Growth spurt gave rise to ocean giants

UNITED STATES: Millions of children have gazed up at massive blue whale models in museums and wondered at the sheer size of the largest animal ever to have lived. Now scientists believe they have discovered why whales became so big.

Blue whales can grow to 30 metres, but such size is a relatively recent feature in their evolutionary history.

Thirty million years ago, similar filter-feeding whales were much smaller, typically a maximum of 10m long. Very large whales began appearing only about two to three million years ago, according to a study of fossil whale skulls by the Smithsonian National Museum of Natural History in Washington, DC.

Researchers found that the increase in size coincided with the formation of glaciers in the northern hemisphere. Meltwater from the glaciers flushed nutrients from the land into coastal waters. The nutrients acted as fertiliser for phytoplankton at the base of the ocean food chain, resulting in periodic surges in the prey whales feed on, such as krill and other small crustaceans.

Larger whales could make more efficient use of the dense patches of food, and were also better able to migrate thousands of kilometres to find those seasonally abundant supplies, said the research, published in Proceedings of the Royal Society. They could survive for months without eating, thanks to their vast fat stores.

Nicholas Pyenson, curator of fossil marine mammals at the Smithsonian, said studies showed that different species of whale all grew larger at around the same time. ’’We see the extinction of much smaller baleen whales and the sudden appearance of very large body sizes like the blue whales and fin whales that we see today.’’

Other species of filter-feeding whales, such as the humpback, gray and right whale, were also now ‘‘substantially bigger than anything we find in the fossil record’’, he added.

Graham Slater from the University of Chicago, a co-author of the study, said the ancestors of today’s filter-feeding whales were originally about 3m long and achieved a maximum size of 10m after ten million years. - The Times

PHOTO: REUTERS Scientists say large filter-feeding whales like the blue whale trebled in size two to three million years ago thanks to more abundant suplies of food, fuelled by nutrients washed into the oceans by meltwater from glaciers.