Platysomus parvulus, a species of ray-finned fish that lived 310 million years ago, had a unique way of eating never seen in ray-finned fish from that time — a ‘tongue bite’, using a special set of teeth on the floor and roof of the mouth to help it crush and chew tough food like shells or insects.
An artist’s impression of Platysomus parvulus. Image credit: Joschua Knüppe.
Platysomus parvulus lived at the beginning of the Pennsylvanian subperiod of the Carboniferous period, 310 million years ago, at a time when a group of fish called ray-finned fish were exploring new ways to make a living.
The species had a plate of teeth suspended by a cradle of jointed bones that also supported the gills it used to breathe.
The plate of teeth, situated on the floor of the mouth like a tongue, was in direct opposition to a plate of teeth above it, and the fish used the plates to crush and grind food.
As it turns out, this ancient fish was the first to evolve this feeding structure called a tongue bite.
Until now, the oldest known fish with such a dental arrangement lived about 150 million years later.
“One of the most powerful things we have for understanding evolution is adaptation,” said Dr. Matt Friedman, a paleontologist at the University of Michigan’s Museum of Paleontology and the Natural History Museum, London.
“We can see that different kinds of creatures can adjust to similar kinds of demands in different ways.”
“But in this case, this is cool because it’s showing us a convergent adaptation.”
“This extinct group of fishes discovered this trick, and actually, it turns out that many different groups of fishes figured out this trick at later times.”
“After multiple times, that tells us a little bit about what the constraints on evolutionary change might be, or if there are pathways that are easier to evolve along than others.”
The Platysomus parvulus fossil was discovered in Carboniferous rock formations in the UK county of Staffordshire.
Dr. Friedman and his colleagues used high-resolution CT scanning to reconstruct the internal anatomy of the specimen.
They were surprised to see a series of well-developed tooth plates inside the mouth of the animal.
“They’re deep-bodied animals. They look a little like an angel fish,” Dr. Friedman said.
“But not only were they flat in life, they’re typically squished even more flat as fossils.”
“So although whole fossil fish skeletons are common, it’s often hard to extract details of the internal skeleton. Fossils probably preserve those parts, but they’re deadly flat.”
“Our discovery helps us understand how fish evolved after the end-Devonian mass extinction, which wiped out many species,” said Professor Sam Giles, a paleontologist at the University of Birmingham.
“After this extinction event, fish started to change and develop new body shapes and ways of feeding.”
“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.”
“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,” said Dr. Matthew Kolmann, a paleontologist at the University of Louisville.
“Platysomus parvulus is like a missing link between simple jawed fish and more advanced tongue-biters.”
The team’s results were published on September 3, 2025 in the journal Biology Letters.
_____
Sam Giles et al. 2025. Tongue-bite apparatus highlights functional innovation in a 310-million-year-old ray-finned fish. Biol. Lett 21 (9): 20250270; doi: 10.1098/rsbl.2025.0270
