Paleontologists have unearthed a complete skull and skeleton of a Triassic lepidosaur species — named Agriodontosaurus helsbypetrae — in the Helsby Sandstone Formation of Devon, the United Kingdom.
Agriodontosaurus helsbypetrae. Image credit: Bob Nicholls.
The Lepidosauria is the most species-rich group of land-dwelling vertebrates.
The group includes around 12,000 species of lizards and snakes and one species of Rhynchocephalia, the tuatara (Sphenodon punctatus) from New Zealand.
Collectively known as squamates, lizards and snakes owe their success to their generally small size, but also to their highly mobile skull that enables them to manipulate large prey.
These key features of their skulls are not seen in the tuatara, which makes it important to understand the nature of their common ancestor.
Lepidosaurs originated in the Triassic period, 252 to 201 million years ago, but confusion has arisen because of incomplete fossils, many of which are generalized lepidosauromorphs, neither squamates nor rhynchocephalians.
“It was always expected that the first lepidosaurs would have had some of the lizard characters such as a partially hinged skull, an open lower temporal bar, and abundant teeth on the roof of the mouth (palate),”
“These are all features of modern lizards and snakes that enable them to manipulate large prey by opening their mouths super-wide (skull hinge) and use teeth on the palate to grasp wriggling small prey animals.”
“The lower temporal bar is essentially the cheek bone, a bony rod that runs between the cheek and the jaw hinge and is absent in lizards and snakes today.”
“Snakes and many lizards have all these features, as well as some additional flexibility of the skull.”
“Only the tuatara has a complete lower temporal bar, giving it an archaic look reminiscent of some of the earliest and ancestral reptiles; and it also has some large palatal teeth.”
The fossilized remains of Agriodontosaurus helsbypetrae were found back in 2015 on the beach in Devon, the United Kingdom.
The specimen dates back 242 million years (Middle Triassic epoch), just before the dinosaurs appeared.
It is around 3-7 million years older than the oldest currently known lepidosaur: Wirtembergia from the Erfurt Formation.
“The new fossil shows almost none of what we expected,” said Dan Marke, a paleontologist at the University of Bristol and the University of Edinburgh.
“It has no teeth on the palate, and no sign of any hinging. It does though have the open temporal bar, so one out of three. Not only this, but it possesses some spectacularly large teeth compared to its closest relatives.”
Agriodontosaurus helsbypetrae had a body length of about 10 cm and a unique combination of features.
“When you look at the fossil, the whole skeleton sits in the palm of your hand,” said University of Bristol’s Professor Michael Benton.
“But after the scans and the hard work of our students cleaning up the scan data, we can see the most amazing detail.”
“The new beast has relatively large triangular-shaped teeth and probably used these to pierce and shear the hard cuticles of its insect prey, pretty much as the tuatara does today.”
“The new animal is unlike anything yet discovered and has made us all think again about the evolution of the lizard, snakes and the tuatara,” Marke said.
The findings were published today in the journal Nature.
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D. Marke et al. The oldest known lepidosaur and origins of lepidosaur feeding adaptations. Nature, published online September 10, 2025; doi: 10.1038/s41586-025-09496-9
