Nerves in general are not very extensible, while "nerve stretch injury" is a common form of nerve trauma in humans. But Canadian and U.S. researchers said Monday rorqual whales have nerves in their mouths and tongues that can stretch like bungee cords.

"This discovery was totally unexpected and unlike other nerve structures we've seen in vertebrates, which are of a more fixed length," study author Wayne Vogl of the University of British Columbia (UBC) said in a statement.

The elastic nerves, which can more than double their length with no trouble, support the animals' unique and extreme lunge feeding strategy, the researchers reported in the U.S. journal Current Biology.

Rorqual whales represent the largest group among baleen whales weighing 40 to 80 tons, and include blue whales and fin whales.

To eat, the whales open their mouths and lunge while their tongues invert and their mouths fill like giant water balloons full of floating prey.

Those prey are concentrated by slowly expelling the water through baleen plates. The volume of water brought in with a single gulp can exceed the volume of the whale itself.

"Rorqual whales attained large body size with the evolution of a bulk filter feeding mechanism based on engulfing huge volumes of prey-laden water," Vogl said. "This required major changes in anatomy of the tongue and ventral blubber to allow large deformation, and now we recognize that this also required major modifications in the structure of nerves in these tissues so they could withstand the tissue deformation."

Vogl and his team made the discovery after one of the researchers picked up a white cord-like structure in their lab and found it can stretch.

At first, they assumed that it was a blood vessel, which ought to be stretchy, but realized upon closer inspection that it was a nerve.

The nerves of other species are generally surrounded by a thin collagen wall, and any stretch can pull and damage the nerves.

In the whales, the nerve cells in the whales are packaged inside a central core in such a way that the nerve fibers simply unfold. A very thick and stretchy outer wall, full of elastin fibers like elastic bands, surrounds that nerve core.

The researchers planned to keep studying the whales' nerves in greater detail, in hopes of understanding better how the nerve core is folded to allow its rapid unpacking and re-packing during the feeding process.

"This discovery underscores how little we know about even the basic anatomy of the largest animals alive in the oceans today," said co-author Nick Pyenson, a former UBC postdoctoral researcher currently at the Smithsonian's National Museum of Natural History.

"Our findings add to the growing list of evolutionary solutions that whales evolved in response to new challenges faced in marine environments over millions of years."