May 24, 2012
Newly Discovered Organ Could Explain Size, Eating Habits Of Some Whales
Scientists with the Smithsonian Institution and the University of British Columbia (UBC) have discovered a new sensory organ in the rorqual family of whales -- a discovery which sheds new light on their unique feeding behavior and explains why they grow to such massive sizes.
The US and Canadian biologists involved in the study located the organ at the tip of the chin of blue, humpback, minke and fin whales, contained within a batch of ligaments connecting the lower jaw bones, according to AFP reports published on Wednesday.
The previously hidden organ is made up of nerves, and "orchestrates dramatic changes in jaw position" required for rorqual whales to feed by opening their mouths wide and gulp massive amounts of water in order to consume large amounts of fish or krill in a single bite, LiveScience Staff Writer Jennifer Welsh explained.
Next, the water is filtered back into the ocean through baleen at the front of the creature's mouth, which allows it to return to normal size and keep the food swallowed, she added. The whole process is completed in about six seconds and is made possible because rorqual whales have a pair of large connected jawbones that are loosely attached to the rest of their skull.
"The odd arrangement of tissues didn't make much sense to us at first, but then we realized that this organ was perfectly placed, anatomically, to coordinate a lunge because that soft structure is pinched by the tips of the jaws, and deforms through the course of a lunge," Nicholas Pyenson, paleobiologist at the Smithsonian's National Museum of Natural History and lead author of research published in the journal Nature.
"This deformation is registered by the nerves inside the organ, informing the gulping whale about its gigantic jaws, which must close before prey escape," he added. "This finding answers several outstanding theoretical questions and puzzling field data that suggest rorquals actively control their lunge, rather than letting their mouths passively inflate like a parachute."
In the study, Pyenson called the rorquals' feeding methods one of the most extreme amongst all aquatic vertebrates, according to BBC Nature Writer Victoria Gill. He also said that the structure resembled a "gelatinous mess," which could explain why it had previously been dismissed by scientists as simply a "fluid-filled joint" located between the two bottom jaw bones. It wasn't until they dissected the organ that they discovered its true complexity, she added.
"We think this sensory organ sends information to the brain in order to coordinate the complex mechanism of lunge-feeding, which involves rotating the jaws, inverting the tongue and expanding the throat pleats and blubber layer," Pyenson said. "It probably helps rorquals feel prey density when initiating a lunge."
"In terms of evolution, the innovation of this sensory organ has a fundamental role in one of the most extreme feeding methods of aquatic creatures," added UBC Zoology Professor and study co-author Bob Shadwick. "Because the physical features required to carry out lunge-feeding evolved before the extremely large body sizes observed in today's rorquals, it's likely that this sensory organ — and its role in coordinating successful lunging — is responsible for rorquals claiming the largest-animals-on-earth status“¦ This also demonstrates how poorly we understand the basic functions of these top predators of the ocean and underlines the importance for biodiversity conservation."
Image 2 (below): A new sensory organ, found within the chin of rorqual whales, is responsible for coordinating the biomechanics of their extreme lunge-feeding strategy. Left, a fin whale after lunging; right, anatomy of the new sensory organ. Art by Carl Buell, arranged by Nicholas D. Pyenson / Smithsonian Institution.