EVOLUTION OF THE SKULL AND TEETH OP EOCENE TITANOTHERES 

 Evolution of proportions of LimnoTiyops — Continued 



305 



" Estimated. 



The foregoing table brings out the following facts: 



1. The cranial increases in length and width are not 

 accompanied by proportional dental increases. 



2. Relatively large-skulled and extremely brachy- 

 cephalic animals (i. monoconus) occur in the lower 

 Bridger levels. 



3. There is no evidence of progressive monophyletic 

 change such as we see in Palaeosyops. (See p. 313.) 



Limnohyops laevidens (Cope) 



Plate LVII; text figures 96, 258, 259 

 [For original description and type references see p. 163] 



Type locality and geologic horizon. — The type speci- 

 men represents the smallest, most primitive, and 

 geologically earliest LimnoTiyops at present known. It 

 is somewhat doubtfully recorded from Bridger B 2(?), 

 as represented in the deposits of Cottonwood Creek, 

 Bridger Basin, Wyo. If from this level, it is slightly 

 more recent than the geologically early and most primi- 

 tive discovered stage of Palaesoyops, known as P. 

 paludosus, referred specimens of which have been 

 found in Bridger B 1 . 



Specific characters. — Inferior in all dimensions to 

 type of L. laticeps; p'-m', 141 millimeters; p^-m^ 

 129; p'-p*, 57; p^ rounded or transversely oval, with 

 tritocone rudimentary or absent. A large hypocone 

 on m'. 



Materials. — The type specimen of L. laevidens (Am. 

 Mus. 5104; see revision of the nomenclature, Chap. 

 Ill) is a part of an aged skull containing a well-worn 

 dental series, from which it is difficult to determine 

 positively the characters of this animal. The specific 

 name laevidens (from laevis, (Zens = imperfect tooth) 

 was assigned to this specimen by Cope in recognition 

 of the supposed absence of the tritocone on p^. It is 



probable that in the unworn condition this cusp was 

 present but very rudimentary. 



Cope's type of Palaeosyops laevidens 



Teeth. — The teeth of the type of P. laevidens (Am. 

 Mus. 5104), belonging to an aged animal, are especially 



Figure 258. — Anterior part of skull of Lim7iohyops laevidens 



One-fourtli natural size. Am. Mus. 5104 (type), reversed; Cottonwood Creeli, 



Bridger Basin; level Bridger B 3. Ai, Side view; A2, front view. 



interesting because they exhibit the influences of age 

 in rounding off the angles, wearing away the cusps, 

 and smoothing down the cingula. Professor Cope 

 was probably misled when he described this type as 

 lacking a tritocone on p'; we now recognize that the 



