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


Abstract and Figures

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.
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3-D radar imaging unlocks
the untapped behavioral and
biomechanical archive of
Pleistocene ghost tracks
Thomas M. Urban1*, Matthew R. Bennett
2*, David Bustos3, Sturt W. Manning1,
Sally C. Reynolds2, Matteo Belvedere
2, Daniel Odess4 & Vincent L. Santucci5
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.
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 increas-
ing number of sites and are found primarily in unlithied, erodible substrates15. 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 loca-
tions, 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 oering 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
ichnology811, 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 ndings from White Sands National Monument (WHSA), New Mexico, USA. Our work
demonstrates the eectiveness and eciency of non-destructive GPR for detecting and documenting fossil foot-
prints in so 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. ey occur on an extensive gypsum playa (Alkali
Flat, Fig.1), the erosional relict of ancient Lake Otero, dating from the Upper Pleistocene. e sheer number
of tracks, tens of thousands extending over large areas, allows animal and human-animal interactions via true
‘paleo-tracking’ to be deduced7. is valuable resource however is only intermittently and partially visible at the
surface during specic moisture/salt conditions, and when visible may be covered quickly by driing sand. e
1Department of Classics and Cornell Tree Ring Laboratory, Cornell University, Ithaca, NY, 14853-3201, USA. 2Institute
for Studies in Landscapes and Human Evolution, Bournemouth University, Poole, BH12 5BB, UK. 3National Park
Service, White Sands National Monument, P.O. Box 1086, Holloman AFB, NM, 88330, USA. 4National Park Service,
Cultural Resources Directorate, Washington, DC, 20240, USA. 5National Park Service, Geologic Resources Division,
Washington, DC, 20240, USA. *email:;
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occasionally visible tracks are therefore known colloquially as ‘ghost tracks. Given the scale of the site the resource
management challenges are considerable.
e aims of the GPR survey were: (1) to test whether animal tracks, including those of humans, could be
detected and usefully resolved with this method, including evaluating the potential of GPR to unpack multiple
superimposed track-making events at dierent horizons; and (2) to explore the 3-D subsurface below larger ani-
mal tracks, including how these may be altered by the track-making event. In both cases the geophysical survey
was undertaken prior to any excavation or surface preparation with the exception of the removal of loose surface
pebbles in order to ensure a smooth traverse for the antenna to improve data quality. 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.
Site. On the eastern side of Alkali Flat there is a double trackway of human prints that extends for over 800 m.
is trackway is currently under investigation and appears to represent a single individual walking rst north and
then returning south aer an unknown interval. e two trackways are parallel but o-set by a distance varying
between one and two metres. Individual tracks are visible at the surface under appropriate moisture conditions
Figure 1. Map showing the White Sands National Monument, Alkali Flat, and the study site. Digital elevation
model is from Shuttle Radar Topography Mission 1 arc-second data with the surcial geology taken from U.S.
Geographical Survey maps (relief in .). Note the precise location of the study site is withheld in accordance
with the requirements of the National Parks Service (NPS) compliance with U.S. law. Interested parties may
apply to the NPS for the specic site location. Data from and map made with
ArcMap 10.1 (
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and sections of the trackway have been excavated (Fig.2). e GPR survey reported here was undertaken along
this trackway at a location where a series of proboscidean tracks, presumably Mammuthus columbi13, cross in a
westerly direction perpendicular to the two human trackways (Fig.3a). Deformation in front of one of the mam-
moth’s manus tracks partially closed two tracks of the northbound human trackway, showing that the mammoth
crossed that human trackway aer it was made. In turn, a single human footprint of the southbound human
trackway is superimposed on a mammoth manus track, showing that the human crossed the mammoth track on
Figure 2. Photographs of the study site at WHSA. (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 specic 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) GPR equipment used in this study. (d) Gridded foam mats used to protect the surface during the GPR survey
following Jacob et al.30. (e) Excavated human tracks at the study site.
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the return. is provides a clear sequence for the tracks, demonstrating co-association. ough the time-lapse
between each of the three track-making events is unknown, the mammoth track is temporally book-ended by
the two human trackways (believed to be the same individual). Current N. American dates for an initial human
presence along with dates for mammoth extinction on the continent support a late Pleistocene biostratigraphical
dating of the tracks at WHSA7,14.
Figure 3. (a) e 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 (2.0 to 4.0 ns). Human prints that
were excavated and used for analysis are indicated with (+) while an unexcavated sloth trackway (identied in
subsequent eldwork) is indicated with (x).
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Location-1: e results of our GPR survey (Fig.3; see Material and Methods section for parameters) demonstrate
that human footprints can be identied with GPR with horizontal resolution sucient to estimate stride-length
(Fig.4). Table1 compares the stride and step estimates measured aer excavation to those estimated from GPR
data at Location-1. e results are broadly comparable and signicantly show similar variance. e GPR survey
only failed to identity one human track out of the 27 present at Location-1. e survey line interval of 12.5 cm
meant that occasionally a human track could be entirely missed or insuciently sampled, suggesting that 100%
successful detection could be achieved thorough minor modications to the survey design. Importantly, the
survey was able to resolve targets for excavation that are not visible at the surface (Figs3, 4). Such areas warrant
further investigation in the future.
