Granny Magda writes:
I am interested in why they might be supposed to have radiated out faster than placental mammals. What reason could there be for this? What exactly would give marsupials the edge? And most importantly of all, what is the evidence for this?
Of course, you won't find any evidence that any of this is true, mostly because it's not true. There is no reason to assume that marsupials would be any better at migrating than placentals. There is no evidence that such a thing ever happened. This is an especially glaring example of a flimsy post hoc excuse. CMI appear to have pulled this one directly out of their collective ass; note the weasel words "They could have dispersed". No evidence is presented for this claim.
So basically, I want to know how this could have happened and why we should think that it did happen.
Good post Granny however I suspect you won’t get a reply of any substance as the ‘models’ that CMI have proposed look like they were cobbled together during a Friday afternoon drinks session before knock-off time. In particular I wonder whether CMI have thought about the ‘dispersal’ rates of some of these marsupials:
Wombats: as noted in my link, wombats are slow moving animals of nocturnal habit, returning to their large and extensive burrows before dawn to rest during the day. So not only are they slow movers, they need to dig a burrow to live in.
Koalas: Koalas are uniquely adapted for life in trees. They have slow metabolisms and sleep for up to 20 hours per day. Their waking hours are spent almost exclusively eating and they only eat Eucalyptus leaves. Not the ideal lifestyle if you need to get from A to B in a hurry.
Numbats: while a bit more motile than my other examples, numbats are highly territorial and on top of that they have a very restricted diet — they only eat termites and an adult male requires up to 20,000 termites per day. Naturally they spend most of their waking hours looking for food.
Marsupial moles: a few relevant quotes from my link: they are arguably the world's most burrow-adapted mammal, they tunnel and backfill as they go...at the same time they squeeze their tubular body forward a few centimetres at a time, marsupial moles seem to flounder in loose sand ... and struggle to drag themselves along the surface. What more can I say?
Yet somehow these animals (not to mention the monotremes) managed to get to Australia before antelopes, horses, cats, monkeys, apes, etc, etc, the list is endless. Common sense, however is in short supply...
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