Development of the Chondrocranium of the Loggerhead Turtle,

To better understand the evolution and development of the amniote cranium, it is necessary to examine non-avian, non-mammalian embryos. Herein, development of the chondrocranium in the loggerhead turtle, Caretta caretta, is described based on whole-mount and sectioned specimens. Primitive characteristics were found to be established rather early in development; at these stages, the cranium resembled not only the early amniote chondrocrania, but also those of anamniote embryos. Several characteristics were noted in the late chondrocranium that represent shared, derived characteristics of chelonians. In particular, one amniote-specific characteristic, the tropibasic trabecula, appeared at an intermediate stage of development. In addition, developmental changes in the orbital cartilage were reemphasized, and the morphological significance of the crista sellaris was discussed in terms of the basic architecture of the vertebrate neurocranium.