146 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



same genus as the type of B. ingens, a skull that 

 certainly belongs to another genus (Menodus). In 

 consequence of this initial confusion he erected a new 

 genus (Titanops) for skulls that should have been 

 referred to Brontotherium. Many of his conceptions 

 of the interrelations of the genera and species proposed 

 by him were erroneous. Although recognizing the 

 fact that the genera Brontops, Allops, and Teleodus 

 were all allied to " BrontotTierium" — that is, as repre- 

 sented by the skull of "BrontotTierium [Menodus] 

 ingens" — he nevertheless thought thsLt Diplodonus was 

 related to Titanops (the true BrontotTierium), and he 

 referred to Menops (a near ally of his "BrontotTierium'' 

 ingens) a well-preserved skull that is now known to 

 belong to BrontotTierium proper. In fact, in common 

 with Cope and others. Marsh apparently faUed to 

 recognize the comparatively wide phyletic gap between 

 the true BrontotTierium (his Titanops) and Cope's 

 Symborodon on the one hand and the supposed genera 

 Brontops, Allops, Menops, and Menodus (his "Bronto- 

 tTierium ingens") on the other. Consequently his 

 generic definitions are unsatisfactory, and he was 

 certainly not overconservative in proposing new 

 generic and specific terms. 



SUMMARY OF COPE'S CONTRIBUTIONS 



The next year (1874) after publishing his prelimi- 

 nary descriptions of the several species of Symborodon 

 and allied genera Cope (1874.2) gave full descriptions 

 of these forms in his "Report on the vertebrate pale- 

 ontology of Colorado," which was accompanied by 

 eight lithographic plates. He presented a careful 

 review of the general morphology of the skull, includ- 

 ing the brain case and cranial antra, which was fol- 

 lowed by a review of the work of preceding authors and 

 by a tabular analysis and detailed description of the 

 species of Symborodon. He recorded many interesting 

 facts, such as the similarity of the dentition of Sym- 

 borodon to that of Palaeosyops and of CTialicotTierium 

 and the mingling of proboscidian and rhinoceros 

 analogies in the limbs. He considered the indications 

 that Symborodon possessed a short proboscis. In his 

 tabular analysis of species he indicated the differences 

 in the shape of the horns and noted that in S. trigono- 

 ceras and S. Tiypoceras the upper premolars have a 

 strong internal basal cingulum, whereas in S. bucco 

 and S. altirostris the premolars are "without inner 

 basal cingulum." 



Cope, like Marsh, failed to distinguish the sexes as 

 well as the separate groups or phyla of titanotheres. 

 His "S." trigonoceras , for example, is a Menodus, a 

 member of an altogether different group from his "S." 

 Tiypoceras, which is a BrontotTierium. 



After an interval of 12 years, in 1886, Cope (1886.1) 

 described the first Canadian species, Menodus angusti- 

 genis, basing it upon fragments discovered by Mc- 

 Connell and Weston for the Geological and Natural 

 History Survey of Canada. Three years later (1889.1, 



p. 153) he referred this form to a new genus, Hapla- 

 codon, and in the same year (1889.2, pp. 628, 629) he 

 described two other Canadian species. His review 

 (1891.2, p. 17) of these forms and attempted revision 

 of the nomenclature were involved and unsatisfactory. 

 He recognized only two genera, Menodus and Symbo- 

 rodon. The last species of titanothere described by 

 him was his Menodus peltoceras (1891.1), which is 

 probably a female of Marsh's BrontotTierium curtum. 



EEINTERPRETATION AND PHYLOGENETIC STUDY 



(OSBOEN, 1887-1919) 



STUDY OF CERTAIN FEATURES 



Before Marsh and Cope had ceased naming new or 

 supposedly new genera of titanotheres a turn was 

 given to the trend of study by a paper by Scott and 

 Osborn (1887.1, pp. 157, 158), entitled "Preliminary 

 account of the fossil mammals from the White River 

 formation contained in the Museum of Comparative 

 Zoology." This paper, which was a description of the 

 interesting collection made by Mr. Samuel Garman 

 under the auspices of Prof. Alexander Agassiz, reacted 

 from the polynomial systems of Marsh and Cope and 

 tended toward a mononomial system. In this paper 

 the Perissodactyla were described by Osborn, the 

 Artiodactyla and Carnivora by Scott. Before de- 

 scribing the new titanothere material the authors 

 noted the difficulty in deciding where to draw generic 

 lines, a difficulty that is increased by the fact that the 

 mandibles are seldom found with the skulls. 



As in Uintatherium, the variability in the various portions of 

 the skull, especially in the region of the horns, is so extreme that 

 no two skulls are found which are exactly alike. But the denti- 

 tion, which is constant among the Dinocerata, here greatly com- 

 plicates the problems of classification. The premolars vary in 

 number, and the incisors, always of relatively small size and 

 fairly constant in number in the upper jaw, vary from three to 

 none in the lower jaw." In all the lower jaws found in Professor 

 Cope's collection of Menodontidae from northern Colorado there 

 are no incisors, and the mandibular symphj'sis is extremely 

 narrow. In the lower jaws of the Cambridge and Princeton 

 collections, which are all from the Nebraska and Dakota 

 exposures, the symphysis is broad, and the incisors, where pre- 

 served, are two in number, while in one of the Cambridge 

 specimens no less than three incisor alveoli may be counted 

 upon one side of the symphysis. 



We might infer from this that Symborodon can be clearly 

 separated from Menodus by the absence of the lower incisors, 

 accompanied by a narrowing of the symphysis; but Professor 

 Cope has recently described a new species, M. angustigenis, 

 from the Swift Current Creek region (Cope, 1886.1, p. 81c), 

 which combines the narrow type of symphysis with the presence 

 of two incisors. The separation of these genera is rendered 

 still more improbable by the parallelism which exists between 

 the skulls from the Nebraska and Colorado localities, especially 

 in respect to the conformation of the nasal bones and the 

 horns. The genus Symborodon is, however, provisionally 

 adopted at present to include the species with a narrow man- 

 dibular symphysis and no lower incisors. 



The genus Brontotherium Marsh (that is. Marsh's "Bronto- 

 therium" ingens, not the true Brontotherium) can not be dis- 

 tinguished from Menodus. It rests in part upon the premolar 



I' One of the Cambridge skulls, M. coloradensis, has but a single upper incisor. 



