Why do turtles have shells?

Turtles are a very strange reptile compared to other reptiles, especially in the carapace. 'Why do turtles have shells?', 'when did turtles have shells?', and similar questions that have puzzled paleontologists for centuries. In the following article, we invite you to learn about how turtles evolved and grew their unique shells.

A fossil turtle was found at the end of the 19th century, and since then the debate has raged

In 1887, a scientist in Germany announced the discovery of an interesting animal fossil. It was clearly a tortoise with a thick shell on its back and a flat bib under its abdomen, qualifying it as a tortoise, just that it had not yet developed the indented shell 'feature' of modern turtles. stop.

Not only was this a new genus of tortoise, it was also the oldest species of tortoise discovered at the time. It is called proganochelys, modern science has determined that it lived 210 million years ago, the end of the Triassic period. The fact that this tortoise was found with an intact shell has helped identify it as a tortoise, but also leaves many questions about how that shell evolved. To solve that question, we need to know when and where the shell came from on the body of the turtle ancestors.

The turtle shell growing from the chest up or from the back is a question that is a headache for paleontologists

For a long time since the late 19th century, most paleontologists believed that turtles evolved from the reptile genus Pareiasaurus. They were muscular, well-rounded, and many species in this genus had hard scales on their backs, typically bradysaurus, which lived 260 million years ago, or a newer, more developed scaled pareiasaurus than anthodon. Therefore, it is not difficult to understand when they speculate that the system of scales on the backs of Pareiasaurus species became more and more developed, at some point, they fused together, becoming the shell on the back and then connecting with the bones. rib below to form a complete carapace like what we see today.

 Bradysaurus

It sounds reasonable, but it's not that simple. By the 1920s, when science was more advanced and paleontologists studied more deeply the process of formation and development of organisms from fetus to adult, they realized that the ribs in front of their chest rafters, then join together to form the plastron (the 'bib') and then extend this structure up the back, forming the carapace (the dorsal carapace). And these two combine to form a complete shell. So some scientists want to overturn the above hypothesis and put forward another theory that turtles develop shells from the chest first and then on the back.

One phase said the turtle shell developed from the back scales down, the other side said it was from the ribs on the front chest. Both sides have evidence to support their hypothesis. So which side is right? Fortunately, palaeontologists later found a creature that could decide whether to win or lose - a primitive turtle.

Turtles develop a 'bib' first and then have a rear shell

In 2008, paleontologists were shocked when the fossils were interesting in China. This is a creature very similar to a turtle, but it only has a bib, not a back shell. Its back is still a regular rib. Paleontologists call this animal genus odontochelys, which lived about 220 million years ago, that is, 10 million years before the primitive tortoise proganochelys was found in Germany.

The fact that odontochelys had a bib and not a shell is pretty clear evidence that turtles developed a front bib and then a rear carapace.

The discovery of odontochelys prompted paleontologists to study another species, eunotosaurus, in 2010. This species lived 260 million years ago in Africa, long before proganochelys and odontochelys. Fossils of this species were found in 1892, but most experts at the time believed it was not an ancestor of turtles because it had no shell. It did, however, have broad, flat ribs, and modern paleontologists have found it to be very similar to odontochelys.

In 2015, researchers found another primitive tortoise in Germany, which they called the pappochelys or 'grandfather's turtle'. This species lived 260 million years ago. It had broad ribs and its sternum had begun to coalesce but had not yet turned into a full armor. This primitive tortoise is evidence of the transition of turtles, from eunotosaurus to odontochelys with stiff bibs.

These studies, and findings, fill in the gaps in the history of turtle evolution. However, we still have a question to ask here, which is why turtles form that shell when such an ultra-wide frame slows them down. Surely the shell must have some effect for it to be developed by the turtle.

At first, the turtle had a bib to make 'home' easy, later it carried the 'house' with it

In 2016, paleontologists again pulled the oldest ancestor of the tortoise, Eunotosaurus, to further study and realized something interesting about this species. They evolved to adapt to burrowing. Their heads are shaped like a shovel, their forelimbs are stronger than their hind limbs, and huge claws. All of this proves that these guys have had a great digging career, they live in burrows and dig very well. This also explains why they have wide ribs.

A wide body and raft will give them more stability when digging with both front limbs. With such a wide body and short legs, of course walking will also be difficult and slow them down. So they will need more protection. And that's when the ribs began to fuse and become a shell that protects the entire body of modern turtles. Over time, the evolutionary purpose of the tortoise shell has changed. Previously it was for them to make a better home, now tomorrow has become their armor as well as their mobile home, protecting them at all times.

Above is an article about the evolutionary history of turtles, more specifically how they form their trademark shells. Hope to have brought you interesting information. Thank you for your interest in watching and wish you always love science.