Researchers have discovered an extinct prehistoric reptile that lived among the dinosaurs

An artistic interpretation of a newly discovered extinct species of lizard-like reptile belonging to the same ancient lineage as the living tuatara of New Zealand. The newly discovered Opisthiamimus gregori preyed on a now-extinct aquatic insect (Morrisonnepa jurassica), while in the background the predatory dinosaur Allosaurus jimmadseni guards its nest. The landscape is the floodplains of a river in late Jurassic Wyoming, about 150 million years ago. Credit: Julius Csotonyi for Smithsonian Institution

Smithsonian researchers have discovered a new extinct species of lizard-like reptile that belongs to the same ancient lineage as the living tuatara in New Zealand. A team of scientists, including National Museum of Dinosaur Natural History curator Matthew Carano and research fellow David DeMar Jr as well as University College London and the Natural History Museum London scholar Mark Jones have described the new species Opisthiamimus gregori, which once inhabited Jurassic North America. About 150 million years ago alongside dinosaurs such as Stegosaurus and Allosaurus, in a research paper published today in Journal of Systematic Paleontology. In life, this prehistoric reptile was about 16 cm (about 6 inches) long from nose to tail – and would have curled up in the palm of an adult human – and likely survived on a diet of insects and other invertebrates.

“What’s important about the tuatara is that it represents this enormous evolutionary story that we are fortunate enough to know in what is likely to be its closing event,” said Carano. “Although it looks like a relatively simple lizard, it exemplifies a whole evolutionary saga going back more than 200 million years.”

This find comes from a few specimens including a very complete and well-preserved fossil skeleton excavated from a site centered around an Allosaurus nest in the Morrison Formation of northern Wyoming. Further study of the discovery could help reveal why the ancient order of reptiles of this animal disappeared from being diverse and numerous in the Jurassic to the surviving New Zealand tuatara today.






The research team set out to survey the fossil using 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 separate CT facilities, including one at the Smithsonian’s National Museum of Natural History, to capture everything they could about the fossil. Once the fossil bones were digitally submitted, the team set out to reassemble the digitized skull bones, some of which had been crushed, misplaced or lost on one side, using software to create an almost complete 3D reconstruction. Credit: D. DeMar

The tuatara look somewhat like a particularly powerful iguana, but the tuatara and its newly discovered relatives aren’t actually lizards at all. They’re actually rhynchocephalians, Carano said, something that differed from lizards at least 230 million years ago.

At the height of the Jurassic period, rhynchocephalians were found almost all over the world, and they came in large and small sizes, occupying ecological roles ranging from aquatic fishermen to huge plant cutters. But for reasons that are still not fully understood, both rhynchocephalians disappeared as lizards and snakes grew to become the most common and most diverse reptiles around the world.

This evolutionary chasm between lizards and rhynchocephalians helps explain tuatara’s peculiar features such as fused teeth in jaw boneUnique chewing action that slides the lower jaw back and forth like a saw blade, 100+ year life and withstands cold climates.

Following O.Gregori’s official description, Carano said the fossil has been added to the museum’s collections where it will remain available for future study, and perhaps one day help researchers figure out why tuatara It is all that remains of the rhynchocephalians, while lizards are now found all over the world.

Smithsonian researchers discover extinct prehistoric reptiles that lived among the dinosaurs

Fossil skeleton of a new lizard-like reptile Opisthiamimus gregori. The fossil was discovered in the Morrison Formation of the Bighorn Basin, north-central Wyoming, and dates back to the late Jurassic period, about 150 million years ago. The researchers named the new species after volunteer Joseph Gregor at the Smithsonian Institution’s National Museum of Natural History, who spent hundreds of hours meticulously scraping the bones and chiselling them with a chisel from a stone block first discovered by the Museum of Fossil Museum curator Pete Krehler in 2010. The fossil was added to the museum’s collections. It will remain available for future study. Credit: David Demar of the Smithsonian Institution

“These animals may have disappeared partly because of competition from lizards but perhaps also because of global changes in climate and habitat change,” Carano said. “It’s amazing when one group’s dominance gives way to another over evolutionary time, and we still need more evidence to explain exactly what happened, but fossils like this group is how we’re going to put it together.”

Researchers named the new species after museum volunteer Joseph Gregor who spent hundreds of hours meticulously scraping and sculpting bones from a block of stone that caught the attention of Museum fossil curator Pete Kroehler in 2010.

“Pete is one of those people who has some kind of X-ray vision for this kind of thing,” Carano said. “He noticed two small pieces of bone on the side of this block and marked it to be put back without any real idea what was inside. As it turned out, he hit the jackpot.”

The fossil is almost completely complete, except for the tail and parts of the hind legs. Such a complete skeleton is rare for small prehistoric creatures like this because their weak bones were often destroyed either before they were petrified or as they emerged from an eroded rock formation today, Carano said. As a result, paleontologists mostly know about paleontologists from small fragments of their jaw and teeth.

After Kroehler, Gregor, and others freed as much of the small fossil from the rock as was practical due to its brittleness, the team led by DeMar set out to survey the fossil using high-resolution computerized tomography (CT), a method that uses multiple X-ray images from different angles to create A three-dimensional representation of the sample. The team used three separate CT scanning facilities, including one at the National Museum of Natural History, to capture everything they could about the fossil.

Once the fossil bones were digitally displayed at a resolution of less than a millimeter, DeMar proceeded to reassemble the digitized skull bones, some of which had been crushed, misplaced or lost on one side, using software to create a nearly complete 3D image in the final reconstruction. The now reconstructed 3D skull provides researchers with an unprecedented look at the head of this Jurassic reptile.

Given the Opisthiamimus’ small size and shape of its hard teeth and skull, it likely ate insects, DeMar said, adding that prey with tougher shells such as beetles or water bugs may also have been on the list. In general, the new species looks somewhat like a miniature version of its only surviving relative (the tuatara is about five times longer).

“Such a complete specimen has enormous potential to make comparisons with fossils collected in the future and to identify or reclassify specimens already in a museum drawer somewhere,” Demar said. “With the 3D models that we have, at some point we can also do studies that use software to look at the mechanics of this creature’s decoding.”


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more information:
The nearly complete skeleton of a new species of eusphenodontian from the Upper Jurassic Morrison Formation, Wyoming, USA, provides insight into the evolution and diversity of Rhynchoceexpress (Reptilia: Lepidosauria), Journal of Systematic Paleontology (2022). DOI: 10.1080 / 14772019.2022.2093139

the quote: Researchers Discover Extinct Prehistoric Reptiles That Lived Among Dinosaurs (2022, September 15) Retrieved September 15, 2022 from

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