Triassic herbivores starved to death as diet took toll on teeth, study suggests

A sheep-sized reptile that roamed the earth between 250 and 225 million years ago eating tough vegetation eventually starved to death due to its diet weakening its teeth, new research has suggested.

Little is understood about rhynchosaurs who thrived during the Triassic Period, a time of generally warm climates and tough plants.

For the new study, researchers studied specimens found in Devon, using scans to see how the teeth wore down as they fed, and how new teeth were added at the backs of the tooth rows as the animals grew in size.

The findings indicate that it is likely these early herbivores eventually starved to death in old age, with the vegetation taking its toll on their teeth.

Team leader Professor Mike Benton, from the University of Bristol’s School of Earth Sciences, said: “I first studied the rhynchosaurs years ago and I was amazed to find that in many cases they dominated their ecosystems. If you found one fossil, you found hundreds.

“They were the sheep or antelopes of their day, and yet they had specialised dental systems that were apparently adapted for dealing with masses of tough plant food.”

Dr Rob Coram, who discovered the Devon fossils, said: “The fossils are rare, but occasionally individuals were entombed during river floods.

“This has made it possible to put together a series of jaw bones of rhynchosaurs that ranged in age from quite young, maybe even babies, through adults, and including one particularly old animal, a Triassic old-timer whose teeth had worn right down and probably struggled to get enough nutrition each day.”

Thitiwoot Sethapanichsakul who studied the jaws as part of his MSc in palaeobiology said: “Comparing the sequence of fossils through their lifetime, we could see that as the animals aged, the area of the jaws under wear at any time moved backwards relative to the front of the skull, bringing new teeth and new bone into wear.

“They were clearly eating really tough food such as ferns that wore the teeth down to the bone of the jaw, meaning that they were basically chopping their meals by a mix of teeth and bone.”

Dr Coram added: “Eventually though, after a certain age – we’re not sure quite how many years – their growth slowed down and the area of wear was fixed and just got deeper and deeper.

“It’s like elephants today – they have a fixed number of teeth that come into use from the back, and after the age of 70 or so they’re on their last tooth, and then that’s that.

“We don’t think the rhynchosaurs lived that long, but their plant food was so testing that their jaws simply wore out and presumably they eventually starved to death.”

Experts suggest rhynchosaurs were an important part of the ecosystems on land during the Triassic, when life was recovering from the world’s greatest mass extinction, at the end of the preceding Permian Period.

Researchers compared examples of earlier rhynchosaurs, such as those from Devon, with later-occurring examples from Scotland and Argentina.

They were able to show how their unique teeth enabled them to diversify twice, in the Middle and then in the Late Triassic.

But in the end, climate change, and especially changes of available plants, seem to have enabled the dinosaurs to take over as the rhynchosaurs died out.

The findings are published in the Palaeontology journal.