Menoceras arikarense Rhinoceros Skull

       

July's Fossil of the Month is a complete skull of the prehistoric rhinoceros, Menoceras arikarense, that was formerly in the Carnegie Museum Collection. It was collected by O.A. Peterson around 1906 at Carnegie Hill in the Agate Fossil Beds National Monument in Nebraska.

This skull is 15 inches (40 cm) long and is one of only a handful of fossils that is legally in a private collection because it was discovered and collected before Agate Springs became a national park. It was originally classified as Diceratherium sp. due to the paired nasal horn, however, in 1921, Troxell proposed a new slightly smaller species, Menoceras arikarense, when slight differences were discovered. As characteristic of Menoceras, the skull exhibits a saddle-shape from the side, a frontal convex, and the paired knob-like horns at the tip of the nasals.

Menoceras ("Crescent Horns") was a small rhinoceros the size of a sheep that could be found throughout North America during the Miocene roughly 30 to 20 million years ago. It is believed they lived in large herds because many Menoceras fossils have been discovered in one area--particularly Agate Springs and Cady Mountains Horse Quarry in California. 

Males exhibited two horns at the top of the nose, but females had no horns at all. Both genders grew to the same length of 5 feet and weighed an average 830 pounds. Menoceras was a grazer and probably a quick runner.

 

Rhinoceros Skull
Menoceras arikarense (Barbour, 1906)
Formerly classified as Diceratherium
Miocene: Anderson Ranch Formation
Cook Ranch, Agate Springs
Sioux County, Nebraska
Collected by O.A. Peterson, ex Carnegie Museum
Ex George S. Tennis III, ex. Dickenson College

(Reproduction image by https://en.wikipedia.org/wiki/Menoceras#/media/File:Diceratherium_cooki.jpg)