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Snakes aren’t just lizards without any legs. But a curious group of long, legless lizards look suspiciously like snakes themselves.
Also known as "worm lizards" (aka amphisbaenians), these small serpentine reptiles have evolved a limb-free body plan and strong heads that are handy for their burrowing lifestyle. So are they the snake's closest lizard relatives?
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Many had assumed they were, but a fossil found in Germany suggests that snakes and these sinuous lizards developed their streamlined shapes quite separately in the past tens of millions of years.
The nearly complete fossil skeleton is lacking only a portion of its tail and is described in a new paper published online May 18 in Nature. It belonged to a previously undescribed species (Cryptolacerta hassiaca) that lived during the Eocene, some 47 million years ago (Scientific American is part of Nature Publishing Group).
"This fossil refutes the theory that snakes and other burrowing reptiles share a common ancestry," Johannes Müller, a professor at Humboldt-Universität in Berlin and lead of the new study, said in a prepared statement. Using x-ray computed tomography (CT), the research team studied details of the wee-lizard's anatomy, looking for clues to compare with modern snakes and legless lizards. Rather than uncovering internal workings in Cryptolacerta that were sliding in a snakelike direction, the imaging and analysis "reveal a mosaic of lacertid and amphisbaenian anatomical characters," the authors wrote.
The group also conducted genetic analysis to back up their imaging finds: monitor lizards—the group that includes Komodo dragons—rather than legless lizards are the closer cousins of today's snakes.
Aside from separating the snakes from the snakelike, the new find helps to clarify the lizard family tree as well. It shows that these bizarre burrowing lizards are more closely linked to lacertids, which include many common lizards in Africa, Asia and Europe.
The C. hassiaca shares some early characteristics of today's worm lizards, such as "superficially small limbs" and a slightly stronger skull, which suggest it did a little burrowing itself, the researchers report. "Based on this discovery, it appears that worm-lizards evolved head first," Jason Head, a paleontologist at the University of Toronto Mississauga and co-author of the new paper, said in a prepared statement.
"Cryptolacerta shows us the early ecology of one of the most unique and specialized lizard groups," Head said. He and his colleagues propose the extinct animal likely lived among fallen leaves and could burrow to hide from predators—providing inspiration for its genus, which means "hidden lizard."
These big-picture pronouncements are based on a lizard whose body is just seven centimeters long. "It is particularly exciting to see that tiny fossil skeletons can answer some really important questions in vertebrate evolution," Robert Reisz, also of the University of Toronto Mississauga, said in a prepared statement.
Images courtesy of Robert Reisz
