A 345-Million-Year-Old Fossil Reveals a Surprising Mix of Fish and Reptile Features

A small fossil from Scotland has given scientists a new look at one of the most important stages in the evolution of animals living on land.

The fossil belongs to Westlothiana lizziae, a 345-million-year-old animal discovered in Scotland in 1984. For decades, it was regarded as one of the earliest known reptiles or reptile-like land animals. A new study published in Nature has now revealed that the animal had several features that were much more fish-like than previously recognized.

A Fossil That Kept Its Secrets

The specimen, nicknamed “Lizzie,” is preserved between two crushed slabs of rock. Its skeleton includes four limbs with fingers and toes, features that originally helped make the animal look more like an early land-dweller.

However, the fossil is heavily compressed, making some of its internal structures difficult to study. Researchers therefore turned to powerful X-ray imaging at the European Synchrotron Radiation Facility in France.

Hidden Gills Come Into View

The detailed scans revealed structures that had been hidden inside the rock for millions of years. Scientists identified evidence of gill-related anatomy as well as fish-like teeth.

These findings suggest that Westlothiana was not simply an early version of a modern reptile. Instead, it had a combination of characteristics that reflected the complicated transition between aquatic and land-based vertebrates.

What the Discovery Means

The study does not simply replace one label with another. Instead, it shows that the early history of land animals was more complicated than a simple progression from fish to reptiles.

Animals living around 345 million years ago were experimenting with different body structures and ways of moving through their environments. Some possessed limbs that could function on land while retaining other features associated with aquatic life.

The researchers say the discovery highlights how much information can remain hidden inside fossils that have already been studied for decades.

Technology Changes What Scientists Can See

The new findings were possible because modern imaging technology allowed scientists to examine structures that could not be seen clearly from the surface of the fossil.

Instead of physically removing more rock and potentially damaging the specimen, researchers were able to look inside it using high-resolution X-ray scans.

The case demonstrates how old museum specimens can continue to provide new scientific information when researchers have access to better technology and new analytical methods.

Sources

• European Synchrotron Radiation Facility — “Early fossil reveals fish-like and reptile-like traits” — September 30, 2026.
• EurekAlert! / American Museum of Natural History — “Fossil long known as world’s oldest reptile dethroned” — September 30, 2026.
• Phys.org — “Fossil long known as world’s oldest reptile dethroned” — September 30, 2026.
• Nature — Research on Westlothiana lizziae and early land vertebrates.