Reptiles and Birds
Biology I: Chapter 31-1
REPTILES
Reptile Characteristics
• Subphylum: Vertebrata
• Dry, scaly skin, and lungs
• Dry, scaly terrestrial eggs
with several membranes
Reptile Characteristics
• Backbone
• Tail
• Two limb girdles
• Four limbs
• Example: iguana
Exceptions
• Snakes are limbless!
•
Turtles have hard
shells fused to their
vertebrae!
Reptiles
• Dry body prevents water
loss in a dry environment
• Disadvantage: the skin
must be shed as it grows
• Can live across the globe,
except in extremely cold
environments
Evolution of Reptiles
• Reptiles were the first animals
to adapt their eggs to dry
habitats
• First reptiles are from 350 mya
• Did not become common until
about 40-50 million years later
when the conditions of Earth
were drier
Mammal-Like Reptiles
• At the end of the Permian Period ~245 mya, a
great variety of reptiles roamed the Earth
Mammal-Like Reptiles
• Displayed a mixture of mammalian and
reptilian characteristics
• Dominated many land habitats
• Became extinct in just a few million years
• Replaced by another group of reptiles…
Enter the Dinosaurs
• Late Triassic and Jurassic
periods
• Two groups of large aquatic
reptiles swam in the seas
• Ancestors of modern
turtles, crocodiles, lizards,
and snakes populated many
land habitats
Enter the Dinosaurs
• Dinosaurs were
everywhere!
• Saurischia: lizard-hipped
dinosaurs
• Ornithischia: bird-hipped
dinosaurs
• Dinosaurs are the
ancestors of modern birds
Exit the Dinosaurs
• Mass Extinction 65 mya: the end of
the Cretaceous Period
• Caused by a dramatic series of natural
disasters
• Volcanic eruptions, dropping in sea
level, huge asteroid or comet
smashing into the now Yucatan
Peninsula in Mexico, etc.
• Opened up niches on land and in the
sea, providing opportunities for other
kinds of organisms to evolve
Form and Function in Reptiles
• Adaptations that have
contributed to the success
of reptiles on land:
• Well developed lungs
• Double-loop circulatory
system
• Water-conserving excretory
system
Form and Function in Reptiles
• Adaptations that have contributed to the success of reptiles
on land (continued):
• Strong limbs
• Internal fertilization
• Shelled, terrestrial eggs
• Control of body temperature by changing environments
Body Temperature Control
• The ability to control body temperature is an
enormous asset for active animals
• Ectotherm: animal that relies on interactions
with the environment to help it control body
temperature
• Turtles, snakes and other modern reptiles
Body Temperature Control
• To keep warm: bask in the sun during the day
or stay under water at night
• To cool down: move into the shade, go for a
swim, or take shelter in underground burrows
Body Temperature Control
Feeding
• Eat a wide variety of foods
• Iguanas are herbivores and have long
digestive systems to break down plant
material
• Snakes, crocodiles and alligators are
carnivores
• Chameleons have sticky tongues as
long as their bodies to catch insects
Respiration
• Lungs are spongy, providing more gas-exchange area
than those of amphibians
• Many have muscles around their
ribs that expand the chest cavity
to inhale and collapse the cavity to
force air out
• To exchange gases with the environment, reptiles
have two efficient lungs, or like some snakes, one
lung
Circulation
• Efficient double-loop circulatory system
– Blood to/from: lungs
– Blood to/from: body
• 2 atria and 1 or 2 ventricles
– Most have 1 ventricle with a partial septum, or wall,
separating the oxygen-rich and oxygen-poor blood
Circulation
• Crocodiles and alligators
have the most developed
hearts of living reptiles
• 2 atria and 2 ventricles
• Arrangement also found
in birds and mammals
Circulation
Excretion
• Urine is produced in the kidneys
• Urine contains either
ammonia or uric acid
• Ammonia: those reptiles
that drink a lot of water;
i.e. crocodiles and alligators
• Uric acid: those reptiles that need to conserve water, that live
entirely on land; eliminated into a pasty white solid
Response
• Pattern of brain is similar to that of an
amphibian
• The cerebrum and cerebellum are large
compared to rest of the brain
• Active during the day
Response
• Tend to have complex eyes
and can see color well
• Pair of nostrils: snakes have
a good sense of smell
• Pair of sensory organs in the
roof of the mouth: detect
chemicals
• Simple ears with an external
eardrum
Movement
• Reptiles with legs:
– Run, walk, burrow,
swim or climb
• Reptiles without legs:
– Squirm and twist
• Backbones of reptiles help accomplish much
of their movement
Reproduction
• All reproduce by internal
fertilization
• Most males have a penis
that allows them to deliver
sperm into the female’s
cloaca
• The fertilized egg is
covered with a leathery
shell
Reproduction
• Most are oviparous and lay the
eggs in nests
• Amniotic egg: egg composed of
shell and membranes that create
a protected environment in
which the embryo can develop
out of the water
• An important adaptation to land
Groups of Reptiles
• The four surviving groups of reptiles:
– Lizards and snakes
– Crocodilians
– Turtles and tortoises
– Tuatara
Lizards and Snakes
• Order Squamata: scaly reptiles
Most lizards:
• Legs
• Clawed toes
• External ears
• Movable eyelids
Lizards and Snakes
• Order Squamata: scaly reptiles
Most snakes:
• Lost both pairs of legs during
their evolution
• Highly efficient predators
• Some can produce venom
Crocodilians
• Order Crocodilia
• Alligators, crocodiles,
caimans, and gavials
• Long, broad snout and
squat appearance
• Fierce carnivores
Crocodilians
• Maternal care of young
• Live only in the tropics and
subtropics
• Alligators: live only in
fresh water, exclusively in
North and South America
• Crocodiles: live in either
fresh or salt water and are
native to Africa, India and
Southeast Asia
Turtles and Tortoises
• Order Testudines
• Shell built into the skeleton
• Carapace: the dorsal part of the shell
• Plastron: ventral part of the shell
• Lacking teeth, these reptiles have horny ridges that
cover the upper and lower jaws
Turtles and Tortoises
• Turtle: live in the water
• Tortoises: live on land
• Terrapin: turtle that is found in
water that is somewhat salty
Tuataras
• Order Sphenodonta
• Only member of its order
• Found in a few small islands off the coast of New Zealand
• Resemble lizards
• Lack external ears and retain primitive scales
• “Third eye”: part of a complex organ located on top of the
brain…function still unknown
Ecology of Reptiles
• Many are in danger because of loss of habitat
• Humans also hunt them for food, to sell as
pets, for their skins, etc.
• Some are now protected
