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• Subphylum: Vertebrata
• Dry, scaly skin, and lungs
• Dry, scaly terrestrial eggs with several membranes
• Backbone
• Tail
• Two limb girdles
• Four limbs
• Example: iguana
• Snakes are limbless!
• Turtles have hard
shells fused to their
vertebrae!
• 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
• 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
• At the end of the Permian Period ~245 mya, a great variety of reptiles roamed the Earth
• 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…
• 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
• Dinosaurs were everywhere!
• Saurischia: lizard-hipped dinosaurs
• Ornithischia: bird-hipped dinosaurs
• Dinosaurs are the ancestors of modern birds
• 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
• Adaptations that have contributed to the success of reptiles on land:
• Well developed lungs
• Double-loop circulatory system
• Water-conserving excretory system
• 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
• 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
• 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
• 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
• 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
• 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
• Crocodiles and alligators have the most developed hearts of living reptiles
• 2 atria and 2 ventricles
• Arrangement also found in birds and mammals
• 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
• 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
• 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
• Reptiles with legs: – Run, walk, burrow,
swim or climb
• Reptiles without legs: – Squirm and twist
• Backbones of reptiles help accomplish much of their movement
• 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
• 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
• The four surviving groups of reptiles:
– Lizards and snakes
– Crocodilians
– Turtles and tortoises
– Tuatara
Order Squamata: scaly reptiles
Most lizards:
• Legs
• Clawed toes
• External ears
• Movable eyelids
Order Squamata: scaly reptiles
Most snakes:
• Lost both pairs of legs during their evolution
• Highly efficient predators
• Some can produce venom
• Order Crocodilia
• Alligators, crocodiles, caimans, and gavials
• Long, broad snout and squat appearance
• Fierce carnivores
• 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
• 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
• Turtle: live in the water
• Tortoises: live on land
• Terrapin: turtle that is found in water that is somewhat salty
• 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
• 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
Reptiles Vertebrates Common characteristics
Strong, bony skeleton Toes with claws Ectothermic Dry, scaly skin Well-developed lungs Internal fertilization Amniotic eggs with
leathery shells
Examples: Snakes
The king cobra is the
largest venomous
snake (up to 18 ft).
Kingsnakes often eat rattlesnakes. They are immune to the venom.
The hognose snake will often “play dead” when threatened.
The world’s longest snake is the reticulated python (may
exceed 30 ft.). The heaviest is the anaconda (up to 500 lbs.).
Most reptiles lay eggs, but
some give live birth. Babies are usually
independent at birth.
Australia is the only continent where
venomous snakes outnumber non-venomous ones
Snakes can dislocate their
jaws, which allows them to swallow prey much larger than themselves.
Australia is the only continent where
venomous snakes outnumber non-venomous ones
Reptiles Vertebrates Common characteristics
Strong, bony skeleton Toes with claws Ectothermic Dry, scaly skin Well-developed lungs Internal fertilization Amniotic eggs with
leathery shells
Examples: Snakes Lizards
The king cobra is the
largest venomous
snake (up to 18 ft).
The Komodo dragon is the largest living lizard, reaching lengths of up
to 10 ft.
Chameleons can move their eyes independently.
Marine iguanas can dive
over 50 ft. to feed on
algae.
Kingsnakes often eat rattlesnakes. They are immune to the venom.
The hognose snake will often “play dead” when threatened.
The world’s longest snake is the reticulated python (may
exceed 30 ft.). The heaviest is the anaconda (up to 500 lbs.).
Most reptiles lay eggs, but
some give live birth. Babies are usually
independent at birth.
Most lizards have 4 legs, but a few have only 2 legs. Some are legless!
Snakes can dislocate their
jaws, which allows them to swallow prey much larger than themselves.
Reptiles Vertebrates Common characteristics
Strong, bony skeleton Toes with claws Ectothermic Dry, scaly skin Well-developed lungs Internal fertilization Amniotic eggs with
leathery shells
Examples: Snakes Lizards Crocodilians Tuataras
The king cobra is the
largest venomous
snake (up to 18 ft).
The Komodo dragon is the largest living lizard, reaching lengths of up
to 10 ft. The largest reptile
is the saltwater crocodile, which
grows up to 23 ft.
Australia is the only continent where
venomous snakes outnumber non-venomous ones
Chameleons can move their eyes independently.
Marine iguanas can dive
over 50 ft. to feed on
algae.
Tuataras Not lizards! (differences are mainly in
internal anatomy & development) Virtually unchanged for about 200
million years Sole survivor of ancient group of
reptiles called beak-heads Most ancient of all living reptiles
(older than dinosaurs!) Only found in islands of New Zealand Can live up to 100 years
Kingsnakes often eat rattlesnakes. They are immune to the venom.
The hognose snake will often “play dead” when threatened.
The world’s longest snake is the reticulated python (may
exceed 30 ft.). The heaviest is the anaconda (up to 500 lbs.).
Most reptiles lay eggs, but
some give live birth. Babies are usually
independent at birth.
Most lizards have 4 legs, but a few have only 2 legs. Some are legless!
Tuataras do not have
external ears.
Snakes can dislocate their
jaws, which allows them to swallow prey much larger than themselves.
Reptiles Vertebrates Common characteristics
Strong, bony skeleton Toes with claws Ectothermic Dry, scaly skin Well-developed lungs Internal fertilization Amniotic eggs with
leathery shells
Examples: Snakes Lizards Crocodilians Tuataras Turtles & tortoises
There are 7 species of sea turtles, and all are
endangered.
The king cobra is the
largest venomous
snake (up to 18 ft).
The Komodo dragon is the largest living lizard, reaching lengths of up
to 10 ft. The largest reptile
is the saltwater crocodile, which
grows up to 23 ft.
Australia is the only continent where
venomous snakes outnumber non-venomous ones
Chameleons can move their eyes independently.
Marine iguanas can dive
over 50 ft. to feed on
algae.
Tuataras Not lizards! (differences are mainly in
internal anatomy & development Virtually unchanged for about 200
million years Sole survivor of ancient group of
reptiles called beak-heads Most ancient of all living reptiles
(older than dinosaurs!) Only found in islands of New Zealand Can live up to 100 years
Kingsnakes often eat rattlesnakes. They are immune to the venom.
Snakes can dislocate their
jaws, which allows them to swallow prey much larger than themselves.
The hognose snake will often “play dead” when threatened.
Most reptiles lay eggs, but
some give live birth. Babies are usually
independent at birth.
Most lizards have 4 legs, but a few have only 2 legs. Some are legless!
Green sea turtles are not green. They get their
name from the fact that their blubber is green due
to their diet of algae.
The world’s longest snake is the reticulated python (may
exceed 30 ft.). The heaviest is the anaconda (up to 500 lbs.).
Tuataras do not have
external ears.
