We trained AI to recognise footprints, but it won’t replace forensic experts yet


Matthew Robert Bennett, Bournemouth University and Marcin Budka, Bournemouth University

We rely on experts all the time. If you need financial advice, you ask an expert. If you are sick, you visit a doctor, and as a juror you may listen to an expert witness. In the future, however, artificial intelligence (AI) might replace many of these people.

In forensic science, the expert witness plays a vital role. Lawyers seek them out for their analysis and opinion on specialist evidence. But experts are human, with all their failings, and the role of expert witnesses has frequently been linked to miscarriages of justice.

We’ve been investigating the potential for AI to study evidence in forensic science. In two recent papers, we found AI was better at assessing footprints than general forensic scientists, but not better than specific footprint experts.

What’s in a footprint?

As you walk around your home barefoot you leave footprints, as indentations in your carpet or as residue from your feet. Bloody footprints are common at violent crime scenes. They allow investigators to reconstruct events and perhaps profile an unknown suspect.

Shoe prints are one of the most common types of evidence, especially at domestic burglaries. These traces are recovered from windowsills, doors, toilet seats and floors and may be visible to or hidden from the naked eye. In the UK, recovered marks are analysed by police forces and used to search a database of footwear patterns.

The size of barefoot prints can tell you about a suspect’s height, weight, and even gender. In a recent study, we asked an expert podiatrist to determine the gender of a bunch of footprints and they got it right just over 50% of the time. We then created a neural network, a form of AI, and asked it to do the same thing. It got it right around 90% of the time. What’s more, much to our surprise, it could also assign an age to the track-maker at least to the nearest decade.

A series of footprints with a heat map over them.
The footprints analysed by the Bluestar AI, with a heat map over them suggesting areas of ambiguity. Matthew Bennett, Author provided

When it comes to shoe prints, footwear experts can identify the make and model of a shoe simply by experience – it’s second nature to these experts and mistakes are rare. Anecdotally, we’ve been told there are fewer than 30 footwear experts in the UK today. However, there are thousands of forensic and police personnel in the UK who are casual users of the the footwear database. For these casual users, analysing footwear can be challenging and their work often needs to be verified by an expert. For that reason, we thought AI may be able to help.

We tasked a second neural network, developed as part of an ongoing partnership with UK-based Bluestar Software, with identifying the make and model of footwear impressions. This AI takes a black and white footwear impression and automatically recognises the shape of component treads. Are the component treads square, triangular or circular? Is there a logo or writing on the shoe impression? Each of these shapes corresponds to a code in a simple classification. It is these codes that are used to search the database. In fact the AI gives a series of suggested codes for the user to verify and identifies areas of ambiguity that need checking.

In one of our experiments, an occasional user was given 100 randomly selected shoe prints to analyse. Across the trial, which we ran several times, the casual user got it right between 22% and 83% of the time. In comparison the AI was between 60% and 91% successful. Footwear experts, however, are right nearly 100% of the time.

One reason why our second neural network was not perfect and didn’t outperform real experts is that shoes vary with wear, making the task more complex. Buy a new pair of shoes and the tread is sharp and clear but after a month or two it becomes less clear. But while the AI couldn’t replace the expert trained to spot these things it did outperform occasional users, suggesting it could help free up time for the expert to focus on more difficult cases.

Will AI replace experts?

Systems like this increase the accuracy of footwear evidence and we will probably see it used more often than it is currently – especially in intelligence-led policing that aims to link crimes and reduce the cost of domestic burglaries. In the UK alone they cost on average £5,930 per incident in 2018, which amounts to a total economic cost of £4.1 billion.

AI will never replace the skilled and experienced judgement of a well-trained footwear examiner. But it might help by reducing the burden on those experts and allow them to focus on the difficult cases by helping the casual users to identify the make and model of a footprint more reliably on their own. At the same time, the experts who use this AI will replace the ones who don’t.

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Marcin Budka, Professor of Data Science, Bournemouth University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Laetoli Footprints

A new species of early human? Why we should be cautious about new fossil footprint findings

Dawid A. Iurino for THOR, Author provided

Matthew Robert Bennett, Bournemouth University and Sally Christine Reynolds, Bournemouth University

A collection of fossil footprints at Laetoli in Northern Tanzania, preserved in volcanic ash and dated to 3.66 million years ago, are still yielding surprises almost 45 years after their discovery.

