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Reptilian Groups
Chapter 26
I. Diversity
 First truly terrestrial vertebrates
 7000 species; 300 in U.S.
 Age of Reptiles lasted over 165 my, including
dinosaurs
 Mass extinction at end of Mesozoic; modern
lineages are survivors
 Lizards and snakes underwent further radiation
into diverse and abundant groups
Carboniferous Forest
II. Origin & Adaptive Radiation
 Arose from amphibian-like
tetrapods, the
anthracosaurs, during
Carboniferous
 3 lineages:
 Anapsids—turtles
 Diapsids—
ichthyosaurs, lizards,
snakes, crocodilians,
tuatara, plesiosaurs;
this lineage also gave
rise to birds
 Synapsids—mammallike reptiles (all
extinct)
Tetrapod Skulls
III. Characteristics
A. Skin
 Tough, dry, scaly which




protects and prevents
dessication
Epidermis shed periodically
in lizards and snakes;
formed of scales made of
keratin
Turtles add new layers
under old, forming platelike
scutes
Crocodiles and many lizards
also have bony plates called
osteoderms beneath scales
Thicker dermis has
chromatophores that
provide color
B. Shelled Egg
 Main factor in reptiles success
 Shell permits eggs to be laid
on land; porous, parchment-like
or leathery
 Extraembryonic membranes
from previous aquatic stages
maintained; protective
membranes support
development
 Allantois is respiratory
surface and chamber for
storing waste
 Chorion allows oxygen and
carbon dioxide to pass easily
 Young hatch as lung-breathing
mini adults
C. Reptilian Jaws
 Jaw muscles become larger to allow for
mechanics of chewing
D. Internal Fertilization
 Required because sperm
must reach egg before it
is enclosed
 Males have copulatory
organ; testes produce
sperm
 Female has oviducts and
paired ovaries; oviducts
secrete albumin and shells
for eggs
E. Circulatory System Changes
 Right and left atria completely partitioned
 Right atrium receives deoxygenated blood from
body; left oxygenated blood from lungs
 Ventricle incompletely separated but only a little
mixture of the blood occurs
 In crocodilians, ventricles are completely
separated
 Blood pressure is also higher than amphibians
F. Lungs
 Better developed
 Pull air in by enlarging
thoracic cavity:
 Snakes and lizards
move rib cage
 Turtles and
crocodilians move
internal organs to
create negative
pressure
G. Water Conservation
 Metanephric kidney which concentrates solutes
and excretes wastes as uric acid; uric acid has
low solubility and precipitates readily requiring
less water for elimination
 Salt glands nears eyes or nose secrete excess
salts
H. Support of Limbs for
Locomotion
 Better body support (except limbless reptiles)
 Walk with legs splayed outwards and body close
to ground
 Most dinosaurs and some modern lizards have
more efficient method with legs directed
beneath body
I. Nervous System
 More complex
 Brain small but cerebrum a little larger; in
crocodilians a true cerebral cortex permitting
more complex behaviors
 Sense organs well developed except hearing
 Jacobson’s organ is highly developed in lizards
and snakes to detect odors carried to senses by
tongue
IV. Reptilian Orders
A. Anapsida; Order Testudines
 1. General Characteristics
 Appeared in Triassic, 200 mya
 Shells have dorsal carapace and ventral plastron;
outer horny layer and inner layer of bone
 Limbs and limb girdles far from ribs
 No teeth; use horny plates to rip food
2. Respiration
 Can’t expand chest because of rigid shell
 Movement of abdominal and pectoral muscles
associated with limbs create space for air to
move in or compress viscera to push air out
 Movement of limbs helps ventilate lungs
 Some aquatic turtles gain enough oxygen by
pumping water in and out of mouth cavity
3. Reproduction
 Oviparous
 Eggs buried in ground in nest; no care of young
 In crocodiles, some turtle families, and some
lizards, nest temperature determines sex of
offspring; low temperatures are males and higher
temperatures are females
4. Types
 Giant turtles
 Marine turtles may reach 2 m long and 725 kg in
weight; Galapagos tortoises reach several hundred
kilograms
 Low metabolic activity allows lifespan of 150 yrs
 Box turtle
 Hinged plastron allows it pull in all parts and close up
completely
 Snapping turtles
 Reduced shell prevents full withdrawl of body
 Strong jaws used defensively and for hunting
 Eat fish, frogs, waterfowl
B. Diapsida; Order Squamata
 Most recent and diverse, making up 95% of living
reptiles
 Lizards appeared in Permian but did not radiate
until Cretaceous
 Snakes appeared in late Cretaceous
 Amphisbaenas appeared in early Cenozoic
