Belongs within: Vombatomorphia.
The Diprotodontidae are a group of sometimes large herbivorous marsupials known from the late Oligocene to the Pleistocene of Australia.
The diprotodontids: marsupials go large
Published 12 June 2015
Prior to the arrival of humans, the Australian fauna included many strange, and often dramatic, animals that are sadly no longer with us. Enormous python-like snakes, monitors that would have made a Komodo dragon look underwhelming, drop bears, and of course the notorious demon duck of doom. But among the most iconic of Australia’s extinct fauna were the Diprotodontidae, heavyset herbivores that included the largest of all marsupials. Diprotodontids are sometimes referred to in the popular press as giant wombats, but this is a bit misleading: though more closely related to wombats than any other living marsupials, they were a quite distinct group of animals (besides, they shared their world with actual giant wombats that reached the size of a cow). A potentially more appropriate descriptor that has been suggested is ‘marsupial rhinos’, though at least some diprotodontids were decidedly not like rhinos either.
The most famous of the diprotodontids was also the first to be described, and indeed the first fossil mammal of any kind described from Australia. Diprotodon optatum, named by Richard Owen in 1838, was the largest of the diprotodontids, sometimes standing more than six feet tall at the shoulder, and reaching estimated weights of around two and a half tonnes. At the time of human arrival, Diprotodon would have been one of the dominant herbivores in the arid central region of Australia. A number of species of Diprotodon have been named over the years, but a review of the genus by Price (2008) recognised only a single species, with the two different size classes present probably representing the different sexes. In the less arid coastal regions, Diprotodon was replaced by various species of the slightly smaller (but still formidably sized) genus Zygomaturus (Long et al. 2002). The best known species in this genus, Z. trilobus, bore a distinctive large bony boss on the snout, giving its skull a profile reminiscent of a cartoon bear. Two other diprotodontid species that would have come into contact with humans are known from the Pleistocene of montane New Guinea, Hulitherium tomasettii and Maokopia ronaldi. Both these species were smaller than the mainland Australians, being about the 100 kg mark. Maokopia has been interpreted as a grazer, while Hulitherium has been seen as a browser, and suggested as a direct analogue of the Asian giant panda (Long et al. 2002).
The broader record of diprotodontids goes back to the Oligocene, with two main lineages being recognised, the Diprotodontinae and Zygomaturinae. Of the species referred to above, all but Diprotodon optatum are zygomaturines. The two groups are primarily distinguished by their dentition, with the premolars being generally more complex in zygomaturines than diprotodontines. In both lineages, the earlier members were smaller: Long et al. (2002) describe a number of genera as ‘sheep-sized’. The smallest known diprotodontid, the late Oligocene Raemeotherium yatkolai, they describe as ‘lamb-sized’. Black et al. (2012) estimated the weight of the middle Miocene Nimbadon lavarackorum as abut 70 kg. They also suggested that it was an adept climber, in a similar manner to the modern koala, making it the largest known arboreal mammal from Australia. It might seem odd to picture an animal of this size up in a tree, even allowing for the higher density of the canopy in Australia’s Miocene rainforests. However, there are larger arboreal mammals alive even today: male orangutans, for instance, may weigh over 100 kg.
Interestingly, Nimbadon is not placed as a particular basal diprotodontid in the phylogeny of zygomaturines presented by Mackness (2010). As other related marsupial families, such as koalas or thylacoleonids (marsupial lions), also include climbers, it would not be unreasonable to consider such habits plesiomorphic for diprotodontids as a whole. The ‘rhino-like’ appearance of the later giants would then be something of a novelty, an adaptation to the drier conditions and more open woodlands that arose at the end of the Miocene. If we are to regard the diprotodontids as marsupial rhinos, then we must consider the possibility of rhinos in trees.
Systematics of Diprotodontidae
Characters (from Long et al. 2002): Medium-sized to large browsing quadrupeds. Dental formula I1-3/1, C1/0, P3/3, M1-4/1-4; molars simple, transversely lophodont but lacking longitudinal links. Lower jaw with masseteric foramen absent.
