Metatherians (Part 2 of 2): Odd Living Representatives

…so, some more about those metatherians/marsupials.

In the previous part to this two part series, I went over some of the now-extinct metatherian megafauna that once graced Australia and South America. These animals were fantastic and marvelous pinnacles of metatherian specialization, yes, but there are plenty of surviving metatherians, all of them of the ‘marsupial’ clade, that are also largely ignored and their lives obscured. There are some truly bizarre and amazing marsupials outside of the traditional koala/kangaroo/wombat/possum group that essentially everyone on the planet associates with the marsupial infraclass, and all of them somehow survived invading hoardes of humans and other placental species (although, in most cases, just barely).

But, perhaps it’s best to start with answering the question of just why it is that marsupials have been, time and time again, outmatched by placental counterparts. The great metatherian reign over the past few tens of years was a phenomenon restricted to the isolated island continents of Australia and South America, and as soon as placentals came into these areas (via the Isthmus of Panama from North to South America, and through humans using the Ice Age land bridge from Southeast Asia to Australia), there was a mass extinction of all of the most specialized metatherian endemics. In the northern continents of Eurasia and North America, and Africa, where there were large placental mammalian presences…there were essentially no pouch-bearers to be found…and when placentals invaded metatherian territory, the dethroning was swift and bloody. This occurred without fail, for millions of years, resulting in a comparatively very low species diversity of metatherians compared to their eutherian overlords.


So, why is it, exactly, that metatherians have wussed out in competition with eutherians, over and over and over again? It would be tempting to say that metatherians are somehow ‘less evolved’ and inherently ‘inferior’ to their eutherian counterparts. However, evolution doesn’t work like a linear ladder from ‘least evolved’ to ‘most evolved’. Marsupials and their kin are simply an old offshoot of the main mammalian line, and they have gone through just as much adaptation and retooling in response to their environment as eutherians, often with even more specialization (see: Thylacoleo from Part 1). Marsupials aren’t ‘less evolved’ than placentals; they just shared a common ancestor with placentals much further back than placentals do with each other. However, that doesn’t mean that there aren’t certain aspects of marsupial/metatherian biology that may have put them at a disadvantage against placental invaders.

But first, there are certain pros to being a metatherian. The most obvious is tied to their brand of reproduction. Marsupials completely side-step a lot of the risks associated with pregnancy and long gestation that are common to placental mammals. Marsupials produce very small, undeveloped young, sometimes only a couple weeks after zygote formation. This means that female marsupials spend a minimal amount of calories on pregnancy, and in times of stress or crisis, can lose or terminate the offspring without much ‘wasted effort.’ This also reduces the amount of danger to the mother if she is pregnant during times of scarcity; there’s not a giant ‘energy sink’ that puts her at risk of starvation or malnutrition. Marsupials are far more flexible when it comes to the initial process of reproduction, and large marsupials of the same mass as a placental counterpart typically will have much higher levels of lifetime reproduction in comparison. The tiny size of the offspring even at the peak of pregnancy, smaller than a jelly bean, means that there is no ponderous, debilitating pregnancy common to many placental mammals. This relative, temporary reduction of mobility is very dangerous to female placental animals, especially if they are prey items. This is probably most pronounced in human females, who are not only lucky enough to have very long gestation periods, but also are bipedal…which makes everything even harder.

Marsupials also avoid the risks associated with the birthing process, since the joeys are so tiny when born. This would seem to be a huge advantage for marsupials. Female marsupials churn out minuscule joeys like ambulatory jelly bean factories, hardly missing a beat between pregnancies. Sure, a lot of these joeys die before maturity, but it’s no sweat for mom, who can just make half a dozen more next year. Placental mammals go through an arduous process growing a gigantic offspring, which acts like a brick of lead in the gut when fleeing from predators, and could actually kill the mother whenever it decides it’s time to move out.

Another advantage, it would seem, especially for carnivorous marsupials, is that across the board, pound for pound, marsupials possess significantly stronger bite forces than placental mammals. Thylacoleo could produce the strongest bite force, per kilogram, of any mammal ever. The thylacine (Tasmanian wolf) had a stronger bite than a comparatively sized gray wolf. Various living species of carnivorous marsupial have among the most powerful jaws in the whole mammalian class.

But of course, those pros are a mote of dust in a cavern of cons for marsupials. Most of these, interestingly enough, are caused by their reproductive strategy. Yes, marsupials have far more efficient pregnancies than placental mammals, but that is just one facet of reproduction. That whole short pregnancy thing actually has its origins in a relatively underwhelming quirk of marsupial reproductive biology. In placental mammals, soon after fertilization and the growth of a blastocyst (a transitory mass of cells that will eventually form an embryo), a layer of cells encases the newly forming offspring. This is known as the ‘trophoblast’ and it serves to protect the progeny from…the mother. Since the offspring has genetic material from its father, a foreign entity, the mother’s immune system, relatively quickly in the pregnancy, would attack and reject the unknown lifeform. The trophoblast acts like an invisibility cloak, hiding the offspring from mom’s trigger-happy immune responses. It also is instrumental in the attachment of the blastocyst to the wall of the uterus and the formation of a placenta.

