Introduction to Amphibia

Introduction to Amphibia
Frogo torpedo
Why are frogs so happy?
They eat whatever bugs them!

Amphibians in the fossil record
Shown at the left is
Phlegethonia, an
aistopod from the
Pennsylvanian.
!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.

Amphibians in the fossil record
♦The later Paleozoic saw a great
diversity of amphibians, ranging
from small legless swimming
forms (Aistopoda) to bizarre
"horned" forms (Nectridea).
The fossil frog
pictured above
comes from the
Eocene, only 45 to
55 million years ago
♦Other Paleozoic amphibians
more or less resembled
salamanders outwardly but
differed in details of skeletal
structure

Amphibia: Life History and Ecology
The name amphibian means
"double life", and is given to
members of this group for
the double life that they lead.
Young amphibians spend their early years in the
water breathing through gills in the side of their
head in much the same way as fish do.

Amphibia: Life History and Ecology
As they mature, amphibians will usually lose
their gills and develop legs (Metamorphosis).
However…..
A number of
salamanders, such as the
North American
"mudpuppy", develop
legs but retain their larval
gills and stay in the water
throughout their lifetimes
Mudpuppy (Necturus maculosus)
This is a classic example of an evolutionary
phenomenon known as neoteny – the retention of
larval or juvenile features in mature adults.

Origin and Evolution of the Class Amphibia
♦Devonian – Age of Fish and
Amphibians
♦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 First
gymnosperms appeared
Ichthyostega, a small, early amphibian (3ft / 1m) from Greenland

Why leave the water?
Hynerpeton bassetti is one of
the 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

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

Tetrapods and The Move to Dry Land
♦Tetrapods (tetra=four,
pod=feet) were the first
vertebrates to truly walk
the land.
♦Before tetrapods
existed, vertebrates were
all confined to living in
aquatic habitats.
♦They began their conquest of land in the Paleozic
around 360 million years ago.

This point represents one of the great
events of vertebrate history: the
development of four limbs in the common
ancestor of all tetrapods

Where did tetrapods come from?
2 possible ancestors
- Lung fish
- Crossopterygian fish
(Lobe-finned fish)
1. Lungfish
♦As the name implies lungs are
present, as are modified fins
♦The heart is partly divided
into a left and a right half as in
true land vertebrates.
South American Lungfish
Life on land is possible, but…

♦Dermal Bones - don’t match size, shape, or
positioning of modern amphibians
♦Limb structure - don’t have radius, ulna, humerus,
wrist, or fingers
♦Lack teeth in margins of the skull - found in first
amphibians
There are 3 living groups of
lungfish.
Their distribution suggests
that at some point the land
masses were linked together
Read web sections on Laurasia,
Gondwanaland and continental drift

2. Crossopterygian Fish
♦Had what appeared to be a
radius, ulna, finger structure, etc.
Modern coelacanth
♦Presence of labrynthodont
tooth. Found in only two groups
of vertebrates: Lobe-finned fish
and early amphibians

♦Dermal Bones matched those of first amphibians
Lobe-finned fish
Parietal foramen
First Amphibians

Modern Coelacanth
Early Amphibian
♦Many bottom-living modern fish use their fins to help
them 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.

♦The most likely ancestors of
the amphibians were the
Rhipidistians - a type of
crossopterygian 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.

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 is
found in all the land vertebrates.

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.