Tiny reptile with giant teeth redefines the origins of lizards

On a beach in Devon, a chunk of sandstone has forced scientists to rewrite reptile history. Inside that rock was the skeleton of a reptile no bigger than a hand, yet fierce enough to crush cockroaches.

The animal lived 242 million years ago, long before dinosaurs rose to power. Its skull revealed teeth so large that researchers named it Agriodontosaurus helsbypetrae – the fierce-toothed lizard.

Oldest lizard ancestor

“The new animal is unlike anything yet discovered and has made us all think again about the evolution of the lizard, snakes and the tuatara,” noted study lead author Dan Marke from the University of Bristol.

What he and his team found looked nothing like what textbooks had predicted. This ancient reptile lacked the flexible skulls seen in modern lizards and snakes. It also missed the rows of palatal teeth that many reptiles use to pin down prey.

Instead, it carried a bone linking cheek to jaw, a feature found today only in the tuatara of New Zealand.

Lizard with giant teeth

“The new fossil shows almost none of what we expected,” said Marke. The jaws held spectacularly oversized teeth, far bigger than those of close relatives. Study co-author Michael Benton explained how those teeth worked.

“The new beast used these teeth to pierce and shear the hard cuticles of its insect prey, pretty much as the tuatara does today,” noted Benton. One bite could pierce and slice in a single motion. That design turned this palm-sized reptile into a deadly insect hunter.

Obtaining high resolution images

The fossil itself posed a challenge. The skull measured only 1.5 centimeters wide and was locked inside a block of stone.

Traditional tools couldn’t reveal its structure without destroying it. So the team turned to the European Synchrotron Radiation Facility in France. The machine blasted X-rays 100 billion times brighter than those in hospitals.

“The Synchrotron allowed the scientists to zoom in on large objects and obtain very high-resolution images,” noted Vincent Fernandez, a paleontologist at the facility. The scans uncovered every ridge, tooth, and joint in extraordinary detail.

Lizard evolution pushed back

The analysis pushed the origin of lepidosaurs – the group that includes lizards, snakes, and tuataras – further back than ever.

With an age between 245 and 241 million years, Agriodontosaurus marked the earliest known member of this lineage.

That finding means the split between Rhynchocephalia (tuatara and extinct cousins) and Pan-Squamata (lizards and snakes) happened earlier than anyone thought.

This single fossil resets the evolutionary clock for one of the most successful reptile groups on the planet.

Life in Triassic Devon

The sandstone that preserved Agriodontosaurus came from ancient riverbeds. Seasonal floods swept animals into channels, covering them in fine sand. Alongside the lizard ancestor, scientists found fish, amphibians, and other reptiles.

The Triassic landscape was tough – semi-arid, storm-prone, and unstable. Yet in this harsh setting, small hunters like Agriodontosaurus carved out their niche.

Its discovery shows that even during periods of recovery after mass extinction, ecosystems could still support predators that evolved sharp tools for survival.

Rethinking the history of reptiles

This fossil showed more than sharp teeth. It revealed a story of unexpected adaptations. Scientists had assumed early lepidosaurs kept palatal teeth and only later lost them. 

Agriodontosaurus helsbypetrae proved the opposite: those teeth disappeared early, while other lineages re-evolved them much later. That reversal forces researchers to rethink how traits appear and vanish.

It shows evolution does not always progress in a straight line but can circle back, reusing old designs in surprising ways. This tiny reptile turned a simple assumption about dental history into a puzzle that now reshapes the larger story of reptile evolution.

Evolution, it seems, did not follow a straight path. Instead, it experimented, discarded, and sometimes returned to old solutions. The reptile’s strong jaw muscles also point to a bite more powerful than expected, suggesting that feeding strategies evolved faster than skeletal changes.

Significance of the lizard ancestor

For paleontologists, the fossil is a reminder that even the smallest bones can carry the biggest surprises.

The discovery of Agriodontosaurus helsbypetrae locks a new date into the reptile family tree and highlights Europe as a cradle for early lepidosaur evolution, showing how unexpected finds can completely change long-held scientific views.

“The new animal is unlike anything yet discovered and has made us all think again about the evolution of the lizard, snakes and the tuatara,” noted Marke.

The study is published in the journal Nature.

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