No, they have nothing to do with zombies, nor is it a new version of the weeble-wobble. It is the term for “mammals shaped like wombats.”

Shaped like this, mostly.
I’m lazy. Why should I come up with all the biology and ecosystem and other stuff for a new planet if I can steal borrow and then change? I knew I didn’t want to do reptiles, because I’ve been doing reptiles. And no cats. The Kzinti are already taken and the saber-toothed not-really-cats of North America are too well-known. What to do, what to do . . . And then I remembered reading a chapter in a collection of academic papers about the extinction of the Pleistocene megafauna in Australia, and how odd the critters were. Three weeks and $9 in interlibrary loan fees later, I have a viable ecosystem to play with and mess up (or not).

Whazzup, dude? Reconstruction of “giant” wombat.

OK, so it was pretty large. Really large. Exceedingly large.
And if you think that’s odd . . .

Everything’s bigger in the pre-Pleistocene.
You want some predators (besides the meat-eating kangaroo? Yes, really.)

Nice kitty, um, boy, um, tiger, er, stay!
If you just want to spend wayyyy too much time looking at long-gone critters, http://www.prehistoric-wildlife.com/index.html
The Marsupials of Unusual Size served a similar function to mastodons in North America, as large, herd-dwelling browsers. Ditto the giant kangaroos (there were a couple of versions). If you want things with trunks, there seem to have been one or two, but the trunks are not as long as elephants, more like tapirs. The smaller carnivorous kangaroos ate birds, lizards, small mammals. The Thylacaleo and friends were the size of a jaguar or a touch smaller, and some may have hauled their prey up into the trees, like modern leopards. There’s a version that had a grasping thumb with a long claw that allowed it to take a very firm grip in its prey.

The kangaroo is over 6′ (2m) tall.
Unlike New Zealand and South America, the so-called “terror birds” seem to have been vegetarians in Australia, at least those found so far. But I can borrow from South America, and it still fits an effective niche. And there’s a few monotremes tossed in just for fun. It was wild, strange, different, is unfamiliar, and easy to riff off of.

The original image is from a great book about the Riversleigh fossil site in northern Queensland, back of Burke, beyond the black stump, waaaay over yonder.
OK, so I have a large bank of critters, I have an ecosystem, and I have M.M. Kaye’s autobiography about growing up in India during the Raj. I’ve also been reading about colonial societies, and space-travel, and caldera eruptions and climate disruption around 535-540 or so, and ancient plagues . . . This is going to be an interesting book or three.