Modern toothed whales have two major physical differences from their baleen brethren (apart from the whole teeth thing): they use echolocation, and they have asymmetrical skulls. It was thought that these toothy whales' twisted bones evolved alongside echolocation, but new research indicates it may go back much further than that, to their 37 million-year-old predecessors.
The researchers were analyzing the skull of Basilosaurus isis, and originally assumed that its deformed shape was due to the process of fossilization. However, when they digitally straightened it, the teeth no longer fit together, and they realized that asymmetry in whale skulls goes back much further than previously thought — and these mammals didn't have the correct organs for echolocation.
This three-dimensional torsion of their skulls is thought to be linked to an older auditory trick — directional hearing in the water. It's thought that the asymmetry would allow them to more accurately locate and differentiate sounds, a convergent evolution you see with some other animals, like owls, too.