B7 vertebrates

Question 1

Fish to land

Answer 1

Movement is not limiting, crutching may have been the most successful method for teleosts moving on land.

Respiration is not limiting, advantage of breathing air. Air also had a higher O2 conc at that time.

Terrestrial reproduction to avoid predation, drove fish out of the water.

Feeding in air requires morphological modification so they may remain tied to water to feed.

Question 2

Class Sarcopterygii

Answer 2

26,742 exstant species, only 8 extant fish species. Enamelled teeth, fleshy and lobed fins, Cosmoid scales.

Question 3

Subclass Coelacanthimorpha

Answer 3

2 living species. Appeared in Devonian, max diversity in Triassic. 3 lobed tail, hollow spine. Unconstructed, unossified notochord. Double gular plate (stony plate to protect fish throats), spiny dorsal fin, cranio-vertebral joint.

Question 4

Subclass Dipnotetrapodomorpha

Answer 4

Dipnomorpha (lungfish, 6 living species, all freshwater, all living)
Tetrapodomorpha (large predatory fish, symmetrical tails, may have functioning swim bladder)

Question 5

Infraclass Tetrapoda

Answer 5

(us in fish phylogeny) = ‘ a divergent sideline with the fishes that ascend onto
land and into air, and secondarily
return to water’.

Question 6

Tetrapodomorphs

Answer 6

Peaked in late Devonian, extinct in permian. Robust limb skeleton, rotational shoulders (good for land), dorsally placed eyes. Could grow to 6m, 1 pair of external nostrils (incurrent), choana (excurrent nostrils moved to palate). Thought to be ambush predators (sort of crocodile like).

Question 7

Evidence of movement to land

Answer 7

Choana are actually palatally displaced posterior nostrils. Lobed fins thought to become finger-like.
‘Tiktaalik’ = all fish features + functioning wrist joint. Eye development = important.

Question 8

Breathing oxygen

Answer 8

Harder on land (more oxygen inhaled at once, water loss, less viscous, no low O2 air).
Water breathers with lungs take one breath every hour (those that go to surface, obligate air breathers need per 3-10 minutes (us).

Most efficient, fewer breaths = fewer surface trips. Bimodal breathing is best.

Air breathing fish are common (370 known species, evolved x50). Air breathing organs derived from gut (lungs, bladder, stomach, intestine), head/pharynx (gills, mouth, opercles).

Question 9

Origin of lungs

Answer 9

Air breathing to cope with dry spells, exploit new habitats, to survive in low O2 waters, couldn’t stay down for long enough to go deep.
Could be due to myocardial hypoxia (heart is starved of oxygen), lungfish developed a long to avoid this. Normally occurs since heart is the last place to receive oxygen (so if the fish is exercising, it may not receive any oxygen).

Question 10

monophyletic group

Answer 10

common ancestor + all descendants

Question 11

paraphyletic group

Answer 11

doesn’t have all descendants of one ancestor

Question 12

polyphyletic group

Answer 12

descendants of different ancestors

Question 13

Water vs Air

Answer 13

High density (heavy) Low density
High viscosity Low viscosity
Low O₂ areas O₂ always available

Available everywhere Surface access

Easy to expel metabolic Hard to expel
waste

Question 14

Double circulatory system/separate circulation

Answer 14

1.Head: Blood flows in through the arteries (red) and returns through veins (blue).
2.Gills: Blood flows from the gills to the heart.
3.Heart: Blood is pumped to the liver.
4.Liver: Blood continues to the trunk and guts.
5.Trunk & Guts: Blood flows toward the kidney.
6.Kidney: Blood returns through veins from the kidney back to the heart, completing the circuit.