The 3 tonne (3.3 US ton) wombats that roamed Australia during the Ice Age undertook great seasonal migrations, presumably for food. This is the first time this behavior has been found in marsupials, despite being common among large vegetarian mammals.
Australia's environment was once dominated by diprotodons, giant relatives of wombats that were comparable to rhinoceroses in size. They were so enormous and so numerous that their loss probably had a large impact on the continent. But since scientists have never had the chance to study one directly, we know little about their behavior.
Dr Gilbert Price of the University of Queensland has filled in one piece of the puzzle, however, by examining the fossilized incisor of Diprotodon optatum, the largest marsupial of all time.
“It goes back to that old saying ‘you are what you eat’, because the chemicals of the food they consumed became part of their teeth,” Price said in a statement. “But it’s also true that ‘you are where you ate’, especially if you are a plant eater, because the geochemistry of the soils where plants grow also become fixed into a herbivore’s tooth.”
By analyzing the enamel layers of one D. optatum individual, Price found that the species migrated at least 200 kilometers (120 miles) annually across the Darling Downs. The findings are reported in Proceedings of the Royal Society B.
Although small birds migrate 100 times further, seasonal migrations are usually restricted to large species of mammal. Large beasts are in danger of eating all the locally available food, particularly if, like D. optatum, they live in herds. The need to keep moving to find fresh pastures could easily have led to regular migrations influenced by rainfall patterns.
We don't yet know whether other members of the diprotodontid family did the same thing, but the new discovery is significant.
“Why this is exciting is, although marsupials like kangaroos might migrate on a nomadic basis, there are none today that follow set seasonal patterns,” Price said.
He is particularly interested in what happened when the diprotodons died out, as it might indicate what to expect if other continents lose their migratory grazers. It is likely that diprotodon extinction affected the landscape of Australia and killed off predators, but we don't know for sure.
Ecologists have found that, in areas where cattle have replaced zebra or antelopes, it is best to try to replicate migratory patterns, where grasslands are eaten intensively for short periods of time. This has yet to be applied to Australian ecosystems, which were not thought to be adapted to this particular grazing pattern.