Looking at a turtle skull, what kind of image do you have in your mind? Would you see a beautiful, modelled turtle? A majestic, huge turtle that towers over you? Or would you have thoughts of a little hatchling wrapped up tightly in a soft warm towel? This article briefly looks into the various taxonomic forms of turtles and gives examples of how turtle skeletons are classified.

One of the most common turtle taxonomy forms is the semi-precious fossil record called the Triassic. This group of dinosaurs evolved from the Mesozoic era, between two million years ago and three million years ago. At the start of the Triassic period, this ecosystem was populated by a diverse range of small seafood animals including fish, crocodylids, various dinosaurs and the very first turtles.

The first Triassic turtles were so closely related to modern-day turtles that some believed they might be a transitional species between the prehistoric turtle and the modern turtle. Its soft-shelled body and adult legs have the same dimensions as that of the egg. It possessed large claws and complete forelimb and hind limbs, which is perhaps why it was able to squeeze through narrow passageways in the many marine spaces where the ocean waters at the time was warm and abundant. Its soft-shelled head with long, spiraled antennae was similar to that of modern-day elfish and its mouth was relatively small, being smaller than that of modern-day box turtles.

A small appendage on its back called a carapace is well-defined and found in all members of the Triassic group of reptiles. It is composed of several bones connected by a thin membrane and is very flexible, but also thick enough to protect the body from the effects of cold and fresh water. The carapace was divided in two parts before the onset of the Triassic period. The first part contained a smooth bony cover called a plastron and had no apparent purpose. The second part contained the soft, pliable plastrons and contained numerous ridges and grooves along its length, allowing the turtle skeleton to fit better.

The first section of the carapace of a Triassic turtle skeleton has been compared to that of an egg’s shell. The shape of the plastrons resembles that of an eggshell, while the size, thickness and number of teeth are like that of an arm or a leg. The entire arrangement has been likened to that of the gonads of modern-day turtles. Plastrons formed the ventral border of the turtle skeleton, protecting the caudal and pectoral fins.

The second section of the plastrons of a Triassic turtle skeleton had a slightly different arrangement. Instead of forming a hard border around the shell, the plastrons have an overlapping border inside the shell, with three to nine spines protruding from it. Each of these spines was capable of secreting mucus, which protects the body against the drying effects of the ocean. Mucus also serves as a filter for carrying food into the stomach, as well as a thermos for storing the consumed heat of prey.

The last part of the turtle’s carapace is composed of short ribs, which are not present in a complete adult turtle. These short ribs also serve to reinforce the flippers. Long, segmented plasts that reach up to the lipped rear end of the turtle were present on both the pre-Tricaceous and the Triassic rocks. However, unlike the latter, these plasters had been reduced to a few stubs, possibly to improve breathing, since the air would have difficult entering through the openings.

The neck of the turtle is also comprised of small, stiff gill covers called scutes. The exact relationship between these states and the plastrons of the turtle remains controversial. Scutes, if they really existed, must have come into play after the tail fluke, since they are more closely associated with swimming than with walking. It is more likely that the scutes were present at the base of the tail, since tail flukes were discovered much later, during the Cretaceous geological period. Whatever the case may be, the evolution of scutes on the turtle body represents one of the major transitions in the history of these animals.