Scientists have discovered a 30-million-year-old whale that used its teeth to both bite and catch prey, and filter seawater for food. This ancestor of the modern baleen whale gives us new information on how cetaceans evolved, showing that ancient whales were filter feeders even before developing the filtering structures modern whales use today.
Modern baleen whales — like the blue whale or the humpback whale — catch their food by taking in vast quantities of water into their mouths, and expelling the water through keratin sieves called baleen. The baleen traps small creatures such as fish or plankton. Scientists have long been trying to understand when the baleen structure evolved, since ancient whale ancestors don’t have it.
This new specimen, called Coronodon havensteini, was discovered near Charleston, South Carolina, and is described today in a study published in Current Biology. Coronodon isn’t the oldest such ancestor, but it does provide a new evolutionary link between the modern baleen whale and the group of toothed whales from which they are descended, known as archaeocetes.
By studying the Coronodon’s teeth and body, the researchers concluded that the prehistoric animal fed in two different ways. The teeth’s wear patterns suggest that the ancient whale likely hunted down its prey, biting it to catch it. But its body size and structure also suggest that the Coronodon wasn’t very good at this so-called raptorial feeding.
Instead, the cetacean had large and broad lower molars it used to feed by filtering seawater. The whale didn’t suck up water; instead it opened its mouth and scooped up water and prey, a method known as ram feeding. The whale then expelled the water through tiny gaps between its teeth — about 0.59 by 1.42 inches in size — capturing prey into its mouth. The whale also had a wide snout, which suggests “a crucial adaptation for filter feeding,” the study says.
The discovery of Coronodon helps us understand how cetaceans evolved — showing that ancient whales developed their “filter feeding” behavior before developing the baleen used today to filter water for food.
Next, the researchers want to study the body size of ancient whales, to determine where there's any relationship between body size and teeth. Hopefully, that will help scientists better understand when baleen first appeared and how filter feed developed.