Stellasaurus ancellae

Stellasaurus (meaning “star lizard”; both in reference to the shape of its head ornamentation and as an homage to the song “Starman” by David Bowie) is a genus of centrosaurine ceratopsid dinosaur that lived in Montana during the Late Cretaceous. The type and only species is Stellasaurus ancellae. Its remains have been found in the late Campanian-aged Two Medicine Formation, the same geological unit which its relatives Rubeosaurus (now seen as a synonym of Styracosaurus), Einiosaurus, and Achelousaurus were discovered in.

Originally proposed as a distinct taxon in 1992, the specimens were later assigned to Rubeosaurus. In 2020, a re-evaluation questioned the referral and named it as a distinct species in a new genus. The describers saw it as a transitional form between Styracosaurus albertensis and Einiosaurus on a single evolutionary line that led to Achelousaurus and Pachyrhinosaurus.