It's not often that a fossil shakes up our understanding of an entire group of animals, but a 240-million-year-old fossil that we discovered 15 years ago has done exactly that.
The fossil of a Megachirella wachtleri lizard provides a link in the evolution of Squamata, or scaled reptiles, the largest order of reptiles that encompasses lizards and snakes.
"It's almost a virtual Rosetta stone in terms of the information that it gives us on the evolution of snakes and lizards," Michael Caldwell, a paleontologist at the University of Alberta, said in a video about the find. (The video is embedded above.)
A lizard with a long tale
Today, the planet is inhabited by about 10,000 species of lizards and snakes. That's nearly double the number of known mammal species. Despite this, we know precious little about the early stages of their evolution. The latest evidence suggests the order dates back some 250 million years, but the earliest known fossil from the Squamata order is 70 million years younger than that.
"That's more time than there is between us and the dinosaurs, and we had no clue what was going on," Tiago Simões, a paleontologist at the University of Alberta, told The Washington Post.
This is where the Megachirella wachtleri lizard enters the scene.
The fossil was discovered in Northern Italy's Dolomites Mountains back in 2003 by amateur fossil hunters. The fossil was formally described the same year, receiving the name Megachirella wachtleri, named for its sizable hands ("mega" and "cheiros" are ancient Greek words for "large" and "hand," respectively). The researchers also categorized it as belonging to the Lepidosauromorpha clade, a branch of reptiles that includes lizards. Ten years later, another study confirmed the classification using more advanced computer-generated comparisons with other species.
Still, the lizard posed some mysteries, and researchers took the fossil to the Multidisciplinary Laboratory of the Abdus Salam International Center for Theoretical Physics (ICTP) in Trieste, Italy. There, the fossil was subjected to a high-resolution micro CT scan that allowed scientists to see the parts of the lizard that were still encased in rock.
With this scan, along with comparisons to other reptiles, researchers were able to identify features of the lizard that earlier studies simply couldn't due to technical limitations. The micro CT scan allowed scientists to pick out features regarding its brain case, collar bone and wrists, features that are unique to lizards. However, the scan also revealed vestigial traits that more modern members of Squamata have lost, including a small cheek bone and belly bones that were found in many dinosaurs.
The researchers published these findings in Nature.
Between these features and some molecular data the researchers gathered, a few other things became apparent about Megachirella wachtleri. First, the lizard was a squamate, a member of the Squamata group, and this pushes that family tree back by some 75 million years. Scientists now have insights into how these animals evolved over time.
Second, the data indicated that the earliest squamates originated just before before the "Great Dying," a mass extinction event that wiped out 90 percent of marine life and 70 percent of terrestrial vertebrates 252 million years ago.
"Squamates, for example, were actually there before the extinction, they went through [it] in some way, and they took the opportunities that opened up just after the extinction," Massimo Bernardi, co-author of the study and a professor at the University of Bristol, told The Guardian.
As for the Megachirella wachtleri itself, researchers have yet to glean any behavioral information from the fossil beyond suspecting that it liked living on beachfront property. This is a guess since the Dolomites at the time the fossilized lizard met its demise were a series of lush islands with sandy beaches.