The blue whale, measuring up to 100 feet long and weighing up to 170 tons, was traditionally regarded as the largest animal to have ever lived. However, its status as world-record holder was briefly threatened when paleontologists discovered fossilized remains of the sauropod dinosaur Argentinosaurus in 1993. While early estimates indicated that Argentinosaurus was longer and heavier than the blue whale, further research has led the scientific community to generally accept that the blue whale still holds its title as the largest animal to have ever lived.
Whales are divided into two taxons, or evolutionary lineages: baleen whales and toothed whales. The baleen whale group includes blue whales, right whales, and humpback whales, while the toothed whale group includes sperm whales, orcas (killer whales), dolphins, and porpoises. Baleen whales tend to be bigger, while there is some overlap some toothed whales, such as the sperm whale, may be bigger than some smaller species of baleen whale.
One of the most remarkable things about baleen whales is that they eat very small organisms ocean plankton, such as krill, which may be smaller than an inch! To catch these krill, they filter them out of the water using baleen, the large tooth-like appendages in their mouths. Imagine that the largest animal on earth eats some of the smallest! This unique feeding behavior and great size are just two of the reasons why whales remain some of the most magnificent creatures on Earth.