84 



TITANOTHEBES OP ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



ZONE 11: PAIEOSYOPS PALUDOSUS-OEOHIPPUS ZONE 

 [Bridger B; upper Intetian of Europe] 



The richly fossiliferous deposits belonging to the 

 Paleosyops paludosus-OroMppus zone (Bridger B) 

 are exposed chiefly in the northern area of the Bridger 

 formation, near Fort Bridger, along Blacks Fork and 

 its tributaries. They represent a very long period and 

 consist of 450 feet of tuffs and sandstones (fig. 4) 

 divided into two principal escarpments, which are 

 separated by Cottonwood Creek valley. 



In this zone the titanotheres and other mammals 

 undergo notable progressive evolution, and there is a 

 marked succession of species. (See fig. 57.) 



The succession of the species of titanotheres in 

 Bridger B, in descending geologic order, is as follows: 



Limnohyops monoconus Os- 

 born, type. 



Limnohyops matthewi Osborn, 

 type. 



Palaeosyops paludosus Leidy. 



Palaeosyops paludosus, re- 

 ferred. 



Palaeosyops paludosus, type. 



?Mesatirhmus Junius Leidy. 



Palaeosyops major Leidy, hy- 

 potype. 



Limnohyops laevidens Cope, 

 type. 



Palaeosyops major Leidy, re- 

 ferred. 



Limnohyops monoconus Os- 

 born, referred. 



The species of titanotheres found in Bridger B 

 belong exclusively to the subfamily Palaeosyopinae 

 and represent the two generic branches Palaeosyops 

 and LimnoTiyops, closely related animals with broad 

 spreading feet and heavy limbs, slow in gait. The 

 reference to Mesatirhinus of the species P. Junius 

 Leidy is somewhat doubtful. The lower half of 

 Bridger B at Grizzly Buttes (PI. VII, B) , an escarp- 

 ment along Smiths Fork, is by far the richest collect- 

 ing ground in the Bridger Basin; thousands of speci- 

 mens have been taken from it, including many more 

 or less complete skulls and skeletons, all recorded 

 from Bridger B 2. Beds at a slightly higher level, in 

 Bridger B 2 and in Bridger B 3, on the escarpment 

 along Cottonwood Creek, have yielded a number of 

 complete skeletons, including those of several species 

 of Equidae (OroTiippus), a variety of catlike and dog- 

 like creodonts {Limnocyon, Harpagolestes), abundant 

 small civet-like creodonts (Viverravus, Sinopa), an- 

 cestral canids (Miacis, Uintacyon), a surviving (?) 

 condylarth (Hyopsodus) ; also ancestral Edentata 

 {Metacheiromys, armadillo-like) and the rodent-like 

 tillodonts {Tilloiherium fodiens, Trogosus). They 

 have also yielded many rodents (Paramys, Sciuravus), 

 as well as a rich primate fauna of lemuroids (Noth- 

 arctus). The entire fauna has been very carefully 

 reviewed and analyzed by Matthew (1909.1, pp. 

 298-302). 



Rich as is the fossil life of the lower Bridger, many 

 mammalian subfamilies and many genera and species 

 are lacking which occur abundantly in the upper 

 Bridger. Noticeable is the absence of uintatheres 

 (Uintatherium) and of three important genera of ti- 

 tanotheres {Manteoceras, Telmatherium, Mesatirhinus), 

 which appear abundantly in the upper Bridger. 



The "Cottonwood Creek white layer," marking 

 the summit of Bridger B, indicates a long period of 

 shallow lake flooding of the Bridger Basin during 

 which the large amblypod uintatheres and the more 

 advanced titanotheres entered the basin. Vintaihe- 

 rium is not found in Bridger B, but it occurs at the 

 very base of Bridger C, the lowest level of the upper 

 Bridger. 



ZONE 12: UINTATHERIUM-MANTEOCERAS-MESATniHINUS ZONE 

 [Bridger C and D, Wasliakie A, and Uinta A; part of Bartonian of Europe] 



The fauna of zone 12 in the Bridger Basin, which 

 includes deposits 725 feet thick (Bridger D, 375 feet; 

 Bridger C, 350 feet; see fig. 58), may be clearly dis- 

 tinguished from that of zone 1 1 (lower Bridger = Bridger 

 B and A) by its content of the remains of the animals 

 listed below: 



Titanotheres : 



Palaeosyops robustus Leidy. 



Palaeosyops copei, type. 



?Telmatherium validum, type. 



Manteoceras manteoceras. 



Mesatirhinus petersoni, type. 



Palaeosyops leidyi, type. 



Limnohyops laticeps, type. 



Mesatirhinus megarhinus, type. 



?Telmatherium cultridens. 

 Other mammals : 



Hyrachyus princeps (cursorial rhinoceros). 



Patriofelis ferox (catlike creodont). 



Isectolophus latidens (tapir). 



Uintatherium robustum (four-horned amblj-pod) . 



Notharctus crassus (large lemuroid). 



Pantolestes natans (aquatic insectivore) . 



Homacodon vagans (primitive artiodactyl) . 



LTintatherium mirabile (amblj'pod uintathere). 



Orohippus sylvaticus (primitive equine). 



Bridger C. — The lowest beds of the horizon Icnown 

 as Bridger C are exposed at the foot of Sage Creek 

 Mountain, along the southern slope of Henrys Fork 

 Table; also at the foot of Twin Buttes and along the 

 slopes north of Twin Buttes. They consist of 350 feet 

 of gray and greenish-gray tuffs, divided into a lower 

 and an upper half by the "Burnt Fork white layer" 

 and bounded above by the "Lone Tree white layer." 

 After careful analysis of the fauna of Bridger C, Mat- 

 thew concluded (1909.1, p. 304) that its marked dis- 

 tinction from the fauna of Bridger B was due to the 

 immigration of several new genera into the Bridger 

 Basin. Among these especially are the titanothere 

 genera Manteoceras, TelmatJieriurn, and MesatirJiinus, 

 which appear to be really newcomers and not in any 

 sense descendants of the lower Bridger genera Palaeo- 

 syops and Limnohyops. The two genera last named, 

 however, are represented in Bridger C by distinctly 

 new specific forms, much more progressive than those 

 in Bridger B. Thus Bridger C is characterized both 

 by marked evolutionary changes in mammals that pass 

 over from the lower levels and by the introduction of 

 a fauna that is more or less new. Of this new fauna 



