‘Lizzie’ the Oldest Reptile Fossil Just Got Dethroned

Some fossils only give up their secrets decades after they’re found, and only once someone finally looks inside the rock rather than just at its surface.

A 30-Year Icon of Early Evolution

Discovered in Scotland in 1984, the fossil of Westlothiana lizziae earned the nickname Lizzie for its distinctly lizard-like appearance. Described from what was visible on the surface of its two crushed stone slabs, it showed a nearly complete skeleton with four limbs, including fingers and toes tipped with superficially claw-like structures, features that set it apart from many contemporaries, which tended to have more fin-like limbs. Since its formal description in 1990, researchers have repeatedly cited Westlothiana as a landmark example of an early amniote, the group of vertebrates that includes reptiles, birds, and mammals, and one of the earliest animals clearly adapted to life on land.

Finally Looking Inside the Rock

A new study published in Nature, led by researchers at the American Museum of Natural History and the University of Oxford, working with the European Synchrotron Radiation Facility in Grenoble, France, used x-ray scanning to look through the surrounding rock and reconstruct anatomical structures invisible on the fossil’s surface. “Lizzie has been an icon for the early evolution of amniotes for decades,” said Xavier Jenkins, a postdoctoral fellow in the Museum’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.”

Gills and a Mouth Full of Tiny Teeth

The scans revealed a primitive skull, along with ossified internal gills and a fish-like mouth lined with thousands of tiny teeth, features that rule out any possibility that Westlothiana was an ancestor of true reptiles. Ben Igielman, co-lead author of the study, who began this research during his graduate work at Oxford, said the surprisingly primitive skull shows Lizzie wasn’t simply not a reptile, but belonged to a much more ancient lineage altogether. “It turns out looks can be deceiving,” Igielman said, “and Lizzie lived a completely different lifestyle than we previously thought.” Researchers now believe the animal was aquatic or amphibious rather than a land-dweller.

Claws Evolved Earlier Than Anyone Thought

The findings mean that anatomical traits once assumed to be exclusive to land-adapted amniotes, including Westlothiana’s claws and its five-toed hands and feet, a pattern still seen in mammals and reptiles today, had actually already evolved among earlier, more water-based members of the broader tetrapod lineage, the larger group of four-limbed animals that includes amniotes alongside amphibians. “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.”

Rewriting How to Read Ancient Footprints

The implications reach well beyond this one fossil. The findings directly affect how scientists interpret ancient fossil trackways that have recently been used to argue amniotes originated during the Devonian Period, more than 359 million years ago. Those trackways preserve impressions of an animal walking on four limbs with claw-like digits. If early tetrapod relatives like Westlothiana also had claws, then clawed footprints alone can no longer prove the animal that made them was actually an amniote. Some ancient trackways previously credited to early amniotes may instead have been left behind by more primitive, amphibious relatives still living in and out of the water. “The broader lesson,” Jenkins said, “is that terrestrial-looking traits, such as a reptile-like foot, a weight-bearing forelimb, and claw-like phalanges, were not unique features of tetrapods, but rather accumulated piecemeal in their close relatives, in animals that were still living in and out of the water.”

Sources

This report draws on the American Museum of Natural History’s own announcement of the peer-reviewed study by Jenkins, Igielman, and colleagues, published in Nature (2026).