Turtles are undoubtedly one of the most successful species to evolve in nature.
Turtles can live for hundreds of years, making them one of the longest-living animals on the planet. Once they achieve full bodily status, turtles become masters of survival, possessing a strong defensive shell that intimidates any potential foe. All these feats are attributed to their unique, sturdy shell.
Is a Hard Shell the Key to a Turtle’s Invulnerability?
Crocodiles are one of the few creatures capable of directly breaking a turtle’s shell
A turtle’s shell is the nightmare of countless predators – a feast that cannot escape and cannot fly is right in front of them but remains untouchable. No matter how strong their teeth are, it is incredibly difficult to penetrate this tough shell.
You might have heard the tale of eagles preying on turtles: the eagle swoops down, grabs a turtle, flies high, and drops it to shatter the shell before consuming the flesh inside. However, in reality, most eagles only target smaller turtles; they directly use their sharp beaks to poke into the gaps of the turtle’s shell and then tear at the flesh to eat.
When confronted with an adult turtle, eagles typically do not attack directly. A fully developed turtle shell is hard and smooth, making it difficult for eagles to grasp it with their talons. The process of “butchering” a turtle takes an eagle a long time and considerable effort, so they prefer to catch a few rodents or rabbits instead.
In nature, crocodiles are among the few creatures capable of directly breaking a “complete” turtle shell with their powerful bite. However, there are many instances where crocodiles find themselves powerless against the hard shell.
Here, we must mention a common factor: The biting force varies among different crocodile species, and turtles have diverse body structures.
Generally, most turtle species have a slightly domed shell – a structure that makes it hard for predators to bite and crush. However, to facilitate underwater activities, many aquatic turtles develop relatively flat and lightweight shells, which do not offer as strong a defense as terrestrial turtles.
As a result, even ferocious crocodiles seldom “pick fights” with turtles that have hard shells, opting instead for river turtles.
Crocodiles tend to target river turtles more often.
Additionally, animal enthusiasts might note that the jaguar is the only other fearsome creature besides crocodiles that can bite through a turtle’s shell.
However, in reality, jaguars only hunt sea turtles. When sea turtles come ashore to lay eggs at night, jaguars take advantage of this vulnerability, biting at the turtle’s neck until it dies.
The reason jaguars can enjoy sea turtles as a regular meal is that sea turtles cannot completely retract their heads and limbs into their shells. Living in the ocean year-round, sea turtles have fish-like shapes that reduce drag and resistance in the water, allowing them to swim faster and more easily.
However, this also means they lose the ability to “shrink.” In the ocean, the scales on their heads and limbs can generally protect them, but they become ineffective on land.
Thus, it is impossible for jaguars to “bite through a turtle’s shell” to kill a sea turtle. Jaguars can only attack when sea turtles are in their most vulnerable reproductive period, exposing their weaknesses.
Sea turtles cannot fully retract their heads and limbs into their shells.
In summary, in the natural world, no animal can directly attack and break a turtle’s shell.
The Nightmare of Experts
In Asia, there is a type of turtle that can be called the ultimate master of the strategy “withdrawing for defense.” They belong to the genus Cuora, also known as Asian box turtles.
The defensive mechanism of turtles.
From the image above, you can also see that when this turtle enters defense mode, its limbs and head retract completely into the shell, forming an almost invulnerable “ball.”
This “comprehensive lockdown” model is very similar to the ability of the nine-banded armadillo to curl into a round ball. The hard armor of the nine-banded armadillo is so formidable that there have been instances where a ricochet from a bullet has “killed” people.
However, from a biological perspective, the turtle shell and armadillo armor are two different models.
The armor of the armadillo is a hardened bony plate formed through dermal ossification, similar to the scaly armor on a crocodile’s back. A turtle’s shell consists of a dorsal and ventral shield. The shell is divided into two layers: the inner layer and the outer layer, with the inner layer being its skeleton – including the rib cage and spine. The outer layer is made of keratin or hard skin originating from the epidermis.
The two structural layers are arranged in a staggered manner, adding overall strength to the turtle’s shell. While the armadillo’s armor and crocodiles seem covered by a chainmail layer, a turtle’s shell is an advanced version of “chainmail and plate armor” with multiple internal and external layers.
Nevertheless, scientists focus more on researching the mechanical properties of the structure and the biological applications of the turtle’s shell.
Another mystery that researchers are very interested in is the evolutionary process of the turtle shell.
Throughout the long history of the Earth, what species did turtles evolve from? What factors have driven the complex structure of the turtle shell to be enhanced to its current state? These are questions that zoologists and paleontologists are eager to answer.
From giant turtles to small freshwater turtles, the turtle has given rise to countless “miraculous” variations during its evolution over hundreds of millions of years.
Nowadays, scientific experts can only study through fossils.
However, over 100 years of archaeological exploration have increasingly baffled scientists regarding this species. Some major discoveries about ancient turtle fossils have completely “slapped” previous research conclusions in the face.
For instance, in 1887, a 200-million-year-old fossil was discovered in Germany. This ancient creature, named “Proganochelys,” had a fully developed dorsal shell, leading scientists to conclude it was a precursor to modern turtles.
And because its skull had a complete temporal region, turtles were classified under the subclass Anapsida (a group of animals with amniotic membranes and skulls without temporal fenestrae near the temples).
However, a fossil known as Eunotosaurus was also excavated in South Africa. This 260-million-year-old ancient creature shows that its limbs, carapace, and ribs were in the process of developing long and wide. This indicates a turtle in the process of evolution.
However, this fossil has both upper and lower temporal fenestrae in the skull, leading to the conclusion that both Eunotosaurus and turtles should be classified under the subclass Diapsida. But according to current biological science, there are virtually no creatures that can belong to both subclasses Anapsida and Diapsida simultaneously.
Skull (top) and postcranium (bottom).
Moreover, there are contradictory findings regarding the aquatic and terrestrial aspects of turtles.
Currently, based on breathing patterns, movement styles, and the structure of the turtle’s ventral shell, experts deduce that turtles originated from aquatic animals, then moved onto land and evolved. But based on the Triassic turtle fossils excavated, scientists found that they all lay within the continental strata.
There are many archaeological discoveries and scientific research conclusions that cannot be similarly explained; these contradictory findings have made the origin of turtles a source of confusion and a shared nightmare for researchers for over a century. Therefore, experts continue to strive to unearth more fossils and conduct advanced analyses and studies to find reasonable answers.
