도마뱀분양 Reptiles are a very diverse group of animals. Their rough skin is covered in horny plates called scutes, whose shape, number and position distinguish each animal species.
Crocodiles have a powerful stomach that digests meat and bone by crushing it with a special stone, like a bird gizzard (called gastroliths). They also have glands for excreting salt.
The skull of a reptile is quite complex. Students should work with a collection of fossilized skulls (perhaps 3D printed models) to identify similarities and differences between reptile and mammal skulls.
A classic reptilian skull has a pair of temporal vacuities on each side of the skull, guarded by the parietal bone above and the postorbital and squamosal bones below. This type of skull is found in crocodiles and dinosaurs.
This pattern eventually led to the diapsid group of tetrapods, which evolved lighter skulls and allowed for greater space for the attachment of jaw muscles. This group includes lizards, birds, crocodiles and snakes. Living diapsids also have fewer, more loose connections between the skull bones, so they can move their head freely and quickly.
Reptiles have a variety of eyes, some with lids and others lidless. They have a wide range of pupil shapes, too. The most common is a rounded one, which helps the animal see light from front and back. This allows a reptile to be on constant alert for predators.
The retina has two main types of photoreceptors, rods and cones. Rods sense light but can’t distinguish color, while cones can. Nocturnal reptiles have more rods than diurnal species.
Snakes and geckos lack moveable eyelids but have a transparent scale that acts as a lens covering the eyes. This scale, called a brille, is shed with the rest of the snake’s skin during shedding.
The limbs of reptiles are often short and stubby, a reflection of their evolutionary devolution from limb-bearing ancestors. Reptiles do not walk or run; instead they crawl along the ground.
The teeth of most reptiles are sharp, pointed and horny. They have no incisors, canines or molars, although some snakes have hollow fangs for injecting poison.
Some reptiles, such as the crocodile and marine turtles, use lateral undulations of their body and tail to move through water. Others, such as flying lizards, have wings shaped from their ribs. The skeletons of aquatic reptiles are often covered with bony plates, such as the scales of the crocodile. This spotted snake, Breyers’ Long-Tailed Skink, appears to be walking its jaws along prey.
The tail of a reptile is more difficult to figure out than it might be for some other animals. This is because the tail doesn’t really protect any major organs, so it can be slimmer and closer to the end of the body.
If you looked at a snake’s skeleton, you would see that the ribs travel down its entire body. At some point, however, the ribs will stop and the tail begins. This occurs at different points in different species of snakes, but it is usually very close to the end of the body. It is sometimes almost half the length of the snake’s body. This is known as the “snake’s tail.” It serves many purposes for the animal.
Reptiles have a large stomach which stores the food and helps to transport it to the intestine. The pharinx is a muscle which communicates the digestive and respiratory systems and during digestion closes to prevent food entering the lungs.
The kidneys are paired and bean-shaped organs, situated in the pelvis. Some species, particularly iguanas and chameleons, have a longer renal structure which extends cranially into the coelomic cavity (see Figure 17.6).
Snakes have a kinetic skull, allowing them to move the upper jaw like a hinge => wider gape during feeding. They can also move their quadrate bone which articulates with the lower jaw. They are very sensitive to vibrations in the ground and can hear them through their skin.
Unlike mammals, reptiles lack a diaphragm. Instead they have a common body cavity (coelom).
A trachea bifurcates in the cranial thorax to supply two lungs. The lungs have large bulla-like divisions and alveoli. Herbivorous species, such as green iguanas and chuckwallas, have large intestines that are sacculated to increase intestinal surface area for microbe colonisation during vegetation digestion.
The heart is a three-chambered organ with two atria and a variable partitioned ventricle. It can shunt blood from the body to the lungs and back again, aiding thermoregulation and longer diving times in aquatic species.
Reptiles have two kidneys that have bean-shaped segments. These segmented kidneys produce a salty, clear liquid called urine. Its function is to maintain a normal concentration of water and salt in the body, excrete waste, regulate acid-base balance and produce hormones.
Only chelonians and some lizards have bladders; snakes do not. Their kidneys have ureters that empty across their ventral surfaces into the dorsal urodeum, a division of the cloaca. The cloaca is the common emptying chamber for the digestive, urinary and reproductive tracts.
Like mammals, reptiles have a three-chambered heart with two atria and one ventricle. This allows them to bypass their lungs in times of oxygen stress, such as when they dive or swallow large prey items.
Reptiles are a class of vertebrates, like mammals, birds and amphibians. They are covered with a dry, thick skin made of keratin with very few glands.
They lay eggs, and some species have the ability to reproduce asexually through parthenogenesis. Some lizards and snakes give birth to live young instead of eggs. This type of reproduction is called vivipary.
Male reptiles have two testicles, which are housed within their bodies. They also have a copulatory organ, either a single penis (turtles and tortoises) or a pair of hemipenes, which are seen as bulges behind the cloaca at the base of the tail.
A cloacal prolapse is usually diagnosed on physical examination, although hematology and plasma biochemistry may be useful for identifying infectious and metabolic disturbances. Treatment consists of analgesia, lubrication and manipulation to reduce the prolapsed tissue.