Tetrapods Flashcards Preview

BI1512 - Diversity of Life 2 > Tetrapods > Flashcards

Flashcards in Tetrapods Deck (18)
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1
Q

When did aquatic vertebrate move to the land?

A

Devonian period (416-359 MYA)

2
Q

What methods can we use to date rocks and fossils?

A
  • Relative dating; order of decomposition

- Absolute dating; radiometric dating - decay of radioactive isotope; palaeomagnetism

3
Q

There is evidence that the closest ancestors to tetrapods is ___________ fish.

A

Sarcopterygian

4
Q

Name at least 3 suggested advantages of moving to land.

A
  • Increase in range of habitats & food (vascular plants, snails, arthropods already on land)
  • Avoidance of aquatic predators and competitors
  • Abundant oxygen
  • Raise in body temperature (accelerates metabolism)
5
Q

Name at least 3 disadvantages of leaving water

A
  • Gravity: water supports body with little difference in density. Air less viscous and dense (need support for body for locomotion and prevention of lung collapse)
  • More abundant oxygen but need adaptation of respiratory system (lungs)
  • Skin to resist desiccation
  • Greater fluctuations in temperature (thermoregulation)
  • Sense organs respond to different stimuli
  • Reproduction
  • Blood circulation more difficult (pumping)
  • Different food and methods of capture
6
Q

Name at least three tetrapod characteristics

A
  • Paired hind and forelimbs with digits
  • Pectoral girdle separated from skull with mobile neck
  • Hyomandibular bone (formerly supporting the jaw) becomes stapes conducting sound to ear
  • First cervical vertebra modified to allow skull movement
7
Q

Briefly describe the middle ear of tetrapods

A
  • Derived from spiracle

- Hyomandibular (freed from jaw) modified to stapes

8
Q

Briefly describe vision of tetrapods

A
  • Easier in air: flatter lens’ than in fish

- Eyes on top of the head

9
Q

What is the name of the “intermediate”?

What features of lobe-finned fish did it possess?

What feature land-living animals did it possess?

A

(1) Tiktaalik
(2) fins; scales; primitive jaws; gills and lungs
(3) neck; wrists; flat skull with eyes on top; expanded ribs

10
Q

There are 5 names key to the movement to land, what are they?

A
  • Sarcopterygii
  • Eusthenopteron
  • Tiktaalik
  • Acanthostega
  • Ichthyostega
11
Q

What period were terrestrial tetrapods confirmed?

A

Carboniferous

12
Q

What were the three major events during the movement to land?

A
  • Origin of limbs with digits (also changed vertebral column, braincase, ear)
  • Origin of walking
  • Origin of terrestriality (adaptations for living on the ground)
13
Q

Name at least three modifications that were considered useful for life on land.

A
  • Paired internal nares (choanae) connect external nostril to buccal cavity
  • Air-filled cavity connected to pharynx “lungs”. First appeared in fish before tetrapods (swim bladder later?)
  • Bony elements of paired fins

Available for later modification for terrestrial breathing (lungs/double circulation) and support

14
Q

Briefly describe the characteristics found in Acanthostega

A
  • No wrists or ankles
  • Paddle-like limbs
  • 8 digits
  • Internal gills
  • Limbs and spine would not support much weight
15
Q

Briefly describe what is significant about the vertebral column of ichthyostega

A
  • Zygapophyses (bony projections) brace against each other and help support spine in absence of water
  • Overlapping ribs prevent crushing of lungs but inhibit side-to-side movement
16
Q

How was the skull adapted to breath above water?

A
  • Elongation of the snout, fewer bones meant stronger structures, gives lift out of water
  • Strong bones at back of head for muscle attachment
  • Fusing of bones of lower jaw for “buccal pump”
  • Mouth cavity bellows-like action, gulping air forced into air
17
Q

What was significant about carboniferous tetrapods?

A
  • Bony spine with interlocking vertebrae with centra (obliterating notochord)
  • Flex wrists and ankles
  • Polydactyl but one group with 5 digits emerged as ancestral to pentadactyl limb of all living tetrapods (might have helped make ankle joint more stable for weight bearing and flexible for walking gait)
18
Q

Briefly describe the pentadactyl limb of tetrapods

A
  • Example of homologous structures
  • All tetrapods have 5 digits at some stage in embryonic development, presumably inherited from the common ancestor
  • Digits may be lost secondarily at later stages of development
  • Origin of tetrapod digits not by new genes but redeployment of gene activity present in earlier fish