About 77 species of whales occur worldwide in oceans and other water bodies. Though perfectly adapted to an aquatic way of life, whales probably evolved 65 million years ago from a land-living ungulate that fed on dead animals.

Whales are cigar-shaped and have vestigial hind limbs. Their skeletons are not designed to carry body weight but instead are merely a place to attach muscles. Many whales have blubber that can be up to eight inches thick, serving primarily as a food store and secondarily as insulation.

The huge baleen whales include only 10 species, such as the blue whale, which is the largest animal to ever live, measuring about 100 feet long and weighing as much as 33 African elephants. Baleen whales are toothless and possess baleen, which are horny plates that originate from the upper jaw and may be up to eight feet long. Baleen filter tiny plankton (up to three inches long) as food, much like a comb.

The right whale is another baleen whale. It was hunted off the eastern coast of North America beginning in the 16th century, influencing settlement of the coast by Europeans in New England. It was the "right" whale to hunt because it swam only about 4 mph and provided about 120 to 130 barrels of oil (used as an illuminant), meat (about 1,500 pounds) and baleen (used to stiffen clothes for "fashionable" women). However, since 1970, right whales and other whales have been protected as endangered species.

Another famous baleen whale is the humpback whale, which can be seen around Cape Cod. Songs of this whale, which can last from six to 35 minutes in length, were discovered during World War II when they interfered with naval acoustics. Their songs probably serve some communication role in reproduction.

Besides the baleen whales, there are about 67 species of toothed whales. Depending on the species, the number of peg-like teeth may range from two to 200. The toothed whales, known as sperm whales of Moby Dick fame, have huge heads that are one-third their body length (about 50 feet). Sperm whales are champion divers, being able to feed on the sea bottom at least two miles below the ocean's surface.

One interesting toothed whale is the beluga or white whale of the Arctic. They are sometimes called sea canaries because of their musical trills.

Dolphins and porpoises are small toothed whales, measuring five to 18 feet in length. Dolphins have a well-defined beak, whereas porpoises have a more rounded head. Probably one of the most feared dolphins of Hollywood fame is the killer whale, or orca. This 30-foot-long dolphin hunts in packs, much like wolves, and feeds on sea animals, ranging from other whales to seabirds. Speaking of musical whales, what do you call a whale band? An orca-stra.

Bottlenose dolphins are conspicuous along shorelines and often are seen in groups by people vacationing at the shore. This dolphin also is commonly found in captivity at aquarium displays. Dolphins are extremely smart. In fact, they can train a human to stand on the side of a pool and feed them fish (just kidding). The harbor porpoise is seen occasionally in the lower Delaware River in southeastern Pennsylvania. Unlike dolphins, porpoises are usually inconspicuous, are not gregarious and seldom are used in aquarium displays.