The tetrapod invasion of land Flashcards
What are the advantages of evolving onto land?
– 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?)
Why would respiration on land be a driving factor for evolution?
Air was higher in O2 at the time
Why was movement on land a driving factor for evolution?
– Many extant teleosts can move over land
– Crutching (like mudskippers) may have been the common method
What are the key traits of the CLASS Sarcopterygii?
– enamelled teeth
– fleshy, lobed fins
– cosmoid scales
How many species are in the class Sarcopterygii?
– 26,742 extant species
– only 8 extant fishes
What taxonomic order is Coelacanthimorpha?
Subclass – of Sarcopterygii
What is true of Coelacanthimorpha (sc)?
– 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
How many living species of Coelacanthimorpha are there?
2 living species (considered extinct until 1938)
What are 2 infraclasses of the subclass Dipnotetrapodomorpha ?
– Dipnomorpha (inc. lungfish – 6 living species, FW)
– Tetrapodomorpha (all X exc. infraclass tetrapoda)
What are key traits of tetrapodomorpha?
– Large predatory fishes
– Symmetrical tails
What is a monophyletic group?
Consists of a common ancestor plus all descendants of that ancestor
What is a paraphyletic group?
Does not contain all the descendants of a single ancestor
What is a polyphyletic group?
Containing descendants of different ancestors
What are key traits of tetrapodomorphs?
– 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?
What is the breathing frequency of obligate air breathers?
1 per 3-10 minutes
What is the breathing frequency of water breathers with lungs?
1 per HOUR
What is the benefit of having a longer breathing frequency?
Fewer breaths = fewer trips to the surface
What is true of O2 in air vs water?
Air is more O2 rich: 21% O2 in air vs <1% in water
– diffusion from air to blood is also faster
How many species of air breathing fish are there?
> 370 known spp (49 families)
How many times have air breathing fish evolved?
~50?
What is true of the air-breathing organs of air breathing fish?
– Derived from gut (lungs, gas bladder, stomach, intestine)
– Head & pharynx (gills, mouth, pharynx, opercles)
– Skin
What could be reasons for the evolution of lungs/air-breathing?
– To cope with seasonal dryness?
– Exploit new habitats/ release competition?
– To survive low O2 waters?
– To avoid myocardial hypoxia ?
How could having lungs avoid myocardial hypoxia?
– 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
What is true of direction of flow (circulation) in Chondrichthyes and Actinopterygii?
Sinoatrial and atrioventricular valves maintain unidirectional flow
What is true of the circulatory system in Chondrichthyes and Actinopterygii?
- Positioned behind gills
– 4 chambers in series
What are the 4 chambers in the circulatory system in Chondrichthyes and Actinopterygii?
- Sinus venous
( a reservoir to collect blood, assures easy filling) - Atrium
- Ventricle (pump)
- Conus/bulbus arteriosus
(conus, muscular in sharks – bulbus, elastic in bony fish)
What features are central to the evolution of tetrapods?
- Pectoral (and pelvic) fins
– Respiratory system
– Circulatory system
– Reproduction, digestive system, sensory system
What could be the origins for the separation of circulation?
– To survive low O2 waters?
– Atrium fully divided
– Ventricle functionally divided
– Oxygenated blood –> reduced gills
– Systemic blood –> gills then lung §