Further, certain 3-D properties of the human footprints also appear to be resolvable within the GPR data, with
the prints exhibiting detectable variation with depth (Fig.4). Detailed topological information for the plantar
surface of human tracks is beyond the resolution of the present data set, but for the majority of tracks visible, both
the presence and relative depth could be inferred from the GPR data. Precise GPR velocity estimates would be
needed to provide accurate absolute depth estimates from two-way travel times. Comparison of excavation depths
of tracks with GPR data, however, suggests a velocity of 0.05–0.06 m/ns, a normal range for a moist, ne-grained
substrate. e potential here for future development is clear and with higher antenna frequencies, closer survey
line spacing, and transillumination (multi-directional data collection), improved 3D resolution should be achiev-
able, including potentially topological information for the plantar surface of smaller tracks, (e.g., human ones).
Location-2: Both mammoth and human tracks have been identied and excavated at Location-2, along with
a range of other potential tracks which have yet to be excavated. For example the anomalies at the western side
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 (le) shown beside a
close-up view of the corresponding GPR anomaly (right) at a depth of 5–10 cm, collected prior to excavation.
GPR Derived (mm) Field Derived (mm)
Mean Standard
Deviation NMean Standard
Deviation N
S Bound Foot Size 281.23 2.38 8 266.78 8.31 15
N Bound Foot Size 281.8 2.13 12 257.02 8.02 13
North Step Length 804.7 1.53 12 712.52 2.89 16
South Step Length 798.02 2.62 10 693.14 2.22 14
North Stride Length 1463.33 2.43 12 1422.02 4.21 16
South Stride Length 1451 4.35 9 1404.78 4.18 14
Table 1. Human foot size, stride and step length calculations derived via the GPR survey for Location 1. e
eld derived track data are based on eld survey of excavated tracks using a grid and o-set method, while the
GPR derived track data are based on GPR anomalies marked for Location 1 (Fig.3b).
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of Location-2 (Figs3, 4) provided future excavation targets that were not visible in any form at the time of the
survey. ese were later determined to be sloth tracks aer becoming partially visible following a period of rain
(though interpretation is preliminary as these remain unexcavated) (Fig.5). e largest of the mammoth foot-
prints (837 × 714 mm; Fig.3, T1) has been excavated (Fig.6c). Deformation in front of this track partially closed
the northbound human tracks 200–300 mm to the west. e track was subsequently overprinted by one of the
south bound human tracks (Fig.6a,c). e exact outline of the mammoth track, believed to be made by a manus,
is not well-dened but by analogy with extant Loxodonta africana would most likely correspond to a mature (>50
years) bull with a potential shoulder height of over 3 metres1517.
Deformation structures below and around mammoth tracks elsewhere at WHSA have been investigated
using a series of hand-dug trenches. Deformation occurs initially through loading below the anterior part of the
track-maker’s foot, followed by a posterior-directed shear component as toe-o occurs, before nally pressure
release induces uid escape. e specic structures present vary with sub-surface stratigraphy but are always
driven by anterior loading. ese observations compare well to mean plantar pressure data obtained for African
elephants (Loxodonta africana) trained to walk across force plates18. For African elephants mean plantar pressure
peaks in the lateral and distal parts of the foot19,20 which corresponds to areas of maximum sub-track deforma-
tion18. Figure6 shows two depth slices through location-2; the bottom or near bottom of the tracks appear in
Fig.6a (4 to 6 ns), also showing a human print in track 1 (T1), which is further illustrated in Fig.6c. At depths
just below (6 to 8 ns) shown in Fig.6b, GPR amplitude variations are visible across the mammoth tracks, with
higher amplitudes in the anterior and lateral sides of individual tracks. is layer corresponds to that immediately
below the surface of the true track. is is broadly similar to the plantar pressure observed by Panagiotopoulou
et al.20 for extant African elephants (Loxodonta africana; Fig.6d). In vertical cross section (Fig.7a) the amplitude
pattern continuing below the tracks has a hook-shape with the apex at the anterior side of the track; that is in
the direction of travel. Bennett et al.18 have shown that this corresponds to an area of peak deformation below
mammoth tracks at WHSA due to the biomechanics of the locomotion. e patterns reported here are consist-
ent across all the mammoth tracks in the surveyed area (Fig.7a,b), with a consistent 3-D structure (Fig.7b). We
suggest that variations in amplitude with depth are detecting sediment compression consistent with the plantar
pressure records for extant Proboscidea. Deformation by the weight-load of the mammoth would cause compres-
sion of the substrate and in theory increase electrical permittivity in the compacted sediment, by reducing the
low-permittivity air-fraction per unit volume. In turn this should increase the surface area per unit volume, along
with associated soil moisture, and the net result is a slight reduction in radar velocity resulting in higher ampli-
tude GPR reections where the compacted substrate occurs. We suggest therefore that the GPR data is picking up
some semblance of a plantar pressure record for the extinct mammoth.
