The World’s Most Perfectly Adapted Creatures: crocodiles, alligators and caiman
Crocodilia are arguably the world’s most amazing creatures. They are built for survival, like nothing else on the planet.
Crocodilia refers to all members of the crocodile family, including alligators, caiman, and gharials.
One of the most amazing things about them is that they have survived since the Cretaceous Period, first appearing on earth some 84 million years ago. But, once you know more about their adaptive abilities you might be more surprised if they hadn’t survived that long.
Crocodilians have seen several major climatic changes during their 84 million years on earth. They have lived through at least three ice ages, and they’ve seen several more drastic shifts in atmospheric and oceanic currents, which were severe enough to kill off many other species.
And they survived the biggest one of all: The asteroid that wiped out 75 percent of all species on Earth.
Since we’re talking about crocodilia, let’s begin with their teeth. All crocodilia have thecodont dentition, which simply means the root of the tooth is fixed firmly in a socket of the jawbone, which is a characteristic they share with mammals (the teeth of all other reptiles are fixed only in their gums). But that’s not the impressive part. Crocodilia continuously replace their teeth throughout their lifetime. It may go through as many as 3,000 teeth in its lifetime. Crocodilia teeth are conical and hollow. In the hollow spot below each tooth a new tooth is growing. As soon as the outer tooth falls out a new tooth there in its place.
Crocodilia have a four-chambered heart, another trait they share with mammals. Other reptiles have three-chambered hearts. “The crocodilian heart has a partitioned ventricle,” says Lynne Kelly, author of Crocodile. Evolutions Greatest Survivor. “One side of the heart pumps blood to the lungs, the other pumps it around the body. When the system becomes really impressive is when the crocodile submerges. If it can’t get fresh air into its lungs, it redirects the blood to the vital organs. The crocodile can control the flow so precisely that the blood goes directly to the brain and heart, where it is most needed.”
Crocodilia can stay under water for as long as an hour, but typically only ten to fifteen minutes, says Kelly. “When under water and stationary, the crocodile’s heat rate drops to as low as two or three beats per minute. Crocodile blood has a remarkable capacity to release the oxygen it carries as it is needed.”
Crocodilia can also shunt blood directly into their gut without oxygenating it. It’s believed that this non-oxygenated blood, which is high in carbon dioxide, creates high acidity in its stomach acid, allowing it to better digest its prey. Crocodilians can digest bones, horns, and feathers.
Crocodilians don’t chew their food; they just rip it off and swallow it. The “chewing” is done in their stomach. A crocodilians stomach is divided into two chambers. The first chamber is muscular and acts like a bird gizzard. Crocodilians swallow rocks, which are held in the first chamber, and the movement of the rocks helps break down the food. The rocks also act as ballast.
Crocodilia have vertical pupils, which allows for better night vision. In addition, the backside of their iris is covered with a layer of tapetum, which is reflective. Light entering the eye of animals without tapetum strikes the retina, but much of the light is reflected back out the pupil.
In crocodilians, and other animals with tapetum, the light bouncing off the retina is recaptured by the tapetum and re-reflected back onto the retina, greatly increases the animal’s night-vision.
Tapetum is common in many vertebrates including cats, dogs, raccoons. Tapetum is what makes an animal’s eyes appear to glow in the dark when light is shined on them.
Crocodilian eyes also contain a nictitating layer, which is essentially a transparent eyelid, which protects their eyes when they’re underwater, but still allows them to see.
Crocodilian skin is composed of scales made from keratin, which is the same protein as hooves and horns, making it extremely tough. These bumpy scales also act like solar panels, which absorb heat from the sun. This heat is slowly radiated back into the crocodilian’s body after the sun has gone, which allows them to maintain a higher metabolic rate and remain active far after other reptiles have fallen back into an ectothermic stupor.
And beneath their horny layer of skin, crocodilians grow small plates of bone, called osteoderms. It is safe to say that crocodilians are armor plated. The osteoderms have annual growth rings, like a tree, and it is possible to know a crocodilian’s age by counting the growth rings of their osteoderms.
But, crocodilians still have surprisingly sensitive skin, thanks to sensory pits which grow along their jaws and body, called Dermal Pressure Receptors (DPRs). The DPR look like small black speckles on the skin, but they are filled with bundles of highly sensitive nerve fibers, that can feel the slightest disturbance in surface water, which allows them to detect prey and danger, even in total darkness.
One of the most interesting things about crocodilia is that their sex is determined by the temperature of their nest during incubation. Nest temperatures between 90 to 91 degrees will produce male alligators. Eggs incubated between 82 to 86 degrees will produce females. Eggs incubated between 87 to 90 degrees will produce a mixture of males and females. Nest temperatures below 82 degrees, or above 93 degrees may cause the incubating eggs to die.
When the alligators are about to hatch, they start chirping while still inside their shell. This signals the mother, who is usually nearby guarding the nest, that they’re about to hatch and the mother will come back and open up the nest.
After hatching the mother will carry her babies, inside her mouth, back to her den. In the wild, baby alligators will stay near their mother’s den for their first year, and sometimes longer.
Because crocodilians are cold-blooded they don’t waste any energy producing heat. Thus, if necessary, alligators can survive for more than a year without eating.
They can run extremely fast, and even gallop, if necessary. They can reach speeds of seven to nine mph, and they’ve been clocked as high as 12 mph when escaping a threat.