Tetrapods
Many intermediate fossils have recently been discovered
Millions of years ago
420 415 400 385 370 340 325 310 295 280 265
355
Silurian Devonian Carboniferous Permian To
present
Paleozoic
Ray-finned fishes
Coelacanths
Lungfishes
Acanthostega
Amphibians
Figure 34.20
1
Dipnoi
Myxini
Reptilia
Actinistia
Amphibia
Mammalia
Urochordata
Actinopterygii
Chondrichthyes
Cephalochordata
Cephalaspidomorphi
Acanthostega was a fish-like tetrapod
- aquatic (gills)
- four limbs
Devonian period (405-360 mya) had frequent droughts
2
Class Amphibia: amphibians
MEIs:
1. Adults partially terrestrial
a. better lungs
- still not very efficient (few, large alveoli)
- cutaneous breathing also
b. stronger skeleton
c. tetrapod (4 limbs)
- from paired fins
But larvae are still aquatic (gills, fins)
3
2. 3-chambered heart
a. separate pulmonary and systemic circulation
b. single ventricle
3. Poison glands in skin (alkaloids)
4
Arose ~360 mya
5,000 species, mostly frogs and toads
2. Includes sharks, skates, rays
- 750 species
3. Cartilaginous skeleton
- reversal
4. Lateral line senses pressure
Adaptive radiation during warm, wet
Carboniferous period (360-300 mya)
 Age of Amphibians
5
Earth was warmer, so sea level was much higher
6