312 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



forming a sharply convex ridge below the orbits, with 

 a narrow V-shaped union with the maxillaries anteri- 

 orly ; (7) in lateral view the nasals are slightly deciu-ved 

 anteroposteriorly; (8) the infraorbital foramen is above 

 the third and fourth premolars, or about 34 milli- 

 meters below and anterior to the orbit. 



Dentition of the type. — The premolars of the type of 

 L. laticeps are much more progressive than those of 

 the types of L. laevidens and L. priscus. The range 

 of progression is parallel with that of P. leidyi in the 

 following respects: (1) A larger tritocone is developed 

 on p^; (2) a distinct mesostyle is observed in the 

 ectoloph of p*; (3) the protoconule of p'* is larger. 

 Comparison of these teeth with Leidy's superior pre- 

 molar and molar types of P. paludosus shows that the 

 ectoloph of p^ is identical in measurement in the two 

 specimens and that the measurements and characters 

 of m^ are very similar except that in the type of L. 

 laticeps the anterior cingulum is somewhat more 

 accented. 



In the type of L. laticeps p^-m^ measures a few 

 millimeters less than in Am. Mus. 2361. The inner 

 side of the crown of p^ (ap. 1 1 mm.^^) is preserved, show- 

 ing a postero-internal cingulum; p^ is a transversely 

 oval tooth like that of P. laevidens; p^ (ap. 14 mm., 

 tr. 19) is more progressive than in L. priscus in its 

 slightly better developed tritocone, more sharply 

 ribbed protocone, stronger internal cingula; in p* 

 (ap. 17 mm., tr. 24) we observe the slightly more 

 distinct development of the conule above mentioned 

 and the presence of a mesostyle on the tooth of the 

 right side, which, however, is wanting in that of the 

 left. 



The molar series measures 90 millimeters in length, 

 and the anteroposterior by transverse dimensions of 

 the teeth are, m' 24 by 26 millimeters, m^ 31 by 35, 

 m^ 33 by 38, the teeth thus being broader than long; 

 the slopes of the cusps are vertically striated but less 

 strongly so than in Palaeosyops; both protoconules 

 and metaconules are present, small, of transversely 

 lophoid shape; in m^, however, the protoconule is 

 more distinct, the metaconule is vestigial, and the 

 cingulum rises into a distinct cingular hypocone (see 

 fig. 265); the vertical ridges of the ectoloph are 

 slightly fainter than in Leidy's cotype of P. jmludosus, 

 and the external crescents are slightly more open. 



Jaw oj the type. — The posterior portion of the jaw 

 as preserved shows that the angle descends almost 

 vertically below the condyle and does not extend 

 backward so far as in Palaeosyops. The lower border 

 of the angle is 157 millimeters below the condyle. 

 The coronoid is stout, relatively low and broad. 



23 The anteroposterior measurements given here and elsewhere are talien across 

 the middle of the crown. 



Palaeosyops Leidy 



Plates XVI, XXVII, XXVIII, XLIV, L, LIII, LV, LVI 

 LVIII-LXII; text figures 27, 28, 33, 88, 88, 89, 97, 108, 118- 

 120, 210, 214-220, 227, 254r-257, 266-288, 305, 405, 407, 482- 

 485, 508-516, 519-523, 528, 533-537, 539-550, 552, 559, 571, 

 645, 661, 685, 686, 703, 711, 713, 714, 716, 718, 721, 724, 727, 

 732, 733, 737-742, 745, 760 



[For original description and type reference see p. 157. For skeletal character 

 see p. 619] 



Type locality and geologic horizon. — Bridger Basin, 

 Wyo., Bridger formation, levels B, C, and D; Wash- 

 akie Basin, Wyo., Uintatherium-Manteoceras-Mesati- 

 rhinus zone (Washakie A). 



Specific characters. — Brachycephalic. Grinding 

 teeth persistently brachyodont; metaconules on the 

 molars persistent or absent; third superior molar with- 

 out hypocone. Skull and skeleton robust; feet broad; 

 manus with well-developed fifth digit; lunar resting 

 subequally on magnum and unciform. Four sacral 

 vertebrae. 



Geographic and geologic distribution. — This type 

 genus of the family Palaeosyopinae embraces a re- 

 markable series of stages of evolution of animals, which 

 are subdivided into eight species, found in ascending 

 geologic succession — namely, P. fontinalis, P. longiros- 

 trisf, P. paludosus, P. major, P. grangeri, P. leidyi, 

 P. roiustus, and P. copei. The members of the phylum 

 belong chiefly to the Bridger formation and increase 

 steadily in size from its base to its summit, or from 

 level B to D. P. grangeri and P. copei are not in- 

 cluded in the direct line. 



The specimens listed below were collected from the 

 Bridger formation at the levels indicated. 



13032, B 1. 

 10276, B 1 or B 2. 

 12182, B 3. 

 13116, B 2. 

 12185, C 3. 

 10009, C or D. 

 12196, C 2. 

 1544, C 4. 



11678, D 4. 

 5106, D (?). 

 10282, D (?). 

 11683, D 3. 

 12189, C 1. 

 11708, D 3. 

 11692, B 2. 

 11680, B 1. 



12181, B 3. 

 12165, B 2. 

 12183, B 3. 

 Type of P. r, 



2(?). 

 12200, C 4. 

 12188, C 5. 

 12205 a, D 1. 



Comparatively few specimens of Palaeosyops have 

 been found in the more easterly Washakie Basin, only 

 80 kilometers (50 miles) distant. This fact implies a 

 difference of living conditions, because the deposits of 

 the Washakie Basin are much less rich in fossils and 

 because the greater part of the fossiliferous "Washa- 

 kie" exposures are of more recent age than the Bridger. 

 Only the lower "Washakie" (horizon A) was syn- 

 chronous with the summit of the fossiliferous Bridger 

 (horizon D). 



The evidence afforded by our present knowledge in- 

 dicates that the quadrupeds now known as Palaeosyops 

 disappeared from this region or died out during or 

 soon after the deposition of Bridger D. Palaeosyops 



