A new species of armoured fish, dating back 254 million years, has been discovered in Brazil

The new species has been named Leolepis matogrossensis. The fossil was found in the state of Mato Grosso, not far from the Araguaína crater — the largest known impact structure in South America.

Initially, local residents mistook the flat imprint of the animal for the remains of a frog. Subsequent research revealed that the scientists were looking at an ancient ray-finned fish – a member of the evolutionary group to which the vast majority of modern bony fish belong, including tuna, salmon and cod.

Such a find is particularly valuable for the Permian deposits of Brazil. Usually, ancient fish from this region are known only from individual teeth, scales and bone fragments. The skeleton of Leolepis matogrossensis, by contrast, was sufficiently well-preserved for researchers to describe a previously unknown species and study the features of its anatomy.

Details

The animal was about 15 centimetres long. Unlike most modern ray-finned fish, which have thin and flexible scales, the body of Leolepis was protected by hard armour.

The scales consisted of dentine and an enamel-like substance — durable materials that also play a part in the formation of vertebrate teeth. This protection made the fish’s body resemble a small armour.

Its small teeth suggest that the animal fed on small invertebrates and, possibly, plant matter. However, this is a preliminary reconstruction: no stomach contents or other direct evidence of its diet have been preserved in the fossil.

Around 254 million years ago, what are now South America and Africa formed part of the supercontinent Gondwana. At the site of the discovery, there was a vast inland body of water formed by a receding sea.

Leolepis matogrossensis was part of this Late Permian ecosystem. Its fossil reveals which animals inhabited the water bodies of the Southern Hemisphere shortly before the global biological catastrophe that brought the Permian period to an end.

The Permian–Triassic extinction event occurred approximately 252 million years ago and was the most extensive of all known mass extinctions. The main cause is believed to have been prolonged volcanic eruptions, which triggered drastic changes in climate and the chemical composition of the oceans.

The fish was discovered in the vicinity of the Araguaína crater, formed by the impact of a celestial body approximately three kilometres in diameter. The impact occurred at roughly the same geological time as the Permian–Triassic extinction event.

Scientists suggest that the impact may have had a further effect on ecosystems in the Southern Hemisphere. However, the new study does not prove that it was the impact of this particular object that caused the mass extinction or directly destroyed the body of water in which the ancient fish lived.

Nor can it be claimed that Leolepis survived the impact. The fossil predates the estimated time of the crater’s formation and is more likely to reflect the state of the ecosystem prior to the catastrophic events of the late Permian period.

Why this is important

Ray-finned fish are today the most diverse group of vertebrates. However, the early stages of their evolution in South America are far less well understood than finds from Europe and North America.

The almost complete specimen of Leolepis matogrossensis allows researchers to study not only individual teeth or scales, but also the overall body shape, fin arrangement and features of the cutaneous covering. The find adds to the sparse record of Palaeozoic ray-finned fish in South America and suggests that other unknown species may still exist in the region.

Source

Study: Valéria Gallo et al. Leolepis matogrossensis gen. et sp. nov., an Upper Permian actinopterygian fish from the Corumbataí Formation, in the vicinity of the Araguainha impact crater, State of Mato Grosso, mid-western Brazil.

Journal: Journal of South American Earth Sciences, 2026.