Megacauda sungei fossil reveals early mammalian aquatic adaptations

Researchers have identified a new species of Jurassic mammaliaform, Megacauda sungei, through a fossil discovery in Inner Mongolia, China. Living approximately 165 million years ago, this creature is considered the oldest known mammal relative to exhibit a semi-aquatic lifestyle, similar to a modern platypus or otter.

Measuring roughly 50 centimeters in length and weighing between one and two kilograms, Megacauda sungei was significantly larger than many of its contemporaries. The fossil, which includes well-preserved impressions of skin and fur, reveals a wide, flattened tail and specialized teeth capable of shearing meat, suggesting a diet of fish, invertebrates, and possibly salamanders.

A critical finding in the study, published in the journal Nature, is the preservation of the throat and pharyngeal structures. The fossil contains a complex hyoid apparatus similar to that found in modern therian mammals, including marsupials and placentals. This anatomical feature allowed for advanced swallowing mechanisms, enabling the animal to consume nutrient-rich milk and swallow against gravity—a key evolutionary adaptation that facilitated later brain development in the mammalian lineage.