Scientists have traced the evolution of whale sizes back 30 million years and discovered how the giant mammals got so big.
In a study published in Proceedings of the Royal Society B, the researchers revealed that the shift towards sizes of over 10 metres long appeared in baleen whales just two to three million years ago.
According to the authors of the study, the relatively recent timing suggests that changes in the climate affected the diet of some whales.
The study posits that due to changes in ocean water temperature, krill and small fish – an important part of the whales’ diet – started to get packed into smaller areas. After this, evolution simply favoured the bigger whales that were better at eating these dense pockets of food. One type of whale that benefited from the increase in food was the blue whale.
Blue whales are so big that they are not only the biggest creature on Earth now, but the biggest ever. Belonging to the baleen whale family, they can measure up to almost 30 metres long and weigh up to 180,000 kilograms.
In order to eat, baleens take a huge gulp of water and then partly shut their mouths, forcing the water out and trapping the food.
The researchers found that around the time baleens started to get larger, the Earth was entering ice ages. They think that the change in climate led to “run-off” from glaciers pouring more nutrients into coastal waters.
Meanwhile, something called an “upwelling” was taking place in the ocean. This happens when wind pushes surface water offshore and causes deeper waters to rise and replace it.
The combination of the ice ages and upwelling led to the increased patches of food in certain parts of the ocean that just happened to be populated by growing whales.
Olivier Lambert, a palaeontologist from the Royal Belgian Institute of Natural Sciences, who was not involved in the study, told The Guardian that the research provided a convincing scenario for one of the last stages in the evolution of size among baleen whales.
However, he did add that other factors such as the evolution of large predators and other climatic events could have played in role in the whales’ increased gigantism.
Nicholas Pyenson, a co-author of the study, sees the research as containing potential lessons about our current situation. “An animal’s size determines so much about its ecological role,” Pyenson said in a statement. “Our research sheds light on why today’s oceans and climate can support Earth’s most massive vertebrates.”
“But today’s oceans and climate are changing at geological scales in the course of human lifetimes,” he added. “With these rapid changes, does the ocean have the capacity to sustain several billion people and the world’s largest whales? The clues to answer this question lie in our ability to learn from Earth’s deep past—the crucible of our present world—embedded in the fossil record.”