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About 165 million years ago, while dinosaurs dominated the planet, a furry creature swam like a platypus, hunted like an otter, and had a tail like a beaver in the lakes and rivers of what is now China. Researchers have now described it from an exceptionally preserved fossil found in Inner Mongolia: a new species named Megacauda sungei, roughly 50 centimetres long and weighing 1 to 2 kilograms. And hidden in its throat is a secret that rewrites how mammals learned to feed their young.
Meet Megacauda: the Jurassic's biggest little mammal
Most mammals of the Jurassic were tiny, shrew-sized creatures scurrying in the shadows of dinosaurs. Megacauda was a giant by comparison — twice as big as the next-largest member of the mammalian lineage at the time, as reported by Reuters and New Scientist. The fossil, found by local farmers in the Daohugou area and studied by an international team led by University of Chicago paleontologist Zhe-Xi Luo, preserves even skin and fur impressions, giving a clear body contour. Its flat, stout tail (the "mega cauda" — big tail — that names it, honouring paleontologist Sun Ge), short-haired coat, and paddling feet all point to a semiaquatic lifestyle: the oldest-known example of a swimming mammal in evolutionary history. Its sharp, curved teeth were built for catching slippery prey like fish and salamanders.
The throat that changed everything
The real breakthrough is not the swimming — it is the swallowing. The fossil preserves the throat bones (hyoids) in three dimensions, letting scientists reconstruct the animal's entire throat anatomy for the first time in any early mammaliform. Megacauda had the same pharynx structure that lets modern mammals — including humans — squeeze chewed food down the throat one small lump at a time instead of in massive gobs, and the soft-palate arrangement that makes suckling possible. In other words, this creature that lived long before the last common ancestor of all living mammals — monotremes, marsupials, and placentals — already had the feeding machinery that defines mammals today. Study author Thomas Martin of the University of Bonn noted that the soft palate and the shaping of the mouth and pharynx are directly linked to the evolution of mammals themselves — the adaptation that ultimately made complex brain development, and eventually humans, possible.
Why it matters beyond the fossil
Suckling looks simple to us, but it is one of the most distinctive biological adaptations on Earth — unique among living vertebrates. By pushing its origin back 165 million years, before the crown group of mammals even existed, Megacauda shows that the mammalian way of feeding was already taking shape while dinosaurs still ruled. The study was published this week in the journal Nature. Every time a baby mammal nurses, it is using throat machinery invented by creatures like this Jurassic swimmer.
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