Are Turtles Vertebrates Or Invertebrates?

Back in your school days way back when you may recall learning all about vertebrates and invertebrates. For those of you who need a recap, an invertebrate is any animal that does not have a backbone or spinal column; while a vertebrate does have one.

And you may have wondered whether a turtle’s shell counts as its backbone, or whether it does indeed have a spinal column in its body somewhere underneath that hard shell.

closeup picture of turtle on red background

Well, this article is going to tackle exactly that, and answer all of your most frequently asked questions on the subject along the way.

By the end of the article, you will be much more knowledgeable and well-informed, and able to impress your family and friends with just how much you know on the subject.

(Please feel free to scroll ahead to any section that jumps out at you.) Here goes!

All About Turtles

Turtles are considered to be reptiles, but they do not fit the definition of being either a reptile or amphibian. They are actually more closely related to mammals than they are to lizards or snakes.

The word “turtle” comes from the Latin word for tortoise, Testudo, which means “a sheltering place”. Turtle shells were used by early humans as shelters, and so the name stuck.

Why Are Reptiles Cold-Blooded?
Why Are Reptiles Cold-Blooded?

There are over 300 species of turtles worldwide, although only around 100 of them live in North America. 

Turtles are most easily identified by their carapace (backbone), which covers their head, neck, shoulders, chest, belly, legs, and tail. The carapace is made up of two layers of overlapping plates called scutes.

Each plate has small holes through which blood can flow. These holes allow the turtles to breathe without having to open their mouths.

Each turtle also has a pair of lungs located inside its shell. This allows the turtle to take in oxygen and expel carbon dioxide.

In addition to these features, turtles have four limbs, three eyes, and a mouth. Their teeth are replaced every year, and they shed their skin each time they grow a new set.

Turtles use their sense of smell to find food, navigate, and communicate with other individuals. They have very sensitive nostrils and are capable of detecting minute amounts of chemicals in the air.

They also have a highly developed sense of hearing and can hear sounds up to 1,000 times quieter than we can.

So, Does the Turtle’s Shell Count as a Backbone? Is it a Vertebrate?

A turtle’s shell is part of its skeleton; therefore, a turtle counts as a vertebrate. So the answer is Yes, turtles are in fact vertebrates. And, according to Wikipedia, “Vertebrate” refers to any organism with a spinal column (a backbone).

And “Invertebrate” refers to organisms without a spine. So since turtles have a spine, in the form of their shell, they can and are considered to be vertebrates.

However, unlike our own bones, which contain marrow, a turtle’s bone contains no marrow. This makes it impossible for a turtle to produce red or white blood cells, making it unable to fight infections.

However, turtles are still able to get rid of waste products through their kidneys, and they are even able to sweat.

Does That Mean That Turtles Are Actually Closer to Land-based Creatures Than They Are to Fish?

No, because turtles belong to the class Reptilia, which includes all reptiles, including snakes, lizards, frogs, crocodiles, and turtles.

And while many people think of turtles as cold-blooded animals, this is not true. All turtles are warm-blooded, meaning that they maintain a constant internal temperature despite external environmental conditions.

Turtles are very different from fish, however, in one important way: while fish lay eggs hatch out into larvae, turtle eggs hatch out directly into adult form.

Are Turtles Born With Their Shells, or Do They Grow Over Time?

The majority of turtles have hard, bony shells that cover their entire body. Some turtles, however, such as tortoises, have soft fleshy shells that protect their softer parts.

Most turtles develop their shells during early development, but some species, such as sea turtles, may not fully mature until adulthood.

Why is a Turtle’s Shell So Different From a Regular Spinal Column?

Unlike mammals, reptiles have a single layer of tissue covering their backbones. This tissue is called the dermis, and it provides support for the muscles attached to the spine.

This means that when you look at a reptile, you will see a smooth, shiny surface on top of the animal’s spine. The only thing separating the two layers of tissue is a thin membrane known as the periderm.

What Makes a Turtle Shell So Hard?

To make a shell, a turtle must first deposit calcium carbonate onto itself. Then, using enzymes, it begins to dissolve the calcium carbonate to create an organic matrix. Finally, it adds minerals to the matrix to strengthen it.

How Did the Turtle Evolve to Have a Shell For a Backbone?

As mentioned before, turtles are more closely related to mammals rather than lizards or snakes. It was once believed that turtles evolved from dinosaurs, but now scientists believe that turtles evolved independently of dinosaurs.

It is thought that the first turtles appeared about 250 million years ago, during the Triassic period. Over the next 200 million years, turtles diversified into many different types.

These included:

  • Tortoises – These include the familiar garden variety turtle, the box turtle, and the snapping turtle.
  • Terrapins – These are aquatic turtles found in freshwater.
  • Sea turtles – These are marine reptiles living on tropical reefs.
  • Freshwater turtles – These are freshwater turtles found in ponds, lakes, rivers, and streams.
  • Marine turtles – These are sea turtles that spend all or part of their lives at sea.

Why Did the Turtle Evolve to Have a Shell for a Backbone?

big turtle on grass

The evolution of the turtle shell occurred predominantly because it provided excellent protection against predators.

When an animal grows larger, it needs more space to move around. A large body takes up more room, so it becomes easier for predators to catch smaller animals.

If you look at a turtle, you’ll notice that its large shell can easily protect it from being eaten by predators by hiding the turtle’s body.

This means that if a predator wants to eat a turtle, it must first break the turtle’s shell. Once this happens, the turtle will be vulnerable to attack.

This is why most turtles have shells made out of such hard substances, not dissimilar in solidness to rock and wood. The harder the shell, the better it protects the turtle inside.

Other Benefits To Turtle Shells

And as it happens, it turns out that there are numerous additional benefits to turtles besides protecting them against predators.

For example, turtles’ shells are also used to help them breathe. When a turtle breathes, it uses its shell to pump air into its bloodstream. Because turtles don’t have lungs like us, they need to use other means to keep their blood circulating in order to survive.

Another benefit to having a shell is that it helps protect the turtle when it dives into the ocean. If a turtle doesn’t have a shell, then it would be easy for it to drown.

Wrap Up

So, there you have it. Because a turtle’s shell is classed as its spinal column, it is in fact a vertebrate. We hope you’ve enjoyed learning about turtles!

Kerry White is an avid dog lover and writer, knowing all there is to know about our furry friends. Kerry has been writing for PetDT for three years now, wanting to use her knowledge for good and share everything she can with new dog owners. Kerry has two dogs herself - a German shepherd called Banjo and a chocolate labrador called Buttons. Kerry knows more than anyone how adjusting to new life with a puppy can turn your life upside down, and she wants to ease some of the burdens through her articles.

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