258 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



cephaly are among the dominating tendencies affecting 

 the skull and grinding teeth of titanotheres, but 

 that they are not invariably correlated with similar 

 abbreviation or elongation iu the trunk and limbs. 



The principle of correlation, however, was found 

 to explain a vast number of dry detailed facts concern- 

 ing all parts of the skulls of titanotheres, including the 

 teeth, which had been recorded by Cope, Marsh, Earle, 

 Osborn, and others without any appreciation of their 

 morphologic significance. 



In brief, the progressive doUchocephaly or brachy- 

 cephaly of the skull is found to dominate the shape 

 of every bone in the skull but more particularly that 

 of the nasals, horns, zygomatic arches, and palate, 

 as well as the confluence or separation of the foramina 



Manteoceras 



J)oiic?>orfiinus 



Figure 216. — Cranial proportions in man (A) and 

 in the titanotheres (B) 



Viewed from above. Used in reference to man the words brachyce- 

 phalic, mesaticephalic, and dolichocephalic denote, respectively, 

 brachycranial, mesaticranial, and dolichocranial. In other words, 

 they describe the proportions of the cranial cavity. Used in refer- 

 ence to the titanotheres the same words describe the relative length 

 and breadth of the entire skull. 



in the base and sides of the skull, the form of the 

 occiput and of the mastoid, and the relations of other 

 bones around the auditory meatus, the shape of the 

 premaxillary and mandibular symphyses, the dias- 

 temata between and behind the teeth, the number 

 and shape of the teeth, the shape, number, and rela- 

 tions of the cusps of the teeth, and even, it would 

 appear, the cingulum around the grinding teeth. 



The three skulls of middle and upper Eocene 

 titanotheres shown in Figure 216 also illustrate 

 admirably the extremes of brachycephaly and doUcho- 

 cephaly and the intermediate condition of mesa- 

 ticephaly. 



The skulls are those of the species Palaeosyops 

 major, with its extremely broad head, of the mod- 

 erately broad-headed Manteoceras manteoceras, and of 

 the extremely long and narrow-headed DoKcJiorMnus 

 Jiyognathus. 



The cranium of these titanotheres varies in width 

 like the skulls of man (fig. 216) and the rhinoceros, 

 and the excessive width is contributed chiefly by the 

 great expansion of the zygomata. The skull of Doli- 

 chorhinus as a whole, however, is far more elongate than 

 that of Palaeosyops. We find also very pronounced 

 differences of proportion in every bone and every 



Aa 



Figure 217. — -Natural and artificial brachycephaly and doUcho- 

 cephaly. After Osborn, Science, 1908, pp. 750, 751 



A, Palaeosyops, extreme brachycephalic type, superior view; Aa, Palaeosyops, arti- 

 ficial dolichocephaly produced by stretching A to length of C; B, Mesatirhinus, 

 primitive dolichocephaly, palatal view; Ba, Mesatirhinus, artificial dolicho- 

 cephaly, palatal view, produced by stretching B to length of C ; C, Dolkhorhinus, 

 progressive dolichocephaly, superior view; C, BolichoThinus, progressive dolicho- 

 cephaly, palatal view. 



tooth when we compare Palaeosyops and DolichorMnus 

 minutely. The table on page 259 presents some of 

 the extremes of structure observed especially in the 

 titanotheres, in which the most careful comparison of 

 dolichocephalic and brachycephalic skulls has been 

 made. 



When we compare a long-skulled with a short- 

 skulled titanothere the skull at first appears to be 



