London: The first known fossil of a four-legged snake dating back 110 million years has been discovered in Brazil, which shows that the serpents evolved from burrowing lizards and not from marine creatures. "It is generally accepted that snakes evolved from lizards at some point in the distant past.
What scientists don't know yet is when they evolved, why they evolved, and what type of lizard they evolved from," said Dave Martill, from the University of Portsmouth, who led the study. "This fossil answers some very important questions, for example it now seems clear to us that snakes evolved from burrowing lizards, not from marine lizards," Martill said.
The fossil, from Brazil, dates from the Cretaceous period and is 110 million years old, making it the oldest definitive snake, researchers said. "A four-legged snake seemed fantastic and as an evolutionary biologist, just too good to be true, it was especially interesting that it was put on display in a museum where anyone could see it," said Nick Longrich from the University of Bath, who studied the evolutionary relationships of the snake.
The snake, named Tetrapodophis amplectus, is a juvenile and very small, measuring just 20 cm from head to toe, although it may have grown much larger. The head is the size of an adult fingernail, and the smallest tail bone is only a quarter of a millimetre long. The most remarkable thing about it is the presence of two sets of legs, or a pair of hands and a pair of feet, the researchers said. The front legs are only about one centimetre long, and have little elbows and wrists and hands that are just five millimetre in length.
The back legs are slightly longer and the feet are larger than the hands and could have been used to grasp its prey. The fossilised snake also has the remains of its last meal in its gut, including some fragments of bone. The prey was probably a salamander, showing that snakes were carnivorous much earlier in evolutionary history than previously believed.
"The preservation of the little snake is absolutely exquisite. The skeleton is fully articulated. Details of the bones are clearly visible and impressions of soft tissues such as scales and the trachea are preserved," said expert German palaeontologist Helmut Tischlinger, who prepared and photographed the specimen.
Tetraphodophis has been categorised as a snake, rather than a lizard, by the team due to a number of features. The skeleton has a lengthened body, not a long tail. The tooth implantation, the direction of the teeth, and the pattern of the teeth and the bones of the lower jaw are all snake-like, researchers said.
The fossil displays hints of a single row of belly scales, a sure way to differentiate a snake from a lizard. The study was published in the journal Science.
