You’re unlikely to see any of these bad boys walking—or scurrying—around, since the species, known as Pegomastax africanus, vanished 150 million years ago. But it was only in 2012 that scientists first began studying its fossilized remains and identified it as a whole new type of dinosaur. About the size of a cat, it is a vivid and decidedly unlovely illustration of how evolution can sometimes cobble together critters from what amounts to off-the-shelf parts. It’s the same kind of hobby-shop design that gives us the duckbilled, beaver-tailed, egg-laying platypus. But while the platypus has its own homely cuteness, the Pegomastax can claim no such charms. Even its discoverer, paleontologist Paul Sereno of the University of Chicago admits, “I would suggest, modestly, that Pegomastax would make a good Halloween mask.”