crocodile

crocodile

This entry is compiled and applied by "popular science China" Science Encyclopedia

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Crocodile is a kind of carnivorous oviparous vertebrate reptile. It is the oldest reptile in the same era with dinosaurs more than 200 million years ago, and it is also one of the most primitive animals living so far. Crocodile has become one of the oldest living fossils on the earth because of its strong vitality. Crocodile is an endangered wild animal, which is listed as class I protected endangered wild animals and plants in the world. Alligator sinensis (Alligator sinensis), a Chinese specialty, is listed as the first-class wild animal under national protection. In 2003, the State Forestry Administration approved three crocodile species, namely, Crocodylus niloticus, C. porosus and C. siamensis, to be listed in the first batch of 54 commercially available wild animals.

Appearance features

Crocodile is an advanced reptile. It breathes with its lungs. Its heart is divided into four chambers. There is a bone palate on the top wall of its oral cavity, which separates the nasal cavity from the oral cavity. Its teeth only grow in the alveoli of the upper and lower jaws. These are similar to mammals, which indicates that mammals evolved from reptiles. The crocodile has two eyes at the top of its head. In addition to its eyelids, it also has a transparent blink membrane, which enables it to adapt to the water environment. Because the crocodile's nostril is located at the back of the upper end, and there is a valve in it, when it submerges into the water, the valve will automatically close, which can prevent water from flowing into the nostril. In its pharynx, there is a thin and elastic membrane. When this membrane is closed, its mouth and respiratory tract will be separated. Therefore, even if it opens its mouth in the water, water will not enter the respiratory tract and lungs. Its long and thick tail is not only a "rudder" for swimming, but also a tool for predation and a weapon for defending the enemy.

Among alligators, the largest is the alligator, with an average body length of 4 meters. The smallest is the Chinese alligator living in China, with a body length of only about 1.25 meters. Because of people's indiscriminate hunting and killing, the number of crocodiles is decreasing, and various crocodile producing countries have formulated laws to protect them. Although Alligator sinensis only lives in China, it has become a rare and precious wild animal in the world. In 1973, it was listed as a endangered species and a prohibited species by the International Wildlife Conservation Congress,

Chinese alligator has been listed as a first-class protected animal in China.

Life habit

Crocodiles usually like to live in the marshland of lakes and swamps or in the humid areas of hills and streams. Crocodiles often give people the impression that they are slow in action. Other people describe crocodiles as staggering, four legged, floating and trailing, instead of crawling forward with their bodies close to the ground. In fact, this description is an illusion of crocodile. In fact, the crocodile's hearing, vision are extremely sensitive, the body's activities are very flexible. Crocodile is also a clever animal. For example, the crocodile's method of predation is very strange. Whenever it swims in the water, it suddenly finds a small animal. It is not in a hurry to catch it. Instead, it first hides its body to the bottom of the water, and then swims quietly towards the small animal. First, it stares at each other motionlessly, then suddenly jumps up to catch the small animal. Finally, it takes it into the river with its mouth, drowns it, and then hurts Have a good meal. According to anatomical analysis, crocodiles like to eat: ducks, rabbits, frogs, mice, fish, snails and other animals.

Nile crocodiles have the habit of living with thousands of birds. The bird often lives on the sand banks of the Nile River. It and crocodile are good friends, often in the crocodile body looking for insects to eat, sometimes can enter the crocodile's mouth to eat leeches parasitic in the crocodile's mouth. Interestingly, sometimes the crocodile's mouth is closed accidentally, and the little bird is locked in the crocodile's mouth, but the crocodile does not swallow the bird. The little bird will gently hit its upper and lower jaw, and the crocodile will immediately open its mouth and let the bird fly out. Qianniao is a kind of sensitive bird. As long as it hears a little movement, it will make noise. Therefore, whenever the crocodile sleeps, the little thousand birds will sometimes "stand guard" for it. Once there is a "situation", the thousand birds will immediately make noise, thus waking up the sleeping crocodile, so that the crocodile can immediately sink into the bottom of the water and avoid a disaster.

Habitat

It lives in fresh water (alligators can live in sea water). Crocodiles live in rivers, lakes and swamps in tropical and subtropical areas, and some in shoals near the coast.

