Outwardly, viriosaurs closely resemble such Late Cretaceous basal neornithischians as Thescelosaurus, with small, birdlike heads atop long necks, long tails, and (generally) a bipedal stance. This resemblance to familiar ornithopods and certain other neornithischians is quite misleading, however. In their 66 million years of evolution, the viriosaurs' internal anatomy has gone through some changes.