Toothed whales, or odontocetes, are marine mammals belonging to the parvorder Odontoceti, which includes dolphins, porpoises, beaked whales, and sperm whales. They are one of the two existing groups of cetaceans, with the other being baleen whales (Mysticeti). Unlike baleen whales, which use keratinized baleen plates to filter food, toothed whales have true teeth for capturing prey. They rely on echolocation, emitting high-frequency ultrasonic sound waves, to navigate and hunt, a trait absent in baleen whales. The toothed and baleen whales are believed to have diverged around 34 million years ago. Both groups of whales are closely related to hippopotamuses and share a common ancestor that lived about 54 million years ago.
Toothed whales inhabit both marine and freshwater environments, feeding primarily on cephalopods, crustaceans, bivalves, and fish. Despite their typically large size, they can fall victim to predators such as killer whales and, in some cases, terrestrial hunters like polar bears. In addition to natural threats, they face significant dangers from human activities, including illegal hunting, entanglement in commercial fishing nets, and water pollution.
They are generally smaller than their relatives, the baleen whales. Toothed whales vary greatly in size, ranging from the smallest, the vaquita, measuring 4.5 ft (1.4 m) and weighing 120 lb (54 kg), to the largest, the sperm whale, which reaches 66 ft (20 m) and 55 t.
Most species exhibit sexual dimorphism, with the females being larger than the males. However, sperm whales are an exception, as males grow significantly larger than females.
Toothed whales have streamlined torpedo-shaped bodies with two flippers (modified forelimbs with four digits) on the front and a large tail fin. They have bulbous heads with long beaks (except sperm whales) and small eye orbits.
Though most toothed whales lack fully developed hind limbs, some, like the sperm whale, have rudimentary appendages.
All toothed whales, except river dolphins, have a thick, insulating layer of blubber under their skin. In polar species, this fatty layer can reach up to 28 cm (11 in) in thickness, helping them retain body heat in cold environments. This blubber aids in buoyancy and also provides protection from predators.
Unlike baleen whales with keratinized oral plates (baleen), toothed whales have monophyodont dentition, with only a single set of functional, bony teeth throughout their lives. Their numbers vary, with some, like dolphins, having as many as over 100 teeth in their jaws. In contrast, beaked whales are almost toothless, while narwhals possess single long tusks.
Unlike human teeth covered by enamel, the teeth of these whales possess cementum outside the gum. If the cementum at the tip wears away, the underlying enamel becomes exposed.
Auditory
The ears of toothed whales are specially adapted for detecting sounds underwater. Unlike humans with an intermediate middle ear that equalizes impedance between the outer and inner ears, these whales receive sound through their throat, transmitting it via a low-impedance, fat-filled cavity to the inner ear. Moreover, the ear is acoustically isolated from the skull by air-filled sinus pockets for directional hearing.
Toothed whales use a specialized, fat-filled organ in their skull called the melon to generate and focus ultrasonic sound waves for echolocation. This allows them to navigate, communicate, and detect prey with precision. This is in contrast to baleen whales, which produce low-frequency infrasonic sounds.
Vision
The eyes of toothed whales, which are relatively small compared to their body size, are located on either side of their head, providing two fields of vision instead of a binocular view (as found in humans). Most of these whales have slightly flat eyeballs and cornea, enlarged pupils, and a retroreflective tapetum lucidum, all of which allow ample light to pass through the eye. Whales, in particular, have multiple glands on the eyelids and the outer corneal layer that lubricate and protect the cornea.
Belugas have both rod and cone cells in their eyes and thus can see clearly in both dim and bright light.
Olfactaction and Gustation
They lack both olfactory lobes and the vomeronasal organ found in baleen whales and, thus, are thought to lack a sense of smell. Additionally, their taste buds are either highly atrophied or entirely absent, suggesting they also have little or no sense of taste.
The term Odontoceti is derived from the Greek words odontos (meaning tooth) and ketos (meaning whale). The 73 described species are grouped under 10 families.
Both toothed and baleen whales are believed to be descendants of terrestrial artiodactyls (even-toed ungulates).
Members of the genus Squalodon, which lived around 33 to 14 million years ago, exhibit skull features similar to modern toothed whales and serve as the first example of the hypothesized appearance of echolocation in this group.
These whales range from the Arctic to the tropics and occupy both freshwater and marine habitats.
The only species to have a fairly restricted range is the vaquita. It is confined to the Gulf of California in Baja California, Mexico.
They are generalist and opportunistic carnivores that typically consume cephalopods, crustaceans, bivalves, and fish, such as demersal rays. Sperm whales primarily feed on medium-sized squids, but they are also known to consume giant squids, colossal squids, and octopuses.
Many toothed whales are highly social and move around in groups called pods.
These whales have different strategies for capturing prey. Sometimes, they may also forage with other animals, like seals.
These cetaceans propel through the water by moving their tail fin and lower body up and down, allowing for vertical motion. Additionally, they use their flippers constantly to steer forward. Sometimes, they also move to the surface of the water (logging) so that they can travel faster.
They are fast swimmers and typically cruise at around 9 to 28 km/h (5.6 to 17.4 mph). The sperm whale is even faster, traveling at speeds of up to 35 km/h (22 mph).
Dolphins produce three main types of vocalizations through their nasal sacs: burst-pulsed sounds, frequency-modulated whistles, and high-pitched clicks. These clicks are directional and are essential to echolocation (discussed later).
Bottlenose dolphins, in particular, communicate through some signature whistles, which are used to identify individuals. They reciprocate each other by mimicking the whistles and eventually remembering them for the future.
Sperm whales produce three distinct vocalizations: creaks (rapid high-frequency clicks used for hunting prey), codas (short click patterns, typically 3 to 20, used for social identification), and slow clicks (typically heard in the presence of males).
Echolocation
Most toothed whales emit high-frequency clicks through the nasal sacs, focus them using their melon, and receive returning echoes via their lower jaw, which, in turn, transmits vibrations to the inner ear. These clicks help determine the distance of predators, prey, and impediments on their path.
Toothed whales are polygynous, where the males or bulls typically mate with multiple females (cows) every year. A single female typically mates every two to three years.
After a gestation period of about a year, the females give birth to a single calf (typically during spring or summer) in a tail-first position to prevent it from drowning. The mother then nurses the young, squirting milk into its mouth. The young are weaned within 1 to 2 years and reach sexual maturity approximately 7 to 10 years later.
These whales are preyed upon by orca or killer whales and terrestrial predators like polar bears. Dolphins (particularly the calves) are attacked by large sharks, such as the bull shark, dusky shark, tiger shark, and the great white shark.
All toothed whales face both direct and indirect threats to their existence.
Keeping in mind the threats these cetaceans face, they have been listed under the CITES appendices, and hence, their international trade is fairly limited. Moreover, the ASCOBANS protects small whales in the North and Baltic Seas and the northeast Atlantic, while the ACCOBAMS protects species in the Mediterranean and Black Seas.
The UNEP Convention on Migratory Species lists 7 species in Appendix I and 37 in Appendix II.
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