Ancient ‘Living Fossil’ Tanyka Had Sideways Teeth and a Twisted Jaw

Lead: Paleontologists have named a bizarre 275-million-year-old animal, Tanyka amnicola, from what is now northeastern Brazil after nine lower jaw fossils were recovered from a dry riverbed. The jaws, each about 15 cm (6 in) long, show a pronounced twist that directed the teeth outward, an arrangement not seen in virtually any other tetrapod. The fossils were described in Proceedings of the Royal Society B on March 4, 2026, and the authors interpret Tanyka as an aquatic stem tetrapod with an unusual grinding surface of denticles that suggests a distinctive feeding strategy. The team says Tanyka behaved like a “living fossil” in its ecosystem, representing a surprisingly archaic lineage persisting deep into the early Permian.

Key Takeaways

• New species: Tanyka amnicola is described from nine fossil lower jaws recovered in northeastern Brazil and formally published on March 4, 2026, in Proceedings of the Royal Society B.
• Age and setting: The specimens date to about 275 million years ago (early Permian) and were found in sedimentary rocks interpreted as lake or fluvial deposits, consistent with aquatic habits.
• Jaw morphology: Each lower jaw measures roughly 15 cm (6 in) and shows a consistent torsion that turns marginal teeth to face laterally rather than upwards.
• Feeding features: The inner (lingual) surface bears dense denticles forming a grinding surface, implying processing of small invertebrates or possibly some plant matter.
• Size estimate: Based on relatives, the animal may have reached about 91 cm (3 ft) in total length, though a complete skeleton is lacking.
• Paleobiogeography: The find expands knowledge of early Permian Gondwanan vertebrate communities and indicates an archaic stem tetrapod lineage survived longer than previously known.

Background

The stem tetrapods are a paraphyletic assemblage of early four-limbed vertebrates that branched off before the crown group giving rise to modern amphibians, reptiles, birds and mammals. In the Devonian and Carboniferous, many stem tetrapods experimented with varied body plans and ecologies; by the early Permian, more derived tetrapod groups dominated many terrestrial and freshwater niches. Discoveries of archaic lineages surviving alongside more modern tetrapods are rare but important because they reveal how ecological communities retained deep evolutionary relics.

Brazil in the early Permian was part of Gondwana, a supercontinent that hosted distinct vertebrate faunas compared with contemporaneous Laurasian assemblages. Sediments preserving freshwater habitats in northeastern Brazil have yielded a growing record of early Permian amphibians and reptiles; however, stem tetrapod remains from this interval are relatively uncommon. The new Tanyka material therefore fills a geographic and temporal gap, offering direct evidence of how Gondwanan aquatic communities were structured about 275 million years ago.

Main Event

Researchers identified the new species from nine isolated lower jaws recovered from a single dry riverbed exposure. Each specimen is approximately 15 cm long and shows a reproducible pattern of torsion: the posterior portion of the bone is rotated so that the tooth row faces outward. The team initially considered post-mortem distortion but ruled it out because multiple well-preserved jaws display the same morphology, showing the twist is biological rather than taphonomic.

Detailed description of the lingual surface revealed a dense field of small, tooth-like denticles that would form a grinding surface opposite the marginal dentition. This combination—laterally oriented marginal teeth and a lingual grinding surface—suggests a feeding method unlike that inferred for most other stem tetrapods, which are reconstructed largely as carnivores using upward-projecting teeth to seize prey.

Given the jaw size and comparisons with related taxa, the authors estimate a total body length of about 91 cm (3 ft), roughly salamander-like but with a proportionally longer snout. The sedimentology of the deposit and associated fauna indicate lake or slow-channel freshwater conditions, supporting an interpretation of predominantly aquatic habits. Because no skull or postcranial remains have yet been reported, reconstructions of complete body shape and locomotion remain provisional and based on close relatives.

Analysis & Implications

Tanyka’s jaw anatomy reframes assumptions about ecological breadth among stem tetrapods late into the early Permian. The lateral orientation of marginal teeth would change how the animal captured or processed food: rather than piercing prey with vertically oriented teeth, Tanyka may have used lateral shearing combined with an internal grinding surface to process small shelled invertebrates or detrital/plant material. If plant or omnivorous feeding is confirmed, it would be one of the first well-supported examples of non-carnivory in a stem tetrapod lineage.

Ecologically, the presence of such a specialized feeder implies niche partitioning in early Permian freshwater ecosystems. Contemporary vertebrate assemblages included fish, temnospondyl amphibians, early amniotes and other aquatic tetrapods; Tanyka adds a morphologically distinct guild that likely reduced direct competition for the same prey. The discovery suggests that Gondwanan lakes hosted more complex trophic webs than previously appreciated, with specialized processors coexisting with active predators.

From an evolutionary perspective, the persistence of an archaic stem lineage into the early Permian qualifies Tanyka as a contemporaneous “living fossil”—a surviving member of a deep branch that otherwise is better known from earlier periods. That persistence underscores uneven evolutionary turnover: while many novel tetrapod clades radiated in the Permian, some ancient lineages retained specialized morphologies and survived in stable ecological refugia. Tanyka therefore provides a data point for models of survivorship and ecological conservatism across major faunal transitions.

Comparison & Data

The table summarizes the key morphological differences between Tanyka and a generalized stem tetrapod condition. While jaw length alone does not determine body mass or ecology, the presence or absence of a jaw twist and of lingual denticle fields is diagnostic for feeding strategy. Without additional skeletal elements, quantitative comparisons of bite force or gape remain speculative, but the consistent presence of twisted jaws across nine specimens supports a functional interpretation rather than an aberrant pathology.

Reactions & Quotes

Lead author Jason Pardo (Field Museum) emphasized the repeated pattern across specimens and the team’s efforts to rule out deformation.

“The jaw has this weird twist that drove us crazy trying to figure it out… we’ve got nine jaws from this animal, and they all have this twist.”

Jason Pardo, Field Museum (research associate)

Co-author Ken Angielczyk highlighted the broader ecological implications of finding such an archaic lineage in Gondwana’s freshwater systems.

“Tanyka is telling us about how this community actually worked, how it was structured, and who was eating what.”

Ken Angielczyk, Field Museum (curator of paleomammalogy)

Unconfirmed

• The hypothesis that Tanyka consumed significant plant material remains tentative; tooth wear and gut contents are not preserved to confirm herbivory.
• Estimated total body length (~91 cm) is provisional because no complete skeleton has been recovered; proportions are inferred from related taxa.
• The precise mode of life (e.g., bottom-walking, active swimming) cannot be resolved without postcranial remains.

Bottom Line

Tanyka amnicola represents a striking example of morphological experimentation among early tetrapods and shows that some archaic lineages persisted well into the early Permian in Gondwana. Its twisted lower jaws and lingual denticle field point to a feeding strategy unlike that of most contemporaneous stem tetrapods, implying specialized ecological roles in freshwater systems roughly 275 million years ago.

Future discoveries of skull and postcranial material, plus micro-wear or isotopic analyses, will be critical to test dietary hypotheses and to place Tanyka more precisely within tetrapod evolutionary history. For now, the repeated, consistent anatomy preserved in nine jaws makes a strong case that this was a real, functional adaptation rather than fossil damage—expanding our view of how diverse early Permian freshwater life could be.

Sources

• Pardo et al., Proceedings of the Royal Society B (2026) – academic journal, original peer-reviewed description
• LiveScience article – news coverage summarizing the study and quoting authors