New Mesozoic reptile was an ancient relative of the tuatara

Tuataras are strange reptiles found living only in New Zealand. A few key traits like teeth fused to jaws and an odd chewing motion point to their divergence from lizards some 230 million years ago. Instead of lizards, tuataras are rhynchocephalians. Now, scientists from the Smithsonian have found the fossil remains of another member of rhynchocephalia. 

The newly discovered animal was described in the Journal of Systematic Palaeontology. The reptile, named Opisthiamimus gregori, lived in Jurassic North America alongside such superstars as Stegosaurus and Allosaurus. The animal in question was much smaller, only about 6 inches long, but representative of a massive evolutionary epic.

“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,” said Matthew Carrano, the National Museum of Natural History curator of Dinosauria. “Even though it looks like a relatively simple lizard, it embodies an entire evolutionary epic going back more than 200 million years.”

The discovery comes from several specimens, including a complete one, discovered in a Morrison formation quarry in Wyoming focusing on an Allosaurus nest. During the late Jurassic, rhynocephalians were common. 

At the peak of their existence, rhynocephalians were found all over the world and made a diverse group from herbivores to dedicated fishers. As lizards and snakes grew in diversity, for unclear reasons, rhynocephalians dwindled. Today, the tuatara is the only living representative. 

“These animals may have disappeared partly because of competition from lizards but perhaps also due to global shifts in climate and changing habitats,” said Carrano. “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.”

—

By Zach Fitzner, Earth.com Staff Writer