The Origin and Early Evolution of Amniotes

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The Origin and Early Evolution of Amniotes

• Amniotes diverged from anthracosaurs in the
  Carboniferous period (late Paleozoic)
• The Amniotic Egg (shelled egg) - Enclosing the
  Pond
• Amnion membrane enclosing the embryo (cushioned
  in amniotic fluid)
• Allantois sac serves as respiratory surface and
  waste container highly vascularized
• Yolk Sac contains nutrients for embryo modified
  into part of placenta in live-bearers
• Chorion outer membrane highly vascularized (gas
  exchange occurs)
• Shell porous, parchment-like or leathery in
  reptiles calcium absorbed by growing embryo
• Skull Morphology and Amniote Radiation
• Anapsid no temporal opening behind orbit
  (extinct groups, incl. mesosaurs)
• Diapsid two pairs of temporal openings,
  separated by arch (incl. extant reptiles)
• Synapsid single pair low on cheeks, bordered by
  arch (extinct taxa, led to mammals)
• Other Derived Characteristics of Amniotes
• Jaws bones and muscles allow crushing and
  gripping forces (vs. suction of fishes)
• Rib ventilation draw air into lungs
  (aspiration) limbs freed rib muscles for new
  function
• Thicker, waterproofed skin more keratin (beta
  keratin in reptiles) ? scales and scutes
• Circulation atria completely partitioned two
  ventricles incompletely separated (excl.
  crocodiles, w/ complete separation)
  functionally separated pulmonary, systemic flows
• Excretion excretion of ammonia (amphibians)
  involves loss of water bladder in reptiles
  absorbs water, nitrogenous waste excreted as
  uric acid
• Nervous system enlarged cerebrum related to
  sensory integration and locomotion

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FIG. 26.3
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Fig. 26.1
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Fig. 26.2
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Fig. 26.4
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Class Reptilia Diversity and Taxonomy

• Class Reptilia 8,000 extant species Age of
  Reptiles in Mesozoic era (165 my span) most
  ectothermic many extinct forms (ex. dinosaurs,
  ichthyosaurs)
• Order Testudines (Chelonia) Turtles
• Little change in morphology from appearance in
  Triassic
• Shell with carapace (dorsal) and plastron
  (ventral) outer layer of keratin and inner layer
  of bone (fused ribs and vertebrae) limbs and
  girdles positioned inside ribs, can be withdrawn
  (and head) for defense
• Respiration hindered by shell lungs ventilated
  by limb movement and false diaphragm
• Small brain, poor hearing, but acute olfaction
  and vision
• Internal fertilization oviparous, with gender
  dependent on nest temperature in some (high
  temperatures produce females)
• Diversity includes snapping turtles, giant
  tortoise, desert tortoise, sea turtles (incl.
  leatherback)
• Order Squamata Lizards and Snakes (95 of
  extant reptiles) with kinetic skulls
  (movable joints) that allow prey manipulation
• Suborder Sauria (lizards) include geckos,
  iguanids, skinks (reduced limbs), monitors (incl.
  Komodo dragon), chameleons, and beaded lizards
  (venomous) ectothermic eyelids
• Suborder Serpentes (snakes) limbless two halves
  of lower jaw kinetic (allows ingestion of large
  prey) opening of trachea anterior rely mainly
  on chemoreception most oviparous
• Order Sphenodonta Tuataras
• Two species of Sphenodon in New Zealand
  (protected) living fossils parietal (3rd) eye
• Order Crocodilia Crocodiles and Alligators
• Elongated skull with massive jaw muscles
  secondary palate allows breathing with full
  mouth oviparous, with high nest temperatures
  producing males (vs. females in turtles)
• Traits shared with birds true four-chambered
  heart, thecodont teeth (in sockets)
• Diversity includes American alligator, saltwater
  crocodile, Nile crocodile, caimans

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Fig. 30.16
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Fig. 26.6
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Fig. 26.9
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Fig. 26.12
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? FIG. 26.13
FIG. 26.14 ?
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FIG. 26.15
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? FIG. 26.16
FIG. 26.18 ?
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Fig. 26.17
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Fig. 26.19
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Fig. 26.20
? FIG. 26.20
FIG. 26.24 ?
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Fig. 26.27
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FIG. 26.28
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Fig. 26.5
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Snakes Locomotion, Prey Capture, and Special
Senses

• Locomotion
• Lateral undulation lateral force exerted against
  surface irregularities
• Concertina movement braces S-shaped loops
  against sides of channel
• Rectilinear movement sections of body rest on
  ground with intervening sections pulled forward
  by muscles
• Side-winding throws body forward in loops with
  body at 60 angle to direction of travel
  little contact with ground used by sidewinder
• Prey Capture most snakes capture prey with
  mouth and swallow alive
• Venom 20 of species vipers with movable,
  tubular fangs in front of mouth cobra family
  (incl. mambas, coral snakes, and kraits) with
  short, erect fangs in front of mouth most sea
  snakes rear-fanged Australia 4/1 ratio
  venom/non
• Constriction capture prey larger than mouth
  most ambush (ex. pythons)
• Special Senses
• Jacobsons (vomeronasal) organs pair of pit-like
  organs in roof of the mouth, lined with
  chemoreceptors forked tongue picks up scent
  molecules of prey (can impart direction to prey)
  
• Pit organs found only in pit vipers (Subfamily
  Crotalinae, incl. cottonmouths, copperheads, and
  rattlesnakes) heat-sensitive pit organs between
  nostrils and eyes enclose free nerve endings
  sense differences of 0.003 C track prey and
  aim strikes

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Fig. 26.22
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Fig. 26.26
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Fig. 26.23
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Fig. 26.21
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Fig. 26.25
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The Evolution and Extinction of the Dinosaurs and
Other Mesozoic Reptiles

• Diversity of Extinct Reptiles evidence of
  parental care, herding, and endothermy for
  certain taxa
• Order Saurischia (lizard-hipped)
• Sauropods herbivorous, massive, quadrupedal (ex.
  Brachiosaurus)
• Theropods carnivorous, bipedal
  (ex.Tyrannosaurus, Velociraptor) certain taxa
  gave rise to birds
• Order Ornithischia (bird-hipped) most armored
  or with horns all herbivorous (ex. Stegasaurus,
  Triceratops, hadrasaurs)
• Order Pterosauria winged, flying archosaurs (ex.
  Pteranodon)
• Therapsids and Pelycosaurs early mammal-like
  amniotes (ex. Dimetrodon) relatives of early
  mammals
• Ichthyosaurs dolphin-like marine reptiles (incl.
  Shonisaurus)
• Plesiosaurs large, long-necked marine reptiles
• Extinction of the Dinosaurs
• Evidence suggests that many dinosaurs were
  already in decline before meteor impact at end
  of Cretaceous (K/T boundary) impact crater
  located off Yucatan Peninsula evidence for
  impact included shocked quartz, iridium layer

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