382 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



TRANSITIONAL TITANOTHERES IN THE EOCENE OF EUROPE 



Brachydiastematherium Biickh and Maty 



Plate LXX; text figures 100, 315 

 [For original description and type references see p. 166] 



Geologic Jiorizon. — Recorded as lower Eocene, but 

 more probably middle Eocene (Abel), upper Eocene 

 (Osborn), or even lower Oligocene (Stehlin). 



Generic and specific cliaracters. — Brachycephalic. 

 Size large, about that of Protitanoiherium superium. 

 Dentition: ly, Cx, P4, M^. Lower incisors large) 

 heavily cingulate posteriorly, is larger than 12; post- 

 canine diastema very short; canines stout, with short, 

 heavily cingulate crowns; pi compressed, P2-P4 pro- 

 gressive, submolarif orm ; premolar entoconids rela- 

 tively well developed. 



Brachydiastematherium transilvanicum Bockh and Maty 



Materials. — The type species, B. transilvanicum, horn 

 Andrashaza, in Transylvania, Hungary, is represented 

 by a fragmentary lower jaw. As shown by every 

 detail of the dentition this animal was unquestionably 

 a titanothere, much resembling Protitanotherium, and 

 not, as its describers supposed, a relative of Palaeo- 

 therium. 



Geologic age. — The age was originally recorded as 

 lower Eocene, but it is probably upper Eocene. The 

 question of the geologic age of this specimen is one of 

 the most important in the chronology of the titano- 

 theres. Pavay, its discoverer, as well as Bockh, its 

 describer, and A. Koch, who studied the strata in 

 which the type was found, assigned a lower Eocene 

 age to the species, and their opinion was accepted by 

 Dep^ret, who placed the genus among the upper 

 Ypr^sien fauna, which is correlated by Osborn with 

 the lower part of the middle Eocene Bridger of North 

 America (Bridger B), which contains the relatively 

 primitive Palaeosyops pdludosus. 



This animal was found in the same beds as Prohyra- 

 codon orientale Koch. In his monograph "Die Sauge- 

 thiere des schweizerischen Eocans" Stehlin (1903.1, p. 

 125, note) remarks: " Ich hege indess einen starken Ver- 

 dacht, dieser Prohyracodon mochte, wie Koch selbst 

 friiher annahm, oligocanen und nicht mitteleocanen 

 Alters sein." Schlosser (1901.1, p. 27) points out 

 that Prohyracodon is not, as Koch had believed, a 

 forerunner of Hyracodon but is closely related to the 

 aceratheres (hornless rhinoceroses). Abel (1910.1, 

 p. 24) appears to be doubtful as to the geologic age of 

 Prohyracodon but considers it the most primitive of 

 the European rhinoceroses, more primitive than 

 Meninatherium, which is Aquitanian. From Abel's 

 figure of Prohyracodon Matthew (letter, 1914) infers 

 that it is of lower Oligocene or at most of upper Eocene 

 age. It is closely allied, as Schlosser and Abel state, 

 to the earlier Oligocene aceratheres, and it is much 

 more progressive than Hyrachyus or Amynodon. 

 Brachydiastematherium should therefore be considered 

 of lower Oligocene or upper Eocene age. 



Characters. — Every detail of the dentition shows 

 that, as compared with the American titanotheres, B. 

 transilvanicum is in an upper Eocene stage, closely simi- 

 lar to that of animals found in horizon C of the Uinta 

 Basin. The indications are that titanotheres migrated 

 from some northern center at about the same time 

 into eastern Europe and into North America. 



Brachydiastematherium agrees with the upper Eocene 

 Protitanotherium superbum in general appearance and 

 in the dimensions of pi to mi. The canines have a 

 peculiar very heavy curved internal posterior cin- 

 gulum ridge, and the crown seems shorter and more 

 recurved than in P. superbum. All the premolars 

 appear to be in a slightly higher stage of evolution, 

 and the pronounced external cingula are horizontal 

 rather than festooned. The postcanine diastema is 

 much shorter, an indication of a higher specialization. 



From P. emarginatum this species differs not only in 

 the more advanced evolution stage of the premolars 

 and shape of the canine but apparently also in the fact 

 that is is the largest of the series, if Bockh and Maty's 

 identification of this tooth as is is correct. The in- 

 cisors are also larger and more heavily cingulate 

 posteriorly. 



Brachydiastematherium differs from Telmaiherium 

 altidens especially in the obtuse shape of the canines 

 and in the much more progressive ■pi-p4. The large 

 size of the heavily cingulate incisors suggests, however, 

 the possibility that the genus under consideration may 

 rather be an ofi^shoot of the Telmatherium than of the 

 Manteoceras-Protitanotherium series. From Stheno- 

 dectes incisivus, which it resembles in having three very 

 large incisors on each side of the jaw, Brachydiaste- 

 matherium differs in the much more progressive 

 evolution stage of the inferior premolars, p2-p4- 

 Derivation from Sthenodectes or from a nearly related 

 form is suggested by the general appearance of the 

 incisors, canines, and grinding teeth. 



The incisors of B. transilvanicum, with their broad 

 i posterior cingula, parallel those of the Brontotherium 

 type among the American Oligocene phyla. 



Brachydiastematherium is completely transitional 

 between the Eocene and Oligocene titanotheres, in 

 so far as it retains six large lower incisors of Eocene 

 type in company with very progressive lower pre- 

 molars of Oligocene type. 



The measurements (estimated from the original 

 illustrations) in comparison with those of the nearest 

 American titanotheres show that the incisors, canines, 

 and p4 are all very large, the diastema very short, 

 the grinders broad. 



On the whole, the evidence indicates that Brachy- 

 diastematherium represents a distinct European phy- 

 lum, which closely paralleled certain upper Eocene 

 American titanotheres in many respects but was 

 distinguished by the combination of three large lower 

 incisors; heavy, blunt canines; very short diastema; 



