Reptiles
Reptiles

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First truly terrestrial
vertebrates
~7000 species
worldwide
~300 species in U.S.
and Canada
Reptiles
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
Probably best
remembered for what
they once were,
rather than what they
are now
Mesozoic era - age of
reptiles
Dominant group for
>150 millions years
Reptiles


12 or so principal
groups of reptiles
evolved
Only 4 groups remain
today
Order Squamata
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Snakes and lizards
>5800 species
Most successful
group
Order Crocodilia

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Crocodiles, alligators,
caiman
~25 species
Have survived for 200
million years
Today: concerns that
humans may drive
them to extinction
Order Chelonia (Testudines)
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Turtles
~330 species
Ancient group that
survived, remained
mostly unchanged
from early ancestors
Order Rhynchocephalia
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Snout head or tuatara
Only 1 species
From New Zealand sole surviving species
of ancestral stock
Reptilian Characteristics

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Tough, dry scaly skin
Protection against
desiccation, physical
injury
Thin epidermis shed
periodically
Much thicker dermis
with chromatophores
Reptilian Characteristics

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Dermis converted into
snakeskin, alligator
leather for shoes,
purses, and so on
Scales of keratin
(epidermal)
Not homologous to
bony, dermal fish
scales
Reptilian Characteristics
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Crocodilian scales
remain throughout life
Grow gradually to
replace wear
Reptilian Characteristics
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In snakes and lizards,
new scales grow
beneath old
Old scales shed with
old skin
Reptilian Characteristics

Turtles add new
layers of keratin
under old layers of
the plate-like scutes
(modified scales)
Shedding

Snakes turn old skin
(scales, epidermis)
inside out when
shedding
Shedding

Lizards split skin and
leave it right side out,
or slough it off in
pieces
Amniotic Egg
Chorioallantoic
membrane
Amniotic Egg


Reptiles are able to
lay their eggs in
sheltered locations on
land
Young hatch as lungbreathing juveniles,
not aquatic larvae
Amniotic Egg

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Amniotic egg widened
division between
amphibians and
reptiles
Probably greatly
contributed to decline
of amphibians and
rise of reptiles
Reptile Jaws
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Reptile jaws designed
for crushing prey
Fish, amphibian jaws
designed for quick
closure, but little force
after
Reptile jaw muscles
larger, longer,
arranged for better
mechanical
advantage
Reptile Copulatory Organ
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Copulatory organ
permitting internal
fertilization
Internal fertilization
required for a shelled
egg
Copulatory organ
formed from an
evagination of cloaca
Reptile Circulation
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More efficient
circulatory system,
higher blood pressure
All reptiles have at
least an incomplete
separation of the
ventricles
Flow patterns prevent
mixing
Reptile Circulation

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Crocodilians have two
completely separated
ventricles
All reptiles have two
functionally separate
circulations
Reptile Lungs
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Improved lungs
Depend almost
exclusively on lungs
for gas exchange
Supplemented by
pharyngeal
membrane respiration
in some aquatic
turtles
Reptile Lungs

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Lungs have larger
respiratory surface
than in amphibians
Air sucked into lungs
rather then forced in
by mouth muscles
Negative pressure
Skin breathing
completely
abandoned
Reptile Kidney
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Kidneys more
advanced
(metanephric)
Very efficient at
conserving water
Excretes uric acid
(rather than urea,
ammonia)
A semisolid paste
Better Body Support

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Limbs better design for walking on land
More ventral, less lateral
Many dinosaurs walked on only hindlimbs
Nervous System
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Much more advanced - relatively larger
cerebrum
CNS connections more advanced - permit
complex behaviors not found in amphibians
Nervous System

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Sense organs generally well-developed
Hearing generally poorly developed in most
Order Chelonia
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Turtles
Very ancient group
Little change in
morphology since
Triassic period
Order Chelonia
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Body enclosed in
shell
Dorsal carapace
Ventral plastron
Order Chelonia
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Thoracic vertebrae
and ribs built into
shell
Shell of two layers
Inner of bone
Outer of keratin
New keratin
deposited under old
as turtle grows, ages
Order Chelonia

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Jaws lack teeth
Equipped with tough,
horny plates for
gripping, chewing
food
Order Chelonia
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Respiration poses a
problem
Shell prevents
expansion of chest for
breathing
Adapted to use
certain abdominal,
pectoral muscles as a
“diaphragm”
Order Chelonia

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Air drawn in by
contracting limb flank
muscles to make
body cavity larger
Exhalation also active
- shoulder muscles
contracted, viscera
compressed, air
forced out of lungs
Order Chelonia
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Deformable plastron
in snappers allows
some elastic recovery
during exhalation
Compressive force of
water against body
also can force air out
Order Chelonia
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Many water turtles
acquire enough O2
when inactive by
pumping water in and
out of mouth
Pharyngeal breathing
Can stay submerged
for extended periods
Must lung breathe
more frequently when
active
Order Chelonia
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Nervous system - tiny brain
Typical of most reptiles
Never exceeding 1% of body weight, but
cerebrum larger than in amphibians
Turtle can learn, as quickly as a rat, to run a
maze
Order Chelonia

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Have both middle
& inner ear, but
sound perception
is poor
Turtles are virtually
mute
Tortoises may
grunt or roar
Order Chelonia

Poor hearing
compensated for
by:
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Good sense of
smell
Acute vision
Color perception as
good as that of
humans
Order Chelonia
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Mating & reproduction
Many varieties of
courtship
Males of aquatic
species may swim
around looking for
proper leg stripe
pattern
Pheromones also
Males use claws
Order Chelonia

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Terrestrial species
may vocalize
Males may track
females
(pheromones) for
days
Order Chelonia

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Males may mark
territory with fecal
pellets
Courtship involves
rubbing limbs against
scent glands
(underside of jaw)
and sniffing
Order Chelonia
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Biting, ramming,
hooking are directed
at other males
Biting - head & limbs
Ramming - rearing
up, smacking shells
Hooking - bulldozing
under plastron to flip
or hurry
Order Chelonia
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Turtles are
oviparous
Fertilization is
internal, and all
species bury eggs
in ground in nests
4 to >100 eggs
Order Chelonia
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Exercise care in
constructing nest
Deposit eggs and
abandon them
Incubation 1-14
months
40-60 days most
typical
Order Chelonia
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Movements to nesting
areas very faithful
Terrestrial species
use familiarity with
area, sun
Marine species use
variety of
mechanisms to
traverse large
distances
Order Chelonia
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Earth’s magnetic field
Polarized light
Sun & stars
Low frequency
sounds
Green sea turtles find
Ascension Island (20 km)
in mid-Atlantic from
coastal Brazil - 2200 km
Order Chelonia
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Size - marine turtles
largest
Buoyed by aquatic
environment
May reach 2 m in
length, 725 kg in
weight
Biggest species is
leatherback
Order Chelonia

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Green sea turtle may
exceed 360 kg
Economically
valuable - heavily
exploited - rarely gets
to large size
Order Chelonia
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Land tortoises
generally not as large
as aquatic forms
Some may weigh
several hundred kg
Giant tortoises of
Galapagos Islands
among world’s largest
terrestrial turtles
Order Chelonia
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Lifespan - turtles are
most long-lived
vertebrates
Individuals of at least
5 species known to
live 100 years or
longer
Some believed to
have lived more than
150 years
Order Chelonia

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Longevity attributed to
slow rate of
metabolism
Galapagos tortoise
top speed: 300 m/hr
Reports of box turtle
caught in U.S. with
“1850” carved into
plastron
 Skepticism!
Order Chelonia

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Protective shell
Head, appendages
can be drawn in for
protection
Box turtles
especially good
because of hinged
plastron
Order Chelonia

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Shell not as
protective in many
species
Soft, leather-like in
softshell turtles
Order Chelonia
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Shell too small for
protection in other
species, e.g.,
snappers
Other means of
defense - ferocious,
short-tempered
“Tigers of the pond”
Order Chelonia
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
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Entirely carnivorous fish, frogs, ducks,
whatever they can
catch
Alligator snapper
hides on bottom and
waves worm-like
tongue to attract fish
Wholly aquatic - come
ashore only to lay
eggs
Turtle Conservation

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Slow growth, long
time to maturity
predispose many
species to risk of
extinction
Changing conditions
may increase adult
mortality, juvenile
recruitment
Turtle Conservation

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Problem severe for
large tortoises, sea
turtles
Largest, slowestgrowing
Human and animal
invasion of beaches,
isolated island
habitats
Turtle Conservation
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Herbivores compete
with tortoises for
limited vegetation
Eggs, young fall prey
to dogs, cats, rats
Turtle Conservation
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Protection of land
tortoises simpler than
protection of sea
turtles
Limited range (single
island) defines limits
where protection is
needed
Turtle Conservation
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Sea turtles range over
international, national
borders
Limited number of
breeding sites
Problems with
exploitation controlled or outright
ban?
Turtle Conservation
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Ocean plastics
pollution - bags look
like natural jellyfish
prey
Not enough known
about biology do
devise protective
management program
Tag a turtle? 2000 X
Order Squamata
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“characterized by
scales”
Lizards, snakes,
worm lizards
Most recent products
of reptile evolution
Most successful 95% of known living
species of reptiles
Order Squamata
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Lizards began
diversifying at time
when dinosaurs were
near end of their
dominance
Were successful
because of adaptability
Adopt various body
forms, occupy various
habitats
Order Squamata

Snakes likely arose
from group of lizards
whose descendents
include monitor lizards,
but fossil record poor
Order Squamata

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Legless character
apparently evolved as
adaptation to
burrowing lifestyle
Snakes since have
radiated into
terrestrial, aquatic,
arboreal niches
Order Squamata
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Two adaptations
characterize snakes:
Extreme body
elongation displacement,
rearrangement of
organs
Highly mobile jaws swallow prey larger
than own diameter
Order Squamata

Two suborders:

Sauria - lizards
 “lizard”

Serpentes - snakes
 “to creep”
Lizards
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Very diversified group
(3300 species)
Terrestrial, burrowing,
aquatic, arboreal,
aerial
Many familiar groups:
Lizards
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Geckos

Mostly small,
nocturnal, with
adhesive toe pads
(walk anywhere)
Lizards

Iguanas

Often bright-colored
New World lizards

Marine iguana - only
marine lizard in world
Lizards

Skinks

Elongate bodies,
reduced limbs
Lizards

Chameleons

Arboreal

Tongue flicked to
greater distance than
body length
Prehensile tail
Zygodactylous feet
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Lizards

Independently
moveable eyes
elevated on cones good eyesight gauge distance
accurately
Lizards
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Lizard body form not
as distinctive as other
reptiles
Many functional,
behavioral
modifications
e.g., degenerate or
absent limbs - no
good in dense grass
Lizards

Differ from snakes:

Halves of lower jaw
firmly united at
mandibular
symphysis

Teeth, but not
developed into fangs
Lizards

Moveable eyelids
(snake eyes covered
with permanent,
transparent cap)

Keen daylight vision
Lizards

Size - 3 cm to 3 m

Hawaiian gecko


Komodo dragon
75 kg

Fossils: 5.5 m, >1000 kg
Lizards
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80% of lizards are
<20 g in weight
Generally
insectivorous
(opportunistic),
although some
specialists
N. Amer. horned
lizards eat only ants
Lizards
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Most large lizards are
herbivores
Trees in tropics,
ground vegetation on
oceanic islands,
seaweed in ocean
Lizards
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Monitor lizards are
exception to
vegetarians
Food of vertebrates
(birds, mammals),
invertebrates
Komodo - ambush
predator on large
mammals (deer,
goats, water buffalo)
Lizards

Foraging strategies:

Sit and wait (insects
come to them)

Active foragers (move
to encounter prey)
Lizards
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Foraging modes
alternate at
successive levels of
food chain
Moving insect -> sitand-wait lizard ->
active predator
Sitting insect -> active
lizard -> sit-and-wait
predator
Lizards
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May use territorial
and courtship
behaviors
Male anoles have
gular fan (dewlap) for
conspicuous displays
Skin distended by
hyoid apparatus
Lizards

Behaviors include:

Extending,
contracting fan
Pushups
Bobbing head


Lizards

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Territories defended
by males for access
to females (bite &
chase, but no fighting)
Females have nonoverlapping home
ranges for feeding
Male territory includes
several females mates with all
Lizards

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Mate by pressing
cloacal regions
together
Males grip female’s
neck, shoulders
Males have paired
copulatory organs hemipenes - to aid
sperm transfer
Lizards

Range of reproductive
modes from oviparity
to viviparity

Skinks - eggs
retained in oviducts,
receive nutrients
across a “placenta”
Lizards


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All-female
(parthenogenetic)
species occur in at
least 6 families
Especially common
among racerunners
(Teiidae)
Diploids and triploids
known
Lizards

