The bottlenose dolphin is a in the genus Tursiops. They are common, members of the family , the family of . show the genus contains three : the (Tursiops truncatus), the (Tursiops aduncus), and (Tursiops erebennus). Others, like the (Tursiops (aduncus) australis), may be alternately considered their own species or be subspecies of T. aduncus. Bottlenose dolphins inhabit warm and seas worldwide, being found everywhere except for the and regions. Their name derives from the Latin tursio (dolphin) and truncatus for the truncated teeth (the type specimen was old and had worn down teeth; this is not a typical characteristic of most members of the species).

Numerous investigations of bottlenose dolphin intelligence have been conducted, examining , use of , object categorization, and . They can use tools (sponging; using marine sponges to forage for food sources they normally could not access) and transmit cultural knowledge from generation to generation, and their considerable intelligence has driven interaction with humans. Bottlenose dolphins gained popularity from shows and television programs such as . They have also been trained by militaries to locate or detect and mark enemy divers. In some areas, they cooperate with local fishermen by driving fish into their nets and eating the fish that escape. Some encounters with humans are harmful to the dolphins: people hunt them for food, and dolphins are killed inadvertently as a of fishing and by getting caught in .

Bottlenose dolphins have the third largest levels of any mammal on Earth (humans have the largest, followed by ), sharing close ratios with those of and other , while being twice as high of other . This more than likely contributes to their high .

Taxonomy

Scientists have been long aware of the fact that the Tursiops dolphins might consist of more than one species, as there is extensive variation in color and morphology along its range. In the past, most studies used morphology to evaluate differences between and within species, but in the late 20th century, combining morphological and molecular genetics allowed much greater insight into this previously intractable problem. Since the late 1990s and early 2000s, most researchers acknowledged the existence of two species: the (T. truncatus), found in coastal and oceanic habitats of most tropical to temperate oceans, and the (T. aduncus), that lives in coastal waters around , northern Australia, South China, the , and the eastern coast of Africa.

In 2011, a third distinct species was described, the (T. (aduncus) australis), found in the and areas of , Australia, after research showed it was distinct from T. truncatus and T. aduncus, both in morphology and genetics. Also, evidence has been accumulating to validate the existence of a separate species, Lahille's bottlenose dolphin, T. gephyreus, that occurs in coastal waters of Argentina, Uruguay and southern Brazil. Other sources accept the Pacific bottlenose dolphin (T. t. gillii or T. gillii), that inhabits the Pacific, and has a black line from the eye to the forehead.[] T. gillii, first described in 1873, is currently considered a of T. truncatus. Additionally, T. nuuanu was described in 1911 for bottlenose dolphins along the Pacific coast in Central America. An analysis of T. gillii and T. nuuanu specimens supported T. gillii as a synonym of T. truncatus, while T. nuuanu was recognized as a subspecies. In general, genetic variation between populations is significant, even among nearby populations. As a result of this genetic variation, other distinct species currently considered to be populations of common bottlenose dolphin are possible.

Much of the discussion and doubts about its taxonomy is related to the existence of two of bottlenose dolphins in many part of its distribution. For example, the two ecotypes of the common bottlenose dolphin within the western North Atlantic are represented by the shallower water or coastal ecotype and the more offshore ecotype. Their ranges overlap, but they have been shown to be genetically distinct. In 2022, Costa et al. established morphologic, genetic, and evolutionary divergence between the two ecotypes in the western North Atlantic, resurrecting Tursiops erebennus for the coastal form while the offshore form was retained in T. truncatus.

The 's Committee on Taxonomy presently recognizes three species of bottlenose dolphin: T. truncatus, T. aduncus, and T. erebennus. They also recognize three subspecies of common bottlenose dolphin in addition to the : the Black Sea bottlenose dolphin (T. t. ponticus), Lahille's bottlenose dolphin (T. t. gephyreus), and the Eastern Tropical Pacific bottlenose dolphin (T. t. nuuanu). The IUCN, on their of endangered species, currently recognises only two species of bottlenose dolphins. The also recognizes only two species. While acknowledging the studies describing T. australis, it classifies it within T. aduncus.

