Unusual endosteally formed bone tissue in Saltasaurus loricatus (Dinosauria: Sauropoda)

ANUSUYA CHINSSAMY-TURAN; IGNACIO A. CERDA; JAIME POWELL

Bonn

Simposio; 3rd International Symposium on Paleohistology?; 2015

The presence of highly vascularized endosteal bone in the medullary region of nonavian dinosaurs has been invoked as evidence of medullary bone (specialized endosteal bone formed during ovulation). However, a pathological origin has been verified some of these reports. Here we report on the occurrence of unusual endosteally formed tissue in several bones of Saltasaurus loricatus (an armoured titanosaur sauropod from the Upper Cretaceous of Argentina): i) within the medullary cavity of a metatarsal, ii) inside a pneumatic cavity of a posterior caudal vertebra, iii) lining large vascular canals and iv) in intra-trabecular spaces in an osteoderm. The endosteal bone is composed mainly of woven and, to a lesser extent, parallel fibred bone. In these tissues vascularisation is high, bone cell lacunae are abundant and they have an irregular arrangement. In the metatarsal and caudal vertebra vascular spaces are lined by lamellar bone. The presence of two shallow, irregular depressions overlain by a highly fibrous tissue in the metatarsal suggest a pathological origin for the endosteal bone in this element. There is no evidence of reactive periosteal bone in the vertebra and the osteoderm. Our results provide new evidence for the possibly pathological origin of the highly vascularized endosteal tissue in Saltasaurus and demonstrate that, as in other onithodirans, this tissue can be formed not only in the diaphysis of long bones, but also in the axial and dermal skeleton.