May 12, 2008 -- One of the largest studies ever of modern and fossil whales has determined that virtually all modern whales appear to have evolved safeguards against the bends, a sometimes fatal condition in which nitrogen bubbles form in blood and tissues after too rapid decompression.
Whales turn out to be masters of bubble management, comparable to the proper serving of fizzy drinks, such as soda and beer.
Lead author Brian Beatty explained to Discovery News that "whale blood vessels themselves are extremely smooth-walled, preventing cavitation (bubble formation), much in the same way that bubbles in a beer have a harder time forming on the walls of a glass than a plastic cup, which is why the bubbles last longer in a glass, making the beer taste better."
"Bubbles carry odor to your nose, where much of the taste is (registered)," added Beatty, an assistant professor of anatomy at the New York College of Osteopathic Medicine.
He and coauthor Bruce Rothschild analyzed vertebrae from 331 modern and 996 ancient fossil whales housed at museums and universities across the United States. They subjected the whalebones to standard X-rays and fluoroscopy, a process that allows for real-time video images, in order to detect bone damage linked to the bends.
Beatty explained that pressure changes can "cause a bit of fat or gas to form an embolism in a blood vessel" and that, in turn, can be a literal bone buster, since the blood vessels "have little room to expand within the bone."
The researchers discovered that toothed whales, a group that includes killer, sperm and beaked whales, along with dolphins, likely would have suffered from the bends some 32 million years ago, while another whale group known as the mysticetes would have got the bends some 22 million years ago.
The mysticetes include humpback, blue, gray and other whales that have baleens, or rows of plates that look like giant combs. These allow for filter feeding and are used instead of teeth.
The findings, which have been accepted for publication in the journal, Naturwissenschaften, have multiple implications that could change current views on whale evolution.
The first is the ancestor to all whales was probably not a deep-sea diver, as had been previously proposed. Instead, the research suggests it was most likely a crocodile-type shoreline ambush hunter.
Today's sperm whales can dive for more than one hour to depths greater than 4,000 feet below the water's surface. If the "mother of all whales" had tried such a dive, its bones probably would have shattered to bits.
The study also indicates toothed and baleen whales independently evolved anatomical and behavioral abilities to cope with the bends, with toothed whales developing the skills long before baleen whales did. This provides evidence that the two major groups of whales split from their common ancestor early on and went down their own evolutionary paths, perhaps explaining the tremendous amount of diversity seen among whales today.
Erich Fitzgerald is a noted whale evolution expert and a paleontologist at Australia's Museum Victoria.
Fitzgerald described the new research as "quite important, and it presents a novel hypothesis on the evolution of one of the critical aspects of cetacean biology."
He said that "it seems the odontocetes evolved their 'tool kit' for deep diving and hunting in the dark using sound, very early on," while "the baleen whales were on a different evolutionary timetable, 'modernizing' much later in their evolutionary history."
"This is fascinating, and we need further analyses of relevant fossils to test these ideas," Fitzgerald added.
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