Some recent genetic evidence suggests the Indo-Pacific bottlenose dolphin belongs in the genus , since it is more like the (Stenella frontalis) than the common bottlenose dolphin. However, more recent studies indicate that this is a consequence of (such as past hybridization between Stenella and ancestral Tursiops) and , and thus support T. truncatus and T. aduncus belonging to the same genus.

Hybrids

Bottlenose dolphins have been known to with other dolphin species. Hybrids with occur both in the wild and in captivity. The best known hybrid is the , a -bottlenose dolphin hybrid. The wholphin is fertile, and two currently live at the Sea Life Park in Hawaii. The first was born in 1985 to a female bottlenose. Wholphins also exist in the wild. In captivity, a bottlenose dolphin and a hybridized. A -bottlenose dolphin hybrid born in captivity lives at California. Other hybrids live in captivity around the world and in the wild, such as a bottlenose dolphin-Atlantic spotted dolphin hybrid.

Fossil species

Bottlenose dolphins appeared during the . Known fossil species include Tursiops osennae(late Miocene to early ) from the coastal mudstone, and Tursiops miocaenus (Miocene) from the marine sandstone, all in Italy.

Description

The bottlenose dolphin weighs an average of 300 kg (660 lb), but can range from 150 and 650 kg (330 and 1,430 lb). It can reach a length of just over 4 m (13 ft). Its color varies considerably, is usually dark gray on the back and lighter gray on the flanks, but it can be bluish-grey, brownish-grey, or even nearly black, and is often darker on the back from the rostrum to behind the . This is called and is a form of . Older dolphins sometimes have a few spots.

Bottlenose dolphins can live for more than 40 years. Females typically live 5–10 years longer than males, with some females exceeding 60 years.This extreme age is rare and less than 2% of all Bottlenose dolphins will live longer than 60 years. Bottlenose dolphins can jump to a height of 6 metres (20 feet) in the air.

AnatomySee also:

Their elongated upper and lower jaws form what is called a rostrum, or snout, which gives the animal its common name. The real, functional nose is the on top of its head; the is visible when the blowhole is open.

Bottlenose dolphins have 18 to 28 conical teeth on each side of each jaw.

The flukes (lobes of the tail) and dorsal fin are formed of dense and do not contain or . The dorsal fin usually shows phenotypic variations that help discriminate among populations. The animal propels itself by moving the flukes up and down. The (at the sides of the body) are for steering; they contain bones to the forelimbs of land mammals. A bottlenose dolphin discovered in Japan has two additional pectoral fins, or "hind legs", at the tail, about the size of a human's pair of hands. Scientists believe a caused the ancient trait to reassert itself as a form of .

Physiology and senses

In colder waters, they have more body fat and blood, and are more suited to deeper diving. Typically, 18%–20% of their body weight is blubber. Most research in this area has been restricted to the . Bottlenose dolphins typically swim at 5 to 11 km/h (1.4 to 3.1 m/s), but are capable of bursts of up to 29 to 35 km/h (8.1 to 9.7 m/s). The higher speeds can only be sustained for a short time.

Senses

The dolphin's search for food is aided by a form of known as : it locates objects by producing sounds and listening for the echoes. Clicking sounds are emitted in a focused beam in front of the dolphin. When the clicking sounds hit an object in the water, like a fish or rock, they bounce off and come back to the dolphin as echoes. Echolocation tells the dolphins the shape, size, speed, distance, and location of the object.To hear the returning echo, they have two small ear openings behind the eyes, but most sound waves are transmitted to the inner ear through the lower jaw. As the object of interest is approached, the echo becomes booming, and the dolphins adjust by decreasing the intensity of the emitted sounds. (This contrasts with and sonar, which reduce the sensitivity of the sound receptor.) The interclick interval also decreases as the animal nears the target. Evidently, the dolphin waits for each click's echo before clicking again. Echolocation details, such as signal strength, spectral qualities, and discrimination, are well understood by researchers. Bottlenose dolphins are also able to extract shape information, suggesting they are able to form an "echoic image" or sound picture of their targets.

