week 3 Flashcards
(25 cards)
1
Q
what are tetrapods
A
- the clade comprising the first 4-limbed vertebrates + all their descendants
- they are sarcopterygians, with lungfish and coelacanths as their closest living relatives
2
Q
characteristics of ray-finned fishes
A
- swim bladder (gas-filled organ used to control buoyancy)
- breathe via their gills
3
Q
compare actinopterygians vs sarcopterygians
A
actinopterygians:
- ray-finned fishes (thin rod-like bones)
- muscles inside the body wall
sarcopterygians:
- lobe-finned fishes (thick and fleshy)
- muscles attached to bony elements within the fin
4
Q
what are coelacanths
A
- a group of lobe-finned, marine fishes thought to have gone extinct in the Cretaceous
- paired lobed fins
- 3-lobed tail
- jointed jaw
- teeth restricted to front
5
Q
describe lungfish
A
- sarcopterygians
- 3 living genera - all in southern hemisphere
- live in freshwater environments exposed to seasonal drying
- fossil record extends back into the Early Devonian
- fixed skull
- heterocercal tail
- cartilaginous notochord
- no teeth- plates instead that form a uniform crushing surface
- breathe air by gulping
- can survive for a time outside of water
- aestivation in some species (hibernation)
- have gills and primitive lungs
6
Q
describe lungs
A
- lungs and swim bladders = homologous structures
- first lungs were simple sacs connected to the gut that allowed the organism to gulp air under oxygen-poor conditions
- swim bladder of ray-finned fishes evolved from such an early lung, as did the ‘derived’ lung of lobe-finned fishes
- a vestigial lung not known to be present in the coelacanth too
7
Q
describe the ichthyostega
A
- well-developed ribs
- clearly has limbs suited to supporting itself on land
- still had gills and fish-like tail
8
Q
problems with living out of the water
A
- without the ability to breathe air, locomotion on land becomes an extremely time-limited activity
- need to be able to support body on land, without buoyancy of water
- how to give birth on land without desiccation of eggs (spawn)
9
Q
what is buccal pumping
A
mouth cavity expands and contracts like bellows to gulp air and force it into the lungs e.g. in frogs
10
Q
what was the ‘transitional’ fossil?
A
- tiktaalik
- had a neck, wrists, flat head and expanded ribs like a land-living animal
- had fins, scales, primitive jaws like a lobe-finned fish
11
Q
why are fish skulls the way they are
A
- most fish have skulls that are tall and narrow, with eyes facing sideways and forwards
- this allows them to look around in their watery environments for predators/prey
12
Q
how did skulls evolve from fish to tetrapods
A
- as ancestors of the first tetrapods began to live in shallower waters, their skulls evolved to be flatter, with eyes on the tops of their heads, allowing them to look up to spot food
13
Q
how did necks evolve from fish to tetrapods
A
- fish have no necks, their heads are simply connected to their shoulders
- vertebral column evolved with transition to land
- mobile necks allow land animals to look down to see the things on the ground that they might want to eat/avoid being eaten by
14
Q
how did ears change from fish to tetrapods
A
- the gill bone moves and becomes the stapes, the rod-like bone that magnifies sound waves
- transmits them from the eardrum to the inner ear
15
Q
key anatomical changes from fish to tetrapods
A
- fins to limbs: ankles, digits, etc
- interlocking vertebrae
- loss of tail fin
- separation of skull from shoulder
- robust skull with fewer bones
- changes in dentition
- changes in the ear
- loss of bones covering gills and loss of gills
- longer ribs: needed to stop chest cavity and lungs collapse
16
Q
what is exaptation
A
- the process by which features acquire functions for which they were not originally adapted or selected
- development of limbs was not initially used for walking on land
- the use of the swim bladder for buoyancy in ray-finned fish is also an exaptation
17
Q
why would early tetrapods need to stay close to the water
A
- early tetrapods had to return to the water to lay eggs, like modern amphibians
- amniotic eggs only evolved in the Carboniferous
- early tetrapod fossils were found in shallow water environments in subtropics
18
Q
why did our ancestors leave the water
A
- terrestrial plants had diversification bursts in the Devonian
- this led to increasing oxygenation
- but also led to increasing continental weathering and decaying plant matter run-off into water
- evidence for marine anoxic conditions globally
- possibly driven by oxygen-consuming bacterial/algal blooms
- increased capacity for air-breathing and ability to lift their head out of water to gulp air gave tetrapod ancestors an advantage over other vertebrates during a period of high levels of anoxia in water systems
- they could exploit the richer O2 available in the atmosphere, rather than the low levels in the water
- perhaps allowed tetrapods to exploit ecosystems unavailable to sharks/other fishes (low competition/predation)
19
Q
what are lissamphibians
A
- a non-amniote tetrapod
- e.g. frog, toad, salamander
20
Q
what is an amniote
A
- reproduction occurs without the need of water through a specialised cleidoic egg
- gas exchange still needs to occur through the shell to provide O2 and remove CO2 from the embryo: enabled through semi-permeability of eggshell
21
Q
how did the end-carboniferous affect amniotes
A
- end-carboniferous saw a major climatic shift from dominantly humid to arid conditions
- led to the carboniferous rainforest collapse
- early amniotes that could reproduce without relying on water were at a major advantage over other tetrapods
22
Q
how are amniote skulls classified
A
- into categories of skull fenestration
- fenestra = temporal opening
- synapsid and diapsid
- facilitates evolution of large muscle groups by increasing muscle attachment surface area
23
Q
what are synapsids
A
- have one skull fenestra
- a diverse group with a long evolutionary history that gave rise to modern mammals
- more closely related to living mammals than to living reptiles
24
Q
what are diapsids
A
- have 2 skull fenestrae
- sometimes difficult to see the fenestration or it is secondarily lost
- part of a larger reptile clade
25
describe the end-permian mass extinction
- volcanic eruptions produced gases that led to global warming, acid rain and ocean stagnation
- decimated amniote diversity, with only a small number of groups surviving into the Triassic
- one group of diapsids, archosaurs, would eventually flourish
