Fossil from China shows a platypus-like mammal relative swam and hunted 165 million years ago
Scientists led by Zhe-Xi Luo of the University of Chicago, publishing in Nature, described Megacauda sungei, a semiaquatic mammal relative found in Inner Mongolia that lived alongside dinosaurs. The fossil, about 1 to 2 kilograms, is the largest known Jurassic mammaliaform and the earliest known semiaquatic one, pushing back evidence of suckling and swallowing. The find matters to anyone tracing how mammal traits evolved.
Bottom line — The fossil pushes evidence of mammalian suckling back to at least 165 million years ago, before modern marsupials and placentals split.
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Luo described Megacauda as 'a chimera': its hind half resembles a platypus, while its skull and teeth are closer to a river otter's, according to the University of Chicago palaeontologist.
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Analysts at New Scientist's coverage noted the fossil was found by local farmers in the Daohugou area, while Live Science reported the specimen was unearthed in 2016 and ABC reported 2015, a discrepancy the sources do not resolve.
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Suzanne Hand of the University of New South Wales, who was not involved in the study, said the animal shares foot, ankle, pelvis and rib features with the platypus, including webbed feet and a flattened tail.
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Luo said the teeth were strong canines and shearing cheek-teeth for carnivorous feeding in water, and tiny salamander-like limb fragments in the stomach area suggest the animal's last meal.
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Preserved throat bones, including the hyoid, let researchers reconstruct the swallowing and suckling anatomy for the first time in any mammaliaform, according to the study team quoted by New Scientist.
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Jessica Theodor of the University of Calgary, not involved in the research, described lactation as a long-running 'conversation' between mother and baby that began early in the Mesozoic.
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Sue Hand of the University of New South Wales told Live Science that suckling behaviour 'now appears to have evolved well before' previously assumed, in a common ancestor at least 165 million years ago.
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Tim Flannery of the Australian Museum Research Institute said an aquatic lifestyle 'arose often in early mammal-like species'.
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Luo noted that 140 living mammal species are riparian-dependent today, placing the Jurassic find in a longer history of semiaquatic mammals.
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The Australian Broadcasting Corporation report noted the earliest known semiaquatic true mammal, Dongoconodon platycauda, lived about 120 million years ago in a Chinese fossil deposit.