![]() That such a major change in overall morphology could happen so quickly is intriguing." Not only that, but paper suggests that the change from a platypus-like body form to an echidna-like body form appears to have happened surprisingly quickly, in less than 15 to 25 million years. "This hypothesis has been suggested before, but the current paper provides the most compelling evidence yet that this is what actually happened. "Another interesting aspect of this study is that it suggests that the echidna evolved from an ancestor that was very like a modern platypus, despite the fact that echidnas and platypuses are anatomically very different," Beck added. "To put it simply, the bones and the genes appear to be telling essentially the same story, which is reassuring." "Matt Phillips and colleagues have reassessed both the fossil and molecular data and concluded that the platypus-echidna split is in fact relatively recent," said mammalogist Robin Beck at the American Museum of Natural History in New York. These findings remove an apparent contradiction between fossil data and DNA evidence, said Zhe-Xi Luo, curator of vertebrate paleontology at the Carnegie Museum of Natural History in Pittsburgh.Įvolutionary biologist Peter Waddell at Purdue University at West Lafayette, Ind., explained that an earlier study based on early monotreme fossils had suggested the platypus and the echidna diverged more than 110 million years ago, while the molecular data suggested a far more recent divergence. The researchers conjecture that marsupials could not afford a substantial invasion of aquatic environments because when they are born, they need to suckle milk constantly for weeks newborn marsupials could drown if their mothers ever had to venture into the water. Their new findings suggest "the lack of early echidna fossils was in fact because they simply had not evolved yet." It was thought that the much shorter fossil record for echidnas, from about 13 million years ago, was just due to the patchy nature of the fossil record," Phillips said. "Platypus-like fossils are known from at least 61 million years ago. ![]() A number of aspects of echidna biology are consistent with an amphibious platypus-like ancestor - a streamlined body, rearward-jutting hind limbs that could act as rudders, and the contours of a duck-like bill during embryonic development. This means echidnas recently had semi-aquatic predecessors and only later recolonized the land. However, new genetic evidence and comparisons with fossil monotremes suggests that echidnas only diverged from platypuses 19 to 48 million years ago. Platypuses are amphibious creatures, while echidnas - the anteaters - are terrestrial. Now Phillips and his colleagues suggest that platypuses and echidnas lived on because their ancestors sought refuge where marsupials could not follow - the water. The mystery then is why any monotremes survived. The struggle marsupials presumably had with all the animals on these continents during this journey might have primed them for competition, "while the Australian mammals that went extinct upon the arrival of marsupials had for the most part been isolated in Australia for a very long time," explained researcher Matthew Phillips, an evolutionary biologist at the Australian National University in Canberra.Īll these strengths help explain why marsupials triumphed in Australia. Moreover, before the marsupials reached Australia, they had migrated from Asia to the Americas to Antarctica. Marsupials appear to have a number of advantages over monotremes - their bodies seem more efficient at locomotion, and the fact that they give birth to live offspring could provide better care of young. The monotremes were almost totally swept aside when their pouch-bearing marsupial cousins - modern examples of which include the kangaroos - invaded Australia 71 million to 54 million years ago.
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