Lecture 21

Question 1

Evolution of jaws

Answer 1

derived from gill arches of chordates –> earliest jawed fishes, dermal armour

Question 2

Cartilaginous fish

Answer 2

Skeleton
Maintaining water balance is major issue (high levels of urea in blood)
eg. shark and rays

Question 3

Bony (ray finned) fish

Answer 3

Ridgid bony skeleton (cartilage replaced)
paired fins
Swim bladder for bouyancy
usually single dorsal fin

Question 4

Evolution of legs

Answer 4

Most bony fish have fins of long rays of bone

unusual limbs

Question 5

Reptiles

Answer 5

have scales
cold blooded
most lay eggs
no aquatic larval stage

Question 6

Mammals

Answer 6

• Upright stance –> hip joints and upper limb bones changed in mammals and dinos (quicker movement)
• jaw articulation –> squamosal and dentary
• Fur
• Warm-blooded
• Milk
• 3 inner-ear bones
• -> Prototheria (platypus, echidna)
• -> Metatheria (marsupials)
• -> Eutheria (placental mammals)