Affixes

The strict difference between these endings is that ‑saurus indicates a systematic genus name, while ‑saur appears in Anglicized common names. For example, a tyrannosaur (Greek turannos, tyrant), a carnivorous dinosaur of the late Cretaceous period, is placed in the genus Tyrannosaurus (the species best known is actually Tyrannosaurus rex). However, it is common for the genus names to be used as common names, but with lower-case initial letter—for example, brontosaurus (Greek brontē, thunder) is more common than brontosaur.

The first such formation was dinosaur (Greek deinos, terrible) as a general name for the group. Many others exist, such as ichthyosaur (Greek ikhthus, fish), mosasaur (Latin Mosa, for the River Meuse near which it was discovered), plesiosaur (Greek plēsios, near), and stegosaur (Greek stegē, covering, referring to its bony back plates). All these, except dinosaur itself, have associated genus names in ‑saurus (Ichthyosaurus, Stegosaurus).