562 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



judge by alveoli, of large canine teeth, which are re- 

 duced in all chalicotheres; (4) absence of the meta- 

 stylid, in contrast with the presence of the metastylid or 

 reduplication of the metaconid in all chalicotheres. 



Thus in spite of the authority of Von Zittel, who 

 also suggested reference of the types to the Chali- 

 cotheriidae, the anatomical evidence is absolutely 

 against the affinity to the Ancylopoda. On the other 

 hand, comparison of casts of three specimens kindly 

 presented to the American Museum by the late 

 Professor Toula shows a close resemblance to the large 

 Oligocene titanotheres in the structure both of the 

 teeth and of the jaw. The chief or distinctive char- 

 acters are as follows: 



Symphysis massive, canines probably large, four 

 lower premolar teeth, lower molars without internal 

 or external cingula, hypoconulid ms without strong 

 internal crest. 



Apparently this type is very similar to Brontotherium 

 in its measurements and in the structure of the jaw so 

 far as preserved but especially in the structure of the 

 grinding teeth. The entire absence of internal and 

 external cingula on the grinding teeth forbids reference 

 to Menodus and relates the animal certainly to 

 Brontotherium, in which the cingula are reduced. The 

 massive symphysis of the lower jaw and the reduced 

 crest of the hypoconulid on ma are, it is true, features 

 which suggest a member of the Menodontinae; but on 

 the whole the prevailing characters relate this animal 

 certainly to a branch of the Brontotherium phylum. 



Brontotherium hypoceras (Cope) 



{Symborodon hypoceras Cone, 1874; " Brontotherium hypoceras " 

 Osborn, 1902) 



Plates CLXVI, CLXX, CLXXXIII; text figures 174, 399, 457, 



458, 461 



[For original description and type references see p. 216] 



Geologic horizon. — Middle Titanotherium zone 

 (Chadron B) ; possibly also in lower beds of the upper 

 zone (Chadron C). 



Specific characters. — Skull larger than B. leidyi 

 (premaxillaries to condyles 715 mm., estimated), free 

 nasals shorter (74 mm.). Horns placed anteriorly, 

 oval from base to summit, outside length 140 milli- 

 meters; buccal processes prominent. M'-m' 305 milli- 

 meters (Nat. Mus. 4273) — that is, somewhat longer 

 than in B. leidyi. A single superior incisor in adults (?). 



The specific name apparently refers to the erroneous 

 opinion of Cope that there was a second pair of horns, 

 consisting of low protuberances, behind and on a lower 

 level than the first pair. 



Materials. — The materials consist of the type and 

 of two imperfect skull specimens in the National Muse- 

 um. Cope's imperfect type of this species (Am. Mus. 

 6361) consists principally of a horn tip, the bridge 

 over the infraorbital foramen, and parts of a zygoma, 

 which fortunately offer characters of diagnostic value. 



The type horn apparently belonged to a young adult or 

 female; it was taken to Washington and closely 

 compared with two relatively complete specimens in 

 the National Museum, with the gratifying result that 

 specific identity was established. These two National 

 Museum skulls are from the upper levels of the lower 

 Titanotherium zone, or the lower and middle levels of 

 the middle zone, and are distinguished by short, 

 transversely oval horns, similar in section to those of 

 B. gigas, but about only one-third as long and as 

 massive. 



The first skull (Nat. Mus. 4702, skull k') was recorded 

 from the lower beds of upper level C, but Mr. Hatcher 

 regards the record as doubtful. This skull is a B. 

 hypoceras in its horn and nasal development, but it has 

 the dental size and development of B. gigas (see table 

 above). It is therefore somewhat problematic. Un- 

 fortunately it lacks the canines, so we can not deter- 

 mine the sex positively. The very marked develop- 

 ment of the tetartocones on the premolars indicates an 

 affinity to B. gigas; it also proves that this is a suc- 

 cessor to B. leidyi or of more recent geologic age. In 

 p* the tetartocone is fully as large as the deuterocone 

 and entirely separate; the crowns of the premolars are 

 exceptionally smooth, rounded, devoid of cingulum, 

 with obtuse cusps. The molars are also devoid of 

 cingulum. In m^ the hypocone is a prominent 

 cingule. The nasals are thin and resemble those in 

 B. gigas. The horns are very small and have the 

 characteristic oval B. gigas section from base to sum- 

 mit; they are placed remarkably far forward. In 

 superior view the skull resembles that of B. leidyi on a 

 larger scale. The top of the cranium narrows grad- 

 ually, with the occipital pillars apparently slender 

 (although this part is largely restored), the occiput 

 being deeply indented; the zygomata have flattened 

 posterior expansions which recall in contour those of 

 B. gigas, although less robust. 



The second, the neotype skull (Nat. Mus. 4273, 

 skull 1) is correctly recorded from the middle Ti- 

 tanotherium zone, level Chadron B 2. The skull (con- 

 sisting of only the anterior portion) is small, although 

 it belongs to a very old animal in the tenth stage of 

 growth. It corresponds to the preceding skull, but 

 the horns are longer and placed equally far forward; 

 as shown in the section (fig. 461, C) there is a low 

 connecting ridge. 



Dentition. — In the neotype skull (Nat. Mus. 4273) 

 the dental measurements are rather close to those of 

 B. leidyi, save that the premolar series is longer, but 

 the "free nasals" are much shorter and the horns 

 longer. Extremely valuable evidence is afforded 

 by the short, obtuse canines with strong posterior 

 cingula, which resemble those of B. gigas on a small 

 scale. In B. leidyi a reduced upper median incisor 

 was observed; but in this specimen no trace of the 

 upper median incisor is found, there being only one 

 pair of well-developed lateral incisors. The loss of 



