The origins of mammals and birds are relatively well understood, while the roots of squamates have been obscure. In a new paper (Whiteside et al. 2022) report a modern-type lizard from the Late Triassic of England [202 million years (Ma)], comprising a partial skeleton, skull, and mandibles. It displays at least 15 unique squamate traits and further shares unidentatan and anguimorph apomorphies. The new discovery fixes the origin of crown Squamata as much older than had been thought, and the revised dating shows substantial diversification of modern-type squamates following the Carnian Pluvial Episode, 232 Ma ago.
The new fossil has three profound effects on our understanding of squamate evolution. First, it alters our understanding of the origins of numerous included clades, such as Unidentata, Episquamata, Toxicofera, and Anguiformes. Dating all these clade origins is crucial for setting the time scale of modern squamate biodiversity. Identifying Cryptovaranoides as an anguimorph squamate pushes many of the deep divergences within Squamata back from Middle-Late Jurassic to Late Triassic, a span of 30 to 50 Ma. This will have substantial effects on calculations of rates of evolution of traits in future macroevolutionary work.
Southern England and Wales were very different places during the Late Triassic. At the time, the area around what is now Bristol and Cardiff is believed to have been part of an archipelago of small islands where dinosaurs such as Pendraig milnerae roamed.
Beneath their feet, Cryptovaranoides microlanius is thought to have lived among the cracks in the limestone that made up the islands. While these crevices would have provided safety from predators, they are also where this animal ultimately met its fate.
Buried in the crevice and covered over, its fossilized remains were preserved beneath the ground for over 200 million years.
This type of deposit, known as a fissure fill, are sometimes uncovered as part of quarrying in the Cardiff and Bristol area, with the site in Cromhall known to be a particularly rich source of fossils for species including Agnostiphys cromhallensis.
It was from this quarry that Cryptovaranoides microlanius was unearthed in the 1950s by Professor Pamela L. Robinson from University College London.
While she was able to partially prepare the specimen, and other bones from the species also found at the site, the risk of damaging the fossil and the limited scanning technology available at the time meant that the lizard’s identity remained a mystery.
It was stored in the Museum for many years until Dr David Whiteside, a scientific associate at the Museum, renewed and led the research into the new species.
‘The specimen was located in a cupboard full of Clevosaurus fossils,’ David says. ‘Clevosaurus was a common enough fossil reptile and a close relative of New Zealand’s tuatara, the only survivor of a group of reptiles known as the rhychocephalians.’
‘The Cryptovaranoides specimen was simply labelled as “Clevosaurus and one other reptile.” As myself and my colleagues continued to investigate the specimen, we became increasingly convinced that it was more closely related to modern day lizards than the rhynchocephalians.’
