A remarkably preserved fossil uncovered in China has provided researchers with new insights into the early evolution of mammalian traits. Discovered in 2015 within the Haifanggou Formation in south-east Inner Mongolia, the ancient creature has been named Megacauda sungei. Living approximately 168 to 163 million years ago during the middle Jurassic period, this creature now stands as the earliest-known semiaquatic mammal-like animal.
The Discovery
The fossilized remains are remarkably intact, preserving the vast majority of the creature's bones alongside soft throat tissues. A study published in Nature places Megacauda on the mammaliaforms family tree under Docodonta, an extinct branch of early mammal cousins. Found in rock layers that were teeming with ancient salamanders, the discovery demonstrates that the capacity to swim emerged early in the evolutionary journey of mammal relatives.
What Scientists Found
Weighing between 1 and 2 kilograms, Megacauda is the largest known Jurassic mammaliaform, matching the size of a modern platypus. Scientists noted several physical features adapted for living in aquatic environments:
- A platypus-like body frame with webbed feet, expanded ribs, an otter-like flattened tail, and exceptionally thick fur.
- A canine-like head armed with strong canine and sectorial teeth, which allowed it to feed on small fish and salamanders in the water.
- Preserved throat structures indicating it was suited for drinking milk as an infant and swallowing food as an adult.
Why It Matters
This species officially takes the title of the earliest-known semiaquatic mammaliaform from Castorocauda, a beaver-like fossil discovered in the same region. Experts note that shifting to a semiaquatic lifestyle provided several evolutionary advantages, such as tapping into abundant food supplies, avoiding land-based resource competition, opening new travel routes, and surviving catastrophic events better than strictly terrestrial animals.
Source: dinosaur fossil discovery - BingNews · Published October 07, 2026 · Photo by Smithsonian on Unsplash