Marsupial Pegs in Ecological Holes

 This really shows how marsupials evolved to fill ecological niches occupied elsewhere by placental mammals. In the prehistoric past there were many more--huge lumbering diprotodonts, the marsupial "tapir" palorachestes, the panda-like homaldotherium from the bamboo-forested highlands, and of course, the feline imitation thylacoleo, the size of a jaguar and capable of taking down the giant ten-foot kangaroo procoptodon. More bizarre were the carnivorous roos, elketadia and propliopus, the giant monitor lizard megalania, the size of a Kodiak and weighing more then a rhino, and the ankylosaur-like turtle meiolania.

On the subject of thylacoleo, though, the most surprising think about it was it was relatively unrelated to the other marsupial carnivores, such as the thylacine and Tasmanian devil. Those, the quolls and the dunnarts, all belong to the dasyurid or thylacinid families. Those are both share kin with with the opossums and extinct borhyenids of the Americas. But thylacoleo was a descendent of phalangers, tree-climbing herbivores, sometimes called possums, but unrelated to the opossums of America. It was the phalangers that eventually gave rise to the kanagroos, during the long period of when Australia was a huge rain forest. Once the grasslands spread, new herbivores evolved to exploit them. 

One of thylacoleo's ancestors was wakaleo, a Miocene forest-dweller the size of an ocelot. Thylacoleo was larger, designed to tackle large prey. Scientists were long puzzled by the animal's teeth, which were unlike that of any other carnivorous mammal. It was eventually revealed they had evolved from the shearing incisors of the phalangers. Only modified to tear flesh, in the Australian version of the leopard or jaguar. 

One thing rather curious about thylacoleo, though, was the evidence of its striped coat! Prehistoric aboriginal paintings of the animal, some of them anyway, clearly show the opposable tree-grasping thumbs that were characteristic of the animal. But some of them also show a series of stripes that were apparently prominent along its backside, very similar to those possessed by the Tasmanian tiger. Except perhaps that they are a bit more uniform. But both animals, predators belonging to entirely separate families, share virtually identical markings? It would seem so, on the testimony of the only people around then to observe them. 

There is the strange matter of the mysterious Queensland Tiger a crypid that is sometimes believed to be a surviving thylacoleo, and is sometimes described as sporting stripes similar to the thylacine. One mystery-phot appears to confirm this. The pic below however, which looks like a make-over of another sketch I've seen appears more like a genuine feline (which is not possible, for a true native of Australia) than a modified phalanger. In a thylacoleo, the phalanger ancestry would be apparent if you were to look closely enough. The illustrations above demonstrate this is no cat, merely a marsupial facsimile. 

There is also the related issue of the thylacine's kinship with the rusty numbat, a highly endangered species of marsupial anteater found in sparse regions on the mainland. Unlike their placental (and monotreme) counterparts, numbats are small,  skittish and fleet, zipping for cover at the first sign of a predator. They are also the only example of a marsupial that technically lacks an actual pouch--the undeveloped young merely cling to their mother's belly. 

The Tasmanian devil was once believed to be the thylacine's closest living relative--a very reasonable assumption. And also the best candidate for thylacine cloning (as marsupials bear undeveloped young, size is not the problem it would be for placental mammals). However recent DNA has revealed that the numbat, is in fact, nearer in genetic relation to the thylacine! Perhaps it is likely then, that the termite-eating numbat branched off from the marsupial carnivore lineage sometime in the remote past. It seems rather bizarre that the striped coat of two physically disparate animals might have persisted for millions of years!