341 — Seasonal migration of marsupial megafauna in Pleistocene Sahul (Australia–New Guinea)

Seasonal migration is, if you think about it, weirdly common across all animal species. Or at least, it feels that way to me. How is it that seasonal travel is a behavior found in species as different as birds and whales and butterflies?

Here’s one type of animal that does not migrate: Marsupials. No marsupial alive today migrates. And while marsupials are small, which would make a seasonal migration more arduous…well, butterflies migrate. So clearly size isn’t the only factor in play here.

If only we had migratory marsupials against which we could compare nonmigratory marsupials! Then surely we would know what lies at the heart of this distinction, would we not?

This paper helps us achieve all our dreams, by shedding light on the marsupial megafauna during the Pleistocene. Diprotodon optatum, a wombat-like marsupial, did indeed migrate in accordance with the seasons:

Diprotodons were the largest marsupials ever, and their two-meter fuzzymonster selves lived in Australia during the Pleistocene. They ate mostly grasses, shrubs, the greenery from trees. This is really important, because in Australia, many grasses undergo C₄ photosynthesis whereas C₃ photosynthesis is found only in shrubs and trees.

Likewise, strontium distribution varies with geography across the Australian continent.

Why do we care?

Here is why we care, dear reader: Diprotodon teeth grow gradually over the course of its lifetime. So if you carve a long core out of a tooth and measure carbon and strontium distribution along that axis of growth, you can effectively map both the habitat and diet of the animal.

The results show that (at least one) Diprotodon traversed the continent (and a bit further, since there used to be a land bridge to New Guinea) several times during its life, suggesting that the species was either seasonally migratory or perhaps multiannually migratory. This differs damatically from nomadic migrations seen in many other animals including the red kangaroo.

So what happened to the Diprotodon?

Humans ate them.