Ancient whale smiled like a sieve.

Ancient whale smiled like a sieve

The modern blue whale, the largest animal on Earth, is a toothless giant of the deep that feeds by filtering sea-water through a comb-like structure called baleen. Scientists have long thought that Blues and other baleen whales, which belong to a suborder called Mysticetes, evolved millions of years ago from ancestral toothed whales, but they have lacked detailed fossil evidence to chronicle the transition from teeth to baleen. A Canadian paleontologist has now identified a previously unknown type of ancient whale from Antarctica with a gap-toothed smile that helps fill in the dental story.

Edward D. Mitchell of the Arctic Biological Station in Ste-Anne-de-Bellevue, Quebec, described a new genus and species of extinct whale called Llanocetus denticrenatus from remains found on Seymour Island along the Antartic Peninsula. The animal, which lived about 40 million years ago, had an unusual set of notched teeth arranged in a widely spaced row along its cheek, Mitchell reports in the December 1989 CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES.

Judging from the shallow roots to the teeth and the shape of the notches, Mitchell says the whale could not have eaten by gripping, piercing or tearing its prey. Instead, he proposes the animal used the notches in its teeth as a filter to catch fish or shrimp-sized invertebrates. While no modern whales use their teeth to feed this way, Mitchell notes that the Crabeater seal, which does not eat crabs, has notched teeth that is uses to filter krill and other invertebrates.

L. denticrenatus represents a "missing link" that fits somewhere between ancient toothed whales and the first known fossils of the toothless Mysticetes, says Mitchell, who suggests filter feeding in whales first developed in forms with notched teeth. These animals may also have had baleen, which is made of fingernail-like keratin that does not fossilize.