Calvarius

Calvarius (meaning "suffering") is a genus of styracosternan ornithopod from the Late Cretaceous Talarn Formation of Spain. The genus contains a single species, Calvarius rapidus, known from a single metatarsal.

Discovery and naming
The holotype specimen, MCD-8734, is a single fourth metatarsal discovered in 2019 at the Pallars Jussà locality of the Talarn Formation of the Tremp Group, located in Catalonia, Spain.

It was named as the holotype of a new genus of styracosternan dinosaur in 2023 by Albert Prieto-Márquez and Albert Sellés. The genus name, "Calvarius", is Latin for "suffering" (cf. Calvary), and refers to the type locality, Serrat del Calvari, as well as the genus' proximity to the K-Pg extinction event. The specific name, "rapidus", means "rapid", and refers to its likely cursorial habits.

Classification
Calvarius was in 2023 assigned by its describers to the Styracosterna. A more precise position could not be determined because a phylogenetic analysis only places it in a large polytomy of styracosternans.

Paleobiology
The highly modified metatarsal of Calvarius has no known equivalents among other ornithopods. It was convergently more similar to those of more basal ornithischians such as Hypsilophodon and Dysalotosaurus than to other styracosternans, and may have filled their niche on its island habitat.

The Talarn Formation also produced the remains of the troodontid Tamarro insperatus.