Ancient Jurassic Fossil Reveals Earliest Semiaquatic Mammaliaform with Platypus Traits
A near-complete fossil of Megacauda sungei, a 160-million-year-old mammaliaform with platypus-like features, was uncovered in Inner Mongolia, showing the earliest known semiaquatic lifestyle among mammal ancestors.
A remarkably intact specimen of Megacauda sungei, an early mammaliaform from the middle Jurassic, was recovered from the Haifanggou Formation in southeast Inner Mongolia, China. Dating to roughly 168-163 million years ago, the creature combined a platypus-like body, otter-like tail, and canine-type teeth, pointing to a semiaquatic habit of hunting small fish and salamanders. Weighing about 1-2 kilograms, it is the largest known Jurassic mammaliaform and falls under the extinct Docodonta lineage, an early branch of mammaliaforms.
Lead author Zhe-Xi Luo of the University of Chicago highlighted that swimming abilities appeared early in mammal evolution, while paleontologist Suzanne Hand noted numerous morphological parallels with modern platypuses. The fossil also preserves soft-tissue structures related to milk feeding, underscoring complex mammalian traits well before true mammals emerged.
Why it matters
The discovery pushes back the origin of semiaquatic adaptations in mammal ancestors, reshaping our understanding of early mammalian evolution.
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