Footprints of migration into the Americas

The story is all over the web, as confirmed by Google and Technorati searches, but few details are available. The best story I've seen yet is at Nature news:

Researchers think they may have found footprints in southern Mexico that mark the oldest evidence for the presence of humans in the Americas.
The impressions, preserved in volcanic ash outside the city of Puebla, have been dated to about 40,000 years ago, beating the oldest accepted evidence of humans in the Americas by some 25,000 years. If proven, the prints would lend support to controversial theories that people reached this land much earlier than previously thought.
The researchers themselves say more work needs to be done to confirm that they have found the mark of human steps. "I believe they are footprints," says geoarchaeologist Silvia Gonzalez of Liverpool John Moores University, UK, who is originally from Mexico. "But we are being cautious, as we need to do more work."

The research is to be published in Quaternary Science Review, but is not available yet. The news stories all agree in noting that the date comes from shell and from direct dating of overlying ash layers. Nature makes a point of skepticism about the footprints themselves, an aspect I've not seen yet in other accounts. The pictures accompanying the stories certainly look like human footprints, but I would expect them to pick the most human-looking ones for the closeup.

I looked for information about the lead researcher, Silvia Gonzalez (John Moores University). She has done a lot of work in geoarchaeology, including some previous work on footprints. Her last project, described by Discovery Channel News focused on the craniometrics of early Americans, and concluded that multiple migrations may have happened. The footprints certainly fit into that pattern.

There really isn't enough information here to make a reasoned opinion possible, so I guess we'll wait and see.

Other stories:

New Scientist
Telegraph (UK)
Technorati search
Google News