The coastlines of southern Africa are famous gathering places for seals. These charismatic sea-goers aren't just popular with human tourists – hungry predators are also big fans. And apparently this isn't a new thing in this part of the world. The discovery of thousands of seal bones scored with bite marks at a fossil site in South Africa reveals that this region has been a popular spot for seals – and their predators – for a long time.
The fossils come from West Coast Fossil Park at Langebaanweg, which lies about 120 kilometres north of Cape Town. The site was originally discovered during phosphate mining in the 1940s, and in the time since then, many thousands of fossils have been found here, including the remains of familiar animals like elephants, giraffes and antelopes, as well as more exotic creatures like saber-toothed cats, giant pigs and three-toed horses. Dating back to the early Pliocene Epoch, about five million years ago, it's among the most plentiful fossil sites of its age anywhere in the world.
There are also seals here. Lots of them. More than 3,000 seal bones have been discovered, the fossilised remains of hundreds of these marine mammals. And many of them bear distinctive markings left behind by the scraping and chomping of sharp teeth. These seals were someone's lunch.
Exactly what was nomming on these seals isn't fully known. A small percentage of the tooth marks are clearly from sharks, and there are even some signs of gnawing by the large incisors of ancient porcupines. But most of the conspicuous tooth marks came from large terrestrial carnivores, and the top culprits are hyenas and bears – that's right, there were bears in South Africa five million years ago!
"What is also interesting about this site is we have adults, juveniles and we have pups, so we know this was a breeding site," said Romala Govender, curator of Cenozoic palaeontology at the Iziko Museum in Cape Town, where the Langebaanweg fossils are stored. Govender spoke with me while presenting the latest on this research at this year's meeting of the Society of Vertebrate Paleontology.
If you visit the fossil site now, you'll find yourself some way from the coast, but five million years ago, it was only one kilometre upriver from the ocean. Today, Cape fur seals famously establish their breeding colonies on coastlines in South Africa and Namibia, or on islands not far offshore. Back during the Pliocene, the seals were different (they were "true seals" as opposed to the eared seals that live there today), but they may have been congregating in the same way.
According to Govender, there was an archipelago of islands offshore at that time, and it's likely that these ancient seals were gathering there, while the chewed-on bones at the fossil site probably came from the bodies of dead seals that washed up on shore (this happens today, too), where hungry scavengers could find them.
"We can't really say hunting versus scavenging," Govender noted. Because of how fragmented and scattered the bones are, there's little opportunity to find direct evidence one way or the other. What is clear is that these seals were feeding a variety of carnivorous mouths, both on land and in the sea.
The next step of this research is to confirm which animals left the tooth marks, and that means first categorising them by shape. "We're trying to classify the data in terms of pits, scratches and scores," Govender explained.After that, the researchers will compare these marks to those left by living animals, which means a trip to the taphonomy collection, where examples of bones chewed on by modern-day African carnivores can be found.
"Fortunately for us, our lab is right next door to the taphonomy collection!" said Govender. But while that collection houses bones gnawed on by the continent's modern predators, for bear bite marks, they'll have to look elsewhere!
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Top header image: Federico Moroni, Flickr
Fossils
Discoveries
Predator vs Prey
