GPR Imaging Unlocks Images of the Pleistocene Period

Posted: 2020-1-23

Source: Nature

https://www.nat...598-019-52996-8

Footprint evidence of human-megafauna interactions remains extremely rare in the archaeological and palaeontological records. Recent work suggests ancient playa environments may hold such evidence, though the prints may not be visible. These so-called "ghost tracks" comprise a rich archive of biomechanical and behavioral data that remains mostly unexplored. Here we present evidence for the successful detection and 3-D imaging of such footprints via ground-penetrating radar (GPR), including co-associated mammoth and human prints. Using GPR we have found that track density and faunal diversity may be much greater than realized by the unaided human eye. Our data further suggests that detectable subsurface consolidation below mammoth tracks correlates with typical plantar pressure patterns from extant elephants. This opens future potential for more sophisticated biomechanical studies on the footprints of other extinct land vertebrates. Our approach allows rapid detection and documentation of footprints while enhancing the data available from these fossil archives.

Introduction

Trace fossils in the form of footprints (tracks) occur more frequently in the palaeontological and archaeological records than is commonly assumed. Holocene and Plio-Pleistocene examples have been described at an increasing number of sites and are found primarily in unlithified, erodible substrates1,2,3,4,5. Footprints provide evidence of an animal’s presence, pedal anatomy, abundance, co-association with other animals and behavioral ecology, and have been used to infer not only body size and mass, but also pedal anatomy and biomechanics6. At some locations, especially in the American southwest, these important yet delicate fossils may hold the key to unanswered questions about human behavior during the upper Pleistocene, particularly those related to hunting activity, with footprints offering access to predator-prey interactions outside the more typical "site" locus of a kill or camp7. How researchers detect and record fossil footprints is a burgeoning area of method development in contemporary ichnology8,9,10,11, and crucial to both maximizing the information yielded and also preserving these fragile traces of the past12. Former lake beds and playa sites, which occur extensively across the Americas and in parts of Africa, have the potential to hold these latent ichnological archives.

Here we present findings from White Sands National Monument (WHSA), New Mexico, USA. Our work demonstrates the effectiveness and efficiency of non-destructive GPR for detecting and documenting fossil footprints in soft sediments, including human tracks. Ichnofossils of extinct Rancholabrean fauna occur widely at WHSA and include tracks of Proboscidea (mammoth), Folivora (ground sloth), Carnivora (canid and felid), and Artiodactyla (bovid and camelid), as well as humans. They occur on an extensive gypsum playa (Alkali Flat, Fig. 1), the erosional relict of ancient Lake Otero, dating from the Upper Pleistocene. The sheer number of tracks, tens of thousands extending over large areas, allows animal and human-animal interactions via true ‘paleo-tracking’ to be deduced7. This valuable resource however is only intermittently and partially visible at the surface during specific moisture/salt conditions, and when visible may be covered quickly by drifting sand. The occasionally visible tracks are therefore known colloquially as ‘ghost tracks’. Given the scale of the site the resource management challenges are considerable.

Read the full article at Nature.com.