Scientists Discover New Grapefruit Sized Sensory Organ in Chin of Rorqual Whales
Posted on May 27, 2012
Scientists from the Smithsonian Institution and University of British Columbia have solve the mystery of how lunge feeding works through the discovery of a grapefruit sized sensory organ in the chin of rorqual whales that communicates to the brain. Lunge feeding in rorqual whales - a group including blue, humpback and fin whales - is unique among mammals.
When rorqual whales feed, they rush forward, engulfing more than their own body weight in water and then filter out the millions of krill and small fish inside their mouths. This all takes place within seconds. The researchers say the feeding technique is made possible by several morphological specializations, including hyper-expandable throat pleats, a Y-shaped cartilage structure connecting the chin to the throat pleats and a lower jaw made of two separate bones that move independently. The discovery of the sensory organ is shedding new light on how these features coordinate to create successful feeding. The organ provides an explanation for how the whales control the expansion of their throat pouch and mouth during lunge feeding
The organ is composed of connective tissue with papillae that contain nerves. It is suspended in a gel-like material and located in the whale's chin in the space between the tips of the two lower jaw bones. Vascular and nervous tissue from an ancestral front tooth socket connects to the sensory organ. Evidence indicates that the sensory organ responds to jaw rotation when the whale opens and closes its mouth and when the whale's throat pleats expand as it takes in water.
Nicholas Pyenson, paleobiologist at the Smithsonian's National Museum of Natural History and lead author of the research, says, "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. This deformation is registered by the nerves inside the organ, informing the gulping whale about its gigantic jaws, which must close before prey escape. 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."
Pyenson also says, "It is a supreme irony, that even after several decades of whaling where scientists had the opportunity to observe hundreds of thousands of whale carcasses, we are still only beginning to understand the anatomy of the largest ocean predators of all time."
The team's research is the featured cover story in the May 24 issue of the journal Nature.
Image: Art by Carl Buell, arranged by Nicholas D. Pyenson / Smithsonian Institution / Photo: Nicholas Pyenson / Smithsonian
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