On a balmy morning in mid-August, Timothy Linder lifts the latch on a refrigerated trailer and opens both doors wide, releasing a wave of cold air heavy with the stink of fish guts. “I don’t even smell it anymore,” says Linder, a wildlife biologist with United States Department of Agriculture’s Wildlife Services. After hoisting himself…

Rodrigo 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…