Missing link to legless lizards found
The fossil of a legged ancient relative of legless lizards has been found — and it's nothing like a snake.
Legless lizards, or amphisbaenians, are tiny subtropical burrowing reptiles that look "remarkably similar" to blind snakes, which has led some scientists to debate whether the two might be related, said Robert Reisz, a paleontologist at the University of Toronto Mississauga campus.
But the new species described this week in Nature by Reisz and Johannes Muller, the German paleontologist who led the study, provides new evidence that amphisbaenians are closely related to common European lizards called lacertids and unrelated to snakes. The fossil, from the Eocene period about 65.5 million years ago, also provides hints about how the lizards came to lose their legs.
"That's why it's a wonderful missing link," Reisz said.
Amphisbaenians have long been distinguished from snakes by their chunky, lizard-like skulls — very different from the loosely constructed skulls that snakes have, Reisz said.
Recent genetic studies had suggested amphisbaenians might be related to lacertids, but the two kinds of lizards don't have much in common physically, Reisz said. Lacertids tend to have a chunky body, and their backbones are constructed very differently from those of amphisbaenians.
The new fossil, known as Cryptolacerta hassiaca, has a lacertid-like backbone and limbs, although its feet are very small, suggesting that it may be moving toward leglessness. The ancient reptile also has a lot of amphisbaenian-like features that showed it burrowed with its head. Its skull is reinforced, it had a large jaw, and it has fewer teeth than lacertids.
A lifestyle that involved a lot of head-first burrowing may have made it advantageous not to have legs.
In contrast, Reisz said, evidence suggests that snakes are closely related to iguanas and monitor lizards, and they lost their legs for an entirely different reason — to adapt to living in the water.
The small fossil, which is less than 10 centimetres long, was dug up in the 1980s from Germany's Messel Pit World Heritage Site, a former coal and shale mining area. It was sent to a museum in Frankfurt, where Muller saw it and suspected it might be something special. He and Reisz spent three years analyzing it.