marsupials

Question 1

Where are marsupials found

Answer 1

• South America

- Australia

Question 2

what did marsupials (metatheria) derive form

Answer 2

Theria - gave rise to

1) metatheria (maruspials)
2) Eutheria (placentals)

Question 3

How do Metatherians differ from Eutherians

Answer 3

1) Bone structure - usually posses an opposable digit on hind foot
2) Teeth - generally more incisors and molars
3) extremely small young - typically born at 1% body mass
4) lower body temp and basal metabolic rate
5) smaller relative brain size

Question 4

Differences in reproductive anatomy between metatheria and eutheria

Answer 4

1) Bifurcated reproductive tact (both sexes)
2) simple placenta in some species (used for short time pre-pouch)
3) Pouch present in 505 species

Question 5

how are marsupial orders classified

Answer 5

• by digits and dentition

1) Digits : syndactylous feet vs, non-syndactylous feet
2) Dentition: = diprodont vs, polyprotodont

Question 6

syndactylous

Answer 6

A condition where one or more digit are fused together

Question 7

diprodont

polyprotodont

Answer 7

diprodont =have a pair of large, procumbent incisors on the lower jaw, a common feature of many early groups of mammals and mammaliforms.

polyprotodnt = four or more upper incisor teeth on each side of the jaw

Question 8

what are the 7 orders of metatheria

Answer 8

1 )Diprodontia - koalas, kangas, wombats

2) Didelphimorphia - opossums
3) Paucituberculata - shrew possums
4) Dasyuromorphia - Tasmanian devil, numbat
5) Microbiotheria - monito del monte
6) Notoryctemorphia - Marsupial moles
7) Peramelomorhphia - bilbies and bandicoots

Question 9

marsupial evolution

Answer 9

1) Australia split from antartica (45MYA)
2) S.America split from antartica (30MYA)
3) split from eutherian mammal 100 MYA
4) basal split amongst marsupial orders 80 MYA
5) mass extinction in cretaceous ( meteors) - 505 of genera became extinct
6) Marsupials colonised Australia from S.America/ Antarctica

Question 10

Marsupial reproduction

Answer 10

1) paired vaginae transport sperm
2) birth is via a pseudovaginal canal
3) two uteri
4) simple placenta

Question 11

Female marsupial reproduction

Answer 11

1) Highly atrical young , short gestation time
2) Flexible : can have newborn attached at nipple, fertilised blastocyst in uterus and young at foot.
3) similar oestrous cycle to Eutherian (same hormones)

Question 12

Male marsupial reproduction

Answer 12

1) combined urogenital tract in males + females -cloaca
2) scrotum cranial to the penis
3) bipartite penis

Question 13

Costs and benefits of marsupial vs. placental

Answer 13

1) Placentals -> cant off load embryo, female structure + fitness has to be altered for birth , had to develop triploblast to protect embryo
2) Marsupials -> Restriction of forelimb development , reduced brain size
- opportunity to learn by observation

Question 14

Examples of convergent evolution between metatheria and eutheria

Answer 14

1) Arboreal E.g. lemurs + possums
- comparable diet
- low fecundity
- similar general behaviour
2) Diet specialisation E.g. striped possum + aye-aye
- posses an extended finger for extracting insect larvae
3) Gliding E.g. squirrel gliders and flying squirrels