Extinct prehistoric reptiles that lived among the dinosaurs discovered by Smithsonian researchers

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. newly discovered Let’s pray to Gregory preys on a now-extinct aquatic insect (MorrisonNepa Jurassica), while in the background a predatory dinosaur Allosaurus jimmadseni He guards his nest. The landscape is the floodplains of a river in late Jurassic Wyoming, about 150 million years ago. A team of scientists describes the new species, 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 the Journal of Systematic Paleontology. In life, this prehistoric reptile was about 16 cm (about 6 inches) long from nose to tail and could have been curled up in the palm of an adult human hand. 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. Credit: Julius Csotonyi for Smithsonian Institution

The find sheds light on the tuatara, the last living member of a diverse group of reptiles that has been almost completely replaced by lizards.

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. new species Let’s pray to Gregorythat once dwelt[{” attribute=””>Jurassic North America about 150 million years ago alongside dinosaurs like Stegosaurus and Allosaurus, is described in a paper published on September 15, 2022, in the Journal of Systematic Palaeontology. In life, this prehistoric reptile would have been about 16 centimeters (about 6 inches) from nose to tail—and would fit curled up in the palm of an adult human hand. It likely survived on a diet of insects and other invertebrates.

A team of scientists, including the National Museum of Natural History’s curator of Dinosauria Matthew Carrano and research associate David DeMar Jr. as well as University College London and Natural History Museum, London scientific associate Marc Jones, contributed to the research.

“What’s important about the tuatara is that it represents this enormous evolutionary story that we are lucky enough to catch in what is likely its closing act,” Carrano said. “Even though it looks like a relatively simple lizard, it embodies an entire evolutionary epic going back more than 200 million years.”

Fossil Skeleton of the New Lizard-Like Reptile Opisthiamimus Gregori

Fossil skeleton of the new lizard-like reptile Opisthiamimus gregori. The fossil was discovered in the Morrison Formation of the Bighorn Basin, north-central Wyoming, and dates to the Late Jurassic Period, approximately 150 million years ago. Researchers named the new species after Smithsonian’s National Museum of Natural History volunteer Joseph Gregor who spent hundreds of hours meticulously scraping and chiseling the bones from a block of stone that first caught museum fossil preparator Pete Kroehler’s eye back in 2010. The fossil has been added to the museum’s collections where it will remain available for future study. A team of scientists describes the new species, which once lived alongside dinosaurs like Stegosaurus and Allosaurus, in a paper published today in the Journal of Systematic Palaeontology. In life, this prehistoric reptile would have been about 16 centimeters (about 6 inches) from nose to tail—and would fit curled up in the palm of an adult human hand—and likely survived on a diet of insects and other invertebrates. Credit: David DeMar for the Smithsonian Institution

The discovery comes from a handful of specimens, one of which was an incredibly complete and well-preserved fossil skeleton excavated from a site centered around an Allosaurus nest in northern Wyoming’s Morrison Formation. Further investigation of the find could help reveal why this animal’s ancient order of reptiles was winnowed down from being diverse and numerous in the Jurassic to only New Zealand’s tuatara surviving today.

Although the tuatara looks a bit like a particularly stout iguana, the tuatara and its newly discovered relative are in fact not lizards at all. They are actually rhynchocephalians, an order that diverged from lizards at least 230 million years ago, Carrano said.


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 rendered, the team set out to reassemble the numbered skull bones, some of which had been crushed, misplaced, or lost on one side, using software to create a near-complete 3D reconstruction. A team of scientists describes the new species Opisthiamimus gregori, which once lived alongside dinosaurs such as Stegosaurus and Allosaurus, in a research paper published today in the 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. Credit: D. DeMar

At their height during the Jurassic period, rhynchocephalians were found almost all over the world and came in both large and small sizes. They have performed ecological roles ranging from aquatic fishermen to massive 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. These include a lifespan of over 100 years, teeth integrated into the jawbone, and a unique chewing motion that glides the lower jaw back and forward like a saw blade, and withstands colder climates.

Opisthiamimus gregori Skull

3D skull reconstruction Let’s pray to Gregory, a new extinct species of lizard-like reptile from the late Jurassic period in Wyoming, individual US bones color-coded. Credit: D. DeMar

next Hey GregoryCarano’s official description, said the fossil was added to the museum’s collections where it will remain available for study in the future. Perhaps one day it will help scientists figure out why the tuatara survived all that remained of the rhynchocephalians, while lizards are now found all over the world.

“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 you have the dominance of one group giving way to another over evolution time, and we still need more evidence to explain exactly what happened, but fossils like this are how we’re going to put them together.”

The new species is named after Joseph Gregor, a museum volunteer who spent hundreds of painstaking hours scraping and carving bones from a block of stone that caught the attention of Pete Kroehler, curator of the Paleontological Museum, 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 turned back without any real idea of ​​what was inside. And as it turned out, he hit the jackpot.”

Opisthiamimus Gregori Skeleton

Photo (top) and explanatory drawing (bottom) of the skull and skeleton of Let us pray to Gregorya new extinct species of lizard-like reptile from late Jurassic Wyoming, US Credit: Demar (image, top), James Morrison (illustration, bottom).

The fossil is almost completely complete, except for the tail and parts of the hind legs. Such a complete skeleton is rare for such small prehistoric creatures, Carano said, because their weak bones were often destroyed either before they were petrified or when they emerged from an eroded rock formation today. 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). This is a method that uses multiple X-ray images from different angles to create a three-dimensional representation of the sample. The research team used three separate CT scan facilities, including one housed in the National Museum of Natural History, to capture everything about the fossil that might be possible.

Once the fossil bones were digitally presented using a file[{” attribute=””>accuracy smaller than a millimeter, DeMar set about reassembling the digitized bones of the skull. Some of them were crushed, out of place, or missing on one side, so software was used to eventually create a nearly complete 3D reconstruction. This reconstructed 3D skull now provides scientists with an unprecedented look at this Jurassic-age reptile’s head.

Given Opisthiamimus’s diminutive size, tooth shape, and rigid skull, it likely ate insects, said DeMar, adding that prey with harder shells such as beetles or water bugs might have also been on the menu. Broadly speaking, the new species looks quite a bit like a miniaturized version of its only surviving relative (tuataras are about five times longer).

“Such a complete specimen has huge potential for making comparisons with fossils collected in the future and for identifying or reclassifying specimens already sitting in a museum drawer somewhere,” DeMar said. “With the 3D models we have, at some point, we could also do studies that use software to look at this critter’s jaw mechanics.”

Reference: “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)” 15 September 2022, Journal of Systematic Palaeontology.
DOI: 10.1080/14772019.2022.2093139

Funding and support for this research were provided by the Smithsonian and the Australian Research Council.