Inside Nature's Giants

Experts in anatomy, evolution and behaviour got under the skin of the crocodile, while evolutionary biologist Professor Richard Dawkins explained how little the crocodile has changed since the age of the dinosaurs.

Who: carnivore
What: eats animal flesh: fish, turtles, birds, crustaceans, mammals (baboon, impala, hyena, wildebeest, zebra, etc.)
Where & When: sealth tactic - lie and wait, daytime (less active at night - cold blooded body needs sun's heat to warm core temperature and increase muscle activity)

Interesting fact: Unique deoxygenated arterial blood flow to GI tract (using a second aorta to take blood originally destined for the lungs). This deoxygenated blood has a high carbon dioxide content, which helps lower stomach acid. By lowering the stomach pH (like an acid bath dissolving flesh), this alternate circulation may help break down food faster.

Hide: The triangular head shape allows the snout to fit within the shape of sloped bank meeting water surface, thereby allowing crocodile to hide in very shallow water with mouth near water's edge. Counter-shading colouration and rough tree-bark-like texture of skin allows additional camouflage.

Jaw action: The jaws have only a simple motion of open or close – no side-to-side movement (like the giraffe) or protraction/retraction (like the whale). They can close very quickly, trapping prey. Jaw closure is accomplished by muscles pulling from underneath the head, rather than on top of it as in most other animals. This reduces the profile of the head, allowing more stealth in hiding at water's surface without protruding above waterline.

Grasp: Crocodiles use their teeth to trap prey. The teeth are all similar - cone shaped. There are no molars or shearing/cutting teeth to process food into smaller pieces. The pointy teeth function only to grab/trap/hold prey, or to grasp a chunk of flesh from a very large animal. For large prey, a chunk of flesh can be torn off when the crocodile grabs it in its teeth and then performs a barrel roll. This causes the flesh to be twisted off from the body.

Killing: Crocodiles can grasp the nose of a drinking mammal and pull it under the water, thereby drowning it. The crocodile can continue breathing while drowning prey because its nostrils are at the top of the rostrum (snout) and may stay above the water, while the rest of the mouth is submerged. The crocodile may also "hold its breath" while completely submerging the prey (it can probably suspend breathing longer than an mammal or bird, due to its lower metabolic rate).

In either case, the respiratory and digestive tracts must remain separated and protected from each other, so the crocodile doesn't flood the larynx (voice box) with water from the open mouth. This is accomplished by the palatal valve, a flap of soft tissue from the palate. The interlock of the palatal valve flap with the front of the larynx creates a wall that blocks food and water from entering the pharynx (food channel) or the larynx (voice box). While food and water remain behind the dam in the mouth, a separate and protected path is created behind the dam for the respiratory tract (allowing air to flow from the nose to the trachea).

Swallow: Small prey can be swallowed whole, including all the bones. Large pieces of an animal can also be swallowed whole. These large prey items can be accommodated in extra large and stretchy oesophagus. The trachea has an interesting S-shaped bend, which may allow flexibility for it to be stretched or pushed out of the way of an expanded oesophagus.

Stomach: The presence of occasional stones may help in digestion by mechanically breaking down the food (like a bird's gizzard - instead of grinding teeth). The stomach is fairly large and can accommodate the large whole prey item for a long time, while it is digested in acid (including bones!).

Intestines: The intestines are relatively simple and fairly short. Their function is absorption of nutrients. There was no obvious distinction between the small and large intestines.

Cloaca: The crocodile has a cloaca, which is a common chamber used by the intestinal, urinary, and reproductive tracts.

Richard Dawkins on the Evolution of the Crocodile

When one says that crocodiles have been around for a very long time what one means is they haven't changed very much for a very long time.

Presumably what it means is that they've found a very satisfactory way of life and there's no particular reason to change it.