amphibian evolution

8/2/2019 Amphibian Evolution

1/19

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?


2/19

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.


3/19

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


4/19

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.


5/19

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)


6/19

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


7/19

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


8/19

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


9/19

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.


10/19

This point represents one of the great

events of vertebrate history: thedevelopment of four limbs in the common

ancestor of all tetrapods


11/19

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


12/19

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


13/19

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.


14/19

Dermal Bones matched those of first amphibians

Parietal foramen

Lobe-finned fish First Amphibians


15/19

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


16/19

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


17/19

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?


18/19

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.


19/19

amphibian evolution

Documents