An awesome set-up, right? Well, marsupials don’t have any of that going on. They do not produce nice little trophoblast cages around their rapidly-budding prides-and-joys. Instead, they simply engage in an insanely short pregnancy…before the mother’s immune system can tear apart Baby like a dutiful guard dog. Marsupials obviously take this situation in stride, but it leaves them with a number of obstacles that are not shared with their placental cousins.

For one, although their pregnancies are much shorter and use much less energy, marsupials have a very protracted nursing period on the other end. This means that marsupials have their kids on the teat, literally, far longer. Milk is really, really energetically expensive to make, compared to feeding an offspring in utero via a placenta. Instead of just dipping into the sugar/carbohydrate/protein/fat stores that mom has been taking up in her food supply, marsupials take food energy that the mother has processed, and then uses that to make a secondary milk product for the joeys. That extra step loses a lot of energy, and puts extended strain on the mother that placental mammals never experience. It’s like ordering delivery pizza, but sending it to a location 10 miles from your apartment, which means you need to get in your car and drive over to pick it up…when you could have just sent the damn thing to your front door.
As I’ve said before, nature (through evolution) is a merciless accountant. Energy waste does not escape tallying, and if the new crew in town is better with their expenditures than you are, it won’t be long until your species is reduced to a few dusty, plushy additions to museum collection, and nothing more.

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.

The early affixture of the joey to the nipple also limits cranial development. There needs to be early ossification (the setting of bone in place of other tissues like cartilage) in order to do anything like use force on the mouth to attach to anything. The head being a big blob of amorphous crap isn’t going to work. This early bone growth in the head of young joeys impacts head development further down the road. Marsupial brains don’t have the same amount of time for growth and expansion of size, which results in smaller brains in adults. Almost without fail, in comparisons between marsupial skulls and placental skulls from animals of equivalent mass and ecological niche, the brain case is a good deal smaller in the marsupial example. This is most noticeable in the neocortex, that area of the brain that allows for cognitive process and more abstract thinking and planning. This is partially the reason why there are no intelligent, marsupial ‘monkey’ equivalents. It may be that placentals in the same ecological niche as a given marsupial are simply more intellectually capable, and more adaptable on the fly; this would translate into some serious competition troubles for the marsupial.

Marsupials also have some differences in brain morphology and anatomy compared to placentals. Marsupials lack a corpus callosum, which is a structure in the brain that connects the tissue of the left and right hemispheres of the brain. Only placental mammals have this feature, and it is thought to be instrumental in the streamlining of information transfer and communication between two hemispheres of the brain. It may be that in ecological confrontations between invading placentals and marsupials, a major factor in competition is the fact that placentals had an extra intellectual edge, and were able to process information and adapt to their surroundings in a more effective way than endemic marsupial species.

Placental mammals also had an edge just in their evolutionary history. For tens of millions of years, placental mammals toiled in the cauldron of natural selection that made up the northern continents and Africa. These were massive land areas, with variable and unpredictable elements that needed to be overcome; plate tectonics, climate change, and range expansion into novel environments were commonplace, and lineages of organisms not able to cope with such rapid changes were quickly extirpated from the environment by natural selection. Whole orders of placental mammals rose and fell into extinction over this period of time, and due to the brutal nature of being in such a diverse and rapidly changing environment, cumbersome ‘experimental’ forms and strategies that couldn’t cut the mustard were cropped away. In contrast, on the small southern landmasses of South America and Australia, which were islands, there were no regular transferals of new organisms from outside sources into their environment, through climate change or the movement of the plates. The challenges that honed and culled and obliterated scores of lineages of placentals were not shared by marsupials to the south; they had a very stable 60 million years or so after the dinosaurs went extinct. Niche competition was something marsupials had not as often encountered, so this led to specialization and an inability to adapt to new factors in their ecosystem.

The greatest metatherian megafauna were outsmarted, they were rendered too reproductively inefficient, and they were far to inflexible. The remaining species, already facing threats from human encroachment, are fighting the same battles against all the placental invasives that humans bring along with them (cats, foxes, rats, pigs, etc.), and they are losing quite badly. Most of the animals in this entry are on some level endangered (some critically so), and some are as rare as other famously uncommon animals like pandas and tigers…but get no attention, mostly because they aren’t ‘charismatic’ enough to be marketable as an example of biodiversity in distress.

One group of marsupials containing some particularly rare members is the tree kangaroos. And no, I’m not making that up. There are kangaroos that live in trees and they look like this:

If you’re thinking to yourself ‘how the hell does a kangaroo get up in a tree?’ then know that you are correct in being skeptical. A kangaroo trying to climb a tree is like a human trying to do the same thing, but with skis attached to their feet. The thin, long feet of most kangaroos are ideal for launching the body off the ground, but don’t have much function beyond that. Tree kangaroos, all members of the genus Dendrolagus (which literally translates to ‘tree rabbit’), have gone through some modifications that have allowed them to recolonize the rainforest canopy. I say ‘recolonize’ because the ancestors of kangaroos started off in the treetops, like many generalist, arboreal marsupials shortly after the dinosaurs went extinct. The earliest ancestors of kangaroos, as well as lots of other members of the Diprotodontia order, were likely tree-dwelling possum-like (not to be confused with opossum) herbivores. As the Australian continent dried, the rainforests retreated, and some of these possum-like animals became terrestrial, grassland animals that locomoted on their hopping hind legs. During this time, their broad, grasping feet became thin and sinewy for the hopping, ground-dwelling lifestyle; this trend culminated in the specialized elastic springs that move large kangaroos and wallabies along the deserts and plains of Australia today.

