PART 2: CLASSIFICATION AND DESCRIPTION 

 OF MAMMALS 



Order MULTITUBERCULATA Cope, 1884 



Douglass' first collection included no multituberculates, but in his 

 second collection (see Douglass, 1908) there were several teeth of this 

 group. A jaw fragment with P4 and Mi was made type of Ptilodus 

 montanus, and other specimens of that species were mentioned. 

 Several upper teeth were referred to Chirox, not then known to be 

 S3^nonymous with Ptilodus, and the probable presence of other species 

 of Ptilodus was mentioned. An incisor with limited enamel band 

 (Douglass, 1908, pi. 1, figs. 18, 20) was tentatively referred to Mixo- 

 dedes but may also be multituberculate (cf. Eucosmodon) . 



Among the first discoveries made by Mr. Silberling for the Na- 

 tional Museum was the now famous specimen that includes skull, 

 jaws, and some skeletal parts of Ptilodus. This was described, as a 

 new species, Ptilodus gracilis, by Gidley (1909) in the first of his 

 notes on this fauna. This is still the finest single multituberculate 

 specimen known. It enabled Dr. Gidley to demonstate that Chirox 

 is merely the upper dentition of Ptilodus (and by analogy, Bolodon 

 that of Plagiaulax, in the Jurassic) and for the first time to establish 

 the true characters of this extraordinary group. He concluded that 

 Ptilodus and its kin were diprotodont marsupials. Although this 

 conclusion now seems untenable, it should be emphasized that such 

 a conclusion was logical, if not inevitable, at the time ^^ and that 

 Gidley's work on this form was very able. Gidley also noted the 

 presence of at least two other, smaller, species in the Fort Union 

 collection, although the limited material then available did not per- 

 mit their description, and he tentatively referred them to two Cre- 

 taceous species described by Marsh. 



Granger and Simpson (1929), revising the Paleocene multitubercu- 

 lates, restudied Ptilodus montanus, Douglass' type, concluding that 

 it was doubtfully distinct from Ptilodus mediaevus and P. gracilis. 

 The latter species was not reexamined, as Dr. Gidley was then living 

 and planning a definitive study of liis material. It was suggested 

 that no valid distinction from P. montanus had been given, but the 

 species was accepted pending Dr. Gidley's definitive study. Two 

 Torrejon specimens were doubtfully (and, as now appears, incorrectly) 

 referred to P. montanus. 



As regards these three species, the conclusion below is that Ptilodus 

 gracilis is a synonym of P. montanus, which is distinct from the 

 Torrejon P. mediaevus, although very closely related. 



22 Interesting unpublished correspondence shows, for instance, that Dr. W. D. Matthew went over 

 Gidley's argument with great care at the time and agreed with his conclusion, although later new evidence 

 forced him to change his mind and to reach essentially the conclusion here supported. 



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