codus) and the peculiar ungulate Hyopsodus, now re- 

 garded as a condylarth. No other exposures con- 

 taining this very primitive Wasatch fauna have thus 

 far been discovered. 



ZONE 7: SYSTEMODON-COEYPHODON-EOHIPPUS ZONE 

 [Third Wasatch life zone, Big Horn C; upper Sparnacian of Europe] 



The "Gray Bull beds" of Granger (1914.1, pp. 203, 

 204), in the Big Horn Wasatch, lie at a horizon that 

 is distinguished by the presence of the earliest tapirs — 

 the pseudotapirs (Systemodon). These beds were at 

 first called the Ralston,^ a name that had been pre- 

 occupied. They are exposed principally in the Clark 

 Fork and Big Horn Basins south of the Yellowstone 

 (PI. V, B) and are at least 600 feet thick. They may be 

 correlated with part of the "Almagre" of the Wasatch 

 of New Mexico. As this is the first appearance of the 

 tapirs, and as their remains are mingled with those 

 of horses, this horizon may be known as the Syste- 

 modon-Corypliodon-EoMppus zone. These beds are 

 exposed chiefly along the south side of GreybuU 

 River, where they extend over many miles. From 

 this horizon was made the larger part of Cope's col- 

 lection from the lower Eocene of the Big Horn 

 Basin, including the classic skeleton of Phenacodus 

 primaevus, as well as the skeleton of P. copei '° and 

 that of Eohippus, besides many species of CorypTiodon. 

 One of the most common forms is the pseudotapir 



>"Ealston" was the name given by Sinclair and Granger (1912) to the Clark 

 Fork beds. "Clark Fork" was substituted by Granger (1914) because "Ralston" 

 had been previously used otherwise. Sinclair and Granger (1912) referred the beds 

 between the "Lysite" and the "Ralston" to the "Knight" formation. Granger 

 (1914) separated the " Knight beds " into two horizons, which he called " Gray Bull " 

 and "Sand Coulee." The "Gray Bull" and the overlying "Lysite" of Buffalo 

 Basin constitute the "Big Horn Wasatch" of Cope and Wortman. The "Gray 

 Bull" is exposed almost entirely in the Big Horn Basin, although a small area of it 

 overlies the " Sand Coulee" beds at the head of Big Sand Coulee in the Clark Fork 

 Basin (Granger, 1919). 



1 'The type of Phenacodus wortmani is from Wind River. Cope's reference of the 

 small Big Horn skeleton to this species is not correct. Granger (1915) renamed the 

 skeleton P. copei. 



Systemodon, which includes the species S. tapirinum, 

 and it is noteworthy that this genus, which is in- 

 directly related to true tapirs, does not appear in 

 the overlying beds. 



ZONE 8: HEPTODON-COEYPHODON-EOHIPPUS ZONE 

 [?ourth Wasatch life zone. Big Horn D and Wind River A ; lower Ypresian of Europe] 



To zone 8 belong the "Lysite beds" (PI. V, A) of 

 the Big Horn Basin Wasatch, Wyoming (Big Horn D); 

 the lower level of the Wind River formation (Wind 

 River A) ; a part of the Knight formation of the typical 

 Wasatch group; and parts of the "Almagre" and 

 "Largo" of the New Mexico Wasatch. In this life 

 zone Heptodon takes the place of Systemodon, which 

 disappears or is not thus far recorded. The grace- 

 ful lophiodont Heptodon appears at the very summit 

 of the underlying "Gray Bull beds," is abundant in 

 the "Lysite," and continues into the "Lost Cabin," 

 its presence being one of the means of correlating the 

 fauna of these beds with that of the typical Wasatch 

 group in the Knight formation. This Knight fauna 

 occurs in the CorypJiodon-henrmg layer, which Cope 

 describes as 500 feet above the base of this division 

 of the typical Wasatch of the Evanston region, or 

 about the middle third of the formation according to 

 Granger. 



The typical Heptodon zone (= "Lysite") of the 

 Wind River beds, 350 feet in thickness, is distinguished 

 by the absence of titanotheres (LamidotJierium, 

 Eotitanops), which are very abundant in the super- 

 imposed "Lost Cabin beds." The "Lysite" or 

 Heptodon zone in the Big Horn Basin is 400 feet thick. 

 Anacodon, one of the arctocyonid creodonts, which 

 has flattened or pavement-like teeth, is characteristic 

 of the Heptodon zone. This zone is faunistically but 

 not lithologically separated from the overlying Lamh- 

 dotJierium zone. 



ZONE 9: 1AMBD0THEEHTM-E0TITAN0PS-C0RYPH0D0N ZONE 



[Fifth Wasatch life zone. Big Horn E, Wind River B, and Huerfano A; upper 

 Ypresian of Europe] 



Geology and fauna. — To zone 9 belong the typical 

 Wind River of Hayden and of Cope in the Wind 

 River Basin, Wyo. ( = the "Lost Cabin" of Granger 

 and Sinclair); the "Lost Cabin" (Granger) of the 

 Big Horn Basin Wasatch; part of the "Largo beds" 

 (Granger) of the San Juan Wasatch of New Mexico; 

 part of the Green River lacustrine formation of 

 Wyoming; and the lower level of the Huerfano for- 

 mation (Hills) of Colorado or Huerfano A. This is 

 the typical Wind River life of all the literature of 

 Cope. (See PI. VI.) 



The Lamldotherium life zone is distinguished by the 

 arrival in the Rocky Mountain basin region of the 

 first titanotheres, which are abundantly represented 

 in remains of the smaller, cursorial Lambdotherium 

 and the larger, mediportal Eotitanops. It includes the 



