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.
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."
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.
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.
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 different. Its lower jaw was twisted so that the teeth pointed outward to the sides instead of upward. At the same time, the inner surface of the jaw, which faces the tongue in humans, was oriented upward.
This inner surface was covered with small teeth called denticles, forming a rough grinding area similar to a cheese grater. Scientists believe the upper jaw likely had a similar structure.
"We expect the denticles on the lower jaw were rubbing up against similar teeth on the upper side of the mouth. The teeth would have been rasping against each other, in a way that's going to create a relatively unique way of feeding," says Pardo.
This type of tooth-to-tooth grinding is typically associated with animals that process plant material. "Based on its teeth, we think that Tanyka was a herbivore, and that it ate plants at least some of the time," says Juan Carlos Cisneros, an author of the paper at the Federal University of Piauí (UFPI) in Brazil. Researchers note that this is surprising, since most stem tetrapods are thought to have been carnivorous.
The discovery of Tanyka helps scientists better understand life during the early Permian Period. Around 275 million years ago, the region that is now Brazil was part of Gondwana, a vast supercontinent that included South America, Africa, Australia, and Antarctica. Fossils from this time and place are relatively rare compared to those from regions in the Global North.
"The Pedra de Fogo Formation in Brazil is one of the only windows we have into Gondwana's animals during the early Permian Period of Earth history, and Tanyka is telling us about how this community actually worked, how it was structured, and who was eating what," says Angielczyk.
The study was co-authored by Jason Pardo (Field Museum, University of Vilnius), Claudia Marsicano (Universidad de Buenos Aires, CONICET), Roger Smith (Iziko South African Museum, University of the Witwatersrand Johannesburg), Ken Angielczyk (Field Museum), Jörg Fröbisch (Museum fur Naturkunde -- Leibniz-Institut fur Evolutions- und Biodiversitatsforschung), Christian Kammerer (North Carolina Museum of Natural Sciences), and Martha Richter (Natural History Museum, London).
