March 13, 2014
New Whale Fossil Species Sheds Light On Evolution Of Echolocation
Lawrence LeBlond for redOrbit.com - Your Universe Online
Echolocation is an important tool for several modern species, including bats and some birds. Previous research from New York Institute of Technology’s College of Osteopathic Medicine has found that this powerful navigational tool also existed in a 28-million-year-old relative of modern-day toothed whales, dolphins and porpoises.
Geisler noted that the most important conclusion in his team’s research “involves the evolution of echolocation and the complex anatomy that underlies this behavior.”
“This was occurring at the same time that whales were diversifying in terms of feeding behavior, body size, and relative brain size,” he added.
In most mammals, including humans, low frequency sounds are produced in the larynx. In toothed whales, dolphins and porpoises, however, high-frequency sound is produced through a constricted area in the animal’s nasal passages below the blowhole. This sound-producing mechanism in toothed whales is very complex, consisting of large muscles, air pockets and bodies of fat all packed into a small region of the face.
The evolution of complex adaptations have been studied widely and new fossil discoveries have often revealed that adaptations evolve in a step-wise fashion and usually over long periods of geologic time. In the study of the C. macei skull, Geisler and his colleagues concluded that this whale echolocated similarly to its modern-day relatives.
“Its dense bones and air sinuses would have helped this whale focus its vocalizations into a probing beam of sound, which likely helped it find food at night or in muddy water ocean waters,” Geisler said in a statement.
Through detailed analysis and comparisons with living and fossil whales, the team determined that C. macei belonged to an extinct family of whales that split from other whales about 32 million years ago. The analysis, when taken into context with the entire toothed whale family tree, reveals that a rudimentary form of echolocation evolved in the common ancestor of this animal and other toothed whales, between 35 and 32 million years ago. Once C. macei evolved, the fossil record indicates that there was a progressive increase in size and complexity of the air sacs and muscles used to control the sound generating apparatus in the face.
This fossil species had some very distinct features, according to Geisler. It had a deep cavity on the top of its head – “cavity head” is a loose translation of the name Cotylocara – for an air sinus that stored air while diving and may have reflected sound generated in the face. Also, a radar-dish-like shelf of bone around the nasal openings was found that may have reflected sound and improved the animal’s ability to echolocate.
“The anatomy of the skull is really unusual. I’ve not seen anything like this in any other whale, living or extinct,” Geisler concluded.