Thanks to a hundred years of Hollywood movies, many people are convinced that mammoths, mastodons and other prehistoric elephants lived alongside dinosaurs. In fact, these huge, lumbering beasts evolved from the tiny, mouse-sized mammals that survived the K/T Extinction 65 million years ago. And the first mammal even remotely recognizable as a primitive elephant didn't appear until five million years after the dinosaurs went kaput.

The Phosphatherium

That creature was Phosphatherium, a small, squat, pig-sized herbivore that popped up in Africa about 60 million years ago. Classified by paleontologists as the earliest known proboscid (an order of mammals distinguished by their long, flexible noses), Phosphatherium looked and behaved more like a pygmy hippopotamus than an early elephant. The giveaway was this creature's tooth structure: we know that the tusks of elephants evolved from incisors rather than canines, and Phosphatherium's choppers fit the evolutionary bill.

The two most notable proboscids after Phosphatherium were Phiomia and Moeritherium, which also lived in northern African swamps and woodlands circa 37-30 million years ago. The better known of the two, Moeritherium, sported a flexible upper lip and snout, as well as extended canines that (in light of future elephant developments) could be considered rudimentary tusks. Like a small hippo, Moeritherium spent most of its time half-submerged in swamps; its contemporary Phiomia was more elephant-like, weighing about half a ton and dining on terrestrial (rather than marine) vegetation.

Yet another northern African proboscid of this time was the confusingly named Palaeomastodon, which should not be confused with the Mastodon (genus name Mammut) that ruled the North American plains 20 million years later. What's important about Palaeomastodon is that it was recognizably a prehistoric elephant, demonstrating that by 35 million years ago nature had pretty much settled on the basic pachyderm body plan (thick legs, long trunk, large size and tusks).

Toward True Elephants: Deinotheres and Gomphotheres

Twenty-five million years or so after the dinosaurs went extinct, the first proboscids appeared that could easily be discerned as prehistoric elephants. The most important of these, from an evolutionary perspective, were the gomphotheres ("bolted mammals"), but the most impressive were the deinotheres, typified by Deinotherium ("terrible mammal"). This 10-ton proboscid sported downward-curving lower tusks and was one of the largest mammals ever to roam the earth; in fact, Deinotherium may have inspired tales of "giants" in historical times, since it survived well into the Ice Age.

As terrifying as Deinotherium was, though, it represented a side branch in elephant evolution. The real action was among the gomphotheres, the odd name of which derives from their "welded," shovel-like lower tusks, which were used to dig for plants in soft, swampy ground. The signature genus, Gomphotherium, was especially widespread, stomping across the lowlands of North America, Africa and Eurasia from about 15 million to 5 million years ago. Two other gomphotheres of this era--Amebelodon ("shovel tusk") and Platybelodon ("flat tusk")--had even more distinctive tusks, so much so that these elephants went extinct when the lakebeds and riverbeds where they dredged up food went dry.

The Difference Between Mammoths and Mastodons

Few things in natural history are as confusing as the difference between mammoths and mastodons. Even these elephants' scientific names seem designed to befuddle kids: what we know informally as the North American Mastodon goes by the genus name Mammut, while the genus name for the Woolly Mammoth is the confusingly similar Mammuthus (both names partake of the same Greek root, meaning "earth burrower"). Mastodons are the more ancient of the two, evolving from gomphotheres about 20 million years ago and persisting well into historical times. As a rule, mastodons had flatter heads than mammoths, and they were also slightly smaller and bulkier. More importantly, the teeth of mastodons were well-adapted to grinding the leaves of plants, whereas mammoths grazed on grass, like modern cattle.

Mammoths emerged on the historical scene much later than mastodons, popping up in the fossil record about two million years ago and, like mastodons, surviving well into the last Ice Age (which, along with the hairy coat of the North American Mastodon, accounts for much of the confusion between these two elephants). Mammoths were slightly bigger and more widespread than mastodons, and had fatty humps on their necks, a much-needed source of nutrition in the harsh northern climates in which some species lived.

The Woolly Mammoth, Mammuthus primigenius, is one of the best-known of all prehistoric animals since entire specimens have been found encased in Arctic permafrost. It's not beyond the realm of possibility that scientists will one day sequence the complete genome of the Woolly Mammoth and gestate a cloned fetus in the womb of a modern elephant!

There is one important thing mammoths and mastodons shared in common: both of these prehistoric elephants managed to survive well into historical times (as late as 10,000 to 4,000 B.C.), and both were hunted to extinction by early humans.