We have recently reported on the use of magnetic sensors to detect mammoth foot prints at WHSA11 and the lim-
itations reported in that work are overcome by the use of GPR in the work reported here. First, the magnetometer
is less reliable in detecting smaller tracks such as those made by humans. Human tracks are only detected if the
base of the true track (plantar contact surface) is deeply impressed relative to the surface (>200 mm). Track depth
and therefore ll-volume appears critical. Mammoth tracks are always detected, however. e instrument is also
subject to intermittent external electromagnetic noise from nearby military activity which is specic to WHSA
but none the less important. Lastly, magnetic data are not well-suited to providing 3D data, which are especially
valuable in instances where tracks comprise a palimpsest of overwritten track-making events7. It does, however,
Figure 5. Close up 3-D GPR perspective of mammoth track 1 (T 1) along with human and sloth tracks. e
presence of sloth tracks was not known prior to the GPR survey and was later conrmed when the prints
became partially visible aer a period of precipitation. e sloth prints remain unexcavated at this location.
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Figure 6. Location- 2 GPR slices at given travel-times with comparative data. Each 2 ns slice represents
an estimated thickness of 5–6 cm. (a) Bottom or near bottom of true tracks, with a superimposed human
footprint seen in the perimeter of T1. (b) Slice immediately beneath the tracks yield amplitude patterns similar
to observed plantar pressure data. (c) Depths derived from excavation of the largest mammoth track (T1)
with human print. (d) Mean plantar pressure data from African elephants (Loxodonta africana), curtesy of
Panagiotopoulou et al.20. is based on the mean records of ve elephants and the methods are described in
Panagiotopoulou et al.20. Means for each of the ve animals are based on between 1 and 24 pressure records.
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oer a method of broader prospection that could be applied where there are surface-evident tracks, or for gen-
eral reconnaissance of suspected track locations, particularly for larger fauna. For example, shore normal survey
transects at playas and former lake beds should in theory identify tracks by analogy with the types of distribution
described in recent eld observations21,22.
GPR surveying, on the other hand, was able to resolve 96% of the human tracks present and all of the larger
vertebrates. Results suggest, however, that with rened survey design all human tracks could be detected simply
as a matter of scaling. e tracks are detectable due to the inll which exhibits higher amplitude GPR reections
than the surrounding substrate. is contrast is likely due to stronger electrical properties within the tracks than
in the surrounding sediment matrix and the higher electrical permittivity probably reects a dierence in water
content due to textural contrasts. In this case, the GPR response suggests that the substrate lling the prints holds
more moisture than the surrounding sediment even under dry conditions, something that is evident when the
tracks are excavated.
However, it is the subsurface amplitude variations below the mammoth tracks that we consider to be of par-
ticular signicance. ese are manifest as areas of higher amplitude that likely have a dierent explanation from
that postulated above for the prints themselves. With the sub-track anomalies, it is not newly introduced sedi-
ments that explain the reections, but we theorize this is caused by compression of the existing sediments which
alters the electrical permittivity. e similarity between the plantar pressure records of extant elephants and the
areas of anomalous high amplitude immediately beneath the area the footprint is striking, and suggests GPR
is detecting a plantar pressure record below the mammoth track due, we suggest, to compression of sub-track
sediment. is proposed compression pattern was not visible with excavation, and appears at least at the tested
location to be only discernible with GPR.
Conventional biomechanical inference from footprints oen relies on a pressure to depth substitution in
which deeper areas reect higher plantar pressures. is has been found to only hold however for shallow tracks
in the case of human footprints23, but is something that is rarely questioned in ichnological studies for larger
or extinct trackmakers. Other experimental studies that have examined this relationship in modern human
footprints have also found the relationship to be tenuous24,25. ere are many reasons why strain may not be
solely accommodated by footprint volume (i.e. depth), and moreover taphonomic processes can rapidly modify
observed footprint topology obscuring any relationship26. For example, the topology of the manus track (T 1) in
Location-2 (Figs2b, 6c) does not reect the sub-surface pressure anomalies (Fig.6b). Our results suggest that
irrespective of variation in track depth, a pressure record is encoded via sub-track sediment properties (likely
compression), and in some cases this is independent of the track and its topology.
Taken to its logical extent, potentially thousands of plantar pressure records are waiting therefore to be col-
lected at sites like WHSA and elsewhere in North America1,7 and Namibia26,27 without the need for tracks to be
excavated. e potential here to enhance our understanding of the biomechanics of extinct animals may yield
important information for developing more sophisticated biomechanical models from and for extant elephants
and by analogy from anatomically similar dinosaurs such as sauropods28. It may also improve the quality of geo-
technical models applied to both elephants and mammoth tracks since it would allow estimated plantar pressures
to be used rather than as now uniform indenters29.
