Synchrotron science uncovers the origins of lizards

A tiny fossil from Devon has shed new light on the origins of lizards, thanks to advanced synchrotron imaging carried out at Diamond Light Source and the European Synchrotron Radiation Facility (ESRF).

Researchers from the University of Bristol have identified the fossil as the oldest known member of the lizard lineage, dating back 242 million years to the Middle Triassic, just before the rise of the dinosaurs. Their findings, published in Nature, reveal unexpected details about the early evolution of lizards, snakes, and their relative, the tuatara, a group collectively known as the Lepidosauria.

Three-dimensional reconstruction of the lizard's skull.

Lepidosaurs are today the most successful group of land vertebrates, with more than 12,000 living species. Scientists long assumed their earliest ancestors would share key features of modern lizards and snakes, such as hinged skulls and palatal teeth. However, the new fossil challenges those assumptions.

“The new fossil shows almost none of what we expected,” said Dan Marke, who led the project as part of his studies for the MSc in Palaeobiology at Bristol. “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.”

Professor Genoveva Burca, Principal Beamline Scientist of I12-JEEP, said: "We are pleased to contribute to the scientific understanding of this sample. The unique capabilities of the the beamline, including its large beam size and high energy, combined with our expertise in advanced imaging methods, underscore the crucial role that synchrotron light sources like Diamond play in advancing palaeontological research."

Because the specimen’s skull measures only 1.5 cm, traditional CT scans could not resolve the fine details. To overcome this, the team turned to high-energy synchrotron X-ray imaging. Using two powerful beamlines, I12 at Diamond Light Source and one at ESRF, the researchers were able to produce exceptionally detailed 3D models of the skull without damaging the delicate fossil.

One of I12's scientists, and co-author of the paper, Alexander Liptak, explained: "I12 was the only beamline at Diamond suitable for this experiment. The study required a large beam size and high beam energy to accommodate both the fossil's dimensions and attenuation, as well as the necessary contrasting medium introduced to account for the fossil's high aspect ratio. Furthermore, the high photon flux available at I12 enabled us to virtually ‘inspect the sample’ by performing rapid exploratory XCT acquisitions and partial reconstructions, which were used to directly inform the necessary positioning and resolution requirements for subsequent scans."

The new species has been named Agriodontosaurus helsbypetrae, meaning “fierce-toothed lizard from the Helsby rock”, after the Helsby Sandstone Formation in Devon where it was discovered.

Professor Michael Benton, co-supervisor from the University of Bristol, added: “The animal is unlike anything discovered before, and it forces us to rethink the earliest stages of lizard and snake evolution.”

This discovery not only pushes back the fossil record of lizards but also highlights the importance of advanced imaging technologies. By working with Diamond, the team was able to unlock crucial evolutionary details from a fossil small enough to fit in the palm of a hand.

To find out more about the I12 beamline, or to discuss potential applications, please contact Principal Beamline Scientist Prof Genoveva Burca, Genoveva.Burca@diamond.ac.uk