Fossil discovery in stash closet pushes origin of modern lizard back 35 million years

A specimen recovered from a cabinet in the Natural History Museum in London showed that modern lizards originated in the Upper Triassic and not the Middle Jurassic as previously thought.

This fossilized relative of living lizards such as monitor lizards, gila monsters and slowworms has been identified in a museum collection stored in the 1950s, including specimens from a quarry near Tortworth in Gloucestershire, south -West of England. The technology did not exist then to exhibit its contemporary characteristics.

As a modern-like lizard, the new fossil impacts all estimates of the origin of lizards and snakes, collectively called Squamata, and affects assumptions about their rates of evolution, and even the key trigger for the origin of the group.

The team, led by Dr David Whiteside from Bristol’s School of Earth Sciences, dubbed their incredible discovery Cryptovaranoides microlanius meaning “little butcher” in homage to his jaws filled with sharp cutting teeth.

Dr Whiteside explained: “I first spotted the specimen in a cupboard full of Clevosaurus fossils in the reserves of the Natural History Museum in London where I am a scientific associate. It was a fairly common fossil reptile, a close relative of the New Zealand Tuatara which is the sole survivor of the group, the Rhynchocephalia, which split off from the squamates over 240 million years ago.

‘Our specimen was simply labelled’Clevosaurus and another reptile.’ As we continued to investigate the specimen, we became increasingly convinced that it was in fact more closely related to modern lizards than the Tuatara group.

“We did X-ray scans of the fossils at the University, and that allowed us to reconstruct the fossil in three dimensions, and see all the little bones that were hidden inside the rock. »

Cryptovaranoids is clearly a squamate as it differs from Rhynchocephaly in the puzzle, in the vertebrae of the neck, in the region of the shoulder, by the presence of a middle upper tooth at the front of the mouth, the way the teeth are shelved in the jaws (rather than fused to the crest of the jaws) and in the architecture of the skull such as the lack of a lower temporal bar. There is only one major primitive feature not found in modern squamates, an opening in one side of the end of the arm bone, the humerus, where an artery and a nerve pass. Cryptovaranoids has other apparently primitive characters such as a few rows of teeth on the bones of the roof of the mouth, but experts have observed the same in the living European glass lizard and many snakes such as boas and pythons have several rows of large teeth in the same area. Despite this, he is advanced like most living lizards in his puzzle, and the bony connections in the skull suggest he was flexible.

“In terms of significance, our fossil shifts the origin and diversification of squamates from the Middle Jurassic to the Late Triassic,” says co-author Professor Mike Benton. “It was a period of major restructuring of terrestrial ecosystems, with the appearance of new groups of plants, in particular the modern-type conifers, as well as new types of insects, and some of the earliest modern groups such as turtles, crocodilians, dinosaurs, and mammals.

“The addition of the oldest modern squamates then completes the picture. It seems that these new plants and animals appeared as part of a major reconstruction of life on Earth after the mass extinction at the end of the Permian 252 million years ago, and in particular the Carnian Pluvial Episode. . , 232 million years ago, when climates oscillated between wet and dry and caused great disruption to life. »

PhD student Sofia Chambi-Trowell commented: “The name of the new animal, Cryptovaranoides microlanius, reflects the hidden nature of the beast in a drawer but also its likely way of life, living in fissures in the limestone on small islands that existed around Bristol at the time. The species name, which means “little butcher”, refers to its jaws filled with sharp sharp teeth and it is said to have fed on arthropods and small vertebrates. »

Dr Whiteside concluded: “This is a very special fossil and likely to become one of the most important discovered in recent decades. It is fortunate to be kept in a national collection, in this case the Natural History Museum in London. We would like to thank the late Pamela L. Robinson who recovered the fossils from the quarry and did a lot of preparatory work on the type specimen and associated bones. It’s such a shame that she didn’t have access to CT scan technology to help her observe all the detail of the specimen. »