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1

Tetrapods aka

"four foot"

2

Tetrapod show evolutionary transition

from life in water to land

3

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")

4

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

5

life in the "Devonian" aka

the "age of fishes"

6

Devonian period began

>400 mya

7

Devonian land masses & temperatures

- near the equator, swampy w/ FW, low elevation
- mild & consistent temperatures BUT many FW environments unstable (alternating wet & dry periods)

8

Early Tetrapod Origins Groups

Eusthenopteron, Panderichthys, Tiktaalik, Acanthostega

9

Eusthenopteron moves

along bottom of ocean w/ lobed fins

10

Eusthenopteron pectoral girdle attached to

skull (fish characteristic, not synap)
- t.f. no neck in fish

11

Eusthenopteron shows early origin of

limbs

12

Sarcopterygian (rhipidistian lineage) lobed fins homologous to

elements of tetrapod limb (arm) bones

13

Panderichthyes skull

depressed w/ eyes on top like early tetrapods

14

Panderichthyes lived

in shallow H2O (t.f. depressed skull)

15

Panderichthyes loss & reduction

loss: dorsal & anal fin
reduction: caudal fin

16

Panderichthyes girdle attached

still to skull (no neck)
- by bony gill coverings

17

Tiktaalik aka

"fishapod"

18

Tiktaalik lived

in late Devonian

19

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

20

most compelling example to date of an animal close to the transition between water and land?

Tiktaalik

21

Acanthostega pectoral girdle

not attached to skull (had neck)

22

Acanthostega appendages

well-formed limbs (increase mobility)

23

Acanthostega fin rays on

tail

24

Acanthostega digits?

many digits (reduction & loss in modern tetrapods)

25

Acanthostega show homology in fish thru

stapes & hyomandibular????

26

Carboniferous radiation of tetrapods

- time of warm, moist, swampy environment w/ many insects on land & invertebrates in waters
- opportunity for tetrapods to invade habitats and diversify (adaptive radiation)

27

2 major lineages of tetrapods have extant representatives

Lissamphibia
Amniota

28

Temnospondyli =

extinct lineages + lissamphibia

29

Lissamphibia =

3 modern amphibian clades:
- Anura
- Caudata
- Gymnophiona

30

Temnospondyli monophyletic or paraphyletic?

monophyletic clade