SYSTEMATIC CLASSIFICATION OF THE TITANOTHERES 



245 



SUBFAMILY NAMES AND PHYLA PROPOSED BY STEIN- 

 MANN AND DODERIEIN (1890), EARLE (1892), AND RIGGS 

 (1912) 



Subfamily Falaeosyopinae Steinmann and Doderlein, 1890 



Original reference. — Elemente der Palaontologie, 

 p. 777, 1890 (Steinmann and Doderlein, 1890.1). 



Included genera. — The authors divide the Chali- 

 cotheriidae into three subfamihes — Falaeosyopinae, 

 Brontotheriinae, Chalicotheriinae. The Falaeosyo- 

 pinae include the genera Palaeosyops, "Limnohyus" 

 {Limnohyops) , Diplacodon. 



Present determination. — Falaeosyopinae Steinmann 

 and Doderlein, 1890, thus has priority over Falaeo- 

 syopinae Earle, 1892. 



Subfamily Falaeosyopinae Earle, 1892 



Cf. Falaeosyopinae Steinmann and Doderlein 



Original type reference. — Acad. Nat. Sci. Fhila- 

 delphia Jour., 2d ser., vol. 9, pp. 272 et seq., 1892 

 (Earle, 1892.1). 



Included genera. — Lamidotherium, Limnohyops, 

 Palaeosyops, Telmatherium, Haplacodon [Megacerops 

 angustigenis]. 



Present determination. — Earle gives a detailed and 

 accurate description of the subfamily characters 

 (pp. 274-276). The term is preoccupied by Falaeo- 

 syopinae Steinmann and Doderlein, 1890, and in its 

 content is preoccupied by Lambdotheriidae Cope, 

 1889. 



Subfamily Dolichorhinae Riggs, 1912 



Cf. Dolichorhininae 



Original reference. — Field Mus. Nat. Hist. Fub. 159, 

 Geol. ser., vol. 4, No. 2, p. 25, June, 1912 (Riggs, 

 1912.1). 



Included genera. — Middle Eocene titanotheres 

 having nasals elongate and deeply recessed laterally, 

 face shorter than cranium, an infraorbital process 

 more or less developed, and molars only moderately 

 expanded. 



This group is proposed in order to designate those 

 long-nosed titanotheres which evidently sprang from 

 a common stock and form a natural and homogeneous 

 group. It includes the genera MesatirJiinus, Meta- 

 rJiinus, Dolichorhinus, and RhadinorJiinus. 



DIVISION OF THE OLIGOCENE TITANOTHERES INTO FOUR 

 CONTEMPORARY PHYLA, OSBORN (1902) 



Original reference. — Am. Mus. Nat. Hist. Bull., vol. 

 16, pp. 91-109, February 18, 1902 (Osborn, 1902.208). 

 Included genera. — Osborn writes: 



The Oligocene titanotheres consisted of at least four contem- 

 porary phyla, to which the prior generic names Titanotherium, 

 Megacerops, Symborodon, and Brontotherium may be applied. 



They represent an adaptive radiation for different local hab- 

 itat, different modes of feeding, fighting, locomotion, etc., which 

 took origin, in part at least, in the middle or upper Eocene. 

 Europe and Asia also may have shared in this radiation, since 

 titanotheres are now definitely known in the Balkan region. 



The main phyletic characters are analogous to those recently 

 (Osborn, 1900, p. 231) determined among rhinoceroses; the 

 great antiquity of the lines leading to the existing species of 

 rhinoceroses necessitated the revival of a number of discarded 

 generic names to distinguish them. Similarly the separateness 

 of four of the titanothere phyla, throughout the Ohgocene and 

 possibly from the Eocene, renders it desirable to revive certain 

 generic names which in my first review I considered undefinable. 



Radiation involved three main sets of characters, two of 

 which were correlated: 



First, doliohocephaly and brachycephaly, associated with 

 numerous changes in the skull and teeth and, in at least two 

 phyla, with longer and shorter limbs. 



Second, four distinct types in the shape and position of the 

 horns, correlated with the structures of the nasals and frontals 

 and indicative of different modes of combat among the males. 

 (See fig. 209.) 



Third, canines of different form; and, finally, the presence 

 of one or two pairs of functional incisor teeth, or the total 

 degeneration of these teeth. 



Titanotherium Leidy applies to long-limbed animals with 

 long skulls, persistently long and broad nasals, short triangu- 



MegaceropSy Upper Beds. 



Diplodonus, Upper Beds. 



Syiiiborodoti. Upper Beds, 



.Brontotkcriuv!, Upper Beds, 



Figure 209. — Characteristic basal sections of horns of 

 Oligocene titanotheres 



l.ar horns placed slightly in front of the eyes, vestigial incisors, 

 ^:?, large canine teeth. Known from the base to the summit of 

 the Oligocene. 



Megacerops Leidy applies to titanotheres with broad skulls, 

 nasals progressively shortening, short horns rounded or oval in 

 section, shifting anteriorly, one or two pairs of incisor teeth, 

 ^, medium-sized canine teeth. Known from the base to the 

 summit of the Oligocene. 



Probably related to this are the subgenera of the types named 

 Allops and Diploclonus by Marsh, differing from the above in 

 horn characters. Known chiefly from the upper beds. 



Symborodon Cope includes titanotheres with skulls of vary- 

 ing proportion, nasals slender and progressively shortening, 

 horns elongate and peculiar in being placed above the eye 

 instead of shifting forward, incisors vestigial, |^, canines small, 

 appro.ximated. Known only from the middle and upper beds. 



Brontotherium Marsh embraces the largest titanotheres, with 

 very broad zygomatic arches, nasals shortening while horns 

 elongate and shift forward; incisors persistent, f in the males, 

 canines stout and obtuse. 



Representatives of Titanotherium and Megacerops can now 

 be continuously traced from the base to the summit of the 

 Oligocene. Primitive species of Brontotherium also appear at 



