Discovered in the UK! Ancestor of Dinosaur-Era Lizards: Huge Teeth, Zero Palatal Teeth—The Oldest Lepidosaur Challenges Evolutionary Theories

A palm-sized fossil collected in 2015 from the coast near Sidmouth, Devon, UK, has been identified as one of the oldest members of Lepidosauria (lizards, snakes, and tuatara) and was published in Nature on September 10, 2025. The new species is named Agriodontosaurus helsbypetrae ("fierce-toothed lizard of Helsby sandstone"). It dates back to the Middle Triassic Anisian stage, approximately 244 to 241.5 million years ago, pushing back the known oldest record by 3 to 7 million years. Surprisingly, it lacked the "movable skull" and palatal teeth seen in many modern lizards and snakes, while the lower temporal bar remained open. Additionally, it had relatively large, triangular teeth, suggesting it preyed on insects with hard exoskeletons by tearing them apart. Using synchrotron CT at ESRF and Diamond Light Source, the fine structure was visualized, allowing high-resolution reconstruction of the internal details of the small fossil. The discovery directly impacts the reevaluation of the origins of skull function and diet in Lepidosauria and their divergence dates, indicating that the "oldest member" might have been a minimalistic and specialized insectivore with both "tuatara-like" and "lizard-like" features.