They also have . The calves are born with two slender rows of whiskers along their snout, which fall off soon after birth, leaving behind a series of dimples known as vibrissal pits able to sense electric fields.

Dolphins have sharp eyesight. The eyes are located at the sides of the head and have a , or reflecting membrane, at the back of the retina, which aids vision in dim light. Their horseshoe-shaped, double-slit pupils enable dolphins to have good vision both in air and underwater, despite the different indices of refraction of these media. When under water, the eyeball's lens serves to focus light, whereas in the in-air environment, the typically bright light serves to contract the specialized pupil, resulting in sharpness from a smaller aperture (similar to a ).

By contrast, a bottlenose's sense of smell is poor, because its blowhole, the analog to the nose, is closed when underwater and it opens only for breathing. Like other , it has no olfactory nerves or olfactory lobe in the brain.Bottlenose dolphins are able to detect salty, sweet, bitter ( ), and sour () tastes, but this has not been well-studied.Anecdotally, some individuals in captivity have been noted to have preferences for food fish types, although it is not clear if taste mediates this preference.

In 2022, a study at the in Scotland found that dolphins were able to identify their "friends" and family members by the taste of their urine in the water.

Communication

Bottlenose dolphins communicate through burst pulsed sounds, whistles, and body language.Examples of body language include leaping out of the water, snapping jaws, slapping the tail on the surface and butting heads. Sounds and gestures help keep track of other dolphins in the group, and alert other dolphins to danger and nearby food. Lacking , they produce sounds using six air sacs near their blow hole. Each animal has a uniquely identifying, frequency-modulated narrow-band signature vocalization ().

Signature whistles, which are in a higher range than humans can hear, have an important role in facilitating mother–calf contact. In the Sarasota Dolphin Research Program's library of recordings were 19 female common bottlenose dolphins (Tursiops truncatus) producing signature whistles both with and without the presence of their dependent calf. In all 19 cases, the mother dolphin changed the same signature whistle when the calf was present, by reaching a higher frequency, or using a wider frequency range.Similarly, humans use higher fundamental frequencies and a wider pitch range to inflect (CDS). This has rarely been discovered in other species. The researchers stated that for humans are cueing the child to pay attention, long-term bonding, and promoting the development of lifelong , with parallels in these bottlenose dolphins in an example of .

Researchers from the Bottlenose Dolphin Research Institute (BDRI), based in (Italy) have now shown whistles and burst pulsed sounds are vital to the animals' social life and mirror their behaviors.

The tonal whistle sounds (the most melodious ones) allow dolphins to stay in contact with each other (above all, mothers and offspring), and to coordinate hunting strategies. The burst-pulsed sounds (which are more complex and varied than the whistles) are used "to avoid physical aggression in situations of high excitement", such as when they are competing for the same piece of food, for example. The dolphins emit these strident sounds when in the presence of other individuals moving towards the same prey. The "least dominant" one soon moves away to avoid confrontation.

Other communication uses about 30 distinguishable sounds, and although famously proposed by in the 1950s, no "dolphin language" has been found. However, , Richards, and Wolz demonstrated comprehension of an artificial language by two bottlenose dolphins (named and Phoenix) in the period of skepticism toward following 's critique.

IntelligenceSee also: Cognition

abilities that have been investigated include , sensory skills, and mental representations. Such research has been ongoing since the 1970s. This includes: acoustic and behavioral mimicry, comprehension of novel sequences in an ,, monitoring of self behavior,discrimination and matching, comprehension of symbols for various body parts,comprehension of pointing gestures and gaze (as made by dolphins or humans), , and numerical values.

