Taxonomy • Domain: Eukarya • Kingdom: Animalia • Phylum: Chordata • Class: Reptilia
Reptiles • Reptiles have an endoskeleton, closed circulatory system, notochord, nerve cord, pharyngeal slits, and a tail. • Reptiles are highly cephalized just like human. • The first appearance of the reptile was 300,000,000 years ago, and the first known reptile was the Hylonomus. • Reptiles have many defensive mechanisms. • Some snakes like cobras and rattlesnakes inject poison through their fangs made from venom glands behind their eyes. • The two main types of venom poison are neurotoxins (nerve poisons), and hemotoxins (blood and tissue poisons). • Crocodiles just bite their enemies, or use their tails for protection. Crocs have a bite force of 3000 pounds per square inch. • Reptiles usually like to live in warm climates like tropical rainforests, warm waters, and deserts since they are cold-blooded. Hylonomus – first reptile
Respiratory System • Since reptiles breathe less they have less spongy and more hollow lungs, which makes it less efficient at getting oxygen. • Most reptiles also do not have diaphragms so they have to breathe by moving their ribs or throats. • Some reptiles like turtles however have permeable skin for gas exchange, and other species have modified their cloaca to increase the area of gas exchange. • Because of a turtle’s shell however turtles cannot breathe like other reptiles, instead there is a sheet of muscle that envelops the lungs and when it contracts the turtle exhales, and when it protracts it can inhale. • Crocodiles have muscular diaphragm that pulls the pelvis back to make room for the lungs to expand. • Snakes have 2 lungs however the right lung is way bigger than the left lung, and a snake may move its windpipe off to the side to continue breathing as its feeding. • Snakes have a trachea, air sac, and bronchi. The left bronchi leads to the left lung which is small and non-functioning, and the right bronchi leads to the right lung which is elongated. • The forward portion of the snake’s lungs function for gas exchange and the second half is the air sac which extends to the tail. The air sac regulates pressure inside the body cavity.
Respiratory System A. TracheaB. EsophagusC. ThymusD. ThyroidE. HeartF. Vestigial left lung G. Right lungH. Air sacI. LiverJ. Gall BladderK. StomachL. Spleen M. PancreasN. Testis (right)O. Adrenal glandP. Ductus deferensQ. Kidney (right)R. Ureter S. ColonT. CloacaU. Scent glandsV. HemipenesW. Small intestine
Circulatory System • Reptiles have a closed circulatory system similar to humans. • Most reptiles have 3 chambered hearts consisting of 2 atria, two aortas, and a partially separated ventricle, while some have an actual divided ventricle. • In some conditions aquatic reptiles can move their deoxygenated blood back to the body and their oxygenated blood to their lungs for longer dive times. • Crocodiles on the other hand have a 4 chambered heart, and can bypass their pulmonary circulation, which carries oxygen depleted blood to the lungs and oxygenated blood to the heart. • Pythons and some lizard species have a 3 chambered heart, but is capable of changing it into a 4 chambered heart during contraction. A muscular ridge subdivides the ventricle making it 4 chambered. • The right and left atria receive blood from the lungs and body, and pass it to the ventricle to be circulated again. • The snake’s heart is encased in a sac called the pericardium that is located at the branching of the bronchi, that enables the heart to move around but not be harmed when digesting large prey.
Nervous System • Reptiles have the same basic parts of the amphibian brains, except they have larger cerebrums and cerebellums. • Reptiles have 12 pairs of cranial nerves like humans, and unlike mammals their spinal cords extend to the tip of their tails. • These cranial nerves help reptiles see, smell, and eat. • A reptile’s brain however is still relatively small. • Reptiles have highly developed sense organs, except for the fact that snakes don’t have external ears. • A snake’s tongue includes highly sensitive smell sensors that can pick up odor particles. • Snakes also have one special organ called the Jacobson’s organ located in the snout but behind the nostrils. This organ chemically analyzes particles that the snake may pick up. • The Jacobson’s organ also allows snakes to find mates, and identify food and predators. • Crocodiles have extremely good eyesight due to their cat-like eyes and may even have color vision similar to humans • Crocs have sensory pits in their lower and upper jaw that contain nerve fibres to detect disturbances in the water.
Nervous System Snake’s Jacobson’s organ that chemically analyzes particles. Crocodiles cat-like eyes enable them to see in the dark.
Digestive System • A reptiles digestive system includes the esophagus, stomach, small intestine, and large intestine. • Snakes do not chew their food, instead they eat their food whole. • The food first enters the esophagus, and into the stomach of the snake, then the stomach breaks the food down but secreting hydrochloric acid. The food then goes to the small intestines, and the waste is passed into the large intestine and then the cloaca and it is then excreted out of the body. • The snake’s liver and pancreas also secrete digestive enzymes to help the breaking down of food. • Since crocodiles don’t chew their food because their teeth aren’t well aligned they usually swallow their food whole. • Crocodiles have 2 stomachs, 1 is a muscular gizzard, and the other has powerful acids to further break down the food. • Turtles try to rip their food to small pieces using their claws, feet, an essentially one big tooth. • Crocodiles, snakes, and turtles may go up to weeks or months without eating as they slowly digest large meals.
Reproduction • Most reptiles reproduce sexually, however some kind reproduce asexually. • All reproductive activity occurs through the cloaca. • Males and females usually put their cloaca together and the male excretes sperm. • Most reptiles lay eggs in the ground, or some species retain their eggs until they are just about to hatch and then lay them down. • Not all reptiles lay eggs, some snakes like rattlesnakes, garter snakes, and water snakes may give birth to live young.
Excretory System • Reptile excretion is performed by 2 main kidneys. • Uric acid is the main waste product, but urea is the main product for turtles. • Since reptiles cannot produce liquid urine more concentrated than their body fluid their large intestines (colons) help absorb excess water. Bladder helps do this too.