Evolution of Turtles
The first turtles
Paleontologists still haven't identified the exact family of prehistoric reptiles that leads to modern turtles, but fossil evidence linking to the Odontochelys. This soft-shelled marine turtle possessed a full set of teeth, which turtles gradually shed over tens of millions of years of evolution. Odontochelys lived the shallow waters of eastern Asia about 220 million years ago. Another prehistoric turtle, Proganochelys, shows up in the western European fossil record about 10 million years later. This bigger turtle had fewer teeth than Odontochelys, and the spikes on its neck meant that it couldn't fully retract its head under its shell. Most important, the shell of Proganochelys was hard, and impervious to predators.
The Giant Turtles of the Mesozoic and Cenozoic Eras
By the early Jurassic period, about 200 million years ago, prehistoric turtles and tortoises were pretty much had the same body plan like modern turtles. Two marine turtles that swam in water were theArchelon and Protostega, both measuring about 10 feet long and weighing about two tons. These giant turtles were equipped with broad, powerful front flippers. Their closest living relative is the much smaller is the Leatherback
If you go 60 million years ahead, to the Pleistocene epoch, to find prehistoric turtles that were about the size of one-ton. The southern Asian Colossochelys can pretty much be described as a larger Galapagos tortoise, which had the basic turtle body plan with a spiked tail and a huge, armored head.
The turtles today:
Turtles today have a hard shell. The shell is internal and it is part of the turtle's skeleton.
The shell is composed of two layers, an outer layer of thin plates called scutes and an inner layer of bone. The underside of the turtle's shell, the plastron, protects its belly. Turtles do not have teeth, instead they have a sharp beak that enables them to tear their food.