Month: April 2022

Crocodilians are some of the most aggressive and fiercest predators of the animal world.  The young of all species can swim and catch food as soon as they hatch, but will continue to feed on the yolk sac in the egg for at least the first several days.  As they grow, young eat insects, snails, and frogs.  Hunting mainly at night, adults eat mostly fish, but they will also attack anything that wanders by too closely, including birds, snakes, turtles, raccoons, zebra, cattle and horses.

Crocodilians often sit quietly and wait for prey to come to them, although they can be active hunters.  Three methods of capturing food include lunging for prey on land; leaping out of the water to surprise an animal then pulling it under the water to subdue it; and sweeping their open mouths from side to side underwater to catch fish.  Crocodilians do not have the ability to chew, but will tear off pieces and swallow each chunk whole.  Every part of the prey, including bones, is eaten.

Crocodilians begin mating activities when they are about eight years old.  Females tend to be a little older, and males a little younger.  Unlike many reptiles that provide no family care, female crocodilians make gentle, caring parents, protecting eggs and young, assisting at feeding times, and staying with them for their first few years.  However, there are many predators on land and in the water, and even with adult supervision, only about 10% of babies will live past their first year.

Crocodilians inhabit warmer climates, and most live in freshwater habitats, although a few live in saltwater.  They prefer shallow wetlands offering plenty of bottom rooted vegetation that attracts prey and keeps the hunter well hidden.  Gentle banks allow them to easily crawl out on land for basking and to reach egg laying sites.  Crocodilians save energy by moving around in water instead of overland because the water supports their heavy bodies.

Many animals provide vital services in their home habitats.  Alligators dig large holes in limestone river beds, called gator holes. In hotter weather, as rivers dry up, these holes stay full of water, providing water and cool places for animals to hide from the heat of the day.  Crocodilians are great scavengers.  They keep their range clean by eating any dead animals.

Very few species threaten adult crocodilians, and one of their biggest threats are humans.  They are hunted for their skins for clothing and jewelry, and various body parts used for medicinal purposes.  Bones are ground into fertilizer and animal feed.  Meat and eggs are used for food.  Sex organs, musk and urine are all used in the perfume industry.

Habitat preservation and education about their importance is needed.  Efforts to halt illegal poaching and smuggling and enhance captive breeding and wild release are being stepped up to conserve these species.  Several farms have been started to prevent the need for crocodilians to be taken from the wild, and to generate income, via tourism, for local economies.  You can visit your local natural history museum or zoo to learn more about these amazing animals.

There are between 20 and 30 recognized species of living crocodilians, who, along with birds, are the only two surviving groups of Archosauria, a group that has existed for 250 million years and includes the now extinct dinosaurs.  Key characteristics of crocodilians include an elongated, structurally reinforced skull, powerful jaw muscles, young born from eggs, and parents providing extensive care to young. 

Crocodilians vary greatly in size.  Cuvier’s Dwarf Caiman, living in northern South America, is one of the smallest species averaging four feet long and weighing 13 to 15 pounds.  The saltwater crocodile, living in brackish and saltwater habitats from southern India to northern Australia, may grow to 20 feet or more, and tip the scales at close to 3,000 pounds.  For those of us in the United States, the two commonly found species include the American alligator, living along the southeastern coastal states and averaging 12 to 16 feet and 1,000 to 1,300 pounds, and the American crocodile, found only on the southern tip of Florida, growing up to 20 feet and 2,000 pounds.

Bone structure, like the rest of the body, make crocodilians well-adapted to living in the water.  A strong, flexible spine starts at the base of the neck and runs to the end of the tail.  Tails are used to propel them through the water, and they are able to tuck their feet close to their sides, using them as rudders.  Crocodilians may look ungainly on land, but can get around easily.  Using the high walk, the animals can lift their entire torso off the ground to walk on all four legs.  Some species can also gallop on all fours at speeds up to 11 mph for short distances.  In muddy areas and when close to water, they slide on their belly, pushing off with their legs, able to quickly move into the water.

Crocodilian snout shape, size, and dentition is influenced by their prey and how it is caught.  Gharials and crocodiles have long, slim snouts for sweeping through the water catching fish.  Alligators and caiman have shorter, broader snouts with powerful jaw muscles to overpower birds, mammals, and other prey, some even larger than themselves.  The bite force in crocodilians is the strongest of any living animal. 

