Fossil reveals earliest tongue bite in ancient fish

Fossils sometimes rewrite the rules of history. In Staffordshire’s Carboniferous rocks, scientists discovered a 310-million-year-old ray-finned fish that carried extra teeth deep inside its mouth.

The fossil, Platysomus parvulus, reveals one of the earliest examples of a tongue bite mechanism – a feeding innovation that allowed fish to process prey in entirely new ways.

Platysomus parvulus used a specialized set of teeth on the floor and roof of its mouth to crush hard prey such as shells and insects.

Unlike most fish that rely on jaws, this ancient species supplemented its bite with opposing tooth plates, creating a powerful second chewing surface.

Today, similar mechanisms exist in groups like bonefish and trout, but Platysomus pushes the origin of this strategy back over 150 million years, showing early experimentation in feeding methods that shaped evolutionary success.

Evolution of the bite mechanism

The fossil shows a lower tooth plate made of multiple pieces opposing a narrow upper plate. Both carried a single layer of pointed teeth, suggesting a primitive stage in tongue bite evolution.

These early arrangements were less efficient than the later crushing plates but reveal the first stages of experimentation with prey processing.

By relying on pointed cusps arranged in rows, Platysomus could grip and pierce softer shells or insect cuticles, though it lacked the durability of thicker, layered structures.

This demonstrates how evolutionary progress often began with modest modifications that opened the door to more powerful innovations.

Steps of feeding system specialization

Later fish such as bobasatraniids developed consolidated plates with multiple tooth generations, forming advanced crushing tools ideal for hard food.

Their dense, layered arrangements allowed them to grind down even the toughest prey, including mollusks and heavily armored crustaceans.

The stepwise assembly highlights how feeding systems gradually grew more specialized, shifting from simple gripping mechanisms to elaborate crushing complexes.

The progression also shows that functional changes in the mouth and gill skeleton did not appear all at once but emerged through a sequence of refinements, each offering a survival advantage in ecosystems filled with competition and changing food resources.

Understanding how fish evolved

Study lead author Professor Sam Giles is a professor of palaeobiology the University of Birmingham.

“Our discovery helps us understand how fish evolved after the End-Devonian Mass Extinction, which wiped out many species. After this extinction event, fish started to change and develop new body shapes and ways of feeding,” noted Professor Giles.

“Tongue bites have evolved many times in different fish groups – including in modern ones such as trout and bonefish, demonstrating that it is a useful tool that helps fish eat a wider variety of food and survive in different environments.”

Unusual traits of Platysomus parvulus

Unlike later species that abandoned their jaws, Platysomus still used them alongside its tongue bite. Researchers suggest this dual system was an evolutionary bridge between simple jawed fish and later specialists that relied entirely on the tongue bite.

The preserved skull also shows unusual traits, such as an enclosed spiracular canal, linking Platysomus to bobasatraniids while keeping its own primitive features.

“Later fish, like the Bobasatrania group, had more advanced tongue bites and did not use their jaws at all, relying on their tongue bite to crush hard food,” noted study co-author Dr Matthew Kolmann from the University of Louisville.

“Platysomus parvulus is like a missing link between simple jawed fish and more advanced tongue-biters.”

Fish feeding strategies

The Carboniferous period marked a burst of anatomical experimentation among ray-finned fishes. Platysomus arrived after other lineages had already evolved traits for eating hard prey, including beak-like jaws and dense dental plates.

Its delayed but distinct tongue bite adds to the evidence that feeding strategies diversified over millions of years rather than in a single burst.

“Tongue bites are just one of many feeding innovations that emerged during this time. This fish represents a key evolutionary step and helps us understand how ancient ecosystems functioned and how modern fish lineages came to be,” said co-author Professor Matt Friedman from the University of Michigan.

Tongue bite evolution in fish

The study supports the long-fuse model of diversification, where changes unfolded gradually after the End-Devonian extinction. Platysomus parvulus captures an early experiment in prey processing, one that set the stage for later groups.

Its mix of primitive jaws and developing tongue bite illustrates how survival often depended on combining old tools with new innovations, highlighting that evolutionary progress was not sudden but built through steady adaptations that prepared species for shifting ecosystems and long-term survival challenges.

This discovery also suggests that ancient fishes were experimenting with different feeding strategies far earlier than once believed, proving that the ecological pressures of the time sparked a wave of gradual but transformative change.

By linking primitive traits with emerging specializations, Platysomus parvulus shows how evolution often works as a stepwise process, bridging the gap between survival after mass extinction and the flourishing of complex ecosystems millions of years later.

The study is published in the journal Biology Letters and bioRxiv..

Image Credit: Joschua Knüppe

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