One group of rock-wallabies, back in the mid-Miocene some 15 million years ago, had returned to the forest environments in northern Australia. These forests were different than the ones that the first macropods (kangaroos) left for the Australian savannah, and were instead a type imported from the Indonesian islands and Southeast Asia. These versatile and agile rock-wallabies eventually started spending more time in the trees, and their hopping back feet started, over the generations, re-broadening into a more appropriate shape for life in the forest canopy.

The above illustration shows the hypothesized progression in foot morphology, using modern analogues, starting from a possum ancestor, continuing through forest floor kangaroos, to rock-wallabies, and back to the trees with Dendrolagus individuals.
Tree kangaroos currently occupy a range that includes Papua New Guinea, various other east Indonesian islands, and extreme northern Australia. They are restricted to rainforest habitat, and tend to inhabit higher elevation areas that receive even more precipitation. They are, of course, herbivorous, and many species subsist on a wide range of forest plant material. Tree kangaroos are awkward and clumsy on the ground, and tend to spend as much time up in the tree tops as possible. This complete dependence on their rainforest home means that they are more sensitive than most animals to rainforest logging and habitat loss. Their range extending primarily in one of the least populated forest areas in Australasia also means that they are rarely seen, and make themselves hidden to humans and other predators (which include pythons, marsupial carnivores, and birds of prey).

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.

Welcome to Endor! May I take your coat?

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.
Basically, what I’m trying to say is that this thing makes panda cubs look like that pile of gunk in your yard that may or not be dog puke. The stuff with the white mold on top.

Such a nice moment almost makes you forget that they are going extinct. And they are.
Matschie’s tree kangaroos, like all tree kangaroos, are specialized canopy dwellers, and as their habitat is cleared for lumber production and for crop planting, they don’t have any options but to die. While they have, somehow, escaped the exotic pet trade, humans also more directly impact them by hunting. The people of Papua New Guinea have hunted them for millennia for meat and their soft fur. This was done at subsistence levels in the past, but the combination of habitat destruction and increased human population and hunting is taking its toll.

It doesn’t help that these kangaroos don’t have a lot of defenses. They can’t rear up and use their legs as weapons like their ground-living cousins. The Matschie’s tree kangaroo, for example, has only one real option for escaping predation, and it involves hiding. The high altitude cloud forests, thousands of feet up in the mountains of the Huon Peninsula, are a place that has quite a bit of moisture in the air. The ‘cloud forests’ are so called due to a nearly constant presence of overcast and dense fog, saturating the rainforest air. Because of this, there is a lot of moss that can survive and absorb water from the fog up in the canopy. Great, brownish mounds of moss cover portions of tree branches across the canopy. That reddish-brown coloring of the Matschie’s tree kangaroo helps them blend in with the moss when they feel threatened. Yes, this is an animal so benign and harmless that it takes refuge in moss…the plant world’s fluffy pillow. Only an animal that looks like the Matschie’s tree kangaroo would decide that the perfect thing to do in a crisis is to find a place comfortable enough to take a nap.

Jesus, zookeepers. You could have at least gotten him a Tempur-Pedic.

There are efforts by conservation groups and scientists to save this species, among others in the tree kangaroo genus, and there has been promising co-operation with various remote townships in New Guinea to start setting aside areas for these animals without interference. Some populations exist in zoos across the world, but hopefully these won’t be the species’ final homes. Luckily, tree kangaroos tend to thrive in captivity (unlike those libido-less pandas), so there is little danger that this species will go extinct in the proper sense, but obviously no one wants to see the wild population dwindle to nothing. If that day is inevitable, one can only hope that caretakers in the future remember not to feed them after midnight. For the love of god, don’t feed them after midnight.

Tree kangaroos aren’t alone as the only arboreal rainforest marsupials in their home. Inhabiting the same general region as the tree kangaroos, the rainforests of Indonesia and northern Australia, is this thing:

It may look like some ungodly combination of lemur, dairy cow, and gecko, but it’s just another weird-ass marsupial. This is a common spotted cuscus (Spilocuscus maculatus), one species in a group of possums (Phalangeridae) known as cuscuses…all of them sharing long, partially naked prehensile tails, smallish ears, and a slow, measured way of movement not unlike sloths or lorises. Their odd appearance and slight lemur-like appearance caused much confusion when cuscuses were first encountered by Western scientists. Cuscuses were assumed to be primates at first glance, and ecologically speaking, they really are the closest marsupials have gotten to evolving a prosimian primate equivalent to the placental versions. The name may look like ‘couscous’ (“the food so nice they named it twice”), but it is pronounced ‘cuss cuss’, which is an onomatopoeia of the hissing noise they make when threatened. There are actually four different genera of cuscus, Spilocuscus just being one example, and they vary in coloration and general appearance widely. Most of them are native to the same rainforest region, and they all tend to fill similar ecological niches as their more nimble possum brethren, munching on leaves and fruit up in the treetops. They are all very nocturnal, and possess large eyes and a facial expression that perpetually makes them look like they just discovered they left the oven on.

