SÃO PAULO, BrazilRodrigo Müller was working a block of rock and dirt at the base of Agudo Hill, an hour from Porto Alegre, when he first saw an unusual set of osteoderms, bony deposits that form plates on the skin of a reptile or amphibian.

“It was a surprise, because we had never seen anything like this in Brazil before,” Müller, a paleontologist at the Federal University of Santa Maria, says of what was otherwise an ordinary visit to the Janner dig site, once home to some of the earliest dinosaurs to roam Earth.

As he continued his delicate work, he brushed dirt from an intact cranium and several other fossilized bones. Together, the collection formed a well-preserved and almost complete skeleton of