118 years of Trust Nature THE TRIBUNE
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Sunday, October 18, 1998
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This fortnightly feature was published on October 11

Crocodiles cannot chew. They swallow their food in large lumps
Crocodiles are the closest living relatives of dinosaurs which perished
about 65 million years ago, says Nutan Shukla
Reptiles that are useful to man

THE expression crocodile tears is commonly used to denote the false display of emotions in human beings. In fact, tears do stream down the crocodile’s eyes though we can be reasonably sure the cold-blooded creature feels no twinge of emotion. In fact, tears are the work of salt glands which work to rid the animal of excess salt as it does not sweat like we do. For many years it was believed that this was the only method by which crocodiles secreted salt.

Now comes the discovery that salt is also discharged along with the crocodile’s tongue fluid.

Australian biologists Laurence Taplin and Gordon Grigg were the first to confirm the existence of salt glands in the tongues of crocodiles. They washed the mud and brine of 29 salt water crocodiles, rinsed their mouths and dried their membranes. They then administered shots of methacholine chloride into their bellies and later siphoned the secretions that welled up from their tongues which confirmed the presence of salt.

Crocodiles are the closest living relatives of dinosaurs which perished about 65 million years ago. Adult crocodiles carry stones, weighing approximately one per cent of their total body weight, in their stomaches.

It is believed that the stones act as a ballast, enabling the crocodile to adopt the familiar, almost submerged, log-like pose. The stones may also serve another purpose. These creatures have a two-chambered stomach, the larger part of which is very muscular and usually contains a few kilos of pebbles.

Crocodiles cannot chew, and so swallow their food in large lumps. As the stomach churns, the action of the pebbles help grind the food, facilitating efficient digestion.

Crocodiles, universally loathed by humans, are, in fact, very useful to man. These large water-living reptiles keep waterways clean by feeding on decomposed carcasses, in addition to their diet of fish. Though their fearsome-looking jaws seem powerful enough to take a chunk out of almost any animal, the truth is crocodiles must rip the meat off their prey thrusting their whole bodies underwater after drowning their victims.

Fisherman once killed crocodiles because they thought the reptiles ate prodigious quantities of fish and were competing for catch. It is now known that in spite of its bulk, a crocodile possibly consumes even less fish than a stork ! The secret lies in the reptiles’ "cold-blooded" fuel-efficiency. As it uses solar energy to warm its body, it consumes very little food.

These creatures are exclusively adapted to an aquatic existence, and are generally found in lakes, rivers, swamps and estuaries. They are divided into two families, namely, Crocodylidae (crocodiles, alligators and caymans) and Gavialidae (with one member, the Indian gharial).

While, the families display similar habits, they are externally quite different. True crocodiles, caymans and alligators all have enlarged fourth teeth in their lower jaws. In true crocodiles, these theeth are visible even when their mouth is closed.

In caymans and alligators, however, the teeth remain hidden. The gharial’s most distinctive feature is, obviously, its long, slender snout and males have ghara shaped (pitcher or pot-like protuberance) nostrils because of which the gharial has got its name.

All crocodiles possess raised nostrils which allow them to breathe with the rest of their body submerged. They can also feed while submerged, thanks to an air passage with a valve, which can exclude water from the windpipe.

Crocodiles are first recorded from Triassic rocks (from 225 million years to 40 million years ago) and were the only "ruling reptiles" to survive the Mesozic Era (It lasted 160 million years, beginning with the Triassic 225 million years ago and ending 65 million years ago at the start of the Tertiary).

Crocodile females are protective mothers. However, maternal instincts are more likely to be associated with mammals than with reptiles. After mating is over she will carefully select a nest site preferably near water, in the shade of some overhanging vegetation.

Using her powerful forelimbs she will now excavate a pit into which around 50 eggs may be laid. Then earth is thrown over the eggs and for the approximately three-month incubation period she will zealously guard her eggs from predators such as mongooses, lizards and birds.

It is only the saltwater crocodile which makes a nest. When it is time for the female to lay eggs, she sweeps up leaves, twigs and earth with her tail to build a dome-like nest. The nest may be as much as 1 metre high and 2 metres wide at the base in which she lays her eggs.Back

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