275-Million-Year-Old Fossil With a Twisted Jaw Reveals an Unexpected Tetrapod

In the bed of a dry river in northern Brazil, paleontologists discovered the same strange bone. Each was about six inches long, curved, thick and undoubtedly twisted. At first, the fossilized jaw looked like a deformation. But as more examples emerged from the same ancient rock layers, it became clear that twisting was a defining characteristic of the animal.

Now in Proceedings of the Royal Society Bresearchers describe the animal behind these bones: a previously unknown species that lived 275 million years ago and may represent one of the first four-limbed vertebrates to grind up plants for food – and a survivor of a lineage that scientists thought was already extinct. They named it Tanyka amnicola — “jaw” in the local Guarani language and “river dweller” in Latin.

“Tanyka “This is a very strange animal,” Jason Pardo, the study’s lead author, said in a press release. “We scratched our heads for years.”

An ancient lineage of tetrapods survived into the Permian

Tanyka belonged to the tetrapods, four-limbed vertebrates which today include reptiles, birds, mammals and amphibians.

But it was not among the more familiar branches that would come to dominate life on earth. Instead, it came from an older lineage that had largely faded away as more modern tetrapods diversified.

“Tanyka “is kind of like a platypus,” Pardo explained, a species that comes from an older evolutionary branch that persisted even as new groups of tetrapods evolved. Much like how egg-laying mammals such as the platypus still exist today alongside more modern mammals, Tanyka appears to represent a lineage that survived long after most of its relatives had died out. In this sense, it was something of a “living fossil” in its time.

Fossils from this period, the early Permian, are rare in what was once Gondwana, the southern supercontinent that included modern-day South America, Africa, Antarctica and Australia.

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A twisted jaw that helped early tetrapods crush plants

In most animals, the lower jaw is tilted upward, with the teeth aligned toward the palate. In Tanykathe lower jaw was twisted so that the main teeth pointed outwards and slightly to the sides. Meanwhile, the inner surface of the jaw (the part that would face the tongue in humans) faced upward and lined with rows of small, closely packed teeth called denticles.

These surfaces would have created a grinding motion as the lower denticles scraped similar structures in the upper jaw. Rather than slicing flesh, the teeth appear designed to crush and shred plant matter.

The fact that it ate plants is remarkable, as most of its close relatives were carnivorous. If confirmed, this finding indicates that phytophagous adaptations evolved earlier and in more unexpected branches of the tetrapod family tree than previously thought.

Nine fossil jaws offer clues to life in Gondwana

Despite the discovery of nine distinct jaws, no clearly associated skulls or skeletons were found. This leaves much of the animal’s body unknown.

Compared with related species, researchers estimate that Tanyka may have resembled a salamander with a slightly elongated snout and could have grown to three feet long. Surrounding rock layers suggest it lived near lakes or slow-flowing streams.

The fossils come from Brazil’s Pedra de Fogo Formation, one of the few sites preserving animals in Gondwana during the Early Permian. Discoveries from this formation are helping paleontologists reconstruct how vertebrate communities functioned in the southern supercontinent 275 million years ago.

Even with a handful of twisted jaws, Tanyka adds an unexpected piece to this ancient ecosystem.

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