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My work is full of fossilised poop, but ichnology is not an icky study

By The Conversation - May 27th 2022
Ichnologists examining an area with trace fossils - a way to reconstruct ancient life even in the absence of body fossils. Jurassica Museum. [The Conversation]

If you had told 18-year-old me that I would, one day, be an ichnologist I wouldn’t have believed you – or even known what that was. But, more than 15 years later, I get to introduce myself as an ichnologist.

Like my teenage self, many people outside the discipline don’t know, or have a limited understanding of, what ichnology is. It’s the study of the tracks and traces made by animals and plants in the fossil record, also called trace fossils. These can range from animal footprints, invertebrate trails, feeding traces on fossil leaves, fossilised faeces, tooth traces on bone/wood, to burrows and borings all preserved in the sedimentary rock record. When someone mentions seeing a “dinosaur footprint” they are talking about ichnology.

It may seem strange to spend so much time looking at fossils from the distant past. But doing so doesn’t just help scientists to understand animals and plants that existed long ago: it also informs our understanding of the environments they occupied and other aspects of the past world like extinction events or climate change. That can help us understand how things might shift in future.

Maybe this all sounds rather dry; fossil bones tend to grab people’s imagination far more. But ichnology is a very rich source of information about an animal that could not be deduced from the bones alone. A once living animal is leaving a clue about what it was doing, the way it was doing it, and the conditions around it.

Trace fossils even preserve moulds and casts of body parts – for instance, a fossil footprint can be thought of as a partial 3D mould of the animal’s foot, its flesh and bone.

My current work in ichnology deals with fossil footprints of one of the largest animals to have walked the earth: the sauropod. These dinosaurs of the Jurassic and Cretaceous periods (~200 and 150 million years ago) are like nothing we know today.

Some, like the Titanosaurs, were colossal. Others were the size of a cow or smaller. Our knowledge about sauropods is collated from their body and trace fossil records. Sauropod tracks tell us the morphology of the feet, anatomical details such as toes and claws, and occasionally, with exceptional preservation, the texture of the skin via skin impressions.

Tracks can reveal how the animal gripped the substrate as it walked, how fast it was moving, or simply show that it was there, especially if no body fossils are available. In northern Zimbabwe, for example, sauropod body fossils are very rare but sauropod tracks have been found and indicate enormous animals with feet 94 cm long and 54 cm wide. By comparison, an African elephant has a footprint length of between 30-40 cm. Collections of tracks and trackways can act as indirect evidence of sauropods moving together in a herd, something harder to deduce from their body fossils alone.

Where fossil footprints may indicate the movement of an animal and other associated behavioural characteristics, a fossil burrow is another type of trace fossil and provides evidence for the excavation of a dwelling, a refuge, or even a trap for prey. South Africa’s Karoo Basin preserves some of the world’s finest and most unusual fossil burrows. Burrows’ walls, lining and infill can preserve evidence of excavation with scratch marks from claws and teeth and even the animal’s butt imprint being preserved. These are crucial in helping identify a possible burrow-maker and its behaviour.

And while the idea of fossilised faeces might gross you out, coprolites reveal what that animal ate and may preserve in it fragments of fossil bone, insects, and plant matter. A coprolite might even show evidence of other trace fossils, like traces related to beetle’s borings – insects eating and digesting the coprolite while it was still fresh. It can even show that it was stepped on by another animal. One incredible example was recently discovered in Vietnam. It shows evidence of being produced and stepped on by a crocodilian; a fossil footprint and fossil dung all wrapped up in one.

Collectively, this evidence helps to paint a picture of long-gone landscapes and the creatures and plants that populated those spaces.

Another branch of ichnology, neoichnology, studies the modern traces and tracks of animals. It’s a highly relevant field of study because knowing how and why modern animals move and interact with different substrates informs us about how extant animals may have done so.

For centuries, humans have examined the tracks and traces of animals and plants. Today, only a few people worldwide have this specialised knowledge and skill. In Botswana, trackers from the indigenous !Xo and /Gwi nations, for instance, use their superior tracking neoichnological knowledge as citizen-scientists in the management and conservation of wildlife. From tracks, dung and other evidence of animal behaviour, these neoichnologists know and interpret the movement, sex, species, timing, and speed of animals passing through an area.

So, how do you go from high school to a career in ichnology like I did? There isn’t always one single, linear route. Ichnology often requires a good understanding of biological and abiotic processes in the spheres of geology, zoology, and botany – as well as in chemistry, physics, and maths. There’s a wide scope of subjects you could study to pursue a career in ichnology and you certainly don’t need to be an expert in all of them. You just need to be curious!

As an example, I studied sedimentary geology, which is used in teasing apart trace fossil information as it is often preserved in sedimentary rocks. It can help explain how sediment and animals interact and what processes were involved in the shaping and preservation of a trace like a footprint or burrow. Geology will assist in reading the rocks in which the trace fossils are preserved. Biology and zoology will assist in understanding the behaviour of animals making and leaving those traces in the sedimentary rock record.

Altogether, ichnology helps us investigate our near or distant past to learn from it. A trace fossil is a little secret snapshot of an animal’s day: a private view into who it was and what it was up to.

The writer is a postdoctoral research fellow, Jurassica Museum - theconversation.com    

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