Dolphins, porpoises, and other toothed whales

Toothed Whale Facts

• Classification:

• Kingdom: Animalia
• Subkingdom: Bilateria
• Phylum: Chordata
• Subphylum: Vertebrata
• Class: Mammalia
• Order: Cetacea (whales)
• Suborder: Odontoceti (toothed whales)
• Families: Delphinidae (dolphins, seventeen genera); Monodontidae (white whales, two genera); Platanistidae (river dolphins, four genera); Phocoenidae (porpoises, four genera); Physeteridae (sperm whales, two genera); Ziphiidae (beaked whales, six genera)
• Geographical location: Found in all earth’s oceans, harbors, and some rivers
• Habitat: Salt water in oceans, brackish water, or freshwater, depending on family
• Gestational period: Between nine and sixteen months, depending on species; one large, well-developed calf (occasionally two) born, tail first; calves often half as long as mothers
• Life span: Estimated twenty-five to forty years, depending on species
• Special anatomy: Toothed mouth; lungs like land mammals; blow hole; flippers evolved from front legs; horizontal tail, nasal cavity that produces echolocation and vocalization

Dolphins and porpoises are toothed whales of the order Cetacea, suborder Odontoceti. Like their distant relatives, baleen whales, toothed whales are mammals that spend their entire lives in earth’s waters. Most toothed whales are found in oceans, but some inhabit harbors and rivers. Odontoceti make up close to seventy of the more than eighty cetacean species, in six families: river dolphins, porpoises, dolphins, sperm whales, white whales, and beaked whales.

All male toothed whales are larger than females. Male sperm whales, the largest toothed whales, are the largest toothed animals in the world. They grow to seventy-foot lengths and seventy-five-ton weights. Sperm whales dwarf all other Odontoceti—Herman Melville’s “Moby Dick” was a male sperm whale. Like all whales, toothed whales are thought to be descended from a land animal, believed to have been an ungulate (hoofed mammal). However, their earliest ancestor was not the same as that of baleen whales. Why ancestors of toothed whales entered the oceans, seventy million years ago, is unknown. It may be that their return to the oceans was due to the need for a new food supply or to escape from predators.

Physical Characteristics of Odontoceti

The most characteristic physical feature of toothed whales is teeth that seize prey. Prey range from small crustaceans for small river dolphins, to squid and cuttlefish for larger dolphins and sperm whales, to walruses and seals or other whales for killer whales. As in all whales, evolution produced streamlined, fishlike mammals, whose front legs became flippers. Flipper bones resemble jointed limbs and some flippers show evidence of digit bones. External hind limbs are long gone, although their vestiges are still seen, internalized. Horizontal tail flukes that propel toothed whales are not anatomically related to hind limbs. As in baleen whales, flukes are made of boneless fibrous-elastic tissue, oriented horizontally, unlike fish tail fins, which are oriented vertically and differ in composition.

The bodies of whales are surrounded by thick blubber (fat) layers. This enhances buoyancy, insulates by preserving body heat, and is a fine energy store. Toothed whales are very fast, some swimming twenty-five miles per hour for prolonged periods and forty miles per hour in short bursts. Specially adapted Odontoceti lungs enable dolphins to dive to depths of almost one-quarter mile. Larger species dive deeper; for example, sperm whales dive to over 1.25 miles. This is because of the presence of waxy spermaceti around sperm whale nostrils. Cooling the spermaceti—by filling nasal passages with cold seawater—raises the whale’s density and helps account for tremendously deep sperm whale dives.

Toothed whales have lungs and breathe air through a nostril. Nostrils, in blowholes atop the head, are closed tightly just before dives. Submerged indefinitely, out-of-breath Odontoceti would drown, though some can submerge for over an hour. Part of the ability to remain submerged is that 30 to 40 percent of oxygen in Odontoceti bodies is stored in muscle in a usable form (compared to 10 to 13 percent in humans). Also helpful to Odontoceti—especially dolphins—is the ability to move blood bidirectionally in blood vessels. This minimizes the effects of diving on the blood pressure and allows blood shunting to or from different organs as needed.

Dolphins, family Delphinidae, travel in groups that vary in number from thousands to a few members. Most dolphins are found in oceans and seas and have, as special characteristics, beaks of varied length. Best known are common dolphins (Delphinus delphis) and bottle-nosed dolphins (Tursiops truncatus). Common dolphins, in legend and in reality, are great friends of humans. Bottle-nosed dolphins are frequent performers in marine aquariums. Both species cavort in the open oceans, leaping with backs arched from waters near ships. Smaller river dolphins live in Asia and South America. Examples are near-sighted buffeo dolphins (Sotalia fluviatilis) and the South Asian river dolphins (Platanista gangetica), which navigate solely by echolocation. Other beakless Delphinidae are large, dangerous killer whales (Orcinus orca) and intelligent pilot whales (Globicephala melas).

