Biggest Animals Ever!

Blue whales are big—really big! They’re the largest animals that have ever lived on Earth. These giants of the sea can grow to be longer than two school buses parked end-to-end and weigh 300,000 pounds or more. That’s about as heavy as 24 elephants!

“No dinosaur ever weighed as much,” says Nick Pyenson. He’s a paleontologist at the Smithsonian National Museum of Natural History in Washington, D.C. “Blue whales are the animal size champions of all time!”

Pyenson and a team of researchers decided to find out how these supersized swimmers got so enormous. The scientists think that a change to the blue whale’s diet millions of years ago helps explain why they are so huge today.

Blue whales belong to a group of animals called baleen whales. These whales don’t have teeth like other whales do. Instead, they have hard structures called baleen plates. Baleen plates hang down from the whales’ upper jaws like teeth on a hair comb.

Whales use their baleen plates to feed upon tiny creatures called zooplankton. These animals swim in schools that contain millions of individuals (see Meet the Real Plankton). In a single day, a blue whale can eat up to 8,000 pounds of zooplankton. These huge meals likely explain how blue and other baleen whales became giants. But Pyenson says baleen whales weren’t always so big.  

Pyenson and his team studied more than 140 fossils of baleen whales that once swam in Earth’s oceans. They looked at how the whales’ size changed over the past 30 million years.

The scientists found that for tens of millions of years, baleen whales were about the size of a minivan—much smaller than today’s whales. But about 3.5 million years ago, the whales became jumbo-sized.

What helped baleen whales get so big? The team found that back when whales were smaller, zooplankton were less concentrated, or more spread out, in the ocean than today.

Earth then went through a cooling period. Glaciers formed at the North Pole, reaching as far south as places like modern-day New York City. These masses of ice pushed nutrients from the land into the sea. This created more food that zooplankton eat. As a result, schools of zooplankton grew. Baleen whales could then gobble up much more food in a single bite. Over time, their bodies grew.

The researchers credit the cooling of Earth’s ancient climate for allowing whales to grow into colossal beasts. But today, Earth’s weather patterns are doing the opposite.

The planet’s average temperature is rising. This is also causing Earth’s oceans to heat up. Scientists have a lot of questions about what this will do to the ocean’s ecosystems.

Pyenson explains that warming seawater could cause zooplankton numbers to decrease. If that happens, it might be difficult for baleen whales to find enough food to support their size. “For some big whales, that could be a big problem,” says Pyenson.