Bone histology of Gasparinisaura cincosaltensis, a basal ornithopod dinosaur from the Upper Cretaceous of Patagonia

IGNACIO A. CERDA; ANUSUYA CHINSSAMY-TURAN

Plaza Huincul, Neuquén, Argentina

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica; 2008

Museo Carmen Funes de Plaza Huincul

The bone histology of Gasparinisaura cincosaltensis, a basal ornithopod from the Upper Cretaceous of Patagonia, was examined. An analysis of 30 thin-sections of several postcranial bones (including tibiae, fibulae, femurs, ribs, metatarsals, pedal phalanges and vertebrae) from juveniles and sub-adults specimens reveals a predominance of fibrolamellar bone with randomly distributed globular osteocyte lacunae. Vascular canals are organized as primary osteons. There are no indications of secondary osteons. All long bones shafts show a well developed medullary cavity. Although the presence of lines of arrested growth (LAGs) are not registered, the samples obtained from the midshaft of a femur from and sub-adult specimen exhibit a zonal pattern of bone deposition: well vascularized fibrolamellar bone alternates with bands of poorly vascularized tissue, which contains mostly flattened osteocyte lacunae in a linear arrangement (lamellar bone). The high prevalence of fibrolamellar bone tissue suggests an overall rapid periosteal osteogenesis and an overall fast growth, but the presence of bands of poorly vascularized lamellar tissue indicate periods of slow growth after which, fast growth resumed. Gasparinisaura exhibited a pattern of bone deposition different from that shown by histological studies in other basal ornithopods, where the growth was continuous as in Dryosaurus, Hypsilophodon, Leaellynasaura and Lesothosaurus or where growth was interrupted by LAGs as in Orodromeus and Tenontosaurus. The periods of slow growth registered in the femur of Gasparinisaura are possibly related to seasonal changes and could be important for future skeletochronological assessments for this dinosaur.