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Dec 31, 2023

Ancient reptiles starved thanks to some pretty tough plants

There was a time before the dinosaurs when ancient sheep-sized reptiles thrived

There was a time before the dinosaurs when ancient sheep-sized reptiles thrived on Earth. While they were numerous, a new study reveals that their diets actually led to their own starvation by wearing out their teeth.

Before the dinosaurs, roughly 250-225 million years ago, tough vegetation thrived in mostly gentle climates across the planet. Feeding on these chewy plants were a species of reptile known as rhynchosaurs. These Triassic-aged creatures were an integral part of the development of life on Earth, as they helped repopulate the planet after the mass extinction event that happened at the end of the Permian Period. That event led to the annihilation of 70% of land animals and 95% of sea life.

While researchers probably know more about dinosaurs than this precursor species, new research carried out by the University of Bristol has shed light on how what the animals ate led to their own demise.

Using CT scans of a range of rhynchosaur fossils representing different ages of the reptile, they determined that as the animals aged, the tough plants on which they fed ground their teeth down to such a point that they would no longer be able to get adequate nutrition, which would lead to starvation and death. This is despite the fact that the study also revealed that the animals added teeth towards the back of their mouths as they aged.

"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," said study co-author Thitiwoot Sethapanichsakul. "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."

The fossils used in the study were all found in Devon, in southern England, by UB's Rob Coram.

"The fossils are rare, but occasionally individuals were entombed during river floods," he said. "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."

Coram said that even the new tooth growth eventually couldn't outpace the continued grinding it was subjected to. He compared the loss of teeth in the ancient reptiles to what happens with modern-day elephants.

"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," he said. "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."

The study also revealed that the dentition of the rhynchosaurs diversified twice during their evolution. The first time, they developed tooth plates with multiple rows of teeth with grooves and ridges on the bottom of the teeth. The second phase of adaptation saw the teeth organize into a single row with even deeper grooves.

The researchers have published their findings in the journal, Palaeontology.

Source: University of Bristol