At sites such as White Sands, a new data archive in the form of a rare and unique ichnological record is there
to be unlocked. Accessing this record in all conditions using non-destructive geophysical methods has signi-
cant implications for the eectiveness of research, conservation and resource management at White Sands and
Figure 7. (a) GPR fence diagram showing amplitude variations below the mammoth tracks. Note the ‘hook-
shaped’ structure indicated by the white arrows consistently points in the mammoth’s travel direction. (b)
GPR amplitude isosurface from T3 rotated to show several perspectives of the 3-D structure of the sub-track
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beyond. Knowing where unexcavated tracks are located is a key step in management, monitoring and prioritiza-
tion for resource conservation, especially since excavation leads ultimately to loss. With higher resolution surveys
possible, we anticipate in the future that excavation may not always be necessary on an extensive scale for study of
such tracks. Unpublished experimentation with dierent antenna frequencies has shown that the most consistent
results are obtained with a 250 Hz antenna, at least at WHSA where the substrate exhibits high electrical conduc-
tivity, and that enhanced resolution can be obtained by increasing the grid resolution and combining perpen-
dicular lines. Our unpublished tests with higher antenna frequencies (500 MHz and 1 GHz) show some promise
in obtaining ner detail on smaller tracks in some cases, such as those of humans, which will be the subject of a
future paper. Irrespective of this, the power of the approach lies not just in imaging buried track topology but in
the additional information obtained on sub-track compression. So beyond the immediate and obvious benets
of locating and imaging the tracks themselves, GPR oers ancillary information on pressure and momentum due
to detectable eects on sediments below and around the tracks. Resolvable and consistent trends in the GPR data
suggest that each footprint has an associated sub-structure caused by compaction of surrounding sediment. Initial
ndings suggest that this is related both to compression from the weight of the track-maker, along with shearing
forces from the momentum of the trackmaker. erefore, information about the size and direction of the track-
maker are likely exhibited in the broader GPR patterns, oering a previously uninvestigated avenue into the bio-
mechanics of extinct species such as the mammoth. is has implications for the study of fossil tracks well beyond
White Sands, including the possibility that under suitable conditions these sub-track compaction contrasts could
be retained aer lithication and therefore be present below the tracks of dinosaurs or other extinct vertebrates.
Materials and Methods
e study site was selected from the total length of the double trackway (>800 m) on the basis of having a com-
bination of dierent animal tracks. e area to be surveyed was staked out and photographed before and aer
excavation using a monopole. Ortho-rectied photo mosaics were made using Agiso Photoscan Pro (v. 1.5.0;
www.agiso.com). Tracks were excavated with brushes and dental picks. Once excavated 3D models of the tracks
were made using DigTrace ( which uses OpenMVG an open-source structure from motion
photogrammetry engine. Plantar pressure records were proved by Olga Panagiotopoulou19. is consisted of
multiple plantar pressure records for each foot of 5 African elephants collected using a Zebris Medical plantar
pressure platform. Means for each foot were co-registered and combined to produce the data.
GPR equipment included a Noggin series 250 MHz unit by Sensors and Soware Inc. (https://www.senso.
ca/products/noggin/overview/). Instrument parameters included a 120 nanosecond time-window, 8 stacks, and
5 cm trace interval. GPR data processing was done with EKKO_View; EKKO_mapper (Sensors and Soware Inc.)
and included dewow, gain, and envelope. GPR images were produced with VOXLER 4 and Surfer 14 by Golden
Soware Inc. www.goldenso
10 mm thick interlocking foam mats were used to cover the site in sections for the geophysical survey. ese
were pre-marked with lines at 12.5 cm intervals. e GPR line spacing of 12.5 cm gave coverage of 18 m²/hr, for
parallel transects, inclusive of setting up and moving the protective foam pads. Although intensive, this provided
a fairly rapid and non-destructive option to gather information where tracks are suspected. Once excavated, these
tracks begin to degrade immediately and need to be digitized in 3D (via photogrammetry, or optical laser scan-
ner), or physically cast for conservation purposes. By comparison, excavation and 3D capture, via photogramme-
try, of Location-1 took approximately 26 hours or 0.15 m²/hr.
Data availability
Data related to this paper may be requested from the authors.
Received: 27 February 2019; Accepted: 25 October 2019;
Published: xx xx xxxx
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is work was funding by a cooperative agreement between White Sands National Monument and Cornell
University. Views and conclusions are those of the authors and do not necessarily reect policies of the National
Park Service (NPS). MRB acknowledges Natural Environment Research Council grants (NE/H004246/1 and NE/
M021459/1). e authors would like to extend their sincere thanks to Olga Panagiotopoulou for providing access
to the African elephant plantar pressure data.
Author contributions
e eldwork was undertaken by T.U., D.B., M.R.B., V.S. and D.O. in April 2018. Geophysical processing was
undertaken by T.U. M.R.B. was responsible for the links to plantar pressure and wrote much of the manuscript
with T.U. M.B., S.M. and S.C.R. contributed to the write-up or added specic perspectives or insight relevant to
their areas of expertise.
Competing interests
e authors declare no competing interests.
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Correspondence and requests for materials should be addressed to T.M.U. or M.R.B.
