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The ontogenetic pattern of neurocentral suture closure in the axial skeleton of Hyperodapedontinae (Archosauromorpha: Rhynchosauria) and its evolutionary implication

Citation

Heinrich, Clara et al. (2021), The ontogenetic pattern of neurocentral suture closure in the axial skeleton of Hyperodapedontinae (Archosauromorpha: Rhynchosauria) and its evolutionary implication, Dryad, Dataset, https://doi.org/10.5061/dryad.zcrjdfn9c

Abstract

Understanding ontogeny of a taxon is a crucial step to properly elucidate its taxonomy and evolution. However, aside from histological data, osteological criteria for assessing maturity are considered lineage specific or controversial. The sequence of neurocentral suture closure of the axial skeleton of extant crocodilians, which occurs in a postero-anterior sequence, has being used as a non-destructive method to determine maturity in extinct reptiles. However, the use of this criterion in extinct archosaurs not closely related to crocodilians is debatable, as the ancestral condition of Archosauria is unknown and variation occurs in timing and sequence orientation within the clade. We have assessed the pattern of neurocentral suture closure of the Hyperodapedontinae rhynchosaurs, an early archosauromorph clade distantly related to archosaurs. Different from extant crocodilians, they exhibit an antero-posterior sequence neurocentral suture closure. Relative size and other ontogenetic markers suggest the neurocentral closure in the Hyperodapedontinae is correlated to aging, although closed sutures were rare in the sample. A high number of open or partially open sutures in mature individuals indicate that they remained open during most of their life. Our study indicates that (i) the delayed neurocentral closure can be a paedomorphic heterochronic process in Hyperodapedontinae, as it contrasts with the fully closed neurocentral sutures of early diverging non-hyperodapedontine rhynchosaurs; (ii) the assumption opened neurocentral sutures indicates immaturity in extinct reptiles is not always correct; and (iii) the delayed closure may have originated independently in several archosauromorph lineages, but the ancestral condition of Archosauria likely follows the crocodilian closure pattern.

Funding

Deutscher Akademischer Austauschdienst