A tiny fossil discovered in Devon has revealed unexpected traits in one of the earliest known members of the lizard lineage. The 242-million-year-old specimen, named Agriodontosaurus helsbypetrae, lacks typical features like palatal teeth and skull hinging but boasts large blade-like teeth. Researchers from the University of Bristol used advanced scans to uncover these details, prompting a rethink of lepidosaur origins.
In 2015, Dr. Rob Coram found a small fossil on a Devon beach, initially unsure of its significance due to limited exposure. The specimen, from the Helsby Sandstone Formation, dates to the Middle Triassic period, about 242 million years ago, just before dinosaurs emerged. Now, high-resolution synchrotron CT scans from the European Synchrotron Radiation Facility in France and the Diamond Light Source in the UK have exposed intricate details of its 1.5 cm skull.
Led by Dan Marke during his MSc in Palaeobiology at the University of Bristol, the study reveals that Agriodontosaurus helsbypetrae deviates from expectations for early lepidosaurs. "The new fossil shows almost none of what we expected," Marke said. "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."
The fossil's triangular teeth likely pierced and sheared insect cuticles, similar to modern tuatara. Co-supervisor Dr. David Whiteside noted the scans' value: "The exceptional resolution and quality of scans from synchrotron X-ray sources show us all the fine details and save any risk of damage." Professor Michael Benton added, "When you look at the fossil, the whole skeleton sits in the palm of your hand... we can see the most amazing detail."
This discovery challenges assumptions about lepidosaur evolution, the group encompassing over 12,000 species of lizards, snakes, and tuatara today. Marke explained, "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." The findings, published in Nature, highlight the tuatara's ties to a diverse ancient reptile order and early adaptations like flexible jaws that aided survival alongside dinosaurs.