Jake Buehler is a young biology major, bound for grad school, who set out to create a website that was not only informative about the wonders of nature, but also funny. His site is called Shit you didn’t know about biology; and judging by the latest (and long) post that I’ve recently read, “Metatherians (Part 2 of 2): Odd living representatives,” he’s succeeded beyond his wildest dreams. I mean, this kid is good.
Metatherians are a superclass that includes all living and extinct pouched mammals, and to us that means “marsupials.” Buehler’s post, 37 pages when printed out (with many large pictures), is compulsively readable and funny as hell. (There’s an earlier post, “Megatherians (Part 1 of 2): Extinct megafauna,” which recounts the evolutionary history of the group. I haven’t yet read it, but it looks equally good.)
There’s a lot of solid biology in Part 2, and a lot of comic writing, and they’re often mixed together. I’ll give a few excerpts and show some of the pictures with Buehler’s LOLzy captions:
Another effect of that short gestation is some serious impact on development after birth. Newborn joeys have to, crazy as it sounds, climb along the mother’s fur from the birth canal all the way up to the pouch, where it attaches itself to a nipple and doesn’t really budge until much later in development. Keep in mind that this is a fetus; blind, pink, without even facial features or hind limbs…and it has to drag itself through a thicket of fur for the equivalent of hundreds of feet, and get to the right destination. The mother also doesn’t really help out much. Some species may lay down a wet saliva trail for the joey, but that’s about it. Perhaps they figure if the little bastard is going to be living rent-free in a pocket made out the mother’s own flesh for months on end, then they can figure out their own damn way there.
This epic journey requires that even at such a rudimentary developmental stage, the joey must have overly-developed forelimbs, strong enough to pull the nubby body that great distance. These forelimbs must also be able to grasp and lock onto the fur. This severely limits the evolutionary avenues for marsupials in general; because of this reproductive strategy, climbing forelimbs must be in play. That is why there are no fully aquatic marsupials with flippers, no flying marsupials with wings, and no hoofed marsupials. With Australia’s wide, flat plains, you would expect a whole host of fleet, running, herbivorous marsupials to evolve, but because of that need for a climbing forelimb, you get things like kangaroos instead. There are gliding marsupials, but no flying species. You’ll never see a marsupial ‘whale’, a marsupial ‘bat’, or a marsupial ‘horse’. Marsupial reproduction is a massive wet blanket on evolutionary creativity in locomotion.
Well, given that evolution is cleverer than we are, I wouldn’t be so quick to say what marsupials could or could not evolve. After all, a climbing forelimb could develop into a flying forelimb.
Here are a few beasts themselves, the main topic of Buehler’s piece. His text is indented.
Matschie’s tree kangaroo:
One species that is especially threatened is the Matschie’s tree kangaroo (Dendrolagus matschiei) of the Huon Peninsula in eastern New Guinea. They inhabit the mountain forest there on the rugged peninsula (and only on that peninsula) up to 10,000 feet in elevation. The joeys of this species also look a little like ewoks.
Look at that cute little shit! It’s surprising to me that there isn’t more worldwide outrage, pledge drives, and ‘Save the Roo’ merchandise being hawked for this animal’s survival. It looks like what emerges from the very bottom of a pit of adorable Pokemon starters, Internet bunny videos, and every carnival plush animal on the planet after decades of fermentation. I’m still slightly suspicious that it was developed in a lab specifically to be a widely loved ‘spokesperson’ for fabric softener commercials. It’s an organism of unrealistically pure, distilled, baby-talk inducing infatuation. You drop a crate of tree kangaroo joeys into the middle of war zone, and you’ll have peace in ten minutes.
Here’s the numbat:
The next metatherian on this list is technically a member of that carnivorous Dasyuromorphia order, and is relatively closely related to quolls, Tasmanian devils, and the like, but it is definitely a weird example. It is known as the numbat (also called the ‘walpurti’ and the ‘banded anteater’), and while it used to be widespread across southern Australia, it is now restricted to several tiny areas along the southern and western perimeters of the continent and is severely endangered. It is the only species in the genus Myrmecobius and the only member of the family Myrmecobiidae, meaning it was unlike anything we know living.
Genetic studies place it in with the Dasyuromorphia, but it likely diverged from other members as far back as 40 million years ago or so. It appears to be a highly-derived offshoot dasyuromorph that has taken up a lifestyle of eating small insects (termites, to be exact), and only that. The numbat could be erroneously called a marsupial ‘anteater’ (since it only eats termites), and is a striking example of convergent evolution on a common form evolved several times across the world; anteaters in Central and South America, aardvarks in Africa, pangolins in Africa and southern Asia, armadillos in the Americas, the echidna of Australasia, and finally the numbat. In order to engage in this diet, it has specific adaptations, including reduced, non-functional teeth, and a ridiculously long, sticky tongue.
There are many more. Here’s the most bizarre: the bilby:
If tiny, termite-eating, tiger-striped squirrel things like the numbat weren’t weird enough, then get a load of the bilby (Macrotis lagotis) of the arid interior of Australia.
This is, apparently, what happens when a rabbit gets its face stuck in a Chinese finger trap for a few years. ‘Bilby’ is a short name for what is, from initial appearances, a ponderous chimera of a bunny, a shrew, and a pig, mashed together in a comically ridiculous mockery of the natural order.
There are a lot more pictures, many of them showing convergent (independently evolved) adaptations in marsupials similar to those in placentals. I’ll refer you to his site to see Buehler’s discussion of the rare marsupial mole:
Go have a look ASAP.