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... High-resolution geophysics has recently become of interest even for archaeological and paleontological studies, especially for the reconstruction of human and megafauna interactions by means of their fossil footprints. Urban et al. [120] successfully detected and imaged these kinds of footprints, even in cases of simultaneous presence (specifically, sloths, humans and mammoths), using GPR (central frequency 250 MHz, inter-line distance 12.5 cm). They occurred on an extensive gypsum playa, the erosional relict of ancient Lake Otero, dating from the Upper Pleistocene, and were intermittently and partially covered by drifting sand. ...
... Close up 3D GPR perspective of mammoth track 1 (T 1) along with human and sloth tracks. The presence of sloth tracks was not known prior to the GPR survey and was later confirmed when the prints became partially visible after a period of precipitation (a) [120]. Three-dimensional trackway surface generated with horizon detection methods applied to a very high-resolution GPR dataset and the same result following subtraction of the trend surface (b) [121]. ...
Full-text available
Applications of non-invasive sensing techniques to investigate the internal structure and surface of precious and delicate objects represent a very important and consolidated research field in the scientific domain of cultural heritage knowledge and conservation. The present article is the first of three reviews focused on contact and non-contact imaging techniques applied to surveying cultural heritage at micro- (i.e., manufacts), meso- (sites) and macro-scales (landscapes). The capability to infer variations in geometrical and physical properties across the inspected surfaces or volumes is the unifying factor of these techniques, allowing scientists to discover new historical sites or to image their spatial extent and material features at different scales, from landscape to artifact. This first part concentrates on the micro-scale, i.e., inspection, study and characterization of small objects (ancient papers, paintings, statues, archaeological findings, architectural elements, etc.) from surface to internal properties.
... Generally speaking, however, the fossil track record of Proboscipeda panfamilia is essentially formed by footprints, trackways and undertracks (e.g. McDonald et al., 2007;Neto de Carvalho, 2009;Urban et al., 2019;Helm et al., 2021Helm et al., , 2022Neto de Carvalho et al., 2021). ...
... The gypsum lacustrine beds of Paleolake Otero in the Tularosa Basin of southern New Mexico contain suspected Late Pleistocene-age human footprints in possible association with extinct Ice Age megafauna tracks and trackways (Bennett et al., , 2020(Bennett et al., , 2021Bustos et al., 2018;Urban et al., 2019). Interestingly, unusual ball-like aggregations of plant materials occur on the eastern shoreline of the paleolake, occasionally in association with the tracks and trackways. ...
Full-text available
Ruppia cirrhosa (Ruppia) seed layers have been used to constrain the age of footprints along the eastern shoreline of Paleolake Otero in southern New Mexico to around 21,000–23,000 calibrated years before the present. However, there remain two unresolved questions that can affect the reliability of the age(s) of the footprints. First, what is the nature of the geological context of the seed layers? Second, did the hard‐water effect impact the accuracy of the radiocarbon dates? It has been argued that the dated Ruppia plants grew in situ in a very shallow, freshwater‐infused system that minimized the hard‐water effect. Many of these Ruppia seed layers contain ball‐like aggregations made of Ruppia plant materials. We provide new evidence that these balls and seed layers were introduced to the discovery site by high wind seiche events during Late Pleistocene thunderstorms. In our proposed site formation model, the Ruppia plants and seeds originated in deeper water settings outside the site, thus it is very likely that the hard‐water effect has impacted the accuracy of the radiocarbon dates. As such, the radiocarbon assays of Ruppia seeds previously used to date the prehistoric footprints along Paleolake Otero could be thousands of years too old.
... In recent years, the use of non-invasive geophysical and geomatic techniques has assumed an increasingly important role in the field of cultural heritage, especially by supporting conservation and restoration projects. Geophysical methods are very useful for assessing the presence of underground structures in preventive archeology at different scales [1][2][3][4][5][6]; addressing conservation and stability issues of architectural monuments by inspecting soil foundations; assessing the mechanical properties of structural elements [7][8][9][10][11][12][13]; and exploring internal and superficial structures of precious and delicate targets, such as statues, wall paintings and mosaics [7,[14][15][16][17][18]. Among these techniques, ground-penetrating radar (GPR) is widely used thanks to the miniaturization of the instrumentation, the high investigation resolution and the minimal impact on the analyzed surfaces. ...
Full-text available
The application of non-invasive geophysical techniques and digital surveys to explore cultural heritage is becoming a very important research field. The capability to detect inner and superficial changes in the inspected surfaces allows for imaging spatial inhomogeneity and material features and planning targeted conservation and restoration interventions. In this work, the results of a research project carried out on the famous Battle of Issus Mosaic, also known as the "Alexander Mosaic", are presented. It is a masterpiece of ancient art that was found in 1831 in the House of Faun, the most luxurious and spacious house in Pompeii. It is notable for its size (3.41 × 5.82 m), the quality of workmanship and the subject that represents the culminating phase of the battle between Alexander Magno's army and the Persian one of Darius. In 1916, it was moved inside the National Archaeological Museum of Naples, where the original horizontal location was changed with a vertical arrangement supported by an inner wooden structure, whose exact manufacture is unclear. Today, the mosaic is affected by important instability phenomena highlighted by the appearance of the significant detachment of tiles, superficial lesions and swelling of the surface. Given the important need to preserve it, a high-detail diagnostic study was realized through a digital survey and non-invasive geophysical surveys using ground-penetrating radar (GPR). The investigation was repeated after two years, in 2018 and 2020, with the aim of verifying the evolution of degradation. The work provided a high-resolution estimate of the state of the health of the mosaic and allowed for obtaining a three-dimensional reconstruction of the internal mosaic structure, including the formulation of hypotheses on the engineering supporting works of the twentieth century; this provides an essential tool for the imminent conservation project, which also implies restoring the original horizontal position.
