| Diet | Herbivore |
| Height | 3m |
| Length | 9m |
| Weight | 3 tonnes |
| Environment | Land |
| Era | Cretaceous |
| Period | Late Cretaceous |
| Type | Ornithopod |
| Location | North America |
Stephanosaurus is a problematic ornithopod dinosaur known from fragmentary remains dating to approximately 83.6 million years ago during the Late Cretaceous period. Originally described from fossils found in Alberta, Canada, this creature has one of the most complicated taxonomic histories in palaeontology, having been shuffled between multiple names including Trachodon marginatus and Kritosaurus marginatus.
As an ornithopod belonging to the hadrosaurid family, Stephanosaurus would have been a duck-billed dinosaur adapted for herbivorous feeding. Like other members of this group, it likely possessed the characteristic flattened, duck-like bill used for cropping vegetation, along with batteries of grinding teeth for processing tough plant material. The creature would have measured roughly 9 metres in length and stood about 3 metres tall at the hip.
The fragmentary nature of the fossils means that many details about Stephanosaurus remain uncertain. Some material once attributed to this genus has since been reassigned to other dinosaurs, including the crested hadrosaurid Lambeosaurus. This has led many palaeontologists to consider Stephanosaurus a dubious name, as the original fossil material may not be sufficient to distinguish it as a separate genus.
Despite these taxonomic uncertainties, the fossils attributed to Stephanosaurus provide valuable insights into the diversity of duck-billed dinosaurs that flourished in Late Cretaceous North America, when these ornithopods were among the most successful herbivorous dinosaurs of their time.
Due to the fragmentary nature of the fossils and taxonomic confusion, specific distinguishing features of Stephanosaurus cannot be reliably identified. The original remains consisted mainly of incomplete skull and jaw fragments.
Like other hadrosaurids, Stephanosaurus would likely have lived in herds and been capable of both bipedal and quadrupedal locomotion. It probably spent much of its time foraging for vegetation in the coastal plains and forests of Late Cretaceous North America.
Stephanosaurus was first described by Lawrence Lambe in 1914. The original fossils were discovered at Alberta, Canada.