Based on a re-analysis of fossil footprints from one of Laetoli’s sites, the authors of a new study published in the journal Nature say they’ve discovered evidence of a previously unknown early human species at this spot. However, there are reasons to be cautious about this conclusion.

Before we delve into these new findings, let’s orientate ourselves. Laetoli, an area well-known for paleontological excavations, has a number of distinct sites, each denoted by letters of the alphabet. British paleoanthropolgist Mary Leakey and her colleagues first reported fossil footprints in 1978 at Site G, the main track site at Laetoli.

In 2016, a team led by Fidelis Masao, an archaeologist in Tanzania, uncovered additional tracks close to Site G, at Site S. The footprints from Sites G and S are usually assigned to the well-known ancestral human (hominin) species Australopithecus afarensis, of which the skeleton “Lucy” is the best-known example.

Less well-known is the fact that in 1976, two years before Leakey’s famous discovery, a set of five footprints were found at Site A. Importantly, all these sites occur on the same ash surface, so we know they date from the same time period.

But the five footprints from Site A were largely forgotten, eclipsed by Leakey’s later discovery. This was understandable because the footprints at Site A had poor morphological shape, or definition, and there were fewer of them (there are more than 30 individual footprints at Site G).

In 1987, American paleoanthropologist Russell Tuttle suggested that these footprints may have been made by a species of bear, or by a different hominin from those of Site G. He also cautioned that the diversity in the footprints’ form as compared to those at Site G might simply reflect the changing properties of the ash layer over which the hominin walked.

Seeking to find out who these footprints belonged to, a team of international researchers re-excavated the tracks from Site A in 2019. Their findings are the focus of the new paper in Nature.

The researchers used various methods including photography and 3D scanning to inspect the Site A footprints. They compared the width and length with footprints from black bears, chimpanzees and humans, as well as the tracks from Sites G and S. They also explored the bear hypothesis by examining video footage of modern black bears which, on rare occasions, walk upright.

The authors concluded that on balance, the footprints at Site A did not resemble bear tracks, and were different from the footprints at Sites G and S.

One particular feature they draw attention to is that the Site A trackway cross-steps, almost as if one was attempting to toe a line as part of sobriety test. Based on this and their other findings, the authors suggest that the tracks at Site A were made by a different hominin than those at sites G and S. They argue that two hominin species walked the Laetoli landscape 3.66 million years ago.

A footprint from Site A on the left and Site G on the right. Image on left by Jeremy DeSilva and on right by Eli Burakian/Dartmouth.

The broader evolutionary context at this time suggests what the authors are proposing would be possible. There was more than one species of hominin on the African landscape during this period, and we’ve seen anatomical variation in the foot within some Australopithecus species. That said, it’s quite a significant leap to identify a second species based on a handful of poorly defined tracks.

Variation in trackways is the key issue here. Imagine going for a walk down a beach or sandy path. The footprints you make will vary from one step to the next. This reflects natural variability in human gait, as well as subtle differences in the characteristics of the ground you’re walking on.

In a recent paper we suggested that you need a minimum of between ten and 20 footprints before you can confidently quantify the variability in just one dimension, such as footprint length, let alone several. Others have suggested that you may need over 250 tracks to adequately quantify the three-dimensional form of a footprint.

Footfall and the resulting footprints are more variable than once thought and some have argued that even individuals of the same species may have highly unique gaits.

In this context it is rather surprising that the authors of this paper make inferences not just about one individual, but a whole species.

One way to strengthen their conclusions would be to use modern “whole foot” methods to statistically compare the best footprint at Site A with those at Sites S and G. This could be an approach for future research.

Certainly more evidence is needed to determine whether these footprints justify this excitement, and do indeed belong to another early human species.

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Sally Christine Reynolds, Principal Academic in Hominin Palaeoecology, Bournemouth University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Fossil footprints prove humans populated the Americas thousands of years earlier than we thought

Are these the footprints of the first-known American teen? Matthew Robert Bennett, Author provided

Matthew Robert Bennett, Bournemouth University and Sally Christine Reynolds, Bournemouth University

Our species began migrating out of Africa around 100,000 years ago. Aside from Antarctica, the Americas were the last continents humans reached, with the early pioneers crossing the now-submerged Bering land bridge that once connected eastern Siberia to North America.

