For dolphins and other toothed whales, the ocean is a vast soundscape. Even when they cannot visually see their surroundings, they can still picture what’s going on by sending out sound and listening to the image of the returns – echolocation. But when did whales gain this fantastic ability?
A fossil skull described last year holds an important clue. Paleontologist Jonathan Geisler and colleagues named it Cotylocara macei – a whale that swam the sea off South Carolina around 28 million years ago. The marine mammal wouldn’t have looked quite like a modern whale – especially with its wicked smile of triangular teeth – but several features in the skull hint that Cotylocara was among the first whales to use echolocation.
Some of the characteristics are easy to see. The snout of Cotylocara is turned down – to better direct sounds – and the skull has a slight asymmetry, which allowed the whale to better pinpoint the location of objects given away by return calls. But the strongest evidence, Geisler and coauthors reported, are air sinuses that helped the whale produce the high-frequency sounds critical to echolocation.
This ability only exists in toothed whales – whale biologists call odontocetes. (Baleen whales like humpbacks make sounds, too, but they don’t have the directed echolocation abilities of their relatives.) Cotylocara was along the evolutionary stem leading to what we think of as modern toothed whales, meaning that the development of echolocation originated a little before the last common ancestor of today’s dolphins, sperm whales, and other species that use echolocation. And with this evidence in hand, paleontologists can go back to look at other fossil whales from this time to see if they, too, heard the see in surroundsound.
Geisler, J., Colbert, M., Carew, J. 2014. A new fossil species supports an early origin for toothed whale echolocation. Nature. doi: 10.1038/nature13096