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Class Reptilia

Class Reptilia. Fred Searcy ZOO2010. Class Reptilia (L. repto = to creep). Movement to Terrestrial Existence Greatest innovation is the shelled egg Shelled egg maintains aquatic environment Leathery or Hard Embryos of reptiles birds and mammals have four extraembryonic membranes

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Class Reptilia

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  1. Class Reptilia Fred Searcy ZOO2010

  2. Class Reptilia(L. repto = to creep) • Movement to Terrestrial Existence • Greatest innovation is the shelled egg • Shelled egg maintains aquatic environment • Leathery or • Hard • Embryos of reptiles birds and mammals have four extraembryonic membranes • Amnion • Yolk sac • Chorion • allantois

  3. Amnion • Surrounds embryo • Amniotic fluid • Yolk sac • Yolk a mixture of proteins and lipoproteins • Chorion • Involved in gas exchange • Membrane next to shell • Shell porous to gases • In mammals, chorion forms placenta • Allantois • Holds metabolic wastes as uric acid • As embryo develops, also aids in gas exchange with chorion

  4. Class Reptilia • Dinosaurs – reptiles or birds? • Mass extinctions of many reptiles at end of Mesozoic • 8,000 extant terrestrially and aquatic • Adaptations of reptiles • Shelled egg • Tough, dry, keratinized skin • Powerful jaw enclosure • Internal fertilization • Ability to conserve water

  5. Reptile Ancestors • Ancestors had extraembryonic membranes • Called amniotes • Three lineages from amniotes • Anapsids – no openings in temple behind eye sockets – gave rise to turtles • Diapsids – two pair openings in temple behind eye sockets – gave rise to other reptiles and birds • Synapsids – one pair openings – gave rise to mammals

  6. Scales • Skin is especially adapted to prevent water loss • Epidermis (thick) • Hydrophobic lipids to retard water loss • Scales (composed of β-keratin) • Alligators keep scales their lifetime • Crocodilians and some lizards may have bony plates beneath scales in dermis - osteoderms • Dermis (thicker) • chromatophores

  7. Jaws • Skulls are better adapted for muscle attachment at foramina of skull • Allows stronger and better grip • Reptiles can hold closure very long times

  8. Internal Fertilization • Reptiles have a hemipenis • Evagination of cloacal wall which protrudes when engorged with blood

  9. Circulatory System • Two functional, separate systems • Pulmonary • Systemic • Heart • Right atrium has deoxygenated blood • Left atrium oxygenated • Ventricle partly partitioned to prevent mixing • Crocodilians have two ventricles (4 chambered heart) • Allows blood to flow even when oxygen not entering lungs during • Aestivation or • Swimming underwater • Higher blood pressure than amphibians • Ectothermic but with some behavioral thermoregulation

  10. Gas Exchange • Lungs (increased emphasis) • Skin (reduced importance) • Air brought in by muscles associated with rib cage to expand thoracic cavity or by • Movement of internal organs • Cutaneous respiration may occur through cloacal or pharyngeal membranes in aquatic turtles

  11. Osmoregulation & Excretion • Paired metanephros kidneys • No loop of Henle to concentrate solutes in urine in reptiles • Salt glands take over this function • Nose • Tongue • Eye • Uric acid

  12. Support & Locomotion • Strong endoskeleton • Limbs thrown outward • Abdomen closer to surface • Five toes • Limbs adapted for • Climbing • Running • Paddling • Some snakes & lizards are limbless • One occipital condyle to attach to the atlas (humans have two)

  13. Nervous & Sensory System • Cerebrum largest part of brain – more complex behaviors • Well developed • Sight • Infrared detection • Olfactory • Jacobson’s organ • 12 cranial nerves

  14. Order Testudines(Chelonia) • Turtles • Generally aquatic • Tortoises • Generally land dwellers • Little changed since Triassic (200 mya) • Shell 

  15. Shell • Two parts • Dorsal carapace • Ventral plastron • Composed of • outer keratinized layer and • inner bony layer • Fused ribs, vertebrae and other bony substances in skeleton • Limbs & girdles are found within the rib cage (no other vertebrate) • No teeth (jaws of keratinized bone)

  16. Shell continued • Individual plates which make up shell are named according to their location

  17. Gas Exchange • Turtles cannot expand chest to breathe • Abdominal and pectoral muscles pull air in like diaphragm • Exhalation when animal pulls his anterior portion of body back into the shell (walking also aids in this) • Aquatic species have membranes rich in blood vessels in • Mouth • Cloaca

  18. Senses • Middle and Inner ear • Not especially good for sound detection • Excellent • Smell • Vision with color perception

  19. Reproduction • Oviparous • Internal fertilization • Males have modified indention in shell to allow him to mount female • Females bury eggs and desert nest • Vertical distribution of eggs plays role in sex determination • Cooler (deeper) = males • Due to no sex chromosomes

  20. Aquatic and Terrestrial • Leatherbacks larges marine species (2 m and 725 kg) • Giant tortoises of Galapagos 150 years old

  21. Order SquamataSuborder Sauria - Lizards • Tetrapods or legless • Geckos, iguanas, skinks, chameleons, glass snakes • Most have moveable eyelids • Color vision excellent • External ears but doesn’t necessarily rely on hearing (most lizards are non-vocal) • Ectothermic and behavioral thermoregulation • Stilting • Dew nap

  22. Gila monster only poisonous lizard in US • Food reserves in tail

  23. Order Squamata Suborder Amphisabenia – Worm Lizards • Legless • Name of order means they can move backwards or forwards equally fast

  24. Order SquamataSuborder Serpentes - Snakes • Limbless • Pythons & boas have pectoral and pelvic girdles • Organs reduced and/or shifted • Capable of disarticulation of jaws • No external ears • Most with poor vision (except arboreal species) • Have fovea rich in cone cells.

  25. Infrared Vision • Some snakes “see” using infrared • Pit vipers • Facial pits rich in temperature receptors

  26. Oviparous but some Ovoviviparous & Viviparous • Egg tooth

  27. Identification • Shape of head & body • Arrangement, number & type of scales • Keeled • Unkeeled • Anal plate • Divided • Undivided

  28. Poisonous Snakes U.S. Image courtesy of http://www.agassiztrading.com/contact.htm • 4 poisonous species • Rattlesnake • Cotton mouth • Copperhead • Coral snake Coral snake, cottonmouth courtesy of www.brevardanimalservices.com.

  29. Poisonous Snakes • Two basic toxins • Neurotoxins • Hemorrhagins • Some toxins are body region specific • Effects based on • Size of prey • Size of snake • Amount delivered, etc. • LD50 indicates Australian tiger snake and some sea snakes are most deadly. Based on size and amount delivered, King Cobra most dangerous.

  30. Order Spenodonta(Tuataras) • Specific islands off coast of New Zealand • Most closely resembles extinct Mesozoan species • Third eye (parietal eyeon top of head) • Detects light • Has lens, retina and connections to brain • Covered by scales

  31. Order CrocodiliaCrocodiles, Alligators, Caimans (Caymans), Gavials • Only survivors of Mesozoic reptiles • Unchanged for 200 million years • Caimans & alligators are New World • Crocodiles worldwide • Gavial restricted to India and Burma

  32. Alligator mississippiensis in U.S. • American Crocodile Crocodylus acutus

  33. Order Crocodilia • Jaw muscles • Wide gape • Quick closure • Little force necessary to keep closed • Teeth in sockets (thecodont dentition) • Bulls vocal in mating season • Hatchlings vocal and heard by mother • Low nest temperatures = females, higher temperatures = males

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