Then there was the American Mastodon, Mammut americanum. Just another elephant you say ?

Put 'em side by side and they look no more alike than a collie and a pit bull!

(These lineages diverged in the These lineages diverged in the Oligocene!Oligocene!)

This is a major ecological difference - a grazer (Mammuthus) and a browser (Mamut). They occupied different habitats entirely. How do we know?

Look at the teeth!At right, a pair of

mastodon molars - below, mammoth.

These are lineages that diverged in the Oligocene, over 20 million years ago ...

Mammuthus primigenius

Mammuthus columbi

Mammuthus exilis

Dima, a juvenile mammoth carcassfound in Siberia ca. 1974

Archidiskodon meridionalis, the giant Siberian mammoth of the middle Pleistocene

Mammuthus columbi, the Columbian mammoth, of North America

The saiga, the Mongolian steppe antelope, was also a member of the circumpolar Pleistocene mammal fauna.

Aren't those tiny feet cute?

Aren't those tiny feet cute?

Smilodon, the sabre-toothed cat, is another Pleistocene animal of near-mythic proportions. This predator is the official state fossil of California.

Carnivore teeth tend to be high-crowned and three-lobe pointed, like these examples. Above, a cave bear from Siberia. Upper right, a shrew mandible fragment. At right, an extinct wild dog mandible.

Wild horses, believed to have been closely related to the Siberian wild ass (Equus przewalskii, above) were widespread and highly varied across North America. Teeth at UR are from Florida, the one to the right is Alaskan.

MOST important, most abundant, and most informative, are actually the teeth of microtine rodents - the mice, voles, lemmings, and other tiny critters. These are the most rapidly evolving group of organisms on the planet, the most widespread of mammals, and the most abundant in terms of numbers per any given area (or volume of sediment!)