(from "The Research on the Whale Stock in the Antarctic
- The Result of the Preliminary Study in 1987/88", ICR, 1989)
Just as interesting as the legs are the teeth: the existence of toothless whale. The ancestors of baleen whales did have teeth. Tooth-buds are observed on the upper and lower jaws of whale fetuses in the early stage of pregnancy. As the fetus grows, baleen plates appear on the upper jaw while the tooth-buds completely disappear. These are evidence that baleen whales evolved from ancestors with teeth in their upper and lower jaws. In other words, ontogeny repeats itself phylogenically.
In the evolvement of the baleen whales, the baleen emerged as the teeth disappeared. This evolutionary process has much to do with the baleen whales' feeding on the plankton, which are small but vast biomass, as the animal shifted its habitat from the land to the ocean. Using the baleen to sieve the krill out of the sea water is the most efficient feeding method, since the krill is only a few centimeters long but abound in several thousand million tons in the Antarctic. For example, whale sharks that have little affinity with baleen whales use their gills as filtrator when feeding on small planktons. In a similar way, the planktons themselves use the bristies on their legs as filter for feeding on diatoms.
Fig. C-5 illustrates how baleens hang down from the upper jaw in the oral cavity of a whale. The baleen has the same histological properties as the nails of human beings - flexible but strong. The outer edge is smooth; the inner edge is frayed. Inside the oral cavity the bristies of the baleen plates intertwine to form a coarse-fibered mat which functions as a filter. Samples of the baleen of each species of baleen whales are given in Fig. C-4. They vary in shape and size, and also in the process of food intake and storage in the oral cavity.
Greenland right whales and right whales have 500 - 600 baleen plates each of which are 2 to 4 meters long. Those of gray whales and fin whales are shorter at less than one meter (98 cm for blue whales and 20 cm for minke whales) but large in number; an average blue whale has 800 and a minke whale 600.
The upper jaws are significantly curved in an arch so as to accommodate such long baleens as those of right whales in the oval cavity. The lower jaws are also well developed to function as a cover for both sides of the mouth. When the jaws are fully opened, the baleen stretches beyond the bottom of the oral cavity; when the jaws are closed, the tip of the baleens are rolled inward in the oral cavity. In baraenopteridae the upper jaws do not curve and the lower lips are undeveloped.
A right whale swims into krills, mouth ajar, then flushes the water out through the gap between the baleen so that only the particles of food is left behind. It subsequently closes its mouth, lifts its tongue and supposedly pushes the food down its throat. Minke whales feed in the same manner as fin whales. It first expands what is commonly called ventral grooves - grooves under and in the back part of the oral - so that the storing part of the oral cavity is expanded, take in the food and sea water together in one gulp, squeezes the water out with the use of its tongue etc., and swallows the food.