Ancient whale fossils reveal early origin of echolocation
The skull of a newly discovered whale species reveals distinctive density variation and shapes suggestive of echolocation.
Thu, Mar 13, 2014 at 09:10 AM
An illustration of the new species, Cotylocara macei. (Image: Carl Buell)
An ancient whale used sound beams to navigate and stalk prey 28 million years ago, an analysis of a new fossil suggests.
The new whale species, called Cotylocara macei, contains air pockets in the skull similar to those used by porpoises and dolphins to send out focused sound beams. The discovery pushes back the origins of the ability, called echolocation, to at least 32 million years ago, said study co-author Jonathan Geisler, an anatomist at the New York Institute of Technology.
"It suggest echolocation evolved very, very early in the history of the group that involved toothed whales," a group that includes sperm whales and killer whales, as well as dolphins and porpoises, Geisler said. [Image Gallery: Russia's Beautiful Killer Whales]
About 10 years ago, scientists unearthed a complete toothed whale skull, along with a few neck vertebrae and some ribs in a fossil-rich region near Charleston, S.C. An international collector named Mace Brown acquired the find, and then invited Geisler to take a look at it. (The new species is named after the collector.)
The ancient whale, which was about 28 million years old, grew to about 10 feet (3 meters) long and looked somewhat similar to modern-day dolphins or small cetaceans, though they are not closely related. It likely lived in shallow marine environments, such as the mouth of an estuary or a little further offshore, Geisler said.
C. macei also had several distinctive features, including bone density variations and several deep air cavities, including one on top of the skull and one on either side of the base of the snout, Geisler said.
Those air sinuses looked similar in purpose to those found in toothed whales, or odontocetes. In odontocetes, the air sinsuses help them form nearly continuous, focused sound beams to investigate or search for prey in dark or muddy water. They then process the reflections of those sound beams through internal ears on the side of their heads, or through air spaces between their jaws, to create a sound-based map of the world around them.
"Odontocetes don't produce sound in their voice box, it's originated in the face," Geisler told Live Science.
The ear bones and soft tissue from the whale weren't preserved, so they don't know for sure how the whale's echolocation would have sounded or how it processed the reflections from sound beams they sent out, Geisler said.
The new discovery suggests that echolocation evolved very early in whale evolution, likely soon after odontocetes diverged from the ancestors of baleen whales.
The findings were published March 12 in the journal Nature.
More on LiveScience and MNN:
This story was originally written for LiveScience and has been repubished wtih permission here. Copyright 2014 LiveScience, a TechMediaNetwork company.
Photo credit: James Carew and Mitchell Colgan