The paleontologists have found a complete skull and a skeleton of a species of trias lepidosaurus – named Agriodontosaurus Helsbypetrae – In the formation of Helsby of Devon, the United Kingdom.
Agriodontosaurus Helsbypetrae. Image credit: Bob Nicholls.
Lepidosauria is the richest group in species of field vertebrates.
The group includes approximately 12,000 species of lizards and snakes and a species of rhynchocephalia, tuatara (Sphenodon punctatus) New Zealand.
Collectively known as squamates, lizards and snakes owe their success to their generally small size, but also to their very mobile skull which allows them to manipulate great prey.
These key characteristics of their skull are not seen in Tuatara, which makes it important to understand the nature of their common ancestor.
The lepidosaurs are from the Triassic period, 252 to 201 million years ago, but the confusion was born due to incomplete fossils, many of which are generalized lepidosauromaps, neither pronounced nor rhynchocephalians.
“We always expected that the first lepidosaurs would have had some of the characters of lizards such as a partially hinge skull, an open lower time bar and abundant teeth on the roof of the mouth (palace)”, “
“These are all characteristics of modern lizards and snakes that allow them to handle large prey by opening their super wide mouth (skull of the skull) and use teeth on the palate to grab the small prey that tortiles.”
“The lower time bar is essentially the bone of the cheeks, a bone rod flowing between the cheek and the hinge of the jaw and is absent in lizards and snakes today.”
“Snakes and many lizards have all these features, as well as additional flexibility of the skull.”
“Only Tuatara has a complete lower time bar, giving it an archaic aspect recalling some of the first ancestral reptiles; and it also has large palatin teeth.”
The fossilized remains of Agriodontosaurus Helsbypetrae were found in 2015 on Devon beach, the United Kingdom.
The specimen dates back 242 million years (era of the average Triassic), just before the appearance of dinosaurs.
It is about 3 to 7 million years older than the currently known lepidosaurus: Wirtambergia of the formation of Erfurt.
“The new fossil shows almost nothing about what we expected,” said Dan Marke, paleontologist at the University of Bristol and the University of Edinburgh.
“He has no teeth in the mouth, and no signs of a hinge. He has the open time bar, so one in three. Not only that, but he has spectacular teeth compared to his closest parents.”
Agriodontosaurus Helsbypetrae had a body length of about 10 cm and a unique combination of characteristics.
“When you look at the fossil, the whole skeleton is in the palm of your hand,” said Professor of the University of Bristol, Michael Benton.
“But after the analyzes and the hard work of our students to cleanse Scan’s data, we can see the most amazing details.”
“The new beast has relatively important triangular teeth and probably used them to pierce and shear hard cuticles of its prey of insects, roughly as Tuatara does today.”
“The new animal is not very much discovered and made us all think about the evolution of the lizard, the snakes and the Tuatara,” said Marke.
The results were published today in the journal Nature.
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D. Brand and al. The oldest known lepidosaurus and the origins of the lépidosaurie food adaptations. Naturepublished online on September 10, 2025; DOI: 10.1038 / S41586-025-09496-9
