Biological Insights From the Osteohistology of a Nile Crocodile

While long bones are mostly utlised for skeletochronology of extant and extinct vertebrates, among crocodilians, dermal bones have also been studied. However, there is a lack of a systematic and comprehensive study of the variation in osteohistology and skeletochronology of limb, axial, and dermal bones of extant crocodilians. Here, we undertake a comprehensive assessment of the histology of multiple postcranial elements of a single, captive adult Crocodylus niloticus (with approximately known age) to assess their utility for skeletochronology. We document the intraskeletal histological variability in the skeleton and show that despite the gastralia recording the highest number of growth rings, the radius, ulna, and fibula are more reliable for skeletochronology. We show substantial variation in the histology of the osteoderms depending on the plane of sectioning, as well as their location on the body of the crocodile. Additionally, we report that anteriorly sectioned dorsal osteoderms preserved the highest number of growth marks. Our study provides important information regarding intraskeletal variation in osteohistology and presents key information regarding the choice of skeletal elements for reliable life history reconstruction of C. niloticus.