SYSTEMATIC CLASSIFICATION OF THE TITANOTHERES 



247 



Type and geologic horizon. — "The terminal portion 

 of the lower jaw of a huge mammal " (Am. Mus. 7387), 

 from the Miocene of Oregon. 



Present determination. — The genus and species be- 

 long in the family Entelodontidae (Peterson, 1909.1, 

 p. 63). 



SECTION 2. CLASSIFICATION OF THE TITANOTHERES 

 ADOPTED IN THIS MONOGRAPH 



SYNOPSIS OF THE CLASSIFICATION 



The natural classification or ancestral tree of the 

 titanotheres is based on the characters of the skull 

 and teeth, as set forth in Chapters V and VI, com- 

 bined with those of the limbs and feet, as set forth in ' 

 Chapter VII. The full definitions of the family and 

 of the 12 subfamilies into which the titanotheres are 

 now divided are presented in Chapters V and VI, of 

 which the following classification is a synopsis. It 

 should be compared with the phylogenetic tree given 

 m Chapter X (p. 769). Each of the chief phyla has 

 H subfamily name. 



A. Wind River titanotheres, face longer than cranium: 



I. Lambdotheriinae, light-limbed, cursorial: 

 Larnhdoiherium. 

 II. Eotitanopinae ( = ?Palaeosyopinae), medium- 

 limbed, mediportal: 

 Eoiitano-ps. 



B. Bridger and succeeding titanotheres, cranium longer than 



face: 



III. Palaeosyopinae ( = ?Eotitanopinae), short-limbed, 



brachycephalic: 



Palaeosyops, Limnohyops. 



IV. Telmatheriinae, mesatioephalic to dolichocephalic: 



Telmatherium, Sthenodectes. 

 V. Manteoceratinae ( = Brontopinae), mesaticephalic to 

 brachycephalic, accelerated development of the 

 horns, mediportal: 



Manteoceras, Protitanoiherium, Brachydiasie- 

 ntatherium. 

 VI. Dolichorhininae, mesaticephalic to dolichocephalic; 

 limbs, so far as known, abbreviate; facial region 

 downturned: 



Eomeiarhinus, Dolichorhinus, Mesatirhinus, 

 Sphenocoelus, Metarhinus. 

 VII. Rhadinorhininae ( = ?Megaceropinae), mesatice- 

 phalic, facial region cyptocephalic, upturned: 

 Rhadinorhinus. 

 VIII. Diplacodontinae ( = ?Menodontinae, =7Bronto- 

 theriinae), dolichocephalic, with accelerated 

 molarization of the premolars, imperfectly 

 known: 



Diplacodon, Eotitanoiherium. 

 IX. Brontopinae (= Manteoceratinae), brachyce- 



phalic, horns abbreviated, rounded or oval, 

 incisors persistent; premolars retarded: 



Teleodus, Brontops { = Megacerops), Diplo- 

 clonus. 

 X. Menodontinae ( = ?Diplacodontinae), mesatice- 

 phalic to dolichocephalic, with abbreviate, tri- 

 angular horns, with incisor teeth reduced or 

 wanting, feet and limbs elongate, premolars 

 accelerated: 



Menodus {= Titanotherium) , Allops. 



B. Bridger and succeeding titanotheres — Continued. 



XI. Megaceropinae ( = ?Rhadinorhininae), mesatice- 

 phalic to extreme brachycephalic, horns elon- 

 gate, vertically placed, no incisor teeth: 

 Megacerops {=^ Symhorodon) . 

 XII. Brontotheriinae ( = ?Diplacodontinae), mesatice- 

 phalic to brachycephalic, horns elongate, trans- 

 versely flattened and divergent, premolars 

 accelerated: 

 Bronlotherium. 



Suggestions as to resemblance or the affinity between 

 subfamilies are given above in parentheses, and the 

 families are arranged according to the general geologic 

 sequence. One of these suggestions of ancestral 

 affinity is now apparently well established, namely, 

 that the Manteoceratinae are ancestors of the Bron- 

 topinae. 



I. TITANOTHERES OF LOWER EOCENE TIME 



(Face elongate) 

 Group I. Hornless: 



1. Subfamily Lambdotheriinae Osborn. "Lamb- 



dotheres." (Lower Eocene titanotheres. 

 Long-headed, very small; body and limbs 

 slender and cursorial; face longer than cra- 

 nium, slender.) Pages 



Genus Lambdolherium Cope 168,279,690 



Species priscum Osborn 194, 286, 590 



primaevum Loomis 178, 283, 590 



popoagicum Cope 168, 281, 590 



progressum Osborn 194, 286, 590 



magnum Osborn 199,288,590 



2. Subfamily Eotitanopinae (— ?Palaeosyopinae) 



Osborn. " Eotitanopines. " (Lower Eocene 

 titanotheres of intermediate size. Head of 

 medium length; body and limbs less slender 

 and cursorial than in the lambdotheres; gait 

 submediportal; face longer than cranium.) 



Genus Eoiitanops Osborn 179, 289, 591 



Species gregoryi Osborn 192, 291, 593 



brownianus (Cope) 169,292 



borealis (Cope) 168,292,593 



princeps Osborn 193,295,593 



major Osborn 193, 296, 597 



minimus Osborn 199,296 



II. TITANOTHERES OF MIDDLE AND UPPER EOCENE TIME 

 (Face abbreviate) 



Group II. Retarded horn rudiments: 



3. Subfamily Palaeosyopinae (=? Eotitanopinae) 



Steinmann and Doderlein. "Palaeosyo- 

 pines." (Titanotheres larger than tapirs. 

 Broad-headed, skull and limb proportions be- 

 coming stout; skull broad; zygomata progres- 

 sively brachycephalic; grinders small; nasals 

 tapering distaUy; face shorter than cranium; 

 feet abbreviate, brachypodal; gait gravi- 

 portal.) Pages 



Genus Limnohyops Marsh (mesaticephalic 



to brachycephalic) 170,303,612 



Species prisons Osborn 180, 306 



laevidens (Cope) 163,305 



matthewi Osborn 180, 308 



monoconus Osborn 180, 309, 614 



laticeps Marsh 160, 311, 618 



