A specimen from a cabinet at the Natural History Museum in London has shown that modern lizards are Late Triassic and not Middle Jurassic as previously thought.
This fossilized relative of living lizards such as monitor lizards, Gila monsters and duds has been identified in a 1950s stored museum collection, including specimens from a quarry near Tortworth in Gloucestershire, South West England. The technology did not exist then to reveal its contemporary characteristics.
As a modern lizard, the new fossil affects all estimates of the origin of lizards and snakes, collectively known as squamata, affecting assumptions about their rates of evolution and even the main trigger for the origin of the group.
The team led by Dr. Bristol School of Earth Sciences’ David Whiteside has named his incredible discovery Cryptovaranoides microlanius meaning “little butcher”, in homage to its jaws, which were filled with sharp-edged incisors.
dr Whiteside explained: “I got the copy in a closet full at first clevosaurus Fossils in the storerooms of the Natural History Museum in London, where I am a Research Associate. This was a fairly common fossil reptile, a close relative of the New Zealand tuatara, the sole survivor of the group, the Rhynchocephalia, which split from the squamates over 240 million years ago.
“Our copy was simply labeled ‘clevosaurus and another reptile.” As we examined the specimen further, we became more and more convinced that it was in fact more closely related to modern-day lizards than to the Tuatara group.
“We took X-rays of the fossils at the university and this allowed us to reconstruct the fossil in three dimensions and see all the tiny bones that were hidden in the rock.”
cryptovaranoids is clearly a squamate as it differs from rhynchocephalia in the braincase, cervical vertebrae, shoulder region, by the presence of a central upper tooth in the front of the mouth, by the way the teeth rest on a shelf in the jaw ( rather than fused to the ridge) and in cranial architecture such as the absence of a lower temporal bar. There is only one important primitive feature not found in modern squamates, an opening on one side of the end of the humerus, the humerus, through which an artery and nerve pass. cryptovaranoids has some other seemingly primitive features such as a few rows of teeth on the bones of the palate, but experts have observed the same thing in the living European glass lizard, and many snakes such as boas and pythons have multiple large rows of teeth in the same area. Despite this, like most living lizards, it is advanced in its braincase and the bony connections in the skull suggest it was flexible.
“In terms of significance, our fossil shifts the origin and diversification of squamates back from the Middle Jurassic to the Late Triassic,” says co-author Professor Mike Benton. “This was a period of major restructuring of ecosystems on land, with the origins of new plant groups, particularly modern conifers, as well as new species of insects and some of the first modern groups such as turtles, crocodiles, dinosaurs, and mammals.
“The addition of the oldest modern squamats then completes the picture. It appears that these new plants and animals appeared as part of a major rebuilding of life on Earth after the mass extinction event at the end of the Permian, 252 million years ago, and specifically the Carnic Pluvial Episode, 232 million years ago, when the climate 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 animal’s hidden nature in a drawer, but also in its probable lifestyle, living in cracks in the limestone on small islands that existed near Bristol at the time. The species name, meaning “little butcher,” refers to its jaws, which were filled with sharp-edged, cutting teeth, and it would have preyed on arthropods and small vertebrates.”
dr Whiteside concluded: “This is a very special fossil, and probably one of the most important, to be found in recent decades. It is fortunate that it is held 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 much preparatory work on the type specimen and associated bones. It was such a shame she didn’t have access to CT scanning technology to help her observe all the detail of the specimen.”