A new genus and species of archaic stem tetrapod from the Permian period has been identified from fossil jawbones found in Brazil. Named Tanyka amnicola, this strange amphibian relative had sideways-facing teeth and a rasp-like grinding surface, suggesting that some ancient four-limbed vertebrates began experimenting with plant-eating far earlier than paleontologists expected.
Tanyka amnicola. Image credit: Vitor Silva.
Tanyka amnicola lived on the southern supercontinent of Gondwana during the Early Permian epoch, around 275 million years ago.
“Tanyka amnicola is from an ancient lineage that we didn’t know survived to this time, and it’s also just a really strange animal,” said Dr. Jason Pardo, a paleontologist at the Field Museum.
“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.”
“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.”
Tanyka amnicola was a stem tetrapod, the oldest tetrapod lineage that eventually split into two groups — ones that laid eggs outside of water, and ones that laid their eggs in the water.
Today’s reptiles, birds, and mammals are all descendants of the branch that laid watertight eggs on land; modern amphibians like frogs and salamanders are the relatives of the tetrapods whose eggs needed to remain moist.
But even after the tetrapod family split into these new groups, some of the stem tetrapods remained. Tanyka amnicola was one of them.
“In the sense that Tanyka amnicola was a remaining member of the stem tetrapod lineage, even after newer, more modern tetrapods evolved, Tanyka amnicola is a little like a platypus. It was a living fossil in its time,” Dr. Pardo said.
There’s a lot about Tanyka amnicola that remains a mystery: namely, its body.
“We found these jaws in isolation, and they’re really weird, and they’re very distinctive,” said Dr. Ken Angielczyk, a curator of paleomammalogy at the Field Museum.
“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 amnicola.”
But Tanyka amnicola’s jawbone alone was enough to show the researchers what an unusual animal it was.
“Run your tongue over the teeth on your lower jaw. Feel how the tops of your teeth are facing up, towards the roof of your mouth?” they said.
“In Tanyka amnicola, the lower jaw was twisted, so that instead of facing up, the teeth pointed out to the sides.”
“Meanwhile, the part of its jawbone that, in us, faces the tongue, in Tanyka amnicola is facing up towards the roof of its mouth.”
“This surface of Tanyka amnicola’s jawbone is covered in a series of smaller teeth called denticles, which form a grinding surface sort of like a cheese grater.”
The scientists have yet to find the bones that would make up Tanyka amnicola’s upper jaw, but they imagine its top teeth and denticles were oriented similarly to the ones on the lower jaw.
“We expect the denticles on the lower jaw were rubbing up against similar teeth on the upper side of the mouth,” Dr. Pardo said.
“The teeth would have been rasping against each other, in a way that’s going to create a relatively unique way of feeding.”
In general, teeth that are able to grind against each other are used for crushing up plant material.
“Based on its teeth, we think that Tanyka amnicola was a herbivore, and that it ate plants at least some of the time,” said Dr. Juan Carlos Cisneros, a researcher at the Federal University of Piauí.
“It’s surprising that a stem tetrapod like Tanyka amnicola would have evolved to eat plants, since most of its fellow stem tetrapods only ate meat.”
The findings appear in the journal Proceedings of the Royal Society B.
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Jason D. Pardo et al. 2026. An aberrant stem tetrapod from the Early Permian of Brazil. Proc Biol Sci 293 (2066): 20252106; doi: 10.1098/rspb.2025.2106
