Oldest lizard fossil fills evolutionary 'missing link'

A finger-sized fossilized creature found in the Italian Alps is the earliest lizard ever discovered, a new study suggests, filling a longtime gap in the fossil record and in the reptile family tree.

An analysis of Megachirella wachtleri identifies the tiny creature as the closest thing we know to the ancestor of all lizards and snakes, says Tiago Simoes, a postdoctoral researcher at the University of Alberta, who led the study published today in the journal Nature.

I immediately thought that it could be this missing link that we were hoping for.- Tiago Simoes, University of Alberta

Megachirella is 75 million years older than any previously known lizard fossils, which suggests lizards evolved significantly earlier than previously thought.

Megachirella would have scampered through a subtropical, coastal forest about 240 million years ago. Somehow, misfortune struck, and it was washed out to sea, buried and fossilized.

The eight-centimetre-long fossil includes the creature's skull and back, but cuts off before its pelvis and tail.

The fossil was discovered more than 15 years ago on Monte Pra della Vacca, in the Dolomites mountain range of northern Italy, by Michael Wachtler, a self-described explorer and "philosopher of nature" who has discovered many other fossils.

Researchers who studied the reptile fossil soon after its discovery named it after Wachtler. They suspected it was related to lizards, but didn't have enough information to figure out precisely what it was.

Up until now, the oldest lizard fossils found were from about 170 million years ago, during the Jurassic Period. That's 70 million years after the earliest known dinosaurs began roaming the Earth.

But based on genetic evidence and fossils of other reptiles, paleontologists suspected that lizards actually evolved much earlier — there was just a gap in the fossil record.

Simoes first saw the fossil of Megachirella in 2015, while completing his PhD. He was working with University of Alberta biology professor Michael Caldwell to create a detailed family tree of living and extinct reptiles; the project took him to over 50 different museum and university collections in 17 countries to examine specimens.

When Simoes spotted Megachirella, he was struck by how similar it looked to a lizard, even though it was much older than the oldest known lizards.

"I immediately thought that it could be this missing link that we were hoping for," he recalled.

Digital digging

Since the fossil's discovery, a new technology had become available — micro CT scanning — that would allow researchers to X-ray the fossil and view parts of it that were still embedded in the rock, such as its belly.

"It can digitally remove that rock," said Simoes.

With such a small, fragile fossil, physically removing the rock would've been impossible without damaging the fossil.

The CT scan revealed many features — in its skull, its clavicle, its arm and its wrist — that are found only in lizards.

"It's pretty much all over the body," Simoes said.

The fossilized creature also has a lot of features that are found in other reptiles, but no longer exist in modern lizards and snakes, such as extra ribs in its belly region and an extra opening in its upper arm bone.

The new findings confirm that early lizards scampered among the first dinosaurs. In fact, it now appears that like the branch of reptiles that led to dinosaurs, lizards first evolved before the End-Permian extinction, a catastrophe 252 million years ago that wiped out 96 per cent of marine species and 70 per cent of vertebrates on land. Though it seems, of course, that at least some early lizards and dinosaurs survived and went on to diversify into a huge variety of species.

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Marc Jones, a researcher who studies small vertebrates such as reptiles at the University of Adelaide and the Natural History Museum in London, says the study looks like a fair assessment of the available evidence, although some scientists might be disappointed about parts missing from the fossil, such as the knee and ankle, that also contain key lizard features.

"Lizards are a highly diverse and ecologically important group today but their early evolution remains mysterious. Any new developments such as this discovery will be significant," Jones added in an email. "It's great to see lizards, rather than dinosaurs or mammals, get some attention for a change."

While the word "dinosaur" means "terrible lizard," Simoes notes that lizards and dinosaurs are not at all closely related. "They're on opposite sides of the reptile tree of life," he said.

Dinosaurs are on the genetic branch that includes birds and crocodiles, while lizards, snakes and tuataras, a lizard-like animal, are on a completely different branch.

In addition to Simoes and Caldwell, the new study on Megachirella included researchers from Poland, Italy, the U.K., Australia and the U.S. It was funded by the Vanier Canada and Izaak Walton Killam Memorial scholarships, the Euregio Science Fund, Midwestern University, the Natural Sciences and Engineering Research Council of Canada, the Alberta Ukrainian Centennial scholarship, and the National Science Centre of Poland.