The mysterious marsupial mole
John Pickrell is the editor of Australian Geographic. He is a science writer, author, nature lover and self-confessed geek. Blog posts range over Southern Hemisphere palaeontology, dinosaurs, megafauna, archaeology, palaeoanthropology and a smattering of other topics.
I LOVE A GOOD biological oddity. And if eccentric animals float your boat then Australia is the place to be.
From the tree kangaroo to the platypus, we have them by the truckload. Most owe their singular nature to a quirk of plate tectonics that split the southern continent of Gondwana asunder tens of millions of years ago, and sent Australia sailing northward with a cargo of curious creatures.
The stage was set for a grand experiment in evolution, which saw Australia’s isolated marsupial and monotreme inhabitants develop quite independently from mammals elsewhere in the world.
Desert dwelling conundrum
Not least among the cast of oddities is the desert-dwelling marsupial mole. It is so little known that people who’ve lived in the western and central deserts their entire lives may have never seen one.
There are two largely similar species. Itjaritjari (the southern marsupial mole) is found in the sandy deserts of the NT, central WA and northern SA. Kakarratul (the northern marsupial mole) is known from the Great Sandy, Little Sandy and Gibson deserts of WA.
Small enough to fit on the palm of your hand, and with glossy, creamy yellow fur, these animals are ingeniously adapted to desert living. Because surface temperatures jump from one extreme to the other, many desert creatures shelter underground, but the mole hardly ever surfaces.
It ‘swims’ through the sand, backfilling its tunnels behind it as it goes, and survives on the air between sand grains. Its metabolism is pared down to the point that its body temperature mirrors its surroundings. It has a small tail and ears, and no discernible eyes whatsoever. The snout has a tough, scaly pad, which it uses to plough through the ground, while the front paws have two large, flat claws that act as shovels.
Example of convergent evolution
Marsupial moles feature in the Dreaming of several Aboriginal groups. To the Anangu of the Red Centre, Minyma Itjaritjari is a playful ancestral being who lives in a cave in the side of Uluru. But European colonists didn’t set eyes upon a marsupial mole until 1888, when one was collected at a station on the NT’s Finke River. It was sent on to E.C. Stirling, director of the South Australian Museum, but arrived so decomposed that he struggled to identify it.
Some experts decided the creature wasn’t a marsupial at all, but related to the golden moles of Africa, which are placental mammals.
They were wrong, but it’s easy to understand the confusion – the marsupial mole is surprisingly similar to Grant’s golden mole of the Namib Desert, which has similar fur and also ‘swims’ through the sand. One difference is that the Namib mole can scurry on the surface, an environment in which its marsupial doppelganger finds itself ill at ease.
The remarkable resemblance between the species is down to convergent evolution, where similar environmental problems lead to similar solutions to overcome them in different groups of animals.
Features of their bones tell us that the marsupial moles are not closely related to any other marsupial groups, and they may have split off as many as 64 million years ago, shortly after an extinction event killed off most of the dinosaurs.
Marsupial mole fossil
Intriguingly, a 20-million-year-old fossil found at Riversleigh, Queensland, in 2010 suggests the mole evolved in the damp soils of Australian rainforests, only later adjusting to the deserts as moisture sapped from the continent.
Following discovery by western science, moles were briefly prized for their lustrous golden fur, and thousands of pelts were traded by Aboriginal people to Europeans and Afghan cameleers. Since the 1920s, however, the animal has been rarely seen. Dr Joe Benshemesh of La Trobe University, Melbourne, estimates that actual sightings have occurred just 5–10 times a decade.
A 2007 AG Society-sponsored survey in the Simpson Desert found no sign of them, but Joe thinks they may be more common than supposed. Similar surveys in the Red Centre reveal up to 60km of backfilled tunnels per hectare, suggesting that moles may be abundant and ecologically important for perturbing desert soils.
Our lack of knowledge of their abundance is just another of the mysteries surrounding these fascinating arid-zone enigmas.
John Pickrell is the author of Flying Dinosaurs: How fearsome reptiles became birds, published by NewSouth Books in June 2014. Follow him on Twitter @john_pickrell.
This column, was first published in the Sep/Oct 2013 print edition of Australian Geographic.