298 



TITANOTHEEES OP ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



The resemblances and contrasts between the three I proportional and numerical evolution explained on 

 chief genera included in these two subfamilies are in- j pages 251-262. 

 dicated in the following manner, on the principles of i 



Proportional and numerical characters oj titanotheres of the palaeosyopine group 



Telmatherium 



Skull and skeleton very robust; skuU de- 

 cidedly broad and massive; feet short. 



Fore feet short, more paraxonic, the fifth 

 digit larger. 



Skull rounded, occiput stout, sagittal 

 crest of medium length, forehead pro- 

 tuberant or convex. 



Jaws robust, chin prominent, angulate; 

 mandibular rami massive below grind- 

 ing teeth; coronoid at base very broad 

 and concave anteriorly. 



Premaxillary symphysis short and 

 rounded. 



Maxillary splint on side of malars; malar 

 section rounded. 



Incisors more transverse; canines sub- 

 lanceolate to round; premolars com- 

 pressed anteroposteriorly; molars broad 

 or quadrate, with strong, rounded para- 

 styles. 



Conules on superior molars more or less 

 persistent, rounded. 



Grinders persistently brachyodont. 



Last superior molar usually without hypo- 

 cone or second postero-internal cusp; 

 crown subtriangular, rounded. 



Ectolophs of superior premolars in some 

 specimens resembling those of molars 

 (that is, with mesostyles). 



Skull and skeleton more slender; skull 

 broad, brachycephalic, less massive; 

 feet narrow. 



Fore feet short, more mesaxonic, with the 

 fifth digit reduced. 



A more elevated occiput, higher and 

 thinner sagittal crest; forehead con- 

 cave, without protuberance. 



Jaws somewhat more slender, chin slop- 

 ing, rami less massive below grinders, 

 anterior face of coronoid less broadened. 



Premaxillary symphysis rounded. 



Maxillary splint extending from side to 

 beneath malars; malar section de- 

 pressed. 



Incisor series obliquely placed; canines 

 slightly more compressed and ridged; 

 molars with ridged parastyles and 

 ridged conules. 



Conules on superior molars persistent, 

 ridged or lophoid. 



Grinders persistently brachyodont. 



Last superior molar usually with a dis- 

 tinct hypocone; crown more quadrate. 



Skull and skeleton rather slender; skull 

 decidedly elongate, dolichocephalic. 



Fore feet long, more mesaxonic, the fifth 



digit elongate. 

 Occiput very high; sagittal crest elongate; 

 forehead plane, no protuberance. 



Jaws more slender; chin deep; symph3'sis 

 elongate. 



Premaxillary symphysis elongate. 



Maxillary splint elongate, extending be- 

 neath malars; malar section rectangular. 



Incisor series more parallel; canines high, 

 sublanceelate; premolars elongate; mo- 

 lars narrow, more sharply crested or hyp- 

 sodont, with feeble parastyles or none. 



Conules on superior molars disappearing 



early. 

 Grinders progressively hypsodont. 

 Last superior molar without hypocone; 



crown quadrate. 



SUBFAMILY PAIAEOSYOPINAE (STEINMANN AND DODEELEIN) 



The Palaeosyopinae consist of the Limnohyops and 

 Palaeosyops generic phyla. They were abundant 

 chiefly in lower and middle Bridger time, beginning 

 to decline in upper Bridger time. Limnohyops is sub- 

 brachycephalic to brachycephalic, mediportal; Palaeo- 

 syops is brachycephalic to hyperbrachycephalic, 

 graviportal. They were larger than tapirs, propor- 

 tions stout, becoming graviportal; feet of brachypodal 

 type; skuU broad, progressively brachycephalic, facial 

 region abbreviate, nasals tapering distally, nasofrontal 

 horns retarded in development; cranial region and 

 zygomata broadening; grinding teeth persistently 

 brachyodont; canines stout, subconical. 



They make their appearance at the base of the 

 Bridger or in Bridger A, in the species Palaeosyops 

 fontinalis, and the last member known is the species 

 Palaeosyops copei, of Bridger D or Washakie A. The 

 Palaeosyopinae thus formed the first titano there sub- 

 family to appear in the middle Eocene and also the 

 first, so far as known, to disappear geologically. 



The subfamily name Palaeosyopinae is taken from 

 the name of the classic genus Palaeosyops leidyi, the 

 first Eocene titanothere discovered. These titano- 

 theres are broad-headed, chiefly of lower and middle 

 Bridger age, reaching a climax and beginning to decline 

 in upper Bridger time. The cranial region of the skull 

 is longer than the facial region; the head is short and 

 broad (brachycephalic); the horns are relatively late 

 or retarded in development; the feet are short and 

 broad (Palaeosyops), or less broad (Limnohyops). 



The two phyla, Palaeosyops and Limnohyops, were 

 contemporaneous, their remains being found in the 

 same deposits. 



SEPARATION OF PAIAEOSYOPS AND IIMNOHYOPS GENEKIC PHYIA 



In the middle Eocene of the Bridger region in west- 

 ern Wyoming the animals known as Palaeosyops and 

 Limnohyops are the earliest to occur geologically — 

 namely, in Bridger A, B, and C. They were browsing 

 animals, with short-crowned teeth and broad heads, 

 which increase in breadth in the successive descendants 



