Part and counterpart of the Tetrapodophis fossil, or the so-called "snake with four legs," which researchers said in a new study was misclassified as a snake when it was discovered. Photo courtesy of Michael Caldwell
Nov. 18 (UPI) -- A fossil thought to be the missing link between modern-day lizards and the planet's first snakes is, in fact, not, paleontologists said in a paper published Thursday by the Journal of Systematic Palaeontology.
The finding means the fossil from the so-called "snake with four legs" is actually the bones of a long-bodied marine lizard, the researchers said.
"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," co-author Michael Caldwell said in a press release.
"There are many evolutionary questions that could be answered by finding a four-legged snake fossil, but only if it is the real deal," said Caldwell, a professor of biological and earth and atmospheric sciences at the University of Alberta in Canada.
"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," he said.
The "snake with four legs" fossil, from an animal dubbed Tetrapodophis amplectus, was discovered in 2015, as documented in an article published at the time by the journal Science.
Initially, the fossil, which was discovered in Brazil, was dated to Early Cretaceous Crato Formation of the South American region, or about 113 million years ago, according to the 2015 article.
It was described as link between prehistoric snakes and modern-day lizards, such as alligators and crocodiles, which have four limbs.
However, the finding immediately became a subject of much debate among paleontologists and other researchers.
For this analysis, Caldwell and his colleagues studied the rock that originally contained the fossil as well as the fossil itself.
The initial report, authored by the researchers who made the discovery, "only described the skull and overlooked the natural mold, which preserved several features," Caldwell said.
Analysis of the mold made "it clear that Tetrapodophis did not have the skull of a snake, not even of a primitive one," he said.
"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 mold preserving the shape of each on the opposite side," Caldwell said.
The new study of Tetrapodophis revealed a number of mischaracterizations of the anatomy and morphology of the specimen, according to Caldwell and his colleagues.
These traits that initially seemed to be shared most closely with snakes, suggesting this might be the long-sought-after snake with four legs, they said.
However, the new analysis revealed that "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 said.
"The major conclusion of our team is that Tetrapodophis amplectus is not in fact a snake and was misclassified," he said.
Although Tetrapodophis may not be the snake with four legs that paleontologists prize, it still has much to teach us, according to study co-author Tiago Simões.
However, access to the specimen has been challenging because "it has been housed in a private collection with limited access to researchers," Simões, post-doctoral fellow at Harvard University, said in a press release.
"The situation was met with a large backlash from the scientific community," Simões said.
"We lay out the important legal status of the specimen and emphasize the necessity of its repatriation to Brazil, in accordance not only with Brazilian legislation but also international treaties and the increasing international effort to reduce the impact of colonialist practices in science," he said.