Whalebone is not bone at all, but the stuff of fingernails
Some whales feed through a curtain of plates hanging from the upper jaw, each up to 3.5 metres long and fringed with bristles. People called it whalebone, but it is keratin, the same protein in your hair and nails. Unborn baleen whales still start out growing teeth before swapping them for this filter.
Feeding is a matter of gulp and squeeze. The whale opens wide and takes in a dense shoal of krill, copepods or small fish along with a huge volume of seawater, sometimes an unlucky seabird too. Then it half-closes its mouth and presses its tongue upward, driving the water sideways out through the plates so that the prey stays behind to be swallowed. The racks have been likened to sieves or Venetian blinds. Plates are widest at the gum, can weigh up to 90 kilograms, and vary by species: bowheads carry plates of different lengths, gray whales use only one side, and sei whales have bristles stiffened with calcium.
Under the microscope the material is a composite of hollow tubes wrapped in a calcium-rich layer, packed inside a solid shell. That arrangement makes it both strong and flexible, stiffer lengthwise than across, which is why people once prized it for so many uses. The word itself comes from Latin and Greek words for whale.
Baleen rarely fossilises, so the oldest true specimens are just 15 million years old, but telltale skull features point to a much earlier start, around 30 million years ago. It may have grown from a hard, gummy upper jaw like that of the Dall's porpoise, which grips squid against its palate. Its spread probably coincided with the Early Oligocene, when Antarctica separated from Gondwana and a new current around it created rich feeding grounds where warm and cold waters met.
The switch from teeth seems to have happened gradually. Modern embryos form teeth and then lose them, and the gene for tooth enamel stopped working roughly 28 million years ago. Fossils of Aetiocetus suggest bundles of baleen sat between widely spaced teeth, a halfway stage.
Source: Baleen
