Marsupials are an infraclass of mammals, characterized by a distinctive pouch (called the marsupium), in which females carry their young through early infancy.

History

Isolated petrosals of Djarthia murgonensis, Australia’s oldest marsupial fossils

It was once commonly believed that marsupials were a primitive forerunner of modern placental mammals, but fossil evidence, first presented by researcher M.J. Spechtt in 1982, conflicts with this assumption. Instead, both main branches of the mammal tree appear to have evolved concurrently toward the end of the Mesozoic era. In the absence of soft tissues, such as the pouch and reproductive system, fossil marsupials can be distinguished from placentals by the form of their teeth; primitive marsupials possess four pairs of molar teeth in each jaw, whereas placental mammals never have more than three pairs.

Using this criterion, the earliest known marsupial is Sinodelphys szalayi, which lived in China around 125 million years ago. This makes it almost contemporary to the earliest placental fossils, which have been found in the same area.

The discovery of Chinese marsupials appears to support the idea that marsupials reached Australia via Southeast Asia. There are a few species of marsupials still living in Asia, especially in the Sulawesi region of Indonesia. These marsupials coexist with primates, hooved mammals and other placentals. However, due to the fact that Australia and China were separated by the wide Tethys Sea in the early Cretaceous into the Northern continent of Laurasia and Southern continent of Gondwana, marsupials had to take a much longer route around. From their origin in East Laurasia (modern day China), they spread westwards into modern North America (still attached to Eurasia) and skipped across to South America, which was connected to North America up until around 65MYA. Here they radiated into Borhyaenids and Shrew Opossums, creating a unique fauna found in South America and Antarctica (which were connected until 35MYA). Marsupials reached Australia via Antarctica about 50MYA just after Australia had split off, suggesting a single dispersion event of several of just one species, related to South America’s Monito del Monte (Microbiothere), rafted across the widening, but still narrow gap between Australia and Antarctica at that time. In Australia, being the only mammals present (except a few Austrosphenids like echidnas and platypuses) they radiated into the wide varieties we see today, even island hopping some way through the Indonesian archipelagos, almost completing a circumnavigation back to their homeland in China.

On most continents, placental mammals were much more successful and no marsupials survived, though in South America the opossums retained a strong presence, and the Tertiary saw the genesis of marsupial predators such as the borhyaenids and the saber-toothed Thylacosmilus. In Australia, however, marsupials displaced placental mammals entirely, and have since dominated the Australian ecosystem. Marsupial success over placental mammals in Australia has been attributed to their comparatively low metabolic rate, a trait which would prove helpful in the hot Australian climate. As a result, native Australian placental mammals (such as hopping mice) are more recent immigrants.

Description

An early birth removes a developing marsupial from its parent’s body much sooner than in placental mammals, and thus marsupials have not developed a complex placenta to protect the embryo from its mother’s immune system. Though early birth places the tiny newborn marsupial at a greater environmental risk, it significantly reduces the dangers associated with long pregnancies, as there is no need to carry a large fetus to full-term in bad seasons.

Because newborn marsupials must climb up to their mother’s nipples, their front limbs are much more developed than the rest of the body at the time of birth. It is possible that this requirement has resulted in the limited range of locomotor adaptations in marsupials compared to placentals. Marsupials must develop a grasping forepaw during their early youth, making the transition from this limb into a hoof, wing, or flipper, as some groups of placental mammals have done, far more difficult.

There are about 334 species of marsupial, and over 200 are native to Australia and neighboring northern islands. There are also 100 extant American species; these are centered mostly in South America, but the Great American Interchange has provided Central America with 13 species, and North America with one (the Virginia Opossum).

A feature of marsupials (and also monotremes) is that they don’t have a gross communication (corpus callosum) between the right and left brain hemisphere.

Reproductive system

Marsupials’ reproductive systems differ markedly from those of placental mammals (Placentalia). Females have two lateral vaginas, which lead to separate uteruses, but both open externally through the same orifice. A third canal, the median vagina, is used for birth. This canal can be transitory or permanent.^[11] The males generally have a two-pronged penis, which corresponds to the females’ two vaginas.^[12] The penis is used only for discharging semen into females, and there is instead a urogenital sac used to store waste before expulsion.

Pregnant females develop a kind of yolk sac in their wombs, which delivers nutrients to the embryo. Marsupials give birth at a very early stage of development (about 4–5 weeks); after birth, newborn marsupials crawl up the bodies of their mothers and attach themselves to a nipple, which is located inside the marsupium. There they remain for a number of weeks, attached to the nipple. The offspring are eventually able to leave the marsupium for short periods, returning to it for warmth, protection and nourishment.

Koalas and kangaroos are two of the favorite things to see when visiting Australia. These two animals are like mascots for the great down under. Many people have written about how the koala and kangaroo are different but let’s examine how the koala and kangaroo are similar.

