Rhynchosaurs starved to death because their diet left them without teeth

June 9 () –

Rhynchosaurs, an ancient herbivorous reptile ancestor of the dinosaurs, probably starved to death in old age, since eating vegetation took its toll on their teeth.

Rhynchosaurs, which walked the earth between 250 and 225 million years ago, are a little-known group of ancient, sheep-sized reptiles that thrived during the Triassic Period, a time of generally warm climates and hardy vegetation.

In a new study published in paleontologythe researchers studied specimens found in Devon, England, and used a CT scan to see how the teeth wore down as they fed, and how new teeth were added to the back of the tooth rows as the animals grew. in size.

“I first studied rhynchosaurs years ago,” he said. it’s a statement team leader Professor Mike Benton, from the University of Bristol’s School of Earth Sciences, “and I was surprised to find that in many cases they dominated their ecosystems. If you found one fossil, you found hundreds.” Were they the sheep or the antelopes of his day? and yet they had specialized dental systems that were apparently adapted to deal with masses of hard plant foods.”

Dr Rob Coram, who discovered the Devon fossils, said: “Fossils are rare, but occasionally individuals were entombed during river flooding. This has made it possible to piece together a series of rhinchosaur jaw bones that were aged very young, perhaps even newborns, to adults, and including one particularly old animal, a Triassic veteran whose teeth had worn away and was probably struggling to get enough nutrition every day.”

“By comparing the sequence of fossils over their lifetime, we were able to see that as the animals aged, the area of ​​the jaws that was worn at any time moved rearward relative to the front of the skull, which it caused the wear of new teeth and new bones,” he said. Thitiwoot Sethapanichsakul, who studied jaws as part of her Master’s in Paleobiology. “Clearly they were eating really tough foods like ferns, which wore down the teeth down to the jaw bone, which means they were basically cutting up their meals with a mixture of teeth and bones.”

“Eventually though, after a certain age, we’re not sure how many years, their growth would slow and the area of ​​wear would get deeper and deeper,” Coram added. “It’s like elephants today: they have a fixed number of teeth that are used at the back, and after the age of seventy they have the last tooth left, and that’s it.”

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

Rhynchosaurs were an important part of terrestrial ecosystems during the Triassic, when life was recovering from the world’s largest mass extinction, at the end of the previous Permian Period. These animals were part of this recovery and set the stage for new kinds of ecologies as early dinosaurs and then mammals became dominant. as the modern world slowly built.

By comparing earlier examples of rhynchosaurs, such as those from Devon, with later examples from Scotland and Argentina, the team was also able to show how their dentition evolved over time and how their unique teeth allowed them to diversify twice, in the Middle Triassic and then in the Superior. But in the end, climate change, and especially changes in available plants, they seem to have allowed the dinosaurs to take over the extinction of the rhynchosaurs.