A tiny Scottish fossil nicknamed "Lizzie" has been dethroned as one of the world's earliest reptiles. A new study in the journal Nature reveals that the 345-million-year-old fossil — long celebrated as the oldest reptile — was not a reptile at all. X-ray scans show it had hidden internal gills and a fish-like mouth lined with thousands of tiny teeth, pointing to an animal that lived in water, not on land.
What is the Lizzie fossil?
Westlothiana lizziae — Lizzie for short — was discovered in Scotland in 1984 and formally described in 1990. Its nearly complete skeleton, just 20 centimeters long, had four limbs with five digits on each and claw-like tips, setting it apart from many Carboniferous contemporaries that had fin-like limbs. Because the fossil was crushed between two slabs, researchers based their interpretation mostly on what they could see on the surface. It was widely cited as the earliest land-adapted amniote — the vertebrate group that includes reptiles, birds and mammals — and used for decades as a landmark fossil in debates about when amniotes originated. Its lizard-like looks earned it the nickname and, formally, the species name lizziae.
X-ray scans reveal a very different animal inside
The new study, led by researchers at the American Museum of Natural History and the University of Oxford, in collaboration with the European Synchrotron Radiation Facility in Grenoble, France, used intense synchrotron X-rays to see through the rock and digitally reconstruct anatomy hidden inside the crushed fossil. What they found was unexpected: a surprisingly primitive skull, ossified internal gills, and a fish-like mouth lined with thousands of tiny teeth.
"Lizzie has been an icon for the early evolution of amniotes for decades," said co-lead author Xavier Jenkins, a postdoctoral fellow in the Museum's Division of Palaeontology. "But when we were finally able to see inside the fossil, we found an animal that looked very different from what we expected."
"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," added co-lead author Ben Igielman, who began the research during his graduate work at the University of Oxford. "It turns out looks can be deceiving, and Lizzie lived a completely different lifestyle than we previously thought."
Why Lizzie's demotion matters for evolution
The findings do more than reclassify one fossil — they rewrite the rules for reading the whole early history of land animals. Features once treated as hallmarks of terrestrial amniotes — claw-like toes, five-toed feet, sturdy weight-bearing limbs — had already evolved among earlier, more aquatic members of the tetrapod stem lineage, in animals still living in and out of the water. As Jenkins put it: "Terrestrial-looking traits... 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."
The result also complicates interpretations of ancient clawed trackways recently used to argue that amniotes originated in the Devonian Period, more than 359 million years ago. If a non-amniote like Lizzie had claws too, clawed footprints alone can no longer prove the track-maker was an amniote.
"This is a big surprise," said study co-author Roger Benson, the Museum's Macaulay Curator of Palaeontology. "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."
Takeaway: Lizzie is no longer the first reptile — and that's arguably more exciting. The "oldest reptile" title was built on surface impressions; the real animal, revealed inside the rock, shows evolution testing land-ready features in the water long before reptiles existed.
Watch: Latest videos and explainers about the Westlothiana "Lizzie" fossil study on YouTube
Sources: BrightSurf — fossil long known as world's oldest reptile dethroned; The Brighter Side — Scotland's famous Lizzie fossil was not the early reptile scientists thought; YourWeather — Lizzie wasn't an early reptile after all; Earth.com — famous fossil Lizzie was mistaken for an early reptile.