The common spotted cuscus is somewhat unique among cuscuses in that its diet is a little more generalized and it has been seen feeding in the daylight hours, which is something unheard of in other cuscuses. They can grow to about the size of a house cat, and live exceedingly solitary lives, only interacting favorably in times of mating. Males of this species are highly territorial, and mark their claim in the canopy by using a potent musk and their own saliva, which they coat tree branches with. Transgressions by other males are met with surprising levels of aggression, noise, and violence.
Spotted cuscuses have a diet that is mostly comprised of leaves, fruit, and flowers, but will also consume insects and bird eggs, and anything else slow enough to get caught in its path. Males in this species are almost always spotted with gray or brown blotches, while females are more often purely white or purely gray in color. Male coloration is odd, but female coloration, in the darkness of the rainforest, must be striking.

Who taught that seal pup how to climb trees?

That’s the other thing too; like tree kangaroos, cuscuses, with their soft pelts, fat, slow bodies, and giant eyes would theoretically make for brilliant poster-animals for conservation efforts. However, cuscuses, with the exception of the bear cuscuses in the genus Ailurops, there aren’t any immediate threats to their survival. Cuscuses are used for food and fur in New Guinea, and there hasn’t yet been a major blow dealt to their species integrity.
Cuscuses in general are an integral part of traditional life in many parts of Papua New Guinea. Their meat is an excellent source of protein in the rainforest, and their fur is used to make ceremonial headpieces and other ornamentation, often highly cherished and passed down from generation to generation. Since cuscuses are incredibly shy creatures, and very rarely seen in the forest (even by the New Guineans who live in close proximity to the wilds their entire lives), actively hunting them isn’t feasible. Instead, many are hand-reared as pets, and then eventually killed in adulthood. The cuscus, if reared from infancy, can actually be an easy to care for pet. They don’t tend to stray too far or move too quickly, they lack any real capacity to do a lot of damage if they do happen to become aggressive, and their instinct to clasp onto high objects means that they spend a lot of their time crawling all over and perching on their owners. They are reportedly fond of clinging stubbornly to human heads and hair, so they can get a good vantage point on their surroundings.

I’m not sure what the legality of keeping cuscuses as pets is outside of New Guinea, but I would bet on the side of illegality, and of course, immorality. Removing wild animals from their home ranges for introduction into a pet trade is never a good decision. I’m not sure how successful a cuscus pet trade would be, even if they are reportedly mellow pets and have all the fuzzy appeal, they might not catch on…mostly because they have startlingly creepy eyes. Really, really creepy.

“Sauron demands more starfruit!”

Enough, you say! Enough with the cute, fluffy herbivores. Certainly there are some overlooked, underloved, and unappreciated carnivorous metatherians to explore, yes? The answer to this question is yes. Although great, giant carnivores like the marsupial ‘lion’ and the sparassadont ‘sabertooth’ from South America are gone, as are the thylacines, some carnivores do remain. In some ways, they are even more acutely threatened from changes to their environment. Not only are they often shoved out of their niches by invading placental carnivores like foxes and cats, but can fall prey to even larger predators like dogs and dingos, and have issues with invasive food items that initially seem like a good idea to try and eat (see: cane toads).

The remaining metatherian carnivores are all in the order Dasyuromorphia. Most are quite small, being mouse-sized predators of things like insects and small lizards. Some are larger, filling the niches of foxes and cats and weasels (precisely why they are so sensitive to those same animals running amok in their habitat). Up until the 1930s, the largest members, the ‘Tasmanian wolves’ filled the large dog niche…and then they went extinct. Another crowning achievement for humankind, I’ll tell you what.

There are only two families remaining in this order, and one of them, the Dasyuridae, is the third largest family of metatherians. This family houses the vast majority of the Dasyuromorphia, and is made up of short-legged, long-snouted carnivorous animals ranging from the size of a shrew to the size of a small dog in the case of the Tasmanian devil (Sarcophilus). While the Tasmanian devil is somewhat more familiar to the majority of folks outside of Australia, its smaller, more wide-ranging cousin, the quoll (a member of the dasyurid family) is not.

There are six living species of quoll (genus Dasyurus), and they range across parts of Australia (mostly near the coasts), Tasmania, and Papua New Guinea. Most are threatened with extinction at some level, some more severe than others. They are essentially marsupial ‘ferrets’, and are nimble, agile predators of both terrestrial and arboreal environments. Due to their superficial appearance to cats or any other small placental carnivore, they were originally referred to as ‘native cats’ by the first Europeans in Australia. The name ‘quoll’, like so many other names of animals in Australia, is a corruption of the Aboriginal name for the same creature. In the Guugu Yimidhirr language (from northeastern Queensland), these little guys are called ‘dhigul’. ‘Quoll’ is about as close as clumsy European tongues could get, apparently. Comparisons with placental ecological equivalents led to other inaccurate naming schemes like ‘spotted marten’ or ‘spotted opossum’ (again, this is an animal very different from American opossums).

