Turtles have been known for their shells located on their backs. It is one of their most distinctive traits.
However, have you ever wondered why they have a shell? Read below to find out why.
Why do Turtles have Shells on Their Backs?
The turtle’s shell is being used for protection, but originally it served a role in digging. Turtles descended from lizards and developed shells through evolution and adaptation. At first, turtles only had ribs. Then those ribs evolved into the shells that we now see in each one of them.
Parts of the Shell
The shell’s top is called “carapace” and its bottom is known as “plastron.” A bridge fuses the two parts together.
When the top and the bottom join each other along the sides of the turtle’s body, they produce a firm skeletal box. This skeletal box is composed of cartilage and bones and is retained throughout a turtle’s life.
The Shell’s Purpose
The shell is an important part of the turtle’s body and they cannot live without it. It is not similar to skin that can be shed, and it is not the same as armors that can be removed.
The shell serves as a protection against predators and compensates for the turtle’s slow speed. Originally though, the shell evolved because of the need for a turtle’s digging.
Disadvantages of Having a Shell
The shell causes the turtle to have slow speed because it decreases their limb mobility. Because the shell is a fused ribcage, it lost its ability to move and decreased its breathing.
The turtle had adaptations on how to create, preserve, and use their oxygen.
Timeline of Turtle’s Shell
Many professionals were originally bothered by the origin of the turtle’s shell. However, after finding fossils and conducting a thorough study, they were able to determine their origin.
The earliest turtles dated back to the Permian Epoch (298.9 million – 251.9 million years ago).
These turtles had teeth but did not have shells, plastron (bottom shell), and carapace (top shell). However, they had precursors of these structures.
Eunotosaurus africanus is considered the first known turtle and was known to live 260 million years ago. They had teeth and an intermediate shell structure which produced the plastron and carapace.
Pappochelys (or grandfather turtle) lived from 242 million years ago to 235 million years ago. Its structure was said to be an intermediate between Eunotosaurus and Odontochelys.
Odontochelys semitestacea appeared approximately 225 million years ago. This ancestor of turtles had a bottom shell but no top shell. They still had teeth on their upper and lower jaws.
Proganochelys quenstedi is a slightly younger species that scientists found fossils of. They also had teeth, but they were located on the mouth’s roof instead of its jaws.
Proganochelys quenstedi had the features of present-day turtles, and their shells encased the pelvic and shoulder girdles.
Why was the Shell Used for Digging?
Eunotosaurus lived in a dry time in South Africa. Therefore, scientists think that they dug to escape droughts from the surface, and travel to a colder place underground.
They found evidence that supports their theory because Eunotosaurus had features that were used for digging. They had big claws for soil breaking and thickened bones to withstand compressive forces.
They did not have shells yet, but they had wide ribs that probably anchored their front legs when they dug the soil.
These ribs were then believed to fuse together to form the shells. The expansion of their ribs was probably to add defensive value.
It wasn’t sure though if Pappochelys and Odontochelys were diggers too.
When the turtles had complete digging features (powerful front limbs and wider ribs), they became great swimmers too. And maybe that’s why they thrived in water.
Turtles that lived Underground
Additional proof about Eunotosaurus’ life was found by scientists. They found a fossil of this creature that contained sclerotic rings, which are bony circles found around its eyes.
Because of this proof, scientists deduced that this species was insensitive to light, thus solidifying the theory that they lived underground.
Trivias about Turtle Shells
- The turtle shell’s inner layer is composed of 60 bones. This includes the ribs, breastbone, and backbone.
- As the turtles grow bigger, their shell grows as well.
- Turtles hide inside their shell when they sense danger. However, a few species of turtles, like the sea turtle, cannot hide their head inside the shell.
- Nerve endings are found on the upper and lower parts of a turtle’s shell.
- ‘Testudinal’ is defined as resembling a turtle or tortoise shell.
Do Turtles and Tortoises have the same kind of shell?
Turtles and tortoises belong to the same order Chelonia or Testudines. Therefore, all tortoises are considered as turtles, but not all turtles are considered as tortoises.
One way to classify turtles from tortoises is by looking at their features. Tortoises do not have flipper-like forelimbs, and they do not have webbed feet.
Tortoises also exclusively live on land, while turtles typically live on the water. Tortoises are vegetarians, while turtles are omnivores.
A remarkable similarity between the two is that they both have shells. However, their shells are different in appearance.
Tortoises have domed and rounded shells, while turtle’s shell is thinner and more water-dynamic.
Frequently Asked Questions about Turtle’s Shell
Do female turtles have the same shell size as male turtles?
No, female turtles have larger domed shells, while male turtles have smaller and flatter shells. This is because female turtles should have the ability to store a large number of eggs.
Male turtles also have greater movement, because they have bigger limb openings.
Do all turtles have the same shell pattern?
Most turtles have uniform shell structures, but color and shape may change depending on the species.
However, pig-nose turtles, soft shell turtles, and leatherback sea turtles have lost their scutes (composed of keratin) and decreased the shell’s ossification (turning cartilage into bones).
Conclusion
In summary, the turtle’s shell evolved because of their need to dig underground. The qualities for digging that they developed helped them became great swimmers.
The shell further evolved to serve as defense against predators.
The shell is a vital part of a turtle’s body, and it will not survive if it will be removed.