Ancient Jaw Reveals Bizarre Feeding Style of Permian ‘River Dweller’

A team of paleontologists working in a dry riverbed in northeastern Brazil has unearthed a remarkable fossil: a lower jawbone roughly six inches long, distinguished by a pronounced twist. The discovery, detailed in a new paper published in Proceedings of the Royal Society B, isn’t just about a single bone, but a collection of nine similar mandibles, all exhibiting the same unusual curvature. This consistent anatomical feature suggests the twist wasn’t a result of damage, but a fundamental characteristic of a previously unknown species of early tetrapod.

Researchers have named the animal Tanyka amnicola, combining tañykã, the Guaraní word for “jaw,” with a Latin term meaning “river dweller.” Living approximately 275 million years ago during the Early Permian period, Tanyka inhabited a Gondwanan landscape—a supercontinent that once encompassed modern-day South America, Africa, India, Australia, and Antarctica. What makes this find particularly significant is that Tanyka represents a lineage of stem tetrapods that had largely disappeared elsewhere, persisting alongside the ancestors of modern amphibians, reptiles, birds, and mammals. As the Field Museum notes, it was a “living fossil” for its time.

The Sideways Chew

The most striking aspect of Tanyka’s jaw is its unusual orientation. Unlike most tetrapods where lower jaw teeth point upwards, Tanyka’s mandible is twisted, causing the chewing surface to face outwards rather than directly towards the palate. This unique structure is coupled with a dense arrangement of denticles—small, tooth-like bumps—on the coronoid bones and the front of the jaw, forming a broad, specialized chewing pad. The researchers describe this as a “remarkable battery” of enlarged denticles showing wear consistent with repeated use.

This arrangement suggests a unique chewing motion, reminiscent of the modern aquatic salamander Siren lacertina, which employs three-dimensional jaw movements to rake food against palatal teeth. While the team hasn’t yet discovered corresponding upper jaw or skull bones, they hypothesize that the twisted jaw facilitated a rasping motion across the palate, utilizing the denticle field as the primary contact point for processing food. The study proposes that Tanyka likely fed on small invertebrates or plant material.

A Gondwanan Holdout

Beyond the peculiar jaw structure, Tanyka’s phylogenetic placement is reshaping our understanding of early tetrapod evolution. Analyses place Tanyka as a stem tetrapod with affinities to baphetid-grade tetrapods—a group primarily known from the northern supercontinent of Laurussia. This is significant because the late Carboniferous period is often viewed as a turning point, where older stem-tetrapod lineages declined as more modern amphibian and amniote groups rose to prominence.

Tanyka challenges this narrative, particularly within the Gondwanan context. The discovery builds on previous findings, such as Gaiasia jennyae, a giant stem tetrapod from Namibia described in 2024, which also exhibits characteristics of earlier northern lineages. These findings suggest that the turnover of stem tetrapods wasn’t a uniform global event, and that Gondwana may have served as a refuge for these older lineages for a longer period than previously thought. The Pedra de Fogo Formation, where Tanyka was discovered, is proving to be a crucial window into this Gondwanan ecosystem.

The researchers emphasize that the Pedra de Fogo Formation represents the most extensive Early Permian tetrapod assemblage yet discovered in Gondwana. This rich fossil record is providing a more nuanced picture of tetrapod evolution during a period of significant environmental change.

Implications for Understanding Tetrapod Evolution

The discovery of Tanyka has implications for how scientists understand the broader patterns of tetrapod evolution. The prevailing view had been that stem-tetrapods were quickly replaced by temnospondyl amphibians and amniotes following the Carboniferous rainforest collapse. However, Tanyka, along with other late-surviving tetrapods like Gaiasia, demonstrates that this replacement was a more complex process. The survival of these lineages in Gondwana suggests that regional environmental conditions and ecological opportunities played a significant role in shaping the trajectory of tetrapod evolution.

Jason Pardo, the study’s lead author, highlighted the initial confusion surrounding the jaw’s twist. “We were scratching our heads over this for years, wondering if it was some kind of deformation,” he said in a statement. “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.”

What Remains to be Discovered

Currently, Tanyka is largely defined by its jaw. The holotype specimen measures 17.2 centimeters (about 6.8 inches), with one individual being approximately 25% larger. However, the lack of associated skeletal remains limits a complete understanding of the animal’s overall morphology and lifestyle. Researchers estimate that, based on comparisons with related species, Tanyka may have resembled a salamander with a slightly elongated snout. Further fieldwork in the Pedra de Fogo Formation is planned, with the hope of uncovering additional skeletal elements that will shed more light on this enigmatic creature. The team is also continuing to analyze the existing jaw specimens, seeking further clues about Tanyka’s feeding habits and evolutionary relationships.

The ongoing research promises to refine our understanding of early tetrapod diversity and the complex interplay between environmental change, biogeography, and evolutionary adaptation. The story of Tanyka amnicola is a reminder that the fossil record continues to yield surprising discoveries, challenging long-held assumptions and revealing the intricate history of life on Earth.