... There is limited evidence for predation on giant ground sloths, either by Pleistocene humans; (1) North America -femur of Megalonyx jeffersonii with possible butchering marks (Redmond et al., 2012); and (2) South America -a Lestodon clavicle with putative marks from butchering (Arribas et al., 2001;Fariña and Castilla, 2007) and associated skeletons of Glossotherium and lithics (Vialou, 2003;Vialou et al., 2017). The putative co-occurrence of sloth and human tracks had been utilized to suggest hunting (Bustos et al., 2018, Urban et al., 2019 but Rachal et al. (2021) suggest that the trackways are not contemporaneous, but reflect humans crossing over re-exhumed, and much older, tracks of sloths (but see Bennett et al., 2021). Radiometric dates of Castrocopros support other evidence that there is less indication of survival of the megafauna into the Holocene in North America (Martin et al., 1985, fig. ...
Full-text available
An extensive record of desiccated coprolites of diverse Late Pleistocene taxa is preserved in caves of the American Southwest. These include 21 caves in Arizona, 12 in Utah, six in Texas, four in New Mexico and one in Nevada. The majority of the coprolites represent herbivores, which is extremely rare for coprofaunas. There are two distinct regions characterized by cave coprolites – a northern realm (northern Arizona and southeastern Utah) is characterized by diverse morphologies of coprolites, and a southern realm (southern New Mexico and West Texas) where caves usually yield only coprolites of ground sloths (Castrocopros martini) and coprolites of the packrat or woodrat Neotoma. The geographic distribution of the localities is governed by precipitation patterns and by the availability suitable cave-producing rock types. Desiccated coprolites can yield some of the highest quality radiocarbon dates, and these demonstrate extinctions of the megafauna between 11 and 12,000 yr B.P. in the terminal Pleistocene. Macro-botanical specimens and pollen provide important evidence of individual diet and the local ecosystem. Castrocopros martini and coprolites of Neotoma are widespread, whereas coprolites of bighorn sheep Ovis canadensis and the extinct mountain goat Oreamnos harringtoni are common in caves in Arizona and Utah, but they are absent from Nevada and New Mexico. Coprolites of a large ruminant (Suaviocopros harrisi igen. et isp. nov.) and mammoths (Mammuthocopros allenorum) are restricted to Utah, which likely relates to topography. We advocate the discontinuation of the term “dung” for the cave coprolites and the use of binomial ichnotaxonomy for Pleistocene coprolites.
... The deepest zone of the track corresponds to its anterior part following the typical rotation during the event foot on-toe off observed in extant elephants (see Fig. 3b, e for a MTS example). The pressure on the feet of elephants is greater on the distal ends of the lateral toes and increases outward from the centre of the foot 24,26,40,41 . This may leave prominent anterior nail impressions in the plastic substrate of Matalascañas for contemporary small and large tracks. ...
Full-text available
Tracks and trackways of newborns, calves and juveniles attributed to straight-tusked elephants were found in the MIS 5 site (Upper Pleistocene) known as the Matalascañas Trampled Surface (MTS) at Huelva, SW Spain. Evidence of a snapshot of social behaviour, especially parental care, can be determined from the concentration of elephant tracks and trackways, and especially from apparently contemporaneous converging trackways, of small juvenile and larger, presumably young adult female tracks. The size frequency of the tracks enabled us to infer body mass and age distribution of the animals that crossed the MTS. Comparisons of the MTS demographic frequency with the morphology of the fore- and hind limbs of extant and fossil proboscideans shed light into the reproductive ecology of the straight-tusked elephant, Palaeloxodon antiquus. The interdune pond habitat appeared to have been an important water and food resource for matriarchal herds of straight-tusked elephants and likely functioned as a reproductive habitat, with only the rare presence of adult and older males in the MTS. The preservation of this track record in across a paleosol surface, although heavily trampled by different animals, including Neanderthals, over a short time frame, permitted an exceptional view into short-term intraspecific trophic interactions occurring in the Last Interglacial coastal habitat. Therefore, it is hypothesized that Neanderthals visited MTS for hunting or scavenging on weakened or dead elephants, and more likely calves.
