3-D radar imaging unlocks the untapped behavioral and biomechanical archive of Pleistocene ghost tracks

Thomas M Urban,Matteo Belvedere,Daniel Odess,Matthew R Bennett,Sally C Reynolds,Sturt W Manning,Vincent L Santucci,David Bustos

doi:10.1038/s41598-019-52996-8

Thomas M Urban, Matteo Belvedere + Show 6 more

Open Access

https://doi.org/10.1038/s41598-019-52996-8

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Abstract

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.

Highlights

Trace fossils in the form of footprints occur more frequently in the palaeontological and archaeological records than is commonly assumed
Our work demonstrates the effectiveness and efficiency of non-destructive ground-penetrating radar (GPR) for detecting and documenting fossil footprints in soft sediments, including human tracks
We found that GPR (1) allows rapid detection and 3-D recording of multiple species, including humans; and (2) provides non-destructive information on conditions beneath the track of larger fauna, from which we suggest biomechanical inferences may be drawn

Summary

Introduction

Trace fossils in the form of footprints (tracks) occur more frequently in the palaeontological and archaeological records than is commonly assumed. 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 deduced[7] This valuable resource is only intermittently and partially visible at the surface during specific moisture/salt conditions, and when visible may be covered quickly by drifting sand. Figure 4. 3-D perspective-view GPR results at various depths revealing hidden tracks and volumetric variations including sub-track consolidation. (a) Just beneath the surface (0–5 cm). (b) 5–10 cm of surface clipped. (c) 10–15 cm of surface clipped. (d) A photograph of an excavated human print (left) shown beside a close-up view of the corresponding GPR anomaly (right) at a depth of 5–10 cm, collected prior to excavation

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