3-5 1 4-5 33-4 1 4-5 3

= 44-54__________5 1 3 44 1 3 4

________ = 50

Marsupial – Eutherian differencesTrophoblast and Placenta

Chorio-vitellinePlacenta

(most marsupials)

Chorio-Allantoic placenta

(eutharians)

Trophoblast(eutharians only)

Costs of pregnancy vs. lactation

Offspring: number vs. size

Marsupial reproduction & developmental constraints

Neonatal movement to the pouch necessitates forelimb function

http://www.arkive.org/species/GES/mammals/Macrotis_lagotis/Macrotis_lagotis_09c.html?movietype=wmMed

from: Shears, K. E. 2004. Constraints on the morphological evolution of marsupial shoulder girdles. Evolution 58:2353-2370

Marsupial developmental constraints

from: Shears, K. E. 2004. Constraints on the morphological evolution of marsupial shoulder girdles. Evolution 58:2353-2370

Marsupial – Placental Forelimb development

Marsupial female reproductive cycles

Macropod marsupialsReproductive flexibility

MARSUPIAL-PLACENTAL CONVERGENCE

Gliders

Burrowers

MARSUPIAL-PLACENTAL CONVERGENCE

Arboreal folivores

Ant-termite feeding

MARSUPIAL-PLACENTAL CONVERGENCECursorial hind limbs

MARSUPIAL-PLACENTAL CONVERGENCECarnivory

http://www.naturalworlds.org/thylacine/films/java/film3/film_3.htm

Thylacine vs. Dingo ecological replacement?

AUSTRALIAN MARSUPIALS Conservation issues

Disproportionate percentage of affected taxa are small- to medium-sized and ground dwelling.

Omnivores & herbivores affected more than carnivores.

Multiple factors involved:

1) Changes in plant community structure due to: a) browsing and grazing by exotic placentals (livestock, rabbits) b) altered fire ecology (decreased frequency and increased severity of fires)

2) Introduced predators (dogs, cats, red fox)

3) Exotic diseases

a) Koala – sexually transmitted Chlamydia causing infertility and other problems b) Tasmanian Devil – facial tumor disease

c) Thylacine -- distemper virus implicated in decline

4) Direct hunting (extinction of thylacine on Tasmania)

MARSUPIAL-PLACENTAL COMPETITION

Predomonance of eutherians on northern continents

Contemporary Asian origin of marsupials and placentals; more rapid spread of marsupials into southern continents

American faunal exchange (late Pliocene- Pleistocene)

Evolutionary dominance of placentals

Extinction of a much larger number of S. American placental groupsNorthern invasion and continued spread of didelphid marsupials

Placental carnivores replaced S. American “marsupicarnivores”

Prehistoric extinctions of Australian marsupials

Late Pleistocene extinction of most large-bodied marsupials,possibly through human hunting or by predation/competionfrom introduced dogs.

Extinctions may have been due to global climate change.Comparable levels of extinction seen for placentals onother continents.

Historic decline & extinction of Australian marsupials

A disproportionate percentage of historic mammal extinctions have involved Australian marsupials. Competition from exotic placentals has been directly implicated in some cases.

Native Australian placentals (rodents) show same dramatic level of decline and extinction. Competition with exotic placentals is only one of many factors endangering marsupials.