Reptiles
Keith Hua
Michael Wu
Taxonomy
 Domain:
Eukarya
 Kingdom: Animalia
 Phylum: Chordata
 Class: Reptilia
Reptiles
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Reptiles have an endoskeleton, closed circulatory system, notochord, nerve cord,
pharyngeal slits, and a tail.
Reptiles are highly cephalized just like human.
The first appearance of the reptile was 300,000,000 years ago, and the first
known reptile was the Hylonomus.
Reptiles have many defensive mechanisms.
Some snakes like cobras and rattlesnakes inject poison through their fangs made
from venom glands behind their eyes.
The two main types of venom poison are neurotoxins (nerve poisons), and
hemotoxins (blood and tissue poisons).
Crocodiles just bite their enemies, or use their tails for protection. Crocs have a
bite force of 3000 pounds per square inch.
Reptiles usually like to live in warm climates like tropical rainforests, warm waters,
and deserts since they are cold-blooded.
Hylonomus – first reptile
Respiratory System
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Since reptiles breathe less they have less spongy and more hollow lungs, which
makes it less efficient at getting oxygen.
Most reptiles also do not have diaphragms so they have to breathe by moving their
ribs or throats.
Some reptiles like turtles however have permeable skin for gas exchange, and other
species have modified their cloaca to increase the area of gas exchange.
Because of a turtle’s shell however turtles cannot breathe like other reptiles, instead
there is a sheet of muscle that envelops the lungs and when it contracts the turtle
exhales, and when it protracts it can inhale.
Crocodiles have muscular diaphragm that pulls the pelvis back to make room for the
lungs to expand.
Snakes have 2 lungs however the right lung is way bigger than the left lung, and a
snake may move its windpipe off to the side to continue breathing as its feeding.
Snakes have a trachea, air sac, and bronchi. The left bronchi leads to the left lung
which is small and non-functioning, and the right bronchi leads to the right lung
which is elongated.
The forward portion of the snake’s lungs function for gas exchange and the second
half is the air sac which extends to the tail. The air sac regulates pressure inside the
body cavity.
Respiratory System
A. Trachea
B. Esophagus
C. Thymus
D. Thyroid
E. Heart
F. Vestigial left lung
G. Right lung
H. Air sac
I. Liver
J. Gall Bladder
K. Stomach
L. Spleen
M. Pancreas
N. Testis (right)
O. Adrenal gland
P. Ductus deferens
Q. Kidney (right)
R. Ureter
S. Colon
T. Cloaca
U. Scent glands
V. Hemipenes
W. Small intestine
Circulatory System
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Reptiles have a closed circulatory system similar to humans.
Most reptiles have 3 chambered hearts consisting of 2 atria, two
aortas, and a partially separated ventricle, while some have an actual
divided ventricle.
In some conditions aquatic reptiles can move their deoxygenated
blood back to the body and their oxygenated blood to their lungs for
longer dive times.
Crocodiles on the other hand have a 4 chambered heart, and can
bypass their pulmonary circulation, which carries oxygen depleted
blood to the lungs and oxygenated blood to the heart.
Pythons and some lizard species have a 3 chambered heart, but is
capable of changing it into a 4 chambered heart during contraction. A
muscular ridge subdivides the ventricle making it 4 chambered.
The right and left atria receive blood from the lungs and body, and
pass it to the ventricle to be circulated again.
The snake’s heart is encased in a sac called the pericardium that is
located at the branching of the bronchi, that enables the heart to move
around but not be harmed when digesting large prey.
Circulatory System
Nervous System
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Reptiles have the same basic parts of the amphibian brains, except they have larger
cerebrums and cerebellums.
Reptiles have 12 pairs of cranial nerves like humans, and unlike mammals their
spinal cords extend to the tip of their tails.
These cranial nerves help reptiles see, smell, and eat.
A reptile’s brain however is still relatively small.
Reptiles have highly developed sense organs, except for the fact that snakes don’t
have external ears.
A snake’s tongue includes highly sensitive smell sensors that can pick up odor
particles.
Snakes also have one special organ called the Jacobson’s organ located in the snout
but behind the nostrils. This organ chemically analyzes particles that the snake may
pick up.
The Jacobson’s organ also allows snakes to find mates, and identify food and
predators.
Crocodiles have extremely good eyesight due to their cat-like eyes and may even
have color vision similar to humans
Crocs have sensory pits in their lower and upper jaw that contain nerve fibres to
detect disturbances in the water.
Nervous System
Snake’s Jacobson’s
organ that chemically
analyzes particles.
Crocodiles cat-like eyes
enable them to see in
the dark.
Digestive System
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A reptiles digestive system includes the esophagus, stomach, small intestine, and
large intestine.
Snakes do not chew their food, instead they eat their food whole.
The food first enters the esophagus, and into the stomach of the snake, then the
stomach breaks the food down but secreting hydrochloric acid. The food then goes to
the small intestines, and the waste is passed into the large intestine and then the
cloaca and it is then excreted out of the body.
The snake’s liver and pancreas also secrete digestive enzymes to help the breaking
down of food.
Since crocodiles don’t chew their food because their teeth aren’t well aligned they
usually swallow their food whole.
Crocodiles have 2 stomachs, 1 is a muscular gizzard, and the other has powerful
acids to further break down the food.
Turtles try to rip their food to small pieces using their claws, feet, an essentially one
big tooth.
Crocodiles, snakes, and turtles may go up to weeks or months without eating as they
slowly digest large meals.
Digestive System
Reproduction
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Most reptiles reproduce sexually, however some kind reproduce
asexually.
All reproductive activity occurs through the cloaca.
Males and females usually put their cloaca together and the male
excretes sperm.
Most reptiles lay eggs in the ground, or some species retain their eggs
until they are just about to hatch and then lay them down.
Not all reptiles lay eggs, some snakes like rattlesnakes, garter snakes,
and water snakes may give birth to live young.
Excretory System
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Reptile excretion is performed by 2 main kidneys.
Uric acid is the main waste product, but urea is the main
product for turtles.
Since reptiles cannot produce liquid urine more
concentrated than their body fluid their large intestines
(colons) help absorb excess water. Bladder helps do this
too.
Turtle’s Respiratory System