Sperm whales spend most of their lives in the deep levels of the ocean, sometimes diving as far down as 3,000 feet to feed on large squid. But locating their favorite prey in these dark waters is no easy task. In order to navigate and forage in areas of the ocean with poor visibility, the ancestors of sperm whales and other toothed whales, including dolphins, orcas and porpoises, evolved an amazing ability to understand their surroundings using sounds. Echolocation, like sonar on a submarine, enables animals to detect objects in their environment by broadcasting out high frequency calls and then listening for the location and distance from where they bounce back.
Surprisingly, this key adaption in toothed whales isn’t shared with baleen whales like blue whales and humpbacks, which feed by straining water through large baleen plates. Fossil evidence shows that toothed whales diverged from the ancestors of baleen whales around 35 million years ago, distinguishing the two modern-day subspecies. When and how echolocation evolved in toothed whales, however, has remained a mystery.
But a new study released in Nature is giving scientists critical insight into the origins of whale echolocation. Researchers at the New York Institute of Technology examined the skull of a newly discovered 28-million-year-old whale species named Cotylocara macei and determined that the extinct mammal likely had sonar ability similar to present day toothed whales. This breakthrough discovery suggests that echolocation began evolving in toothed whales around 32 million to 34 million years ago — very early in the history of this whale subspecies.
“The most important conclusion of our study involves the evolution of echolocation and the complex anatomy that underlies this behavior,” said the study’s lead scientist, Dr. Jonathan Geisler, in a written statement. “This was occurring at the same time that whales were diversifying in terms of feeding behavior, body size, and relative brain size.”
Although the ear bones and soft tissues that capacitate echolocation in modern whales were not preserved in the ancient fossil, distinctive features, including bone density variations and several deep air cavities, indicate the creature had the ability to use sonar. The whale’s genus name, Cotylocara, loosely translates to “cavity head” in recognition of this important characteristic.
Cotylocara macei, which likely hunted in shallow seas and looked similar to modern dolphins, is not related to any living whale species and is thought to have gone extinct about 25 million or 26 million years ago. “The anatomy of the skull is really unusual. I’ve not seen anything like this in any other whale, living or extinct,” Geisler said. Discovered off the coast of South Carolina, Cotylocara macei is the first of it’s kind and provides a rare glimpse into the long evolutionary process that has shaped modern marine mammals.