Markings on the teeth of a 25-million-year-old whale fossil have helped answer one of the biggest (in every sense of the word) questions about the evolution of marine mammals. The find points to how baleen whales, among the largest animals that ever existed, evolved their distinctive whalebone.
Blue, minke, and right whales, among others, have comb-like structures of baleen at the front of their mouths instead of teeth. Baleen is a hard substance made from keratin, the basic protein that makes up hair and fingernails. It works as a filter-feeder system inside the mouth so krill, other plankton, small fish and squid get caught in the baleen and can be removed with the tongue for swallowing without bringing a lot of salty water with them.
Humpback whale showing its baleen. John Tunney/Shutterstock
Biologists as far back as Darwin have been puzzled as to how such unusual mouthparts evolved. One early whale fossil had teeth and what appeared to some people to be early signs of baleen, leading to a theory that the two co-existed for a while, but this has been greatly disputed.
“Alfred”, the name given to a skull of the extinct whale group aetiocetids changes the picture, according to Dr Erich Fitzgerald of the Museum of Victoria. Alfred has no baleen, but his teeth feature tiny horizontal scratches that are also seen in a few living marine mammals, including walruses.
What these mammals have in common is that they suck in water and prey before expelling the water. The prey sometimes comes with sand, which leaves the small scratches on the teeth when scraped across them with the back and forward motion of the tongue.
These marks have never been seen before on an aetiocetid. Fitzgerald takes them as proof that Alfred and his kin were using suction feeding long before they developed baleen. The claim is published in Memoirs of Museums Victoria, a peer-reviewed journal.