Humans can inhabit what is now southern Mexico surprisingly early, between 33,448 and 28,279 years ago, researchers say.
If so, those people arrived more than 10,000 years before people were often labeled as the first Americans (SN: 7/11/18). Other preliminary tests place humans in central Mexico some 33,000 years ago (SN: 22/07/20).
The latest evidence comes from animal bones that anthropologist and biological archaeologist Andrew Somerville and two Mexican colleagues found stored in a laboratory in Mexico City. The bones had been excavated in the 1960s at a rock shelter called Coxcatlan Cave.
Radiocarbon analyzes of six rabbit bones from the deepest sediment at the site produced unexpectedly unexpected ages, researchers reported online on May 19 in Latin American Antiquity. That sediment also contained cut, sharp stones considered tools by the site’s lead excavator.
The higher sediment layers have given clearer examples of stone tools and other remnants of human activity dating back almost 9,900 years. Somerville, of Iowa State University in Ames, initially suspected that the rabbit bones from the deepest sediments were perhaps about 12,000 years old. But analyzes revealed they were much older, suggesting that humans lived in the cave about 30,000 years ago.
Somerville will then determine if other animal bones from the ancient sediment show marks of carnage, breaks where the marrow was removed, or patches burned during cooking. He also wants to locate and study possible stone tools from that same sediment that can be stored in the same lab.
Based on additional radiocarbon dates and comparisons with stone tool finds from other Mexican sites, Somerville suspects that a separate occupation of Coxcatlan Cave occurred between 13,500 and 9,900 years ago. It is possible that regional sources of food and water dwindled when the last Ice Age peaked between 26,000 and 19,000 years ago, causing early settlers to abandon and delay further occupations until conditions improved, Somerville speculates.