Turtles and tortoises are the only reptiles that have tough, bony shells. This solid shell has an outer layer of scutes which are made of hornlike material called keratin. The inner layer is made up of bony plates.
We all know that turtles have shells. If someone is shy, we often refer to them as hiding in their shell. This comes from the idea that turtles stick their heads under their shells when they feel threatened or nervous.
While most of us can identify a turtle immediately, many of us have no clue what their bodies are like underneath that tough, exterior shell.
Well, this shell is there for a reason. It acts like a suit of armor, protecting the turtle’s body. The domed part of the shell is known as the carapace while the flat layer, underneath the belly, is called the plastron.
Okay, that’s all good and well to know but a common question remains: do turtles have a backbone? Well, we are going to find out this and much more about turtles in this article. Together, we will study the anatomy of a turtle and how its skeleton differs from other reptiles.
A Turtle’s Skeleton
As we now know, there are two parts to the shell of a turtle: the upper portion (carapace) and the bottom half (plastron). Both of these shells are made of multiple bones that have fused together.
The carapace is made up of about 50 fused bones including the ribs and vertebrae. The plastron includes the fusion of bones such as the clavicles (collar bones), the bones between the clavicles, and some sections of the ribs.
Although the carapace and plastron are sealed along the sides, there are suitable openings on each end so the turtle can poke its head out as well as its four leathery legs and tail.
In some cases, this leathery skin around the openings has extra tough scales for additional protection.
The carapace and plastron are joined by a bony bridge along the side of the turtle. Some turtles actually sport a moveable joint which is most typically found in the plastron.
This acts as a hinge, allowing the turtle to pull its carapace and plastron together tightly. This usually happens when the turtle reacts to something and retracts its body into its shell.
And these shells are not just fused bones. As a matter of fact, a turtle’s shell also has a blood and nerve supply. Therefore, if the shell is injured or damaged, it can bleed and cause a turtle pain.
The shell is covered with a layer of keratin. That’s right, this is the same kind of material that makes up our fingernails and toenails and even horses’ hooves. This keratin is arranged in patches known as scutes.
A turtle’s carapace tends to have 38 scutes whereas the plastron will sport twelve to fourteen. These scutes will then form a kind of pattern, staggering over the bony plates resulting in a more rigid shell.
Of course, there are different species of turtles. Various aquatic turtles, such as sea turtles and soft-shelled turtles, can have fewer bones in their carapaces. In this instance, the scutes are replaced with leathery skin.
As a turtle’s shell starts to grow, its number of scutes typically stays the same. However, the size of these scutes do change. In some species of turtles, old scutes are shed before being replaced by newer, larger ones.
In species such as wood turtles, box turtles, and tortoises, scutes can grow bigger in diameter when new keratin is formed. To determine the age of some turtles, the “growth rings” of turtles have been studied.
Here are the main components of a turtle’s skeleton:
- Eye socket
- Long, flexible neck
- Shoulder bones
- Backbone (spine)
- Rib bones
- Hip bones
- Inner bony layer
- Carapace (upper shell)
- The plastron (lower shell)
- Outer layer (exoskeleton/shell)
Does a turtle have a backbone?
So, turtles have very tough shells made from fused bones. When we consider a turtle’s backbone, it could be considered that they have two backbones.
Yes, while one is not a pliable sort of spine that a turtle can bend in different ways, it is durable and can withstand severe bangs and knocks. This is what makes a turtle one of the strongest animals and longest living creatures on Earth.
The sturdy shell of a turtle is firmly attached to the bones of its body. Therefore, just like a snail, a turtle is stuck to its one and only shell for life. But, even with this shell, a turtle does indeed have a backbone and all the bones required to form a complete skeleton.
Inside a turtle, there is a jointed endoskeleton and this works with muscle power, just like humans. However, the turtle also has an exoskeleton in the form of its shell, unlike humans.
All of the world’s 220 species of turtles and tortoises have spines and bony endoskeletons. And most of them, but not all, also have armor-plated exoskeletons.
As we mentioned, those that do not have this tough exoskeleton have coatings of tough, leathery material instead.
Tortoises prefer dry land. Therefore, they have very sturdy, tough feet for walking as well as very sharp claws. Turtles, on the other hand, prefer water so their legs are more flipper-like. They use these like paddles as they swim. Then some turtles are equally happy on land or in the water.
Some live their whole lives at sea while others spend most of their time on land. Their bodies and skeletons have evolved in certain ways to deal with the demands and way of life that water or land offers.
Like all reptiles, turtles are cold-blooded vertebrate animals. However, they differ from their lizard and snake cousins due to their backbones and endoskeletons that are reinforced by solid exoskeletons.
The turtle clan has not changed much in the last 175 million years. With an endoskeleton and an exoskeleton for protection, we wouldn’t be surprised if they survive another 175 million years without much variation.