At times throughout the Pleistocene ice age, which ended 10,000 years ago, large ice sheets covered much of Europe and North America. The water locked in these ice sheets lowered the sea level, allowing people to walk the bridge from Asia through the Arctic to Alaska. But during the peak of the last glacial cycle, their path south into the Americas was blocked by a continental-wide ice sheet.

Until now, scientists believed humans only travelled south into the Americas when this ice barrier began to melt – at the earliest, 16,500 years ago. But together with our colleagues, we have discovered a set of fossil footprints that suggest humans first set foot on the continent thousands of years earlier.

two fossil footprints
The fossil footprints. Matthew Robert Bennett, Author provided

These footprints, unearthed at White Sands National Park in New Mexico, were made by a group of teenagers, children and the occasional adult, and have been dated to the height of the last glacial maximum, some 23,000 years ago. That makes them potentially the oldest evidence of our species in the Americas.

Our findings support the idea that humans were present in the southern part of North America before the last glacial peak – a theory that has so far been based on disputed and potentially unreliable evidence.

Step change

There are literally tens of thousands of fossil footprints at White Sands. Together, they tell stories of how prehistoric humans interacted with extinct Ice Age megafauna, such as Columbian mammoths and giant ground sloths.

The tracks were deposited around the margins of a large wetland – perhaps a lake after the rainy season, but at other times more like a patchwork of water bodies. Until now, the problem had been dating these footprints. We knew they were imprinted before the megafauna became extinct, but not precisely when.

This changed in September 2019 when the team found tracks with undisturbed sediment above and below them. Within that sediment were layers containing hundreds of seeds of the common ditch grass Ruppia cirrhosa. These seeds, when radiocarbon dated, would reveal the age of the footprints themselves. Analysis revealed the seeds range in age from 21,000 to 23,000 years old, suggesting humans made repeated visits to the site over at least two millennia.

Some dark brown seeds
Some of the seeds that we extracted from the footprints. Matthew Robert Bennett, Author provided

The White Sands footprints provide unequivocal evidence that people were in the Americas at the height of the last glacial maximum, rather than some time after, as was previously thought. That’s a big deal for our understanding of the peopling of the Americas and the genetic composition of indigenous Americans.

Using the DNA of modern indigenous Americans, scientists have worked out that their ancestors arrived from Asia in several waves, some of which became genetically isolated. The cause of this isolation is not clear. Now, our new footprint evidence provides an explanation, suggesting that the earliest Americans were isolated south of the North American ice sheet, only to be joined by others when that sheet melted.

Our discovery may also reopen speculation about other archaeological sites in the Americas. One of them is Chiquihuite Cave in Mexico. Archaeologists recently claimed that evidence from this cave suggests humans occupied the Americas around 30,000 years ago – 7,000 years before people left the White Sands footprints.

But the Chiquihuite Cave findings are disputed by some, as stone tools can be difficult to interpret and tool-like stones can form via natural processes. Stone tools can also move between layers of sediment and rock. Fossil footprints can’t. They are fixed on a bedding plane, and so provide more reliable evidence of exactly when humans left them.

modern footprints bordering ancient ones.
On the left, modern shoeprints; on the right, footprints millennia old. Matthew Robert Bennett, Author provided

Teenage kicks

We tend to picture our ancestors engaged in life-or-death struggles – forced to battle the elements simply to survive. Yet the White Sands evidence is suggestive of a playful, relatively relaxed setting, with teenagers and children spending time together in a group.

This is perhaps not that surprising. Children and teenagers are more energetic and playful than adults and therefore leave more traces. Adults tend to be more economical in their movement, leaving fewer tracks.

An illustration of prehistoric man and mammoths
What White Sands might have looked like 23,000 years ago. Davide Bonadonna, Author provided

But another interpretation of this new footprint evidence is that the teenagers were part of the workforce in these early bands of hunter-gatherers. It’s possible that the tracks were left by young people fetching and carrying resources for their prehistoric parents.

In any case, the people that left their tracks on White Sands were some of the earliest known American teens. Set in stone, their footprints pay tribute to their forebears, who we now know walked the long land bridge into the Americas millennia earlier than what was commonly believed.

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Sally Christine Reynolds, Principal Academic in Hominin Palaeoecology, Bournemouth University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Parietal Art?

We discovered the earliest prehistoric art is hand prints made by children

One of the hand prints discovered in Tibet that is believed to have been made by children. Matthew Bennett, Author provided

Matthew Robert Bennett, Bournemouth University and Sally Christine Reynolds, Bournemouth University

Fossilised footprints, and more rarely, hand prints, can be found around the world; left as people went about their daily business, preserved by freak acts of geological preservation. In new research our international team have discovered ancient hand and footprints high on the Tibetan plateau made by children.

