Patterns of chondrification and ossification in the skull of Graptemys pseudogeographica, the false map turtle (Emydidae).

Patterns of ossification and chondrification are well-described for several species of turtles, but details of the chondrocranial anatomy are known for only a handful of species. Cleared and double-stained embryos of Graptemys pseudogeographica were used to examine the fully formed chondrocranium and the formation, chondrification, and ossification of the cranium. The chondrocranium of G. pseudogeographica possesses an unusually large, irregularly shaped foramen epiphaniale that is joined with the fenestra olfactoria. As in other emydids, and many turtles generally, the taenia marginalis is present only as a small projection and the taenia medialis is lacking in mature stages of embryonic development. Ossification data for G. pseudogeographica are consistent with those of other Testudines in that the dentary and maxilla (dermal elements of the upper and lower jaws) ossify early, whereas the articular (an endochondral bone of the lower jaw) ossifies relatively late. Additionally, comparative ossification shows that the vomer is quite variable in its relative timing of ossification across Testudines.