Why bandicoots and bilbies evolved such different snouts

Why does a quenda have a short, sturdy snout, while its relative the bilby has such a remarkably long one? New research led by Murdoch University's Harry Butler Institute suggests millions of years of adaptation to different environments across Australia and New Guinea may help explain the difference.

Researchers compared 3D scans of 127 skulls from 25 living and extinct species of bandicoots and bilbies, revealing substantial variation in skull shape across the group. The study, now published in the Zoological Journal of the Linnean Society, found around 35% of the differences in skull shape could be linked to climate, location, and body size.

Associate professor Natalie Warburton said one of the most striking differences was the length and shape of the animals' snouts.

"When people think of bandicoots, they often picture a fairly similar group of small, digging marsupials," Warburton said. "But when we compared their skulls in three dimensions, we found remarkable differences, particularly in the length and shape of their snouts.

"That raises an interesting question about why closely related animals, many of which live in similar ways, have evolved such different-shaped heads," she said.

Short-nosed bandicoots, including the quenda commonly found across southwestern Australia, have relatively short and robust skulls, while Perameles bandicoots and bilbies have much longer, narrower skulls.

Warburton said skull shape could provide clues about how different species adapted to their environments and ways of finding food.

"For animals that spend a lot of their time searching and digging for food, the snout is an important part of how they interact with their environment," she said. "A long, narrow snout may help an animal probe through soil and fallen leaves for food, while a shorter, stronger snout may be better suited to digging."

Importantly, the differences weren't simply because some species were bigger than others.

The study also included extinct species, showing bandicoots and bilbies were once even more anatomically diverse than they are today. The extinct pig-footed bandicoots, Chaeropus, were particularly unusual, with skull proportions unlike those seen in any bandicoot or bilby alive today.

Warburton said examining these differences could help researchers better understand how Australia's distinctive mammals evolved.

"A skull can tell us a surprising amount about an animal," she said. "Its shape is influenced by ancestry, feeding, sensory systems, and the mechanical demands placed on the head, so comparing skulls across species gives us another way of understanding how animals have adapted over evolutionary time."