The giant playtpus and its bone-crushing tooth
It鈥檚 hard to believe, but platypus ancestors were even weirder than modern versions. Today, the toothless, duck-billed, venomous, electric-field-sensing, egg-laying mammals grow up to 50 centimetres long and snack on shrimps, insects and worms.
But millions of years ago, some were metre-long bone-crunchers that probably feasted on turtles and frogs lurking in the Australian outback.
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The only evidence of the new, giant species is a single tooth, but there鈥檚 no doubt it鈥檚 a platypus, says one of the discoverers, Michael Archer at the University of New South Wales in Sydney, Australia.
鈥淧latypuses have such distinctive teeth that, frankly in the pitch black, with the tooth held behind my back, I could tell it鈥檚 a platypus tooth,鈥� he says. The tooth closely resembles the teeth of other extinct platypuses discovered in South America and Australia, but wear patterns on the tooth suggest its owner was more carnivorous. 鈥淭he wear is at the tips of the cusps, indicating it鈥檚 coming down hard on hard material that is held between the jaws,鈥� says Archer. He thinks it would have been feasting on vertebrates, possibly on animals like the turtles and frogs whose fossils were found in the same quarry in Queensland.
Origins of all mammals
The find also opens up new evolutionary questions. Until now, it was thought that platypuses had an unusually linear evolutionary tree, with platypuses getting smaller over time, and slowly losing their teeth. This new specimen, estimated to be between 5 and 15 million years old, doesn鈥檛 fit that narrative. It is more recent than several other known specimens, but larger than any other, and has clearly functional teeth.
鈥淔ossils showed they were getting steadily smaller, that they were losing their teeth and becoming hyper-specialised. And then suddenly this gigantic King Kong platypus turns up. It shows platypuses were experimenting with side branches [on the evolutionary tree],鈥� says Archer. 鈥淭his new giant platypus-zilla, it raises more questions than it answers. If it was so divergent, what was its lifestyle? Did it have venomous spurs? Did it have a flat tail? Was it aquatic?鈥�
Archer is confident they will find more fossils belonging to the same species to help answer some of these questions.
鈥淢onotremes [platypus and echidna] are absolutely fascinating subjects for evolution,鈥� says Jenny Graves from La Trobe University in Melbourne who was part of a team that sequenced the platypus genome in 2008. 鈥淎lthough they are definitely mammals, they retain many reptile characteristics like laying eggs 鈥� they are real evolutionary intermediates.鈥�
鈥淏ut it鈥檚 sometimes hard to tell if a feature was ancestral to all mammals, or specific to platypus or echidna,鈥� she says. Any further information about this new species could therefore be important to understanding how mammals evolved.
Journal reference: Journal of Vertebrate Paleontology, vol 33, p 1
