mammals

Question 1

Mammal features

Answer 1

1) other group of amniotes
2) synapsids (1 hole) - derived from syropsids early on
3) first group to properly invade terrestrial environment
4) mammal numbers began to increase after dinosaurs extinction - thought to be linked to change in vegetation (^flowering plants = ^ insects) and not due to dinosaur extinction
5) when dinosaur numbers were highest only synapsis mammals that persisted was the theropsids

Question 2

what are the 3 main waves of radiation that gave rise to mammals from synapsids

Answer 2

1) Pelycosaurs - basal forms of synapsids + amniotes, large animals , reptilian gate, legs stuck out of body rather than underneath

2) Theropsids - more derived forms , changes in teeth + skull, holes in skull got bigger
- large canines for display + prey capture

3) Cynodonts, gave rise to mammals
- no ribs on lumber vertebrae
- changes in skull (powerful jaws)
- limbs underneath animal + move faster

Question 3

Limb orientation in mammals

Answer 3

• Limbs moved from side of body to underneath due to conflict between moving and breathing
• Originally same muscles used for breathing + moving (couldn’t do both at same time) side to side undulations just moved air between lungs
• Mammals have separated the two by having legs below + the development of rigid thorax and developed diaphragm

*in some mammals increased movement can aint in ventilation

Question 4

Early mammals features

Answer 4

1) small , insectivorous
2) egg laying (basal amniotic condition) = monotremes
3) nocturnal +solitary
- eyes designed for low light (lots of rods)
4) show parental care
5) large olfactory bulb
6) Endothermy - hair provided insulation
7) lactation + suckling

Question 5

Lactation in mammals

Answer 5

1) most mammals = diplyodont (2 sets of teeth, adult +baby)
2) diplyodonty thought to have evolved as mammals were fed milk early on and so didn’t need permanent teeth.
3) lactation pre diplyodonty

Question 6

Evolution of lactation

Answer 6

1) milk may have been produced to protect eggs from dessication + microbes as milk has antibacterial property
2) then offspring started to feed on it and benefit
3) milk produced my mammary glads, - related to aprocrine glands (sweat)

Question 7

Evolutionary advantages of lactation

Answer 7

1) production of offspring separated from seasonal food supply
2) mother not dependant on parental care - does not need male
3) Mother viviparity less strenuous on mother, dont have to carry offspring gin womb
4) suckling unique feature of mmals due to tight sea lin pharnx (disappears in adult human)

Question 8

facial muscles in mammals

Answer 8

• Homologous with neck constrictor muscles in reptiles
• mammals chew food more ( well developed neck)
• facial expression v developed in mammals (used in communication)

Question 9

Prototheria (monotemes) , features

Answer 9

• lay eggs
• branch of ancestral mammals
• 3 species still in existence -> platypus/anteater/echidna

Question 10

Examples of monotremes (aquatic + terrestrial)

Answer 10

Aquatic = playpus

• 40k electrical receptors in bill
• 60k mechanical receptors
• has a giant brain relatively

terrestrial = echidna

• lost electrical ability , nose adapted for terrestrial use
• v sensitive mechanical receptors (mouth)