BIOLOGICAL IMPLICATIONS OF THE BONE MICROSTRUCTURE OF THE LATE CRETACEOUS ORNITHOPOD DINOSAUR GASPARINISAURA CINCOSALTENSIS

Here we present the bone histology of Gasparinisaura cincosaltensis, a basal ornithopod from the Late Cretaceous of Patagonia, and discuss its biological implications. The sample includes axial and appendicular elements from several specimens of different ontogenetic stages. The cortex of most bones consists of fibro-lamellar tissue, with mainly longitudinally oriented vascular spaces, which suggests rapid osteogenesis and fast growth. However, the fibro-lamellar bone is commonly interrupted by lines of arrested growth and/or annuli composed of parallel-fibered bone that indicates that the rapid growth was periodic. Although a true outer circumferential layer was not recorded in any of the sampled elements, in several of the larger samples the woven-fibered matrix of the inner and middle cortex grades into a parallel-fibered tissue, which suggests that the attainment of sexual maturity occurred before skeletal maturity. The growth dynamics of Gasparinisaura are similar to those reported in other basal ornithopods. Inter-elemental, as well as intraspecific, variations in histology were observed in Gasparinisaura. Such variation could be the result of sexual dimorphism, or the effect of localized conditions of growth, or perhaps plasticity in growth in response to local environmental conditions.