Near the end of the Permian, an asteroid hit central Brazil and folded the rock layers around the crater it left. Farther out, one of those layers held a small armored fish fossil, and there the rock was never disturbed at all.

Léo Adriano de Oliveira, a geologist who worked on the Permian rocks of the region, found the fossil in 2005. It came out of a ravine north of the MT-100 highway near Alto Garças, in Mato Grosso state. He deposited it at the Federal University of Mato Grosso in Cuiabá, where it is cataloged as UFMT-353.

The rocks in that ravine formed on the floor of the lake, and geologists working the same beds have found freshwater clams, tiny shelled crustaceans and scraps of other fish. A 2008 paper pictured the fossil, but no one described it formally until now. Gallo’s team built Leolepis out of Oliveira’s first name and lepis, Ancient Greek for scale. The species name comes from the state where he found it.

The animal was about 6 inches (150 mm) long, roughly the length of a dollar bill. This one fossil is all anyone has. It’s preserved in two matching slabs of reddish siltstone. Leolepis was narrow at both ends and deepest through the middle. Roughly 50 rows of scales ran from head to tail, and at least 15 rows were counted around the body. Each scale carried a coating of a hard material called ganoine. Every scale is diamond-shaped and ridged. A single one can bear 8 to 20 parallel ridges, depending on where it was on the animal, and the rear edge of each flank scale is serrated.

Toward the tail, the ridges get shallower and smoother, and on some scales they wander or fan out. The head takes up about a quarter of the total length. Small cone-shaped teeth line the edge of the upper jaw, and the lower jaw appears to carry them too.  Leolepis belongs to the ray-finned fishes, the group whose fins are held open by thin bony rods. They account for 96% of living fish species, more than 30,000 of them.

Fewer than 20 early members have ever been described from rocks this old in South America. Gallo’s team compared 37 species across 92 anatomical features, most of them details of skull bones, and ran the comparison through a program that builds family trees. Leolepis came out closest to Paramblypterus, a genus known from older lake beds in Europe.

Until now, that family had only been found there. Leolepis is its first member from Gondwana, the southern supercontinent, and it lived much later than the European ones. The family tree isn’t settled, though. Gallo’s team also scored how strongly each branch is supported, and most of the scores were under 50%.