Craniofacial ontogeny inCentrosaurus apertus

Abstract

Centrosaurus apertus, a large bodied ceratopsid from the Late Cretaceous of North America, is one of the most common fossils recovered from the Belly River Group. This fossil record shows a wide diversity in morphology and size, with specimens ranging from putative juveniles to fully-grown individuals. The goal of this study was to reconstruct the ontogenetic changes that occur in the craniofacial skeleton of C. apertus through a quantitative cladistic analysis. Forty-seven cranial specimens were independently coded in separate data matrices for 80 hypothetical multistate growth characters and 130 hypothetical binary growth characters. Both analyses yielded the max-limit of 100,000 most parsimonious saved trees and the strict consensus collapsed into large polytomies. In order to reduce conflict resulting from missing data, fragmentary individuals were removed and the analyses were rerun. Among both the complete and the reduced data sets the multistate analyses recovered a shorter tree with a higher consistency index (CI) than the additive binary data sets. The arrangement within the trees shows a progression of specimens with a recurved nasal horn in the least mature individuals, followed by specimens with straight nasal horns in relatively more mature individuals, and finally specimens with procurved nasal horns in the most mature individuals. The most mature individuals are further characterized by the reduction of the cranial horn ornamentations in late growth stages, a trait that similarly occurs in the growth of other dinosaurs. Bone textural changes were found to be sufficient proxies for relative maturity in individuals that have not reached adult size. Additionally, frill length is congruent with relative maturity status and makes an acceptable proxy for ontogenetic status, especially in smaller individuals. In adult-sized individuals, the fusion of the epiparietals and episquamosals and the orientation of the nasal horn are the best indicators of relative maturity. This study recovers no clear evidence for sexually specific display structures or size dimorphism in C. apertus.

A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system

“…Examination of specimens of T. rex reveals the same pattern, where the snout is coarse in relatively young adults (AMNH FARB 5027), whereas it is smoother in relatively old adults (LACM 23844)28. This reduction in texture that is seen among tyrannosaurines is similar to the reduction in cephalic ornamentation that also occurs in other dinosaurs, including ceratopsids525354 and pachycephalosaurians55. It is possible that ornament reduction in adults is an ancestral feature for dinosaurs.…”

A Late Cretaceous diversification of Asian oviraptorid dinosaurs: evidence from a new species preserved in an unusual posture

“…A better parallel may be herbivorous dinosaurs like ceratopsids and hadrosauroids, which although distantly related to oviraptorosaurs were similar in possessing often gaudy head crests and other cranial ornamentation. It is well known that the ornamentation in these dinosaurs changed dramatically during ontogeny474849505152. Therefore, we would expect the head ornaments of oviraptorosaurs to change during growth, making it potentially very difficult to distinguish ontogenetic morphs from separate species in the absence of histological data (which is currently unavailable for the Ganzhou oviraptorids because of the logistical difficulty of destructive sampling) or extremely large sample sizes.…”

A new multi-faceted framework for deciphering diplodocid ontogeny

“…In exceptional ontogenetic studies, large sample sizes including representatives of multiple growth stages allow for more comprehensive histologic and morphological comparisons (e.g., Dodson, 1975;Carr, 1999;Scannella and Horner, 2010;Horner et al, 2011;Frederickson and Tumarkin-Deratzian, 2014;Woodward et al, 2015). While Morrison diplodocids are by far one of the most common of all North American dinosaur groups, taphonomic biases, stratigraphic resolution, and taxonomic uncertainties generally result in largely incomplete and less well understood individuals.…”

“…While the characters used in a phylogenetic analysis are derived from morphologic attributes, this analysis would suggest that many of the characters are ontogenetically dependent. As demonstrated with tyrannosaurs (Carr and Williamson, 2004;Fowler et al, 2011), ceratopsians (Scannella and Horner, 2010;Scannella et al, 2014;Frederickson and Tumarkin-Deratzian, 2014), and hadrosaurs (Campione et al, 2013;Fowler and Horner, 2015), ontogeny (and stratigraphy) does affect taxonomy (likewise echoed in Hone et al, 2016). In animals that undergo an order of magnitude in size change, one could predict that many phylogenetic characters are simultaneously size determinant (ontogenetic in the sense they change as an animal gets larger with age) characters.…”

“…As this analysis calls for the combined efforts of morphologic and histologic observations to better understand ontogeny, perhaps future studies should look to stratigraphy, morphology, and histology as supportive information to enhance phylogenetic studies (such is already being done and is referred to as an ontogram; Frederickson and Tumarkin-Deratzian, 2014). Perhaps the true phylogeny of such conflicting specimens will be resolved from an ontogram-based inclusive approach.…”