The team argues that these traces represent the earliest example of parietal art. Parietal art is paintings, drawings, and engravings on rock surfaces – the sort of thing you would find in a cave, although the Tibetan traces are not in a cave.

The limestone on which the traces were imprinted dates to between around 169,000 and 226,000 BC. This would make the site the earliest currently known example of this type of art in the world. It would provide the earliest evidence for humans and other members of the Homo genus (hominins) on the high Tibetan plateau. This discovery also adds to the research that identifies children as some of the earliest artists.

Hand shapes are commonly found in prehistoric caves. Usually the hand is used as a stencil, with pigment spread around the edge of the hand. The caves at Sulawesi, Indonesia or at El Castillo in Spain have some fine examples and are the oldest known to date.

At Quesang, high on the Tibetan plateau, our team led by David Zhang from Guangzhou University found hand and footprints preserved in travertine from a hot spring. Travertine is freshwater limestone, often used as bathroom tiles, and in this case deposited from hot waters fed by geothermal heat. The limescale that accumulates in your kettle provides an analogy for this. When soft, the travertine takes an impression, but then hardens to rock.

A 3D-relief model of the Quesang fossil hand and footprints with colours showing the depth of the prints within the rocks.

Five hand prints and five footprints appear to have been carefully placed, probably by two children judging by the size of the traces. The prints were not left during normal walking and appear to have been deliberately placed. The child making the footprints was probably around seven years old and the other, who made the hand prints, slightly older, at 12 years of age. The age estimates are based on the size of the traces with reference to modern growth curves such as those produced by the World Health Organization.

Were the children casually playing in the mud while other members of the group took the waters at the hot spring? We do not know, but the team argues that what they left is a work of art, or prehistoric graffiti if you prefer.


The team dated the travertine using a radiometric method based on the decay of uranium found in the limestone. The age is surprising, with the deposit dating to between around 169,000 and 226,000 years ago. This goes back to the middle Pleistocene (mid-Ice Age) and provides evidence for the earliest humans (or their direct ancestors) occupation on the Tibetan plateau. This is quite incredible when you think of the high altitude involved; Quesang has an elevation of over 4,200 metres and would have been cold even during an interglacial period. The age also makes this the oldest example of parietal art in the world.

Were the children members of our own species, Homo sapiens, or members of another extinct archaic human species? There is nothing in the tracks to resolve this question. They may have been an enigmatic group of archaic humans referred to as the Denisovans, given other recent skeletal finds of this species on the plateau.

Should we consider this panel of prints as art? Well, that depends on one’s definition, but the marks were deliberately made, and have a clear composition. Whatever these humble traces represent, they clearly evoke images of children at high elevations, enjoying a spot of creative play.

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Sally Christine Reynolds, Principal Academic in Hominin Palaeoecology, Bournemouth University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Blogged out?

From time to time, I am asked by the Doctoral College at Bournemouth to run various sessions on academic writing.  I am not really sure why except I have done quite a bit of writing over the years, and I don’t find it easy.  One of the things I always trot out in these sessions is the important of practice, you can’t get better at something unless you practice.  Although it seems hackneyed advice it is true – practice makes perfect!  I then get asked; well how do I practice and who will give me feedback?

Curtsy of Shutterstock

My answer is to encourage students to start their own blog.  A post of a few hundred words is just the right length to allow you to form a coherent stream of ideas, but not to long so it needs more than one sitting to write. And there are so many blogs out there it is unlikely to get read, so why be afraid? In terms of getting feedback, well my answer is the best critic is yourself; write something and come back to it a few weeks, or months later and read it again.  Could you have made it clearer?  How else could you have approached the piece?

One of the reasons for starting the Professor Sandcastle blog was to give me the opportunity to practice my trade and also post things for my students more easily than on the official Bournemouth learning environment.  I was quite good at posting stuff to start with, or more precisely re-posting stuff, but I have let that lapse in the last year.

