How Do Turtle Shells Grow?

Have you ever thought about how turtles grow their shells? Are they born with shells? Or did they receive this gift one day out of the blue?

Turtles are born with a shell. It means the primary development of carapace and plastron is seen in embryos. The upper shell grows from the Carapacial Ridge. Meanwhile, the bottom shell is generated from a particular cell called neural crest. Later, the plastron and carapace get connected via suture.

Want more details? Keep reading.

Key Takeaways

• The primary shell development of turtles occurs in the embryo stage.
• Turtles can not grow out of the shell.
• Shells are extended skeletons.

So, This Is How Turtles Grow Their Shells

Odontochelys Semitestacea, the ancestors of turtles, only had a hard shell on their bellies. This was all they had for protection. But with evolution, these reptiles have grown shells on their backs.

This physiology of Odontochelys Semitestacea gives us a significant hint about the turtle’s shell growth. Scientists are very sure that the carapace and plastron are developed separately.

Turtles grow these hard shells when they are just an embryo. Later, the separate carapace and plastron clasp together before the turtles come out of the eggs.

See, at first glance, you will find no differences between a turtle embryo and a bird or mammal embryo. But if you look closely, you will notice the disc-shaped bugle cell called Carapacial Ridge. It is right on the embryo’s back. Yes, this is the carapace of our turtles.

Apparently, the Carapacial Ridge attracts specific cells. Take the rib cells as an example. Because of this trait, the rib formation starts just underneath the carapace. The rib cage makes the curve or shape of the upper shell.

Wait! The process is not finished yet.

The rib cages now promote protein synthesis, which converts the surrounding cells into bone-forming cells. It explains the fusion of bone and spine with the carapace.

What about the scutes we notice on the upper shell? Well, these plates are made of scales. They contain keratin, the same element we have on our fingernails.

Because of the scutes, any load on the turtle shell gets distributed properly. No wonder turtles can carry more weight compared to their size.

The growth of the plastron is different from the carapace. It starts with neural crest cells, which can produce cartilage and bone. These cells are distributed around the belly, forming the 9 plates we see on the plastron.

Now that the individual growth of the carapace and plastron is completed, the separate portions will get connected to the side bridge via sutures.

Turtle Shells Are Made of These 

From the outside, turtle shells look so ordinary. Right? But once you start going deeper, there are layers after layers.

For example, the smoothness of the shell surface comes from the keratin. Yup, the same element we have on our fingernails, turtles have it on their shells. There are no blood vessels or nerves on the keratin layer.

Still, DO NOT DARE to paint or poke turtles on their shells. Turtles can sense your touch and feel the pain.

The carapace, or the upper shell, is made of spine and bones. Scientists claim that more than 50 bones are clasped together in the carapace. No wonder the shell is so hard.

Likewise, the plastron includes the rib and sternum. The carapace and plastron are fused together, giving the final shape to the skeleton.

Turtles Can Not Grow New Shells

Turtles are born with a shell, meaning these reptiles come to this world with that bag on their back. Yes, in the early days, the shells stay smaller, and so are the turtles. As the hatchlings grow older, the shell developments are also visible.

There is no way of changing the shells. It is not a costume that turtles will slip in and out whenever they feel.

Yes, turtles shed their shells and skin just like any other reptile. But that is just the top surface, not the bones and plates.

Before You Go

Turtle shells sell like hotcakes in the souvenir shops. Can you tell if those are real? I have got several tricks to find out.

How Can You Tell If A Turtle Shell Is Real?