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

CERRONI, MAURICIO ANDRÉS; CANALE, JUAN IGNACIO; NOVAS, FERNANDO EMILIO

Congreso; 11º Congreso 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, 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 hyperelongated rod, which was previously considered as an ossified tendon but without a 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 exhibits some degree of diagenetic alteration. It´s composed by nearly avascular pseudolamellar tissue, birrefringent under cross-polarized light, reflecting the mainly concentric character of the fibers. These characteristics allow to confirm that the rod of cervical rib is not an ossified tendon as in sauropods, which are characterized by longitudinally isotropic fibers that reflects the cord-like shape of the precursor tissue. The primary tissue also shows clear lines of arrested growth (LAGs), evidence that Skorpiovenator had periodically cycles where development ceased. The same features were Cenomanian of Neuquén (MMCh-PV 69), which suggest that this growth strategy was common between abelisaurids.