Diving mammals ranging from water shrews, beavers and seals to ancient whales (pictured clockwise from top left) share adaptations in the protein that stores oxygen in muscles.

A team led by Michael Berenbrink at the University of Liverpool, UK, analysed the myoglobin proteins of extant mammals, and from this inferred the sequences of these proteins in the mammals' extinct relatives. Compared with non-divers, long-diving creatures tended to have higher levels of myoglobin in their muscles and these proteins were more highly charged, which probably prevents them from sticking together and reducing their utility. On the basis of this relationship, the team developed a model to estimate how long ancient animals could have stayed underwater. They calculated that after ancestors of whales moved from land to water in the Eocene, 56 million to 34 million years ago, their diving capacity increased from 1.6 to 17.4 minutes.

Credit: TOP LEFT, B. MOOSE PETERSON/ARDEA.COM; BOTTOM LEFT, DE AGOSTINI PL/GETTY; TOP RIGHT, MINDEN PICTURES/SUPERSTOCK; BOTTOM RIGHT, NORBERT WU/MINDEN PICTURES/FLPA

Science http://dx.doi.org/10.1126/science.1234192 (2013)