Mesozoic mammals were fascinating little beasts. They burrowed, climbed, glided, and swam through the Age of Dinosaurs, not as underdogs waiting for their moment to be free of the great reptiles, but as varied, successful creatures. And they keep getting stranger. Mammals previously known only from their dentition are starting to come into view thanks to the discovery of skulls and skeletons. The latest to debut is Vintana sertichi – what looks like a Mesozoic muskrat with some evolutionary tales to tell.

In the big picture of mammalian evolution, Stony Brook University paleontologist David Krause and colleagues write in their description, Vintana was a gondwanathere. That name comes from the lost, southern supercontinent Gondwana that included South America,