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

Abstract

Understanding the 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 posterior–anterior sequence, is a non‐destructive method used to determine maturity in extinct reptiles. However, its use 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 Hyperodapedontinae rhynchosaurs, an early archosauromorph clade distantly related to archosaurs. Unlike extant crocodilians, they exhibit an anterior–posterior sequence neurocentral suture closure. Relative size and other ontogenetic markers suggest that neurocentral closure in the Hyperodapedontinae correlates with 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: (1) the delayed neurocentral closure may be a paedomorphic heterochronic process in Hyperodapedontinae, as it contrasts with the fully closed neurocentral sutures of early diverging non‐hyperodapedontine rhynchosaurs; (2) the assumption that open neurocentral sutures indicates immaturity in extinct reptiles is not always correct; and (3) the delayed closure may have originated independently in several archosauromorph lineages, but the ancestral condition of Archosauria probably follows the crocodilian closure pattern.

Palaeobiological inferences of “rauisuchians” Fasolasuchus tenax (Los Colorados Fm., Argentina) and Prestosuchus chiniquensis (Santa Maria Super sequence, Brazil) from the Middle–Upper Triassic of South America based on microstructural analyses

“…Although this parameter has been shown to yield ambiguous results (Griffin et al, 2020; Irmis, 2007), it gives at least a good approximation to the timing of skeletal maturity, and it is still employed currently in the literature (e.g. ;Fostowicz‐Frelik & Sulej, 2010; Gallina, 2011; Garcia Marsà et al, 2017; Griffin, 2018, Heinrich et al, 2021; Malafaia et al, 2016).…”

On a skeletally immature individual of Unaysaurus tolentinoi (Dinosauria: Sauropodomorpha) from the upper Triassic of southern Brazil

“…Therefore, UFSM 11712 represents an individual with an autopodium roughly half the size of the holotype of U. tolentinoi . Although size independent criteria are not reliable proxies for ontogenetic assessment in dinosaurs (Griffin et al, 2021), the neurocentral suture/fusion have been argued to be indicative of ontogenetic stages for archosaurs (Brochu, 1996; Leal et al, 2004; Roberto‐Da‐Silva et al, 2014; Heinrich et al, 2021). Both preserved vertebrae of UFSM 11712 are composed solely of their centra (Figure 2).…”

Osteohistología de Archosauriformes triásicos sudamericanos (Reptilia: Eucrocopoda): implicancias paleobiológicas

“…Sin embargo, este parámetro ha mostrado resultados ambiguos para evaluar etapas ontogenéticas para varios grupos de vertebrados (Irmis, 2007;Griffin et al, 2020). A pesar de ello, ofrece, al menos, una buena aproximación y se ha empleado repetidamente en el pasado y en la actualidad (e.g., Fostowicz-Frelik y Sulej, 2010; Gallina, 2011;Malafaia et al, 2016;Garcia Marsà et al, 2017;Heinrich et al, 2021).…”

“…Esta característica se encuentra escasamente registrada en los tetrápodos, ya que en general tienen correspondencia temporal, es decir, suelen presentarse más o menos al mismo tiempo en la ontogenia de un individuo (Padian y Stein, 2013). Entre los grupos que muestran las suturas neurocentrales abiertas o parcialmente fusionadas con un aparente estado avanzado de desarrollo se incluyen los rincosaurios (Heinrich et al, 2021), los coristeoderos (Seiffert, 1973;Evans, 1991;Ezcurra et al, 2016), ictiosaurios, sauropterigios (Rieppel, 1989) y el dinosaurio Spinosaurus (Evers et al, 2015). Excepto los rincosaurios, en la mayoría de estos taxones se infirió un hábito acuático o anfibio.…”