Limb histology of the Triassic turtles

Turtles have a characteristic limb bone microstructure: the poorly vascularized tissue grows slowly throughout most of their life; in addition, there is no medullary cavity. This structural pattern is well documented in extant species but fossil turtles are poorly studied in that context. The authors present the bone microstructure of two of the oldest (Triassic, ca. 215-210 Myr) turtles. The typical features of the bone tissue appeared very early in the evolution of these animals. Moreover, divergent growth strategies were already present at the time – the growth tempo differed particularly at a young age, so various species attained comparable body sizes at different stages of life.