The Evolution of Turtles
By : Kristie White
The first proto-turtles are believed to have existed in the late Triassic Period of the Mesozoic era, about 220 million years ago, and their shell, which has remained a remarkably stable body plan, is thought to have evolved from bony extensions of their backbones and broad ribs that expanded and grew together to form a complete shell that offered protection at every stage of its evolution, even when the bony component of the shell was not complete.
Their exact ancestry has been disputed. It was believed they are the only surviving branch of the ancient evolutionary grade Anapsida, which includes groups such as procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygomatic arch). The millerettids, protorothyrids, and pareiasaurs became extinct in the late Permian period, and the procolophonoids during the Triassic
It is also theorized that ancient turtles possessed teeth but lost them. A good example is that Proganochelys had midpalatal homodont ‘teeth’ which were actually the small denticles formed by the development of a tough covering over some of the bones of palate (which modern turtles lack), yet was otherwise similar to modern turtles. The evolution of teeth is the problem evolutionists have to deal with and, conversely, the loss of teeth would be expected in the biblical model of the Fall which predicts corruption of the genome and the accompanying deterioration of the phenotype. A mutation could easily have occurred in one of the ‘tooth’ development genes in turtles that disabled tooth maturation but still allowed the animal to survive. If it proved beneficial for its specific feeding habits, it may even be selected for as a result. Loss of teeth has evidently occurred several times in history in animals, including possibly some birds, and certain monotremes such as the platypus.