Marsupials

Question 1

Give some features of the marsupials

Answer 1

Bones:

• Epipubic bones for pouch support and locomotion although not present in Thylacine
• Skull has large face area but small brain case and rest is similar to primitive mammal
• Jaw has the rear part turned inwards

Teeth:

• More teeth than placentals
• 3 premolars and 4 molars
• 4 or more lower incisors
• 2 lower incisors
• 3-4-4-2

Reproduction:

• Presence of pouch in 50% of species
• Female reproductive system is doubled
• Males have bifurcate penis posterior to scrotum
• Short gestation
• Extremely altricial young (1% of adult body mass)

Lower body temp

Small and less convoluted brain

Question 2

Did marsupials evolve in america or asutralia?

Answer 2

Americas

Dispersed through antarctic to Australia

Question 3

Give the brief evolutionary history of marsupials

Answer 3

100 MYA - marsupials and eutherians diverged

80 MYA - basal split among marsupial orders

65 MYA - Interordinal divergences

34 MYA - most diversification of orders

Question 4

Give the orders of the marsupials and some examples

Answer 4

Diprodontia - pygmy possums, koala and kangaroo

Dasyuromorphia - tasmanian devil and numbat

Notoryctemorphia - karrkaratul

Peramelemorphia - bandicoots

Microbiotheria - monito del monte

Paucituberculata - shrew opassums

Didelphimorphia - opossums

Question 5

How do marsupials reproduce?

Answer 5

Paired vaginae transport sperm

Birth via pseudovaginal canal

Simple placenta

Young are highly altricial when born due to short gestation

Can have newborn attached at the nipple, fertilised blastocyst in uterus and a young at foot

Similar oestrus cycle to eutherians and controlled by same hormones

Question 6

Give some features of newborn marsupials

Answer 6

No eye pigments

No eyelids

Cartilaginous skeletal segments

Separation of heart

Ventricles incomplete

Question 7

What are some pros of marsupial reproduction?

Answer 7

Physiologic and energetic cost is reduced

No need to protect the embryo from the maternal immune system

Less risk for the female

Flexible reproduction

Question 8

What are the cons of marsupial reproduction?

Answer 8

New born at higher risk

Constraint on forelimb evolution

Question 9

Give some convergences of marsupials and eutherians

Answer 9

Arboreal communities

Biogeography

Habitat

Body size

Diet specialisation - e.g. striped possum and aye aye

Fertility

Gliding