Comparative Chondro-Osseous Development and Growth of Marine Turtles

Abstract

Longitudinal skeletal growth in appendicular long bones of Caretta caretta resembles the patterns in Pseudemys scripta and Carettochelys insculpta. A metaphyseal cone of cartilage becomes transiently isolated through the formation of a subphyseal plate of calcified cartilage which undergoes early peripheral vascular irruption and ossification. The noncalcified epiphyseal cartilage remains thin and avascular. Skeletal growth in Dermochelys coriacea is remarkably divergent from other living chelonians. Primary vascular irruption occurs into the noncalcified hypertrophied cartilage of the metaphysis with rapid extension of vascularity also into the non-hypertrophied epiphyseal cartilage. Endochondral ossification of the metaphysis advances contiguously from the diaphysis, a subphyseal calcified cartilage plate does not form, and there is no isolation of a metaphyseal cartilage cone. The noncalcified epiphyseal cartilage remains thick with transphyseal as well as perichondral vascularization through cartilage canals. The pattern in Dermochelys may be due to very rapid skeletal growth to a large body size. The giant Cretaceous Archelon ischyros has a similar skeletal vascular pattern, whereas the giant Tertiary Stupendemys geographicus resembles normal chelonians. In many respects, skeletal growth of Dermochelys resembles marine mammalian patterns.