Turtle evolution and physiology

Saturday, 22 June 2013 06:10 -     - {{hitsCtrl.values.hits}}

Marine turtles have inhabited the earth for over 100 million years. They are a successful group of animals that have witnessed the rise and fall of the dinosaurs and until relatively recently have survived in great numbers. Today seven species of these ocean dwelling reptiles remain. All of them are now threatened with extinction, mainly due to man’s destructive activities. Marine turtles evolved from large land living tortoise-like animals. Over millions of years they have become very well adapted to living in a marine environment. With their long and muscular oar-like fore flippers rudder-like hind flippers and their flattened streamlined shells marine turtles are fast and agile swimmers. Unlike tortoises and freshwater terrapins they are unable to withdraw their head and limbs into their shell. Marine turtles do not have teeth but their sharp beak-like jaws can crush tear or bite depending on their diet which varies according to species. Turtles are reptiles. They are cold-blooded and therefore the environment determines their body temperature. In the morning marine turtles ‘sun bathe’ at the sea’s surface to increase their body temperature. They have lungs and so must breathe air. When feeding, turtles rise to the surface to breathe every 20-30 minutes. At night turtles usually sleep in caves and crevices under the sea. Because they are inactive their body does not need much oxygen and so marine turtles can spend a whole night underwater without breathing. We do not know exactly how long turtles live but they are generally assumed to have a lifespan greater than 80 years. It is thought that marine turtles become sexually mature at about 30 years of age. Until maturity it is difficult to distinguish between male and female turtles. When they reach maturity male turtles develop a long claw on each fore-flipper and a long tail. The only time marine turtles leave the ocean is when the females come ashore to nest. The males spend all their time at sea and little is known about their habits. Most species are highly migratory, moving between nesting and feeding grounds, which can be thousands of kilometres apart. The way that an egg-burdened female finds her way to her nesting beach is still a mystery! Some scientists believe that marine turtles are sensitive to the earth’s magnetic field and use it for navigation. All we know is that turtles are very good at it. They are often found using not only the same sandy beach but also the very same stretch of beach they used in previous years. (Source: http://www.tcpsrilanka.org/)