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A diverse quite of vertebrate traces covers beach, aeolian, and bay-side (deflation flats) surfaces along the NW Black Sea coast of Ukraine. These include avian, ungulate, and canid footprints, as well as mammal burrows (length >5 cm; depth ~2 cm). The preservation of biogenic structures is enhanced by rapid burial (low-energy sedimentation or event deposition), algal mat formation, and salt encrustation. Continuous high-frequency (800 MHz) ground-penetrating radar (GPR) imaging aided in visualizing subsurface sections of an active burrow complex within a beach-dune ridge. Images near an active fox burrow captured distinct subsurface anomalies (point-source hyperbolic diffractions) in the upper aeolian section above the water table. Unfilled tunnel sections are easily distinguished from buried roots and other targets based on signal velocity and polarity reversals relative to air-to-sediment response at the ground surface. The diffraction geometry (angle) is related to signal velocity, providing valuable information about relative saturation of the overlying substrate. Decimeter-scale deformation of shallow reflections may be attributed to tracking surfaces, with similar examples found immediately below modern surfaces affected by anthropogenic trampling. It is likely that muddy lagoonal tracking surfaces may be preserved under layers of sand (overwash or aeolian deposition) and, following saltwater expulsion, may be recognized in geophysical images as clear deformed paleo-surfaces. Heavy-mineral concentrations (e.g. magnetite-rich sand) are common for beach and dune horizons that have undergone reworking and such anomalies often accentuate physical and biogenic deformation structures. Due to moderate-to-high fraction of ferri- and paramagnetic minerals, these anomalies are also well-expressed in GPR images due to its electromagnetic signal response. A conceptual framework of trace preservation potential (taphonomy) and geophysical recognition (GPR) suitability is proposed for this coastal region, with implications to paleo-environmental reconstruction.
In this brief essay, the author critiques the dating and site-formation processes related to the ancient footprints recently reported by M. R. Bennett et al. (2021) in Science (373:1528–1531), and offers an alternative working hypothesis that the features could relate to Clovis, not pre-Clovis humans.
Early footsteps in the Americas Despite a plethora of archaeological research over the past century, the timing of human migration into the Americas is still far from resolved. In a study of exposed outcrops of Lake Otero in White Sands National Park in New Mexico, Bennett et al . reveal numerous human footprints dating to about 23,000 to 21,000 years ago. These finds indicate the presence of humans in North America for approximately two millennia during the Last Glacial Maximum south of the migratory barrier created by the ice sheets to the north. This timing coincided with a Northern Hemispheric abrupt warming event, Dansgaard-Oeschger event 2, which drew down lake levels and allowed humans and megafauna to walk on newly exposed surfaces, creating tracks that became preserved in the geologic record. —AMS
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The application of Ground Penetrating Radar (GPR) prospecting to the search of fossil structures, particularly using advanced techniques like Finite-difference time-domain (FDTD) modelling and GPR attribute analysis, is currently poorly exploited in paleontology. Here, we promote the use of such a GPR workflow at Bargiano (Umbria, central Italy), a unique paleontological site known for the discovery of cetacean skeletons, dolomitized sperm-whale cololites (Ambergrisichnu salleronae), and layered fossil assemblages. The study site is characterized by a very uneven topography shaping highly conductive clayey deposits, representing not exactly ideal conditions for GPR surveying. After generating models encompassing a real topography and variable electrical properties of media, we simulated buried fossil structures at variable depth with different size and geometry, using different operative frequencies. After obtaining information on the characteristics of reflections, investigation depth, and detectability, we provide a comparison with experimental data, also used to compute instantaneous amplitude and phase attributes. Upon depicting a peculiar GPR signature for our targets, we discuss the results in light of ground-truthing performed through trenching. Our workflow allowed us to restrict the excavation areas, extending the surface information in depth in a non-invasive way, and optimizing the field operations, necessary for the preservation of the study site.
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Complex processes in the settling of the Americas The expansion into the Americas by the ancestors of present day Native Americans has been difficult to tease apart from analyses of present day populations. To understand how humans diverged and spread across North and South America, Moreno-Mayar et al. sequenced 15 ancient human genomes from Alaska to Patagonia. Analysis of the oldest genomes suggests that there was an early split within Beringian populations, giving rise to the Northern and Southern lineages. Because population history cannot be explained by simple models or patterns of dispersal, it seems that people moved out of Beringia and across the continents in a complex manner. Science , this issue p. eaav2621
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The collection and dissemination of vertebrate ichnological data is struggling to keep up with techniques that are becoming commonplace in the wider palaeontological field. A standard protocol is required to ensure that data is recorded, presented and archived in a manner that will be useful both to contemporary researchers, and to future generations. Primarily, our aim is to make the 3D capture of ichnological data standard practice, and to provide guidance on how such 3D data can be communicated effectively (both via the literature and other means) and archived openly and in perpetuity. We recommend capture of 3D data, and the presentation of said data in the form of photographs, false‐colour images, and interpretive drawings. Raw data (3D models of traces) should always be provided in a form usable by other researchers (i.e. in an open format). If adopted by the field as a whole, the result will be a more robust and uniform literature, supplemented by unparalleled availability of datasets for future workers.
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Predator-prey interactions revealed by vertebrate trace fossils are extremely rare. We present footprint evidence from White Sands National Monument in New Mexico for the association of sloth and human trackways. Geologically, the sloth and human trackways were made contemporaneously, and the sloth trackways show evidence of evasion and defensive behavior when associated with human tracks. Behavioral inferences from these trackways indicate prey selection and suggest that humans were harassing, stalking, and/or hunting the now-extinct giant ground sloth in the terminal Pleistocene.
