The tetrapod invasion of land

Question 1

What are the advantages of evolving onto land?

Answer 1

– Movement
– Respiration
– Terrestrial reproduction (could be strategy to avoid predation)
– Feeding in air requires much morphological modification (fish remained tied to water by need to feed?)

Question 2

Why would respiration on land be a driving factor for evolution?

Answer 2

Air was higher in O2 at the time

Question 3

Why was movement on land a driving factor for evolution?

Answer 3

– Many extant teleosts can move over land
– Crutching (like mudskippers) may have been the common method

Question 4

What are the key traits of the CLASS Sarcopterygii?

Answer 4

– enamelled teeth
– fleshy, lobed fins
– cosmoid scales

Question 5

How many species are in the class Sarcopterygii?

Answer 5

– 26,742 extant species
– only 8 extant fishes

Question 6

What taxonomic order is Coelacanthimorpha?

Answer 6

Subclass – of Sarcopterygii

Question 7

What is true of Coelacanthimorpha (sc)?

Answer 7

– Appeared in Devonian, max diversity in triassic
– 3-lobed tail supported by hollow spine
– Unconstricted, unossified notochord
– Double gular plate
– Spiny dorsal fin
– Cranio-vertebral joint

Question 8

How many living species of Coelacanthimorpha are there?

Answer 8

2 living species (considered extinct until 1938)

Question 9

What are 2 infraclasses of the subclass Dipnotetrapodomorpha ?

Answer 9

– Dipnomorpha (inc. lungfish – 6 living species, FW)
– Tetrapodomorpha (all X exc. infraclass tetrapoda)

Question 10

What are key traits of tetrapodomorpha?

Answer 10

– Large predatory fishes
– Symmetrical tails

Question 11

What is a monophyletic group?

Answer 11

Consists of a common ancestor plus all descendants of that ancestor

Question 12

What is a paraphyletic group?

Answer 12

Does not contain all the descendants of a single ancestor

Question 13

What is a polyphyletic group?

Answer 13

Containing descendants of different ancestors

Question 14

What are key traits of tetrapodomorphs?

Answer 14

– Robust limb skeleton: hip/shoulder girdles and rotational shoulders
– Could be large: up to 6m in Rhizodontiformes
– Dorsally placed eyes
– 1 pair of external nostrils
– Ambush predators?

Question 15

What is the breathing frequency of obligate air breathers?

Answer 15

1 per 3-10 minutes

Question 16

What is the breathing frequency of water breathers with lungs?

Answer 16

1 per HOUR

Question 17

What is the benefit of having a longer breathing frequency?

Answer 17

Fewer breaths = fewer trips to the surface

Question 18

What is true of O2 in air vs water?

Answer 18

Air is more O2 rich: 21% O2 in air vs <1% in water
– diffusion from air to blood is also faster

Question 19

How many species of air breathing fish are there?

Answer 19

> 370 known spp (49 families)

Question 20

How many times have air breathing fish evolved?

Answer 20

~50?

Question 21

What is true of the air-breathing organs of air breathing fish?

Answer 21

– Derived from gut (lungs, gas bladder, stomach, intestine)
– Head & pharynx (gills, mouth, pharynx, opercles)
– Skin

Question 22

What could be reasons for the evolution of lungs/air-breathing?

Answer 22

– To cope with seasonal dryness?
– Exploit new habitats/ release competition?
– To survive low O2 waters?
– To avoid myocardial hypoxia ?

Question 23

How could having lungs avoid myocardial hypoxia?

Answer 23

– Exercise stimulates air breathing more than aquatic hypoxia
– Death from exercise results from heart failure
– O2 sensores afferent to gill
– Early fish active, high O2 environment

Question 24

What is true of direction of flow (circulation) in Chondrichthyes and Actinopterygii?

Answer 24

Sinoatrial and atrioventricular valves maintain unidirectional flow

Question 25

What is true of the circulatory system in Chondrichthyes and Actinopterygii?

Answer 25

• Positioned behind gills
  – 4 chambers in series

Question 26

What are the 4 chambers in the circulatory system in Chondrichthyes and Actinopterygii?

Answer 26

1. Sinus venous
   ( a reservoir to collect blood, assures easy filling)
2. Atrium
3. Ventricle (pump)
4. Conus/bulbus arteriosus
   (conus, muscular in sharks – bulbus, elastic in bony fish)

Question 27

What features are central to the evolution of tetrapods?

Answer 27

• Pectoral (and pelvic) fins
  – Respiratory system
  – Circulatory system
  – Reproduction, digestive system, sensory system

Question 28

What could be the origins for the separation of circulation?

Answer 28

– To survive low O2 waters?
– Atrium fully divided
– Ventricle functionally divided
– Oxygenated blood –> reduced gills
– Systemic blood –> gills then lung §