THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE IV. VOL. IV. 



No. X.— OCTOBER, 1897. 



o."Kxc3-insr.A.Xi ^^iaariciLES. 



I. — The Skull of Protoceras. 



By Professor 0. C. Marsh, M.A., Ph.D., LL.D., F.G.S. ; 



of Yale College, New Haven, IJ.S.A. 



PLATE XIX. 



THE genus Protoceras, described by the writer in 1891, from the 

 Miocene of South Dakota, is now known to include some of the 

 most interesting extinct mammals yet discovered. It likewise repre- 

 sents a distinct family, and thus deserves careful investigation and 

 description.^ Before this discovery, no horned artiodactyles were 

 known to have lived during Miocene time, and Protoceras is thus 

 the earliest one described. The type-specimen, moreover, had a pair 

 of horn-cores on the parietals, and not on the frontals as in modern 

 forms of this group. The animal was apparently a true ruminant, 

 nearly as large as a sheep, but of more delicate proportions. 



The first skull found, the type-specimen of the genus Protoceras, 

 belonged to a female, as later discoveries demonstrated. The skull 

 of the male proved still more remarkable, and especially resembles the 

 male skull of the Eocene Dinocerata in having several pairs of horn- 

 cores or protuberances upon the head, a feature hitherto unknown 

 among the Artiodactyla. It is an interesting fact, moreover, that one 

 pair of these horn-cores of Protoceras is on the maxillaries, as in 

 Dinoceras, while the posterior pair, as in that genus, is on the 

 parietals. 



The resemblance in the two skulls is further enhanced by the 

 absence of upper incisors and the presence of large canine tusks, 

 forming together a striking similarity in important features, between 

 skulls pertaining to animals of two distinct orders, and from widely 

 different geological horizons. The skull of the male Protoceras is 

 shown in Plate XIX, and that of Dinoceras in the text below. 



It is a noteworthy fact, that in still another order of ungulate 

 mammals, the Perissodactyla, horn-cores in pairs early made their 

 appearance, although none are known in the recent forms. One of 

 the earliest instances is seen in the genus Colonoceras from the 

 Middle Eocene, which had rudimentary protuberances upon its nasal 



^ American Journal of Science, vol. xli, p. 81, January, 1891 ; vol. xlvi, p. 407, 

 November, 1893 ; and vol. iv, p. 165, September, 1897. 



DECADE IV. ^VOL. IV. NO. X. 28 



