"Instead, what we found is that very early in their history, whales went their separate ways from the standpoint of size, and probably ecology," Alfaro said. "This pattern provides some support for the explosive radiation hypothesis. It is consistent with the idea that some key traits opened up new ways of being 'whale-like' to the earliest ancestors of modern cetaceans, and that these ancestors evolved to fill them. Once these forms became established, they remained."
Species diversification and variations in body size were established early in the evolution of whales, Alfaro and his colleagues report.
Large whales, small whales and medium-sized whales all appeared early in the history of whales, with the large whales eating mostly plankton, small whales eating fish and medium-sized whales eating squid.
"Those differences were probably in place by 25 million years ago at the latest, and for many millions of years, they have not changed very much," said the study's lead author, Graham Slater, a National Science Foundationfunded UCLA postdoctoral scholar in Alfaro's laboratory. "It's as if whales split things up at the beginning and went their separate ways. The distribution of whale body size and diet still corresponds to these early splits."
"The shape of variation that we see in modern whales today is the result of partitioning of body sizes early on in their history," Alfaro said. "Whatever conditions allowed modern whales to persist allowed them to evolve into unique, disparate modes of life, and those niches largely have been maintained throughout most of their history.
"We could have found that the main whale lineage
|Contact: Stuart Wolpert|
University of California - Los Angeles