Lect 19

Question 1

Marsupialia

Answer 1

• First diversified in South America
• Extant South American taxa less derived than Australian forms
• Marsupials arrived in Australia in early Cenozoic
• Diversified and filled many empty niches

Question 2

Marsupial characters

Answer 2

• Inward-directed dentary process

• Openings in roof of mouth

• Distinct dental formula
- More incisors, molars, fewer premolars (diff in how many are premolars or molars)

• Epipubic bones (pubic —> pelvis)
- Project anteriorly from pelvis
- Stiffen torso, but restrict some movement of hindlimbs
- Lost in cursorial (running) marsupials

Add support—> restrict movement to som extent
—> postieor trunk of spine
—> fast animals have these reduced

Question 3

Marsupial development

Answer 3

• Do have a rudimentary placenta (simple, less effective)
- Chorion and yolk sac fuse and implant in wall

• Uterine development is short – as few as 10 days

• Offspring born extremely altricial
Can’t do much of anything on own

• Forelimbs developed enough to climb mother’s body

• After birth, much more development takes place in the pouch

• Young attach to nipple, nurse nearly constantly

• Stay in pouch up to one year
Development happen in pouch, nutrients not through blood from placenta —> opposite of uetherians

• Young eventually spend less and less time in pouch

• Not all marsupials have a true pouch
- Usually at least a fold of skin

Question 4

Marsupial reproduction

Answer 4

• Still retain cloaca

• Paired, lateral vagina/penis (extra channels/tubes and allows to retain sperm)

• Females able to retain sperm

• Also able to delay implantation after fertilization

Question 5

New world marsupials

Answer 5

More primitive characters

Opossums
• North and South America
• Semiarboreal, omnivores

Shrew opossums
• Terrestrial or burrowing in
Andes region of S. America
• Carnivores and insectivores

Monito del monte
• Arboreal omnivore
• More closely related to Australian taxa

Question 6

Australian-region marsupials

Answer 6

“Familiar” marsupials
• Kangaroos, wallabies, possums, koala, wombats
• Herbivores, variety of habitats

Marsupial moles
• Fossorial
• Insectivores and carnivores

Small marsupials
• Bandicoots and bilbies
• Terrestrial omnivores

Meat-eating marsupials
• Quolls, numbats, Tasmanian devil
• Terrestrial carnivores

Question 7

Key concepts

Answer 7

• Marsupials are united by an in-turned posterior dentary process, a distinct dental formula, and epipubic bones.

• Marsupial embryos develop partially in the uterus and complete development in the pouch.

• North and South American marsupials tend to be more primitive, Australian marsupials are more diverse and derived and fill a variety of ecological niches.