Scientists have made a key step in understanding the evolution of filter-feeding whales’ enormous mouths, thanks to an ancient fossil. Modern baleen whales, such as blue whales, can filter small marine creatures from huge volumes of water with the help of their “loose” lower jaw joints that enable them to produce a vast filter-feeding gape.
But researchers from Australia and the U.S. who study the ancient jawbone showed that nature’s largest mouths probably evolved to suck in large prey rather than to engulf plankton-filled water.
In modern whales, the lower jaw does not fuse at the “chin". Instead there is a specialised jaw joint that allows each side of the jaw to rotate.
By having two curved lower jawbones that rotate in this way, baleen whales are able to produce huge gapes to take in massive quantities of water and prey.
"This is compelling evidence that these archaic baleen whales could not expand and rotate their lower jaws, which enables living baleen whales to engulf and expel huge volumes of seawater when filter feeding on krill and other tiny animals,” BBC quoted lead researcher, Erich Fitzgerald from the Museum Victoria in Melbourne, as saying. Crucially though, the fossilised whale, named Janjucetus hunderi, did have a very wide upper jaw. Dr. Fitzgerald says that this widening was the earliest step in the evolution of today’s whales’ gigantic mouths.
He charted the anatomical features of whales on an “evolutionary tree” — from Janjucetus hunderi to the blue whale.
The chart indicated that, “the first step towards the huge mouths of baleen whales may have been increasing the width of the upper jaw [to] suck fish and squid into the mouth one-at-a-time.
The study was reported in the Royal Society journal, Biology Letters.