A group of Smithsonian researchers has discovered a new species of reptile that lived in the Jurassic , about 150 million years ago, along with dinosaurs such as the stegosaurus and the allosaurus. The newly named Opisthiamimus gregori would have measured about 16 centimeters from snout to tail and its diet would have consisted of insects and other invertebrates. The researchers claim that it belongs to the same lineage as the New Zealand tuatara. The discovery has been published in the Journal of Systematic Palaeontology .
“The important thing about the tuatara is that it represents this huge evolutionary story that we are lucky enough to capture in what is likely to be its final act,” said Matthew Carrano, one of the researchers, in the press release issued by the National Museum of Natural History. , which is associated with the Smithsonian Institution. “Although it looks like a relatively simple lizard, it embodies an evolutionary epic that dates back more than 200 million years.”
The discovery is the result of the study of a few specimens, including one “extraordinarily complete and well preserved”, which was found in an Allosaurus site in northern Wyoming. Further studies could explain why in the Jurassic there was a variety of these reptiles and now only the New Zealand tuatara survives.
Although the tuatara resembles an iguana, both it and Opisthiamimus gregori , its newly discovered relative, are not lizards, but Rhinocephalians , an order that split from the lizards at least 230 million years ago.
Rhinocephalians had their heyday in the Jurassic. They were present practically everywhere in the world, could be large or small, and carried out ecological functions such as hunting fish or eating plants. It is unknown why they disappeared when lizards and snakes became the most common and diverse reptiles on the entire planet.
Being separated from rhinoceroses from lizards, tuataras have certain special characteristics such as the fact that their teeth are fused with the jaw bone. When they chew they make a saw-like movement , moving the lower jaw back and forth. They can also live for more than a hundred years and tolerate cold climates very well.
The Opisthiamimus gregori fossil is now part of the museum’s collection and may help researchers figure out why the tuatara is all that remains of the rhinocephalians, while lizards inhabit the entire planet.
The researchers believe that O. gregori may have disappeared as a result of competition with lizards, but also because of global climate changes and habitat modifications that have taken place. These are hypotheses that need further study.
the fossil
The new species is named Opisthiamimus gregori in honor of Joseph Gregor, a museum volunteer who spent hundreds of hours working on a block of stone, chiseling away at the animal’s bones.
The fossil is almost complete , missing only the tail and parts of the hind legs. According to the researchers, it is rare to find such a complete remnant of small creatures as O.gregori . The bones of these small animals are often brittle and are destroyed before they fossilize or when they emerge from an eroding rock formation. Paleontologists know rhinocephalians precisely from small fragments of jaws and teeth, not from almost their entire skeleton.
The researchers have subjected the small O. gregori fossil to computerized tomography. This technology uses X-ray images from different angles to create a 3D representation of the animal. Digitized skull bones, some of which were crushed or out of place, have also been assembled. The result has been an impressive 3D image of this Jurassic reptile .
Considering O. gregori ‘s size, the shape of its teeth, and the rigidity of its skull, researchers believe it fed on insects , also with hard shells like beetles. The new species would be a miniature version of its only living relative: the tuatara.
Referencia: DeMar, D., E.H. Jones, M., Carrano, M. 2022. A nearly complete skeleton of a new eusphenodontian from the Upper Jurassic Morrison Formation, Wyoming, USA, provides insight into the evolution and diversity of Rhynchocephalia (Reptilia: Lepidosauria). Journal of Systematic Palaeontology. DOI: https://doi.org/10.1080/14772019.2022.2093139
