Zygomaturus

Zygomaturus ("big cheekbones"), also known by its nickname, swamp cow, is a species of marsupial from the Pleistocene of Australia. It is believed to have acted much like a modern-day pygmy hippopotamus, spending most of its time in swampy water. It went extinct 45,000 years ago.

Description[]

An Australian megafauna species, Zygomaturus trilobus, a relative of today's wombats, was one of the largest marsupials to have ever existed and would have weighed up to 500 kg.

Since its bones have only been found in former swamp-forests, it may have been semi-aquatic like a hippopotamus, scooping vegetation into its mouth with shovel-like incisors. An Australian megafauna species, Zygomaturus trilobus, a relative of today's wombats, was one of the largest marsupials to have ever existed and would have weighed up to 500 kg. Its name derives from its prominent cheek-bones (zygoma), and its skull-structure also suggests that it had a three-lobed nose, and possibly a short trunk.

Zygomaturus trilobus belonged to the now extinct family Diprotodontidae, which in turn falls within the Infraorder Vombatomorphia, a group also including wombats and the marsupial lions (Thylacoleonidae). The diprotodontids were gigantic, lumbering herbivores and the largest of all marsupials.

Diprotodon optatum (rhinoceros wombat) was the heaviest species, at over two tonnes, and may be the animal behind the bunyip of Aboriginal legends. A complete skeleton of Z. Trilobus was discovered by Mr E. C. Lovell in early 1920, while draining his selection at "Mowbray Swamp", now called Mella, three miles west of Smithton. Mr Lovell was no stranger to the remains of megafauna, having found another almost complete skeleton of Z. Trilobus in the swamp ten years earlier.

The 1920 skeleton was carefully excavated under the expert supervision of Mr Hubert Hedley Scott, the then-curator of the Queen Victoria Museum in Launceston. He proclaimed that the skeleton and the "very perfect skull", while stained brown by the tannic waters of the swamp, were well preserved by the prevailing anaerobic conditions. After excavation, the skeleton was acquired by Mr Kenneth M. Harrisson of Smithton, the district surveyor and a well-known megafauna collector for the Queen Victoria and Tasmanian Museums.

Mr Harrisson presented the skeleton to the Tasmanian Museum later in 1920, in time for exhibition at the Science Congress held in Hobart in December of that year. Mr Scott and Mr Clive Lord, the curator of the Tasmanian Museum, formally described the specimen in a Royal Society of Tasmania paper published in 1920.

Paleobiology[]

1920px-Zygomaturus trilobus — Fossil of the animal

Zygomaturus was one of the largest marsupials to have ever lived. Zygomaturus had a massive head, with huge arching cheek bones and widely flared nasal bones which may have supported small horn like structures. It was a large animal, weighing 500 kg or more and standing about 1.5 m tall and 2.5 m long. Much like a hippopotamus, the animal had raised nostrils. Like the wombat, it also had a backwards-facing pouch, which protected its infants from drowning while the animal was foraging in swamps. It had a heavy body and thick legs and is believed to be similar to the modern pygmy hippopotamus in both size and build. It lived in the wet coastal margins of Australia and became extinct about 45,000 years ago.

Zygomaturus also is believed to have expanded its range toward the interior of the continent along the waterways. It is believed to have lived solitarily or possibly in small herds. Zygomaturus probably ate reeds and sedges by shovelling them up in clumps with its lower incisor teeth.

Cranial sinuses result from the resorption and deposition of bone in response to biomechanical stress during a process known as pneumatisation. The morphology of a pneumatic bone represents an optimisation between strength and being light weight. The presence of very large sinuses has been described in a number of extinct marsupial megafauna, the size of which no longer exist in extant marsupials. With advances in digital visualisation, and the discovery of a number of exceptionally preserved fossil crania, a unique opportunity exists to investigate hypotheses regarding the structure and evolution of the atypically voluminous sinuses. Sinus function is difficult to test without first obtaining data on sinus variation within and between species.

Therefore, the crania of seven species of extinct and extant vombatiform marsupials were studied using CT scans to provide a volumetric assessment of the endocast and cranial sinuses. Sinus volume strongly correlates with skull size and brain size. In the extinct, large bodied palorchestids and diprotodontids the sinuses expand around the dorsal and lateral parts of the braincase. Brain size scales negatively with skull size in vombatiform marsupials. In large species the brain typically fills less than one quarter of the total volume of the endocranial space, and in very large species, it can be less than 10%. Sinus expansion may have developed in order to increase the surface area for attachment of the temporalis muscle and to lighten the skull. The braincase itself would have provided insufficient surface area for the predicted muscle masses.

Zygomaturus

Description[]

Paleobiology[]

References[]

Fan Feed