Two giant odd-looking metatherians,
Palorchestes (Fig. 1, as large as a horse) and Diprotodon (Fig. 2, as large as a hippo), enter the large reptile tree (LRT, 1406 taxa, subset Fig. 3) midway between kangaroos and wombats. So, that settles that conundrum. They’re not wombats and they’re not kangaroos.
When I was creating the 1986 book,
Giants of Land, Sea and Air ~ Past and Present, I added the ‘giant kangaroo’ next to the largest living kangaroo, Macropus. Less was known back then. I used an extant kangaroo for a model and scaled it up. Now we all know better.
“Sir Richard Owen first found what he thought was the fragmentary jaw of a prehistoric kangaroo. It was not until more postcranial elements were found did anyone realize that Palorchestes was actually a different kind of diprotodontid, and not a kangaroo.”
Along with traditional diprotodontids,
(wombats, koalas and kangaroos) the LRT adds Middle Miocene interatheres and Pliocene toxodons to the wombat clade. This menagerie of morphologies are all herbivores. The last two are former notoungulates.
Diprotodon optatum (Owen 1838; Pleistocene 1.5–0.05 mya; 3m in length) is the largest known marsupial of all time. Traditionaly the eight species assigned to Diprotodon nest with wombats and koalas, but here they nest between kangaroos and wombats. The pedes turn inward such that digit 5 is the anteriormost toe on this graviportal beast.
Palorchestes azael (Owen 1873; Miocene to Pliocene; 2m in length; Figs. 1, 4) had a tapir-like face, likely sporting a similar long proboscis. The lower jaw had a long symphysis, perhaps indicating a protrusible tongue, like an anteater. Large claws tipped the forelimbs (which I have not seen yet, but for the drawing below). Fossils are rare and incomplete.
Propalorchestes novaculacephalus (Murray 1986; Trusler and Sharp 2016; Miocene) is a smaller, earlier and plesiomorphic relative of Palorchestes. So far I’ve only seen skull data.
Trusler and Sharp 2016 report,
“Propalorchestes (Middle Miocene) cranial morpholgy, suggests a significantly earlier origin for the highly derived facial anatomy in the Palorchestidae.”
Given the Middle Miocene appearance of Interatherium,
(Fig. 6) nesting nearby, that seems reasonable.
A few new clade names are proposed here.
Given that the traditional clade Metatheria is no longer monophyletic, unless it also includes the Eutheria, the following clade names are proposed here for the two major monophyletic metatherian-grade clades, one largely herbivorous, the other larger carnivorous:
- Phytometatheria, defined as Asioryctes, Glironia, their last common ancestor and all descendants. These include the Diprotodontia listed above and many more, including the omnivores, Petaurus, the sugar glider and its sister Thylacoleo, the marsupial ‘lion’. Docofossor, from the Middle Jurassic, and Anebodon, from the Early Cretaceous are clade members.
- Carnimetatheria, defined as Monodelphis, Thylacosmilus, their last common ancestor and all descendants. These include traditional members of the clade, Creodonta, like Oxyaena and Borhyaena. Vincelestes is an Early Cretaceous member, so the genesis of this clade also extends into the Jurassic.
Mackness BS 2008. Reconstructing Palorchestes (Marsupialia: Palorchestidae) – from Giant Kangaroo to Marsupial ‘Tapir’. Proceedings of the Linnean Society of New South Wales, 130, 21-36.
Murray PF 1986. Propalorchestes novaculacephalus gen et sp. nov., a new palorchestid (Marsupialia: Palorchestidae) from the mid Miocene Camfield Beds, Northern Territory Australia. The Beagle, Records of the Northern Territory Museum of Arts and
Sciences 3(1): 195–211.
Murray PF 1990. Primitive marsupial tapirs (Propalorchestes novaculacephalus Murray and Propalorchestes ponticulus sp. nov.) from the mid Miocene of North Australia. (Marsupialia: Palorchestidae) The Beagle, Records of the Northern Territory Museum of Arts and Sciences 7(2): 39–51.
Owen R 1838. Letter in TL Mitchell, Three expeditions into the interior of Eastern Australia. London.
Owen R 1870. On the fossil mammals of Australia. Part III. Diprotodon australis, Owen. Philosophical Transactions of the Royal Society of London. 1870;160:519–578. doi: 10.1098/rstl.1870.0023.
Owen R 1873. On the fossil mammals of Australia. Part IX. Family Macropodidae: Genera Macropus, Pachysaigon, Leptosaigon, Procoptodon, and Palorchestes. Philosophical Transactions of the Royal Society of London 164, 783-803.
Price GJ 2009. Taxonomy and palaeobiology of the largest-ever marsupial, DiprotodonOwen, 1838 (Diprotodontidae, Marsupialia). Zoological Journal of the Linnean Society, 2008, 153, 369–397.
Trusler P and Sharp AC 2016. Description of new cranial material of Propalorchestes (Marsupialia: Palorchestidae) from the Middle Miocene Camfield Beds, Northern Territory, Australia. Memoirs of Museum Victoria 74:291–324.