A newly-discovered 150-million-year-old reptile fits in the palm of your hand

2022-09-16 23:01:20 By : Ms. Alice Chen

Julius Csotonyi for the Smithsonian Institution

About 150 million years ago, lizard-like animals called Rhynchocephalians roamed the Earth alongside gigantic dinosaurs. They were more common than snakes and actual lizards during the Jurassic era. However, today only one species of the Rhynchocephalia order is alive —- the Tuatara, which is only found in New Zealand.

Interestingly, now a team of researchers at the Smithsonian Institution has revealed an extinct Rhynchocephalian species, which also happens to be a relative of Tuatara. They have named the new species Opisthiamimus gregori. This 6-inch long reptile mostly fed on small insects and was spread across North America.

While shedding light on the significance of O. gregori, one of the authors and the curator of the National Museum of Natural History, Mathew Carrano said in the press release, “Even though it looks like a relatively simple lizard, it embodies an entire evolutionary epic going back more than 200 million years.”

David DeMar for the Smithsonian Institution

The remains of O. gregori were chiseled out of a block of stone originally excavated in the past from the Morrison Formation, a region in Wyoming that is rich in Jurassic-era sedimentary rocks. When the block was brought to the museum, nobody had the slightest idea that it was carrying the skeleton of a prehistoric reptile. In 2010, a fossil research and collection assistant at the museum, Peter Kroehler, spotted tiny bones on the stone and marked the region.

“He (Peter Kroehler) noticed two tiny specks of bone on the side of this block and marked it to be brought back with no real idea what was in it. As it turns out, he hit the jackpot,” said Carrano. Later, a volunteer, Joseph Gregory, chiseled the block as per the marking made by Kroehler, and after a lot of hard work and effort, he was able to recover an almost complete skeleton of O. gregori (named after Joseph Gregory).

Although the recovered skeleton was missing the tail and a few bones of the hind leg, it was good enough to get scanned using computer tomography (CT), an X-ray-based method that allows researchers to create a 3D model of an extinct animal from the X-ray images of its remains. Three separate CT scans of the skeleton parts led to the formation of a digital 3D image of O. gregori.

The clear image of the skull and teeth suggested that the reptile ate insects and small invertebrates. It also hinted that O. gregori was about five times smaller in length than Tuatara and was probably one of the smallest members of the Rhynchocephalia order in terms of body size.

Explaining the importance of O. gregori’s fossils, research associate at the National Museum of Natural History, Dave DeMar Jr., wrote, “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.”

As mentioned earlier, Tuatara and its extinct relative are lizard-like animals, but not lizards. For instance, lizards prefer a warm environment and are diurnal, whereas Tuatara is a nocturnal being and is found in cold regions. The alignment of teeth on Tuatara’s jaws is also different from lizards moreover, they have external ears, which are not found in lizards.

However, besides having so many dissimilarities, there is an interesting feature found common in Tuatara and many species of lizards — “the third eye.” Also known as the parietal or pineal eye, the third eye is a primitive photosensitive structure found in the head region of various reptiles. Although it has a lens and a retina inside, the third eye can not function like a normal eye and can only sense the presence of light.

Most species under the Rhynchocephalian order may have gone extinct while competing against lizards or due to changes in global climate conditions, but they are just theories, and nothing has been proven so far.

The authors believe that it is very rare to recover a complete skeleton of a prehistoric species like O. gregori and the remains hold an ample amount of information within them. They might also reveal the factors that caused the extinction of all Rhynchocephalians except Tuatara.

“It’s fascinating when you have the dominance of one group giving way to another group over evolutionary time, and we still need more evidence to explain exactly what happened, but fossils like this one are how we will put it together,” said Carrano.

The study is published in the Journal of Systematic Palaeontology.