Leolepis matogrossensis is a newly described 254-million-year-old ray-finned fish from Brazil. It was only about 15 centimetres long, carried tooth-like armour and lived beside a vast Permian lake shortly before the largest mass extinction in Earth’s history.
The fossil is unusually complete for a South American fish of its age. It was found in reddish siltstone from the Corumbataí Formation in Mato Grosso, roughly 50 kilometres from the Araguainha impact crater.
What kind of fish was Leolepis?
Leolepis belonged to Actinopterygii, the ray-finned fishes. That group now includes the overwhelming majority of living bony fishes, from cod and salmon to tuna and seahorses. The new species represents a much earlier branch of that long evolutionary history.
The fish had a relatively small body, tiny teeth and heavy scales. Researchers infer from the teeth that it probably ate small invertebrates and plant material. Unlike the thin, flexible scales of many modern fish, its armour contained enamel and dentine—the same hard tissues found in human teeth.
Why is the fossil important?
Fossils of Permian fishes from Brazil are often represented by isolated teeth, scales or bone fragments. A largely articulated specimen preserves relationships between parts of the skeleton that scattered remains cannot show.
That completeness helps researchers compare body shape, skull structure and scales with related species elsewhere. It also adds a rare South American data point to the history of ray-finned fishes, a group that later became extraordinarily diverse.
The paper describes the specimen as the first articulated Palaeozoic ray-finned fish reported from the state of Mato Grosso. The fossil has been placed in a scientific collection, allowing it to be re-examined as methods and comparisons improve.
Where did Leolepis live?
The surrounding rocks formed in a shallow “megalake” within the Paraná Basin. In the late Permian, today’s continents were joined differently: South America and Africa were part of Gondwana, and the local landscape developed from an inland sea system.
A lake deposit can preserve fine details when a body settles into soft sediment and is buried before currents, scavengers or decay pull it apart. The reddish siltstone around the specimen records the environment as well as the animal.
Was Leolepis killed by an asteroid?
There is no evidence that the individual fish was killed by the impact. The fossil is older than, or close in age to, the event that formed the nearby Araguainha crater. Researchers estimate the fish lived around 254 million years ago, while the impact occurred around 252 million years ago.
The impactor is thought to have been about three kilometres wide. It struck rock in what is now central Brazil and produced South America’s largest confirmed impact structure. The blast deformed rocks in the wider region, making the survival of a relatively complete fossil particularly striking.
Did the Araguainha impact cause the end-Permian extinction?
The end-Permian mass extinction is mainly associated with enormous volcanic eruptions in what are now Siberia and China. Those eruptions released gases that drove severe climate and ocean changes. Estimates suggest roughly 78% of terrestrial species and as many as 95% of marine species disappeared.
The Araguainha impact may have added regional disturbance in the southern hemisphere, but the new fish does not demonstrate that it caused the global extinction. It offers a view of an ecosystem near the boundary, not a single explanation for the crisis.
Why was the fish once mistaken for a frog?
Local observers initially thought the flattened outline represented a frog. That is understandable: compression can distort anatomy, while a complete small vertebrate looks very different from the isolated scales and teeth more familiar at fossil sites. Detailed preparation and comparison revealed the features of a primitive ray-finned fish.
What does the name mean?
The genus name honours geologist Léo Adriano de Oliveira, who found and collected the specimen, combined with the Ancient Greek lepis, meaning scale. The species name refers to Mato Grosso, the Brazilian state where it was discovered.
Could more fish like it be found?
Probably. A well-preserved specimen in a region better known for fragments suggests that suitable deposits have not given up all their fossils. New fieldwork, careful examination of existing collections and comparison with the newly described animal may reveal related species.
Sources
- Natural History Museum: Ancient armoured fish reveals life before the end-Permian extinction, 3 August 2026.
- Journal of South American Earth Sciences: scientific description of Leolepis matogrossensis.
Fossil ages and environmental interpretations are estimates that can be refined by later research.