New research suggests that what appeared to be a four-legged snake, a missing evolutionary link connecting lizards and snakes, is nothing of the sort. The study has revealed that the specimen is simply a long-bodied marine lizard.
The study, which is published in the Journal of Systematic Paleontology, was led by Michael Caldwell of the University of Alberta.
“It has long been understood that snakes are members of a lineage of four-legged vertebrates that, as a result of evolutionary specializations, lost their limbs,” said Caldwell.
“Somewhere in the fossil record of ancient snakes is an ancestral form that still had four legs. It has thus long been predicted that a snake with four legs would be found as a fossil.”
An earlier study published in the journal Science in 2015, suggested that paleontologists had found the first of these snakes with legs, naming it Tetrapodophis amplectus.
“If correctly interpreted based on the preserved anatomy, this would be a very important discovery,” said Caldwell. However, he disputes the veracity of the study, claiming that T. amplectus was mischaracterized as a snake.
“There are many evolutionary questions that could be answered by finding a four-legged snake fossil, but only if it is the real deal. The major conclusion of our team is that Tetrapodophis amplectus is not in fact a snake and was misclassified.”
“Rather, all aspects of its anatomy are consistent with the anatomy observed in a group of extinct marine lizards from the Cretaceous period known as dolichosaurs.”
Caldwell explained how evidence from the surrounding rock matrix was overlooked in the description of the fossil.
“When the rock containing the specimen was split and it was discovered, the skeleton and skull ended up on opposite sides of the slab, with a natural mould preserving the shape of each on the opposite side.”
“The original study only described the skull and overlooked the natural mould, which preserved several features that make it clear that Tetrapodophis did not have the skull of a snake – not even of a primitive one.”
Despite T. amplectus not being a “missing link” between lizards and snakes, it’s still an interesting fossil to scientists.
“One of the greatest challenges of studying Tetrapodophis is that it is one of the smallest fossil squamates ever found,” said study co-author and Brazilian paleontologist Dr. Tiago Simões. “It is comparable to the smallest squamates alive today that also have reduced limbs.”
Dr. Simões pointed out that the fossil was removed from Brazil without appropriate permits and has since been housed in a private collection, limiting access by researchers. He asks that international treaties be honored and the fossil repatriated to Brazil.