A fossil of a small reptile that lived in what is now Scotland about 167 million years ago, during the time of the dinosaurs, has baffled scientists because it had features of both snakes and lizards. Whether it is an early ancestor of snakes or just an evolutionary "oddity" remains a question. Either way, it was a small but fearsome predator.
The researchers, Reuters reports, said that the creature, named Breugnathair elgolensis, had teeth that were sharply curved and hooked like those of a snake. The way its teeth were set in the jaw and their inward slope also resembled snakes. However, the proportions of its body and head were more lizard-like - with well-developed limbs.
Breugnathair, which was about 30 centimeters long including its tail, lived in an environment similar to today's mangroves, with a tropical climate during the Jurassic period - considerably warmer than in present-day Scotland. It is thought to have fed on insects, small mammals, amphibians and other lizards.
This fossil represents one of the oldest and most complete specimens of a group of reptiles known as squamates, which includes lizards and snakes. With its combination of features, Breugnathair blurred the line between lizard and snake - a kind of "snake lizard" or perhaps a "goose snake."
"Breugnathair is either a lizard-like ancestor of snakes, or a member of a more primitive group of lizards that independently evolved snake-like features associated with a predatory diet. The evidence is so close that we have been unable to decide between the two possibilities," said paleontologist Roger Benson of the American Museum of Natural History in New York, lead author of the study published in the journal Nature.
"The unexpected combination of traits we see shows that early squamate evolution was very complex - and we are only just beginning to understand what was actually happening," Benson added.
The oldest undisputed snakes in the fossil record date back to about 110 million years ago, during the Cretaceous period, according to Susan Evans, a paleontologist and evolutionary morphologist at University College London.
"No one would mistake them for anything else. They have a long body, no trace of forelimbs and reduced hind limbs," Evans said.
But these fossils do not reveal what snakes looked like before they developed their characteristic elongated bodies.
"We don't know, for example, whether snakes evolved head and jaw features first, or their long bodies first. We also don't know where snakes first appeared, or what their ecology was like," Benson said.
Although it is possible that Breugnathair was an early transitional form between lizards and snakes, its anatomy remains puzzling.
"We know from DNA that snakes are related to iguanas, monitor lizards and some other groups of lizards. Therefore, we expect that the ancestor of snakes was lizard-like and shared characteristics with these groups," Benson said.
"But when we look at the details of Breugnathair's anatomy, we don't see many features in common with them. Instead, it has a number of more primitive characteristics that it shares with the earliest lizards - traits that we still find in geckos and skinks today. That's a big surprise," he added.
The fossil was discovered on the Isle of Skye, on the coast near the town of Elgol, and its scientific name means "false snake of Elgol".
If it wasn't part of the lineage that led to modern snakes, Breugnathair may have been an evolutionary dead end - a reptile that independently developed snake-like traits but eventually became extinct, researchers believe.
The earliest reptiles appeared about 320 million years ago, Benson said.
Some of the earliest forms superficially resembled lizards, but they lacked typical squamate features - such as structures that increase skull mobility during feeding or the shoulder structure that allows lizards to take a longer stride.
Breugnathair, scientists conclude, is as mysterious as it is fascinating.
"It may one day help us understand what traits to look for in future fossils to understand the origins of snakes," Evans said.
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