The oldest complete skeleton of its kind ever found, dating to more than 12,000 years ago, is helping solve a mystery about the differences in body types between the first humans to arrive in the Americas and later Native Americans, scientists announced Thursday.

Anthropologists have long puzzled over why Native Americans don't look more like their ancient ancestors, who migrated into the Americas during the Pleistocene, the epoch that encompassed the last ice age and that ended about 12,000 years ago.

The ancient skulls are larger, their faces are narrower and more forward-projecting, and they more closely resemble native peoples of Africa, Australia, and the southern Pacific Rim than they do their supposed American descendants.

Were those differences the product of evolutionary changes