REPTILE NOTES. REPTILES The lifestyles of most reptiles have major adaptations for living on land. For example, the chuckwalla, which is a lizard.
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REPTILES The lifestyles of most reptiles have major adaptations for living on land. For example, the chuckwalla, which is a lizard common to the deserts of the southwestern United States, can survive when temperatures get over 104 degrees and during arid conditions when there is little or no rain.
REPTILES To survive, chuckwallas disappear below ground and aestivate (becoming dormant during the summer). He will not come out until March, when rain falls. He will find water and drink, storing water in large reservoirs under the skin. If threatened, a chuckwalla will hide in the nearest rock crevice. It will inflate its lungs with air, making it fatter and press up against the rock. Friction of its body scales make him nearly impossible to dislodge.
EXTERNAL STRUCTURE AND MOVEMENT The skin of reptiles has no respiratory function. Their skin is thick, dry, and contains keratin. Reptile skin also secretes pheromones that function in sex recognition and defense.
EXTERNAL STRUCTURE AND MOVEMENT All reptiles periodically shed the outer layer of skin in a process called ecdysis. This process usually begins in the head region and the skin usually comes off in one piece.
EXTENAL STRUCTURE AND MOVEMENT Chromatophores in reptiles are similar to those in amphibians. Cryptic coloration, mimicry, and aposematic coloration occur in reptiles.
Support and Movement The reptile skeleton has a lot of bone to provide greater support. The skull is longer than an amphibian skull. They also have a plate of bone, the secondary palate, that partially separates the nasal passages from the mouth cavity.
Support and Movement Reptiles have more cervical vertebrae than amphibians do. The first two cervical vertebrae, the atlas and axis, provide greater freedom of movement for the head. The atlas allows nodding and the axis allows rotation of the head.
Support and Movement The ribs of reptiles are also different. For instance, the ribs of snakes have muscular connections to large belly scales to help with movement. The cervical vertebrae of cobras have ribs that may be flared to show aggression.
Support and Movement The tail vertebrae of many lizards have a vertical fracture plate. When a lizard is grasped by the tail, these vertebrae can be broken, and a portion of the tail is lost. Tail loss, or autotomy, is an adaptation that allows a lizard to escape from a predators grasp, or the disconnected piece of tail may distract a predator from the lizard. The lizard will later regenerate the lost portion. Movement in reptiles is similar to salamanders.
NUTRITION AND DIGESTIVE SYSTEM Most reptiles are carnivores, but turtles will eat almost anything organic. The tongues of turtles and crocodiles do not come out and are helpful for swallowing. Some lizards and the tuatara have sticky tongues for capturing prey. The tongue extension of chameleons exceeds their own body length.
NUTRITION AND DIGESTIVE SYSTEM The most remarkable adaptation of snakes involve the changes in their skull for feeding. The bones of the skull and jaws loosely join and can spread apart to ingest prey much larger than a normal head size. Each half of the upper and lower jaws can move independently of each other.
NUTRITION AND DIGESTIVE SYSTEM Teeth that point backward prevent prey escape and help force the food into the esophagus. The glottis, or respiratory opening, is far forward in the mouth so the snake can breathe while slowly swallowing its prey.
NUTRITION AND DIGESTIVE SYSTEM Vipers have hollow fangs. These fangs connect to venom glands that inject venom when the viper bites.
NUTRITION AND DIGESTIVE SYSTEM The upper jaw bone of vipers is hinged so that when the snakes mouth is closed, the fangs fold back along the upper jaw. When the mouth opens, the upper jaw bone rotates and causes the fangs to swing down. Because the fangs project outward from the mouth, vipers may strike at objects of any size.
NUTRITION AND DIGESTIVE SYSTEM Rear-fanged snakes have grooved rear teeth. Venom is sent along these grooves and into the prey to quiet them during swallowing. These snakes usually do not strike, and most are harmless to humans.
NUTRITION AND DIGESTIVE SYSTEM Coral snakes, sea snakes, and cobras have fangs that rigidly attach to the upper jaw. When the mouth is closed, the fangs fit into a pocket in the outer gum of the lower jaw. Some cobras spit venom at their prey. If not washed from the eyes, the venom can cause blindness.
NUTRITION AND DIGESTIVE SYSTEM Venom glands are modified salivary glands. Most snake venoms are mixtures of neurotoxins and hemotoxins. The venoms of coral snakes, cobras, and sea snakes are primarily neurotoxins that attack nerve centers and cause respiratory paralysis. The venoms of vipers are primarily hemotoxins that break up blood vessels attack blood vessel linings.
