In tropical and subtropical oceans, there live sea turtles that feed on fish, crustaceans, molluscs, and seaweed. While amphibians left the water and crawled onto land, sea turtles, as egg-laying reptiles, had long since left the water and settled on land. However, some of them returned to the water, and the descendants of this part are called "green sea turtles", which are known as "living fossils".

The green sea turtle’s body fat is green, hence its name. Green sea turtles are found around the world's warmest coastlines and feed primarily on seagrass. They sometimes climb ashore to bask in the sun, unlike other sea turtles. It is also a large reptile. Its body is more than 1 meter long, its back is brown or dark green, there are yellow spots on it, its belly is yellow, and its four legs have flipper-like feet, which can be used to paddle in the water like oars, so the turtle can swim very flexibly. .

The turtle's respiratory organ is the lungs. Every once in a while, it will stick its head out of the sea to suck in air, and then return to the water. However, even if a sea turtle does not surface for a long time, it can still breathe oxygen because it has a "belly sac" with special breathing functions. The belly sac can help it directly absorb oxygen from the sea water, so the sea turtle can breathe for a long time. The ground stays under the water.

Still, sea turtles still need to leave the water and climb to shore to give birth to their offspring. The hatched turtles bury themselves in the sand during the day and then rush to the sea after dark. They continue to develop and grow during their journey. After the sea turtles reach adulthood, they will return to their "hometown" to breed and lay eggs. To do this, they sometimes have to travel more than 2,000 kilometers in the sea.

The coreback turtle, one of the sea turtles, lays its eggs in Suriname and then returns to the coast of Ghana after an 11-month long journey across the Atlantic Ocean. In order to lay their eggs, green sea turtles along the coast of Brazil will cross 2,252 kilometers of the ocean to give birth to their children on the beach of a small island in the South Atlantic. Six months later, they will make a long journey back to Brazil. As soon as the newly hatched hatchlings enter the sea, they can swim accurately to the coast of Brazil. Why can sea turtles find their way home so accurately? How could it have such a strange instinct?

It turns out that turtles have a wonderful underwater chemical receptor in their bodies, which allows turtles to sense chemical information from the outside world. There are differences in the temperature and concentration of warm and cold ocean currents, and sea turtles use this difference to identify their paths. When a sea turtle climbs onto the beach from the rough sea, it needs to put its nose into the moist sand and smell it, as if to confirm whether it has reached its destination.

In addition, sea turtles, like some migratory fish, may have some kind of navigation system in their bodies that can use the earth's gravity field to identify directions. It can sense the direction of the earth's magnetic field, and can also refer to ocean currents and changes in different periods. Using the water temperature to correct the course is like carrying a compass, and of course you won’t get lost.

As for why turtles can find their way home, there is no definite answer. There may be many reasons that can be explained, but nature has its own reasons.

There is a kind of turtle that lives in the ocean. It is very big, with its head and limbs so big that it cannot shrink into its shell like other turtles. This turtle is called a loggerhead turtle.

Whenever a loggerhead turtle is caught by a fisherman, it will shed tears and look very sad. Was it really crying because it was sad?

In fact, the reason why loggerhead turtles shed tears all the time is to expel salt from their bodies. Because the kidneys of loggerhead turtles are underdeveloped, they rely on salt glands to expel excess salt from the body. The salt glands grow under the eyes, so loggerhead turtles shed tears constantly even in the sea!

During the mating season, loggerhead turtle mothers return to the coast where they were born to lay eggs. Before they lay their eggs, they carefully survey the terrain before coming ashore. As long as they start laying eggs, they will not stop, even if there is great danger around them, they will not pay attention. Look, how brave the loggerhead mother is!

Newly hatched loggerhead turtles are smaller than the palm of a hand, have a black back, and white abdomen and fin edges. The hatched baby turtle will peck through the egg skin with a small, hard point in front of its nose - this organ will disappear automatically after the turtle sheds its shell. Turtles from the same nest will hatch at the same time, and the baby turtles that emerge from their shells will strive to climb up using the sand that falls from the top into the empty egg skins as a ladder. It takes about 7 days for them to crawl out of their egg nests. Due to their instinct to avoid enemies, hatchlings usually crawl out of the ground at night when the temperature of the beach is low. Using phototropism, baby turtles quickly crawl towards the brighter sea. After arriving at the beach, it will look for the sound of waves, rush into the waves, and swim out with all its strength to reduce the chance of predators from natural enemies. However, street lights next to the beach can also attract these hatchlings that have just left their egg nests and mislead them into thinking that the street lights are the ocean and they cannot find their way home.

Little turtles have many natural enemies. On land, there are various animals that live on the beach, such as sand crabs, livestock, seabirds and humans. In the sea, there are also various carnivorous fish species. Because they have no defense capabilities and their shells are soft, the mortality rate of baby loggerhead turtles is very high. It is estimated that on average, only one in 1,000 baby turtles will grow up to be an adult.

Types of sea turtles

There are 7 species of sea turtles living in the ocean: leatherback turtles, loggerhead turtles, hawksbill turtles, olive green turtles, giant turtles, green turtles, olive ridley turtles and flatback turtles .

Because male turtles and young turtles don't come ashore, it's difficult to know how many turtles there are in the wild. Turtle numbers are generally calculated based on their hatching rate. Research shows that hatchlings of all species are in decline. Giant sea turtles and leatherback sea turtles, in particular, are the species most at risk of extinction of all sea turtles. The most numerous are the olive-green turtles, hundreds of thousands of which nest on the coast of India.