Did you know that a turtle’s shell is not just its home? It is also a part of their body that protects them from predators and the environment.
Turtles and tortoises are the only animals to have shells that are part of their bodies.
Shells are important to the survival of all turtles, and pet species are no different. They provide protection and support many biological processes in a turtle’s body.
It is important for owners to understand why their turtle needs a shell. They should also know what will happen if the shell becomes damaged. Continue reading to learn more…
Table of Contents
Why Do Turtles Have Shells?
Turtles have shells for many different reasons.
However the most important reasons are protection and storage.
There are two main parts to a turtle shell:
- Carapace – the top part that many people consider to be the turtle’s back.
- Plastron – the bottom part which can be considered the turtle’s belly.
Both parts of the turtle shell protect vital organs.
The spinal column and rib cage are built into the carapace. The plastron protects important organs like the lungs and heart.
A shell also protects turtles from predators. It comes in handy when a predator wants to bite into a turtle. Raccoons, river otters, minks, foxes, dogs and cats are common predators of North American turtle species. Many of these predators have strong jaws, but they are no match for a turtle shell.
Shells are covered in hard scales called scutes, which can be as hard as bone.
Many species of turtle can also hide in their shell.
Turtles can pull their legs into their shells. Some can even pull their heads in by bending their neck or pulling their head directly in. But, this depends on the way the shell is designed.
Species that are more aquatic are more likely to dive into deep water to escape predators, rather than hide in their shells.
The shell is used for far more than just protection, however.
It also serves as a reservoir for water, fat, and waste. The shell serves as a turtle’s main reservoir for phosphate, carbon dioxide, and multiple minerals (e.g. calcium, magnesium, and sodium).
Where Did Their Shell Come From?
Scientists are not still completely sure how a turtle’s shell evolved.
It has long been debated in the scientific community as to how and why turtles have shells.
Scientists originally thought that a turtle shell was an extension of their backbone and ribs. However, it was discovered to be much more than that. It not only incorporates their skeleton, but it is also an external bony structure.
One controversial point among scientists was the first step in the evolution of their shells.
A common theory was that their ancestors were turtles without shells. This species then started to have a broadening of the ribs. However, this theory proved controversial as this type of evolution is counterintuitive. The broadening of the ribs would have provided little protection whilst making it harder to move and breathe.
Evidence suggests that the two parts of a turtle’s shell (i.e. carapace and the plastron) evolved separately.
This evidence may suggest that the plastron and the carapace once served two different jobs.
The oldest turtle, Odontochelys semitestacae, dates back 220 million years. This species’ fossil was discovered to have just a plastron (i.e. bottom part of the shell) and not a carapace. This suggests the plastron appeared first in history, and some million years later, the carapace evolved.
However, this is still heavily questioned.
One agreed-upon point is that the modern turtle made its first appearance in the late Triassic Period with the species Proganochelys. This species had a full shell with both the carapace and plastron.
Can A Turtle Survive Without A Shell?
A turtle’s shell is very important for basic survival. Could you take away a turtle’s shell and keep it alive? The answer is no! They likely could not survive a couple minutes or even seconds without it. A turtle’s shell includes bones and nerve endings that it needs to live and function.
The shell is an important part of a turtle’s anatomy which includes their rib cage, spinal cord, and nerve endings. It is made up of bone, nerves and blood vessels.
A turtle can feel if you touch them on the shell because there are nerve endings in it.
Nerves and blood vessels all connect the shell to the turtle’s body. The bones fused to the shell are already a part of their body. There is no barrier between the turtle’s bones and its internal organs.
Not only does it provide vital protection to their internal organs, but vertebrates cannot live without their spinal cord. The spinal cord is the connection between the brain and the nerve endings. Without the spinal cord, no vertebrate would be able to move muscles.
Without a shell, turtles would be the same as an animal with no skin.
It is also important to keep in mind the three other functions of a turtle shell:
- Protection: Many predators in a turtle’s habitat eat their prey using their teeth. However, a shell is often strong enough to prevent any serious bites.
- pH buffering: This makes the blood pH less acidic in order to properly bring oxygen and other essential molecules throughout the body.
- Storage: It also serves as the main storage area for calcium, magnesium, sodium, phosphate, carbon dioxide, water, fat, and waste. All of these nutrients are essential for their normal bodily functions and metabolism.
