Findings in biological anthropology suggest that Native Americans' ancestors probably came to the Americas from northeastern Asia. Turner, for example, has studied the dentition of prehistoric and living Native Americans and northeastern Asians. Based on approximately twenty dental traits, including tooth-crown shape and number of roots, he has defined an overall dental pattern called Sinodonty, which includes three-rooted lower first molars and shovel-shaped incisors. This distinctive pattern is shared among most Native Americans and people from northeastern Asia, but is not found in people who originated in southern Asia, Africa, or Europe. Another less complex pattern—Sundadonty—is shared among the people of southeastern Asia and is also found in prehistoric American populations, but Turner believes that widespread Sinodonty demonstrates most Native Americans' northeastern Asian origins.