<==Diprotodontidae [Nototheriidae] | i. s.: Stenomerus De Vis 1907SM93 |--Diprotodontinae [Nototheriinae]LA02 | | i. s.: Nototherium Owen 1845 (n. d.)LA02 | | |--*N. inerme Owen 1845 (n. d.)LA02 | | `--N. watutense Anderson 1937BA12 [=Kolopsis watutenseLA02] | |--+--Pitikantia Stirton 1967LA02 | | | `--*P. dailyi Stirton 1967LA02 | | `--Ngapakaldia Stirton 1967LA02 | | |--*N. tedfordi Stirton 1967LA02 | | `--N. bonythoni Stirton 1967LA02 | `--+--Bematherium Tedford 1967LA02 | | `--*B. angulum Tedford 1967LA02 | `--+--Pyramios Woodburne 1967LA02 | | `--*P. alcootense Woodburne 1967LA02 | `--+--+--Meniscolophus Stirton 1955LA02 | | | `--*M. mawsoni Stirton 1955LA02 | | `--Euowenia De Vis 1887LA02, M10 [=Owenia De Vis 1887 non Gray 1855LA02] | | `--*E. grata (De Vis 1887) [=*Owenia grata]LA02 | `--+--Euryzygoma Longman 1921LA02 | | `--*E. dunense (De Vis 1888)LA02 [=Nototherium dunenseF71] | `--Diprotodon Owen 1838LA02 | |--*D. optatum Owen 1838LA02 | |--D. annextans McCoy 1861LA02 | |--D. australisF71 | |--D. bennettii Krefft 1873F71 | |--D. loderi Krefft 1873LA02 | `--D. minor Huxley 1862LA02 `--ZygomaturinaeLA02 |--Raemeotherium Rich, Archer & Tedford 1978LA02 | `--*R. yatkolai Rich, Archer & Tedford 1978LA02 |--Silvabestius Black 1997LA02, M10 | |--*S. johnnilandi Black & Archer 1997LA02 | `--S. michaelbirti Black & Archer 1997LA02 `--+--Alkwertatherium Murray 1990LA02 | `--*A. webborum Murray 1990LA02 `--+--+--Kolopsoides Plane 1967M10, LA02 | | `--*K. cultridens Plane 1967LA02 | `--Plaisiodon Woodburne 1967LA02 | `--*P. centralis Woodburne 1967LA02 `--+--Nimbadon Hand, Archer et al. 1993M10, LA02 | |--*N. lavarackorum Hand, Archer et al. 1993LA02 | `--N. whitelawi Hand, Archer et al. 1993LA02 `--+--Neohelos Stirton 1967LA02 | |--*N. tirarensis Stirton 1967LA02 | |--N. scottorrorum (Hand, Archer et al. 1993)LA02 | `--N. stirtoni Murray, Megirian et al. 2000LA02 `--+--Kolopsis Woodburne 1967LA02 | |--*K. torus Woodburne 1967LA02 | `--K. rotundus Plane 1967LA02 `--+--+--Hulitherium Flannery & Plane 1986LA02 | | `--*H. tomasettii Flannery & Plane 1986LA02 | `--Maokopia Flannery 1992LA02 | `--*M. ronaldi Flannery 1992LA02 `--+--Kukaodonta Mackness 2010M10 | `--*K. robusta (De Vis 1891) [=Euowenia robusta, Zygomaturus robusta]M10 `--Zygomaturus Macleay 1858LA02, M10 [Zygomaturini] |--*Z. trilobus Macleay 1858 (see below for synonymy)LA02 |--Z. creedii Krefft 1873F71 |--Z. gilli Stirton 1967 [incl. Kolopsis yperus Murray & Megirian 1992]BA12 |--Z. keani Stirton 1967M10 |--Z. macleayi Krefft 1921LA02 `--Z. nimborensia Hardjasasmita 1985LA02
*Zygomaturus trilobus Macleay 1858 [incl. Nototherium mitchelli Owen 1845, N. tasmanicum Scott 1911, N. tasmaniense Noetling 1912, N. victoriae Owen 1872]LA02
*Type species of generic name indicated
[BA12] Black, K. H., M. Archer, S. J. Hand & H. Godthelp. 2012. The rise of Australian marsupials: a synopsis of biostratigraphic, phylogenetic, palaeoecologic and palaeobiogeographic understanding. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 983–1078. Springer.
Black, K. H., A. B. Camens, M. Archer & S. J. Hand. 2012. Herds overhead: Nimbadon lavarackorum (Diprotodontidae), heavyweight marsupial herbivores in the Miocene forests of Australia. PLoS ONE 7 (11): e48213. doi:10.1371/journal.pone.0048213.
[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.
[LA02] Long, J., M. Archer, T. Flannery & S. Hand. 2002. Prehistoric Mammals of Australia and New Guinea: One Hundred Million Years of Evolution. University of New South Wales Press: Sydney.
[M10] Mackness, B. S. 2010. On the identity of Euowenia robusta De Vis, 1891 with a description of a new zygomaturine genus. Alcheringa 34 (4): 455–469.
Price, G. J. 2008. Taxonomy and palaeobiology of the largest-ever marsupial, Diprotodon Owen, 1838 (Diprotodontidae, Marsupialia). Zoological Journal of the Linnean Society 153: 389–417.
[SM93] Stucky, R. K., & M. C. McKenna. 1993. Mammalia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 739–771. Chapman & Hall: London.