It is hard to find the time to practice, I have let my Welsh slide as well.  [As a dyslexic learning a second language is not easy and Welsh is hard!] I have not painted in a while either, not since last summer in fact when I exhibited in Betws-y-Coed. In my defense I have been busy, last September we published two big stories – the oldest human footprints in the Americas, and the oldest parietal art from Tibet.  Lots of media appearances, popular stories and the like, including a TV documentary for (Nova) PBS America broadcast in April.  I was back in the field in January and April of this year – the Covid layoff was finally over.  I have also been teaching a lot, but you know what? This all sounds like a lot of excuses to me.

Practice matters and all types of writing needs work.  And my art should not be neglected either, after all it is vaguely part of my long-term retirement plan.  As is learning Welsh!  If you stop investing in yourself, you stop growing and that is probably why this summer I feel a bit jaded and stagnant.  So, when the renewal for the blog site came up this month, I thought to myself.  You should catch up with those posts, you should invest more time in your own practice and share more of the downright silly and wacky thoughts that assail my mind every day!  So, a new term is approaching, so here is my resolution, blog and share more!

Tectonic Deformation, or Jam and Yogurt?

The other day I sat down to a summer breakfast of fresh yogurt with a large dollop of homemade blueberry jam.  The dollop was large so please don’t think I am on a health kick, far from it!

Anyway as I mixed the jam into the yogurt, I was reminded of the many times I have used this analogy to explain the stages of tectonic deformation and the origin of such things as tectonic laminations, boudins and even augens.  Out came the phone and as I mixed, I snapped away.

So, we have two materials – jam and yogurt – with different colors and viscosity (rheologies) which we mix slowly.  The mixing is the tectonic bit – folding, faulting and generally stirring up the rock layers. To start with the two materials are quite distinct, but as we mix fine strings of jam get drawn out and incorporated into the yogurt.  These strings are attenuated folds and form what is referred to as tectonic laminations.  You might draw out and stretch a lump of chewing gum thinner and thinner until it breaks.  The same is true of the jam, the spoon folds it over and as you mix the fold is stretch out till it breaks.  The more you mix (deform) the finer the laminations become.  Thicker ‘blobs’ become shaped like sausages (boudins) and form distinct streamlined shapes.  In Photo C you can still see some of the folds but they are getting very attenuated.  Keep mixing the color begins to become more uniform, the tectonic laminations become so fine you can barely see them.  In time you get a complete uniform mix of the two materials.  When mixing sediments we refer to this as diamicton, a sediment with a mix of grain sizes and properties.

Now unlike rocks you can eat yogurt and it is very tasty!

Fossilized Seabed

Take a walk on a sandy beach and the chances are you will see some ripples. Small regular ridges of sand or mud, snaking across the surface in parallel lines.  They come in many different sizes, have different cross-sectional shapes, and have whole taxonomy to themselves, with all sorts of obscure ways of describing them in plan-form. 

Beach ripples, curtsy of Mutan, Shutterstock

Different flow conditions create different ripple sets.  For example, symmetrical ripples form below oscillating currents created by waves, while asymmetrical forms are produced by unidirectional currents.  They are not confined to watery surfaces, but you will find them on sand dunes and the dry upper parts of the beach where the wind is the transport agent.  Collectively we referred to these as sedimentary bedform and they can be recognized geologically in cross section.  For example, sediment moves in the direction of the current up the back of the ripple and cascades down the lee side forming an inclined sediment layer called a foreset.  The bedform migrates as sediment is eroded on the up current side and avalanches down the lee.  In this way the inclined layers are preserved in cross-section and can tell a story about the current direction and its velocity.

Many years ago, as an undergraduate I sat on the mudflats close to Aberystwyth happily measuring modern ripples both in cross-section, using a ripple board1, and in plan form by measuring wavelength and bifurcations in plan-form. I loved it!

It is quite rare, although not unknown, for ripples or mega-ripples (big ripples) to be preserved as three-dimensional forms.  Bury the rippled surface in another layer of sediment, without eroding it to much, then in theory you can lift off (by erosion) the covering layer to reveal fossilized seafloor. A big surge of sediment settling out of the water column might do the burying, especially if the original surface was hardened in some way. Exposure, air drying and a bit of salt crystallization to bind the grains would work to do the hardening.

There are some beautiful examples in Snowdonia from the Ordovician.  I first came across these while writing a book about Snowdon’s geology. Imagine a series of volcanic islands with sub-tropical oceans.  Estuaries indent the shoreline and the rivers within bringing lots of sediment to the shallow sea. Explosive volcanoes like those in Snowdonia at the time generate lots of sediment.  Perhaps the best example are those exposed on the southwest side of the Llynnau Mymbry.  These are stunning, large bedforms (water lain dunes in fact) which snake over the inclined rock surface.  An equally impressive example is to be found at the head of the Dolwyddelan Valley.

