Lizzie the Fossil Was Never a Reptile, Study Finds

For nearly 30 years, one small fossil from Scotland held one of the most famous titles in paleontology: the world's oldest reptile. That title is gone. A new study published September 30, 2026 in the journal Nature reveals that the 345-million-year-old fossil nicknamed Lizzie was never a reptile at all. High-resolution synchrotron X-ray scans showed that the Lizzie fossil belonged to a much more ancient lineage of aquatic animals, and researchers have now reclassified it as a stem tetrapod, a far earlier branch of the four-limbed family tree. The discovery rewrites a chapter of the story of how vertebrates first walked on land.

Lizzie, formally known as Westlothiana lizziae, was discovered in 1984 and described in 1990 from two crushed slabs of rock. On the surface, it looked the part of a pioneering land-dweller: a nearly complete skeleton with four limbs, fingers and toes tipped with what appeared to be tiny claws. Those features made it the textbook example of the earliest land-adapted amniote, the group of vertebrates that includes reptiles, birds and mammals. Generations of researchers cited the Lizzie fossil as a landmark in discussions of when and how amniotes first evolved. "Lizzie has been an icon for the early evolution of amniotes for decades," said Xavier Jenkins, a postdoctoral fellow in the American Museum of Natural History's Division of Paleontology and co-lead author of the study. "But when we were finally able to see inside the fossil, we found an animal that looked very different from what we expected," he said, according to the museum.

What the scans found inside the Lizzie fossil

The research team, led by the American Museum of Natural History and the University of Oxford in collaboration with the European Synchrotron Radiation Facility in Grenoble, France, used powerful X-ray scanning to see through the rock and reconstruct anatomy that could never be observed from the fossil's flattened surface. What they found was not a land animal at all. The scans revealed a surprisingly primitive skull, an ossified internal gill skeleton, and a fish-like mouth lined with thousands of tiny teeth, features that point to an aquatic or amphibious animal that breathed water and likely fed by sucking in prey.

"The surprisingly primitive features of the skull show us that Lizzie was not only not a reptile but belonged to a much more ancient lineage. It turns out looks can be deceiving, and Lizzie lived a completely different lifestyle than we previously thought," said Ben Igielman, the study's co-lead author, who began the research during his graduate work at the University of Oxford, according to the museum. The digital 3D models built from the scans have been made openly available on MorphoSource, so other researchers can examine the anatomy for themselves.

The deeper significance is about timing and traits. When the team fed the new anatomical observations into an expanded evolutionary dataset, the analysis placed Westlothiana not near the base of the reptile lineage but on the much deeper stem of Tetrapoda, the branch that sits outside the group containing modern amphibians and amniotes. That means features long assumed to be exclusive to land-adapted animals, including five-digit hands and feet and claw-like fingertips, had already evolved in earlier, more aquatic members of the stem lineage. "This is a big surprise," said study co-author Roger Benson, the museum's Macaulay curator of paleontology. "It shows that, although we think of amphibians as being more 'primitive' than reptiles today, some of the traits of reptiles were already there in the ancestor of both amphibians and reptiles."

Why dethroning the Lizzie fossil matters

The reclassification has ripple effects beyond one specimen. For years, researchers used the apparent age of Lizzie to anchor timelines for the origin of amniotes, and some pointed to ancient fossil trackways as evidence that amniotes evolved even earlier. But if aquatic stem tetrapods like Westlothiana already had claws, then clawed footprints alone can no longer prove that a reptile made them. The museum notes that the study forces a rethink of how those trackways are interpreted, a reminder that the fossil record rewards humility.

There is also a broader lesson in the Lizzie fossil saga about how science corrects itself. The original 1990 description was based on what was visible on the surface of two deformed slabs, and the technology to see inside simply did not exist yet. It took a synchrotron, a particle accelerator repurposed as the world's most powerful microscope, to look through the rock. As Jenkins put it, terrestrial-looking traits like a reptile-like foot, a weight-bearing forelimb and claw-like digits were not unique features of early land animals but accumulated piecemeal in relatives still living in and out of the water. Lizzie may have lost its crown, but in exchange it gave paleontology a sharper picture of the messy, watery transition that eventually put vertebrates on land.