Why Are Whales So Big?

Weighing up to 200,000 kilograms and covering the entire length of a basketball court, the blue whale is the biggest animal on the planet. They’re nothing short of colossal, and now scientists are claiming to know how the marine mammals managed to get so big.

For decades, the sheer size of whales has been a topic of hot debate. Some biologists maintain that because water supports weight, whales are able to grow to immense sizes. Others argue that whales simply evolved to be larger as a defence mechanism against sharks.

Size does matter

There’s also disagreement over when whales got so big, with evolutionary biologist Graham Slater musing that it happened around 30 million years ago. Meanwhile, whale expert Nicholas Pyenson argues that it was much sooner.

So, the pair decided to team up and settle the debate once and for all.

Working from the Smithsonian Institution's National Museum of Natural History in Washington DC, Pyenson studied its vast cetacean fossil collection. Analysing 63 extinct species and 13 modern species, he found that the size of a whale directly correlates with the width of its cheek bones. He then plotted the data on a timeline, and factored in family trees. The results were surprising.

According to Pyenson, it wasn’t until 4.5 million years ago that baleen whales went “from relatively big to ginormous.” Prior to this growth spurt, the biggest whales in the ocean measured in at just 10 metres long. Today, it’s not unusual for blue whales to grow up to 30 metres long.  

An Ice Age feast

Next, the researchers looked at what environmental conditions could have triggered the change. They found that baleen whale growth coincided with the beginning of the first Ice Age. They speculate that as glaciers expanded, spring and summer runoff drenched the ocean in nutrients. This fuelled explosive growth in krill, shrimp and other small animals that whales feed on. As a result whales enjoyed millennia of feasting ,which allowed them to mushroom in size.

Oceans are the beating heart of the planet, which means it’s critical to protect them at all costs. For a closer look at the impact of a 1967 oil spill disaster, ‘Fifty years after the wreck of the Torrey Canyon’ offers exclusive commentary from Gerald Boalch, Chief Scientist on the Marine Biological Association of the UK research vessel that was on the scene just a week after the spill.