Tyrannosaur teeth in southern England reveal Cretaceous dinosaur ecosystem

Spinosaurs, tyrannosaurs and relatives of Velociraptor once stalked England’s south coast.

While the largest carnivore found in Sussex today is the badger, it was a very different story 135 million years ago. Two-legged dinosaurs known as theropods roamed the countryside, with the largest of these meat-eaters measuring over 10 metres in length.

As bones from dinosaurs of this age are uncommon in England, scientists are reconstructing the region’s distant past using teeth alone. Machine learning was used to analyse these tiny fossils from the Natural History Museum and Bexhill Museum to reveal which carnivores were alive at the time.

Dr Darren Naish, a co-author of the study, says that the discovery of such a diverse group of dinosaurs helps to fill in a long-standing gap in the study of Britain’s palaeontology.

“Southern England has an exceptionally good record of Cretaceous dinosaurs, and various sediment layers here are globally unique in terms of geological age and the fossils they contain,” he explains.

“While these East Sussex dinosaurs are older than those from the better-known Cretaceous sediments of the Isle of Wight, they are mysterious and poorly known by comparison. We’ve hoped for decades to find out which theropod groups lived here, so the conclusions of our new study are really exciting.”

The findings were published in the journal Papers in Palaeontology.

What is the Wealden Supergroup?

Running under large parts of southern England, the rocks of the Wealden Supergroup have long been important for understanding dinosaurs. Some of the earliest dinosaurs ever found, like Iguanodon and Mantellisaurus, were first discovered here over 200 years ago, with many more fossils unearthed since then.

The rocks of the Wealden offer a window into the Early Cretaceous, which lasted from around 145 to 100 million years ago. Palaeontologists are interested in this period because it’s when many groups of dinosaurs rose to prominence, including the ancestors of Triceratops and Tyrannosaurus.

While the Wealden extends across large parts of England, most attention is focused on its outcrops on the Isle of Wight. Dr Simon Wills, a co-author of the paper and Scientific Associate at the Natural History Museum, explains why.

“On the Isle of Wight, there is a constantly eroding coastline which is always exposing new material,” he says. “Meanwhile, on the mainland, palaeontologists are generally restricted to open quarries, where access is not always guaranteed.”

“In the past, there were many more active quarries across the Wealden, throwing up new discoveries. This makes historical collections from now closed or inaccessible quarries important to understand the diversity of the past.”

While skeletons from theropod dinosaurs like Baryonyx have been found on the mainland, herbivore remains are more common. But as full skeletons are rare, the researchers turned to isolated dinosaur teeth to fill in the gaps.

Dinosaurs grew and shed teeth throughout their lives, meaning they’re relatively common. By analysing teeth held in museum collections, the researchers can piece together which theropods were present in the Early Cretaceous.

Tyrannosaur teeth

Identifying dinosaur teeth is no easy task. As University of York PhD student and co-author Lucy Handford explains, the descriptions that collectors assigned to fossil teeth in previous centuries can be unreliable.

“Assigning isolated teeth to theropod groups can be challenging, especially as many features evolve independently amongst different lineages,” Lucy says. “This is why we employed various methods to help refine our findings, leading to more confident classifications.”

One emerging technique for identifying dinosaur teeth is machine learning. Simon has been feeding the measurements of teeth from known dinosaurs into computer models to train them to subsequently spot these patterns in unidentified tooth fossils.

While these models can’t assign the teeth to individual species, they can identify them to the group of dinosaurs it came from. Previous research, for example, showed that other tooth fossils from the UK are the oldest known remains of therizinosaurs and troodontids anywhere in the world.

These algorithms formed one part of the team’s investigation, which focused on four dinosaur teeth from Bexhill Museum and one from the Natural History Museum. These had previously been identified as belonging to a range of dinosaurs including spinosaurs and allosauroids.

While the team were able to confirm the presence of spinosaurs, the ‘allosauroid’ teeth turned out to be from tyrannosaurs instead. This is notable as the first time that remains from these dinosaurs have been identified from sediments of this age and region.

While later tyrannosaurs, like Tyrannosaurus rex, would reach up to 12 metres long, these dinosaurs were around a third of that size. Rather than taking on large prey, these dinosaurs would have hunted a variety of small dinosaurs and other reptiles.  

The team hope to continue examining museum collections, and refine their machine learning models further, to answer further questions about the wildlife of the distant past.