Transcript Z - Reptilia - I Heart Science

Reptilia
• Reptiles are the evolutionary base for the
rest of the tetrapods.
• Early divergence of mammals from reptilian
ancestor.
• Early reptiles arose from amphibian ancestor
and were small, lizard-like insectivores.
Characteristics
• Scales
• Amniotic egg
• Ectothermic
– Must live in favorable conditions or hibernate.
– Being ectothermic enables an organism to
survive on much less food than an
endothermic organism.
• Three chambered heart
– Alligators have 4
• Claws
Characteristics
• Positioning of legs more directly
under animal (more support).
• Paired limbs with five toes.
–Adapted for running, climbing,
swimming.
–Absent in snakes.
Characteristics
• Body covered with horny epidermal scales made
from protein keratin.
– Scales serve to reduce water loss and provide
protection.
– Reptiles molt as they grow.
• Brain = first cerebral cortex (capable of reasoning,
planning, perception)
Respiration
• All reptiles breathe using lungs.
• Aquatic turtles have developed more
permeable skin.
• Some species have modified
their cloaca to increase the area for gas
exchange.
Circulation
• Most reptiles have a 3-chambered heart with a
partially divided ventricle.
– No mixing of blood from lungs with
deoxygenated blood.
– Crocodiles have 4 chambers and a unique
feature: cog teeth.
Cog Teeth
Digestion/Excretion
• Excretory waste =
uric acid
• Lack structures in
nephrons to
reabsorb water, so
water absorption
happens in the
colon.
Reproduction
• Internal fertilization: gametes not subject to
desiccation (drying out).
• Amniote egg = significant evolutionary
breakthrough.
– Egg covered by tough, water-resistant,
leathery or calcerous shell.
– Extra embryonic membranes
compartmentalize the interior for several
functions – keep fetal homeostasis
http://www.youtube.com/watch?v=t1kFiehGh9s
Amniotic Egg
• Chorion = hard covering permeable to
respiratory gases but not water.
• Allantois = functions in gas exchange and
a storage reservoir for metabolic waste.
• Amnion = fluid-filled sac acts as cushion
for embryo and prevents desiccation.
• Yolk sac = food for embryo; eliminates
need for larval stage.
Orders
• Crocodilia = crocodiles, alligators
• Testudines = turtles and tortoises
• Sphenodonta = tuatara
• Squamata = lizards, snakes (largest
group)
Order Crocodilia
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23 species of crocodiles, alligators, & caimans
Largest of the living reptiles
Amphibious carnivores
Live in tropics/subtropics
Lizard-like body with short legs, clawed/webbed
toes, massive tail
• Flat head with nostrils at tip
• Powerful jaws
• Dorsal side armored with dermal plates
Order Testudines
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260 species of turtles/tortoises
Oldest group of reptiles (225 mya)
Only reptile with shell
Only reptile WITHOUT TEETH
All lay eggs on land.
Third eyelid = nictitating membrane.
Longest living vertebrates (100+years in wild)!
Order Testudines
• Protective body shell
– Encases vital organs
– Provides some protection to
head/limbs
– Composed of bony plates
covered by horny epidermal
scales
– 2 parts: upper carapace, lower
plastron
– Loss of body-wall muscles
– Ribs/trunk vertebrae fused to
carapace
Order Squamata
• 4675+ species of lizard
• 2700+ species of snakes
• 140 species of amphisbaenians
– Limbless, burrowing animals
– Vestigial eyes under skin
• Most successful, diversified of
living reptiles.
• Occur in most habitats of world
amphisbaenians
Snakes
• Elongated derivative of lizard (increased
vertebrae, not lengthening of segments)
• Lack limbs, eyelids, ear openings
• Jaw bones are loosely united to allow
swallowing of large prey
• Throat and windpipe are at separate
ends of mouth to allow breathing while
eating
• Can be venomous
(hemotoxin/neurotoxin)
• Tongue to smell, some have heat pits to
sense body heat
Snakes
• No legs
• No external ears
• Jacobson’s organ
– Sense smell with aid of
tongue
• Cornea of eye protected
with a spectacle
– transparent membrane
• Skull bones loose
– Swallow large prey
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Snakes
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An extrasensory organ in the roof of a snake's
mouth
• Sharpens its sense of smell.
• Two hollow, highly sensitive saclike structures
• Allows it to track both prey and potential mates
Snakes
• “Pit" organ located between the eye and the nostril
on each side of the head.
• Detects heat given off by warm-blooded prey
Lizards
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Legs, eyelids, ear openings
Halves of lower jaw united
Small lizards - Adhesive toe pads
Color is variable
Slender body
Small scales
Self amputation to escape predators
– Can’t regrow
– Costly; lose muscle/stored fat
http://www.youtube.com/watch?v=GgB4u6Mgy2M
Chameleon
• How are chameleons able to change color?
– Special cells called CROMATOPHORES
http://science.howstuffworks.com/zoology/28369fooled-by-nature-chameleon-colors-video.htm
Insane in the Chromatophore: