Download Vertebrates

Vertebrates
The Origin of Tetrapods
The first vertebrates on land were
amphibians in the Devonian (400 mya)
 May have arose from the rhipidistian
(features).
 Arose in coastal or brackish marine
environment

Origin of
Tetrapods
Origin of Tetrapods
Tetrapods
Advantages of
Terrestriality
• An increase in
metabolism and
development due to
higher body temperature.
• Energy – An increase of
10 degrees Celsius (from
20 degrees (water temp)
to 30 degrees (air temp)
would allow for a
doubling of their
metabolic rates
Tetrapods
Lungs – To breath air, it
required an increased
vascularization of the
air-filled cavity (a pouch
from the posterior
pharynx similar to the
swim bladder), with a
rich capillary network to
form a lung.
Tetrapods
Double circulatory system
•
Fish have a single circuit
system – low blood
pressure
•
The double circulation
system allows for higher
pressure with one circuit
going to the lungs and
another going to the body.
Tetrapods
Nasal Openings
•
•
Bony fish have 4
external nares (2 on
each side) which
allows water to run
across the olfactory
tissue.
Tetrapods have two
external and two
internal nares in the
palate. This allows air
to be drawn in through
the nose.
Tetrapods – General
Characteristics
Body Density - Limbs
Air is 1000 times less
buoyant then water
• counter the effects
of gravity
• homologous
structures (bones –
humerus, ulna and
radius).
Tetrapods – General
Characteristics
Body Density - Girdles –
• In fish, the pectoral girdle
is attached to the skull.
• Early tetrapods developed
a stronger shoulder
girdle, bulky limb bones
and well developed
muscles.
• The pelvic girdle is fused
to the backbone to
increase the force that
can be generated by the
hind legs.
Tetrapods – General
Characteristics
Body Density Vertebrae and
Ribs –
• Vertebrae have
developed
zygapophyses.
• The development
of ribs can also
protect the lungs.
Tetrapods – General
Characteristics
Body Density - Skull and Neck
•
•
•
The skull has been shortened and the snout elongated.
The head becomes separated from the body by a neck (a
cervical vertebrae) that allows the head to be lifted.
A second vertebrae was then added to allow for a side to
side movement.
Tetrapods – Evolutionary History
1.
Fish
Tetrapods – Evolutionary History


“Fishapod” –
Tiktaalik (375 mya)
A fish with tetrapod
features, this animal
probably could not
walk on land but could
lift itself out of the
water.
1.
2.
Fish Characteristics
– Scales
– Fins
– Gills and lungs
Tetrapod Characteristics
– Neck
– Ribs
– Fin skeleton
– Flat skull
– Eyes on top of skull
Classification
 Phylum:
Chordata
 Subphylum: Vertebrata
 Superclass: Gnathostomata
 Class: Amphibia
– Order: Urodela (Salamanders)
– Order: Anurans (Frogs and Toads)
– Order: Apodans (Caecilians)
Class: Amphibia

Two lives
– refers to metamorphosis of many frogs



Skin smooth, moist (cutaneous respiration), and
glandular (toxins)
Three chambered heart with a double circulation
system
Mesolecithal eggs with jelly-like membrane
Order: Urodela
400 species
 Salamanders
 Retain their tail as
adults
 Limbs are at right
angles to the body
 Carnivorous

Order: Anurans
3500 species
 Frogs and Toads
 Lose their tail as
adults
 Hind limbs are
adapted for
jumping
 Tongue connected
to front of mouth
 Secrete mucus

Order: Apodans
150 species
 Caecilians
 Legless and blind

Thermoregulation
Ectothermic
 Endothermic

Poikilothermic
 Homeothermic

Heat Exchange
Heat Exchange
 Conduction
- direct transfer of heat
 Convection - transfer of heat by the
movement of air or water across a
surface
 Radiation - emission of
electromagnetic waves
 Evaporation - loss of heat from
changing a liquid into a gas
Body
Temp
vs.
Ambient
Temp
Thermoregulation Adjustments
 Adjusting
the rate of heat exchange
– vasodilation/vasoconstiction
– countercurrent heat exchange
 Cooling
by evaporation
 Behavioral responses
 Changing the rate of metabolic heat
production
Amphibians and Reptiles
 Most
are ectothermic
– regulate temperature by behavior
Feedback Mechanisms

High body
temperature
– hypothalamus
activates skin blood
vessels to dilate
and the sweat
glands to produce
sweat

Low body
temperature
– hypothalamus
activates skin
blood vessels to
constrict and the
skeletal muscles
to shiver
Temperature Range
Adjustments
 Slow
changes
– acclimatization (enzymes and
membranes)
 Fast
changes
– heat-shock proteins
Evolution of the Amniotic Egg
 Allows
animals to complete their
entire life cycle on land
 Has shell that retains water (or is
lost when kept inside mammals)
 Specialized extraembryonic
membranes (not part of the animal)
Evolution of the Amniotic Egg
 Amnion
- Protects from dehydration
and mechanical shock
 Yolk Sac - Nutrient storage
 Albumin - Nutrient storage
 Allantois - stores waste, gas
exchange
 Chorion - gas exchange
Amniotes
Amniotes
How Reptiles differ from
Amphibians
Tough, dry skin
 Amniotic egg
 Crushing or
gripping jaws
 Copulatory organs
 More efficient
circulatory system
with a higher blood
pressure

More developed
lungs (thoracic
breathing)
 Better water
conservation
 Better body
support and limbs
 Better nervous
system

Classification
 Phylum:
Chordata
 Subphylum: Vertebrata
 Superclass: Gnathostomata
 Class: Reptilia (not real)
– Class: Testudines (Turtles and
Tortoises)
– Class: Spenodontia (Tuataras)
– Class: Squamata (Lizards and Snakes)
– Class: Crocodilia (Crocodiles and
Alligators)
Reptile
Radiation
Synapsids
(therapsids) - led
to mammals
 Sauropsids

– Anapsids???
(turtles)
– Diapsids (all
others)
Class: Testudines (Chelonia)
Evolved on land
and returned to
water (lay eggs
on land)
 Protective Shell

– Carapace
– Plastron
Class: Sphenodontia

Tuataras
– Two living species
(New Zealand)
– Not a True Lizard
(no external ears)
– Very Primitive
(similar to mesozoic
reptiles
– Well developed eye
below skin?
Class: Squamata

Lizards
– geckos, iguanas, skinks,
chameleons




terrestrial, burrowing,
aquatic, arboreal
moveable eyelids
Paired copulatory organs
Lower jaw not attached
to skull
Class: Squamata
Class: Squamata
Class: Squamata
Class: Squamata
Class: Squamata
Snakes
 Lack limbs
 Lack moveable
eyelids
 Jacobson’s organ
 Pit Vipers (heat)
 Venom

– neurotoxins
– hemolytic
enzymes
Class: Squamata
Class: Squamata
Class: Squamata
Class: Squamata
Feeding
Adaptations
 Teeth
curved and pointed inward
 Hinged Quadrate bone
 Bones of jaw are attached by
muscles and ligaments
 Moveable palate
 Elastic skin
 No sternum
Largest living
reptiles
 Most closely
related to
dinosaurs
 Complete
secondary
palate
 Four
chambered
heart
 Nest
temperature

Class: Crocodilia
Dinosaurs and Pterosaurs

Dinosaurs
– Ornithischian
– Saurischian (closely
related to birds)

Pterosaurs
– flying reptiles