Introduction to Amphibia
Introduction to Amphibia
Introduction to Amphibia
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<strong>Introduction</strong> <strong>to</strong> <strong>Amphibia</strong><br />
Frogo <strong>to</strong>rpedo<br />
Why are frogs so happy?<br />
They eat whatever bugs them!
<strong>Amphibia</strong>ns in the fossil record<br />
Shown at the left is<br />
Phlegethonia, an<br />
ais<strong>to</strong>pod from the<br />
Pennsylvanian.<br />
!<strong>Amphibia</strong>ns go back all the way <strong>to</strong> at least the<br />
Upper Carboniferous (360-286 mya)<br />
!The familiar frogs, <strong>to</strong>ads, and salamanders have<br />
been present since at least the Jurassic Period.
<strong>Amphibia</strong>ns in the fossil record<br />
♦The later Paleozoic saw a great<br />
diversity of amphibians, ranging<br />
from small legless swimming<br />
forms (Ais<strong>to</strong>poda) <strong>to</strong> bizarre<br />
"horned" forms (Nectridea).<br />
The fossil frog<br />
pictured above<br />
comes from the<br />
Eocene, only 45 <strong>to</strong><br />
55 million years ago<br />
♦Other Paleozoic amphibians<br />
more or less resembled<br />
salamanders outwardly but<br />
differed in details of skeletal<br />
structure
<strong>Amphibia</strong>: Life His<strong>to</strong>ry and Ecology<br />
The name amphibian means<br />
"double life", and is given <strong>to</strong><br />
members of this group for<br />
the double life that they lead.<br />
Young amphibians spend their early years in the<br />
water breathing through gills in the side of their<br />
head in much the same way as fish do.
<strong>Amphibia</strong>: Life His<strong>to</strong>ry and Ecology<br />
As they mature, amphibians will usually lose<br />
their gills and develop legs (Metamorphosis).<br />
However…..<br />
A number of<br />
salamanders, such as the<br />
North American<br />
"mudpuppy", develop<br />
legs but retain their larval<br />
gills and stay in the water<br />
throughout their lifetimes<br />
Mudpuppy (Necturus maculosus)<br />
This is a classic example of an evolutionary<br />
phenomenon known as neoteny – the retention of<br />
larval or juvenile features in mature adults.
Origin and Evolution of the Class <strong>Amphibia</strong><br />
♦Devonian – Age of Fish and<br />
<strong>Amphibia</strong>ns<br />
♦Very warm and wet climate; many<br />
shallow, warm, freshwater “seas”<br />
♦Swamps prevailed throughout the<br />
Devonian and in<strong>to</strong> the Triassic<br />
♦Plants dominated by Scale trees<br />
and Horsetails. The First<br />
gymnosperms appeared<br />
Ichthyostega, a small, early amphibian (3ft / 1m) from Greenland
Why leave the water?<br />
Hynerpe<strong>to</strong>n bassetti is one of<br />
the oldest known amphibians,<br />
dating back 363 million years<br />
<strong>to</strong> the Devonian of<br />
Pennsylvania.<br />
♦Escape preda<strong>to</strong>rs<br />
♦Ephemeral nature of particular bodies of water<br />
♦Food Resources<br />
♦Take advantage of two habitat niches
What would you take along (Adaptations)?<br />
♦Skin -- for protection and temp effects<br />
♦Breathing apparatus (lungs)<br />
♦Vision System<br />
♦Locomoter Adaptations (Limbs, vertebral, ribs,<br />
and diaphragm)<br />
♦Digestive system changes<br />
♦Sound reception
Tetrapods and The Move <strong>to</strong> Dry Land<br />
♦Tetrapods (tetra=four,<br />
pod=feet) were the first<br />
vertebrates <strong>to</strong> truly walk<br />
the land.<br />
♦Before tetrapods<br />
existed, vertebrates were<br />
all confined <strong>to</strong> living in<br />
aquatic habitats.<br />
♦They began their conquest of land in the Paleozic<br />
around 360 million years ago.
This point represents one of the great<br />
events of vertebrate his<strong>to</strong>ry: the<br />
development of four limbs in the common<br />
ances<strong>to</strong>r of all tetrapods
Where did tetrapods come from?<br />
2 possible ances<strong>to</strong>rs<br />
- Lung fish<br />
- Crossopterygian fish<br />
(Lobe-finned fish)<br />
1. Lungfish<br />
♦As the name implies lungs are<br />
present, as are modified fins<br />
♦The heart is partly divided<br />
in<strong>to</strong> a left and a right half as in<br />
true land vertebrates.<br />
South American Lungfish<br />
Life on land is possible, but…
♦Dermal Bones - don’t match size, shape, or<br />
positioning of modern amphibians<br />
♦Limb structure - don’t have radius, ulna, humerus,<br />
wrist, or fingers<br />
♦Lack teeth in margins of the skull - found in first<br />
amphibians<br />
There are 3 living groups of<br />
lungfish.<br />
Their distribution suggests<br />
that at some point the land<br />
masses were linked <strong>to</strong>gether<br />
Read web sections on Laurasia,<br />
Gondwanaland and continental drift
2. Crossopterygian Fish<br />
♦Had what appeared <strong>to</strong> be a<br />
radius, ulna, finger structure, etc.<br />
Modern coelacanth<br />
♦Presence of labrynthodont<br />
<strong>to</strong>oth. Found in only two groups<br />
of vertebrates: Lobe-finned fish<br />
and early amphibians
♦Dermal Bones matched those of first amphibians<br />
Lobe-finned fish<br />
Parietal foramen<br />
First <strong>Amphibia</strong>ns
Modern Coelacanth<br />
Early <strong>Amphibia</strong>n<br />
♦Many bot<strong>to</strong>m-living modern fish use their fins <strong>to</strong> help<br />
them maneuver over the bot<strong>to</strong>m. But the pattern of bones<br />
at the base of the fins of most modern fish are quite unlike<br />
those of the limbs of land vertebrates.<br />
♦However, the arrangement of bones within the base of the<br />
fin of the modern coelacanth is very similar <strong>to</strong> the limb<br />
structure of land vertebrates.
♦The most likely ances<strong>to</strong>rs of<br />
the amphibians were the<br />
Rhipidistians - a type of<br />
crossopterygian fish (quite<br />
closely related <strong>to</strong> the coelacanth<br />
line) which were common about<br />
250 mya.<br />
♦The rhipidistians were large fish, up <strong>to</strong> a meter in<br />
length, with deep bodies, and powerful teeth.<br />
♦They were preda<strong>to</strong>rs, and probably lay in ambush <strong>to</strong><br />
catch passing fish.
Considered the most probable ances<strong>to</strong>rs of the<br />
amphibians because the two groups share a<br />
number of important characters;<br />
1. the arrangement of skull bones is similar<br />
2. the amphibian limb can be derived from the fin structure<br />
3. the rhipidistians lived in shallow freshwater lakes and<br />
almost certainly had lungs and breathed air<br />
4. both rhipidistians and early amphibians have a<br />
labrynthodont <strong>to</strong>oth<br />
5. rhipidistians were the only fish which had developed an<br />
opening <strong>to</strong> the nostrils inside the mouth - a feature which is<br />
found in all the land vertebrates.
The Missing Link?<br />
Link????<br />
Many specimens from the<br />
Middle Devonian<br />
Appeared in the Late<br />
Devonian<br />
♦Unfortunately no fossil species which directly link the<br />
two groups have been found during the intervening<br />
period of about 30 million years.