One of the great mysteries of reptile evolution has been solved this week. Paleontologists and herpetologists have believed for years that modern legless snakes must have had four legs at some time in the past. They had found several transitional fossil snake specimens with two legs, but had yet to find the four-legged snake “missing link”.
The 120-million-year-old snake has been named Tetrapodophis amplectus, but probably didn’t actually use its feet to walk. Gioven the morphology of the feet, they might have helped Tetrapodophis hold onto a partner while mating or grip struggling prey, explained study researcher David Martill, a professor of paleobiology at the University of Portsmouth in the UK.
Prior paleontological research has described several two-legged snake fossils, but this is the first known snake ancestor with four legs. Martill added that the four-legged snake fossil evolved from land-based-burrowing creatures, and is a transitional organism representing the evolution from prehistoric lizards to modern snakes.
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The study on the snake missing link was published in the July 24th edition of the academic journal Science.
Statement from lead researcher
“We’ve found the ancestor of all snakes,” Martill enthused in a recent interview with Live Science. “We have found the missing link between four-legged lizards and snakes.”
Martill was leading a group of students on a field trip with his students to the Solnhofen Museum, when he saw a new fossil specimen on display. “I thought, ‘Bloody hell, it’s got back legs!'” Martill said. “It had front legs. Nobody had ever seen a snake before with four legs, and yet evolutionary theory predicts that there should be an animal that is transitional between four-legged lizards and snakes, and here it was.”
He then explained his discovery to the museum and requested a study of the fossil. He brought in Helmut Tischlinger, a German paleontologist, and Nicholas Longrich, a senior lecturer in evolutionary biology at the University of Bath in the UK, to complete the team to study the amazing new fossil
“Snakes are all over the planet now, and it would be nice to know where they actually started,” Martill commented. “If you look at the distribution of fossil snakes, they’re all Gondwanan. So it does look as though snake evolution began in the southern continents.”
New four-legged snake fossil is clearly a transition species
There are a number of signs the new fossil is a transitional snake. Of note, Tetrapodophis has a faint impression of a single row of belly scales, a feature still seen on snakes today, but not present on lizards or crocodiles.
The researchers also used ultraviolet photography to examine the fossil gut. There they discovered partly digested bone fragments, which means the snake ancestor also preyed on small vertebrates, just like modern carnivorous snakes.
Martill continued to point out that Tetrapodophis used its long body to constrict prey, probably creatures like lizards and frogs.
The four-legged fossil had other classic snake features such as a short snout, long braincase, fanged teeth and a flexible jaw enabling it to swallow large prey.. It also has the typical flexible snake vertebrae column so it can easily bend and twist its body.
Finally, Nartill and the team Tetrapodophis does not have the long, laterally compressed tail that characterizes most marine animals, meaning the creature likely descended from burrowing land creatures.