Large estuarine bedforms from the Ordovician of Snowdonia, curtsy of Andrew Bennett

Recently Richard Hart, a mountaineer, has been sending me photos of many more examples across Snowdonia and I have been pleasantly surprised by just how many examples there are.  If any one is looking for a fantastic undergraduate project, whether you be a geology or geography student, exploring the morphology of these ripples would give an interesting insight into the water dynamics around these island arcs.  And I have never looked on these surfaces for animal footprints which might at a pinch just be there!  You could capture these surfaces in 3D using photogrammetry and explore their morphology. If anyone is interested, please get in touch!

Fossilized seafloor, curtsy of Richard Hart

1 A ripple board is simply rectangle of hardboard covered in graph paper and then sealed in clear plastic. You insert it into the sand and right angles to the ripple crests and then trace with marker pen the surface. This allows you to measure wavelength and ripple height.

Lockdown Badgers

“What does a badger look like?” asked my wife one evening from the kitchen a few days into lockdown.

It was an innocent enough question that started an obsession which has helped keep me sane during lockdown. Badgers visit the garden most nights. We saw them that first night, tucking into a chicken carcass left out for the fox who we had been feeding since moving into the house in June 2019. A small rented house with a tiny back garden and a thin gallery of wild woodland behind in an ordinary suburb of Bournemouth.

Now I study fossil footprints and have done so for years so you will understand that the first thing I did was to scatter some sand in the corner of the garden between the fence and the rear hedge. The exact place where the badgers entered the garden that first night. And while we did not see the badgers in person again for a long time, their footprints told a story of their nightly visits. I started to cast the tracks in plaster and the rest is history as they say.


Eight weeks later I have a shed filled with plaster casts of varying size and several hours of video made with a cheap night vision camera bought via Amazon. It may not quite have been an essential order at the time, but hey it saved my mental health, so it was in my book. The camera revealed a male badger, called Boris, a female (Belinda) with what we think are two yearling cubs that follow her around. And yes, rightly, or wrongly we feed them from time to time. The fox gets the bones and scarps we leave out, but the badgers are rather partial to bird seed and water. Neither the badgers, nor the fox are keen on the dog food that may have accidentally fallen into our shopping basket from time to time over the last few weeks. The sand trap has grown and been replenished several times and the casts have got larger as access to both sand and plaster has become easier with the gradual easing of lockdown. You might ask why plaster and not use photogrammetry which is what I use for fossil tracks. Well photogrammetry felt too much like work, although I now have some amazing 3D photogrammetry models as well like the one below.


Apart from the daily pleasure of reviewing the camera footage, checking the sand for tracks, and preparing the casts I am not quite sure of the scientific value of the game. Let us call it a game for now. Badgers tracks are highly distinctive, appear to be sexually dimorphic and before we had the camera were the only real way, we knew they were regular visitors to our garden. I had never seen a badger before that first night, despite spending many hours in the countryside over the years.  There are a few research papers out there that advocate using tracks to monitor endangered, or just interesting, animals around the world and the potential is well illustrated by our garden badgers.  It was the footprints after all that indicated their regular presence.

In time I hope to work through the casts we have and showcase the variability in badger tracks to help others recognise them both for monitoring purposes and for pure interest.  I also have plans to write the work up in time as a case study in track variability.  In the meantime, badgers rock!

Imaging the footfall of Ice Age giants

Understanding how something walks is a fundamental question in vertebrate biology. If you want to study the biomechanics of a living animal, such as a human, you simply get them to walk on a pressure treadmill and this captures the pattern of basal (plantar) foot pressure.  With larger animals it is a little trickier and there is a reason why we only have a small number of pressure records for elephants since it is not that easy to get them to walk on a treadmill!  For an extinct animal, such as a mammoth or a dinosaur, it is impossible.  In such cases we use fossil footprints, substituting footprint depth for pressure, but unfortunately research has shown that this does not work as well as one might hope.  Something called ground penetrating radar (GPR) provides an alternative.