There are multiple prehistoric species in the fossil record from around Australia, New Guinea, and Tasmania, and genetic clock studies infer that quolls diversified in the Miocene epoch between 15 and 5 million years ago, coinciding in a larger, rapid diversification trend in Australian marsupials. Most of the direct ancestors of today’s six species had diverged more than 4 million years ago. Up until very recently, they were found all over Australia, Tasmania, and New Guinea, but now exist in distinct, fragmented geographic areas.

As far as marsupials go, quolls are fairly conventional, despite having the distinction of being the most massive group of carnivorous marsupials still living on the Australian mainland. Mating occurs in the winter, and three weeks later, the female gives birth to as many as two dozen pups, each only the size of a grain of rice. However, since there are only a limited number of teats for them to attach to, most of these young will die. The mad dash to the pouch for these numerous, primordial offspring becomes a contest with life or death consequences. Right out of the vaginal gate, quolls are expected to best their own brothers and sisters in a race to end all races. With this kind of Spartan upbringing, it’s hard to imagine quolls as being anything more than sociopathic.

That, my friends, is the face of an animal that just got done pooping in your hand. Why? Because fuck you, that’s why.

After the lucky six or so that manage to reach the teats first grow to a much higher level of development, all the while surrounded by the decaying corpses of their diminutive, forgotten kin, they venture out of the pouch and attach themselves to the back of mother, where they remain, piggy-backing, for several more weeks. This is a behavior that many in the States have likely seen with opossums.

Quolls, like many marsupials, do not live very long in comparison to placental mammals of the same mass. Quolls reach maturity at a year old, and typically have a lifespan of two to five years. They may be of the same size as a house cat, but they live a fraction as long.

Their cute exterior, made up of delicate white spotted patterns and pink wet noses, masks their status as apex predators.



Those dagger teeth and four sets of curved claws aren’t just for show. Quolls eat just about everything that moves, snapping up large insects, frogs, lizards, birds, and smaller marsupials. Larger quolls, like the tiger quoll (Dasyurus maculatus), may prey upon possums, invasive rabbits, and even outwardly unappetizing animals like the echidna, flipping it over on its spiny back and gouging out the belly. Prey is dispatched with a swift pounce, followed by jaws clamping down on the neck.

It is actually this habit of trying to eat anything once that is one of the factors damaging the quoll’s chances for survival. Cane toads (Bufo marinus), which are massive toads native to Central and South America, were brought to northern Australia to held eradicate insect pests in sugar cane crops. Of course, the population has since exploded and now cane toads are ravaging the ecosystems of provinces in northern Australia. They’re big enough to eat small native animals, and when larger native animals try to feed on them, they puff up and lodge themselves in the throat on the way down, suffocating the unfortunate diner. They are also highly toxic, which means even if an animal is too small to try and swallow it whole, it will still die from the poison. Cane toads eat everything they find, can’t be eaten by anything themselves, and they multiply like crazy…because, of course, even their tadpoles are toxic. They’ve grown to such plague-like numbers that you can drive through parts of rural Queensland where the road is plastered with the bodies of thousands of road killed cane toad carcasses. Due to their harmful presence, people are actually encouraged to try and hit them with their tires on highways, popping them like brown, noxious, meat balloons. Because Australians don’t fuck around.

Highway of Broken Screams

Quolls not only have a hard time dealing with cane toad toxins, and the fact that cane toads will actually devour a lot of the prey animals that normally feed quoll juveniles, but their carnivorous habits are also hurting them in another way. The poison sodium monofluoroacetate is put out into the wild by well-intentioned humans attempting to control populations of invasives like rabbits and foxes and wild dogs. It is sometimes put into cooked meat in order to attract problem carnivores, but is instead eaten by quolls. The poison isn’t quite as toxic to quolls as it is to target canids like foxes and dogs, but smaller animals can easily succumb to the effects. Ironically, efforts to rid the environment of damaging feral competitors of the quoll may actually do more damage.

Quolls are definitely in danger of dying out, since they are dealing with challenges from every possible angle. One somewhat odd idea that has been gaining more attention lately is the possibility of convincing Australians to start hand-rearing quolls as pets instead of comparable, ecosystem-wreckers like cats or ferrets. Quolls are relatively easy to care for, about as friendly as a cat (not saying much, I know), and an effort like this would create a ‘bank’ of individuals in domestic situations in case wild populations crash. Some folks are already breeding them, but it is unknown if the idea will catch on. For one, their short lifespan may be an issue. People are generally ok with the realization that their goldfish may not last more than a month or two. The idea that their fuzzy, big-eyed, mammalian companion that they hand-reared from a tiny pup will likely drop dead before its 4th birthday is more foreign. Also, there’s the consideration that they are still wild animals, despite being ‘tamed’, and have to capacity to become aggressive (especially if other quolls are around, being the territorial hunters that they are).

