Centrosaurinae

The classification of centrosaurines and the relationships among the various species is complicated by a wide degree of variation between individuals and growth stages. Some features that have traditionally been used to classify these dinosaurs, like the number and arrangement of frill ornaments or spikes, have been discovered to be more variable than previously thought. For example, the cladogram presented below follows a 2016 phylogenetic analysis by Chiba et al. (2017). These authors treated the species Rubeosaurus ovatus as distinct from Styracosaurus albertensis, and recovered several distinct clades within Centrosaurini, which together formed a sister group to the Pachyrhinosaurini: }} However, subsequent studies have cast doubt on the usefulness of minor variations in frill spike arrangement for classifying centrosaurines. In particular, large sample sizes of the species Centrosaurus apertus and Styracosaurus albertensis have shown a higher than predicted amount of variation. In 2020, Holmes et al. explored what the effect of recognizing such diversity would have on centrosaur classification. They used the same data as Chiba et al.'s 2017 study, but treated Rubeosaurus as a synonym of Styracosaurus, dropping it from their taxon list. The resulting cladogram (below) found Centrosaurini as a polytomy, a grouping with no discernable sister group relationships within it. The authors concluded that this meant the variation present within these species made it difficult to find any real resolution among them, and may even provide support for the hypothesis that centrosaurines evolved primarily via anagenesis (a single lineage changing through time) rather than cladogenesis (multiple branching lineages with shared common ancestors). }} Pachyrhinosaurini was defined in 2012 by Fiorillo & Tykoski. It was defined as all centrosaurine ceratopsids more closely related to Pachyrhinosaurus canadensis than to Centrosaurus apertus. It was defined during the description of Pachyrhinosaurus perotorum, a species from Alaska. The substituent clade Pachyrostra, compromising centrosaurs with bossed instead of horned noses, is defined as "the least inclusive clade including both Pachyrhinosaurus canadensis and Achelousaurus horneri. ==Biogeography==

, from the municipality of Aldama Centrosaurine fossils have mostly been found in Western North America (Alberta, Montana, and Alaska). ==Body size==

Compared to their sister group, Chasmosaurinae, centrosaurines are relatively small. The primitive Sinoceratops is an exception, with an estimated skull length of . By contrast, the skull length of Albertoceratops was more typical for this group at only . ==Reproduction==

'' Possible neonate sized centrosaurine fossils have been documented in the scientific literature. Research indicates that centrosaurines did not achieve fully developed mating signals until nearly fully grown. Scott D. Sampson found commonality between the slow growth of mating signals in centrosaurines and the extended adolescence of animals whose social structures are ranked hierarchies founded on age-related differences. In these sorts of groups, young males are typically sexually mature for several years before actually beginning to breed, when their mating signals are most fully developed. Females, by contrast, do not have such an extended adolescence. ==See also==