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Two Different Paleo-Indian Populations Coexisted in Late Pleistocene-Early Holocene Mexico

An international team of archaeologists and paleoanthropologists has uncovered the 9,900-year-old remains of a Paleo-Indian woman in the Chan Hol underwater cave near the city of Tulum on the Yucatan Peninsula, southern Mexico. They’ve found that the mesocranial skull morphology of the individual is different to the dolicocephalic morphologies found in equivalent Paleo-Indian age human populations from Central Mexico; this supports the presence of two morphologically different Paleo-Indian populations for Mexico, coexisting in different geographical areas during the Late Pleistocene-Early Holocene.

Two Different Paleo-Indian Populations Coexisted in Late Pleistocene-Early Holocene Mexico
Paleo-Indians hunting a glyptodont by Heinrich Harder, c. 1920.

Humans have been living on Yucatan Peninsula since at least the Late Pleistocene (126,000-11,700 years ago).

Much of what we know about these earliest settlers of Mexico comes from nine well-preserved human skeletons found in the submerged caves and sinkholes in the Tulum area.

Now, Universität Heidelberg’s Professor Wolfgang Stinnesbeck and colleagues report on a new skeleton from the Chan Hol underwater cave within the Tulum cave system. Named Chan Hol 3, it is the third human skeleton discovered from the Chan Hol system.

The cave also preserves evidence for early to mid-Holocene human usage in the form of numerous accumulations of charcoal with radiocarbon dates between 9,122 and 7,951 years ago.

“Not all of the ten skeletons from the Tulum area were complete, but they were well preserved,” Professor Stinnesbeck said.

“They offer valuable archaeological, palaeontological and climatic information about the American continent and its first inhabitants, the Paleo-Indians.”

Professor Stinnesbeck’s team used a non-damaging dating method and took craniometric measurements, then compared the Chan Hol 3 skull to 452 skulls from across North, Central, and South America as well as other skulls found in the Tulum caves.

The analysis showed that the individual was likely a woman, approximately 30 years old at her time of death, and lived at least 9,900 years ago.

Her skull falls into a mesocephalic pattern — neither especially broad or narrow, with broad cheekbones and a flat forehead — like the three other skulls from the Tulum caves used for comparison.

All Tulum cave skulls also had tooth caries, potentially indicating a higher-sugar diet.

This contrasts with most of the other known American crania in a similar age range, which tend to be long and narrow, and show worn teeth — suggesting hard foods in their diet — without cavities.

“The Tulum skeletons exhibit round-headed — mesocephalic — cranial characteristics different to the long-headed — dolicocephalic — morphology of Paleo-Indians from Central Mexico and North America,” Professor Stinnesbeck said.

“Though limited by the relative lack of archeological evidence for early settlers across the Americas, these cranial patterns suggest the presence of at least two morphologically different human groups living separately in Mexico during this shift from the Pleistocene to the Holocene,” the researchers said.

“The Tulum skeletons indicate that either more than one group of people reached the American continent first, or that there was enough time for a small group of early settlers who lived isolated on the Yucatan peninsula to develop different skull morphology.”

“The early settlement history of America thus seems to be more complex and, moreover, to have occurred at an earlier time than previously assumed.”

The research was published in the journal PLoS ONE.

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W. Stinnesbeck et al. 2020. New evidence for an early settlement of the Yucatán Peninsula, Mexico: The Chan Hol 3 woman and her meaning for the Peopling of the Americas. PLoS ONE 15 (2): e0227984; doi: 10.1371/journal.pone.0227984

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