EVOLUTION OP THE SKULL AND TEETH OF EOCENE TITANOTHERES 



319 



Since all these six individuals from Huerfano B 

 agree closely in size with each other and with the type 

 of P.fontinalis, they establish Huerfano B and Bridger 

 A as the Palaeosyops fontinalis zone, distinguished by 

 true ancestors of Palaeosyops inferior in size to any 

 known members of this genus in Bridger B. 



Palaeosyops longirostris Earle 



Plate LVI; text figures 108, 268 



[For original description and type references see p. 172] 



Type locality and geologic horizon. — 

 Cottonwood Creek, Bridger Basin, Wyo; 

 Bridger formation, Palaeosyops paludosus- 

 Orohippus zone (Bridger B). 



Specific characters. — Pi-ma, 156 milli- 

 meters (estimated); p2-m3, 143; mi_3, 90; 

 P4 rather simple. Wide posterior extension 

 of the ramus of the jaw behind ms. Canine 

 large, semiprocumbent. Mandibular sym- 

 physis elongate. 



This little-known form appears to be 

 closely related to but somewhat smaller 

 than the typical P. paludosus. The type 

 specimen, the left ramus of a lower jaw 

 (fig. 268, A), was well described by Earle in 

 his memoir of 1892. No other known 

 material has been referred with certainty 

 to this species. 



Palaeosyops paludosus Leidy 



Plates LII, LVI, LVIII, LIX, LXII; text figures 



86, 88, 267 A, 268 B, 405, 407, 732 



[For original description and type references see p. 157] 



Type locality and geologic horizon. — 

 Bridger Basin, Wyo.; Palaeosyops paludo- 

 sus-Orohippus zone (Bridger B). Bridger 

 B 1, as represented by the base of the sec- 

 tion of Church Buttes, is apparently the 

 type geologic level. The Bridger B 2 

 specimen is from the lower portion of the 

 Grizzly Buttes deposition. 



Specific characters of type and of referred 

 specimens. — Of small size; pa-nis, 152 milli- 

 meters; p^-m^, 144; m2 (ap. by tr.), 33 by 

 20.5; second and third superior and inferior 

 premolars more primitive than in succeed- 

 ing stages ; p^ with a single external cone — 

 that is, no tritocone ; p^ with a rudimentary 

 tritocone; superior molars subquadrate and 

 premolars without mesostyles. No rudi- 

 ments of osseous horns. 



Joseph Leidy, over 50 years ago, aptly characterized 

 this animal specifically as "swamp or marsh loving" 

 ijpaludosus) because its teeth are manifestly adapted to 

 the softer kinds of herbage. 



By Leidy himself and by subsequent authors the 

 term "paludosus" was erroneously applied to the 

 more progressive species which are classified in this 

 monograph under P. major, P. leidyi, and P. roiustus. 



Materials. — Many of the specimens other than the 

 type which were referred to this species in the volumi- 

 nous literature belong on higher geologic levels, such 

 as those from upper Cottonwood Creek (Bridger B 

 4 and 5) and from Henrys Fork (Bridger C and D), 

 and consequently to higher stages of evolution. P. 

 paludosus in the restricted sense is represented by 

 Leidy's isolated type teeth in the National Museum 



FiGUEE 272. — Skull of Palaeosyops major 



One-fourth natural size. Am. Mus. 12182 (neotype skull). Cottonwood Creek, Bridger Basin, 

 Wyo.; Bridger formation, level B 3. Crushed downward but slightly reconstructed from Am. 

 Mus. 1516 (P. leidyi), especially in the infraorbital region. Ai, Side view; As, top view. 



(No. 762 in part), which are carefully distinguished 

 in Chapter III of this monograph. An upper dental 

 series probably preserved in the Philadelphia Acad- 

 emy collection was also referred by Leidy to P. palu- 

 dosus (Leidy, 1873.1, pi. 4, fig. 3) and may possibly 

 be conspecific with the type. In the same stage of 

 evolution apparently is the fine lower jaw (Am. Mus. 

 11680) from MillersvUle, Bridger Basin, level B, which 



