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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

Class Reptilia

Fred Searcy


class reptilia l repto to creep
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
    • 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
class reptilia4
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
reptile ancestors
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
  • 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
  • Skulls are better adapted for muscle attachment at foramina of skull
  • Allows stronger and better grip
  • Reptiles can hold closure very long times
internal fertilization
Internal Fertilization
  • Reptiles have a hemipenis
    • Evagination of cloacal wall which protrudes when engorged with blood
circulatory system
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
gas exchange
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
osmoregulation excretion
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
support locomotion
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)
nervous sensory system
Nervous & Sensory System
  • Cerebrum largest part of brain – more complex behaviors
  • Well developed
    • Sight
    • Infrared detection
    • Olfactory
      • Jacobson’s organ
  • 12 cranial nerves
order testudines chelonia
Order Testudines(Chelonia)
  • Turtles
    • Generally aquatic
  • Tortoises
    • Generally land dwellers
  • Little changed since Triassic (200 mya)
  • 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)
shell continued
Shell continued
  • Individual plates which make up shell are named according to their location
gas exchange18
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
  • Middle and Inner ear
    • Not especially good for sound detection
  • Excellent
    • Smell
    • Vision with color perception
  • 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
aquatic and terrestrial
Aquatic and Terrestrial
  • Leatherbacks larges marine species (2 m and 725 kg)
  • Giant tortoises of Galapagos 150 years old
order squamata suborder sauria lizards
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
order squamata suborder amphisabenia worm lizards
Order Squamata Suborder Amphisabenia – Worm Lizards
  • Legless
  • Name of order means they can move backwards or forwards equally fast
order squamata suborder serpentes snakes
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.
infrared vision
Infrared Vision
  • Some snakes “see” using infrared
  • Pit vipers
    • Facial pits rich in temperature receptors
  • Shape of head & body
  • Arrangement, number & type of scales
    • Keeled
    • Unkeeled
  • Anal plate
    • Divided
    • Undivided
poisonous snakes u s
Poisonous Snakes U.S.

Image courtesy of

  • 4 poisonous species
    • Rattlesnake
    • Cotton mouth
    • Copperhead
    • Coral snake

Coral snake, cottonmouth courtesy of

poisonous snakes
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.
order spenodonta tuataras
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
order crocodilia crocodiles alligators caimans caymans gavials
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
Alligator mississippiensis in U.S.
  • American Crocodile Crocodylus acutus
order crocodilia
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