Tool use and cultureSee also:

At least some wild bottlenose dolphins use tools. In , off , dolphins place a on their , presumably to protect it when searching for food on the sandy sea bottom. This has only been observed in this bay (first in 1997), and is predominantly practiced by females. A 2005 study showed mothers most likely teach the behavior to their offspring, evincing culture (behavior learned from other species members).

Mud plume feeding is a feeding technique performed by a small community of bottlenose dolphins over shallow seagrass beds (less than 1 m) in the in the United States. The behavior involves creation of a U-shaped plume of mud in the water column and then rushing through the plume to capture fish.

Along the beaches and tidal marshes of and in the United States, bottlenose dolphins cooperatively herd prey fish onto steep and sandy banks in a practice known as "strand feeding". Groups of between two and six dolphins are regularly observed creating a bow wave to force the fish out of the water. The dolphins follow the fish, stranding themselves briefly, to eat their prey before twisting their bodies back and forth in order to slide back into the water. While initially documented in South Carolina and Georgia, strand feeding has also been observed in Louisiana, Texas, Baja California, Ecuador, and Australia.

Some dolphins cooperate with human fishermen. The dolphins drive a school of fish towards the shore, where humans await with nets. In the confusion of casting nets, the dolphins catch a large number of fish as well. Intraspecies cooperative foraging has also been observed. These behaviors may also be transmitted via teaching. Controversially, Rendell and Whitehead have proposed a structure for the study of cetacean culture. Similar cases have been observed in in since during 19th century as well.

Near , in , several bottlenose dolphins "", whereby they elevate the upper part of their bodies vertically out of the water, and propel themselves along the surface with powerful tail movements. Tail-walking mostly arises via human training in dolphinaria. In the 1980s, a female from the local population was kept at a local dolphinarium for three weeks, and the scientist suggests she copied the tail-walking behavior from other dolphins. Two other wild adult female dolphins copied it from her, and the behaviour has continued through generations until 2022.

A study conducted by the showed that bottlenose dolphins can remember whistles of other dolphins they had lived with after 20 years of separation. Each dolphin has a unique that functions like a name, allowing the marine mammals to keep close social bonds. The new research shows that dolphins have the longest memory yet known in any species other than .

The bottlenose dolphins of John's Pass in Boca Ciega Bay, , exhibit a rare form of self-decoration and social object use called grass-wearing. Self-decoration by wearing grass appears to be an attention-getting device rather than purely play and varies from a single blade to large clusters of grass. John's Pass dolphins self-decorate with grass primarily when they form new social groups or engage in procreative activities. Grass-wearing behavior among these dolphins is a local behavioral tradition that could constitute a cultural difference from other communities.

Cortical neurons

Some researchers hypothesize that the number of nerve cells () in the predicts intelligence in . A 2019 study estimated the of three common bottlenose dolphins and found numbers ranging from 11.7 to 15.2 billion neurons. The human average being approximately 16 billion, this is likely within the range found in the human population.

Life history

Bottlenose dolphins have a lifespan of 40–60 years. Females can outlive males and live for 60 years or more. Dolphins start to reproduce aged 5 to 15 years.

Respiration and sleep

The bottlenose dolphin has a single located on the dorsal surface of the head consisting of a hole and a muscular flap. The flap is closed during muscle relaxation and opens during contraction. Dolphins are voluntary breathers, who must deliberately surface and open their blowholes to get air. They can store almost twice as much oxygen in proportion to their body weight as a human can: the dolphin can store 36 milliliters (ml) of oxygen per kg of body weight, compared with 20 ml per kg for humans. This is an adaptation to diving. The bottlenose dolphin typically rises to the surface to breathe through its blowhole two to three times per minute, although it can remain submerged for up to 20 minutes.

Dolphins can breathe while "half-asleep". During the sleeping cycle, one brain hemisphere remains active, while the other hemisphere shuts down. The active hemisphere handles surfacing and breathing behavior. The daily sleeping cycle lasts for about 8 hours, in increments of minutes to hours. During the sleeping cycle, they remain near the surface, swimming slowly or "logging", and occasionally closing one eye.

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