amphibian evolution
TRANSCRIPT
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I nt r oduct ion t o Amphibia
Frogo torpedo
They eat what ever bugs t hem!
Why ar e f r ogs so happy?
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Amphibians in the fossil record
!Amphibians go back all the way to at least the
Upper Carboniferous (360-286 mya)
!The familiar frogs, toads, and salamanders have
been present since at least the Jurassic Period.
Shown at the left is
Phlegethonia, an
aistopod from thePennsylvanian.
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Amphibians in the fossil record
The later Paleozoic saw a greatdiversity of amphibians, rangingfrom small legless swimming
forms (Aistopoda) to bizarre"horned" forms (Nectridea).
Other Paleozoic amphibiansmore or less resembled
salamanders outwardly butdiffered in details of skeletalstructure
The fossil frog
pictured above
comes from the
Eocene, only 45 to
55 million years ago
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Amphibia: Life History and Ecology
The name amphibian means"double life", and is given tomembers of this group forthe double life that they lead.
Young amphibians spend their early years in the
water breathing through gills in the side of theirhead in much the same way as fish do.
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Amphibia: Life History and Ecology
As they mature, amphibians will usually losetheir gills and develop legs (Metamorphosis).However..
A number ofsalamanders, such as theNorth American
"mudpuppy", developlegs but retain their larvalgills and stay in the water
throughout their lifetimes
This is a classic example of an evolutionary
phenomenon known as neoteny the retention oflarval or juvenile features in mature adults.
Mudpuppy (Necturus maculosus)
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Origin and Evolution of the Class Amphibia
Devonian Age of Fish andAmphibians
Very warm and wet climate; many
shallow, warm, freshwater seas
Swamps prevailed throughout the
Devonian and into the Triassic
Plants dominated by Scale trees
and Horsetails. The Firstgymnosperms appeared
Ichthyostega, a small, early amphibian (3ft / 1m) from Greenland
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Why leave the water?
Hynerpeton bassetti is one ofthe oldest known amphibians,
dating back 363 million years
to the Devonian of
Pennsylvania.
Escape predators
Ephemeral nature of particular bodies of water
Food Resources
Take advantage of two habitat niches
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What would you take along (Adaptations)?
Skin -- for protection and temp effects
Breathing apparatus (lungs)
Vision System
Locomoter Adaptations (Limbs, vertebral, ribs,
and diaphragm)
Digestive system changes
Sound reception
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Tetrapods and The Move to Dry Land
Tetrapods (tetra=four,pod=feet) were the first
vertebrates to truly walkthe land.
Before tetrapodsexisted, vertebrates were
all confined to living in
aquatic habitats.
They began their conquest of land in the Paleozic
around 360 million years ago.
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This point represents one of the great
events of vertebrate history: thedevelopment of four limbs in the common
ancestor of all tetrapods
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Where did tetrapods come from?
2 possible ancestors- Lung fish
- Crossopterygian fish
(Lobe-finned fish)
1. Lungfish
As the name implies lungs arepresent, as are modified fins
The heart is partly divided
into a left and a right half as in
true land vertebrates.
Life on land is possible, but
South American Lungfish
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Dermal Bones - dont match size, shape, or
positioning of modern amphibians
Limb structure - dont have radius, ulna, humerus,
wrist, or fingers
Lack teeth in margins of the skull - found in first
amphibians
There are 3 living groups oflungfish.
Their distribution suggeststhat at some point the land
masses were linked together
Read web sections on Laurasia,
Gondwanaland and continental drift
2 C t i Fi h
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Modern coelacanth
2. Crossopterygian Fish
Presence of labrynthodont
tooth. Found in only two groups
of vertebrates: Lobe-finned fishand early amphibians
Had what appeared to be a
radius, ulna, finger structure, etc.
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Dermal Bones matched those of first amphibians
Parietal foramen
Lobe-finned fish First Amphibians
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Many bottom-living modern fish use their fins to helpthem maneuver over the bottom. But the pattern of bones
at the base of the fins of most modern fish are quite unlike
those of the limbs of land vertebrates.
However, the arrangement of bones within the base of the
fin of the modern coelacanth is very similar to the limb
structure of land vertebrates.
Modern Coelacanth Early Amphibian
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The most likely ancestors of
the amphibians were the
Rhipidistians - a type ofcrossopterygian fish (quite
closely related to the coelacanth
line) which were common about
250 mya.
The rhipidistians were large fish, up to a meter in
length, with deep bodies, and powerful teeth.
They were predators, and probably lay in ambush to
catch passing fish.
C id d th t b bl t f th
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Considered the most probable ancestors of the
amphibians because the two groups share a
number of important characters;
1. the arrangement of skull bones is similar
2. the amphibian limb can be derived from the fin structure
3. the rhipidistians lived in shallow freshwater lakes and
almost certainly had lungs and breathed air
4. both rhipidistians and early amphibians have a
labrynthodont tooth
5. rhipidistians were the only fish which had developed an
opening to the nostrils inside the mouth - a feature which isfound in all the land vertebrates.
The Missing Link?
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The Missing Link?
Link????
Many specimens from the
Middle Devonian
Appeared in the Late
Devonian
Unfortunately no fossil species which directly link the
two groups have been found during the intervening
period of about 30 million years.
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