UNSW scientists have discovered new species of bizarre, extinct 'hammer-toothed' carnivorous marsupials that likely crunched snails in Australia's ancient rainforests.
Australia's diversity of ancient mammals has gotten a little bit bigger, with UNSW scientists discovering more extinct marsupials at a site in northern Queensland, including two new species.
The new malleodectids – literally "hammer teeth" – are thought to be a bizarre subset of carnivorous marsupials that fed largely on hard shelled organisms like snails.
Around 15 million years ago, a vast rainforest covered pretty much all of Australia, providing habitat for a galaxy of strange and wonderful mammals, many of which have long since gone extinct, including the malleodectids.
Marvels of the Miocene
15 million years ago the Earth was in the middle of the Miocene Epoch, and Australia was about three degrees warmer than it is today and saw a lot more rainfall.
The supercontinent of Gondwana had broken up, Australia had separated from South America and Antarctica, and the Australian landscape was about as diverse as the Amazon, or the tropical rainforests of Borneo are today.
"During this period, we see the most species diversity in the Australian fossil record for mammals," lead author of the study published in the Journal of Mammalian Evolution and UNSW palaeontologist Dr Timothy Churchill said.
"It was really a golden age of mammal evolution in Australia."
It was in this world that a marsupial about the size of a modern quoll, with sharp front teeth and a pair of big, smooth, hammer-like rear premolars for smashing through the hard shells of snails, fell into a limestone sinkhole in what is now the Riversleigh World Heritage Area in far north Queensland and died.
The lime-rich water at Riversleigh would have started fossilising the creature almost immediately, adding it to the many thousands of animals preserved there.
"It really is one of the most amazing fossil sites in Australia," Dr Churchill said.
Let them eat snails
Marsupials are a diverse bunch.
Most of the more than 300 living species of marsupial in the world live in Australia, ranging in size from the more than two-metre-long red kangaroo to the tiny, finger-sized long-tailed planigale.
And that's just of the marsupials that survive, many more are these days confined only to the fossil record.
The two new marsupials Dr Churchill has described in his paper belong to the carnivorous family Malleodectidae – ancient cousins of modern quolls.
Based on their teeth, Dr Churchill believes they mainly ate snails, probably lived in trees, and weighed between 100 and 500 grams.
There are no living marsupials that only eat snails – that ecological niche is now being filled by a type of skink.
"Malleodectids no longer exist but the pink tongue lizard, which is a relative of the blue tongue lizard, is actually Australia's most voracious snail-eating animal," Dr Churchill says.
"It lives in the rainforests of northern Australia, very similar to where the malleodectids once lived."
Tiny fragments
Despite being such a bountiful site in terms of the number of fossils found there, not much remains of the malleodectids Dr Churchill studies – he's based his findings on the few teeth and jaw fragments that scientists have been able to find.
In the paper, Dr Churchill describes a new genus of malleodectid – Weirdodectes napoleoni – and Dr Churchill only had a single tooth to work with.
A genus is a group of closely related species – a taxonomic rank above species and below family.
Weirdodectes got its name because of how weird it is.
"This tooth is unlike any tooth we've ever seen in the fossil record," Dr Churchill said.
"We thought it was fitting to call it Weirdodectes because it was such a weirdo compared to everything we'd seen so far.
"It's got very shortened blades and these very large, rounded cusps that are all very close together which we think it was using to crack through hard objects."
What it ate or even what it looked like, though, are questions that remain unanswered at this stage, but Dr Churchill says its tooth suggests a highly specialised diet.
"It had found a dietary niche that was very different than that occupied by the other malleodictids, but that understanding has been based on the shape of that single tooth – that's all we have of it. So, if the single tooth is this strange, how strange was the rest of the animal?"
The exciting thing for Dr Churchill though is that these new species – however bizarre and unknowable they remain – clearly demonstrate that this was a phenomenally diverse ecosystem at that time.
"There's now seven different species in this family and three genera rather than just one weird animal," he said.
"There must have been enough dietary variety in these ancient rainforests for multiple different species of these shell-crunching marsupials to exist.
"The morphological and ecological diversity of carnivorous marsupials in Australia is much, much greater than we ever previously imagined."
Key Facts:
UNSW scientists have discovered new species of bizarre, extinct 'hammer-toothed' carnivorous marsupials that likely crunched snails in Australia's ancient rainforests.
