Skeletochronology in long tubular bones of the Javan water monitor lizard, Varanus salvator bivittatus in the juvenile stage (Lacertilia: Varanidae)

Abstract

: Age estimation of the juvenile stage of Varanus salvator bivittatus using limb bones, namely the big long tubular bones (femur, tibia, humerus) and the small long tubular bones (fibula, radius, ulna, phalanx), was performed using the skeletochronological method. Samples were from Java Island, Indonesia and provided by the pet exporters. Lines of arrested growth (LAG) were present and the first growth mark was visible on a female with a snout-vent length (SVL) of 18.8 cm, and a male with SVL of 19.3 cm. The process of resorption begins in the juvenile stage, and resorption occurs in all long tubular bones. Inside the big long tubular bones, resorption begins earlier and is more extensive than in the small long tubular bones, and in one individual with SVL 25.0 cm, the endosteal bone had completely eroded in all big tubular bones. Resorption also occurred in the small long tubular bones; however, on one individual with an SVL of 25.0 cm, the remaining endosteal bone was still visible only in fibula bone. Linear regression analysis resulted in a weak correlation, statistically insignificant between the SVL and the diameter of the marrow cavity (d) in the fibula bone, while in other bones the correlations were strong and statistically significant (p < 0.005). Among seven tubular bones, the resorption rate in the fibula bone was the lowest but very high in the phalanx bone. Radial osteon formation has occurred in the smallest individual with SVL 14.4 cm to the biggest one with SVL 25.0 cm, and radial osteon density increases with increased SVL. There was no radial osteon in fibula and phalanx bones in any sampled specimen. In general, there were no significant differences in bone diameter (D), marrow cavity diameter (d) and bone thickness (MP) in all long tubular bones in both male and female individuals, and the density of radial osteon on some tubular bones was influenced by body length, but not by sex.