NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 3 



The incomparable pencil drawings reproduced in the accompany- 

 ing plates (except pi. 11), as well as the text figures, were prepared 

 by Lawrence B. Isham, staff illustrator for the Department of Paleo- 

 biology in the U. S. National Museum. 



HISTORY OF INVESTIGATION 



Discovery and description. — Meniscotherium was first described 

 by Cope in 1874. The specimen on which the type species, M. 

 chamense, was based is a right maxillary fragment exhibiting the 

 molars and outer wall of the last premolar, found that summer in 

 the San Juan Basin of New Mexico in the region between Canyon 

 Largo and Gallina River. No new material was reported until 1881 

 (b) when Cope described a left maxilla with three molars and three 

 premolars and an associated lower jaw fragment with two teeth as 

 representing a new and somewhat larger species, M. terraerubrae. 

 Description of this material was included with that of Torrejonian 

 Paleocene forms from the "Lowest Eocene beds of New Mexico." 

 Cope stated (p. 495) that the new Meniscotherium specimens found 

 by D. Baldwin were from "the red Eocene beds in northwestern 

 New Mexico, from the true Wasatch horizon, or higher than that 

 which produced other species here described." Nevertheless, there 

 must have been some doubt in his mind as to the horizon represented 

 because elsewhere on the same page, in discussing the fauna of the 

 beds he thought were quite possibly the Puerco formation, he stated 

 that he had now added the genera Hyracotherium and Menisco- 

 therium. 



A third and smallest species of Meniscotherium, M. tapiacitis, 

 was described by Cope late in 1882(f). At this time there was 

 apparently no confusion with the Paleocene. M. tapiacitis is stated 

 to have been collected "by D. Baldwin from beds of probably lowest 

 Wasatch age in New Mexico." 



Marsh's description of Hyracops socialis in 1892 was based on skull 

 and foot material collected by David Baldwin in 1878. While Marsh's 

 report on meniscotheriid remains from the Wasatchian of New 

 Mexico was much later than Cope's, Baldwin's collecting for Marsh 

 evidently preceded his employment by Cope. The specimens according 

 to Thorpe (1934) came from the head of Gabilan Canyon, a branch 

 of Canyon Largo in the San Juan Basin. The distinction which 

 Marsh made between Hyracops and Meniscotherium was based es- 

 sentially on the molariform appearance of the last premolar and pos- 

 session of an extra sacral vertebra, features that Thorpe has since 

 shown to be invalid in that the premolar described belonged to the 



