| abstract
| - In Neocene reptiles have made one more resolute attempt to win a sea inhabitancy. Warming of climate in Neocene epoch, and also the mass extinction of cetaceans, pinnipeds and many other sea inhabitants had permitted them to develop pelagic habit of life. In tropical latitudes of Pacific Ocean the huge sharkodile, one of last species of crocodiles reigns. Except for it, various turtles live in sea. They are not descendants of sea turtles of Holocene epoch. Some species of sea turtles of Neocene descend even from tortoises. The algal turtle from Tanganyika Passage separating Africa and Zinj Land is those, for example. But this reptile does not leave far from the coast. But other turtles have developed true pelagic habit of life. They meet at open ocean far from coast, and need the ground only for egg laying. Water literally boils under impacts of mighty flippers, when one of such turtles emerges to the ocean surface to make some breaths. It represents an impressive show: the body is up to five – six meters in length at width over two meters. And the span of huge forward flippers even exceeds the general length of the reptile. They are very similar to wings of huge bat, hence the name of the turtle – the bat turtle. Some loud breaths follow, and the giant plunges in water again. Having emerged to the surface and having recovered breath properly, this turtle may not emerge till two hours. It even sleeps hanging in thickness of water, and only slightly moving by flippers. The body of the bat turtle keeps the flattened streamline form characteristic for turtles, but has no main feature of turtles – firm armour. Instead of corneous scutes it is covered with thick rough skin, as at the leatherback turtle (Dermochelys) extinct to Neocene. But bat turtles are not lineal descendants of these animals – they descend from one species of freshwater turtles of South America. The heavy armour is not necessary for this reptile - it prevents to swim, and speed protects it from enemies, but not only it. The principal organ of movement of this turtle is the pair of long forward extremities similar to wings. Flapping them up and down, the turtle can swim accelerating for a long time the speed more than 30 kms per hour, and at the short distance it even may accelerate up to 60 kms per hour. Shoulder and forearm at this reptile are rather short, but hand and fingers are very long: they amount more than half of length of forward extremity. Bones of fingers are wide and flattened, connected by elastic skin membrane, and the short thumb is not connected by membrane and has some mobility. With its help the male keeps the female at pairing, and the female clings to ground creeping out to the land for egg laying. The back edge of forward extremity is joined to side of turtle with the help of rag of mobile and extensible skin. This feature makes the bat turtle very similar to gigantic bat swimming under water. Back extremities of the reptile are modified to short and wide flippers serving for turns and maintenance of balance. Their length hardly probable makes third of length of forward flippers. The body of this reptile is colored softly dark grey color with small amount of dim dark spots on back. The bottom part of body at these turtles is light grey. Such colouring helps the animal to mask in thickness of water. But masking and speed not always can help to escape from predators, especially to young turtles. Therefore this species has one more weapon very effective against underwater predators, from large squids to the sharkodile. Already at early age at young turtles in cloacal bladders glands secreting very poisonous paralytic substance develop. It represents transparent yellowish liquid; escaping from predator, the turtle emits it out in water. When the predator swims through the cloud of such substance, receptors in its mouth and olfactory bodies appear paralyzed till some hours. Besides these turtles are able to protect themselves actively, biting the enemy by strong jaws. The adult turtle of this species having reached the maximal size does not have enemies. At bat turtle there is wide flattened head with short, narrow and high beak. They eat various food which may be found in sea. Atlantic bat turtle differs in bias to vegetarianism. It often meets by big groups at algal fields near New Azora Island, and near thickets of in Caribbean Sea. Young turtles of this species keep near to coast and eat macroalgae growing at the bottom, and adult individuals pass to pelagic life. Only females once a year come back to land to lay eggs. Pairing at these turtles takes place at open ocean. It is preceded by primitive courtship displays. At this time males chase the female and push each other away from her by body. During courtship displays the skin on head of the male becomes bright: along the side of head through an eye black strip stretches, and the throat turns bright blue color. The iris of the eye at the male is white, and it is clearly distinguished on the background of head. The winner male tries to keep the female, seizing her by beak for edge of the carapace. When he succeeds to do it, he creeps on the female and couples with it. Pairing lasts till some hours. After the pairing in organism of the female eggs ripen within approximately 5 months. They are too small for the multiton giant, but all the same they have the impressive size: length is up to 20 cm at the width about 10 cm. The clutch of this reptile may number up to 100 – 120 eggs. All turtles of this species breed in the same place – in South America, at the land area between Amazon and Hyppolite rivers. They swim up-stream in these rivers to tens kilometers far from the coast, and lay eggs at sandy riverbanks. The nest of this turtle is a hole about one and half meters deep. The female digs eggs in sand and leaves them to the mercy of fate. If 3 months of incubating pass successfully, young little turtle with the length of carapace about 15 cm hatches from egg. The hatching of young turtles passes almost simultaneously, but each young turtle should independently dig the way through the thickness of sand for itself. Such work lasts up to three or four hours. Usually it starts in the afternoon when the sun warms up sand well, and is finished up to the night. Young turtles appear in water simultaneously, form schools and swim downstream to the sea. The mass downstream migration of young bat turtles takes place at night within approximately one week, but separate singles swim downstream till about next two weeks. The considerable part of them becomes prey of fishes and other inhabitants of the river whereas schools of young turtles suffer less damage from predators. Young bat turtles grow rather quickly: till the first years of life they increase 2 – 3 cm in length; farther up to 60-years age they grow up to 5 cm per one year. At this time they reach maturity, but further their growth is slowed down. But they reach the really the monstrous size due to the large life expectancy: the bat turtle may live over 250 years. Other species of this group live in oceans: Pacific bat turtle (Pteromedusa velonectes) differs from the Atlantic congener in smaller size: the length of the adult reptile exceeds 5 meters seldom, and usually exceeds 4 meters only a little. At this reptile colouring of body is gray-blue without dark spots. Sometimes the reptile gets an appreciable greenish shade because of symbiotic green algae settling on its skin. Forward flippers of this turtle are narrower, and back ones are more lengthened, rather than at the Atlantic species. This turtle swims faster, than the Atlantic species. It also differs in greater aggression, and frequently attacks the enemy: some sharkodiles have deep scars on a body, and sometimes the tip of the flipper at them appears bitten off – these are traces of counterattacks of turtles of this species. Pacific bat turtle eats mainly pelagic invertebrates – jellyfishes and gardenersalpas. It breeds at Hawaii, swims upstream in rivers and lays eggs in soft forest ground. Dwarf bat turtle (Micropteromedusa australis) lives in the Southern hemisphere. This species, on contrary to the relatives, do not keep away from coast. It lives along the coast of Meganesia and New Zealand, and the separate population inhabits Eyre Gulf, not having contact to ocean populations of this species at all. The length of body of dwarf bat turtle does not exceed two meters. It also differs in more advanced claws on forward flippers and massive head, and its beak is not cutting, but crushing. This reptile is zoophagous – it eats molluscs, crabs and dead fishes. Populations of open ocean breed at small islands near the coast of New Zealand; for this purpose individuals from the coast of Meganesia gather to schools and cross Tasman Sea. The population from Eyre Gulf breeds at northern coast of Tasmania. For the breeding females of this population had to cross sandy shallows in the mouth of gulf till the inflow.
|
![[RDF Data]](/fct/images/sw-rdf-blue.png)