The tortoise has a serious job to do every single day of its life, it has to carry its house around on its back! This often leads tortoise and turtle owners to wonder about how the tortoise feels about this arrangement and if it can feel its shell at all?
Can tortoises and turtles feel the shell? Absolutely yes! Tortoises and turtles feel their shell very well because there are nerves that lead back to their nervous system. They can feel their shell being stroked, scratched, tapped, or otherwise touched. Tortoise and turtle shells are also sensitive enough to feel pain.
use it to absorb This is why your tortoise may love to be stroked or scratched gently on the outside of their shell.
So, let’s dive into all things shell-like and explore not just the ability to feel through the shell but the basic evolution, biology and purpose of the shell and much more.
An Introduction To The Tortoise & Turtle Shell
The turtle shell is a shield which is found on tortoises, turtles and terrapins though if you asked a zoologist, they’d say “they’re all turtles”. It’s designed to protect all of the interior organs of a tortoise’s body and in some strange cases it has even evolved to protect the head of the animal.
The shell is made out of a modified bone (which is similar to the bones in any other reptile not just turtles) and it consists of skeletal bone but also something called dermal bone, which is bone that is formed by accretion within the dermis (skin) of the tortoise. Unlike skeletal bone – you can’t find any cartilage in dermal bone.
If you’re thinking, do humans have any dermal bone? They do. Our clavicle (the collar bone) is an example of this kind of bone. In fact, almost all fish, mammals, etc. as well as reptiles have some form of dermal bone.
Unlike some other matters relating to tortoises, the shell has been studied extensively. Why? Well, because it makes it easy to identify the species and gender of a tortoise and it helps scientists to better understand the history of tortoises and the movement of tortoise populations.
While the shell of turtles is not, generally speaking used by human beings – the hawksbill turtle’s shell which is known generically as “tortoiseshell” has been used as a decorative material.
Some Of The Important Bits Of A Tortoise’s Or Turtle’s Shell
This is a brief overview of the major construction of a turtle’s shell and it isn’t intended to go into too much depth. There are three key components of the shell: the carapace, the plastron and the scutes.
The carapace is the big piece of shell on the back of your tortioise. It consists of a fusion of derbal bone with the tortoise’s ossified ribs. In essence they’re the spine and ribs merging with the skin to provide the hard exterior for which tortoise’s are famous.
On the outside of the carapace are scutes, which are the little plates that decorate it and which are not made of bone but rather from keratin (that’s the same stuff as found in rhino’s horns, your hair and nails and it’s fairly common in other animals too). These are designed to add an additional layer of protection to the carapace.
Not every turtle is born equal but the majority of turtle species (including all tortoises) have these scutes. There are, however, some aquatic species that have shed the scutes completely and now they have only an uncovered shell.
One odd thing about this development is that most other tetrapods have their shoulder blades on the outside of their ribcage but turtles keep theirs on the insides and they are linked to their ribs. This means that turtles don’t need intercostal muscles (the muscles between the ribs) either and thus, they don’t have them.
The oldest known “turtle shell” appears to have been on a reptile in South Africa around 260 million years ago, which very much upset zoologists at the time of discovery because at that point, they were positive that turtles had only arrived on the planet 220 million years ago.
Nowadays, it’s agreed that they represent the most important “first step” in the proud lineage of turtle-like creatures that carry shells on their backs. However, it’s still not entirely certain that these Eunotosaurus creatures were forebears of the turtle or not.
The plastron is distinct from the carapace and it runs around the belly of the animal. What’s peculiar about the plastron is that it appears to have evolved entirely separately from the carapace and then at some unknown point in time they joined together at the sides.
It contains the bridge of the shell and it is very similar to the collarbones (clavicles) of other tetrapods. The rest appears to be very similar to the group of bones called gastralia which are found in other reptiles, particularly crocodiles.
Some people describe the plastron as an “exoskeleton” but this isn’t accurate and the plastron contains several features that make it, clearly from a biologist’s point of view, not an exoskeleton.
The plastron is, in fact, quite frustrating to biologists because they can’t quite work out how it evolved though many zoologists have tried to crack this puzzle and there are certain clues in the fossil record – the origins remain, for the moment at least, completely unclear.
There are competing theories in the evolutionary zoology world and given that they can’t all be right (given that if one were true, the other would be demonstrably false) we won’t hazard a guess here as to how this peculiar piece of anatomy came about.
What we can say is that in some turtles there’s a sort of hinge that appears in the plastron that allows a turtle to completely encase itself (or almost) in the shell.
In other species of turtle, the plastron is adapted based on the sex of the animal with females having a convex shell which makes it easier for males to get on top to mount them.
There are also scutes on the plastron though they run down the central seam and it’s said that they’re among the most useful when it comes to identifying a turtle or a tortoise.
Fun fact: the Chinese once used a divination technique involved the turtle’s plastron it was called plastromancy and it was practiced during the Shang Dynasty. Interestingly, the plastromancy remains that exist today from that period bear some of the very earliest examples of Chinese handwriting!
The scutes are the least complex bit of the shell. They are, as we’ve touched on before, made of keratin. They each have individual names and they tend to be the same in most species of turtle or tortoise.
