EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



367 



the infraorbital foramen, as in M. petersoni; in skull 

 Am. Mus. 2353, on the other hand, in which the face 

 appears exceptionally short (a condition possibly 

 due in part to crushing), this bridge is abbreviated, 

 the foramen issuing directly in front of the malar- 

 lacrimal maxUlary bar. The maxillaries contribute 

 the anterior portion of this bar. The projecting 

 infraorbital shelf of M. petersoni is absent, being 

 replaced by a prominent, more or less sharply convex 



Figure 305. — Skulls of Manteoceras manteoceras and Palaeo- 



syops leidyi 

 Front view. One-fourth natural size. In Manteoceras (A) the horn region projects 



laterally above the facial concavity. In Falaeosyops {,B) the horn region does not 



so project and there is no facial concavity. 



longitudinal ridge, quite different from the more 

 rounded suborbital bar of Palaeosyops or the broad, 

 gentle convexity of T. cultridens and T. ultimum. 

 Immediately below the orbit the malars are flat, and 

 behind the orbit they are slightly concave; they give 

 off the prominent postorbital processes and then 

 gently arch outward with a convex exterior and a 

 concave interior surface. The malars thus present 

 two very striking differences from the Oligocene 

 type: first, they are much shallower below the orbit 

 and concave instead of convex externally; second, they 

 are relatively slender and constricted behind the 

 postorbital process. The zygomatic portion of the 

 squamosal exhibits a wide superior as well as a broad 



lateral expansion, foreshadowing the decided develop- 

 ment of this bone in the Oligocene titanotheres. 



Dentition in general. — The dentition as compared 

 with that of MesatirJiinus and DolicJiorhinus agrees in 

 the following characters: (1) The incisors are short- 



FiGUBE 306. — Skulls of Manteoceras manteoceras and' M. 

 washakiensis 



Occipital and front views. One-fourth natural size A, M. manleoceras, from speci- 

 mens in the American Museum, chiefly No, 1570, La Clede, Washakie Basin, 

 Wyo., Washakie A. Nasals and occiput restored from No. 1669 (type) , Washakie 

 Basin, Washakie A; canines and incisors from No. 1511, Biidger Basin, and No. 

 12678, Hemys Fork Hill, Bridger Basin, Bridger C 5. B, M. manteoceras, Am. 

 Mus. 1587, Henrys Fork, Bridger Basin, level unknown. C, M. wasfialiensis, 

 Am. Mus. 13165 (type), base of Haystack Mountain, east end, Washakie Basin, 

 Washakie A. • 



crowned and rounded rather than conical, and the 

 disparity of i' over i^ is less marked than in Telma- 

 therium; (2) the sublanceolate canines are broadly 

 obtuse at the base, taper rapidly at the summits, and 

 have faint anterior and posterior ridges; (3) the pre- 

 molars and molars are identical in general structure 



