New fossil shark named from ancient skeleton discovered in southern England

A hidden remnant of the UK’s distant past has shed new light on the evolution of sharks.

While sharks have been a firm fixture of life in the oceans for over 450 million years, their soft skeletons rarely fossilise. As a result, scientists often infer the appearance and behaviour of these animals from fossil teeth and scale which are much more common but less informative.

This makes investigating rare shark skeletons that have fossilised vital to finding out what these predators of the past were really like. This includes those skeletons that are already known in many of the world’s natural history collections which might not have been studied in decades.

New scans of two fossils cared for by the Natural History Museum are already breaking new ground. A team of scientists led by Dr Richard Dearden, who’s based at Naturalis Biodiversity Center in the Netherlands, revealed that they contained the remains of a new species of collared carpet shark, which they called Pararhincodon torquis.

“These ancient sharks have a confusing name, as Pararhincodon translates as ‘nearly whale shark’,” Richard explains. “But collared carpet sharks have always been small sharks less than a metre long.”

“To try and get their true identity across, I decided to name this species after torcs, the Iron Age neck rings, or collars, that were worn by the Celts. This highlights that it’s an ancient collared carpet shark from Europe with many differences from its living relatives found around Australia and southeast Asia.”

The findings of the study, which was funded by the European Union, were published in the journal Royal Society Open Science.

Trapped in the Chalk

As is the case with many scientific achievements, the story of P. torquis began with a happy accident. Richard had been studying a poorly understood fossil shark known as Synechodus and was investigating one of its fossils our collections.

Unlike many shark skeletons, these individuals were preserved in 3D. Emma Bernard, who looks after the fossil fish collections, explains that this is due to how they were preserved.

“The British Chalk is a Lagerstätten, which means they’re rocks with exceptionally preserved fossils,” says Emma. “These animals were buried very quickly, before anything could eat away at them, so their 3D structure remains in the rock.”

“What’s so exceptional about these fossils is that they are sharks. Their bodies are mostly made of cartilage – the same material as our ears and noses. It doesn’t preserve as well as bones and teeth do. So, while we have lots of teeth of ancient sharks, their skeletons are much harder to come by.”

CT scans of the fossil suggested that while it was labelled as Synechodus, the specimen was very different from other remains of this species. A scan of a second unidentified fossil shark from the chalk also had the same anatomy, convincing Richard that the fossils were actually something else.

While the scans provided certain details, extracting the extremely small teeth buried in the chalk was needed to help build the scientists’ case. This task fell to Kieran Miles, who is our fossil preparator.

“I tend to work on dinosaurs and other large fossils, so it’s normally quite obvious where the bones are,” says Kieran. “But in this case, I had to use the CT scans like a map to find where these tiny teeth were embedded in the rock. The first one was easier, as the tip was just poking out of the surface, but the second one was completely hidden in the rock.”

The process began with Kieran carefully scraping away at the rock using a sewing needle. Once he’d managed to remove the chunk of rock containing the tooth, he dropped it into a solution containing acetic acid.

“I cleaned away the chalk with a tiny paintbrush as it was dissolving,” Kieran continues. “This left us with the tooth that could be examined under an electron microscope. It was an incredibly difficult job, but really enjoyable all the same.”

An ancient shark odyssey

By analysing scans of the fossilised teeth and skeletons, the team could clearly see that P. torquis was unique. By comparing the fossil to scans of living shark species provided by Australian collaborators, they were also able to confirm that its closest living relatives were collared carpet sharks.

“These are the only known three-dimensional fossils from these sharks where you can make out details of the skeleton,” says Richard. “Collared carpet sharks are rare today, so this can tell us some exciting things about how they evolved.”

While the two P. torquis fossils were found near Salisbury and Newhaven in southern England, living collared carpet sharks are found half a world away in the shallow tropical and subtropical waters of the Indian and Pacific Oceans. To get there, the animals must have spent millions of years tracking their preferred habitat across the world as the continents and climate changed.

“While a lot of the anatomy of these sharks was laid down before they started to spread, there are a couple of things that seem to have only appeared later,” Richard adds.

“One particularly interesting feature is their fin, which is a bit weird as it only has two parts to its base, rather than the more common three. We thought that might have been something that evolved at the start of the group, but these ancient sharks have three fin bases so it must have happened after they split off from modern carpet sharks.”

The team are confident that further insights into shark evolution, and new species, will be found as scientists revisit British Chalk fossils.