They are the only sea turtles without a bony shell. They have a soft carapace, or shell, covered with skin which is why they are called leatherback sea turtles (Dermochelys coriacea).
Leatherbacks feed in the North Atlantic Ocean and migrate south every winter. The turtles have to know the right time to begin their migration to avoid being caught in winter storms. They have an unusually thin area of bone on top of their heads covered with unpigmented skin. This allows light to reach the pineal gland of the brain. (The pineal gland in humans regulates the daily circadian cycles of sleep and wakefulness in response to ambient light.) Biologists think that with the help of this “skylight” the turtle’s brain computes the time when sunrise and sunset are exactly 12 hours apart signaling that it’s time head south.
Leatherback sea turtles can dive to more than 4000 feet (1200 meters). The pressure at that depth is enormous. They can return to the surface without suffering from decompression sickness, or “the bends.” When you realize that leatherbacks breathe air, and they can stay underwater for hours, you have to wonder how they do it. First, why do they do it? Leatherbacks eat jellyfish which live deep underwater. The predators of leatherbacks are sharks and killer whales which don’t go that deep. So, these turtles find food and escape their enemies by going deep.
How can they go so deep and avoid the bends? As the leatherback goes down, its lungs collapse and it survives on oxygen stored in its blood and muscles. The purging of nitrogen from the turtle’s system prevents it from getting the bends when it returns to the surface. The leatherback is designed to eat, swallow, and digest jellyfish while deep under the water.
One more amazing thing about leatherback sea turtles is their synchronized hatching. Leatherbacks lay their eggs in beach sand above the high-tide line. They excavate the sand with their flippers, lay the eggs, and then cover them and scatter sand to camouflage the nest from predators. The hatchlings emerge at night and immediately race to the water. (As much as turtles are capable of racing.) The reason for the rush is to avoid predators that are waiting for them. To make sure that some of the species survive, the hatchlings all emerge and make the mad dash at the same time. So all over the beach, the baby sea turtles emerge at the same time, and the predators can’t catch them all.
How do the leatherback hatchlings synchronize their hatching and coordinate their run for the water? Scientists have found that after 51 days of incubation, while still under the sand, the turtles begin to communicate by sounds. Then on the day when they are ready to emerge and race for their lives, they give the turtle equivalent of a “ready, set, go!”
Many things about leatherback turtles show engineering design. They have skylights in their heads to tell them when to migrate. The transfer of oxygen from their lungs to their blood and tissue requires amazing engineering. Their synchronized hatching is not something they could learn by trial and error. Were these all merely chance accidents based on random mutations and natural selection, or were they designed for a purpose? The more we examine living things, the more we see design that demands a Designer.
© Roland Earnst