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Little is known about the ice age human occupation of the Pacific Coast of Canada. Here we present the results of a targeted investigation of a late Pleistocene shoreline on Calvert Island, British Columbia. Drawing upon existing geomorphic information that sea level in the area was 2–3 m lower than present between 14,000 and 11,000 years ago, we began a systematic search for archaeological remains dating to this time period beneath intertidal beach sediments. During subsurface testing, we uncovered human footprints impressed into a 13,000-year-old paleosol beneath beach sands at archaeological site EjTa-4. To date, our investigations at this site have revealed a total of 29 footprints of at least three different sizes. The results presented here add to the growing body of information pertaining to the early deglaciation and associated human presence on the west coast of Canada at the end of the Last Glacial Maximum.
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A Late Pleistocene hominin tracksite has been identified in coastal aeolianite rocks on the Cape south coast of South Africa, an area of great significance for the emergence of modern humans. The tracks are in the form of natural casts and occur on the ceiling and side walls of a ten-metre long cave. Preservation of tracks is of variable quality. Up to forty hominin tracks are evident. Up to thirty-five hominin tracks occur on a single bedding plane, with potential for the exposure of further tracks. Five tracks are apparent on a second hominin track-bearing bedding plane. A number of individuals made the tracks while moving down a dune surface. A geological investigation at the site and stratigraphic comparison to published geochronological studies from this area suggest that the tracks are ~90 ka in age. If this is the case, the shoreline at the time would have been approximately 2 km distant. This is the first reported hominin tracksite from this time period. It adds to the relatively sparse global record of early hominin tracks, and represents the largest and best preserved archive of Late Pleistocene hominin tracks found to date. The tracks were probably made by Homo sapiens.
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We report the occurrence at 0.7 million years (Ma) of an ichnological assemblage at Gombore II-2, which is one of several archaeological sites at Melka Kunture in the upper Awash Valley of Ethiopia, 2000 m asl. Adults and children potentially as young as 12 months old left tracks in a silty substrate on the shore of a body of water where ungulates, as well as other mammals and birds, congregated. Furthermore, the same layers contain a rich archaeological and palaeontological record, confirming that knapping was taking place in situ and that stone tools were used for butchering hippo carcasses at the site. The site gives direct information on hominin landscape use at 0.7 Ma and may provide fresh perspective on the childhood of our ancestors.
Implicit in any biomechanical analysis of tracks (footprints), whatever the animal, is the assumption that depth distribution within the track reflects the applied plantar pressure in some way. Here we describe sub-track deformation structures produced by Proboscidea (probably Mammuthus columbi) at White Sands National Monument (WHSA) in New Mexico. Patterns of sub-surface deformation are consistent with the plantar pressure data for modern Proboscidea, but do not reflect track morphology. Our work cautions against overinterpreting track topology of any large animal, including extinct animals such as sauropods, in terms of their biomechanics unless the subsurface stratigraphy and associated variation in shear strength is known.
“There is no branch of detective science which is so important and so much neglected as the art of tracing footsteps. Happily, I have always laid great stress upon it, and much practice has made it second nature to me.” Sherlock Holmes, Study of Scarlet. Despite the fictional nature of Sherlock Holmes this statement rings true today. The study of footwear is neglected in modern forensic practice and does have much to offer. What it needs is an injection of technology and modern analytical tools. These tools are emerging from the digital revolution currently transforming vertebrate ichnology. Ichnology is the discipline of earth science which focuses on the study of trace fossils such as footprints. This book draws upon both disciplines - geology (ichnology) and forensic science - to show how the two have much to learn from each other especially with regard to the digital capture and analysis of footprints. This book presents field and laboratory methods associated with the collection, analysis and presentation of three-dimensional tracks (footprints) whether from a crime scene or a geological/archaeological excavation. It shows students, researchers and practitioners how to collect and analyse 3D data and take advantage of the digital revolution transforming ichnology. This book is not only essential reading for forensic and earth science students but also for professional forensic practitioners as well as for applied computer scientists developing new tools for visualization and analysis of 3D data. The book forms a natural methods focused complement to the successful text Fossilised Locomotion published by Springer 2014.
Tracks and trackways of a range of Pleistocene megafauna can be found in White Sands National Monument, New Mexico, U.S.A. These tracks occur is several forms, not all of which are visible and some of which are only intermittently visible depending on lighting and moisture conditions. Here we present the result of a successful test of cesium vapor magnetometry to detect a known Columbian mammoth trackway. This initial test found that not only the known mammoth tracks were easily detected by the method, but that the tracks of additional species, though not visible to the eye, were detected in the vicinity of the mammoth tracks, including likely giant sloth tracks. Our initial results indicate that resolution may be suitable to distinguish between the tracks of various species, including possibly humans which are known archaeologically to have overlapped temporally with these species in the southwestern U.S. This preliminary result has immediate implications for the detection and documentation of Pleistocene track sites, and further refinement of the procedure is planned in the coming months.