Popular TV shows such as Time Team and The Curse of Oak Island have transformed public understanding of geophysics; tools by which archaeologists and geologists image the hidden subsurface.  As one over enthusiastic presenter once said ‘it allows us to x-ray the ground, like Superman looking through the soil to see what is buried below!’  Ground penetrating radar was first developed in the early 20th Century but was not really developed until the Vietnam War when it was used to image subsurface bunkers and it is now used by engineers to view cracks in railway tracks and girders.  It is essentially an electromagnetic transmitter/receiver, a mobile phone on steroids if you like, and its signal penetrates the ground with varying speed, determined by the properties of that ground.  The signal is reflected back to the surface by boundaries that show marked changes in physical properties, thereby revealing the shape of those boundaries.  It is generally a tool for imaging big stuff (think walls) in the archaeologist’s toolkit.

Our research team have been working for several years at White Sands National Monument (WHSA) in New Mexico which contains the largest assemblage of vertebrate Ice Age tracks, probably in the world.  These tracks are preserved on a dried lake bed (Alkali Flat), but they are difficult to see which is why colloquially they are referred to as ghost tracks.  Seeing them is quite important not only so that we can track and map the interaction of human hunters with extinct Ice Age fauna, but also for their conservation.  Much of Alkali Flat is in co-use with the White Sands Missile Range, famous as the birth place of the American space programme, of the first nuclear blast at Trinity and Regan’s infamous Star Wars initiative.  In places missile debris litters the ground and being able to map conservation priorities is important especially since the true significance of the track assemblage at WHSA became known only in 2018 with the recognition of human tracks.

GPR_Converstion_1Images of Ice Age human footprints at White Sands National Monument (New Mexico), also showing the ground penetrating radar and the foam mats used in the survey [Author supplied]. 

The research team have had some success in using geophysics to map large animal tracks, but to our surprise we found that high-resolution ground penetrating radar gives fantastic results.  Now when we say high-resolution we are spacing our survey lines at around 10 cm or so; typical survey line spacing would normally be measured in metres.  We place foam jigsaw mats out on the desert floor, the sort of things you get at play school or in your home gym, and move the radar across this surface line by line.

Not only can we image large mammoth and giant ground sloth tracks but we can also image to those of human hunters that co-existed with these animals.  The electrical properties between the track fill and the printed ground are subtle but sufficient for the tracks to stand out.  There are many advantages.  Not only does it allow us to prospect for tracks, but it allows us to image buried tracks and deduced sequence of superposition.

op_1GPR imaging of mammoth, giant ground sloth and human tracks at White Sands National Monument [Author supplied].

We also noticed something cool beneath the mammoth tracks.  Below the base of the tracks we consistently saw a radar feature, hook-like in cross-section, we believe is caused by compressed sediment.  Comparing these structures to modern plantar pressure records, kindly donated to us by researchers at the Royal Veterinary College in London and Monash University, we see a tentative match.  It makes sense since that is where the plantar pressure would have been greatest beneath a mammoth’s foot and the sediment most compressed. The radar signal appears to be picking this out.  In fact we can get a similar pressure record off the human and giant ground sloth tracks.  We still have work to do but it appears as if the radar signal is able to give us a plantar pressure record from an extinct animal independent of the footprint itself.  In terms of studying the biomechanics of Ice Age giants this is revolutionary especially for animals like the giant ground sloth which had a peculiar gait, walking on the outside of its feet.

op_4Subsurface anomalies below mammoth tracks.  These are caused of compression below the footprint caused by the plantar pressure.  The spaceship like sculptures shows this; the top disc or surface is the actual footprint and the structure below the anomaly.  They resemble the pressure patterns found for modern elephants [Author supplied].

At this point we firmly move to the near-future, because as with all new ideas there is validation work to be done.  But assuming this all comes good and crucially the technique works outside the specific gypsum rich sediments of White Sands as we believe it will, then the implications are significant for those who study biomechanics.  For example, we might be able to use it map footprints elsewhere especially where digging could be disruptive at such famous footprint sites like that at Laetoli in Tanzania where the oldest human footprints in the world are to be found.  Or alternatively search for buried footprints around shallow or mass graves.  But the big goal is to be able to obtain a plantar pressure record from beneath a dinosaur’s foot.  We are not quite there yet, but given the right geological circumstances it is we believe possible and with funding we hope to try soon.

This work was carried out by: Tommy Urban and Sturt Manning of Cornell University, Matthew Bennett, Matteo Belvedere and Sally Reynolds from Bournemouth University and David Bustos, Daniel Odess and Vincent Santucci from the National Park Service in the USA.