The original inhabitants of North American -- Indians and Eskimos -- migrated here more than 10,000 years ago from central Siberia and north China. They came in three distinct waves by way of a land bridge across the Bering Sea, following the animals they hunted. Much of this is not new, but now Dr. Christy G. Turner II, of Arizona State University, thinks he is on his way to proving it. Turner is a dental anthropologist who has painstakingly examined thousands of teeth, ancient and modern, from the new world and the old. Among the distinctions he has come up with:

Shovel teeth -- The insides of the front teeth or incisors are markedly scooped out, or "shoveled," in Indians, and moderately so in Eskimos. Europeans' never are. "This clearly shows that all the people of the New World had to come from north Asia, where shoveled teeth are also characteristic," Turner said.

Peg teeth -- A large percentage of the people from the Amur River area of northern Asia and, on the other side of the Bering Sea, Eskimos in Alaska and Arctic America have third upper molars that are peg-shaped. Nobody else has teeth like this.

Five cusps -- Asians and American Indians have five cusps (the little bumps or knobs on the back grinding teeth) on their lower second molars. Most Europeans and people from southeast Asia have only four.

Three roots -- some people, typically northern Asians, but never Europeans, have lower first molars with three roots instead of two. On these basis of these and other clues, Turner thinks the ancient migrations went this way: During the last Ice Age, 10,000 to 12,000 years ago, a large ice-free corridor existed, running northeast from the Lake Baikal region of Sibera along the Lena River basin and eventually to the grass-covered Bering Sea land bridge. Asian ancestors of the Indians wandered through this natural corridor following the grazing animals they hunted -- bison, horses, mammoths -- crossing the center of the bridge, which was several hundred miles wide. Another migration probably originated in Mongolia's Amur River valley. These people, probably the ancestors of modern Eskimos, moved along the shore hunting whales and seals, crossing the bridge at the frozen shoreline. Turner, much of whose work is sponsored by the National Geographic Society, theorizes that a third migration took place just before melting of the ice released enough sea water to drown the land bridge.