Ground-Penetrating Radar Reveals Ice-Age Human and Animal Footprints in New Mexico

‘Ghost’ fossilized footprints of human, mammoths, giant sloths and other Pleistocene creatures discovered at the White Sands National Monument in New Mexico reveal a wealth of information about how humans and the ancient animals moved and interacted with each other 12,000 years ago.

Photographs of the study site at the White Sands National Monument, New Mexico: (a) ‘ghost tracks’ – the surface expression of the tracks is poor as can be seen from the image and they can only be seen under specific moisture and salt conditions; scale bar – 500 mm from target to target; (b) tracks at the study site excavated to reveal both human and mammoth tracks; (c) ground-penetrating radar (GPR) equipment used in this study; (d) gridded foam mats used to protect the surface during the GPR survey; (e) excavated human tracks at the study site. Image credit: Urban et al, doi: 10.1038/s41598-019-52996-8.

Ground-penetrating radar is a nondestructive method that allows researchers to access hidden information without the need for excavation.

The sensor — a kind of antenna — is dragged over the surface, sending a radio wave into the ground. The signal that bounces back gives a picture of what’s under the surface.

“We never thought to look under footprints. But it turns out that the sediment itself has a memory that records the effects of the animal’s weight and momentum in a beautiful way,” said Dr. Thomas Urban, a research scientist in the Department of Classics and Cornell Tree Ring Laboratory at Cornell University.

“It gives us a way to understand the biomechanics of extinct fauna that we never had before.”

Dr. Urban and his colleagues from Cornell University, Bournemouth University and the National Park Service examined the footprints of humans, mammoths, giant sloths, canids, felids, bovids and camelids in the White Sands National Monument in New Mexico.

Using ground-penetrating radar, they were able to resolve 96% of the human tracks in the area under investigation, as well as all of the larger vertebrate tracks.

The fossilized footprints at the White Sands National Monument, New Mexico: (a) the principal tracks and trackways observed at the study site which are split into Location-1 and Location-2 (shown in true spatial relationship); (b) GPR amplitude slice; human prints that were excavated and used for analysis are indicated with (+) while an unexcavated sloth trackway (identified in subsequent fieldwork) is indicated with (x). Image credit: Urban et al, doi: 10.1038/s41598-019-52996-8.

“But there are bigger implications than just this case study,” Dr. Urban said.

“The technique could possibly be applied to many other fossilized footprint sites around the world, potentially including those of dinosaurs.”

“We have already successfully tested the method more broadly at multiple locations within White Sands.”

“While these ‘ghost’ footprints can become invisible for a short time after rain and when conditions are just right, now, using geophysics methods, they can be recorded, traced and investigated in 3D to reveal Pleistocene animal and human interactions, history and mechanics in genuinely exciting new ways,” said Professor Sturt Manning, also from the Department of Classics and Cornell Tree Ring Laboratory at Cornell University.

The study was published November 11, 2019 in the journal Scientific Reports.

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T.M. Urban et al. 2019. 3-D radar imaging unlocks the untapped behavioral and biomechanical archive of Pleistocene ghost tracks. Sci Rep 9, 16470; doi: 10.1038/s41598-019-52996-8