Expanded Marsupials: Evolution, Adaptations, and Conservation

Marsupials divergence from placentals

Around 90 million years ago, probably in North America.

Marsupials spread to Australia

Migrated from South America via Antarctica around 65 mya; Australia later became isolated.

Reason for marsupials in Australia

Because immigrant marsupials diversified after Australia became isolated.

North and South America rejoining

Placental mammals invaded South America, outcompeting many marsupials; only one marsupial returned north.

Gestation period of the Virginia opossum

12 days, with high young mortality.

Success of the Virginia opossum

It is an omnivorous generalist with adaptations like an opposable big toe and prehensile tail.

Ecosystem benefits of Virginia opossums

They eat rodents, ticks, and insects, and are immune to rabies and botulism.

Thanatosis

Playing dead ('playing possum') as a defense mechanism.

Monito del Monte

It is the only non-Australian member of its group, adapted to cool, humid forests in South America.

Adaptation of water opossums

Webbed feet and a pouch that seals underwater; they are the only aquatic marsupials.

Traits of shrew and mouse opossums

Arboreal, good climbers, omnivores, short lifespan, many threatened by habitat loss.

Convergent evolution

When unrelated groups evolve similar adaptations due to similar selective pressures.

Niches mimicked by marsupials in Australasia

Rodents, carnivores, grazers, squirrels, anteaters—but not bats.

Quoll's niche

Cat/mongoose-like predator; recovery efforts underway for Western quoll.

Threats to quolls

Predation/competition from introduced red foxes and habitat loss.

Adaptations of Tasmanian devils

Strong jaws, powerful bite relative to body size, adapted to crush bones.

Disease threatening Tasmanian devils

Devil facial tumor disease.

Thylacine

A wolf-like marsupial predator, extinct since 1936 due to hunting and habitat loss.