Date of this Version
Bulletin of The University of Nebraska State Museum Volume 8, Number 6 Pp. 395-412 Figs. 1-10 Tables 1-2
A new species of rhinoceros, Menoceras marslandensis, is here proposed. It is based upon a nearly complete skull from the upper part of the Marsland Formation, Hemingford Group (Miocene), of Box Butte County, Nebraska. The new species was probably derived from Menoceras arikarense (Barbour), collected from the Agate Springs Quarries (Arikaree Group, Harrison Formation) of Sioux County, Nebraska, with which both Diceratherium niobrarensis Peterson and D. cooki Peterson are likely synonymous. From Menoceras arikarense, the presumed ancestral stock, Menoceras marslandensis differs in possessing the following characters: (1) very long, fused but slightly cleft, nasals, with flattened, rugose areas at the tips for the support of the horns; and (2) a convex frontal, also roughened, indicating a base for a well-developed frontal horn. This new species provides additional evidence that the generic separation of Menoceras Troxell from Diceratherium Marsh is warranted, and these two genera evidently lived side-byside in the Medial to Late Miocene of the Central Great Plains. Both stocks, each greatly modified, may have survived into the Pliocene.