Killer whales are an exception, having become larger over the last 10 million years, Alfaro and Slater said. Killer whales are unusual in that they eat mammals, including other whales.
"If we look at rates of body-size evolution throughout the whale family tree, the rate of body-size evolution in the killer whale is the fastest," Slater said. "It came from the size of a dolphin you would see at SeaWorld about 10 million years ago and grew substantially."
Whales range in size from the largest animal known to have ever existed, the blue whale, which is more than 100 feet long, to small species that are about the size of a dog and can get caught in fishermen's nets, Slater said.
Alfaro and Slater do not find evidence for rapid whale diversification, but extinctions may have made it difficult to detect early rapid diversification.
Whales are about 55 million years old, but the first group of whales to take to water is extinct, Alfaro said. Different hypotheses have been proposed to explain the rapid appearance and diversification of modern whales, which coincided with the extinction of the primitive whales.
Before the extinction of the dinosaurs 65 million years ago, there were large marine reptiles in the oceans that went extinct. When the earliest whales first went into the oceans some 55 million years ago, they had essentially no competitors, Alfaro and Slater noted. These primitive whales ranged in size from several feet to 65 feet long and looked similar to land animals, Slater said. They all fed on fish; the earliest whales did not dive deep down to catch squid.'/>"/>
|Contact: Stuart Wolpert|
University of California - Los Angeles