The Tribune... Nature

Nature

Chandigarh, Sunday, July 19, 1998

Their staple diet is jelly-fish
By Nutan Shukla

Tortoises and turtles have been found in the fossil form in deposits from the Carboniferous period, some 280 million (28 crore) years ago, which means they belong to an extremely ancient branch of the class of reptiles. According to fossil records, they were much larger than present species but they were similar in form. During the course of their development their limb girdles (the equivalent of our shoulder blades and pelvis) became enclosed by the rib cage in the very early stage. The ribs themselves expanded and became fused together, with a thick, tough, layer of horny plates on top. This arrangement of natural protection for the soft body parts was so effective that in the ensuing hundreds of millions of years there has been no appreciable change in the body structure of these reptiles.
Usually people get confused with the words ‘tortoise’ and ‘turtles’, because there is no clear-cut difference between the two. Generally speaking those species which inhabit seas and oceans and have flippers instead of feet are called turtles. On the other hand the tortoise has webbed feet with claws and lives partly on land and partly in fresh water habitat.
There are seven species of sea turtles worldwide, and out of these leatherback is the heaviest among both turtles and tortoises, reaching up to 2 metres in length and weighing upto 640 kg. They have large front flippers spreading to 3 metres. The most remarkable feature of this creature is that it has no outside shell, instead the body is covered with skin in which small hard, horny plates are embedded. So it gets its name of leatherback turtle. However, it is also called luth (meaning lute) which comes from the seven ridges which run length-wise along the body and resemble the ancient musical instrument.
A curious feature of the leatherback turtle is that though scales are the hallmark of the reptile order, and these are found over the head and flippers of other turtles, only the young leatherbacks have scales, which are lost with growth. The flesh and skin of this turtle are so highly saturated with oil that even museum specimens keep dripping oil and make permanent preservation difficult.
The most amazing thing with these giant turtles is that they live almost entirely on jelly-fish which is more than 96 per cent water. Sometimes fish, molluscs and shrimps are also found in the stomach of this turtle but it is because they were first caught by the jelly-fish.
Another famous turtle is green turtle which when adult, generally has a brownish shell, but when younger it looks very attractive. The “teenage” turtles are called sunrays because of the warm browns and yellows of the carapace, or top part of the shell.
The name of the green turtle comes from the colour of the fatty tissues, and the flesh of this turtle is the basis of turtle soup. For this reason it is the most hunted of the marine turtles, and also the most studied species.
Although they are marine animals, they must return to land to lay eggs which must be placed above high-water mark, as soaking in salt water can kill the eggs and waves wash them away. Laying takes place in a pit which the female digs with the help of its front flippers. The pit is usually about 25 centimeters across and 40 cm deep. The eggs pour out and in 15 minutes the pit is full of white eggs about the size of ping pong balls. The skin of the green turtle’s egg is tough and elastic, not fragile like a hen’s egg. The egg will even bounce when dropped on firm sand.
After the laying is over female covers up the pit carefully with the sand. She moves forward 3 or 4 metres when doing this, hence effectively disguising the exact site of the egg pit. The sand in the egg pits averages 25°C and the energy produced by the developing embryo raises the egg temperature another 5°. Some six to 13 weeks after egg-laying, depending on temperature, babies come out of the pit and dash to the sea under cover of darkness.
Dash is the proper word because while covering a distance of some 100 yards, from the egg-pit to the sea, they may face many predators, such as ghost crabs, owls, dogs, etc. Even after reaching their destination they are not totally safe because there they are preyed upon by larger fish. According to an estimate, only one or two in a 1,000 hatchlings will ever return to nest when mature.