Triassic reptile with unusual jaws named as a new species

A fossil hotspot in southern England has revealed another of its secrets.

The former quarry located in Cromhall, South Gloucestershire, is renowned as a rich source of Triassic wildlife. Gliding reptiles, dinosaur relatives and even one of the earliest known lizards have all been found at the site over the past few decades.

A new species, named Threordatoth chasmatos, has now been added to the list. Dr Luke Meade, the lead author of research describing its fossils, says the reptile would probably have looked similar to horned lizards alive today.

“Based on its relatives, Threordatoth would have been a small reptile with bony spikes on its head and potentially some bony armour on its body,” Luke says. “I like to imagine them scampering around the sinkholes and fissures of southwest England in the Late Triassic, looking for plants and bugs to eat while avoiding the early relatives of dinosaurs.”

While only incomplete parts of its jaw have been discovered to date, the fossils of Threordatoth are important for understanding a little-known group of reptiles known as the procolophonids. Dr Marc Jones, our Curator of Fossil Reptiles, says that every new fossil brings scientists closer to understanding these prehistoric animals.

“These animals were generally quite small, so their bones are vulnerable to being damaged or destroyed before the process of fossilisation,” Marc says. “Generally, this means that we only have the teeth and jaws of these animals.”

“As a result, there’s still a lot we don’t know about the reptiles. By continuing to investigate sites like Cromhall, we can hopefully answer some of our outstanding questions.”

The findings of the study were published in the journal Papers in Palaeontology.

What are procolophonids?

First evolving around 260 million years ago, the procolophonids were an important part of Earth’s ecosystems from the end of the Permian and into the Triassic.  While they might look lizard-like in appearance, these reptiles aren’t closely related to them. Instead, it’s an example of convergent evolution.

It’s generally thought that the procolophonids are actually distant cousins to all reptiles and birds, but not particularly related to any of them.

Some of the best known procolophonids from the UK have been discovered in geological features known as fissure fills. These deposits, which include Cromhall, formed when the remains of ancient wildlife fell into rocky crevices which were then covered over and buried.

The small size of the fissures mean they only contain correspondingly small fossils, but this material is often exquisitely preserved. As a result, the fossils are highly sought after by palaeontologists.

In the case of Threordatoth, its fossils are scattered between the Natural History Museum, National Museums Scotland, the University of Aberdeen and the University of Cambridge. While these bones had occasionally been referenced by previous scientists, a detailed examination hadn’t been carried out on them.

After carefully using weak acid to remove layers of rock from the bones, the remains were then CT scanned to give the team a closer look. From what they could see, they were convinced that the fossils represented a new species.

“These specimens had a lot of unusual characteristics,” Marc says. “The front of the jaw, for example, isn’t fused together, and there’s no obvious site where they would connect together. Instead, we think that the two halves of the jaw were probably connected by ligaments.”

“If this was the case, the jaw would have been somewhat flexible. It may have aided tooth-on-tooth contact during chewing and provided some shock-absorption potential, preventing forces being transferred between the two sides of the jaw.”

A toothy reptile

The characteristic that really sets Threordatoth apart from its relatives, however, is its teeth.

“The teeth of procolophonids are complicated, with enamel that is relatively thick compared to other reptiles,” Marc explains. “It’s been suggested that the complexity of these teeth allowed them to process a range of foods including plants and insects.”

“Available evidence suggests that procolophonids were most diverse in the Early and Middle Triassic. It suggests that they recovered strongly after the Permian mass extinction, with different species focusing on different food sources.”

Researchers have noticed that procolophonids started to lose teeth over the course of the Triassic, which perhaps suggests the animals were specialising towards certain lifestyles.

“As time passes, we see that most procolophonids develop teeth with two points and reduce their tooth count,” Luke says. “It’s thought this might have allowed these animals to eat tougher diets, perhaps as they became more herbivorous.”

“Threordatoth took the tooth reduction trend further than any other procolophonid in the Late Triassic. It has just four teeth on either side of its jaw.”

However, the teeth of this new species are even more unusual. Unlike any of its relatives, each of the reptile’s teeth has three points. This is so distinctive that the researchers named the species Threordatoth which translates as ‘three-pointed teeth’ in Old English.

The only other procolophonid with teeth anything like this is another similar species unearthed at Cromhall called Hwiccewyrm. As investigations continue at the quarry, the team are hopeful that additional fossils will help to reveal more about the Triassic’s fauna.

“A range of species from all sorts of different groups have already been found at Cromhall,” Luke says. “However, there’s a lot more material that’s yet to be investigated which could contain many other species.”

“Sifting through this material for tiny fossils is time consuming, but it could help to explain more about the diversity of animals like the procolophonids.”