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REPTILE NOTES 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 predator’s 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 snake’s 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 (28-105 degrees). • To sustain activity, body temperatures have to be within a certain range (77-98.6). • 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 sun’s 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 sun’s 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.