A Pliocene Giant
During the Pliocene Epoch, between 5.3 and 2.6 million years ago, much of Australia was a warmer, wetter place than it is today. In the woodlands and forests of what is now Queensland and New South Wales lived a giant marsupial called Euryzygoma dunense. This herbivore was a large animal, reaching about 2.5 meters in length and weighing an estimated 500 kilograms. It belonged to the family Diprotodontidae, it was a relative of the largest known marsupial, Diprotodon, and more distantly related to modern wombats and koalas.
Euryzygoma was a browser, feeding on leaves and shrubs. Isotope analysis of its fossil teeth confirms it preferred C3 plants, which are typical of forests and cooler, wetter environments. It shared its habitat with other megafauna, including giant kangaroos, the earliest known quolls, and even Komodo dragons, which originated in Australia before migrating to Indonesia. The first fossils of Euryzygoma were identified from isolated teeth, but a more complete skull was unearthed in 1912 by workers digging a well on the Darling Downs in southeastern Queensland.
A Skull Wider Than Long
The most extraordinary feature of Euryzygoma is its skull, which was wider than it was long, a rare characteristic among mammals. This extreme width comes from enormous, flange-like extensions of the zygomatic arches, or cheekbones. The name Euryzygoma itself translates to "broad cheekbone." Paleontologists have several theories about the function of these bizarre structures.
One idea is that the flanges supported large, fleshy cheek pouches for food storage. This would have allowed the animal to gather large quantities of vegetation quickly and retreat to a safer location to chew its food, perhaps reducing its time spent at dangerous, crocodile-infested waterholes.
Another theory suggests the cheekbones were for sexual display. Not all Euryzygoma skulls have equally developed flanges, which indicates sexual dimorphism, a distinct difference in appearance between males and females. Wider-cheeked individuals were likely males, using their impressive headgear to attract mates or intimidate rivals, like the antlers of a moose. These bony extensions might also have been used directly in combat between males. The bone at the end of the flanges is smooth, suggesting they were covered in skin, not horn-like growths.