Classification of species

There are 23 species of alligators belonging to 8 genera and 3 families in the world. Most of them are distributed in tropical and subtropical regions such as Africa, Central America and southern Asia. Only Chinese alligator in China and Mississippi alligator in North America are distributed in temperate zone. The main crocodile species cultivated in China are Chinese alligator, Siamese alligator (Thai alligator), Nile alligator, alligator, Mississippi alligator and caiman alligator. Among them, Alligator sinensis is endemic to China, and others are introduced from abroad.

Chinese alligator

Alligator sinensis, also known as alligator (TU ó), is a unique crocodile in China and the most endangered crocodile in the world. China has listed it as a class of national protected animals, and it is strictly forbidden to kill. Chinese alligator is small in size. The adult alligator weighs about 36 kg, and its body length is generally 1.5 meters, rarely more than 2.1 meters. The Chinese alligator has short and thick limbs, five fingers on the front and four toes on the back. Tail length is similar to body length. The head is relatively large with flat head and long snout. The eyes are all black with eyelids and membranes, which can be opened or closed. The back of the body is gray brown, the front of the abdomen is gray, from the anus to the back is gray and yellow, and the tail is flat. The newborn alligator is black with yellow stripes.

Siamese crocodile

Crocodylus siamensis, also known as Thai crocodile, Siamese freshwater crocodile and Singapore small crocodile, is mainly distributed in Southeast Asia, such as Borneo, Indonesia, Malaysia, Thailand and Vietnam. Siamese crocodile leather has a high reputation in the world. Siamese crocodile is a medium-sized crocodile. When young crocodile hatches, it is about 25 cm long. The longest length of adult crocodile can reach 4 meters, and the common crocodile is 3 meters long. Siamese alligator's beak is medium length, slightly concave. There is a pair of short sharp ridges in the front of the two eyes. There is an obvious orbit on the forehead between the two eyes. The scaly bone protrudes into a high ridge. It inhabits in tropical and subtropical swamps, slow flowing rivers and lakes and other fresh water areas, as well as salty water areas. It feeds on fish, amphibians, reptiles and small mammals. They reach sexual maturity around the age of 10. The female can lay 20-50 eggs at a time, and the incubation period is about 80 days.

Nile crocodile

The Nile crocodile (Crocodylus niloticus) is a large crocodile. The adult crocodile is 2-5.5 meters long and weighs up to 120 kg. It is the most studied crocodile among 23 crocodile species in the world. The body color of Nile crocodile is olive green to brown, with black spots and reticular pattern. The Nile crocodile is very strong with a strong tail that helps to swim. The adult body has a faint horizontal band. The larvae are dark yellowish brown, with obvious transverse bands on the body and tail. Female Nile crocodiles can lay more than 50 eggs at a time. After 3 months, the shell hatches. The body length of the newborn little Nile crocodile is about 30 cm. The female crocodile gently holds them in her mouth and puts them into the water. Young alligators can grow to 60 cm at one year old and 1 meter at two years old.

Alligator mississippiensis

Alligator mississippiensis (Alligator mississippiensis), also known as alligator Miho and alligator Americana, is only found in the southeast of the United States and the Mississippi River Basin and so on. The Mississippi alligator is a large alligator with a body length of 4.9-6.1 meters, but few of the existing individuals grow to this size. It is mainly inhabited in swamp area, and also distributed in streams and rivers, even in water body with odor. Mihe crocodiles can communicate with their peers through sound and vision. In the Convention on international trade in endangered species of Wild Fauna and flora, the Mississippi alligator is listed in Appendix II.

Caiman

Caiman crocodile refers to several crocodiles from the South and Central America. They are related to alligators and belong to Alligatoridae. Caimans have a transverse bone ridge at the front of their eyes, which is very similar to the spectacle frame worn by human beings. Therefore, their English name has the name of alligator. The maximum body length of common caiman is 250 cm, the common adult is 150-200 cm, and the newly hatched young is 20-25 cm. The length of the snout is slightly longer than the width of the snout base. The back is olive green, with numerous dark spots on the head, body and tail, dark brown or black stripes on the back and tail, and pure beige or light yellow on the abdomen. There are light spots on both sides of the jaw of the newly hatched alligator, which disappear when the body length is about 35 cm. Caimans are mainly found in fast flowing and rocky rivers.

Alligator

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