Bone and muscle structure have changed very little over the last several million years.  Space for the jaw muscles inside the skull is very large.  Strong muscles are designed to clamp the jaws shut, allowing the quick capture and killing of prey.

Depending on the species, crocodilians have between 60 and 110 teeth.  Teeth grow constantly and are replaced individually about every two years.  Worn teeth simply fall out as a new one grows in immediately.  Each animal can grow up to fifty sets of teeth in its lifetime.

Front teeth are sharp for piercing and holding prey.  Molars towards the rear of the mouth are used for crushing prey.  Crocodilian jaws cannot move from side to side, a requirement for chewing, so prey is swallowed whole or in large chunks.

One way to distinguish crocodiles from alligators is to look at their jaws when closed.  The fourth tooth on a crocodile is outside the jaw, fitting into a pocket on the upper lip.  Alligators and caiman exhibit no teeth when the jaw is closed.

Next week, we’ll wrap up with food, family, and conservation.

Crocodilians, a group of reptiles that have been living since before the age of dinosaurs, include alligators, crocodiles, gharials, and caiman.  For over 200 million years they have adapted to changes in their habitat and food sources.  Considered highly intelligent animals, capable of complex communication, they make attentive parents and are fierce predators.  Two hundred million years ago, before dinosaurs, these reptiles were small land animals with long legs and short snouts.  As dinosaurs took over and ruled the land, crocodilians lived in the seas.  Growing in size, some as long as fifty feet, they still hunted dinosaurs on shore.  As the age of large mammals evolved to smaller species, so did the crocodilians.  They are still considered to be some of the largest species of animals inhabiting our world, today.

Scales cover the outer layer of skin on all reptiles.  The scales on crocodilians are called scutes.  With the density of bone, they are arranged in rows set into the thick, leathery skin.  This provides great flexibility while also creating a well-armored outer covering.  Belly scutes tend to be smooth, allowing for easier movement.  Scutes down the back are heavier and contain small bony disks for extra protection. 

Individual scutes are replaced as old ones wear out.  A new, larger scute grows underneath the old one which falls off when the new one is fully developed.  Skin and scute coloration blend in with the animals’  surroundings.  Patterns and color break up the animal’s outline, making it harder for predators to identify them.  Most baby crocodilians are brightly colored and grow darker as they age.

Skin & scute colors help hide a Nile crocodile in grass, American alligators on a sandy shore, and saltwater crocodiles on a rocky beach.

All reptiles are ectotherms, regulating their body heat from their surroundings.  As the sun rises each day, crocodilians come out of the water and head for shore to lay out and get warm.  When they get too hot, they may move to a shadier area, or back into the water.  Another popular method for cooling down is to sit with mouths agape, letting the breeze blow across the moist inner surfaces to draw out excess heat.  At night, they return to the water, which cools down slower than the land.

Mud wallows are another favorite place for crocodilians to spend the day.  The mud keeps the animal’s body from heating up rapidly, as well as keeping insects and parasites away from the skin.  Scutes along their tails can be flexed open to expose the skin underneath and allow excess body heat to escape.

Crocodilians have well developed senses.  Eye pupils shaped as slits can be narrowed to keep bright light from hurting the inner eye.  The tapetum lucidum, a layer at the back of their eyes, reflects light forward, allowing for excellent night vision.  Immediately behind each eye is a small ear opening that is covered when swimming.  Crocodilians have acute hearing, able to detect both prey and predator from several yards away.  They can easily hear and distinguish sounds from their own young, as well.

Nostrils on the top tip of their snouts allow normal breathing while swimming with most of their body submerged just below the surface.  Sensitive receptors can smell food at distances of over two miles.  Their tongues are wide and attached to the bottom of their mouths, so they are not used when catching prey.  Lined with taste buds, they can distinguish sweet, sour, and salt.  Crocodilians, especially in salt water habitats, accumulate salt in their bodies over time.  Special glands on the tongue allow them to rid this excess salt from their bodies.

Crocodilians are well-adapted to the habitats they live in.  We will investigate further aspects of these remarkable animals next week.