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EFCHED

Human dispersals and environmental controls during the Late Pleistocene/Early Holocene in Mexico: implications for the peopling of the Americas

We set ourselves the following objectives in our research in central Mexico:

  1. To test the affinities and evolution of early humans in Mexico in the context of the archaeology and environmental reconstruction in central Mexico during the Late Pleistocene and Early Holocene.

  2. To integrate environmental and archaeological data using stratigraphy, palaeoclimatic proxies and detailed chronology (14C, Uranium series, ESR, thermoluminescence, tephra studies) from recently excavated sites (Tepexpan, Tocuila, Tlapacoya in the Basin of Mexico) and from new discovered sites (Valsequillo Basin in Puebla State).

  3. To create a database of biological data on Mexican Palaeoamerican populations using craniofacial analysis and ancient DNA studies.

Four of our major findings

1. The recovery of ancient DNA from several early Holocene human skeletons dated to approximately 7.5ka, and from the Pericue Indians from southern Baja California from between 2.5ka and 500 years ago, indicates a general geographic origin from Central and South-East Asia for these human populations.

Information from the craniometric database shows that Late Pleistocene humans, including Peñon Woman, Chimalhuacan Man and Metro Man, were morphologically different to Early Holocene populations from Mexico.

An important point is that the Pericue Indians from southern Baja (a relict Indian population which became extinct during the 18th Century) are morphologically distinct from the Late Pleistocene skeletons from Mexico.

They were a very unique population, whose closest affinities were among other Amerindian hunter-gatherers, including Eskimos.

Location of some important skeletons studied during the project

Images: Location of some important skeletons studied during the project: a) Late Pleistocene Mexican Paleoindian, Peñon Woman III from Mexico City (12.755ka) b) Early Holocene,Texcal Man, Valsequillo, Puebla (9.5ka) c) Pericue Indian from Baja California Peninsula (18th century).

They have been considered in the past to be direct descendents from the earliest Americans, with Australian or Melanesian affinities, however our results indicate that they are very different morphologically and their DNA belongs to the normal haplogroups obtained from Modern Native American Indians (A2, C1, B4a1, B2, and D).

2. Volcanic activity has played a very important controlling part in human migration and the extinction of megafauna in central Mexico, including mammoths, sabre toothed cats, and camels.

This activity has partly obscured the environmental record from central Mexico during the Late Pleistocene to Early Holocene. Two of the oldest Mexican human skeletons, Metro Man and Chimalhuacan Man were found in association with the Upper Toluca Pumice Plinian eruption which occurred approximately 10.5ka, and which is associated with large concentrations of megafaunal remains. After this major volcanic event in central Mexico the megafauna became extinct.

3. Isotope and diatom analysis of a 4m section close to the site of Tepexpan Man suggests Lake Texcoco had highly variable salinity and alkalinity over at least the last 20 thousand years and it is likely that the marginal areas dried out periodically during the Late Pleistocene. Moreover there is evidence for progressive drying through the Holocene period.

Human footprint preserved on volcanic ash from the Valsequillo Basin Mexico (>40ka). Image: S Gonzalez4. The discovery of human and animal footprints preserved in volcanic ash in the Valsequillo Basin, Puebla in Mexico, with an age of at least 40ka, challenges the established model for the colonisation of the Americas.

There is a need to continue with this study into the origin and dating of this site.

To this end, we have been awarded new funding from NERC for the next three years to try to solve the problems associated with the complicated geoarchaeology and geology of the Valsequillo Basin.

This summary was compiled by Silvia Gonzalez (Liverpool John Moores), who is also the PI for this project.

The research was undertaken in collaboration with:

David Huddart (Liverpool John Moores), Marta Mirazon Lahr (LCHES, Cambridge), Matthew Bennett (Bournemouth), Phillip Endicott (Oxford), Jean Luc-Schwenninger (Oxford), Tom Higham (Oxford), Christopher Bronk-Ramsey (Oxford), Alistair Pike (Bristol), Angela Lamb (NERC, Keyworth), Melanie Leng (NERC, Keyworth), Sarah Metcalfe (Nottingham), Rhiannon Stevens (Nottingham), Alberto Gonzalez Huesca (Instituto de Geofisica, Mexico), Maestro Jose Concepcion Jimenez-Lopez (Direccion de Antropologia Fisica, Mexico), Anthrop. Fis. Alfonso Rosales Lopez and Anthrop. Fis. Leticia Sanchez Garcia (INAH, La Paz, Baja California Sur.