Artist's depiction of a Diprotodon "mob" undertaking mass migration, while a giant lizard (Megalania) and a pair of giant grey kangaroos look on. (Image: Laurie Beirne)
New research shows that Diprotodon — the largest marsupial to have ever lived — partook in seasonal migrations that took the now-extinct creature on long journeys across Australia's Ice Age landscape.
Seasonal migrations are a common activity for many large-bodied placental mammals (e.g. wildebeest, elephants, buffalo), but it's strangely absent among all living marsupials — marsupials being a subgroup of mammals whose offspring are born in an undeveloped state and are carried and suckled in a pouch or on the mother's belly (e.g. kangaroos, opossums, and wombats).
Most living marsupials tend to be smaller than migrating mammals, which likely limits their ability to embark on long, perilous journeys to seasonal habitats. New research published in Proceedings of the Royal Society of London B suggests this wasn't always the case, and that at least one species of giant marsupial once embarked upon seasonal migrations.
This species is the enormous wombat-like Diprotodon optatum, a creature that weighed three metric tons, stood 6 feet (1.8 meters) tall, and measured 11 feet (3.5 meters) long. Fossils of Diprotodon, many of which have been unearthed at Queensland's Darling Downs, show that this Pleistocene era creature lived from approximately 1.6 million years ago until its extinction some 46,000 years ago.
Drilling a Diprotodon incisor tooth for the study. (Image: Gilbert Price)
New research conducted by the University of Queensland's Gilbert Price shows that Diprotodon partook in seasonal, two-way latitudinal migrations (i.e. north to south and back again) in eastern Sahul, or Pleistocene era Australia and New Guinea. These annual round-trip journeys saw herds, or mobs, of Diprotodon travelling as much as 125 miles (200 km). It's the first evidence for a repetitive seasonal migration in any marsupial, living or extinct.
Price and his colleagues reached this conclusion by studying the chemical patterns left on a single Diprotodon incisor. Similar to elephant tusks, Diprotodon's front incisors never stopped growing throughout their lives, leaving chemical evidence of where these creatures used to live. Analysis of these patterns show that these animals participated in annual migrations, and that the route was generally the same.
"We were able to do all this by analysing tiny samples from this giant's tooth," said Price in a statement. "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. 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.
Interestingly, some modern marsupials, like kangaroos, migrate on a nomadic basis, but none follow established seasonal patterns.
"It seems that the ecology of Ice Age Australia is so different to that of today," noted Price.