The fossil whale, Mammalodon colliveri, was actually discovered in 1932 in southeastern Australia, but was not studied until recently. Erich Fitzgerald found that it lived 25 to 28 million years ago and was about nine feet long. Its mouth features suggest that it made its living by suction feeding, vacuuming prey from muddy ocean bottoms.
It had the jaw and skull structures distinctive of today's baleen whales, but unlike modern baleens, it also had teeth. Modern baleen whales use fibrous structures called baleen to filter tiny prey called krill from seawater. In contrast, modern toothed whales capture larger prey such as fish or other marine mammals.
Mammalodon colliveri used its mouth structures to suck prey up from the bottom, filtering the prey from the mud. It then had teeth it could employ to eat larger items. This suggests that baleen whales may have evolved from toothed whales that relied more and more on the sucking and filtering aspects of feeding, and less on the need for teeth.