Reptiles all share some common traits. You may think that they are reptiles simply because they lay eggs, have scales, and are cold-blooded. While all of this is true, there is quite a bit more to it than that.
So, what makes tortoises reptiles? Tortoises are reptiles because they have scales and dry skin, they are cold-blooded, and they are descended from dinosaurs.
While that certainly proves that tortoises are reptiles, we’ve got some shocking revelations for you if you read on. The simplest definition of a reptile is a cold-blooded vertebrate (an animal with a backbone) with dry skin that may have scales or plates. But there are some reptiles that don’t fit this mold. So, how does a tortoise fit in here?
Tortoises Are Cold-Blooded
What do we mean when we say reptiles are cold-blooded? It means that they are ectothermic, meaning most reptiles get their energy from an outside source like the heat from the sun. Tortoises are ectothermic so they can’t produce their own body heat.
However, there are reptiles out there who show signs of being partially endothermic, meaning they can use food as a source of energy and create a little of their own heat. Some female pythons, for example, show endothermic abilities when they are laying on their eggs. The female will coil around her clutch and shiver, this shivering will create heat using food that she had ingested long before laying her eggs.
Birds, such as chickens, are actually reptiles, believe it or not! But it’s complicated. They are one of the few reptiles who are endothermic, meaning they use food as a source of energy and they need a lot of food.
Tortoises Have a Backbone
Though you can’t see it, tortoises have a backbone. In fact, it’s fused with their shell. A tortoise’s shell is also attached to their ribs. Their shoulders are set at a different angle because of the shell, allowing them to move freely and take in air. At the base of their backbone, where the tail starts, is where the shell stops being part of the spine, allowing the tail to move freely as well.
Not all reptiles have shells and not all of them have their bones fused with other parts of their anatomy, though. Turtles and tortoises are special. They evolved this way to give them a special edge on predators that would otherwise catch them due to how slowly they move, which is just another reason to love them.
Tortoises Have Scales
While most reptiles—including tortoises—have scales, in recent years, we have seen some species of reptiles with no scales. Some of these were natural mutations while others were helped along by humans selectively breeding. One example is the scaleless ball python.
In addition to these new species, scales can also be lost over time. It’s just like how humans can lose hair as they age. Sometimes they can get destroyed in an accident. They can also simply wear down over time. Considering the tortoise’s long lifespan, that’s understandable.
Of course, we know that tortoises have plenty of scales. This makes them reptiles. Fish also have scales but they are designed and made differently than the scales of a tortoise or snake. Their scales are much more fragile and thin, with a very shiny coloration.
Another reptile that has scales are birds. If you look at a bird’s feet you will see they have dry scaled skin, and their feathers are actually a form of modified scales that have changed over many years of evolution.
Unlike a tortoise scales, the majority of a bird’s scales slowly turned flat and long which then split at the ends, creating the feathers we see today. But how are a bird’s feathers and a tortoises scales related and how does that make them a reptile?
The Difference Between Tortoise Scales and Bird Scales
The tortoise has a strong shell and thick scales to keep it safe. A bird’s feathers are somewhat similar. They serve the same purpose, but with some benefits tortoises don’t have.
As a chick, birds are naked. When they start to develop, you will see thread-like feathers forming and prickling at the skin. Only later will these hard, prickled feathers split open and form that beautiful feathery shape.
As a bird or tortoise embryo, bristles form from tiny patches of skin cells called placodes. These placodes assist in various things, one such thing being the development of scales or hair. For this bristle to form, a group of fast growing cells collect on top of the placodes and create a cylindrical wall which is what gives us this bristle.
For a tortoise, when it is in the embryo its placode genes change. The tortoise’s skin cells only form on the back edge of the placode, which eventually forms scales.
That was a lot of scientific talk, but what it comes down to is all reptiles have placodes to develop scales or feathers. With the crazy science of genetics and mutations these placodes can form in so many interesting ways. Like with a lot of subjects we are covering here, there is a lot more that goes on. If you’re curious here is a good place to read up more on this subject.
Reptiles Descended From Dinosaurs
This isn’t a very surprising thing, just look at our beloved tortoises. The closest relatives to the dinosaurs are actually birds and crocodiles, tortoises being around third on this list. It is kind of a mystery as to where tortoises actually came in during all this, but they are related closely to other lizards and therefore dinosaurs, meaning they are part of the reptile family. And what a family it is!
Tortoise and Reptile Skulls
Another great way to tell reptiles apart from amphibians and mammals is their bones, specifically their skulls.
Reptiles, and therefore tortoises, all have what is called a diapsid skull. This comes from their prehistoric grandparents who all had this skull type. It has changed in the many years, and some reptiles such as birds hardly show it, but what is a diapsid skull and how is it different than other skulls?
In the time of dinosaurs and prehistoric reptiles, many if not all, had a diapsid skull, this means they had at least one temporal hole on either side of the skull behind the eye cavity. This hole would allow extra muscle to go through, giving more power for movements such as biting.
In modern times, however, most reptiles do still have this diapsid skull, but evolution has changed it quite a bit. The diapsid skull is to the point that many turtles and tortoises appear to have lost the back section of their holes, leaving it nearly open. Some argue that they no-longer have a truly diapsid skull, but it is still there, just much larger than their ancestors.
Birds also had a diapsid skull originally. It has changed so much over time that it is hardly visible now, if at all. While reptiles generally have a diapsid skull, due to evolution it is no longer a fully reliable way to tell if an animal is a reptile. You’d also have to remove the animal’s skin and muscles, and we personally prefer our tortoises to remain scaly and whole.
Tortoises are reptiles because they are ectothermic and have scales. They are one of the most closely related to their dinosaur ancestors, along with birds and crocodiles. They also have diapsid skulls as did their ancestors. If you would like to see a bit more information on this, we highly recommend this video which includes many details on reptiles in general. If you like really science-minded stuff, check out this explanation on reptiles and see how tortoises fit into this group.