452 



TITANOTHERES OF ANCIENT "WYOMING, DAKOTA, AND NEBRASKA 



The large size of the first true molar (ectoloph 

 ap. 57 mm.) indicates a larger animal than 5. hracTiy- 

 cephdlus; it is of a size equaled in B. dispar (Nat. 

 Mus. 4290). The horn swellings are small knobs, 

 not much larger than those of very old individuals of 

 Manteoceras manteoceras. The horn swelling on each 

 side consists of a protuberance on the anterior tip 



A2 



Figure 384. — Development of jaws and teeth, stage 4 



Skull and teeth of female calf, Univ. Wyoming Mus. 4, referred to Bronlops iispar. 

 Skull and lower jaw, one-third natural size; Aj, upper teeth, one-half natural siz' 

 lower teeth, one-half natural size. 



of the frontals, which is embraced in a corresponding 

 excavation of the expanded posterior border of the 

 nasals. The free portions of the nasals are short 

 and rounded distally, with sharply decurved lateral 

 borders. The sutures in the region of the horn — that 

 is, the nasofrontal, lacrimal, and maxillary sutures — 

 conform to the plan exhibited in the National Museum 

 skull 4258 and in skulls of other young titanotheres. 



The upper jaw shows the permanent incisor i' (which is 

 exposed in the specimen but was possibly beneath the 

 gum in life) ; a tooth is just coming into place which is 

 apparently p' of the adult; three deciduous premolars 

 (dp^, dp', dp*) are in place. The lower jaw shows \2, (?) 

 pi, and dp2, dps, dp4. M' and mi are buried in the 

 jaws. Measurements of this specimen are as follows : 



Measurements of deciduous teeth 0/ Brontops dispar {Univ. 

 Wyoming Mus. 4) 



Upper jaw 



Millimeters 



P'-dp< 132 



Pi, ap. by tr 18X18 



Dp2, ap. by tr 29X25 



Dp3, ap. by tr 37X32 



DpS ap. by tr 44X33 



Dp*, tr. (across mesostyle) 40 



Permanent m', ectoloph, anteroposterior. 57 



Permanent m', ectoloph, height of meta- 



cone 45 + 



Nasals to middle of horn 75 



Nasals, free breadth (estimated) 55 



Pmx to condyles (rough estimate) 305 



Lower jaw 



Front edge of symphysis to angle 284 



Height condyle to angle 145 



P,-dp4 128 



Dpi, ap. by tr. (trigonid) 11X10 



Dp2, ap. by tr. (trigonid) 31X15 



Dp3, ap. by tr. (trigonid) 37X20 



Dp4, ap. by tr. (trigonid) 49X25 



Stage 5. — A more advanced stage is shown in 

 a young jaw (Carnegie Mus. 124; PI. XXIV, C) 

 referred provisionally to Brontops dispar. The 

 permanent incisors ii and 12 are just coming in, 

 while the deciduous incisors and canines have 

 probably been shed. The permanent canine lies 

 j ust below the surface. The tooth designated ? dpi 

 although associated with mUk teeth, appears to be 

 the permanent pi. The milk molars dpo-dp^ are 

 worn. Ml is just protruding. M2 lies buried in 

 the ascending ramus, below the coronocondylar 

 sinus. 



Stage 6. — A later ontogenetic stage is illustrated 

 in a remarkably complete skull and jaw in the 

 Carnegie Museum (No. 116), which were de- 

 scribed by Hatcher in 1901 (1901.1; figs. 385, 

 386). The specimen was found on Warbonnet 

 Creek, Sioux County, Nebr., near the base of 

 the Titanotlierium zone. The reference to Bron- 

 tops hrachycepJialus is provisional. 

 In the side and top views (fig. 385) it is seen 

 that the horns are formed by the overgrowth of 

 the frontals upon the nasals, as in the Eocene Man- 

 teoceras. The lacrimal is expanded, and its outer 

 ridge is continuous with the external ridge of the horn. 

 The parietals extend forward upon the frontals. The 

 interparietal is apparently distinct. The occiput is 

 shown in Figure 386. 



