Few rhinoceros species remain

If I say rhinoceros, the word probably brings a certain picture to mind. Five species of this animal exist, two in Africa and three in Asia, all quite similar. Yet the rhinos of today are just a small remnant of a once large and varied group.

Rhinos are ungulates, hoofed animals. Today there are two main groups: artiodactyls (the even-toed ungulates, such as antelope, sheep and bison) and perissodactyls (the odd-toed ungulates, including horses, tapirs and rhinoceroses).

Rhinoceroses might well have originated here in America, and we certainly have some of the best fossils. One of the earliest known perissodactyls is Hyracotherium (sometimes called Eohippus) from about 50 million years ago. About the size of a fox, it is often called the first horse, although it could almost as easily be called the first tapir or first rhino.

About 30 million years ago, there appeared a group of long-legged hornless rhinos called hyracodonts, the running rhinoceroses. Hyracodon was about 5 feet long and probably resembled a small pony.

At the other extreme is a group of giant rhinos that lived in Pakistan and China at about the same time. Indricotherium (also called Baluchitherium) was the largest land mammal known. Its skull was more than 4 feet long, it stood 18 feet tall at the shoulder, and it might have weighed 32 tons.

About 11 million years ago, rhinos were among the most common animals on the Great Plains. One kind, Teleoceras, was a short- legged, wide-bodied form that resembled (and probably lived like) the modern hippopotamus. Unlike modern rhinos, which tend to be solitary, Teleoceras congregated in large groups, as shown by a herd of more than 100 that was buried by volcanic ash in central Nebraska.

During the Ice Age, at least two kinds of woolly rhinoceros appeared. Russia was home to Elasmotherium, a large rhino with a single huge horn on its forehead. The animal was of almost elephant proportions, and the horn was more than 6 feet long.

The other woolly rhino was Coleodonta, which had two horns on its snout, one in front of the other. Coleodonta ranged widely, from Britain to Asia, but never reached North America. Not only have corpses been found in frozen gravel in Siberia, but ancient humans also drew detailed pictures of it on cave walls.

Rhinos aren't the only group to originate in North America, spread to other lands in a variety of forms and then become extinct here. I'll tell you about another such group next week.

Dale M. Gnidovec is curator of Ohio State University's Orton Geological Museum.

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