EVOLUTION OF THE SKULL AND DENTITION OF OLIGOCENE TITANOTHERES 



561 



Comparative measurements of Brontotherium? rumelicum, in 



Ms, ap. by tr_ 

 M2, ap. by tr. 

 Pi-p, 



'94X43 



■ 75X42 



= 123 



B. leidyi, 

 Nat. Mus. 

 4249 (type) 



96X41 



68X40 



119 



102X48 



67X48 



113 



Menodus 



trigono- 



ceras, 



Am. Mus. 



1067 



108X45 



74X43 



123 



B. robus- 



tus, Yale 



Mus. 



12048 



(type) 



110X47 



77X46 



133 



"Type. 'Paratype. ■Hererred. 



These measurements offer no very decisive evidence, 

 but a direct comparison of the cast of the referred 

 lower jaw reveals a strong resemblance to the jaws of 

 Brontotherium. 



Comparative measurements of third inferior molar of 

 Brontotherium? rumelicum, in millimeters 



Materials. — Referring to the technical description of 

 Toula (Toula, 1892.1, p. 612) we note that the speci- 

 mens consist, first, of the type, a portion of a ramus 

 containing ms (fig. 463), and secondly of the paratype, 

 an isolated lower molar. This lower molar is cer- 

 tainly a second molar (m2) rather than a first molar 

 (mi) as identified by Toula — first, because this tooth is 

 less worn than mj; second, because it is larger than mi. 

 Both of these specimens were found at Kajali, north 

 of Burgas, eastern E,umelia, near the Black Sea, north- 



Of the highest importance and interest is 

 the question, How many branches of the ti- 

 tanotheres invaded Europe and Asia? There 

 is no doubt that this family was chiefly North 

 American in evolution, but the presence near 

 the Black Sea of the animal described by Toula 

 as Menodus rumelicus, of the previously de- 

 scribed BracJiydiastematherium, and of the 

 newly described Menodus ioJiemicus affords 

 positive proof that at least three branches of 

 the great family of titanotheres actually in- 

 vaded Asia and eastern Europe. The titano- 

 theres discovered in Mongolia by the Asiatic 

 expedition of 1922-23 are described in the ap- 

 pendix (pp. 913, 942). 



Geologic level. — It is a remarkable fact that the 

 geologic records in the present case as well as in that 

 of Brachydiastematherium conflict with those in 

 America. The BracJiydiastematherium is said to have 

 been found in beds of lower Eocene or Ypresian 

 [lower] age. The present type of M. rumelicus, on the 

 contrary, is recorded as of extreme upper Miocene age, 

 or as equivalent to Pikermi. Possibly M. rumelicus 

 represents a survivor of the titanotheres in western 

 Asia and eastern Europe after the period of their 

 extinction in North America; but this is rendered 

 improbable by the fact that the present type is in a 

 lower Oligocene stage of evolution. 



FiGUBB 464. — Lower jaws of Brontotherium? rumelicum and B. leidxji 

 A, Symphyseal region referred to B. rumelkum: B, lower jaw of £. leidyi. One-sixth natural size. 



west of Constantinople. Four years later Toula 

 (1896.1, p. 922) described a portion of a mandibular 

 symphysis which was found in the same locality 

 (figs. 463, 464). 



Affinities. — The resemblances of these specimens to 

 the Ancylopoda {Chalicotherium and Macrotherium) 

 were pointed out by Toula, who, however, finally con- 

 cluded by referring all these specimens to Menodus. 



We note the following marked differences from the 

 Chalicotheriidae: (1) Presence of a strong third lobe 

 on ms, which is absent in all chalicotheres; (2) a mas- 

 sive symphysis and chin, which is reduced and degen- 

 erate in all chalicotheres; (3) presence, so far as we can 



