The first aquatic mammals evolved while dinosaurs still roamed the Earth. The evidence comes from several broad, flat vertebrae that resemble the tail bones of modern beavers and platypuses. Nick Longrich of the University of Calgary, who found the bones in a fossil collection held by the Royal Tyrrell Museum in Alberta, thinks they belong to water-going stagodonts, a group of marsupials that died out alongside the dinosaurs.
Life
Swimming with dinosaurs
10 November 2004
