File:Subhyracodon sp. (fossil rhinoceros) (White River Formation, Oligocene; near Lusk, Wyoming, USA) (33224332270).jpg

Subhyracodon sp. - fossil hornless rhinoceros skull from the Oligocene of Wyoming, USA. (UW 15567, University of Wyoming Geological Museum, Laramie, Wyoming, USA)

From museum signage: Subhyracodon Leidy, 1850

Geologic Range: 38.0-26.3 million years ago (Late Eocene-Late Oligocene)

Geographic Range: Widespread in North America (Wyoming, Nebraska, South Dakota, North Dakota, Colorado, Montana, Oregon, southern California, Mississippi, Saskatchewan).

Adult Size: Weight from 191 to 520 pounds (86.7 to 236.0 kilograms).

Habitat and Diet: Terrestrial. Browsing herbivore.

Characteristics: This skull of Subhyracodon (UW 15567) was collected from the White River Formation near Lusk, Wyoming. Subhyracodon is the most common large rhinoceros found in Late Eocene and Early Oligocene rocks in North America. Although its name suggests a close relationship to Hyracodon, the two are not closely related. Subhyracodon belongs to the group of more "typical" rhinoceroses with more robustly built limbs, which indicate that Subhyracodon was not a fast runner. Subhyracodon is a "true" rhinoceros, classified in the Family Rhinocerotidae, while Hyracodon is placed in the Family Hyracodontidae. Looking at the two skulls, the incisors of Hyracodon are pointed and its canines are small. Subhyracodon has lost the last pair of upper incisors (I3) and its upper canines and the remaining incisors are elongated. Subhyracodon and Hyracodon were contemporaries during the Late Eocene and Early Oligocene.

Classification: Animalia, Chordata, Vertebrata, Mammalia, Placentalia, Perissodactyla, Rhinocerotidae

Locality: unrecorded/undisclosed site near the town of Lusk, eastern Wyoming, USA

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