Principal characters of the Protoceratidae / by O.C. Marsh.

  • Marsh, Othniel Charles, 1831-1899.
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: Principal characters of the Protoceratidae / by O.C. Marsh. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    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 impor- tant features, between skulls pertaining to animals of two dis- tinct orders, and from widely different geological horizons. The skull of the male Protoceras is shown in Plate II, and that of Dinoceras in the text below. Figure 1.—Skull of Dinoceras mirabile, Marsh ; type; seen from the side. One-seventh natural size. Eocene. It is a noteworthy fact, that in still another order of ungu- late mammals, the Perissodaciyla, 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 Colo- noceras from the middle Eocene, which had rudimentary pro- tuberances upon its nasal bones, as represented below, in figure 2. The gigantic Brontotheridce of the lower Miocene all had prominent horn-cores on the maxillary bones, somewhat like those of the male Protoceras. One of the most unexpected examples, however, in this order, appears in the Miocene fenus Psicerat/ierium, the type specimen of which is shown in gure 3. This animal, although a true rhinoceros, had a pair of horn-cores on the nasal bones, while all other rhinoceroses, living and extinct, are either without horns or have them on the median line. In short, horns in pairs are unknown in exist- ing mammals, except in the artiodactyles, an order of later devel- opment, but now the dominant group of ungulate mammals.