Related article: Tortoise Anatomy: What they are made of and why
What’s The Difference Between A Tortoise’s Shell And A Turtle’s Shell?
This is where the major difference between a tortoise’s shell and a turtle’s shell comes into play. A turtle’s scutes must be shed on an annual basis. This is because they are constantly submerged in water and are prone to a myriad of infections and parasites.
By sloughing the scutes and then completely re-growing them, the turtle stays fresh and clean and at less risk of serious diseases.
In the case of a tortoise, however, this isn’t the way things work. A tortoise cannot shed scutes and thus it doesn’t regrow them.
Related article: Can tortoises and turtles live without their shell?
While a turtle will shed its scutes and thus can grow new scutes as it gets larger, when a tortoise gets larger, the whole shell sort of moves upward and a new layer of scutes are grown around the base of the existing shell.
This is quite important to understand because it means that damage to the scutes or infection in the scutes can be much more dangerous to a tortoise in the long-term than it is to a turtle which will eventually, replace the damaged scutes.
Does A Tortoise or Turtle Shell Have Nerves?
It’s kind of a sad story but when human beings first laid eyes on tortoises and turtles they assumed that as these outcrops of their body where made from hair or possibly bone, they wouldn’t have any nerves.
Unfortunately, as human beings often do – they felt that this gave them permission to do fairly horrific things to the turtles and tortoises of the time. They would drill through the shells, for example, and then braid them together.
The people of those days were very, very wrong.
In fact, a tortoise has nerves throughout the carapace, and it is an incredibly sensitive part of its body. While it is, perhaps, not quite as sensitive as the skin – it is living tissue with nerve cells present and it’s sensitive enough that they can feel pain or pleasure through the shell.
Related article: No! Please don’t paint that tortoise shell!
While not every turtle or tortoise enjoys being stroked or scratched on the shell, rather in the same way that not every human being enjoys being hugged or tickled, many do. In fact, if you check out the video below you can see a tortoise that’s absolutely ecstatic to be introduced to some young children.
So, if you feel like giving your tortoise a bit of a stroke, go right ahead, though as you might know, tortoises can be a bit anti-social, so, if he hisses and runs away don’t be offended. They’ll be back again sooner or later for you to give it another go.
However, now that you know that it’s entirely possible for a tortoise to feel actual pain through their shell – you also know that you must never knock on a tortoise’s shell or hit it or drop anything on it. It’s the same as hurting any other animal, even if it doesn’t do such obvious physical damage because the scutes are hard.
How Does The Shell Stay Healthy?
Given that the shell is made of bone and keratin, it needs quite a bit of calcium to thrive. Calcium is the basic building block of both these materials and tortoises need quite a lot of it in their diet. In general, it is quite possible for a tortoise to get all the calcium it needs as long as it is eating dark green, leafy vegetables for about 80% of its intake.
However, if a tortoise is unable to get enough calcium through natural sources – it is also possible to add the mineral to their feed and this comes in a powdered form. It’s important to be careful when adding calcium to their meal though as it appears to have a very bitter taste which can stop the tortoise from eating altogether.
Calcium is also essential for the development of a tortoise’s nervous system and, in part, the reason that a tortoise can feel through its shell is that there is calcium in a tortoise’s diet. If it doesn’t get enough calcium then the shell, the skeleton and the nervous system can all suffer.
It a tortoise is calcium deficient for a long period of time, it will probably die, and the death will be very unpleasant.
To make things complicated for tortoise owners – dietary calcium most outweigh the amount of dietary phosphorous consumed. For some reason phosphorous (which is needed in the tortoise’s body too) blocks the uptake of calcium in the body, so if the tortoise gets too much phosphorous it can appear to be calcium deficient even though it is not.
Finally, in order to use the calcium effectively in their bodies a tortoise must also have a plentiful supply of Vitamin D3. Fortunately, tortoises are capable of making their own vitamin D3 and you shouldn’t need to give a tortoise a vitamin supplement as part of its diet.
In order to make this vitamin all the tortoise needs is sunlight and a little heat. As long as it can bask regularly in sunlight (or artificial light containing UVB) and the temperature is warm enough – a tortoise will be just fine for vitamin D3.
With pet tortoises, it is sometimes hard to tell which of the three (calcium deficiency, phosphorous excess or vitamin D3 deficiency) is the underlying problem for the tortoise and it may require a trip to the vet to work it out.
A Strange Tradition Using Turtle Shells
One unpleasant but now, thankfully, defunct tradition of using turtle-shells could be found among the Torres Strait Islander peoples of the 19th century (and thereabouts). They made masks to cover their own faces out of turtle-shell plates.
They sewed them together and used a fiber underlay to form a coherent pattern. The eyes in the mask were also made of shell but seashell and not turtle shell. These masks are highly sought after by museums and you can see one in the British Museum collection online here.
Can tortoises and turtles feel the shell? Yes, of course, they can. If they couldn’t both feel the shell and feel through the shell, they would be at a serious disadvantage compared to other animals and it’s possible that they might not have survived as a species without the ability to feel.
The shell is actually quite a complex organ and its purpose is to keep the occupant safe. Of course, because of its complexity it’s also at a slight risk of damage or infection and if that happens, it’s vital that you take corrective action because your tortoise is depending on you to keep it safe too.