Australia: The Land Where Time Began

A biography of the Australian continent 

Zygomaturus 

Zygomaturus trilobus was about the size and shape of a pygmy hippopotamus, probably weighing between and 300 & 500 kg. Its name derives from its prominent, wide, cheek bones (zygomatic arches) and the 3 lobes of its premolars. It is believed by some (Long et al., 2002), to have been partly aquatic like hippos, and that it may have lived in swampy areas around the coastal areas and along river systems, and further into the interior, and in Tasmania, possibly in small herds. It seems likely it inhabited areas that were more heavily wooded than Diprotodon. It is also believed it may have had short horns like a rhino. Specimens of Zygomaturus trilobus from the Pleistocene display a high degree of variability, leading some to suggest they may actually represent several distinct species.

Source 4

In Western Australia Zygomaturus inhabited the humid and semi-arid regions of the southwest of the state. Bones of this animal have been found in Mammoth Cave. Zygomaturus first appeared in the Miocene about 6 Ma, though Zygomaturus trilobus is known from the Pleistocene, when it co-existed Diprotodon, these forms being the most recently living members of 2 distinct diprotodontid linages, which separated at least 15 Ma.

Zygomaturus was more similar to Diprotodon than any other contemporary species, though it differed in a number of important features. Zygomaturus was somewhat smaller than Diprotodon, complete skeletons found in Tasmania indicating it was about the same size and shape as a hippopotamus of medium size, and probably weighed about 1 tonne, and was almost 2 m long and 1m high at the shoulder. Both the front and back legs were quite long, though they bore strong muscles. They had especially broad front feet and each of the fingers had a long flat claw, while the back feet were narrower and only weakly clawed, with the exception of the outermost toe. In Zygomaturus the hind feet were turned inward, the animal walking on the sides of its feet, as was the case with Diprotodon, and it is believed to have had a reasonably slow gait.

The skulls of Zygomaturus and Diprotodon differed in a number of significant ways from each other. The weight of the Zygomaturus skull was reduced by the presence of air sinuses, as with the skull of Diprotodon, but these structures developed in different ways in the 2 animals, which indicates the separate, parallel evolution of the 2 forms. The cheek teeth of Zygomaturus indicate it was a browser, the teeth were fundamentally different from those of Diprotodon that was also a browser. Unlike other diprotodontids that had upper premolars that were relatively simple, in Zygomaturus they were much more complicated structurally. The authors⁴ suggest the tooth structural difference between Zygomaturus and Diprotodon was a result of the 2 animals having different diets and different methods of feeding. The teeth of Zygomaturus had teeth that were lower and had broader crests, or lophs, than those of Diprotodon. It is believed Zygomaturus probably ate coarse woody vegetation, that included stems, petioles, roots and bark, with its short face and powerful jaws, its broad teeth that were low-crowned, functioning in a grinding, crushing manner on this type of tough material.

Zygomaturus had pre-nasal bones that were a peculiar feature of its skull anatomy which has been suggested to have possibly supported small, hornlike protuberances. It also had a brow-like bone flange at the front of the skull that is thought to have possibly been an attachment site for strong muscles to control the upper lip. The authors⁴ suggest it may have have had snout mobility like that of a pig, when combined with the strong claws on the front feet such a snout may have helped in the uprooting of entire plants as it grubbed for roots and tubers. It is not known if the hornlike structures were used to assist this process in some way. The suggested method of accessing the roots is for the strong claws on the front feet to have dug the soil around the plant, the loosened soil then possibly being cleared away from the roots by the powerful lips, then grasping the plant with the tusk-like incisors to rip the plant from the soil by use of the animal's undoubted strength. The large molars could then have ground up the plant material.

The authors⁴ suggest that as Zygomaturus occupied the wetter coastal regions of Western Australia, where the vegetation was richer, may indicate that Zygomaturus and Diprotodon fed on different types of plants.

Source 5

The Floraville Local Fauna, north Queensland, has produced an occluded skull and dentaries that has been referred to Euowenia robusta, De Vis, 1891. According to the author¹ the specimen has distinctive zygomaturine features such as a quinquetubercular upper third premolar and lower molars with cristids obliqua, which challenges directly the synonymy of E. robusta with Nototherium inerme and N. mitchelli, as proposed by Woods (1968). It has further been confirmed that E. robusta does not belong within the Diprotodontinae by comparison with the genotypic Euowenia grata (De Vis, 1887). Following examination of all known zygomaturine genera, including a large data set of Zygomaturus trilobus Macleay, 1858,  it is concluded that Euowenia robusta cannot be placed within any known zygomaturine genus and, therefore a new genus is proposed. The author¹ suggests it is possibly the most derived of all zygomaturines that have been described from the Cenozoic in Australia.

Links

• Naracoorte Cave fossils
• Gondwana Studuos
• Zygomaturus - Wikipedia
• Images

Sources & Further reading

1. Death of the Megabeasts, DVD, Madman, SBS
2. Josephine Flood, Archaeology of the Dreamtime, J. B. Publishing, 2004
3. Chris Johnson, Australia's Mammal Extinctions, a 50,000 year history, Cambridge University Press, 2006
4. McNamara, K & Murray, P., May 2013, Prehistoric Mammals of Western Australia, Western Australia Museum
5. Mackness, Brian. "On the Identity of Euowenia Robusta De Vis, 1891 with a Description of a New Zygomaturine Genus." Alcheringa: An Australasian Journal of Palaeontology 34, no. 4 (2010/12/01 2010): 455-69.

• Perameloids
• Murgon Fossil Site
• Riversleigh Fossil Site
• Marsupial vs Placental
• Monotremes
• Naracoorte Fossil Site