Giant platypus a 'fearsome' predator: palaentologists An artist's impression of a giant, extinct platypus feeding on a short-necked tortoise. Artwork by Peter Schouten. The inset photo of the platypus's molar shows it was vastly different to the dysfunctional teeth of living platypuses. Picture: Rebecca Pian. PLATYPUSES may be known for their duck bills and timidity, but an extinct relative was bigger than a bulldog and had teeth strong enough to crush turtles. NSW biologists have identified a previously unknown species of platypus - the fifth and biggest so far - from a tooth found at a renowned fossil site in Queensland's gulf country. "It would have been one of the biggest animals by far in those ancient waterways," said University of NSW palaeontologist Mike Archer. Only crocodiles would have been bigger. Everything else would have thought twice about going for a swim with this platypus-zilla. Before the latest find, three extinct platypus species were known from fossils discovered in Central Australia's Simpson Desert, Argentina's far south and the Riversleigh World Heritage Area in Queensland. The new species is thought to have lived between five and 15 million years ago, reaching a metre in length. The tooth was identified last year by UNSW honours student Rebecca Pian, in a limestone sample excavated two years earlier from Riversleigh. Professor Archer, co-author of a report published today in the Journal of Vertebrate Palaentology, said there was no doubt it came from a platypus because of its W-like shape and "stumpy roots." "It's absolutely distinctive for all the fossil platypuses we've seen from Patagonia to Central Australia to Riversleigh and now to this new thing," he said. Modern platypuses have teeth as juveniles but lose them as adults. Professor Archer said it was unknown why teeth had evolved out in platypuses, but they may have been jettisoned as an "unnecessary luxury" as prey became smaller. He said the "horny pads" in adult platypuses" mouths still delivered a forceful bite. They crush hard-shelled yabbies with no difficulty at all. Prehistoric birds also had teeth. Biologists believe they may have disappeared as modern birds became lighter, making flight easier. The latest discovery contradicts views that the platypus evolved in a "linear" fashion with only one species existing at a time. "There were unanticipated side branches on this (evolutionary) tree, some of which became gigantic," Professor Archer said. He said the discovery reinforced ideas that the platypus's closest relative, the echidna, had evolved after the Patagonian platypus died out about 60 million years ago. "We have to look at echidnas as specialised platypuses that came out of the water, and started chasing termites instead of yabbies," he said. Professor Archer said prehistoric platypuses were thought to have existed in South America and Antarctica before the breakup of the supercontinent Gondwana, tens of millions of years ago. Ms Pian, now a PhD student at Columbia University in New York, said the discovery would help improve understanding of marsupials. "A new platypus species, even one that is highly incomplete, is a very important aid," she said. The species has been dubbed Obdurodon tharalkooschild after a Greek word for "permanent tooth" and the Dreamtime character Tharalkoo, a duck who was accosted by a water-rat and gave birth to the first platypus.