Long bone and vertebral microanatomy and osteo-histology of ’Platecarpus’ ptychodon (Reptilia, Mosasauridae) : implications for marine adaptations

Abstract: The inner bone architecture and histology provide information about life history traits of extant as well as extinct animals. Mosasaurs (family Mosasauridae) are a group of secondarily adapted marine squamates that radiated in the Late Cretaceous, resulting in the evolution of a body plan adapted for pelagic habitats. Specialisa-tions in this group can be observed at different levels of skeletal anatomy, including bone microstructures and osteo-histology. This study describes the histological features and microanatomy observed in bone sections of a vertebra and a long bone (humerus) from derived mosasaur ’Platecarpus’ ptychodon. Bone sections consist mainly of can-cellous bone with a gradual transition to a rather thin outer layer of cortical bone. The bone histology in both sec-tions is characterised by poorly organised tissue; fibro-lamellar bone is abundant throughout the sections, display-ing randomly organised lacunae and lamellar bone in osteons, whereas parallel-fibered bone (lamellar-zonal bone) is observed only in one area of the vertebra. This implies a rapid growth rate possibly similar to some ichthyosaurs and plesiosaurs. The present contribution demonstrates that ’P’. ptychodon exhibit microstructures consistent with life in pelagic environments and show evidence for rapid growth rate and an active marine lifestyle. Furthermore, a structure found in the vertebra is probably related to avascular necrosis, a disease caused by decompression sick-ness, which adds information about the ecology of this species.