BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 25, PP. 403-405 SEPTEMBER 15, 1914 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY

RECENT RESULTS IN THE PHYLOGENY OF THE TITANOTHERES 1

BY HENRY FAIRFIELD OSBORN

(Read before the Paleontological Society December SI, 1913)

Recent discoveries have modified the author’s earlier opinions as to the lines of descent of the titanotheres and still further changes are an­ ticipated with increase of knowledge of the connections between Upper Eocene, or Uinta, titanotheres and those of the Lower Oligocene, or White River. The main lines of division are indicated in the proportions of the limbs, whether cursorial, mediportal, or graviportal; the proportions of the skull, whether mesaticephalic, brachycephalic, or dolichocephalic; the development of fronto-nasal horns, whether accelerated or retarded; the molarization of the premolar teeth, whether accelerated or retarded; the presence or absence of incisor teeth; the abbreviate or elongate, the triangular or oval form of the fronto-nasal horns as developed in Oligo­ cene times. With these criteria the various phyla may readily be distinguished as follows: A. Wind River titanotheres, face more elongate than cranium: I. Lambdotheriinse, light-limbed, cursorial.. Genus, Lanibdotherium II. Eotitanopinse, medium-limbed, mediportal. Eotitanops B. Bridger and succeeding titanotheres, cranium longer than face: III. Palseosyopinae, short-limbed, brachyceph- Genus, Palwosyops, alic. Limnohyops IV. Telmatheriiniie, mesaticephalic to dolicho­ Telmatherium, cephalic. Sthenodectes V. Diplacodontinse, dolichocephalic, with ac­ Diplacodon celerated molarization of the premolars, imperfectly known. VI. Manteoceratinse, mesaticephalic to brachy­ Manteoceras, cephalic, accelerated development of the Protitanotherium horns, mediportal.

1 Manuscript received by the Secretary of the Geological Society June 15, 1914. (403)

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Eocetie 1 Lower Oliproce-ne 404 F gure r u ig F. N R O B S O . F . H 1. yoey f he t hee u ko t Dee r 1013 er, b ecem D to n know us eres th o n ita T e th of hyloyeny P — -- ’ S E R E H T O N A T I T E H T F O Y N E G O L Y I I’l PHYLA OF THE TITANOTHEEES 4 0 5

VII. Dolichorhinse, mesaticephalic to dolicho­ Doliohorhinus, cephalic, limbs, so far as known, ab­ Mesatirhmus, breviate. Sphenocwlus, Metarhinus, Bhadinorhinus VIII. Menodontinse, mesaticephalic to dolicho­ Menodus (= 27- cephalic, with abbreviate, triangular tanotherium), horns, with incisor teeth reduced or Alio its wanting, feet and limbs elongate. IX. Brontopime, brachycephalic, horns abbre­ Brontops (—iJfiff- viated, rounded or oval, incisors per­ aceratops), sistent. Diploclonus X. Megaceropime, mesaticephalic to extreme Megacerops brachycephalic, horns elongate, verti­ (=8ymborodon) cally placed, no incisor teeth. XI. Brontotheriinse, mesaticephalic to brachy­ Brontotherium cephalic, horns elongate, transversely flattened and divergent.

The free use of subfamily divisions to express the distinct phyletic series is similar to that which the author has adopted in the phylogeny of the rhinoceroses. More conservative usage would divide the titano- theres into four subfamilies only.

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