Skeletal development of Kinosternon scorpioides limbs (Chelonia: Kinosternidae)

The morphological study of limbs is important for the understanding of tetrapod biology, where it can be applied to taxonomy and phylogeny, as well ecology and behavior. In this study area, osteogenesis is a subject in Kinosternidae, which has been little researched. The main aim of this study was to characterize the skeletogenesis of Kinosternon scorpioides limbs. Samples were histologically processed, and the embryos were cleared with potassium hydroxide and stained with alcian blue and alizarin red. It was observed that the limbs arose in embryonic Stage 10 as mesenchymal condensate cells. The first stylopodium chondrification centers were noted at Stage 14. Zeugopodium chondrification centers appeared at Stage 15; carpal, metacarpal, tarsal, and metatarsal regions were observed at Stage 16, and the cartilage molds of all bones limbs were present at Stage 18. Ossification began in the humerus and femur at Stage 20, and continued into the radius, ulna, tibia, and fibula bones. By Stage 23, it was already effectively directed toward the bone epiphyses in both limbs. At Stage 26 and hatching, only articular cartilages remained, and in the majority of samples the carpal region showed no affinity for alcian blue or alizarin red staining. This study acts as an indicative parameter of the taxon's normal development and can contribute to the phylogenetic understanding of this group.