EARTH 7 Lecture Notes - Lecture 7: Actinopterygii, Tetrapod, Transitional Fossil
10/19/17
● Vertebrate evolution
○ Two types of “Bony fish” and the transition to land
● ray- finned fish = actinopterygii
○ Actino = ray ptero = wing
● Fleshly-limbed vertebrates = sarcopterygii
○ Sarc = flesh ptero = wing
● Fleshy-limbed Vertebrates
1. Coelacanths
a. Thought to be extinct than found again today
2. Lungfish
a. More complex lungs
b. A living “transitional fossil”
3. Transitional fossils
4. Tetrapods
a. Evolved from fleshly limb fish
b. Sequential acquisition of tetrapod characters over time
c. Four limbs with fingers
i. For locomotion and grasping
d. Vertebrae with struts
i. Help keep backbone rigid on land, since weight is no longer
supported by water
e. Robust hips
i. Attach to spine to support more weight
f. Stapes
i. Bone that connects the eardrum to the inner ear, to help amplify
sound
● Vertebrates
○ Gnathostomes
○ Evolved jaws - first leap in evolution
■ Osteichthyes
● Fleshly-limbed vertebrates
○ Tetrapods
■ amniotes
● Early tetrapods were amphibious - tied to water for reproduction and early development
○ Modern amphibians retain this “ancestral” characteristic
● Amniotes: true land conquerors
○ Later part of paleozoic
○ Form eggs to inside a protective membrane and reproduce vio internal
fertilization
■ Amniotes don’t spawn
● Spawning - releasing sperm and egg directly into water
