An almost complete fossil fish, about 15 cm long, has been found in Upper Permian rocks in Brazil. Its state of preservation is rare for this period in South America. It provides a direct glimpse of animals living in a huge lake shortly before the greatest known extinction.
The specimen belongs to a new species named Leolepis matogrossensis. It is an actinopterygian, the vast group of ray-finned fishes that today includes the vast majority of bony fishes. The fossil was discovered in the state of Mato Grosso and kept in the collections of the local federal university.
Its streamlined body bears at least 50 longitudinal rows of fine ganoid scales. These scales have a hard, shiny outer layer, common in several ancient fishes. The skull, jaw and many bones are sufficiently preserved to allow a detailed comparison with other species of the same age.
The rock surrounding the animal is a reddish siltite, made of particles finer than sand. According to the study, this deposit belonged to a shallow lake occupying part of the Paraná Basin. This continental environment existed during the latest episodes of the Permian, before the biological crisis of the Permian-Triassic boundary.
The discovery is all the more interesting because articulated Paleozoic fishes are rare in Brazil. Researchers much more often have scales, teeth or isolated bone fragments. An almost complete skeleton here makes it possible to observe at the same time the body shape, the organization of the skull and the arrangement of the scales.
The site is also about 50 km from the Araguainha dome, the largest known impact crater in South America. It is dated at 251.5 ± 2.9 million years. The authors indicate that the layers containing the fish could be close in age to this event, without demonstrating that the impact killed this particular animal.
This caution is important. The great extinction at the end of the Permian, about 252 million years ago, is mainly associated with enormous volcanic episodes and their climatic effects. The Araguainha impact remains studied as a regional event that may have added disturbances to a world already under strong environmental pressures.
Leolepis matogrossensis is currently known only from this single individual. New fossils from the same layers would reveal which other fishes shared this lake and whether this species was common. They would also help to refine the age of the deposits relative to the Araguainha crater and the end-Permian crisis.