For 25 million years, rhinos were the most common plant-eating mammals in North America.
Early rhinoceroses were a very diverse group. They ranged from small animals (that looked like tapirs) to large, hippo-like forms. Extinct hornless rhinos are recognized by their distinctive teeth.
The first rhinos were browsers in semi-tropical forests. As climates changed, some rhinos became specialized for grazing, some used prehensile lips to grasp leaves.
running rhinoceroses: early hornless rhinos, including Hyracodon and gigantic Paraceratherium.
New feature:
-
long, slender limbs and feet increased running speeds
rhinocerotines: later, horned rhinos, including Teleoceras and modern rhinoceroses
New feature:
-
nose horn on the end of fused nasal bones
Where's the Horn?
Rhinoceros horns aren't made of bone or horn, but are formed entirely of compressed hair. because hair doesn't usually preserve in the geologic record, there are no fossil rhino horns. We know which species had them, however, because fossilized rhino skulls show roughened areas where, in life, horns were attached.
Enormous Paraceratherium, the largest land mammal of all time, was a long-legged runner, as was the swift, pony-sized rhinoceros called Hyracodon.
40 to 23 million years ago; Asia, Europe
Hippo-like Teleoceras, is an extinct grazing rhinoceros that once lumbered around on the North American grasslands. Specimens of Teleoceras have been found with fossilized grasses perserved in their mouths and stomachs.
12 to 4 million years ago; Asia, North America
PICTURE CAPTIONS:
- Hyracodon
- Paraceratherium
- Teleoceras
- Diceros