A semi-aquatic forebear of living mammals that lived alongside the dinosaurs was also the first known animal capable of suckling. It is also the earliest known example of a mammal that evolved for a semi-aquatic lifestyle. The animal has been dubbed Megacauda sungei, referencing its broad tail and palaeontologist Sun Ge.
The fossil, which is dated to between 163 million and 168 million years ago, was found by local farmers in the Daohugou area of Inner Mongolia, China. But the skull and teeth are analogous to river otters.” With an estimated weight of 1 kilogram, the creature is the largest known mammaliform from the Middle-Late Jurassic, when the planet was dominated by dinosaurs. The pelvis is preserved in 3D, as are its hyoids, or throat bones.
The bone structures under the skull that form the roof of the mouth and throat passage are also visible. This meant that, for the first time in any mammaliform, scientists were able to reconstruct the animal’s entire throat anatomy. Mammals’ throats can form “a suction vacuum for milk and squeeze the chewed food balls and liquid down their throats”, says Luo.
All the features that enable this are present in Megacauda. Now we know their evolutionary origins went back to before the rise of the modern mammals,” he says. The researchers found tiny limb fragments in the fossil’s stomach area that resembled the bones of salamanders, which would have lived in the same environment and may have been the creature’s last meal.
Oliver Griffith at Macquarie University in Sydney says this fossil sits at a key point in mammalian evolution.
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