The shell of a turtle is what sets it apart from every other animal. The type of shell turtles have is unique to them, and it’s also the reason why we can easily recognize a turtle when we see one. But do all turtles have shells, are there any species out there that don’t have any kind of shell? To find out the answer to this question I decided to do some research, and after a few weeks I finally found out the answer, here it is.
Do turtles without shells exist? No, all existing turtle species have a type of shell. The shell of a turtle can sometimes be soft instead of hard, but it’s still a shell, which is a vital part of the turtle’s body.
So at the moment, there are no turtles without shells, but this was not always the case. If you look at the long evolution of the turtles, you can find some of their ancestors that didn’t have a proper shell. But before we go that far, let’s start by first understanding what the shell is and looking at the current types of shells. This will help us get a better understanding of why all modern turtles have shells, and what their purposes are, and why turtles can’t live without them.
The Current Types of Shells
At the moment, the shells of modern turtles can easily be put in two very different groups, softshells, and hard shells.
Both of them are similar in structure, but there is one crucial element that makes them so different. So let’s start with what they have in common and then see what makes them different.
The Structure of the Shell
Like all shells, hard shells cover almost the entire body of the turtle, leaving out only the extremities. The shell is made out of two main parts, and two secondary parts. The man parts are called the carapace and plastron.
As you can see in this picture the carapace is the upper part of the shell, the part that covers the back of the turtle, and the plastron is the posterior part of the turtle.
The carapace is mostly made out of broad and flattened ribs that have fused together, along with parts of the backbone.
The backbone is fused with the rest of the carapace, but a significant part of it can still be distinguished from the rest of the bones, unlike the ribs that have fused completely.
Turtles are the only animals in the world that have all of their ribs fused into one big piece, every other animal has multiple ribs that are separated from each other.
There are over 300 different species of turtles, and all of them have a different shell shape, some of them have a rounder shell, some of them have a more pronounced dome shape, and some of them have almost flat shells, but all of them have the same bone structure on the inside. Even if the shell has a different shape.
The plastron is made up of nine bones and two epiplastra. Here is a list of the names of each bone:
At the moment the evolution of the plastron is a mystery. In the case of the carapace, we know that it was formed due to the fusion of the ribs and the backbone. But when it comes to the plastron there is no sure answer. The most accepted theory was discovered in the 19th century by a French zoologist, who suggested that the plastron is developed by the sternum of the turtle. But at the moment his theory hasn’t been proven.
The carapace and the platoon are the main parts that compose the shell, but the shell has two other important parts, one that connects the carapace and the plastron, and one that protects the carapace.
The Bridge
The bridge is the part that connects the carapace and the plastron, and it can be found on the sides of a turtle.
The origins of the bridge are also unknown. But most probably the bridge is also formed from fused ribs.
The bridge has two roles, to protect the sides of the turtle, and to keep the carapace and the plastron fused. Even if the bridge doesn’t do too many things, the things that it does are vital.
Up until now, everything is mostly the same for all turtle species, the following part is what gives some turtles a hard shell, and others a softshell.
Hard Shells
Turtles with a hard shell have something called scutes that make their shells harder than the rest. Scutes are made out of keratin. Keratin is the same thing that our nails are made out of.
Scutes act as a layer of protection for the carapace. Most turtles are going to shed their scutes and grow new ones. So if an animal bites them, the scutes will get damaged instead of the carapace. And since they can shed the scutes away and grow new ones, it won’t be such a big problem.
Soft Shells
Turtles that have a soft shell, don’t have scutes on their shells, instead, they have a leather-like material that covers them.
While their shells are still pretty though, they are not quite as tough as hard shells, and they definitely don’t look as resistant. But underneath that leathery exterior, they are still made out of bone.
Why Turtles Can’t Live Without a Shell
Before moving to the next part where we talk about ancient turtles without shells, I wanted to sum up in a few words why turtles can’ live without a shell.
The most important reason why turtles can’t live without a shell is that the shell is part of their body. The shell is made out of almost all the bones inside the body of a turtle. The shell is what keeps everything in its right place. Without a shell, a turtle will look like melted jello.
Even if somehow turtles managed to keep their proper shape without a shell, they would be basically left defenseless. The shell of a turtle acts as its primary way of defending itself from predators. If you take that away all turtles will basically be left defenseless.
Now let’s take a look at those shell-less turtles that existed millions of years ago.
The Shell-Less Turtles of the Past
Even if we know what modern shells are made out of, it is still not 100% clear how they came to be, but one thing is sure, at some point, there were turtles on Earth that did not have shells.
A few years ago there were two big theories about how turtles got their shells.
The first one suggested that the earliest turtles didn’t have shells, but instead, they had something similar to the scutes of modern turtles on their back. And that through the ages they gathered even more scutes, that ended up fusing with the bones underneath and ended up forming the shell that we see today.
The other theory suggested that the ribs of the ancient turtles started to extend and broaden, until they ended up fusing together, resulting in the shell that we know.
Today we know that the first theory was wrong and that the shell is the result of the ribs that extended and fused together. But the reason why this happened is still unknown.
Some of the oldest fossils have shown that the first turtles that were getting close to how modern turtles look, only had the plastron, and no carapace. Instead of a carapace, they had ribs like most animals do. The name of that turtle species is odontochelys, and it lived around 220 million years ago.
Here is a simulation of what odontochelys might have looked like.
As you can see the plastron is almost identical to the one we see on modern, full-shelled turtles, but the upper side, the carapace, is completely missing, but we can see that the shape of the shell is there.
In 2016 scientists have come out with a theory that tells us why turtles have evolved to have a shell. Some of the oldest turtle fossils suggest that turtles were not living in the water, instead, they were land animals that liked to burrow. The theory suggests that the wider ribs would provide a lot of stability for the ancient turtles as they were digging.
Wider ribs provide more stability for the trunk, and that is perfect for digging. Similar wide ribs can also be observed in other animals that like to dig burrows, the anteater for example.
The problem with wide ribs is that they greatly reduce mobility. As a result, turtles are not able to move too fast. And this means that the turtles were more vulnerable to predators. At this point, the ribs started to fuse together forming the shell as we know it. This offered turtles more protection and also allowed them to dig.
As turtles evolved they started spending a lot more time in the water, and less time digging. But the shell remains there for the moment. It’s always possible that the shape or the composition of the shell to change.
This is just a theory. There are a lot of things that this theory doesn’t completely explain, but at the moment it’s what we can get with the amount of information that we have.
Here is a short video that shows turtles evolved from normal “lizards” that had a normal ribcage to the shelled animals that we all know and love.
Related Questions
How many bones does a turtle carapace have? A turtle shell has around 50 bones. It’s really hard to see the difference between them since they are fused together, but biologists have determined that there are about 50 bones.
Are turtles born with a shell? Yes, turtles are born with a shell. When the baby turtle emerges from the egg, it emerges with a well-developed shell.
Do turtles shells heal? Turtle shells can heal minor injuries, but if the shell is completely cracked, the turtle will not be able to help its shell.
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