evolution and diversity of the chordates : tetrapods

Question 1

origins of tetrapods

Answer 1

• first amphibians ( e.g acanthostega ) date from late devonian ( 375 MYA )
  
  • common by carboniferous
• limbs evolved from the fins of lobe-finned fish
• lungfish are the closest living relatives of tetrapods

Question 2

amphibia

Answer 2

newts, salamanders, frogs, toads and caecilians

world wide distribution, but most diverse in humid tropics

Question 3

amphibia : characteristics

Answer 3

• thin skin with limited keratinisation
• skin permeable to oxygen and water
• most restricted to damp envionments
• fertilisatio generally external
• eggs have no shell - prone to desiccation and need physical support
• larvae fish-like with gills and lateral line system, lack legs or lungs. usually aqutic herbivores
• adults usually terrestrial carnivores with lungs and 4 legs

Question 4

amniotic egg

Answer 4

four specialised membranes ( amnion, allantois, chorion, yolk sac ) - protect them from desicction, allow gas exchange and store food/waste

allows amnioted to be truely terrestrial

evolved in carboniferous

Question 5

origins of amniotes

Answer 5

• hylonomus is the oldest known amniote. carboniferous period - 312 MYA
• westlothianan ( 338 MYA ) and casineria ( 340 MYA ) may be amniotes

two main clades :
• reptilia
• mammalia

Question 6

testudines ( turtles )

Answer 6

• 360 species in 14 families
• terrestrial , FW and marine
• shells and skeletons unique to clade
• show many ancient reptillian characters :
  •skull morphology
  •scales ( B-keratin )
  • internal fertilisation but lay eggs
  • ectothermic

Question 7

crocodilia ( crocodiles and alligators )

Answer 7

• 27 species in 3 families
• all semi-aquatic predators; most tropical
• have changed little since the triassic
• secondary palate
• heart with septum, ike birds

Question 8

Archaeopteryx

Answer 8

the first bird?

jurassic period ( 150 MYA )

mixture of reptillian and avian characters

Question 9

aves ( birds )

Answer 9

• 10,928 species in 252 families

- global distribution in most habitats

Question 10

aves : characteristics

Answer 10

• feathers ( B-keratin )
• large, keeled sternum
• fore-limbs modified for flight
• hind-limbs for bipedal walking
• interanal fertilization and hard-shelled amniotic eggs
• endothermic

Question 11

sphenodontia ( Tuartara )

Answer 11

• one species of lizard like, carboniferous reptile found on the islands of new zealand
• once a diverse group, but most went extinct 65 MYA
• skull differs from lizard
  •retains ancestoral features

Question 12

squamata ( snakes and lizards )

Answer 12

• 11,000 species in 68 families
• mainly tropical, terrestrial carnivores
• lizards retained ancestoral body plan and characters
• snakes highly specialised :
  • limbless
  •elongate
  •modified jaws and skull

Question 13

origins of mammals - Hadrocodium wui

Answer 13

early jurassic ( 195 MYA ) mammal with a relatively large brain and a malleus and incus in the inner ear as in modern mammals

Question 14

mammalia ( mammals )

Answer 14

• 6490 species in 167 families
• taxonomy being revised constantly
• worldwide distriution in almost all ecosystems