• Koalas and kangaroos both live in Australia.
• Koalas and kangaroos start with the letter K.
• Koalas and kangaroos can have more than one baby but generally only have one a season.
• A koala baby is called a joey. A kangaroo baby is called a joey.
• Koalas and kangaroos are marsupials.
• Koalas and kangaroos both eat leaves.
• Koalas and kangaroos both have pouches.
• Koala and kangaroo parents both digest the food before feeding it to their young.
• Neither koalas nor kangaroos mate for life.

Koala Bear, originally uploaded by cewoldt.

BULLDOZERS rolled in to some of the last remaining koala habitats on the South Coast yesterday, marking the start of what police fear could be a divisive logging operation.

After reading yesterday that we made up some ground in this fight for suitable habitat areas with the 1200 fodder tree sanctuary it is planning, I am discouraged to read this travesty of environmental justice. This must be stopped or the koala will lose its habitat in the South Coast for good. Sheesh! One step forward, two steps back.

Read more of this article here.

Koala, originally uploaded by john white photos.

It seems with all animals suffering from a lack of habitat what we need is some real conservation of land that is just there land; a place where they can not only live but thrive. This simply doesn’t happen often enough, does it?

Well, recently in Australia an agreement was made to do just that for the cute and lovable little koala.

The Australia Zoo working with the SEQ Quarry have come to agreement to create a 1200 fodder trees sanctuary of sorts on the Boral Narangba quarry site just for koala conservation.

Good for them! This will help the local bird population as well as the koala. Finally a positive story worth sharing! This is definitely a step in the right direction.

Koala at Currumbin Wildlife Sanctuary, originally uploaded by whoops vision.

This cute devil knows he takes a good photo! The Currumbin Wildlife Sanctuary is definately worth a visit if you want to see lots of Australia native animals and especially if you are itching to see cute and cuddly koalas!

The albino koala, Lone Pine 1971, originally uploaded by David Stephensen.

I found this photograph on flickr. This is what the photograph posted below the picture in the about section:

A truck driver found this chap on the road and brought him in to the sanctuary. How spectacular he was with his amazing white coat! He seemed quite happy to live there as long as the endless supply of eucalyptus leaves came rolling in each day.

You can see his powerful claws. He also has very powerful jaws and can bite right into your finger. Not nice if he was scared of you.

Some were trained from a young age to be handled. We had to pick them up and carry them by the wrists and ankles. They have very weak rib cages. Picking them up under the armpits feels to them like picking us up by the neck. You can cuddle the trained ones, but they hang onto you with those big claws and it is not so comfortable really. Probably stroking their backs while they hang onto something else is the nicest thing.

And, yes, they spend most of the day asleep.

en.wikipedia.org/wiki/Koala

The Australian Koala Foundation estimates that in excess of 5,000 koalas are killed each year from land clearing, dog attack and being hit by cars. In the state of Queensland approximately 1,500 Koalas are admitted to hospital each year. Thirty to forty percent of admissions are estimated to be due to road related incidents, the second biggest cause of admission next to disease.

The road toll has been so extensive a nationwide awareness program has been created to educate drivers to be alert for koalas crossing roads at night. Koala friendly road signs are displayed throughout the country much to the delight of tourists who do not realize that they are there to warn them of the danger of driving over the little creatures.

Koalas are often called “koala bears” - this is not correct. The Koala is not a bear but a marsupial. The closest relative of koala is a wombat, which also has cute and cuddly appearance, but it’s never called a “wombat bear”

Queensland scientists are using mobile phones to unlock the mystery of why koalas bellow.

The distinctive deep grunts and belows of the male Koalas sound in Australian forests in spring, but researchers still don’t understand what they mean.

Noises from koalas on St Bees Island off the coast of Mackay, in central Queensland, are now being relayed to a Brisbane laboratory via mobile phone technology.

University of Queensland koala researcher Dr Bill Ellis said the information was fed into an acoustic database, and Queensland University of Technology (QUT) researchers were developing software to recognise koala calls automatically.

“We are studying whether males are talking to other males, or to females, and how vocalisations might stimulate breeding behaviour in female koalas,” Dr Ellis said.

QUT Professor Richard Mason said the technology, used at Brisbane Airport to research bird calls, was a good way for Dr Ellis to eavesdrop on the marsupials without disturbing them.

Prof Mason said microphones connected to the phones monitored the island’s acoustic environment for two minutes every half hour.

“The sensors are remote controlled, so that if we want to change the recording schedule in response to data on when the calls are most prevalent, for example, we can,” he said.

The team is excited about the data it has collected so far, as well as the prospect of adapting the technology to other eco systems.

Source: APP

The Koala is one of the few mammals that has fingerprints. In fact, koala fingerprints are remarkably similar to human fingerprints; even with an electron microscope, it can be quite difficult to distinguish between the two.

As shown by Henneberg & als from the Department of Anatomical Sciences, University of Adelaide, koalas have very human-like fingerprints. The main difference is that the entire human palm and fingers are covered with ridges while the koala only has ridges on its fingertips and some areas of the palm.

These similarities between Koalas and Humans is an example of coincidental evolution.

Sources:
Fingerprint homoplasy: koalas and humans - http://naturalscience.com/ns/articles/01-04/ns_hll.html