“AAAUGH! Get it off! The cute….it BURNS!”

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 is unlike anything we know living.

What are you?!

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.

How do you even have room in your head for that thing?

Numbats are unusual among marsupials, especially small, squirrel-sized ones, in that it is diurnal, meaning that it is active during the middle of the day. It scampers around dry eucalyptus woodland undergrowth, digging with its strong front claws to uncover termites beneath the soil at the base of mounds, where it then laps them up. Numbat females are also unique in that they don’t have an actual pouch. Going against the grain and potentially losing their marsupial card forever, numbats have secondarily lost the pouch, and instead have a simple patch of stiff, matted hair that covers and protects the four teats.

Numbats suffered their dramatic drop in numbers solely at the hands of European foxes, which were released in Australia in the 19th century. Numbats don’t have a lot of defenses, and are the perfect size for a fox to pick up as a snack. It also doesn’t help that numbats are active during the day and can’t avoid predators in a way more common to animals their size. Also, their natural predators, predators that they had evolved to cope with, were all birds of prey or large snakes; numbats are relatively unfamiliar with this diurnal, terrestrial, mammalian predator shit (quolls would hypothetically be an issue, but quolls hunt in the nighttime). It’s like studying for weeks to take the SAT, only to find out that the main criterion you’ll be judged on is how well you can whistle. It’s not exactly a fair situation.

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.

You’ve got to be fucking kidding me.

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.

This marsupial is only surviving member of its family (Thylacomyidae), and is a member of  the Peramelemorphia order, which is comprised of bilbies and their more populous, less weird-looking cousins, the bandicoots. Yes, Crash of “Crash Bandicoot” fame was based on a real animal. These critters are essentially the ‘marsupial omnivores’ group, ranging in size from about that of a mouse, up to the size of a rabbit (larger bandicoots and the bilby). Many species appear to be plump, elongated, giant shrew-like animals, but they have diets that more closely resemble those of pigs. Peramelamorphs, including the bilby, will root up insects, small animals, fruit, roots, seeds, fungi, and whatever else they find along the ground. Bilbies are nocturnal, and use their Dumbo-esque ears to listen for predators in the night, as well as grubs and insects along the earth. They are superb diggers, unlike their bandicoot relatives, and dig networks of tunnels in the hot, dusty, desert earth to rest in during the day.

The bilby is currently threatened with extinction due to factors associated with invasive species, most notably foxes, cats, and rabbits. Foxes and cats are adept at killing and eating bilbies, and rabbits, burrowing animals themselves, disrupt and collapse bilby burrows with their own habits. Rabbits also eat a lot of the same foods as bilbies, and have been rapidly starving them out of areas where rabbit populations are high.
Livestock, like sheep and cattle, also consume bilby resources and crush bilby burrow systems. If that wasn’t enough to make you feel the pangs of guilt, consider that in addition to all of this, humans also hunted bilbies for their meat and fur (albeit in less impactful ways than the fallout from invasives). Think of all of that next time another image of a woefully endangered bilby pops up. Like right now.

“That cow crushed our burrow. How will we survive in this harsh desert?”

There are plenty of efforts mounting to save this animal (which may number less than 1000 individuals in the wild), ranging from largely successful breeding programs, to re-branding the Easter Bunny in Australia as instead the Easter Bilby to raise awareness. This, of course, makes perfect sense; the pouch would be a very convenient place to carry a load of eggs. Maybe the Easter Bunny should start watching his back…

Surely, you think, it can’t get any more odd than the bilby, what with its skinny legs, giant ears, and tube-shaped nose…it looks like something that would scuffle around the sands of Tatooine before being squashed by a bantha or something (don’t lie, you totally understood that reference). Surely, the bilby, with its alien charm, is the zenith of marsupial strangeness in the barren sands of interior Australia.


Imagine you’re a lizard, scampering swiftly across the blistering hot sands of central Australia. Even for you, the heat is too much, so you stop and shuffle yourself underneath the sand some to cool off. Your little reptilian heart is fluttering in your scaly chest and you begin to relax. But then, you sense something quickly flying through the sand behind and below you. Before you can react, it’s all over.


Rising from the sands, intercepting its prey like a great white shark torpedoing itself at a sea lion, is the terror of the deep desert; the marsupial mole (Notoryctes). The only marsupial known to have evolved to a chiefly subterranean existence, it is a fucking alien thing to look at. First off, it is completely blind. Its eyes have become vestigial, and exist only as remnant lenses just below the skin. It’s small and stubby, its body shape reminiscent of a hamster, perhaps one born with every chromosomal error possible. Beneath its silky, cream-colored coat is a body rippling with hardened muscle; toned and sculpted by a life of pushing itself through sand dunes. In order to do this, it has two massive front limbs (attached to strong shoulders), each ending in a two-clawed shovel, which doubles as a pair of pincers when tackling larger prey…which it mashes up with a mouth full of sharp, diamond-shaped chompers. Its path through the sand is aided by a hard, leathery shield of skin at the front of its conical face, and its hind limbs have been flattened into a paddle shape to push the sand behind itself as it moves forward. Its neck vertebrae have fused together to help turn the front of its body into a rigid sand ram; this particular adaptation has never been seen in any other burrowing mammal.

