Chapter 20
Reptiles: The First Amniotes
•  External Structure and Locomotion
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Skin has no respiratory function
Skin is thick, dry and keratinized
Scales are modified for different functions
Periodically shed skin (ecdysis)
Chromatophores provide color
•  Cryptic coloration, mimicry, aposematic
coloration, sex recognition
Cryptic coloration
Mimicry
Aposematic coloration
•  Support and Movement
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Skeleton very similar to amphibians
Skull is longer
Secondary palate present in some
Modified neck structure
•  Additional cervical vertebrae gives more
freedom of movement to the head (twisting and
nodding)
•  Modified ribs
•  Turtles - fused with shell
•  Snakes - aid in locomotion, inflate in defense
•  Limbs positioned closer to body
•  Changes movement
•  Nutrition and Digestion
•  Most are carnivores, but can eat many
things
•  Turtles and crocodile’s tongues aid in
swallowing
•  Some lizards have projectile tongues
•  Snake modifications
•  Jaw unhinges
•  Glottis (respiratory opening) is far
forward in the mouth
•  Allows them to breathe while swallowing
•  Vipers have hollow fangs with venom
•  Some spit venom
•  2 types of venom
•  Neurotoxin - attacks nervous system
•  Hemotoxin - breaks down blood cells
•  Circulation, gas exchange, temperature
regulation
•  3 chambered heart
•  Breathe using lungs
•  Cold-blooded
•  Nervous and Sensory Functions
•  Brain larger than amphibians
• Associated with increased sense of
smell, reliance on vision and better
coordination
•  Vision is dominant snese
• Nictitating membrane present
• Median (parietal) eye
•  Jacobson’s organs
•  Pit organs
•  Magnetic detection
• Present in sea turtles
• Used to navigate the ocean
•  Excretion and osmoregulation
•  Kidneys adapted to conserve water
(metanephric kidneys)
•  Cloaca excretes solid/powdery waste
•  Reproduction and development
•  Internal fertilization
• Must occur in reproductive tract of
female
• Must occur before protective egg
membranes are formed
•  Amniotic egg
• Pores in shell allow gas exchange
• Egg provides nutrition for embryo
•  Parthenogenesis
• Does not require egg to be fertilized
• Occurs in some lizards
• Males have never been found
•  Behavior
• Males often seek out females
• Courtship
• Color changes
• Head bobbing
•  tail waving
• Pheromones
• Vocalizations in crocodilians only
•  Egg laying
• Eggs are usually abandoned
• Turtles bury eggs
• In some species, egg temperature
determines sex of offspring
Anapsid Reptiles
•  Subclass Anapsida
•  Order Testudines (Chelonia)
•  Turtles
•  Appear in fossil record 200 million years ago
•  Shell
•  Carapace - dorsal covering
•  Plastron - ventral covering
•  2 layers
•  Outer - keratin
•  Inner - bone
•  Breathing
•  Limited room for lung expansion
•  Expand and contract diaphragm to
breathe
•  Nervous system
•  Small brain
•  Poor hearing
•  Good sense of smell and vision
•  Reproduction
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Oviparous
Internal fertilization
Eggs are buried
Hatchling gender
•  Some turtle families - nest temperature
determines gender
•  Low temp - males
•  High temp - females
Diapsid Reptiles
•  Subclass Diapsida
•  Order Squamata
•  Lizards, snakes, worm lizards
•  95% of all reptiles
•  Snakes
•  Elongated body
•  Rearrangement of internal organs
•  Specializations for eating large prey
•  Kinetic skull - mobile jaws
•  Lizards
•  Geckos
•  Small, agile
•  Nocturnal
•  Adhesive pads on toes
•  Iguanids
•  Brightly colored
•  Throat fans, crests, frills
•  Skinks
•  Elongated bodies
•  Reduced limbs
•  Chamelions
•  Arboreal lizards
•  Specialized tongue
•  Lizard characteristics
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Moveable eyelids
Good daytime eyesight
External ear
Vocalization
•  Geckos are territorial
•  Other lizards are defensive
•  Excretion
•  Semi-solid urine
•  Conserves water
•  Worm Lizards
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Burrowing
No external limbs
Move forward and backward
Eyes are ears hidden by skin
•  Snakes
•  skeleton
•  Limbless, no pelvic girdles
•  Short, wide vertebrae
•  Ribs provide resistance to lateral stress
•  Highly kinetic skull
•  2 halves of lower jaw connected only by muscle
•  Senses
•  Permanent transparent eyelid
•  Jacobson’s organs
•  Venomous snakes
•  Neurotoxic - affects the nerves
•  Hemorrhagin - breaks down red blood vessels
•  Order Sphenodontida
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2 living species
Found in New Zealand
Tuatara
Lizardlike
Live over 75 years
Well developed median eye
•  Order Crocodylia
•  Mostly unchanged for 200 million years
•  3 families
•  Crocodiles
•  Alligators
•  Caimans
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Elongated, well-reinforced skull
Complete secondary palate
4 chambered heart
Oviparous
•  Lay 20 - 50 eggs
•  Care for young
•  Crocs vs. alligators
•  Crocodiles
•  Narrow snout
•  Lower teeth visible when mouth closed
•  Alligators
•  Wider snout
•  No bottom teeth visible when mouth closed
•  Gavials
•  Very narrow snout