PARIS: Biologists have discovered a new sensory organ on blue, humpback, minke and fin whales that helps explain why these mammals are so huge.
In a study appearing in the journal Nature, researchers in the United States and Canada said the organ is located at the tip of the whale’s chin, in a niche of fibrous tissue that connects the lower jaw bones.
Comprising a node of nerves, the organ orchestrates dramatic changes in jaw position that are essential for “lunge” feeding by the rorqual family of whales, Earth’s biggest vertebrates.
Feeding lunge required sensory organ
These whales plunge into banks of krill, gulping up tonnes of water at one go and filtering it in seconds to get the tiny crustaceans needed for food.
A 50-tonne fin whale, the second-longest whale on the planet, can swoosh through 80 tonnes of water in one operation, netting 10 kilos (22 pounds) of krill in the process.
The lunge requires “hyper-expandable” throat pleats, a Y-shaped cartilage structure connecting the chin and a lower jaw, made of two separate bones that move independently.
Sensory organ crucial to size
The researchers report that there is a sensory organ, receptive to mechanical force, embedded between the unfused jaws of rorqual species – the largest group of baleen whales.
“This sensory organ responds to both the dynamic rotation of the jaws during mouth opening and closure, and ventral groove blubber expansion through direct mechanical linkage with the y-shaped fibrocartilage structure,” the researchers wrote.
“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,” said Bob Shadwick of the University of British Columbia in Vancouver, Canada.
“Because the physical features required to carry 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.”