Calvarius
{{Short description|Genus of ornithopod dinosaurs}}
{{Speciesbox
| fossil_range = Late Cretaceous (Maastrichtian), {{fossilrange|66.1|66}}
| display_parents = 2
| image =
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| genus = Calvarius
| parent_authority = Prieto-Márquez & Sellés, 2023
| species = rapidus
| authority = Prieto-Márquez & Sellés, 2023
}}
Calvarius (meaning "suffering") is an extinct genus of styracosternan ornithopod from the Late Cretaceous (Maastrichtian age) Talarn Formation of Spain. The genus contains a single species, Calvarius rapidus, known from a single {{dinogloss|metatarsal}}. The slender morphology of this bone may indicate Calvarius had a cursorial (adapted to run) ecology, in contrast to its slower-moving relatives.
Discovery and naming
The holotype specimen, MCD-8734, is a single fourth {{dinogloss|metatarsal}} discovered in 2019 in layers of the Talarn Formation ('Pallars Jussà' locality, Tremp Group) in Catalonia, Spain. In 2023, Albert Prieto-Márquez and Albert Sellés described Calvarius rapidus as a new genus of styracosternan dinosaurs based on this specimen. The genus name, "Calvarius", refers to the type locality, Serrat del Calvari. It is further derived from the Catalan calvari, meaning "suffering", referencing proximity of the genus to the K-Pg extinction event. The specific name, "rapidus", is a Latin word meaning "fast", referring to the likely cursorial habits inferred by the slender metatarsal anatomy.{{Cite journal |last1=Prieto-Márquez |first1=A. |last2=Sellés |first2=A. |year=2023 |title=Evolutionary convergence in a small cursorial styracosternan ornithopod dinosaur from western Europe |journal=Journal of Vertebrate Paleontology |volume=42 |issue=5 |at=e2210632 |doi=10.1080/02724634.2023.2210632 |doi-access=free }}
Description and classification
{{multiple image
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| image1 = Hypsilophodon UDL.png
| caption1 = Life restoration of the bipedal Hypsilophodon, which Calvarius was convergently similar to
| image2 = Life restoration of Iguanacolossus.jpg
| caption2 = Life restoration of Iguanacolossus, a more typical quadrupedal styracosternan
}}
The highly modified metatarsal of Calvarius is slender and elongated, with no equivalents among its close relatives. It is convergently similar to the corresponding gracile metatarsals of more basal bipedal ornithischians such as Hypsilophodon and Dysalotosaurus. However, various anatomical characteristics indicate Calvarius was a member of the typically quadrupedal Styracosterna. As such, it may have occupied the cursorial niche of the smaller, bipedal non-styracosternan ornithopods.
In their 2023 description of Calvarius, Prieto-Márquez & Sellés were unable to determine a precise phylogenetic position for this taxon via phylogenetic analyses, as these results recovered a large unresolved polytomy of styracosternans.
Paleoenvironment
Calvarius is known from the Talarn Formation, which dates to the latest Maastrichtian age of the late Cretaceous period. At the end of the Cretaceous, much of Europe was an archipelago. The Talarn Formation outcrops represent part of this, deemed the 'Ibero-Armorican Island'. The putative troodontid Tamarro has also been named from the formation. Other European localities of similar age have yielded other dinosaurs including rhabdodontid ornithopods, various hadrosauroids, nodosaurid ankylosaurs, small titanosaur sauropods, and abelisauroid and maniraptoran theropods.{{cite journal|last1=Sellés|first1=A. G.|last2=Vila|first2=B.|last3=Brusatte|first3=S. L.|last4=Currie|first4=P. J.|last5=Galobart|first5=A.|title=A fast-growing basal troodontid (Dinosauria: Theropoda) from the latest Cretaceous of Europe|journal=Scientific Reports|volume=11|page=4855|year=2021|issue=1 |doi=10.1038/s41598-021-83745-5|doi-access=free|pmid=33649418 |pmc=7921422|bibcode=2021NatSR..11.4855S }}