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ETpro's avatar

Why are there so many marsupials in Australia and New Zealand compared to elsewhere?

Asked by ETpro (34415points) December 21st, 2010

Here is a good rundown of what is known about marsupial development.. They slightly predate placental mammals, and inhabited the southern regions of the supercontinent Pangaea before it began to split into Antarctica, Australia, New Zealand, and the smaller islands versus Asia about 100 million years ago. The oldest marsupial fossils are found in modern China, and date to about 125 million years ago. Most of the marsupials in Australia, New Zealand, New Guinea and the smaller islands were isolated there when that landmass split from Antarctica. I am not sure whether conditions there favored marsupials over placental mammals, or they just happened to be the dominant species there upon isolation. Can anyone help fill in my blanks on why marsupials ended up succeeding so well in the Australian island complex?

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13 Answers

Odysseus's avatar

Sorry there are no marsupials in New Zealand. Well none that are native, possums and a small amount of wallabies introduced fairly recently from Australia have continued to survive here.

mithical's avatar

I actually learned about this in Biology class one time. I can only vaguely remember a few details only, though.. Something concerning Pangea and the evolutionary cycle they took. Not to mention environment and climate.

Sorry I couldn’t be of further help!

ETpro's avatar

@Odysseus Yes, I am aware that marsupials are limited in New Zealand. There are fossil records that show they were there.

The current opossums are likely transplants from Australia brought there by European explorers.

@mithical Thanks for the leads, Every additional piece of the puzzle helps.

Odysseus's avatar

@ETpro , was Just answering the main bit-part of your question “why so many Marsupials in NZ” There are not many and the only two we do indeed ‘have’ were introduced from Australia for farming.

ETpro's avatar

@Odysseus Yeah, you are right. That was poorly worded. I was thinking of the chunk of Pangaea and not specific locations. The fact most are concentrated in Australia may well be a clue suggesting that its environment favored them. But I would still like to understand why.

Odysseus's avatar

@ETpro I respect that and apologise for being a touch overly defensive in my demeanour, Its just Ive met dozens of people who consider NZ to be the same as OZ with our boomerangs and kangaroos, it is a touchy subject for me lol.

I have no idea why OZ has so many marsupials, I have always just put it down to the fact that it like Madagascar had been separated from the major landmasses for the longest amount of time therefore its natural evolution took a separate path. Why pouches ? No idea. :)

ETpro's avatar

@Odysseus My initial thought was separate path as well, but opossums are widespread here in the Americas as well. And the oldest marsupial fossils date back to 25 million years before the breakup of Pangaea. That puts a crimp in the simple isolation explanation, it would seem.

Kayak8's avatar

I think this is a fascinating question! Here is one of the bits I found.

crisw's avatar

Remember that marsupials didn’t just flourish in Australia- they also dominated South America, and there are still plenty of them there today.

In South America, the marsupials were outcompeted by the more climate-tolerant, smarter, more generalized mammals that crossed over the Isthmus of Panama in the Pleistocene. The Australian fauna didn’t have such an event to contend with. South America didn’t just lose many marsupials- it lost giant ground sloths, glyptodonts and all sorts of strange and fascinating creatures.

ETpro's avatar

@Kayak8 Thanks so much for the link. Very interesting. Very definitive.

@crisw Thank you for an expert opinion. Interestingly, this is a question I asked on in June of 2009, and never got a useful answer. Here, it took 1 day instead of 1.5 years. What do I love about Let me count the ways.

Kat555's avatar

Marsupials are mostly found in Australia, New Guinea and South America. They are known as less successful than placental mammals, and i do not believe that the conditions would have favoured them over placentals. I think it so happened at the time of the continental split there were no placentals present. In south America, which is not completely isolated from central America, placentals have already moved in and ‘got rid of’ a lot of marsupials. In Australia, which is better isolated, more marsupials remain, however all the introduced placental mammals do threaten them a lot, if by nothing else then habitat competition.

So, marsupials ended up succeeding so well in the ‘Australian island complex’ exactly because it’s an island complex so isolated enough that placentals cannot come and take over in mass numbers.

They predate on placentals VERY slightly. Most marsupials are herbivores, with the only exception of small, rodent size marsupials such as quolls, numbats etc, and even those mostly eat insects, and anything very small, and very rarely take a mammal.

ETpro's avatar

@Kat555 Welcome to Fluther and thanks for a great answer.

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