Scientists have long wondered how marine mammals are able to hold their breath for up to an hour while underwater, one of the most extreme adaptations in the animal kingdom. BBC News reports researchers have now solved the mystery in a new study published in Science.

A team of scientists from the University of Liverpool studied myoglobin, an oxygen-storing protein found in the muscles of mammals. They found that in whales and seals, the protein has special "non-stick" properties, which allow the animals to store large amounts of oxygen in their muscles without "clogging" them. Harbor seals, for example, routinely hold their breath for 30 minutes and even sleep underwater. 

"At high enough concentrations, [proteins] tend to stick together, so we tried to understand how seals and whales evolved higher and higher concentrations of this protein in their muscles without a loss of function," Dr. Michael Berenbrink from the Institute of Integrative Biology at the University of Liverpool said to BBC News.

Dr. Berenbrink, who took part in the study, said that scientists have long wondered how marine mammals are able to pack so many vital proteins in their bodies.

To solve the mystery, researchers extracted pure myoglobin from the muscles of mammals, including cows, semi-aquatic otters and sperm whales, and carefully examined all extractions. Tracing the changes in myoglobin through 200 million years of evolutionary history, the researchers revealed the best breath-holding mammals not only evolved a non-stick variety of myoglobin, but their myoglobin was positively charged as well.

"Like the similar poles of a magnet; the proteins repel one another," Dr. Berenbrink said. "In this way we think the animals are able to pack really high concentrations of these proteins into their muscles and avoid them sticking together and clogging up the muscles."

The discovery helped to explain how animals evolved from land-breathing to aquatic, air-breathing mammals of the ocean, and demonstrated the physiological change that accompanied the transition from land to water.

"The idea that we can estimate maximal dive times for early diverging relatives of today's marine mammals will have a profound impact on how we think about their ancient ecology and biology," Nicholas Pyenson, curator of fossil marine mammals at the Smithsonian Institution in Washington DC, said to BBC News. He said the study is an exciting advancement in the understanding of deep-diving evolution.

"Being able to pick up a few [fossilised] bones of an extinct marine mammal and estimate its dive time from that - that's miraculous," Professor Michael Fedak from the University of St Andrews' Sea Mammal Research Unit, who did not participate in the study, said to BBC News. 

Fedak said at the moment, researchers are looking into how marine mammals are able to survive while repeatedly cutting off and re-establishing the blood supply to their body tissues. He added that although myoglobin was just "part of the story" in understanding the evolution of deep-diving mammals, "it's an important part" nonetheless.