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 sixty-seven of seventy-seven
cetacean species, in six families: river dolphins
(five species), porpoises (six species), dolphins
(thirty-two species), sperm whales (three species),
white whales (two species), 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 anewfood supply or to escape frompredators.
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 onequarter 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 (Turisops truncatis). Common dolphins, in legend and in reality, are great friends of humans. Bottlenosed 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 blind Ganges dolphins (Platanista gangetica), which navigate solely by echolocation. Other beakless Delphinidae are large, dangerous killer whales (Orcinus orca) and intelligent pilot whales (Globocephala malaena). The seven porpoise species 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 catadon) 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 very 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 Odontoceti, 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, but do not rate their communication as language. 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 biosonar, 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. Only the reproduction of bottle-nosed dolphins and sperm whales is 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. At the beginning of the twenty-first century, there is little sanctioned whaling for large Odontoceti, initially due to quotas set by the International Whaling Commission (IWC). By the early 1990's, most whaling by IWC nations stopped. 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 U.S. Marine Mammal Protection Act- amended in 1988 and 1992-diminishes exploitation of dolphins and related mammals.
Order: Cetacea (whales)
Suborder: Odontoceti (toothed whales)
Families: Delphinidae (dolphins, seventeen genera); Monodontidae (white whales, two genera); Platanistidae (river dolphins, four genera); Phocoenidae (porpoises, three genera); Physeteridae (sperm whales, two genera); Ziphiidae (beaked whales, five 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
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