The first turtles saw the light as much as 220 million years ago, at about the same time as the first representatives of another order of reptiles - dinosaurs. But if dinosaurs became extinct 60-70 million years ago, then most of the turtles survived and feel great to this day. These reptiles have a feature that sharply distinguishes them from other oviparous land animals. What is a tortoise shell, what is its purpose, structure and how is it used in human economic activities? Let's consider everything in order.
What is the shell
The turtle shell is represented by two parts:
- plastron - the abdominal part;
- carapace - the dorsal part.
Both the plastron and the carapace consist of a bone base covered from the outside with strong horny plates, or shields. The strength of the shell is simply incredible: it is able to withstand a weight two hundred times greater than the weight of its wearer! In most turtles, the plastron is covered by 16 horny shields, and the carapace has 38 protective plates. The only exceptions are leatherback turtles, whose evolution in the Triassic period (that is, shortly after the appearance of turtles as a biological order) separated from the "mainstream" of general development.
The bony frame of the plastron is a modified clavicle, epiphorax and ribs of the animal. In carapace, a similar role is played by the outgrowths of the pre-sacral vertebrae and the dorsal parts of the ribs. Not all representatives of this order have corneous plates on top of the bone base. For example, a whole superfamily of the shieldless turtles received the name due to the absence of this trait.
Does turtle shell save?
It is clear that the high strength of the shell helps the turtle to defend against enemies with its help. How effective is this protection? The technology of hunting and eating turtles has been worked out very well in land animals and birds. Flying predators, which with the help of their beak and claws, cannot cope with a hard shell, do this: they lift the turtle into the air and throw it from a great height on stones, and after the protective shell breaks, they eat the prey. There is evidence that, for example, foxes act in a similar way: not being able to fly, they throw the turtle off the cliff onto the rocky ground, and the South American jaguar simply picks out the reptile from the shell with its long claws, without gnawing it.
For the inhabitants of the underwater world, everything is even simpler: a white shark easily bites through the shell of a sea turtle. And the harsh Nile crocodiles, although they are not able to gnaw through the bone plates, do not particularly complex from this. They simply swallow the turtles whole, and then the digestive system works.
