Two tiny fossils are prompting an overhaul of theories about marsupial evolution after they revealed unexpected links to South America – and possibly Africa.
One of the fossils, found at the Tingamarra site in south-eastern Queensland, is a 55 million-year-old ankle bone from a mouse-sized marsupial previously known only from South America. The second is a tooth, which derives from a formerly unknown species that shows similarities to fossils found in South America and, surprisingly, North Africa.
The two fragments are set to overturn the conventional theory about the evolution of marsupials, which holds that there was a single migration from the part of the Gondwana 'supercontinent' that became South America to the part that became Australia.
"The origins of Australian marsupials suddenly got a lot more complicated!" said palaeontologist Dr Robin Beck, an ARC DECRA postdoctoral fellow at the University of NSW.
"All the species of modern day marsupials here are quite closely related. The species represented by the ankle-bone belongs to an entirely different group – a group that we know lived in South America but, up until now, we thought never made it to Australia. The tooth is more of a mystery: are its origins in South America, Africa or somewhere else?
"It is impossible to explain the presence of these new fossils in Australia using the single dispersal model. Instead, there may have been multiple movements of marsupials between South America and Australia."
Keep in mind, metatherians were close to, if not truly, dominant in North America prior to the KT Extinction. It was that extinction which set placentals, eutherians really, on their rise to dominance. Otherwise, they would not have.
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