When it isn’t devouring every small desert creature in sight (or, uhm, non-sight), it takes the time to procreate. Females have a pouch that opens backwards, as to avoid it filling with sand as the animal digs. It only has two teats, and can carry only two offspring at a time…because who has time to babysit when you’re busy forcing your body through the fucking earth?

Although it’s called the marsupial ‘mole’, this animal has less in common, ecologically, with true, placental moles than it does with another group of ‘moles’, known as golden moles (family Chrysochloridae). The true moles most of us are familiar with (the ones that turn moist lawns into impromptu mine fields) are members of a clade that includes animals like shrews and hedgehogs. Golden moles, native to sub-Saharan Africa, are more closely related to things like elephants, sea cows, and aardvarks than ‘true moles.’ Golden moles are blind like marsupial ‘moles’, and have a lot of similar traits, including the ability to burrow in arid areas and the possession of large spade-shaped claws and a nose shield. This similarity between golden moles and Notoryctes is a clear example of convergent evolution in action.

Notoryctes contains two species that we know of, the northern and southern varieties, and they occupy large regions of the most isolated and arid parts of central Australia. We’ve known about their existence for more than a century, but they are probably the most poorly understood group of marsupials alive today. Most of this is because they live in a highly inaccessible region of the world, and even active searches for them often come up dry (pun intended). They are either incredibly rare, or just elusive. Since they burrow in sand, and their path fills in behind them, they have no permanent ‘base’ that we can find them in like other burrowing animals. They just swim through the sand as nomads, like miniature Ozzie graboids, chasing and unleashing hell upon anything on the desert floor.

“That’s how they get ya. They’re under the goddamned ground!”

Marsupial moles only turn up sparingly, maybe five to ten times per decade. Because of this, we almost know nothing about them. Their reproductive habits are a mystery, and so is a lot of their other behavior. We have a general idea of what they eat, but that’s about it.

We’re especially confused on how they’re related to other marsupials, and what their evolutionary history was like. Scientists have placed them in their own, separate order (Notoryctemorphia), and our limited molecular data seems to support this distinct status. From what we can tell, they diverged from other marsupials WAY back; between 50 and 64 million years ago. Morphological features haven’t helped much, and only hint, maybe that they might be distantly related to bandicoots and bilbies. Even with the luck of discovering a fossil specimen of an ancestor from more than 15 million years ago (Yalkaparidon), we still don’t know what the hell this animal is, phylogenetically. The fossil had features of both bandicoots (the skull base shape) and diprotodonts (the front incisors were similar). However, the fossil, since it was from an area that was at that period of time tropical rainforest, tells us that it is likely the marsupial moles evolved in a wetter, forested environment, possibly burrowing through loose soil and leaf litter. When the climate changed and the continent became more arid, they would have already been well-adapted to the subterranean lifestyle. It would have been a change of scenery for them, but the job would have been the same, more or less.

As of right now, due to how rarely encountered both species are, they are both listed as endangered. Remains have been found in fox scat at a disturbingly high rate, but it is hard to tell exactly what the conservation status of these animals actually is. This reserved approach to their status remains likely until more data comes in about these bizarre critters. Until then, all one can hope for is that they’ll continue their lonely, gritty lives criss-crossing the sand dune deserts without much interference.

“The Spice must flow.”

The last marsupial in this entry is not closely related to anything previously mentioned. It is a denizen of the Americas, from Mexico south through Central and South America down into Argentina. It is known as the ‘yapok’ or ‘water opossum’, and it is generally referred to as the most aquatic marsupial.

It also wins the title of ‘marsupial with the deadest eyes.’

Modern marsupials primarily diverge into two main groups; one that is found in Australasia and comprises most of what we know as ‘marsupials’ (and includes the highest diversity of form and families) and one that is found in the Americas, but mostly in Central and South America. The Australian clade, the Australidelphia, contains about 75% of all living marsupial species; kangaroos, wombats, koalas, possums, bandicoots, etc. The American clade, the Ameridelphia, contains the rest, and are generally referred to as the ‘opossums’, and they are found all over Central and South America, with one species (the Virginia opossum) managing to live as far north as Canada.

The only exception to this rule is a single, primitive species resting in its own special order (Microbiotheria), that is a member of the Australidelphia group, but happens to be native to the Chilean temperate rainforests. The yapok is an ‘opossum’ and is separated from the ‘possums’ of Australia by many tens of millions of years. Saying the Virginia opossum we have in the U.S. is closely related to the brushtail possums of Australia is akin to saying armadillos are closely related to baboons.

Yapoks are unique in that they have a great deal of adaptations to a semi-aquatic lifestyle that are not found in other marsupials. Firstly, their black and white fur coat is dense and water repellent, as is typical in placental aquatic animals. The yapok solves part of the marsupial evolutionary puzzle regarding aquatic living by having the hind limbs deeply webbed for swimming, while the front feet are free of webbing and quite capable of grasping fish, frogs, and crustaceans…as well as fur in the joey stage on its way from the birth canal to the pouch.

