Bone growth patterns in two cordylid lizards, Cordylus cataphractus and Pseudocordylus capensis

Abstract

Cross-sections through the midshaft of the femora from an ontogenetic range of individuals were examined for Cordylus cataphractus, a heavily armoured, group-living lizard found in the western parts of South Africa, and Pseudocordylus capensis, an agile, montane lizard, occurring in the Cape Fold Mountains of South Africa. Relative bone thickness was found to be high in C. cataphractus and low in P. capensis. Both species displayed a high incidence of double lines of arrested growth. Endosteal resorption and deposition were extensive in C. cataphractus, occurring around the entire medullary cavity margin, and, except in the smallest juveniles, embryonic bone and the birthline had been completely resorbed. In P. capensis, on the other hand, endosteal resorption and deposition were limited and highly localized. Remnants of embryonic bone and a birthline were present in juveniles of varying size, as well as in several adults. These remnants always occurred in the dorsal half of the femoral midshaft and coincided with endosteal deposits, when present. In both species, maximum endosteal deposition and minimum periosteal deposition characterized the dorsal half of the femoral midshaft, while the ventral half was characterized by maximum periosteal deposition and most intensive endosteal resorption. In C. cataphractus, the correlation between medullary cavity area and total bone area differed significantly between the sexes, but not so in P. capensis. The remodelling process in each species can be explained in terms of the respective lifestyles of the species.

Keywords: bone histology, femur, embryonic bone, remodelling, double lines of arrested growth