They discover an extinct prehistoric reptile that lived among dinosaurs

Sep. 15 () –

Smithsonian researchers have discovered a new extinct species of lizard-like reptile that it belongs to the same ancient lineage as the living New Zealand tuatara.

A team of scientists describe in Journal of Systematic Palaeontology the new species ‘Opisthiamimus gregori’, which inhabited the Jurassic of North America about 150 million years ago together with dinosaurs such as the Stegosaurus and the Allosaurus.

In life, this prehistoric reptile would have measured about 16 centimeters from snout to tail, which would fit curled up in the palm of an adult human hand. and probably survived on a diet of insects and other invertebrates.

“The important thing about the tuatara is that it represents this enormous evolutionary history that we are lucky enough to capture in what is probably its final act,” he says. it’s a statement the author of the study Matthew Carrano, curator of Dinosauria at the Museum of Natural History in London,–. Although it looks like a relatively simple lizard, it embodies an evolutionary epic that dates back more than 200 million years.”

The discovery stems from a handful of specimens including a remarkably complete and well-preserved fossil skeleton excavated from a site centered on an Allosaurus nest in the Morrison Formation of northern Wyoming. Further study of the find could help reveal why this animal’s ancient order of reptiles It went from being diverse and numerous in the Jurassic to only the New Zealand tuatara surviving today.

The tuatara looks a bit like a particularly robust iguana, but both it and its newfound relative are not actually lizards. They are actually rhinocephalians, an order that diverged from lizards at least 230 million years ago.Carrano explains.

In their Jurassic heyday, rhinocephalians were found almost everywhere in the world, were large and small in size, and performed ecological functions ranging from aquatic fish hunters to bulky plant eaters. But, for reasons not yet fully understood, rhinocephalians all but disappeared as lizards and snakes became the most common and diverse reptiles in the world.

This evolutionary gulf between lizards and rhinoceroses helps explain the tuatara’s strange features, such as its teeth fused to the jaw bone, a unique chewing motion that slides the lower jaw back and forth like a saw blade, a life of more than 100 years and tolerance to colder climates.

After the formal description of the ‘O. gregori’, Carrano notes that the fossil has been added to the museum’s collections, where it will remain available for future study, and perhaps one day he will help researchers figure out why the tuatara is all that remains of the rhinocephalians, while lizards are now found all over the world.

“These animals may have disappeared in part due to competition from lizards, but perhaps also due to global climate changes and habitat modification,” says Carrano. “It is fascinating that the dominance of one group gives way to another over evolutionary time, and we still need more evidence to explain exactly what happened, but with fossils like this is how we’ll put it in order“.

The researchers named the new species after museum volunteer Joseph Gregor, who spent hundreds of hours meticulously scraping and chiseling bones from a stone block that caught the attention of museum fossil preparer Pete Kroehler in 2010.

“Pete is one of those people who has kind of X-ray vision for this kind of thing,” says Carrano. “He noticed two little specks of bone on the side of this block and marked it to bring without having to.” a real idea of ​​what was in it. Turns out he hit the jackpot“.

The fossil is almost completely complete, except for the tail and parts of the hind legs. Carrano said such a complete skeleton is rare for small prehistoric creatures like this one, because their fragile bones are often destroyed before fossilizing or emerging from an eroding rock formation today. For this reason, paleontologists know rhinocephalians mainly from small fragments of their jaws and teeth.

After freeing as much of the tiny fossil as possible from the rock, given its fragility, the team, led by DeMar, set about scanning the fossil with high-resolution computed tomography (CT), a method that uses multiple X-ray images. from different angles to create a three-dimensional representation of the specimen.

The team used three computed tomography facilities, one of them located at the National Museum of Natural History, to capture as much as possible about the fossil.

Once the fossil bones had been digitally rendered to sub-millimeter accuracy, DeMar set about reassembling the digitized skull bones, some of which were crushed, out of place or missing on one side, using software. to finally create a nearly complete 3D reconstruction. The 3D reconstructed skull now offers researchers an unprecedented view of the head of this Jurassic reptile.

Given Opisthiamimus’s diminutive size, the shape of its teeth and the rigidity of its skull, it likely fed on insects, DeMar says, adding that harder-shelled prey, such as beetles or water bugs, could also have been in your menu. Generally speaking, the new species looks a lot like a miniaturized version of its only surviving relative (tuataras are about five times as long).

“Such a complete specimen has enormous potential to make comparisons with fossils collected in the future and to identify or reclassify specimens that are already sitting somewhere in a museum drawer,” DeMar said. “With the 3D models we have, at some point We could also do studies that use software to look at the jaw mechanics of this bug.”