144 



TITANOTHERES OP ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



theres, which was accompanied by excellent litho- 

 graphs of Prout's and other fragmentary specimens. 

 At this stage of knowledge the only parts figured 

 under the name Titanotherium proutii included the 

 lower molars, a lower premolar, a lower canine, a frag- 

 mentary upper molar, and two upper premolars 

 (Leidy's types of Rhinoceros americanus). Fragments 

 of large upper molars were named Palaeotherium 

 giganteum. 



The "palaeotherian bed" of Owen and Evans is 

 referred to by Leidy (op. cit., p. 13) as the "Titano- 

 therium bed." This appears to be the first use of this 

 term, which was afterward, in the form " Titano- 

 therium beds" (now Titanotherium zone), so widely 

 used by geologists and paleontologists. 



An interval of 15 years in the literature of the sub- 

 ject, from 1854 to 1869, is broken only by Prout's 

 brief notice of an indeterminate molar (now lost) of a 

 titanothere, which he named Leidy otherium. But 

 during this seemingly barren interval Meek and 

 Hayden were making their historical explorations 

 (Merrill, 1906.1, pp. 585-592), which resulted in 

 notable advances in our knowledge of the relations 

 of the geologic deposits of the Rocky Mountains and 

 Great Plains. They also brought back many verte- 

 brate fossils, including specimens of Titanotherium. 



One of the specimens of titanotheres collected by 

 Meek and Hayden included a nearly complete series 

 of upper teeth. This specimen, which belonged to 

 Prof. James Hall and is now No. 433 of the Hall 

 collection of the American Museum of Natural 

 History, was described and figured by Leidy in his 

 memoir of 1869 (1869.1, pp. 206, 207, pi. 24) and was 

 by far the best spec'men that had been described up 

 to that time. Leidy referred it to his species Titano- 

 therium proutii, but it probably belongs in the genus 

 that Marsh afterward named Brontotherium. This 

 specimen misled Leidy into assigning Titanotherium 

 to the Artiodactyla. "From the form of its lower 

 true molars, which were first discovered," he says, 

 "it was supposed to be more nearly alHed with the 

 Palaeotherium and was hence placed among the uneven- 

 toed pachyderms, or Perissodactyla, but the nearly 

 complete dentition of both jaws, since discovered, 

 appears to indicate its position to be as above stated " — 

 that is, it appeared to be "nearly allied with Chali- 

 cotherium, and, like it, approximates the even-toed 

 pachyderms, or Artiodactyla * * * with the Ru- 

 minantia." 



In 1870 Leidy (1870.1, pp. 1, 2) described a frag- 

 mentary fossil from Colorado that had been submitted 

 to him by Doctor Hayden. We now know that this 

 specimen consists of the horn cores and attached 

 coossified nasal bones of a titanothere of some sort, 

 but to Leidy, who knew practically nothing of the 

 skull of the titanothere, it proved "singularly puzzling 

 in character." He at first thought it might pertain 



to Titanotherium, "but in the state of extreme uncer- 

 tainty as to its collocation, it may with equal proba- 

 bility be referred to other genera, perhaps to Megalo- 

 meryx, or it may have been an American species of 

 Sivatherium. Under the circumstances it may be 

 referred to a new genus, with the name of Megacerops 

 color adensis ." 



This problematical fossil was redescribed and figured 

 by Leidy in his memoir of 1873 (1873.1, p. 239). He 

 states that the specimen "appears to correspond 

 with that portion of the face * * * [of Siva- 

 therium] which comprises the upper part of the nose, 

 together with the forehead and the anterior horn 

 cores." He compares the specimen with the corres- 

 ponding parts of the Sivatherium, the rhinoceros, the 

 tapir, and the mastodon. He decides that the frag- 

 mentary horn core formerly attributed to Titano- 

 therium may perhaps belong to another species of 

 Megacerops. 



This erroneous determination, together with the 

 previous assignment of Titanotherium to the Artio- 

 dactyla, shows how greatly Leidy, even with all his 

 skill and caution, was deceived by the lack of well- 

 preserved and definitely associated feet and skulls, 

 a lack which is felt to some extent even at the present 

 time. 



Leidy's description of Megacerops may be regarded 

 as marking the close of the first or pioneer period in 

 the study of the titanotheres, a period characterized 

 by (1) the chance discovery of "Prout's specimen," 

 (2) the exploration of the White River badlands 

 by Evans, Hayden, and others and the resulting 

 knowledge of the general geologic age of the beds, (3) 

 the description of fragmentary remains of titanotheres, 

 chiefly teeth, by Prout, by Pomel, and by Leidy in 

 successive publications, together with the beginnings 

 of the systematic nomenclature, (4) the erroneous 

 reference of Titanotherium to the Anoplotheriidae 

 among the Artiodactyla. 



TAXONOMIC ARRANGEMENT AND COMPARISON 

 WORK OF MARSH AND COPE (1870-1887) 



The second period in the study of titanotheres, 

 which may be called the period of systematic descrip- 

 tion, really began before the first period had closed 

 (1873). 



From 1873 to 1891, inclusive, the literature of the 

 Oligocene titanotheres is dominated almost exclu- 

 sively by the explorations and systematic contribu- 

 tions of Marsh and Cope. During this time Marsh 

 described eight genera and fourteen species as new, 

 and Cope described three genera and twelve species 

 as new. The solution of the exact systematic and 

 phylogenetic interrelations of these genera and species 

 is one of the principal themes of Chapters IV to VII of 

 the present monograph. 



In 1870 Prof. Othniel C. Marsh (1870.1) headed an 

 expedition sent from Yale College to northern Colo- 



