Tetrapods Flashcards
When did aquatic vertebrate move to the land?
Devonian period (416-359 MYA)
What methods can we use to date rocks and fossils?
- Relative dating; order of decomposition
- Absolute dating; radiometric dating - decay of radioactive isotope; palaeomagnetism
There is evidence that the closest ancestors to tetrapods is ___________ fish.
Sarcopterygian
Name at least 3 suggested advantages of moving to land.
- 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)
Name at least 3 disadvantages of leaving water
- 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
Name at least three tetrapod characteristics
- 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
Briefly describe the middle ear of tetrapods
- Derived from spiracle
- Hyomandibular (freed from jaw) modified to stapes
Briefly describe vision of tetrapods
- Easier in air: flatter lens’ than in fish
- Eyes on top of the head
What is the name of the “intermediate”?
What features of lobe-finned fish did it possess?
What feature land-living animals did it possess?
(1) Tiktaalik
(2) fins; scales; primitive jaws; gills and lungs
(3) neck; wrists; flat skull with eyes on top; expanded ribs
There are 5 names key to the movement to land, what are they?
- Sarcopterygii
- Eusthenopteron
- Tiktaalik
- Acanthostega
- Ichthyostega
What period were terrestrial tetrapods confirmed?
Carboniferous
What were the three major events during the movement to land?
- Origin of limbs with digits (also changed vertebral column, braincase, ear)
- Origin of walking
- Origin of terrestriality (adaptations for living on the ground)
Name at least three modifications that were considered useful for life on land.
- 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
Briefly describe the characteristics found in Acanthostega
- No wrists or ankles
- Paddle-like limbs
- 8 digits
- Internal gills
- Limbs and spine would not support much weight
Briefly describe what is significant about the vertebral column of ichthyostega
- 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
How was the skull adapted to breath above water?
- 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
What was significant about carboniferous tetrapods?
- 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)
Briefly describe the pentadactyl limb of tetrapods
- 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