a. General Characteristics
 Lost dermal bone by temporal opening allowing
for a kinetic skull, one that has movable joints
 Can seize and manipulate prey with jaws and
force jaws closed
 Skull mobility is major factor in diversity
b. Reproduction
 Some viviparous or ovoviviparous;associated with
colder climates. Eggs retained longer in oviduct
 Oviparous; associated with warmer climates
c. Suborder: Sauria
 Terrestrial, burrowing, aquatic, aerial, arboreal
 Survive well in hot, dry regions
 External ear; day-active lizards have rods & cones;
nocturnal have only rods
 Keep body temperature constant by behavioral regulation
 Conserve water by producing semisolid urine with highly
crystalline uric acid
 Some store fat in tails to provide energy and water
during drought
 Geckos—small, nocturnal, adhesive pads on toes
 Chameleons—arboreal, color changing, long tongue
 Iguanids—many New World lizards
 Gila monster, beaded lizard, and komodo dragon only ones
with venomous bites
Lizards
d. Suborder: Amphisbaenia
 Most lack any trace of external limbs; skin in
rings; resemble earthworms
 Eyes and ears rudimentary and hidden under skin
 1 species in Florida but mainly South America and
tropical Africa
e. Suborder: Serpentes
(1) Feeding
 Can eat prey several times their own diameter
 Two halves are loosely joined allowing them to
spread apart
 Skull bones loosely articulated so mouth can
accommodate large prey
 To allow breathing during slow process of
swallowing, tracheal opening extended
 Has extra skin infolded between scales; this
unfolds during a big meal
Hunting and Feeding
(2) Senses
 Eyes have reduced mobility and
permanent corneal membrane for
protection
 Most have poor vision except
arboreal snakes
 No external ear and do not
respond to sounds
 Can feel vibrations, especially low
frequencies, and those in ground
 Chemical senses primary on used
for hunting
 Jacobson’s organs are pair of
pits in roof of mouth; lined with
olfactory receptors and forked
tongue picks up particles and
conveys them past organ
 Pit vipers( rattlesnakes) have pits
that detect heat emitted by
warm-bodied prey
(3) Movement
 Limbless and have lost
pectoral and pelvic girdles
(except pythons)
 Vertebrae shorter and wider
to allow undulation
 Lateral undulation is Sshaped movement that pushes
against rough ground and
water
 Concertina movement is
extension of S-shaped loops
to strike or to climb trees
 Rectilinear movement is
straight using minute lifting
of consecutive ribs
 Sidewinding is sideways
looping by desert vipers that
“walks” them across sand
(4) Venom/Venomous Snakes
 Vipers have hollow fangs that are hinged and
inject venom as snake strikes
 Family Viperidae—New World and Old World
vipers with and without pits
 Family Elapidae—cobras, mambas, coral snakes,
and kraits
 Family Hydrophiidae—sea snakes
 Family Colubridae—most non venomous but
boomslang and African twig snake are
Venomous Snakes
Fangs
(5) Snakebites
 8000 snake bites each year in
U.S.; 12 fatal; In India and
Burma alone 200,000
bites/year; 25,000 fatalities
worldwide
 Most venom a combination of
types
 Neurotoxins act on nervous
system causing blindness and
stopping respiration
 Hemorrhagin type breaks
down blood vessels, allowing
blood to leak into spaces
 Sea snakes and Australian
tiger snake have most deadly
venom per unit but large
venomous snakes deliver more
venom, making the king cobra
the most dangerous
“Red next to yellow, kill a fellow.”
Snake Bites
(6) Reproduction
 Most oviparous, laying
eggs under logs, rocks, or
in holes
 Pit vipers are
ovoviviparous
 Some are viviparous
 Sperm may be retained
and several egg clutches
can be laid from a single
mating
f. Order Sphenodonta
 Tuatara sole survivor of group
that evolved 200 mya and went
extinct 100 mya
 3 species live in New Zealand;
once widespread but now
restricted to small islands
 Has a well developed median
parietal eye buried beneath
the skin; function is unknown
 Lives in burrows
 Slow growing and may live to 77
years
 Slowest rates of evolution
among vertebrates
g. Order Crocodilia
 Sole survivor of archosaurs; group radiated
into dinosaurs and birds
 Have changed little since evolved in Mesozoic
 Long, well reinforced skull and jaw muscles
for powerful bite; teeth set in sockets
 Complete secondary palate; feature only
shared with mammals; 4 chambered heart
like birds and mammals
 Oviparous, laying eggs in nest of vegetation
 Alligators and caimans—New World—broad
snout
 Crocodiles—widely distributed; also
saltwater
 Gavials—India and Burma—very narrow snout
Crocodilians