When in isolation, animals evolve bizarre features and behaviours.
Adding to the weird and wonderful fauna on the island of Madagascar, a mammal the size of an opossum that resembled a badger roamed amid dinosaurs and giant crocodiles 66 million years ago, reports a paper published in the journal Nature.
The newly discovered gondwanatherian mammal that lived on the Cretaceous southern supercontinent Gondwana has been named Adalatherium, which translates from the Malagasy and Greek languages as “crazy beast”.
The skeleton is exceptionally well preserved, and by far the most complete for any Mesozoic animal found so far in the southern hemisphere.
Its badger likeness is superficial – beneath the surface is some nature-defying morphology, according to lead researcher David Krause from Stony Brook University, US.
“[K]nowing what we know about the skeletal anatomy of all living and extinct mammals, it is difficult to imagine that a mammal like Adalatherium could have evolved; it bends and even breaks a lot of rules.”
Its snout has primitive features that hadn’t been seen for a hundred million years in the lineage that evolved into modern mammals, with “an amazing mosaic of features, some of which are very standard for a mammal, but some that I’ve never seen before,” Krause says.
Adalatherium had more holes (foramina) on its face than any known mammal, serving as conduits for nerves and blood vessels that supplied a very sensitive snout covered with whiskers.
Other unusual features include a very large hole at the top of its snout, more vertebrae than any Mesozoic mammal, a strangely curved leg bone, and unique teeth construction.
“The strangeness of the animal is clearly apparent in the teeth,” says co-author Alistair Evans, from Monash University, Australia. “They are backwards compared to all other mammals and must have evolved afresh from a remote ancestor.”
Its size was also unusual for its era – most mammals that lived alongside dinosaurs were more mouse-sized, on average.
And its movements defy logic, according to co-author Simone Hoffman from the New York Institute of Technology.
“Adalatherium is the oddest of oddballs,” she says. “Trying to figure out how it moved is nearly impossible because, for instance, its front end is telling us a different story than its back end.”
After 20 years of piecing the mystery creature together since its discovery in 1999, the team is still deciphering the clues, but thinks it was probably a powerful digging animal capable of running, with other possible means of locomotion as well.
Other peculiar back-boned creatures the team has discovered on Madagascar over the past 25 years include a giant, armoured, predatory frog (Beelzebufo), a pug-nosed, vegetarian crocodile (Simosuchus) and a small, buck-toothed dinosaur (Masiakasaurus).
And they’re in good company with endemic Madagascan animals such as hissing cockroaches (Gromphadorhina portentosa), giraffe weevils (Trachelophorus giraffa), tomato frogs (Dyscophus), Satanic leaf-tailed geckos (Uroplatus phantasticus), panther chameleons (Furcifer pardalis) and streaked tenrecs (Hemicentetes semispinosus).
Just a few thousand years ago, 600-kilogram elephant birds (Aepyornithidae), gorilla-sized lemurs and pygmy hippopotamuses roamed the richly biodiverse landmass.
Like these other critters, Adalatherium may be so unusual because it evolved on an isolated island for tens of millions of years – “ample time to develop its many ludicrous features,” says Krause, as it developed its own idiosyncratic ways to move and find food.
The Royal Institution of Australia has an education resource based on this article. You can access it here.
Natalie Parletta is a freelance science writer based in Adelaide and an adjunct senior research fellow with the University of South Australia.
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