“Hey! I believe I was promised fish.”

The yapok swims using its webbed hind feet and flat, paddle-like tail. In order to keep its joeys from being sent directly to a watery grave every time the yapok mother dives, the pouch has a key adaptation to aquatic life. It opens towards the back (like a marsupial mole’s does), and has a ring of strong muscles around the rim. Using these muscles, it can clamp shut with the young inside, creating a watertight seal.

Bizarrely enough, males in this species also have a pouch, although it isn’t used for helping out by carrying the joeys. No, rather than automatically take the ‘marsupial father of the year’ award, male yapoks use their pouch to protect their genitalia while swimming. Yes, yapoks are apparently so well hung that they have to tuck their junk in a skin pocket just so it doesn’t get caught on vegetation. This was a feature that was seen in the (now extinct) thylacine males, for the similar reason of retracting their scrotum. In no other marsupials other than the thylacine and the yapok has this evolutionary obsession with potential penis endangerment been discovered.

Yapoks are about as close as marsupials are likely to get to evolving an ‘otter’, and as of right now, luckily, yapoks aren’t immediately threatened with extinction. They range over vast river basins all over the equatorial Americas, and as long there are plenty of aquatic prey items, and no invasive species to combat, they should be fine for a while, despite their luxurious, two-tone fur occasionally being used to make fur coats.

So, that concludes the extended, two-part series on metatherian oddities of the past and the present. From murderous, hook-clawed, mega-koala things in prehistoric Australia, to truck-sized wombats, to snake-eyed marsupial ‘sloths’, to nimble aquatic predators with an o-ring on their pouch…all treasures that tend to be concealed by our eutherian-biased outlook on the animal kingdom. Life on this planet is fantastically diverse, but as time progresses, that elegant complexity is falling away as innumerable groups of organisms, not only marsupials, succumb to the effects of human activity. I can only hope that at some point, after losing possibly too many gems in the crown of evolution, too many novel experiments, we finally realize that we can no longer destroy in centuries, what nature crafted over countless millions of years.

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2014. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.


22 thoughts on “Metatherians (Part 2 of 2): Odd Living Representatives

  1. I have learn a few just right stuff here. Certainly worth bookmarking for revisiting. I surprise how a lot attempt you put to create this sort of excellent informative site.

  2. egregiously erudite, always with stunning and illustrious illustration , to say nothing of the often
    brilliant insights of the irreverent text. Absolutely brilliant , well done and keep it up.

  3. Where can I read more about the marsupio embriology (not of the joe, but the pouch), evolution and comparative embriology.
    There are pouchs that open at the top, at the botton, with or without esphincter and with diferent opennings.
    I read that monotremos have the marsupial bone. Philogenetically they are nearer each other than eutherians or do we had an involution of this bone?

  4. Pingback: A hilarious and informative series on metatherians « Why Evolution Is True

  5. Wow, I love your blog. Not only because of all the satisfyingly adorable photos of cute animals, but I appreciate when someone loves a subject so much they can’t help but explore the depths of their chosen realm and share their findings. Thanks for writing shit we don’t know about biology, but clearly need to.

  6. Good stuff Jake, you have a talent for engaging and informed biodiversity writing, it would be good if you help discuss problems and solutions to the biosphere and biodiversity crisis some, and perhaps clean up the language a bit to make it a family friendly site as lots of folks might be interested in your work. On my site are some papers regarding conservation that may be of interest. Also, how does one get permission to use some of your photos for education purposes? I have collected many ricinuleids over the years, you have excellent photos of these amazing animals – as you know, they move very methodically and are quite cryptic. Keep up the good work.

    • Thank you! Honestly, the vast majority of photos used on here are not owned by me. There are some representatives of my photography on the Klamath bioregion entry (, but outside of that, the only thing that features my photos is the randomized banner on the site.
      Most of the photos are either in the public domain, or have a creative commons license that allows them to be shared here. I end up using Wikimedia Commons and Flickr to find them, where they are available for public use.
      On the newest entries, I have listed and linked to the sources for the photos at the bottom of the entry.

  7. I’m afraid the part about marsupial trophoblast (my field of research) is completely wrong. The entire marsupial conceptus (embryo + trophoblast) is separated from the uterine endometrium by an enveloping shell coat during early development. By the time the shell coat breaks down (about two-thirds through pregnancy), the amnion is fully formed and there is only trophoblast in direct contact with the uterus. Any differences between marsupials and eutherians in immune tolerance to pregnancy (which are not well understood) are therefore likely to only involve molecular differences in immune regulation, MHC genes, etc.
    “Placental mammal” is actually a terrible name for this subdivision of Eutheria, since both marsupials and monotremes also have placentas (extraembryonic tissues that transfer nutrients from the uterus to the fetus), even though direct physical contact with the uterus is usually minimal or completely absent (in the case of monotremes). In some marsupials such as bandicoots, the placenta is actually highly invasive (similar to many eutherians).

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