Preliminary data on the bone shell microstructure of Condorchelys antiqua Sterli 2008, a stem turtle from the Jurassic of Patagonia

IGNACIO A. CERDA; JULIANA STERLI; TORSTEN M. SCHEYER

Simposio; V Simposio Argentino del Jurásico; 2013

Here we describe and discuss the shell bone histology of Condorchelys antiqua, a stem turtle from the Middle to Late Jurassic of Patagonia. We studied thin sections obtained from two costal and tree neural plates from the Cañadon Asfalto Formation (Queso Rayado Locality, Chubut Province). All the sampled shell bones show a diploe structure with external cortex (ECO) and internal cortex (ICO) framing an interior area of cancellous bone (CB). Both cortices are composed of parallel fibered bone tissue. Sharpey?s fibres are developed in the ECO and they insert at high angles into the cortical bone. The cortical bone itself is vascularised by scattered primary osteons and simple vascular spaces. Some vascular spaces extend up to the outer surface of the ECO. The ICO is commonly less vascularised than the ECO. The ICO in the neural plates is strongly reduced, occupying only 8-13 % of the total thickness of the plate. The CB is well developed and consists of fine trabeculae composed of secondary lamellar bone tissue. The main histological difference between C. antiqua and other basal Testudinata described in previous studies (Proganochelys quenstedti Baur 1887, Proterochersis robusta Fraas 1913 and Kayentachelys sp.) resides in the absence of well developed mineralized structural fibre bundles in the ECO of C. antiqua. Also, the shell bone of C. antiqua (especially neural plates) appears to be more ?porous? (high content of cancellous bone) than the other basal taxa. The internal microanatomy of C. antiqua suggests an aquatic/semi-aquatic lifestyle for this taxon.