Twenty-five million years ago a small whale with big eyes and plenty of teeth patrolled the sea off southern Australia. Janjucetus hunderi was 'Australia's very own T. rex of the oceans' according to Erich Fitzgerald, the Monash University PhD student who described the animal in the latest issue of Proceedings of the Royal Society B.
Fossil whales are always of interest but what makes this one the toast of the town is its teeth. Modern whales are divided into two groups on the basis of what's in their mouths. Toothed whales (such as sperm whales, killer whales and dolphins) have rows of peg-like gnashers. Other whales possess curtains of hairy baleen, which act as filters to strain out krill and small animals from each giant mouthful of water.
Janjucetus had teeth. So that makes it a toothed whale, right?
Wrong. It's a baleen whale. It just doesn't have any baleen.
Filter-feeding evolved relatively recently in whale history. Baleen whales are descended from toothed ancestors. (Embryonic baleen whales show evidence of this. They start to grow tooth buds but the buds are reabsorbed before they develop fully.) Janjucetus is one of the earliest in the group. It possesses many of the anatomical characteristics of baleen whales—except for baleen. That evolved much later. It first appeared alongside teeth. Then the teeth disappeared and the baleen remained on its own. One-at-a-time predators became bulk filter-feeders.
The Loom has an excellent article on Janjucetus and its significance in the whale family tree.
New Scientist article on Janjucetus.