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High reproductive
potential - every
individual capable of
producing offspring
Can repopulate
habitat faster than
bisexual species after
flood, other disaster
Lizards

Parental care

Many lizards remain
with eggs or nest site

Little if any care given
after young hatch or
are born
Suborder Serpentes - Snakes



2300 species
10 cm long up to 10
m long
Highly specialized
body form
Suborder Serpentes - Snakes

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
Entirely limbless
Lack pectoral, pelvic
girdles (except
vestige of latter in
pythons, boas)
Short, wide vertebrae
for quick lateral
undulations
Ribs improve rigidity
Suborder Serpentes - Snakes
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
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Rearranged internal
anatomy
Left lung reduced or
absent
Gall bladder posterior
to liver
Right kidney anterior
to left
Gonads similarly
displaced
Suborder Serpentes - Snakes
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Little modification for
various lifestyles:
Elongate for arboreal
Shorten for burrowing
Broaden for
swallowing big prey
Compress laterally for
swimming
Snake Sense Organs

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Snake, lizard eyes
different: focusing, retina
morphology
Re-evolved from
burrowing ancestors
Permanent transparent
covering - non-blinking
stare
Lack of eyeball mobility
Poor vision - except
binocular in arboreal
snakes
Snake Sense Organs


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Hearing - no obvious
external ear
No obvious response
to aerial sounds
Not deaf - have
internal ears - hearing
similar to lizards
Sensitive to vibrations
carried in ground
Snake Sense Organs



Olfaction important,
but not in nostrils
Jacobson’s organs
(vomeronasal organs)
Tongue carries scent
particles to organ
Snake Feeding





Skull, jaws highly
specialized for feeding
Eat prey several times
their own diameter
Non-joined mandibles
Loose skull bones
Tracheal opening far
forward between
mandibles
Snake Feeding



Prey swallowed head
first
Pulled in by teeth,
jaws, alternating sideto-side
Contractions of neck
muscles force prey
down digestive tract
Snake Feeding

Two ways to subdue
prey:

Constricting - grab
prey in mouth and
suffocate by looping
body coils and
tightening
Snake Feeding



Venom - toxic
concentrations in
saliva
Neurotoxic blindness, paralysis
Hemolytic - ruptures
blood vessels, cells
Snake Feeding





Poisonous snakes in 4
families
Viperidae - viper, pit
vipers (heat sensitive)
Elapidae - coral snakes
(inject venom by
chewing)
Hydrophiidae - sea
snakes
Colubridae - rear-fanged venom to calm, not kill
Snake Feeding

Sea snakes have
most deadly venom

King cobra most
dangerous, largest
(5.5 m) - kill 9,000
people per year
Snake Locomotion


4 basic types:
Lateral undulation - Sshaped path,
pressure against
surface irregularities
Snake Locomotion


Concertina movement
- movement upward
or along narrow
passages
Extend forward while
bracing S-shaped
loops
Snake Locomotion

Rectilinear movement
- slow, straight-line
movement
Snake Locomotion

Sidewinding - sandy
surfaces, body thrown
forward in loops, body
at 60° angle to line of
travel, 1 or 2 parts of
body in contact with
ground at once
Snake Reproduction




Most oviparous - lay
eggs in protected areas
Most of remainder are
ovoviviparous
(including rattlesnakes)
Very few viviparous
Females store sperm
from single mating, can
lay several clutches
over long interval
Order Crocodilia




Unchanged for 160
million years
Crocodiles larger, more
dangerous than
alligators
Prey drowned, ripped
into pieces by rapid
rolling
No natural enemies
Order Crocodilia



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

Oviparous - lay eggs in
mass of vegetation
Guarded by mother
Incubation temperature
determines sex of
alligator hatchlings
Low - females
High - males
5:1 (M:F) in some areas
Order Crocodilia


Vocalizations by
hatchlings cause
mother to open next,
allow hatchlings to
escape
Some adults carry
young to water
Order Crocodilia

Mothers may guard
young in pools for
period of time to
protect them from
predators (fish,
mammals)
Order Sphenodonta




Tuatara - single
species in New
Zealand
Lizard-like, <66 cm
Lives in burrows
Slow-growing, longlived (77 years)
Order Sphenodonta



Living fossil - primitive
features identical to
fossilized forms
Primitive skull
structure
Well-developed
parietal eye with
retina, lens on top of
head (non-functional)