Can Turtles Leave Their Shells?
It is not possible for a turtle to “lose” its shell. Their shell is part of them just as much as our skeleton is a part of us. The turtle is connected to its shell through its nerves, skin, ribs, and spinal cord.
A turtle can however fracture or break their shell.
Unfortunately, it can be a devastating but common injury in pet turtles.
Fractures of breaks can occur from falling out of their tank, being dropped, or being stepped on.
There are two main types of shell injuries:
- Depression fractures.
- Missing shell fragments.
In a depression fracture, there is a fracture along the midline of the carapace (i.e. the top part). This can cause damage to the spinal column. Sometimes these injuries heal on their own, as a turtle shell can repair itself.
Missing shell fragments can range from a small piece that makes no difference to a very large piece that could be fatal.
If your turtle cracks its shell, the first step should be to take it to a vet. The vet will perform a physical exam and will likely take radiographs to see what is broken and assess the degree of the injury.
For mildly displaced fractures the vet may use a method as simple as adhesive tape. When taping is not an option, bridging is a surgical process that involves plate-like implants being fixed to the shell.
Some vets use rigid, semi-permanent dressings like resins, glues, cements, and acrylics. Some of these materials contain chemicals that are toxic to turtles. Due to their toxicity levels and long-term negative effects it is best to not use these techniques.
When a turtle’s shell is injured, it is important to keep it out of water. Water often contains algae or bacteria that could infect the injured area. This is a process called “dry docking”.
Dry docking is a term for keeping the turtle from submerging itself in water.
After a shell fracture the return to water can be difficult. It depends on where the shell is fractured. The main goal of your turtle’s recovery period is to restore sufficient function so that they can survive and live comfortably.
Because many turtles require water for hydration and feeding, fluids may have to be provided to the turtle during this “dry docking” period.
Are Turtles Born With Shells?
Yes. Every turtle is born with their shell. Unlike other reptiles that shed, a turtle will have just one shell for life. It grows as the turtle grows.
So how does this shell grow?
There are two parts to a turtle’s skeleton:
- One is the exoskeleton with the dermal bones, which contains the shell.
- The second is the endoskeleton, which contains the inner skeleton.
Both of these skeletons develop when the turtle is in the egg, before hatching.
The mother turtle lays her eggs very early in the development of a turtle.
After the egg is laid the embryos then develop a supportive structure called a notochord. At the same time, structures called somites develop too.
The first signs of the embryo developing a shell appear when a ridge forms on the side surface. This ridge then extends to form the outer edge of the carapace. It is called the carapacial ridge. At the same time, the turtle’s bones are forming too.
Their ribs are covered by the carapace where the outer layer of skin would normally be.
Unlike many reptiles, the ribs do not extend to the bottom of the turtle to protect the heart and lungs. Instead, they remain integrated inside the carapace. The top parts of the vertebrae bones also fuse with the carapace.
The carapace and plastron are then overlain by keratinous scales.
Turtles have 50 dermal bones that are not found in any vertebrate order other than Tortoises.
An adult turtle will have 59 bones in their dermal layer. Forty of these bones belong to the top of the shell, and nine belong to the bottom.
Growing A Shell
- The mother turtle lays her eggs in the early development of a turtle.
- The embryo develops the notochord and somites, which eventually lead to the formation of the spine.
- The carapacial ridge forms and the embryo now looks more like a turtle.
- The carapace (i.e. top of the shell) grows and the bones start to form.
- As the carapace is growing, the plastron, ribs and vertebrae also form.
- The ribs continue to grow in the carapace.
- The ribs connect to the vertebrae, and the spinal column is fused to the carapace.
- Finally, scales cover the carapace and plastron.
A turtle’s shell is an important part of their body. It is part of them, just as much as our skeleton is a part of us. It includes many vital bones and storage areas for water, fat, and waste.
Why the shell evolved and what its function was has been heavily debated, but whatever the historic purpose, the shell of a modern turtle is important for it to survive.
Their shell protects vital organs from predators and includes many nerves and bones. Shells are covered in hard scales called scutes, which can be as hard as bone.
If a turtle’s shell is fractured or injured, it could be fatal. It is important that owners understand how essential the shell is, and why turtles shouldn’t be dropped.
What is your favorite fact about turtle shells? Let us know in the comments below.