CIRCULATION, GAS EXCHANGE, TEMPERATURE REGULATION The circulatory system of reptiles is similar to amphibians. Because reptiles are larger than amphibians, their blood must travel under higher pressure to reach distant body parts.
CIRCULATION, GAS EXCHANGE, TEMPERATURE REGULATION Like amphibians, reptiles have 2 heart atria that are completely separated and a ventricle that is incompletely divided. Blood low in oxygen enters the ventricle from the right atrium, leaves the heart and goes to the lungs. Blood high in oxygen enters the ventricle from the lungs and leaves through a left and right artery.
CIRCULATION, GAS EXCHANGE, TEMPERATURE REGULATION When turtles go into their shells, their method of lung ventilation does not work. They also stop breathing during diving. During periods of apnea (no breathing), blood flow to the lungs is limited, which conserves energy and allows more efficient use of the oxygen supply.
Gas Exchange Reptiles exchange gases across internal surfaces to avoid losing large amounts of water. They do have a larynx, but usually not vocal cords. Lungs are divided into spongy, connected chambers. These chambers provide a large surface area for gas exchange.
Gas Exchange The ribs of turtles are a part of their shell, so movements of the body wall that have ribs attached is impossible.
Temperature Regulation Unlike aquatic animals, terrestrial animals may face temperature extremes that are not good for their life. Temperature regulation is very important for animals that spend their entire lives out of water. Most reptiles use external heat sources for temperature regulation, and are ectothermic. Brooding Indian pythons, however, can use their metabolism to increase temperature. Female pythons will coil around their eggs and elevate their body temperature as much as 45 degrees above the air temperature.
Temperature Regulation Some reptiles can survive wide temperature fluctuations ( degrees). To sustain activity, body temperatures have to be within a certain range ( ). If that is not possible, the reptile will seek a retreat where body temperatures can be in this range.
Temperature Regulation Most temperature regulations of reptiles are behavioral, especially in lizards. To warm itself, a lizard places itself at right angles to the suns rays, often on a warm surface, facing the sun. It then presses its body to the surface to absorb heat by conduction. To cool itself, a lizard places its body parallel to the suns rays, seeks shade or burrows, or will extend its legs and tail to reduce contact with warm surfaces. In hot climates, many reptiles are nocturnal.
Temperature Regulation As temperatures rise, some reptiles begin panting, which releases heat through evaporation. Marine iguanas divert blood to the skin while basking in the sun and warm up quickly. When diving into cool waters, however, marine iguanas reduce heart rate and blood flow to the skin, which slows heat loss. Chromatophores also help temperature regulation.
Temperature Regulation In temperate regions, many reptiles handle cold winter temperatures by entering torpor (decreased activity in daily life). Reptiles that are usually solitary may migrate to a common site called a hibernaculum, to spend the winter. Heat loss from individuals in a hibernacula is reduced because of clumping together.
Temperature Regulation Unlike true hibernators, a reptile body temperature in torpor is not regulated, and if the winter is too cold or the retreat too exposed, they will freeze and die. Death from freezing is a major cause of mortality for temperate reptiles.
NERVOUS AND SENSORY FUNCTIONS The reptile brain is similar to that of other vertebrates, although larger than the amphibian brain. This increase in size is associated with improved sense of smell. The optic lobes and cerebellum are also larger, which indicates increase reliance on vision and more coordinated muscle function.
NERVOUS AND SENSORY FUNCTIONS Reptiles have very complex sensory systems, as seen in a chameleons method of feeding. Its large eyes swivel independently, and each has a different field of vision. Initially, the brain keeps both images separate, but when prey is spotted, both eyes look at it. Their vision then determines if the prey is within range of the tongue.
NERVOUS AND SENSORY FUNCTIONS Vision is the dominant sense in most reptiles. Snakes focus on nearby objects by moving the lens forward. Reptiles also have a greater number of cones than amphibians do and probably have well-developed color vision.
NERVOUS AND SENSORY FUNCTIONS Upper and lower eyelids, a nictitating membrane, and a blood sinus help protect and cleanse the surface of the eye. The blood sinus, which is at the base of the nictitating membrane, swells with blood to help force debris to the corner of the eye, where it may be rubbed out. Horned lizards squirt blood from their eyes by rupturing this sinus to try and startle predators.
