Coronosaurs

Phylogeny

The cladeNeoceratopsia is defined as "the largest clade containing Triceratops horridus, but not Chaoyangsaurus youngi and Psittacosaurus mongoliensis". By this definition, only the members of Chaoyangosauridae and Psittacosaurus are excluded from Neoceratopsia, while all more derived ceratopsians are part of this clade. A slightly less inclusive group is Euceratopsia, named and defined by Daniel Madzia and colleagues in 2021 as "the smallest clade containing Leptoceratops gracilis, Protoceratops andrewsi, and Triceratops horridus". This clade includes the family Leptoceratopsidae and all more derived ceratopsians. Leptoceratopsids are a mostly North American group of mostly small bodied and quadrupedal ceratopsians. Another subset of neoceratopsians is called Coronosauria, which is "the smallest clade containing Protoceratops andrewsi and Triceratops horridus". Coronosaurs show the first development of the neck frill and the fusion of the first several neck vertebrae to support the increasingly heavy head. Within Coronosauria, two groups are generally recognized. One group can be called Protoceratopsidae and includes Protoceratops and its closest relatives, all Asian. The other group, Ceratopsoidea, includes the family Ceratopsidae and closely related animals like Zuniceratops. This clade is defined as "the largest clade containing Ceratops montanus and Triceratops horridus, but not Protoceratops andrewsi". Ceratopsidae itself includes Triceratops and all the large North American ceratopsians and is further divided into the subfamilies Centrosaurinae and Chasmosaurinae.