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This 275-million-year-old animal had a twisted jaw like nothing alive today

A weird, twist-jawed “living fossil” from 275 million years ago may have been one of the earliest plant-eating vertebrates.

Date:

May 1, 2026

Source:

Field Museum

Summary:

Deep in a dried-up riverbed in Brazil, scientists uncovered a bizarre prehistoric mystery—twisted jawbones from a strange, long-lost animal unlike anything seen before. Dating back 275 million years, this creature, named Tanyka amnicola, belonged to an ancient lineage that should have already faded away, making it a kind of “living fossil” of its time.

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Illustration showing Tanyka amnicola in life, eating underwater plants. Credit: Vitor Silva

In a dry riverbed deep within a forest near the Amazon in Brazil, paleontologists uncovered a fossilized jawbone from a previously unknown ancient animal. As their excavation continued, the team found eight more similar jawbones, each about six inches long. However, they did not recover any additional bones that could clearly be matched to a full skeleton.

Even so, these isolated jaws revealed something remarkable. The fossils belonged to a species that lived around 275 million years ago and would have been considered a "living fossil" even in its own time. The jaws were also highly unusual, with a twisted shape. Some of the teeth pointed outward and sideways, while rows of smaller teeth lined the inner surfaces. This structure suggests the animal may have been among the earliest of its kind to grind plant material.

Naming a Strange New Species

In a study published in Proceedings of the Royal Society B, researchers formally described the species and named it Tanyka amnicola. The name Tanyka comes from the Indigenous Guaraní language and means "jaw," while amnicola translates to "living by the river."

"Tanyka is from an ancient lineage that we didn't know survived to this time, and it's also just a really strange animal. The jaw has this weird twist that drove us crazy trying to figure it out. We were scratching our heads over this for years, wondering if it was some kind of deformation," says Jason Pardo, the study's lead author, who worked on the project during his post-doctoral fellowship at the Field Museum in Chicago. "But at this point, we've got nine jaws from this animal, and they all have this twist, including the really, really well-preserved ones. So it's not a deformation, it's just the way the animal was made."

An Ancient Branch of Tetrapods

Tanyka belongs to a broad group of vertebrates known as tetrapods, which includes all four-limbed animals with backbones such as reptiles, birds, mammals, and amphibians. The earliest tetrapods, called stem tetrapods, eventually split into two major branches. One group evolved to lay eggs on land, leading to reptiles, birds, and mammals. The other group continued laying eggs in water, giving rise to modern amphibians like frogs and salamanders.

Even after this split, some stem tetrapods continued to exist alongside their more recently evolved relatives. Tanyka was one of these holdovers from an older lineage.

A similar pattern can be seen in mammals. Early mammals laid eggs, while later groups evolved live birth. Most modern mammals reproduce by giving birth, but a few species, such as the platypus, still retain the older egg-laying trait.

"In the sense that Tanyka was a remaining member of the stem tetrapod lineage, even after newer, more modern tetrapods evolved, Tanyka is a little like a platypus. It was a a living fossil in its time," says Pardo, who is now a research associate at the Field Museum while working on a postdoctoral fellowship through the University of Vilnius in Lithuania.

What Did Tanyka Look Like?

Much about Tanyka remains unknown, especially its full body shape. "We found these jaws in isolation, and they're really weird, and they're very distinctive. But until we find one of those jaws attached to a skull or other bones that are definitively associated with the jaw, we can't say for sure that the other bones we find near it belong to Tanyka," says Ken Angielczyk, a curator of paleomammalogy at the Field Museum in Chicago, who served as Pardo's advisor during his post-doctoral fellowship there, and a co-author of the paper.

Based on comparisons with related species, researchers think Tanyka may have resembled a salamander with a slightly longer snout. Its size is uncertain, but estimates suggest it could have reached up to three feet in length. The surrounding rock indicates it likely lived in freshwater environments such as lakes.

A Jaw Built for Grinding Plants

Although the rest of its body is still a mystery, the jaw provides clear clues about how Tanyka fed.

If you run your tongue along your lower teeth, you can feel how they point upward toward the roof of your mouth. In Tanyka, this arrangement was completely di