The whales have evolved to gigantic dimensions only recently

A team of scientists was able to track the evolution of whale size over the past 30 million years and found that very large whales appeared along several branches of the evolutionary tree only 2-3 million years ago. The increase in ice cover in the Northern Hemisphere during this period likely changed the nature of whale food distribution in the oceans and increased the advantages of large body size. This is according to a study published in the journal "Science

A blue whale, which uses baleen to filter its prey from ocean water and can reach a length of more than 30 meters, is the largest vertebrate that ever lived. In the list of the largest living creatures to date, the blue whale is at the top of the list of largest creatures along with most of the other species of minke whales alive today. This is according to a new study by scientists at the Smithsonian National Museum of History. According to the researchers, only recently in terms of evolution did the whales become huge.

In a study published in the Journal of the Royal Society of Britain on May 24, Nicholas Fainson, curator of the Museum of Fossil Marine Mammals and his collaborators Graham Slater of the University of Chicago and Jeremy Goldbogen of Stanford University, write that they traced the evolution of whale size over more than 30 million years of history and found Because very large whales appeared along several branches in the family tree 2 to 3 million years ago. Increasing ice cover in the Northern Hemisphere during this period likely caused a change in the way whales distributed their food in the oceans and increased the benefits of large body size, the scientists say.

The question of why whales got so big has remained a mystery until now, in part because of the challenges of interpreting an incomplete fossil record. "We don't have the right data," Feinson said. "How do you measure the total length of a whale represented by a collection of fossils?" Pinson recently determined that the width of a whale's skull is a good measure of its overall body size. With this progress, it is time to answer the long-standing question.

The Smithsonian holds the largest and richest skull collections of both living and extinct whales, and the museum was one of the few places that used a collection that could provide the raw data needed to examine the evolutionary relationships between whales of different sizes. Pinson and his colleagues measured a wide variety of fossil skulls from the collections of the National Museum of Natural History and used those measurements, along with published data on other specimens, to estimate the lengths of 63 extinct whale species.

The fossils included in the analysis represent species dating back to the earliest whales that lived more than 30 million years ago. The team used the fossil data, along with data on 13 species of modern whales, to examine the evolutionary relationships between whales of different sizes. Their data clearly showed that whales as large as those that exist today did not exist for most of the history of whaling. "We live in a time of giants," said Goldbogen. "Mining whales have never been this big."

The research team followed the differences in body size that developed about 4.5 million years ago. Not only do cetaceans with bodies longer than 10 meters begin to evolve around this time, but smaller species of cetaceans also begin to disappear. Pinson notes that large whales appeared in several different dynasties at the same time, suggesting that massive size was of some advantage during this time period.

"We might think that the whales got progressively bigger over time by chance, and maybe that could explain how these whales got so big," said Slater, a former postdoctoral fellow at the museum. "But our analyzes show that this hypothesis did not last. The only way to explain why the minke whales became as huge as they are today is if something changed in the recent past and created an incentive to be huge and also caused landings for small ones."

This evolutionary change, which occurred at the beginning of the Ice Age, corresponds to climatic changes that could have reshaped the food supply for whales in the world's oceans. Before ice sheets covered the Northern Hemisphere, food resources were fairly evenly distributed throughout the oceans, Feinson said. But when the ice began to cover the continents, and in certain seasons part of it melted, the nutrients were washed into the coastal waters and caused an increase in the food supply for the marine mammals.

During this transitional period, the whales were equipped to utilize the abundance of small animals and plants such as krill as food. Goldbogen, who studies the feeding behavior of sperm whales, showed that filter feeding is particularly effective when the whales have access to large concentrations of prey. According to him, this eating strategy becomes more effective as the size increases."
Moreover, large whales can migrate thousands of kilometers to enjoy seasonal food supplies. Therefore, say the scientists, the food filtering systems of the sperm whales that developed about thirty million years ago reached a stage where they affected the increase in the size of the whales due to an increase in the concentration of prey in certain places and at certain times of the year."
"The size of an animal affects its ecological role," Feinson said. "Our research sheds light on why today's oceans and climates can support Earth's largest vertebrates, but today's oceans and climates are changing far more rapidly than any changes to date. Will the oceans be able to support both a large number of billions of people and the world's largest whales?"
"The clues to the answer to this question lie in our ability to learn from the deep past of the earth - the melting pot of our contemporary world - embedded in the fossil record."

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