Porpoises are smaller than dolphins. They have beakless, rounded heads and triangular dorsal fins. Porpoises are rarely seen in open seas. The most plentiful, harbor porpoises (Phocoena phocoena), inhabit estuaries and inlets of large rivers. They do not follow ships or leap like dolphins. There are also three sperm whale species, the huge sperm whales (Physeter catodon) and two eight- to ten-foot dwarf or pygmy Kogia species. All have spermaceti in their heads. Arctic white whales lack dorsal fins and spermaceti. Male narwhals (Monodon monoceros) have spiral horns up to nine feet long, prized by the people who hunt narwhals for food. The white whale (Delphinapterus leucas, or beluga) is also sought for food. Beaked whales, family Ziphidae, are poorly studied and known most for toothed beaks and their ability to dive deeper and stay submerged longer than any other marine organism.

Special Senses and Odontoceti Intelligence

Odontoceti, especially dolphins, were thought intelligent by the ancient Greeks. Current belief in dolphin intelligence has intensified due to the ability of captive dolphins, in sea aquariums, to learn complex tricks and invent games for themselves and their human keepers. Limited study of sperm whales suggests intelligence, supported by the twenty-pound brains of adult males. Intelligence is extrapolated to other Odon toceti, most of which have not been studied well. Almost all species have brains bigger than the three-pound brains of humans.

Many believe that dolphins and sperm whales have spoken languages. These are reported as vocalizations, including calls that keep groups together and signal danger. Dolphins appear chatty, almost constantly making variegated whistling sounds for alarm, sexual arousal, and other emotions. Moreover, they are very social. They show great affection and caring for each other and their calves. In addition, isolated from other dolphins and human keepers, captive dolphins pine away and die. Most linguistic authorities see dolphin and sperm whale intelligence as close to that of primates.

Odontoceti and baleen whales have small eyes, lack external ears and noses but have well-developed inner ears, and some river dolphin species are blind. These characteristics led to proof that Odontoceti use sound and hearing the way vision and smell are used by land mammals. In addition to vocalization (pseudolanguage) they make echolocation clicks as air moves between nostrils and nasal passages to the lungs. Clicks are bio sonar, as in bats. That is, echolocation is the way Odontoceti explore the world. Directing clicks outward toward objects in the environment causes sound waves to hit the objects. Waves that bounce off are picked up by the whales and identify object size, distance, and so on. The great ability of water to carry and amplify sound is deemed to be why cetaceans discarded external ears. Operation of this sensory system has uses in navigation and predation in murky oceans.

The Life Cycle of Odontoceti

Toothed whales reproduce like other mammals, but in the water. Adults participate in complex courtship: swimming close together, caressing, nuzzling, and rubbing bodies. After copulation, females carry young for nine to sixteen months, depending on species. Then, a large, well-developed calf (occasionally two) emerges underwater, tail first. The reproduction of bottle-nosed dolphins and sperm whales are well studied. In both cases, when a calf is born, other females (aunts) ensure it gets to the surface quickly for a first breath. They reportedly continue to help the mother to protect her offspring.

Calves nurse from teats on the mother’s belly. The milk is rich in minerals, protein, and fat, so calves grow quickly. High maternal affection and protection of calves is found in bottle-nosed dolphins, sperm whales, and the other Odontoceti studied. Calves are weaned in one to two years. They are adults, capable of reproduction, in five years. Life spans vary from twenty-five to forty years. As with other wild animals, not all whales—actually, only a few—get to grow old.

Odontoceti as an Endangered Species

In the past, uncontrolled whaling for spermaceti, blubber, and ambergris made sperm whales and narwhals endangered species. In the early 1990s, the International Whaling Commission (IWC) voted to ban commercial whaling by IWC nations. These actions and the absence of clandestine whaling may allow whales to make a natural comeback. Dolphins, never hunted as much as baleen and sperm whales, are endangered because they are trapped and drown in nets used to catch tuna, a species with which many dolphin species swim. This has been reduced by the refusal of tuna canneries to buy tuna from fleets that do not protect dolphins, an attitude driven by activist consumer public opinion. A 1972 US Marine Mammal Protection Act—amended in 1988 and 1992—diminishes exploitation of dolphins and related mammals.

Despite such protections, toothed whales continued to see their numbers decline during the early twenty-first century. The main dangers facing Odontoceti remained entanglement in fishing gear, including traps, trawls, and gill nets; coastal habitat degradation; and lack of food due to overfishing. According to some studies, nearly one-quarter of small cetaceans were threatened with extinction by 2024. Species, such as the Atlantic Humpback Dolphin and x, were listed on the International Union for Conservation of Nature (IUCN) Red List under the Critically Endangered category.

Principal Terms

ambergris: waxy material from the intestines of sick sperm whales, used in perfume

cuttlefish: a squidlike marine mollusk, eaten by Odontoceti

digit: a finger, toe, or related bony animal structure

echolocation: batlike location, from sound echoes, of unseen objects, used by toothed whales

spermaceti: a waxy substance in the heads of sperm whales; usable for candles, ointments, lubricants, and cosmetics

Bibliography

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Culik, Boris M. Odontocetes: The Toothed Whales. CMS Technical Series No. 24, United Nations Environment Programme, 2011, www.cms.int/sites/default/files/publication/TS24‗odontocetes‗toothed‗whales‗online‗version.pdf. Accessed 24 Sept. 2024.

Darling, James, et al. Whales, Dolphins, and Porpoises. National Geographic Society, 1995.

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