The missing link between reptiles, snakes has been debunked

Filling the links in the evolutionary chain with a fossil record of a “four-legged snake” connecting lizards and early snakes would be a dream come true for paleontologists. But a specimen that was previously thought to do the trick isn’t the missing piece of the puzzle, according to a new study by University of Alberta paleontologist Michael Caldwell.

“It has long been understood that snakes are members of a lineage of four-legged vertebrates which, due to evolutionary specializations, have lost their limbs,” said Caldwell, lead author of the study and professor in the departments of biological and earth sciences. and atmospheric sciences.

“Somewhere in the fossil record of ancient snakes is an ancestral form that still had four legs. So it has long been predicted that a four-legged snake would be found in fossil form. “

In an article published in the journal Science in 2015, a team of researchers reported finding what was believed to be an example of the first known four-legged snake fossil, an animal they named Tetrapodophis amplectus.

“If correctly interpreted on the basis of the preserved anatomy, this would be a very important discovery,” Caldwell said.

Caldwell explained that the new study of Tetrapodophis revealed a number of misconceptions about the anatomy and morphology of the specimen – traits that initially appeared to be closest to snakes, suggesting it could be the four-man snake. much sought after paws.

“There are many evolutionary questions that could be answered by finding a four-legged snake fossil, but only if it’s the real deal. The main conclusion of our team is that Tetrapodophis amplectus is not, in fact, a snake and has been misclassified, ”Caldwell said. “Rather, all aspects of its anatomy are consistent with the anatomy seen in a group of extinct Cretaceous marine lizards known as dolichosaurs.”

The clues to this finding, Caldwell noted, were lurking in the rock from which the fossil was extracted.

“When the rock containing the specimen was split and found, 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,” said Caldwell. “The original study only described the skull and ignored natural mold, which preserved several features that clearly show that Tetrapodophis did not have the skull of a snake – not even a primitive one.”

While Tetrapodophis may not be the four-legged snake that paleontologists appreciate, he still has a lot to teach us, said Tiago Simões, co-author of the study, a former doctoral student at State University of Harvard, Harvard postdoctoral fellow and Brazilian paleontologist, who highlighted some of the characteristics that make it unique.

“One of the biggest challenges in studying Tetrapodophis is that it is one of the smallest fossil squamates ever found,” said Simões. “It is comparable to the smaller squamates alive today which also have reduced limbs.”

An additional challenge in studying Tetrapodophis is access to the specimen itself.

“There was no proper permit for the original removal of the specimen from Brazil and, since its original publication, it has been kept in a private collection with limited access to researchers. The situation encountered a strong reaction from the scientific community, ”said Simões.

“In our redescription of Tetrapodophis, we set out the important legal status of the specimen and underline the need for its repatriation to Brazil, in accordance not only with Brazilian legislation but also with international treaties and the growing international effort to reduce the impact of colonialist practices. In science. “

The study, “Tetrapodophis amplectus is not a snake: reassessment of the osteology, phylogeny, and functional morphology of an Early Cretaceous dolichosaurid lizard,” was published in the Journal of Systematic Palaeontology.

| By Andrew Lyle

Submitted by University of Alberta Folio online magazine. The University of Alberta is an editorial content partner of Troy Media.

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