Tetrapod Lecture Flashcards
(71 cards)
Tetrapods aka
“four foot”
Tetrapod show evolutionary transition
from life in water to land
Life on Land opportunities:
O2 more abundant (20x) in air than H2O
O2 more easily acquired in air than H2O
Variety of habitats on land (abundant shelter “vegetative structure” & food “invert.’s”)
Life on Land challenges:
air ~800x less dense than water @STP - no buoyancy / dealing w/ gravity new ways to support body required - girdles (modified) & limbs (evolved) to combat gravity on land - skeletal remodeling
life in the “Devonian” aka
the “age of fishes”
Devonian period began
> 400 mya
Devonian land masses & temperatures
- near the equator, swampy w/ FW, low elevation
- mild & consistent temperatures BUT many FW environments unstable (alternating wet & dry periods)
Early Tetrapod Origins Groups
Eusthenopteron, Panderichthys, Tiktaalik, Acanthostega
Eusthenopteron moves
along bottom of ocean w/ lobed fins
Eusthenopteron pectoral girdle attached to
skull (fish characteristic, not synap)
- t.f. no neck in fish
Eusthenopteron shows early origin of
limbs
Sarcopterygian (rhipidistian lineage) lobed fins homologous to
elements of tetrapod limb (arm) bones
Panderichthyes skull
depressed w/ eyes on top like early tetrapods
Panderichthyes lived
in shallow H2O (t.f. depressed skull)
Panderichthyes loss & reduction
loss: dorsal & anal fin
reduction: caudal fin
Panderichthyes girdle attached
still to skull (no neck)
- by bony gill coverings
Tiktaalik aka
“fishapod”
Tiktaalik lived
in late Devonian
Tiktaalik qualities (fish-like & tetrapod-like)
Fish-like: scales, gills, lateral line, & fins w/ rays (no digits)
Tetrapod-like: depressed skull, & shoulder, elbow, & wrist elements (mobile joints). Skull not attached to pectoral girdle, t.f. most basal “necked” vertebrate lineage
most compelling example to date of an animal close to the transition between water and land?
Tiktaalik
Acanthostega pectoral girdle
not attached to skull (had neck)
Acanthostega appendages
well-formed limbs (increase mobility)
Acanthostega fin rays on
tail
Acanthostega digits?
many digits (reduction & loss in modern tetrapods)
