tetrapodomorpha Flashcards
Tetrapodomorpha
clade of vertebrates consisting of tetrapods and closest sarcopterygii relatives ( that are more closely related to living tetrapods than lungfish)
- Early tetrapods were aquatic animals
what are the Osteolepiforms, give an example plus some features
- Group of prehistoric lobe-finned fishes
- E.G. Elpistostegidae -> most derived form (385 MYA)
- No dorsal + anal fin, reduced tail
- Fins are prop like, used to sit and wait for prey by fish
- ambush predator
- different spiracular region -> beginnings of tetrapod middle ear
When did early tetrapods begin to emerge, give an example
- 365 MYA
- Acanthostega + Ichthyostega
- have robust limbs and ribs
what was discovered as the missing link between early tertapods
Tictaalik - had a very flexible neck allowing it to feed on items close to shore
Order of early tetrapod evolution
1) Panderichthys
2) Tictaalik
3) Acanthostega
4) Ichthyostega
-Each step continued on path of developing stronger + more robust ribs, larger weight carrying limbs, and reduced fins/ tails
Why did tetrapod features evolve
- Tetrapod features advantageous in water, movement across seafloor, propping in place for ambush , reaching food on the shore
- The evolution of tetrapod features and the evolution of terrestrial life are two separate events.
E.g. frogfish - move across sea floor in similar movements to tetrapods
How many toes did early tetrapods have
1) Acanthostega - 8 toes on front and hind feet
2) Ichthyostega - 7 toes on hind feed (forefront unknown)
Polydactyly = having more than 5 feet
- Most tetrapods have lost digits over course of evolution . reduced digits usually associated with locomotion + running faster (i.e. ostrich / deer =2 toes)
What genes control the evolution of limbs
- Fins + limbs are homologous structures , same genes as responsible for digit + ray formation .
- Hox genes
what causes digit loss
1) reduced expression of gene ptch1
OR
2) programmed cell death
- different lineages use different mechanisms, evolved differently but came to digit loss by same way = convergent evolution
What were the two main groups of early tetrapods
1) Batrachomorhphs -> gave rise to the amphibians, they were mainly aquatic forms
2) Reptilomorphs (anthracosaurs) -> gave rise to the amniotes
- it is thought early terapods had gills + lungs
What adaptations did tetrapods need to move from water to land
1) chromatophores in skin to absorb light rays from increased solar radiation
2) Stronger skeleton + musculature
3) Fish-like eye transformed at metamorphosis so as to see out of water
4) evolution of tympanic membrane in ear (3/4 light +sound waves travelled differently)
5) skin vascularised , lungs primary site of gas exchange, allow gaseous exchange to take place without water loss
6) Keratin + mucous in skin , keeps water in. Move to excretion of urea/ uric acid.
7) early on most tetrapod’s returned to water to breed.
what are the 3 main groups of Amphibians
- all have characteristic of permeable skin
1) Urodeles
2) Anurans
3) caecilians
what are urodeles , list some features
- Salamanders + newts
1) Most have 4 limbs - some aquatic forms have lost some limbs or have reduced tiny limbs
2) Undulatory locomotion - similar to lunglfish
3) Most basic form of body shape
what are Anurans, list some features
- Frogs + toads
1) aquatic + terrestrial forms
2) lost tail
3) rigid body
4) legs well developed
5) body shortened through loss of vertebrae
6) Anura body form evolved from advantage of swimming with back legs
7) some are poisonous
What are caecilians, list some features
- legless amphibians
1) burrowing or aquatic
2) look segmented due to folds of skin
