A 165-million-year-old otter-sized swimmer from Inner Mongolia is rewriting how mammals learned to drink milk

An international team led by the University of Chicago, Shenyang Normal University, Shandong University of Science and Technology, the University of Bonn and Ohio University describes Megacauda sungei in Nature: a Jurassic mammaliaform the size of a modern otter, with seal-like cheek teeth and an otter's tail, paddling through freshwater rivers alongside dinosaurs. MicroCT scans revealed tiny bony hooks on the roof of its mouth — the same structures that help modern mammals coordinate suckling and swallowing — the earliest evidence yet that nursing anatomy began evolving 165 million years ago. It also rewrites a textbook assumption: the modern structures didn't descend from the primitive ridges as believed; they coexisted with them. 'The age of dinosaurs was also a time of extraordinary evolutionary innovation among early mammals,' said co-author Peishu Li of Ohio University.