A sequence of fossil footprints discovered in New Mexico, United States, has offered strong evidence that humans were present in North America during the Last Glacial Maximum, at least 20,000 years ago – far earlier than previously thought.
How and when the first humans migrated into the Americas is hotly contested. Viable routes into the continent were believed to have been constrained by the environmental conditions of the Last Glacial Maximum, which lasted from 26,500 to 19,000 years ago. Popular migration theories hold that the earliest Americans traversed an ice-free corridor through western Canada c. 11,000 BC, or skirted the Pacific Coast by boat.
According to a study, recently published in Science, a team of researchers excavated a series of 60 in situ human footprints pressed into seven layers of sediment along the ancient Lake Otero, which now forms part of the Alkali Flat in New Mexico’s White Sands National Park.
Seeds of the aquatic plant Ruppia cirrhosa were recovered from the associated sediment layers and radiocarbon dated, indicating that the tracks are between 23,000 and 21,000 years old.
Evidence of cultural artefacts and occupied sites dated to more than 25,000 years ago have previously been reported; however, their direct relation to humans has been controversial. As footprints have a fixed, primary depositional context, these tracks would present concrete evidence that humans reached North America before glacial advances closed the ice-free corridor and Pacific Coastal Route.
Further analysis also revealed that many of the tracks ‘appear to be those of teenagers and children; large adult footprints are less frequent.’
The authors suggest this may indicate a division of labour, in which the tasks of fetching and carrying were delegated to the younger group members, or could simply represent the ancient traces of children playing along the lakeshore.
Ichnofossils of Pleistocene megafauna, including mammoths and ground sloths, were also found in association with the prints. Consequently, the study emphasises how these dates not only contribute evidence to the antiquity of human occupation of the Americas, but extend the coexistence of megafauna and the earliest settlers.
This could open discussion concerning a possible human role in megafauna extinctions previously thought to predate the arrival of the first Americans.
The research was conducted through collaboration between the US Geological Survey, White Sands National Park, the National Park Service, and the Universities of Bournemouth, Arizona, and Cornell.