A team of researchers from the University of Bristol has shed light on the life of the ancient reptile, Rhynchosaur, which walked the earth 250-225 million years ago, before it was supplanted by dinosaurs.
Rhynchosaurs are a little-understood group of ancient reptiles roughly the size of sheep that thrived during the Triassic period, a time of generally warm climates and harsh vegetation.
In the new study, the researchers studied specimens in Devon and used CT scans to see how the teeth wore down as they fed, and how new teeth were added at the back of the dental rows as the animals grew in size.
Results published today in PaleontologyIt turns out that these early herbivores likely eventually starved to death in old age, and that vegetation took its toll on their teeth.
Team leader Professor Mike Benton from Bristol’s School of Geosciences said: “I first studied rhinosaurs years ago and was amazed to find that in many cases they controlled their own ecosystems. If you find one fossil, you will find hundreds. They were sheep or antelopes.” At their age, however, they had specialized dental systems that were apparently adapted to handle lumps of tough plant foods.”
Dr Rob Coram, who unearthed the Devonian fossils, said: “Fossils are rare, but sometimes individuals are buried during river floods. This has enabled the assembly of a series of jaw bones of rhynosaurs that ranged in age from very young, and perhaps even infants, from During adults, including one particularly ancient animal, an old Triassic whose teeth were worn down and probably struggled to get enough nutrition every day.”
“By comparing the sequence of fossils during their lifetime, we can see that as the animals aged, the jaw region under wear moved at any point backward relative to the front of the skull, which led to wear on new teeth and new bone,” says Thitiwoot Sethapanichsakul who studied jaws as part of his MSc. paleobiology. “They were apparently eating really tough food like ferns, which are tooth-eroding down to the jawbone, which means they were cutting their meals with a mixture of teeth and bones.”
“Eventually, after a certain age – we’re not sure exactly how many years – its growth slowed down and the area of wear was repaired and got deeper and deeper,” added Dr. Coram. “It’s like elephants today — they have a fixed number of teeth that are used from behind, and after the age of 70 or so they’re on their last teeth, and then that’s it.”
“We don’t think rhynchosaurs lived that long, but their plant food was such a severe test that their jaws simply wore out and they supposedly eventually starved to death.”
Rhynchosaurs were an important part of Earth’s ecosystems during the Triassic period, when life was recovering from the world’s largest mass extinction, at the end of the preceding Permian period. These animals were part of this recovery and paved the way for new species of ecology when the first dinosaurs and later mammals became dominant, as the modern world was slowly being built.
By comparing examples of earlier rhynchosaurs, such as those from Devon, with later-occurring examples from Scotland and Argentina, the team was also able to show how their teeth evolved through time, and how their unique teeth enabled them to diversify twice, in the middle and then late Triassic. But in the end, climate change, and especially changes in the available vegetation, seems to have enabled the dinosaurs to take over as the rhynchosaurs became extinct.
the unique teeth of rhynchosaurs and their two-stage success as Triassic herbivores, Paleontology (2023). DOI: 10.1111/pal.12654
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