Bizarro salamander ancestor was an evolutionary oddball

Today, many animals are considered “living fossils.” Once thought to be extinct, the prehistoric coelacanth has been swimming continuously in Earth’s oceans since the time of the dinosaurs. Horseshoe crabs exist in fossil records dating back hundreds of millions of years. Even many sharks appear virtually unchanged from their Cretaceous ancestors. But even if Tanyka amnicola was last observed around 275 million years ago, it was already a living fossil at its time.

It was also a extremely strange creature. So strange, in fact, that paleontologists first thought they were observing an ancient aberration when they discovered the first jaw of this salamander-like creature in a dry riverbed near the Amazon rainforest in Brazil.

“The jaw has this weird twist that drove us crazy trying to figure it out. We scratched our heads for years, wondering if it was some kind of deformation,” recalls Jason Pardo, a paleontologist at the Field Museum in Chicago.

As Pardo and colleagues detail in a study published today in the journal Proceedings of the Royal Society B, TanykaThe strange jaw was simply part of his evolution. And they have eight other similar fossil specimens to prove it.

Tankia (“jaw” in the local indigenous language Guaraní) was an incredibly ancient four-legged vertebrate, or tetrapod. Current examples of four-legged animals are found among birds, mammals, reptiles, and amphibians, but they all trace back to a single lineage called stemmed tetrapods. Eventually, the stem tetrapods split into two groups: one that laid eggs on land and the other that laid eggs in water. Tankiahowever, remained firmly in the “stem tetrapod” camp.

“Tanyka came from an ancient lineage that we didn’t know had survived until now,” Pardo said.

He compares it to today’s platypus. Almost all living mammals reproduce through live births, but the earliest examples laid eggs. The platypus has retained its egg-laying abilities for millions of years, making it an oddity among mammals.

And then there is Tanykathe mouth. The bottom teeth did not face up – instead they pointed towards one side or the other. Meanwhile, the section of the jaw that faces the tongue in humans was oriented toward the roof of the mouth. These surfaces were also covered with tiny teeth called denticles that turned the angled jaw into a grinding surface.

“Based on his teeth, we think Tanyka was an herbivore and ate plants at least occasionally,” said Juan Carlos Cisneros, study co-author and paleontologist at the Federal University of Piauí in Brazil.

This only adds to the uniqueness of the animal, since the vast majority of stem tetrapods were strictly carnivorous.

“We expect that the denticles in the lower jaw would rub against similar teeth in the upper part of the mouth. The teeth would have rubbed against each other in a way that will create a relatively unique way of feeding,” Pardo added.

Based on these details, its closest evolutionary relatives and its riverine habitat, the study authors estimate Tanyka probably looked like a three-foot-long salamander sporting a longer snout. But at least for now, determining what that looks like remains mostly guesswork.

“We found these isolated jaws, they are really strange and very distinctive,” said Ken Angielczyk, curator of paleomammology at the Field Museum and co-author of the study. “But until we find one of these jaws attached to a skull or other bones definitively associated with the jaw, we cannot say with certainty that the other bones we find nearby belong to Tanyka.”

Until then, TanykaThe jawline alone is more than enough to raise eyebrows.

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