South Africa is well known for its fossil heritage, a record of plants and animals that tells us what the world was like long ago.
Over the past 15 years, our research group at the African Centre for Coastal Palaeoscience at Nelson Mandela University has studied some of these ancient species by examining the tracks and traces they left during the Pleistocene Epoch (a period from about 1.8 million years ago to 11,700 years ago, sometimes known as the “Ice Ages”). We have identified more than 350 vertebrate tracksites along the coast from this time. These animals left their tracks and traces in sandy surfaces that hardened into rock over time. The oldest fossil track we’ve found is around 400,000 years old.
All this time we were aware that there might be more, even older trace fossils to find further inland. We knew that up to 30km inland there were cemented dunes formed from wind-blown sand, probably around 3 million years old. These dunes, which are now rock, are known as the Wankoe Formation.
Charles Helm, Author provided (no reuse)
However, there were problems with finding any fossils there. There seemed to be a relatively limited number of suitable rock outcrops, showing what used to be dune surfaces. And often those that we did find were eroded and calcified: good for finding caves and mineral formations (like stalagmites), but not for finding tracks – or so it seemed. In addition, much of the Wankoe Formation is on private property, and permission would be needed to access potential sites.
We realised that to find any fossil traces we would have to focus on the areas where the original rock layers were well preserved and visible.
Then one of our team members, Given Banda, identified what appeared to be a trackway on an inland surface near his home community. This was a spur to action, and next, when staying in the Grootbos Private Nature Reserve to research nearby coastal tracks, we chanced upon more inland track-like features. A more thorough reconnaissance in the reserve followed, and the more we looked, the more tracks we found, including one that’s certainly a trackway (see photo below).
Charles Helm, Author provided (no reuse)
The results of our findings were recently published.
No vertebrate tracks had previously been identified in the Wankoe Formation. We have found that the formation is rich in fossils and that vertebrate tracks are common there. Furthermore, these seem to be the first recorded Pliocene vertebrate tracks described from southern Africa. The Pliocene was an epoch from about 5.3 million to 2.6 million years ago. These findings therefore add to what we know about ancient environments.
New treasure trove of fossil tracks and traces
Charles Helm, Author provided (no reuse)
The Wankoe Formation track discoveries are important for three main reasons:
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they might tell us more about body fossils
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we might find traces of human ancestor species
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the tracks are raised rather than indented, which is rare.
Firstly, there is a wonderful Pliocene body fossil site just a few hundred kilometres away. Known as Langebaanweg or, more popularly, the West Coast Fossil Park, the site boasts a vast array of extinct creatures. The body fossil record and trace fossil (ichnological record can not only complement each other, but have the potential to yield new findings that constructively inform and enrich each other.
For example, on the coast we have found trackways of giraffe and giant tortoises, that were not known to inhabit the region based on the body fossil record. We hope that we can complement the body fossil record with our ichnological findings. Already we have identified a tracksite that suggests a possible wolverine trackmaker, consistent with the finding of an extinct wolverine at Langebaanweg.
Secondly, when we started work on the younger deposits on the coast 15 years ago, we knew that we needed to be on the lookout for hominin tracksites, as we were aware that ancestral hominins had been there at the time. Since then, we have found more than 20 such sites. These make up by far the largest archive of hominin tracksites more than 40,000 years old in the world.
Read more:
Fossil finds: footprints on South Africa’s coast offer a glimpse into our ancestors’ lives
We can try to apply similar thinking to our Pliocene discoveries inland from the coast.
Pliocene deposits are not encountered that often in Africa, and these Western Cape examples seem to be among the only ones described from southern Africa. The Laetoli site in Tanzania is globally famous for its australopithecine trackways, which remain the only tracks of these possible ancestors of our Homo genus from the Pliocene. They are also the oldest unequivocal tracks of their kind in the world.
Read more:
The Maasai legend behind ancient hominin footprints in Tanzania
While we have not yet found tracks that are conclusively of primate origin in the Wankoe Formation, and we do not know precisely when australopithecines may have first appeared in this region, we are aware of the potential, and need to keep exploring.
Charles Helm, Author provided (no reuse)
Thirdly, the tracks we are finding are different, and are special in their own right. Many of them are “pedestalled”, meaning that instead of forming hollows, they are raised above the surface.
The principle of their origin can easily be replicated on a modern dune surface, provided that the sand is slightly moist (cohesive) and a strong wind is blowing. If you walk along such a surface, you will leave your tracks in the form of depressions. But if you return an hour later, they might be raised above the surface. This is because you will have compressed underlying layers when you made your tracks, and the wind has blown the surrounding sand away but is not strong enough to remove the compressed areas below your tracks. The same principle occurs in snow, where it is much more readily observed (see photo below).
Dr Raoul Scoltz, Author provided (no reuse)
Fossilised pedestalled tracks are globally rare, and the potential for finding more of them is intriguing.
Read more:
Fossil treasure chest: how to preserve the geoheritage of South Africa’s Cape coast
More to find?
Our subsequent explorations have continued to deliver results, and we now realise that even rocks that have been weathered can sometimes preserve tracks, sometimes in profile. (See photo: the underlying layers have been distorted by the weight of the trackmaker.)
Charles Helm, Author provided (no reuse)
We have also found body fossils in the form of trees, roots and bone material embedded in these layers of wind-blown, hardened sand that require further study.
It is perhaps not surprising that the dunes that now form the Wankoe Formation contained tracks on their surfaces. However, the welcome news is that despite all the calcification and weathering that has occurred, evidence of these tracks has not been obliterated.
We now realise that if we know where to look, there will be many suitable surfaces and exposures to explore. And the possibility of finding the tracks of ancestral hominins from the Pliocene forms a new “holy grail” for our research team.
by : Charles Helm, Research Associate, African Centre for Coastal Palaeoscience, Nelson Mandela University
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