A fossil of a species with an obscure ancestry has rattled the palaeontology community in a controversy that is as much about the origin of snakes as it is about the politics of science.
Tetrapodophis was hailed as the missing link in the evolution of legless snakes from four-limbed reptiles. The original paper, published in Science last year, suggests the approximately 110-million-year-old fossil to be of a four-legged snake, characterized by hooked teeth and grasping limbs.
Although the closest relatives of snakes are marine lizards, the most primitive snakes were burrowing snakes. As a result, there has been an ongoing disagreement amongst palaeontologists over whether snakes descended from terrestrial or aquatic predecessors.
This rare fossil seemed to be the crucial piece of evidence that pointed to the burrowing ancestry of snakes until recent analyses called its true identity into question. UTM Professor Dr. Robert Reisz and his colleagues have voiced a challenge to the original claim.
“It wasn’t very convincing in the first place because the limbs are tiny and very peculiar-looking,” said Reisz. “I independently became very suspicious and wanted to follow up and look at this.”
The fossil was held in the Bürgermeister-Müller-Museum in Solnhofen, Germany, where Reisz and his collaborator from the University of Alberta, Michael Caldwell, flew to study the fossil in person. Contrary to the initial hypothesis, they found the specimen to have limb anatomy “highly suggestive of aquatic habits.”
“We came to a very different conclusion, which fit actually more in line with what the fossil in general is showing,” said Reisz. They published this alternative interpretation in Cretaceous Research in June 2016.
“That is not an uncommon phenomenon. In fact, it has happened multiple times that lizards reduce, or even lose, their legs,” explained Reisz. “They are still lizards.”
Reisz and his colleagues systematically refuted the original hypothesis in a presentation they delivered at the annual Society for Vertebrate Palaeontology meeting, testifying the misinterpretation of the specimen by the paper’s authors. Instead, they believe the fossil to be that of the oldest known dolichosaur, an extinct genus of aquatic lizard.
When the Tetrapodophis paper was published, the fossil was only temporarily accessible. “The specimen was [later] withdrawn from the museum and was reclaimed by the private collector, so it was never really donated to that museum,” said Reisz. He stated that authors of the original paper gave Science the impression that this was the case, when in reality, “it was just a loan.”
A further complication concerns the legality of exporting a fossil from its country of origin, which in this case is Brazil. “We are fairly certain that this… specimen was illegally exported from Brazil and bought [by] a private collector,” Reisz claimed.
This interfered with the accessibility of the specimen, a standard of utmost importance in science. “Reproducing palaeontological results depends on unrestricted access to fossils described in the literature, allowing others to re-examine or reinterpret them,” wrote Reisz in a correspondence to Nature. “Museums have policies and protocols for keeping materials in the public trust, but accessibility to privately owned fossil collections can be a problem.”
On November 11, Science reported that the fossil will be returned to the Bürgermeister-Müller-Museum.
“It’s kind of a victory on our part, politically speaking, because important specimens should not be in private hands. They should be actually donated to an institution where scientists can study [them],” Reisz argued.
“I think the politics of the whole issue is in many ways just as exciting because it points to what is proper and what is not proper to do in science,” he explained.