An artist’s reconstruction of Cryptovaranoides microlanius. Credit: Lavinia Gandolfi
Modern lizards could have descended from a ‘beast’ roaming in the late Triassic Period, spanning 252-201 million years ago, according to a new study. Previous estimates suggested that modern lizards originated 35 million years later in the Middle Jurassic Period.
The Triassic beast, measuring 25 cm long, is Cryptovaranoides microlanius. Cryptovaranoides means ‘hidden, lizard-like’ animal, while the species name means ‘small butcher’ owing to the presence of sharp-edged slicing teeth, the study published in Science Advances noted.
It belongs to Squamates, a clade comprising 11,000 living species of lizards, snakes, and relatives.
A related clade Rhynchocephalia also originated in the late-Triassic Period, the study noted. Currently, Tuatara, found in New Zealand, is the only survivor of this group. It split from the Squamates over 240 million years ago.
The Triassic Period followed the End-Permian Extinction, popularly called the ‘Great Dying’, where more than 90 per cent of the planet’s species perished. This was about 250 million years ago.
The ‘small butcher’, aged between 201.6 million and 201.8 million years ago, was trapped in a limestone that remained locked in a cupboard of the Natural History Museum in London for nearly 70 years.
It was initially picked up from Cromhall Quarry, Tortworth, Gloucestershire, in the United Kingdom.
“The name of the new animal, Cryptovaranoides microlanius, reflects the hidden nature of the beast in a drawer but also in its likely lifestyle, living in cracks in the limestone on small islands that existed around Bristol at the time,” Sofia Chambi-Trowell, a research scholar from the University of Bristol, explained in a statement.
Researchers from the University of Bristol and The Natural History Museum studied the fossil using CT scanning technology.
“The specimen shows 20 detailed features in the anatomy of the skull that is unique to all living lizards and snakes but not to the tuatara,” Michael Benton, from the University of Bristol and co-author of the study, told Down To Earth.
For example, he said, the bones around the back of the skull show key features of extra flexibility. This is seen in the skull of modern lizards, allowing them to open their mouths very wide.
“Our Triassic beast had these modern features already,” he added.
One major primitive feature is absent in livingSquamates: an opening on one side of the end of the upper arm bone called the humerus, where an artery and nerve pass through, the researchers said.
Further, the ‘small butcher’ had a few rows of teeth on the bones of the roof of the mouth, another primitive feature. But living European glass lizards and many snakes, such as boas and pythons, also share this feature, they added.
These findings, according to them, impact all estimates of the origin of lizards and snakes.
The Triassic Period saw the origin of new life forms — new plant groups, especially modern-type conifers, insects, and the origin of turtles, crocodilians, dinosaurs, and mammals, according to the study.
“Life had been devastated by the end-Permian mass extinction. This led to a complete reset of evolution, and many new groups evolved quite fast,” Benton noted.
He speculated that conditions in the Triassic and the Carnian Pluvial Episode (233-232 million years ago) were ripe for many modern groups’ origins. During this time, the climate fluctuated between wet and dry.
“We can’t say which specific environmental condition gave them the advantage, but would point to the fact that so much had been killed that there were open opportunities for new groups,” he noted.
The diversity of Squamates increased through the Jurassic and Cretaceous. At the same time, the diversity of rhynchocephalians may have declined in the Early Cretaceous Period in Laurasia — one of the two ancient supercontinents that included North America, Greenland, Europe, and Asia, excluding India.
The researchers hope to find more fossil specimens dating back to the Triassic Period. They plan to study the anatomy of the Triassic beast further and compare them with other early lizard-like animals from the Triassic and Jurassic.