Reptiles All Materials © Cmassengale  


Evolution of  Reptiles:

  • Reptiles were 1st vertebrates to make a complete transition to life on land (more food & space)
  • Arose from ancestral reptile group called cotylosaurs (small, lizard like reptile)
  • Cotylosaurs adapted to other environments in Permian period
    1. Pterosaurs – flying reptiles
    2. Ichthyosaurs & plesiosaurs – marine reptiles
    3. Thecodonts – small, land reptiles that walked on back legs
  • Mesozoic Era called “age of reptiles”

  • Dinosaurs dominated life on land for 160 million years
  • Brachiosaurs were largest dinosaurs
  • Herbivores included Brontosaurus & Diplodocus, while Tyrannosaurus were carnivores
  • Dinosaurs became extinct at end of Cretaceous period 
  • Mass extinction of many animal species possibly due to impact of huge asteroid with earth; Asteroid Impact Theory
  • Amniote (shelled) egg allowed reptiles to live & reproduce on land

Amniote Egg:

  • Egg had protective membranes & porous shell enclosing the embryo
  • Has  4 specialized membranes — amnion, yolk sac, allantois, & chorion
  • Amnion is a thin membrane surrounding a salty fluid in which the embryo “floats”
  • Yolk sac encloses the yolk or protein-rich food supply for embryo
  • Allantois stores nitrogenous wastes made by embryo until egg hatches
  • Chorion lines the inside of the shell & regulates oxygen & carbon dioxide exchange
  • Shell leathery & waterproof
  • Internal fertilization occurs in female before shell is formed

Section 1 Review

Terrestrial Adaptations:

  • Dry, watertight skin covered by scales made of a protein called keratin to prevent desiccation (water loss)
  • Toes with claws to dig & climb
  • Geckos have toes modified into suction cups to aid climbing
  • Snakes use scales & well developed muscular & skeletal systems to move
  • Lungs for respiration
  • Double circulation of blood through heart to increase oxygen to cells
  • Partial separation in ventricle to separate oxygenated & deoxygenated blood
  • Ectothermic – body temperature controlled by environment
  • May bask or lie in sun to raise body temperature or seek shade to lower body temperature; known as thermoregulation
  • Water conserved as nitrogen wastes excreted in dry, paste like form of uric acid crystals

Section 2 Review

Modern Reptiles:

  • Only 4 living orders remain
  • Found worldwide except in coldest ecosystems
  • Orders include —– Rhyncocephalia (tuatara lizard), Chelonia (turtles & tortoises), Squamata (lizards & snakes), & Crocodilia (alligators, caimans, and crocodiles)


  • Only one living species, Spenodon punctatus, (tuatara lizard)
  • Live on islands off the coast of New Zealand


  • Spiny crest running down back
  • Grows up to 60 cm in length
  • Has 3rd eye on top of head (parietal eye) that acts as a thermostat
  • Most active when temperatures are low (nocturnal)
  • Often burrow during the day
  • Feed on insects, worms, & small animals at night


  • Includes turtles and tortoises
  • Aquatic, but lay eggs on land
  • Body covered with shell composed of hard plates & tough, leathery skin
  • Carapace or dorsal surface of shell fused with vertebrae & ribs
  • Plastron is ventral shell surface
  • Shape of shell modified for habitat
  • Dome shaped shell helps to retract head & limbs in tortoises
Galapagos Tortoise
  • Water-dwelling turtles have streamline, disk shaped shell to rapidly move in water

spotted turtle photograph
Spotted Turtle

  • Forelimbs of marine turtles modified into flippers

Green Turtle found on Guernsey 1/2003 (Photograph © by Richard Lord, Guernsey)
Marine Turtle

  • River & sea turtles migrate to breeding areas where they hatched to lay their eggs on land


  • Includes crocodiles, alligators, caimans, & gavials
  • Direct descendants of Archosaurs
  • Carnivorous (wait for prey to come near & then aggressively attack)
  • Eyes located on top of head so they can see when submerged
  • Nostrils on top of snout to breathe in water
  • Valve in back of mouth prevents water from entering airway when feeding underwater
  • No parental care of young in most species except Nile crocodile that carry young in their jaws & guards nest
  • Crocodiles are tropical or subtropical, usually nocturnal, reptiles found in Africa, Asia, South America, & southern Florida

Australian photographs - crocodile
Australian Crocodile

  • Alligators are found in China & the southern United States

American Alligator

  • Caimans are native to Central America & resemble alligators

Black Caiman

  • Gavials, living only in India & Burma, are fish eating reptiles with very slender, long snouts



  • Includes snakes & lizards
  • Snakes probably evolved from lizards during the Cretaceous period
  • Snakes have 100-400 vertebrae each with a pair of ribs & attached muscles for movement
  • Interaction of bone, muscles, & skin of snakes allows them 3 ways to move — lateral, rectilinear, & side winding
  • Lateral undulations:
    1. Most common
    2. Head moves side to side causing wave of muscular contractions
    3. Snake uses sides of its body to push off of ground
    4. Snake moves forward in S-shaped path
  • Rectilinear Movements:
    1. Muscular force applied to belly & not sides of snake
    2. Scutes or scales on belly catch on rough surfaces
    3. Body relaxes & then moves forward slowly
  • Sidewinding:
    1. Used by some desert snakes
    2. Sideways movement of body
    3. Head vigorously flung from side to side
    4. Whiplike motion moves body along
  • Do not hear or see well but locate prey using forked tongue that gathers chemical scents
  • Swallow prey whole:
    1. Jaws unhinge for mouth to stretch
    2. Small teeth used to hold prey in mouth
    3. Windpipe thrust into throat while swallowing so snake can swallow & breathe
    4. Swallowing may take several hours
    5. Saliva begins digestion during swallowing
  • Constrictors wrap body around prey & squeeze them to death (boas, pythons, etc.)
  • Snakes may inject venom or poison:
    1. Hemotoxin – poisonous proteins attacking red blood cells (water moccasin & rattlesnake)
    2. Neurotoxin – poison that works on nervous system affecting heart rate & breathing (copperhead)
  • Venomous snakes with 3 types of fangs — rear-fanged, front-fanged, & hinge- fanged snakes
  • Rear-fanged snakes bite prey & use grooved back teeth to guide venom into puncture (boomslang)
  • Front-fanged snakes inject poison through 2 small front fangs that act like a hypodermic needle (cobra)

Spitting Cobra

  • Hinged- fang snakes have hinged fangs in roof of mouth that swing forward to inject poison (rattlesnake, water moccasin, copperhead)


Crotalus viridis viridis, Prairie Rattlesnake Stock Photograph
RattlesnakeWater Moccasin


  • Often camouflaged for defense
  • May use signals such as cobra expanding its hood, rattlesnake shaking its rattle, or hissing for defense
  • Most snakes locate females by scent
  • Internal fertilization with no parental care
  • May be oviparous (eggs hatch outside body) or ovoviviparous (eggs held inside body until hatch)
  • Lizards:
    1. Four limbs
    2. Includes iguanas, geckos, skinks, chameleons, etc.
    3. Rely on speed, agility, & camouflage to catch prey
    4. Feed on insects & small worms
    5. Some, such as anole & chameleon, can change colors for protection
    6. May use active displays such as squirting blood, hissing, or inflating bodies
    7. Some show autotomy (breaking off tail to escape predators)
    8. Two poisonous U.S. species include Gila Monster & Beaded Lizard

Gila Monster
Gila Monster

  • Komodo dragon of Indonesia is largest lizard reaching 3 meters in length

Section 3 Review