Turtles are a very particular type of shelled reptiles that grow to different sizes depending on the species, and even though all species have a body with a shell, some of them have softer shells and some have harder ones. The Soft Shell Turtles, for example, have shells that are leatherier and more pliable. But other species, like the Snapping Turtles, have harder shells. Shells, are typically made of bones, covered by a leathery skin or hard plates. When a turtle feels threatened, the most common behavior is to retract their limbs and head inside of the shell for protection, however, some species are not able to react in said way, so they rely on their ability to bite really hard when they feel threatened. Snapping Turtles, for instance, to serve their name, can actually snap and bite off a finger when they are provoked.
Why the shell?
The exact reason as to why turtles have shells is not known. Some Swiss researchers say the reason is related to survival, being able to very quickly hide their legs and head in their shell definitely keeps them safe from predators, and also for prey capture as they are also able to push their head and neck forward objects to capture unsuspecting animals. This researchers team studied a fossil, the Platychelys Oberndorferi, and saw that the turtle’s neck bones were able to pull the head next to the side of their body. However, other Platychelis species could pull their necks in a vertical direction. Which lead the Swiss team to conclude that the ability to retract their necks into their shell is definitely one that came with evolution.
Given turtles are not a fast reptile, hiding became their best defense to keep themselves from possible threats. However, the shell is not a guaranteed absolute protection, some predators are able to crack them open and feed on the turtle’s flesh. Some birds prey turtles, they catch them and then drop them from a height, just so the shell cracks. But only small-medium sized turtles, as some big turtles are not manageable by birds. Is probably not the ultimate form of safety but hiding in their shells provides the turtles with a sense of security in stressful times.
The evolution of the shell is probably advantageous, and we say this because there is a reason why turtles have retained this feature through several generations and species, making them some of the longest living organisms in the planet. Most likely the shell assists with the sit-and-wait feeding lifestyle turtles have, where they can retract their heads, blend with their surroundings and then push their head out to capture unaware prey, so it is an adaptive feature. However, not all turtles are able to retract their heads and limbs in their shells, as we mentioned before, which is the reason why researchers think it is a behavior that came with evolution to protect them from predators or injuries in general. Both, earth or water turtles, use elements from their environment, like dirt, plants, or algae, to blend and camouflage successfully.