Fossil discovery shifts the origin of lizards back 35 million years

A recent discovery in a quarry near Bristol has sparked intense debate and controversy in the scientific community. Unearthed from Triassic-aged rocks, a tiny fossil skeleton has been identified as Cryptovaranoides microlanius, a modern-type lizard that died at least 205 million years ago.

This remarkable fossil is now the oldest lizard of its kind on record, which reframes our understanding of lizard evolution by pushing the origin of the Squamata group – which includes all lizards and snakes – back by 35 million years.

A hidden predator

The original study, conducted by a team from the University of Bristol, named the creature Cryptovaranoides microlanius. This translates to “hidden lizard, small butcher,” which is a nod to its sharp teeth that probably helped it tear its prey apart.

The research team was led by Dr. David Whiteside, Dr. Sofia Chambi-Trowell, and Professor Mike Benton.

The experts identified key anatomical features of the skull and skeleton that placed the fossil firmly within the Squamata and close to the Anguimorpha group, which includes modern anguids and monitors.

“We knew our paper would be controversial. But we were confident that we had looked at every possible feature and compared it with everything we could,” explained Dr. Whiteside.

Their confidence was rooted in meticulous research, which included detailed examination of the fossil specimen and CT scans to analyze the intricate details of the skull and jaw.

Controversy around the lizard fossil

Despite their thorough investigation, the findings were greeted with skepticism.

In 2023, a rival team of researchers challenged the classification of Cryptovaranoides, suggesting it was not a lizard or even a lizard relative.

Instead, they proposed that it belonged to the archosauromorph group, which includes crocodilians and dinosaurs. This claim surprised the original researchers.

“We were therefore surprised, perhaps even shocked, that in 2023 another team of academics suggested that Cryptovaranoides was not a lizard or even a lizard relative, but in fact an archosauromorph, more closely related to crocodilians and dinosaurs,” said Professor Benton.

Revisiting the lizard fossil

Determined to validate their findings, the Bristol team revisited the fossil and CT scan data. Their reassessment involved examining the original specimen alongside X-ray scans, which revealed details hidden within the rock.

“We had the marvelous images from those CT scans as well as further access to the fossil which enabled us to check all their suggestions. We found that most of the concerns raised were wrong,” noted Dr. Chambi-Trowell.

The team’s new analysis scrutinized the criticisms point by point. They provided detailed descriptions and supplementary evidence, including additional photographs and 3D images, to substantiate their claim.

“All the details of the skull, the jaws, the teeth, and the limb bones confirm that Cryptovaranoides is a lizard, not an archosauromorph,” Professor Benton stated.

“In our new paper, we provide great detail of every criticism made and we provide more photographs of the specimen and 3D images from the scans, so everyone can check the detail.”

World’s oldest modern-type lizard

The team’s confidence was further bolstered by phylogenetic analysis, a method that codes hundreds of anatomical features of Cryptovaranoides and compares them with other modern and fossil lizards, as well as archosauromorphs.

“The result of all this had to be tested by a phylogenetic analysis. This is where we code hundreds of anatomical features in Cryptovaranoides and other modern and fossil lizards, as well as various archosauromorphs,” explained Dr. Whiteside about the rigorous testing process.

“We ran the analysis time after time, and it gave our original result, that the little Bristol reptile is indeed the world’s oldest modern-type lizard.”

Significance of the discovery

This discovery has far-reaching implications for our understanding of reptile evolution.

Squamata, the group that includes all lizards and snakes, is one of the most diverse vertebrate groups today. Tracing its origins back 205 million years provides new insights into how modern reptiles evolved and adapted over millions of years.

Dr. Whiteside and his colleagues hope their findings will settle the debate and reaffirm the significance of Cryptovaranoides.

By pushing the timeline of Squamata’s origin further back, the discovery challenges existing models of reptilian evolution and highlights the importance of continued research and exploration in paleontology.

Visual evidence in the lizard fossil

The fossil’s remarkable preservation has provided invaluable data. Detailed CT scans allowed the team to analyze internal structures and confirm its classification.

One image, created by Dr. Chambi-Trowell, shows the inside of the skull and lower jaw on the right, juxtaposed with an exterior CT scan of the same bones on the left. These images reveal a level of detail crucial for accurate classification.

Future research directions

While this lizard fossil discovery is remarkable, it opens new questions about the early evolution of reptiles. What other fossils might remain hidden in similar Triassic rocks?

Could they reveal even older ancestors of Squamata? The Bristol team’s work underscores the value of re-examining existing specimens and using advanced technologies like CT scanning to unlock hidden details.

“The little Bristol reptile is a remarkable window into the past. It helps us understand the origins of one of the most successful vertebrate groups on Earth,” said Dr. Whiteside.

“We look forward to more discoveries that will continue to illuminate the fascinating history of life on our planet.”

The study is published in the journal Royal Society Open Science.

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