Biomechanical and physiological influences on the osteohistological deposition of Anhangueria (Pterosauria, Pterodactyloidea)

Abstract

The study of bone microstructure preserved in fossils provides substantial information about physiology, growth gradients and strategies, and some ecological considerations. Paleohistology is a useful tool for understanding the biological mechanisms of extinct animals. Presented here is the microstructure characterization of two Anhangueria pterosaurs. Thin sections of the fi rst wing phalanx and metacarpal IV of MN 7060-V have been confectioned, as have sections of the radius, ulna and fi rst wing phalanx of MPSC R2090. The histological analysis of bones of MN 7060-V revealed fi brolamellar tissue, few osteocytes and vascular canals. Bones of MPSC R2090 showed a mixed plexiform-fi brolamellar tissue and histovariability, showing that bones from the same individual grew in different patterns. The vascularization was high in the phalanx, intermediate in the ulna and absent in the radius. The absence of canals in the radius may be related to biomechanical issues, due to torsion resistance during fl ight. The histology and the absence of fused bones suggests that the specimens are not adults. Two distinct moments of growth were established. MN 7060-V is a subadult, with presence of bone porosity and MPSC R2090 is a young animal as determined by the high number of canals and plexiform-fi brolamellar tissues, which indicates fast growth. In this work, we concluded that in the Anhangueria clade, the growth of bones is not compatible with the ontogenetic stage. Young animals may present large proportions, whereas there were older individuals of smaller sizes in the same clade.