NERVOUS AND SENSORY FUNCTIONS Some reptiles have a median eye that develops from the roof of the forebrain. In the tuatara, it is an eye with a lens, a nerve, and a retina. In other reptiles, the parietal eye is less developed. They are covered by skin and probably can not form images. They can tell the difference between light and dark periods and are used to help them orient to the sun.
NERVOUS AND SENSORY FUNCTIONS The structure of reptile ears varies. The ears of snakes detect underground vibrations. Snakes can also detect airborne vibrations.
NERVOUS AND SENSORY FUNCTIONS In other reptiles, a tympanic membrane may be on the surface or in a small depression on the head. The inner ear of reptiles is similar to amphibians.
NERVOUS AND SENSORY FUNCTIONS The sense of smell is better developed in reptiles than amphibians. Many reptiles have Jacobsons organs, which are used to detect smells. The forked tongue of snakes and lizards are organs for tasting chemicals in the air. A snakes tongue goes out and then goes to the Jacobsons organ, which picks up odors. Tuataras use Jacobsons organs to taste objects held in the mouth.
NERVOUS AND SENSORY FUNCTIONS Rattlesnakes and other pit vipers have heat- sensitive pit organs on each side of the face between the eye and nostril. These are used to detect objects with temperatures different from the snakes surroundings.
EXCRETION AND WATER REGULATION The kidneys of reptiles are similar to fish and amphibians. However, life on land, increased body size, and higher metabolism require kidneys that can process waste with little water loss. Most reptiles excrete uric acid. It is not toxic.
EXCRETION AND WATER REGULATION Nocturnal habits and avoiding hot surface temperatures during the day helps reduce water loss. When water is available, many reptiles store large quantities of water in lymphatic spaces under the skin or in the urinary bladder. Many lizards have salt glands below the eyes for helping the body get rid of excess salt.
REPRODUCTION AND DEVELOPMENT The amniotic egg is not completely independent of water. Pores in the eggshell allow gas exchange and also water evaporation. These eggs require a huge amount of energy from the parents. Some reptiles do provide parental care and they may have to provide high humidity around the eggs. These eggs are often supplied with large quantities of yolks for long development periods, and parental energy can be invested in post-hatching care.
REPRODUCTION AND DEVELOPMENT Fertilization must occur in the reproductive tract of the female before protective egg membranes can be laid down around the egg. All male reptiles, except tuataras, possess an external organ for depositing sperm in the female. Lizards and snakes have hemipenes (a pair of penises) at the base of the tail that are turned inside out, like a glove.
REPRODUCTION AND DEVELOPMENT Sperm may be stored in the female reproductive tract. It may be stored for up to 4 years in some turtles, and up to 6 years in some snakes. Sperm can be stored during the winter.
REPRODUCTION AND DEVELOPMENT Parthenogenesis (fertilization with no male present) has been observed in six families of lizard and one species of snake.
REPRODUCTION AND DEVELOPMENT Reptiles often have very complex reproductive behaviors that may involve males actively seeking out females. Head-bobbing displays by some male lizards reveal bright patches of color on the throat and folds of skin.
REPRODUCTION AND DEVELOPMENT Courtship in snakes is based mainly on touch. Tail-waving displays are followed by the male running his chin along the female, entwining his body around hers.
REPRODUCTION AND DEVELOPMENT Lizards and snakes also use sex pheromones to assess the reproductive condition of a potential mate. Vocal sounds are only important to crocodiles. During breeding season, males are hostile and may bark or cough as a warning to other males. Roaring is used to attract females, and mating occurs in water.
REPRODUCTION AND DEVELOPMENT After eggs are laid, reptiles usually abandon them. Most turtles bury their eggs in ground, under debris, or in burrows.
REPRODUCTION AND DEVELOPMENT About 100 species of reptile provide care for their eggs. One example is the American alligator. The female builds a nest of mud and grass. She hollows out the center, partially fills it with mud, lays her eggs, and then covers them.
REPRODUCTION AND DEVELOPMENT Temperatures within the nest within the nest influences the sex of the hatchlings. Temperatures at or below 88.7 will result in female offspring. Temperatures between 90.5 and 91.4 will result in male offspring. Temperatures around 89.6 results in male and female offspring.
REPRODUCTION AND DEVELOPMENT The female remains near the nest throughout development to protect the eggs from predators. She helps hatchlings from the nest in response to high-pitch calls and carries them in her mouth to water. She may remain with them for up to 2 years. Young eat scraps she drops when she feeds and will eat some small vertebrates they can catch on their own.