A tuatara lizard, which shows similarities with the newly found ancestor species. Credit: Stewart Nimmo / Wikimedia Commons / CC BY-SA 4.0
Scientists have identified the oldest known lizard ancestor, a fossil found on a beach in southwest England that dates back 242 million years.
The small reptile, no larger than a human hand, lived in the Middle Triassic period, just before dinosaurs appeared, and relied on oversized teeth to feed on insects such as cockroaches.
The skeleton was discovered in 2015 at a fossil-rich site in Devon and is now recognized as the earliest member of the reptile group lepidosauria, which includes lizards, snakes, and the tuatara of New Zealand. Researchers spent years studying the remains before publishing their findings Wednesday in the journal Nature.
Dan Marke of the University of Bristol, the study’s lead author, said the animal challenges long-standing assumptions about reptile evolution. According to him, the fossil lacked many features typically expected in early lepidosaurs, prompting scientists to reconsider how lizards, snakes, and tuataras developed.
Ancient features that defy expectations
Unlike modern lizards and snakes, which have a partially hinged skull and additional teeth on the roof of the mouth, this early ancestor had neither.
Read about the oldest known lepidosaur: Agriodontosaurus helsbypetrae.
“A tiny, snaggletoothed creature that lived and died 241 million years ago in what is now the coastline of southwestern England belonged to a group that gave rise to a stupendously diverse smattering of… pic.twitter.com/yQ0eWBiKv0
— Manuela Casasoli (@manuelacasasoli) September 13, 2025
Researchers noted its most striking feature was its unusually large teeth compared with close relatives. Another distinctive trait was a bone that stretched from the cheek to the jaw, a feature otherwise seen only in the tuatara, sometimes called a living fossil.
Study co-author Michael Benton, also from the University of Bristol, explained that the reptile likely used its prominent teeth to pierce and shear the tough shells of insects, much as the tuatara does today.
The fossil was difficult to study because of its size. The skull measured only 1.5 centimeters, or about 0.6 inches, and was embedded in a large block of rock. To analyze it, British researchers relied on advanced imaging at the European Synchrotron Radiation Facility in France.
Technology and naming of the fossil
Vincent Fernandez, a paleontologist at the facility, said the synchrotron worked like a powerful microscope, producing X-rays billions of times brighter than hospital machines. This allowed the team to capture highly detailed images of the tiny specimen.
The researchers named the reptile Agriodontosaurus helsbypetrae, after the Helsby Sandstone Formation where it was found.
Its discovery provides scientists with a clearer view of early reptile evolution and offers rare insight into the origins of a group that would later diversify into thousands of species across the world.