Considerations about the cervical rib histology of Skorpiovenator bustingorryi (Theropoda, Abelisauridae)

CANALE, JUAN; CERRONI, MAURICIO; NOVAS, FERNANDO

General Roca

Congreso; Congreso Argentino de la Asociación Paleontológica Argentina; 2016

The Abelisauridae was one of the most widespread meat-eating dinosaur families of Gondwana. Although their remains are the most common theropod records in southern continents, until today only few studies focused on their bone microstructure. In this contribution, we report the results of a paleohistological analysis on the cervical rib of the holotype of Skorpiovenator bustingorryi Canale et al., 2008 (MMCH-PV 48). The abelisaurid ribs are characterized by possessing an expanded proximal section and a thin-caudally directed rod, which was previously considered as an ossified tendon but without an histological analysis to corroborate this. The thin section analyzed shows that the cortical tissue is mostly compact, dominated by multigenerational dense Haversian tissue, which in some places reaches the subperiosteal layer. The primary tissue is circumscript to the most external layer and is composed by nearly avascular pseudolamellar tissue, monorefringent under cross-polarized light, reflecting the mainly longitudinal character of the fibers. These characteristics allows to confirm that the rod of the cervical rib is product of the metaplastic ossification of a tendon. This was already reported in the cervical ribs of sauropods, but in Skorpiovenator clear lines of arrested growth (LAGs) were observed; , unlike sauropods where LAGs in cervical ribs were not reported so far. The presence of these lines evidence that Skorpiovenator had periodically periods where development ceased, and they were also seen in Aucasaurus garridoi Coria et al. and the abelisaurid MMCh-PV 69, which may indicate this growth strategy between abelisaurids would have been more extended than thought.