Mention the word “fossils” to people and most will probably think of bones. Of course, body fossils make up a large part of the global fossil record. But humans and other species leave their mark in other ways too – for instance, their tracks. The study of these fossil tracks and traces is called ichnology.
I am an ichnologist. In 2008 my colleagues and I launched the Cape South Coast Ichnology Project to study a 350km stretch of South Africa’s coastline. We’ve since identified more than 350 vertebrate tracksites, most of them in cemented dunes called aeolianites that date back to the Pleistocene Epoch (also known as the Ice Age), which began about 2.6 million years ago and ended 11,700 years ago.
At a global level it is rare to find fossilised hominin tracks. There is something very special about them: a fossil trackway looks as if it could have been created yesterday, and the fact that our own ancestors would have created such tracks fills them with extra meaning. It’s always a thrill for researchers to find them.
We knew from the region’s extensive archaeological record that ancestral humans inhabited the region during the Pleistocene. And Homo sapiens tracks had been identified elsewhere in South Africa, on the Cape east coast in the 1960s and the Cape west coast in the 1990s. But, given their rarity, we weren’t banking on hominin tracks being among our finds.
We were fortunate. In 2016 we found 40 hominin tracks on the ceiling and side walls of a cave at Brenton-on-Sea, near the town of Knysna on the Cape south coast. In subsequent years we have been privileged to find more hominin tracksites, all on aeolianite surfaces on the Cape coast. One discovery, in the Garden Route National Park, even included the oldest Homo sapiens footprint identified anywhere in the world – it dates back about 153,000 years.
Now we’ve documented a cluster of nine hominin trace fossil sites at Brenton-on-Sea: seven tracksites, and two open-air archaeological sites containing tools, shells and bone (which help us understand the diet of our ancestors). One of the tracksites is the original site found in 2016. Our analysis shows that it contains the oldest known evidence of a human running. Another site shows evidence of toddler tracks alongside those of adults.
Each site within this 1,200 metre stretch of coastline is from a different rock unit and they appear to span a considerable time interval. Adjacent rocks have been dated using a technique known as optically stimulated luminescence to a range of between 113,000 and 76,000 years (that is a measure of how long ago grains deep within the rocks were exposed to light).
The nine sites are not easy to find: some were only briefly exposed following storm surges, and are now again covered by metres of sand, while others can only be safely accessed using ladders. At one site, the space between the track-bearing layer on the ceiling and the surface below it was so tiny that we had to bring in our caving colleagues – who love working in confined spaces – to properly document it. The rest of us struggled to fit into the narrow gap.
Mention the word “fossils” to people and most will probably think of bones. Of course, body fossils make up a large part of the global fossil record. But humans and other species leave their mark in other ways too – for instance, their tracks. The study of these fossil tracks and traces is called ichnology.
I am an ichnologist. In 2008 my colleagues and I launched the Cape South Coast Ichnology Project to study a 350km stretch of South Africa’s coastline. We’ve since identified more than 350 vertebrate tracksites, most of them in cemented dunes called aeolianites that date back to the Pleistocene Epoch (also known as the Ice Age), which began about 2.6 million years ago and ended 11,700 years ago.
At a global level it is rare to find fossilised hominin tracks. There is something very special about them: a fossil trackway looks as if it could have been created yesterday, and the fact that our own ancestors would have created such tracks fills them with extra meaning. It’s always a thrill for researchers to find them.
We knew from the region’s extensive archaeological record that ancestral humans inhabited the region during the Pleistocene. And Homo sapiens tracks had been identified elsewhere in South Africa, on the Cape east coast in the 1960s and the Cape west coast in the 1990s. But, given their rarity, we weren’t banking on hominin tracks being among our finds.
We were fortunate. In 2016 we found 40 hominin tracks on the ceiling and side walls of a cave at Brenton-on-Sea, near the town of Knysna on the Cape south coast. In subsequent years we have been privileged to find more hominin tracksites, all on aeolianite surfaces on the Cape coast. One discovery, in the Garden Route National Park, even included the oldest Homo sapiens footprint identified anywhere in the world – it dates back about 153,000 years.
Now we’ve documented a cluster of nine hominin trace fossil sites at Brenton-on-Sea: seven tracksites, and two open-air archaeological sites containing tools, shells and bone (which help us understand the diet of our ancestors). One of the tracksites is the original site found in 2016. Our analysis shows that it contains the oldest known evidence of a human running. Another site shows evidence of toddler tracks alongside those of adults.
Each site within this 1,200 metre stretch of coastline is from a different rock unit and they appear to span a considerable time interval. Adjacent rocks have been dated using a technique known as optically stimulated luminescence to a range of between 113,000 and 76,000 years (that is a measure of how long ago grains deep within the rocks were exposed to light).
The nine sites are not easy to find: some were only briefly exposed following storm surges, and are now again covered by metres of sand, while others can only be safely accessed using ladders. At one site, the space between the track-bearing layer on the ceiling and the surface below it was so tiny that we had to bring in our caving colleagues – who love working in confined spaces – to properly document it. The rest of us struggled to fit into the narrow gap.
This article is republished from The Conversation under a Creative Commons license. Read the original article.