Dolphins are mammals fully adapted to live in the water. For this, they developed several adaptations during their evolution.

The migration of dolphins to the aquatic environment was a process that lasted millions of years. Moving from the terrestrial to the aquatic habitat entailed a series of adaptations without which this would not have been possible.

Physiology is the science that studies the functions of living beings. In the case of dolphins, it is interesting to know how they perform their physical and chemical functions in their changing environments.

HOW DO DOLPHINS REGULATE THEIR TEMPERATURE?

Dolphins should maintain a constant body temperature of about 36°-37° Celsius degrees.

Dolphins need to keep a body temperature of about 36°-37° Celsius degrees. As they do not have a coat to protect from the cold temperatures of the water, they must regulate their internal temperature in other ways; this process known as thermoregulation is vital for their survival.

Dolphins perform body thermoregulation through a set of internal resources that evolution provided them. Initially, the fat in their body is a thick layer that insulates the inside from the cold water. This layer allows dolphins to retain their body heat. Secondly, their flippers do not contain fat, but instead, they have a lot of veins so that the heat of the blood that runs through the arteries transfers to the blood of the veins. This process is a heat exchange system.

In hot environments, dolphins increase blood flow to their limbs. The veins and capillaries expand, and this way excess heat can be released.

HOW DO THEY SWIM?

The fusiform and hydrodynamic body of dolphins is perfect for reducing water resistance when swimming, which allows them to save energy. Contrary to fish, these cetaceans swim by moving the tail from top to bottom and not from side to side. Their tail has a strong propulsive force, and the flippers are useful to direct their movements.

Typically they do not need to dive very deep, but they can do it for a few minutes to obtain food if needed. Dolphins that inhabit the cooler waters are better suited to dive deeper, as they have more body fat. Besides the time their need to resist down without breathing, the water temperature dramatically drops in places where the sunlight does not reach.

When dolphins dive, their heart rate slows down, and protein molecules take care of providing oxygen to the body tissues.

One of the most evident differences between cetaceans and fish is their swimming method. Fish swim by wiggling left and right, and if you watch crocodiles and snakes, you’ll see the same motion. However, as dolphins are mammals with a different skeletal structure, they make up and down strokes to swim.

Today you can still see some of the remnants of their terrestrial ancestors in the dolphin’s skeletal structure. For instance, they have forelimbs, which became flippers with shortened arm bones and no fingers. Hind limbs exist as vestigial skeletal remains. Most cetaceans, including dolphins, still have a pelvis typical of land animals.

HOW DO DOLPHINS BREATHE?

Dolphins, like other mammals, get the oxygen from the air instead of the water and thus use lungs instead of gills. A dolphin that cannot surface and breathe will drown; this is why dolphins caught in fishing nets die.

Like all mammals, dolphins have a pair of lungs that process the air that they breathe in through their blowhole. That’s why most Dolphins stay close to the surface of the ocean.

Unlike humans that do it instinctively, dolphins have to reach the surface to breathe consciously. When they do this, the blowhole opens to allow the air in and closes when they get back into the water.

The lungs process the air and take the oxygen from it releasing it into the bloodstream and when exhaling the lungs release the carbon dioxide from the blood into the environment.

How do dolphins breathe?
Blowhole.

HOW DO DOLPHINS SLEEP?

As mentioned above, dolphins breathe consciously. Therefore, their brain needs to give the order to reach the surface to get air continuously. As a consequence, they could not sleep until unconsciousness as humans do. Otherwise, they would drown and would be vulnerable to predators.

Dolphin blowhole does not expel a stream of water, it looks this way, but it is only water vapor that condenses in the air when they exhale.

The solution that evolution found for dolphins is that while resting, they have to keep a cerebral hemisphere active to consciously breathe and to stay alerted from dangers. However, the versatile adaptations of dolphins to changing environments is fantastic, because researchers found that captive dolphins apparently have a deeper sleep than dolphins in the wild since they do not react to minor external stimuli while sleeping.

Incidentally, there is a wrong belief that dolphins and other cetaceans expel a stream of water from their blowhole, but this is not the case. It is only water steam that condenses in the air when they exhale.

Blowhole.

HOW DO DOLPHINS REPRODUCE?

The reproduction of dolphins is sexual, and the fertilization is internal. Both males and females have the reproductive organs concealed inside slits in their body. Mothers have the mammary glands also hidden inside slits.

The gestation period has a similar duration to that of humans and females give birth to live and developed offspring, which are fed with breast milk and cared for over a relatively extended period. The relationship between a mother and its offspring lasts forever.

WHAT SENSES DO DOLPHINS HAVE?

They have some of the traditional senses that we have: hearing, sight, taste, and touch, but evolution provided dolphins with an additional sense that only a few animals have: echolocation or biosonar.

Dolphins produce sounds that emit forward and interpret the echo that returns to them with the aim of discovering prey, navigating, communicating or detecting dangers.

Probably one of the most relevant differences between land mammals and dolphins is the way they vocalize. While most terrestrial animals have a larynx or a similar structure to vocalize using throat vibrations and exhaled air. Dolphins and other cetaceans use other organs to make high-pitched sounds either for echolocation or regular communication with others members of the pod.

Regarding the other senses, dolphins do not have external ears, but they have a good hearing capacity with an internal ear that receives sounds through the throat.

Also, Dolphins have a vision much better than one might expect of an animal that uses echolocation as its primary way of sensing the world. Despite this, dolphins can see little or no colors and have limited binocular vision like primates. Their eyes are small but even though they have a good sight with a reduced capability to distinguish colors.

They have an excellent sense of touch improved in some species with sensible hairs and frequently used for social purposes.

Dolphins do not have olfactory lobes. Therefore they lack the sense of smell.

Finally, their sense of taste is not especially good because they do not have a very developed taste buds, but they show some preferences to certain fish species which could be an indicator of taste, although this could be an intuitive behavior because some types of fish have better nutrients for them than others.

These organs and senses are the structures that help these cetaceans to keep in perfect harmony with its context.

References

https://dolphins.org/physiology

Coates, Linda. How to Make a Dolphin: Anatomy, Physiology and Taxonomy (English Edition).

Knut Schmidt-Nielsen. Animal Physiology: Adaptation and Environment. Cambridge University Press, 1997.

Dolphins have the ability to communicate with each other, and for that purpose, they use sounds and body movements. Scientists have been very interested in the way they produce sounds, and the studies they have carried out show that dolphins are animals with a diversity of sounds and a complex language.

Sound waves travel nearly 4.5 times faster in the aquatic environment than in the air. The sounds are essential in the life of any dolphin and in general, of any cetacean. Dolphins communicate, hunt, avoid predators and orient themselves when navigating through sound emissions in the water, therefore, they are very sensitive animals to noises emitted in and out of the water.

Not all sounds are the same. They vary in frequency, volume, wavelength and pattern and depend on the intention or the situation in which the dolphins are. If they are scared, excited or in a context of socialization, they tend to make whistles, but if they are in trouble, they make clicks with their jaws. In general, they communicate using low-frequency sounds but emit other high-frequency signals when using echolocation.

Most people have heard the chirping, squeaking noises made by dolphins which they use to communicate with other dolphins or for echolocation. Dolphins can use echolocation to detect even a three-inch object as far as the length of a football field.

Sounds are essential in the life of any dolphin and in general, of any cetacean.

TYPES OF SOUNDS

Within the range of sounds that dolphins produce are whistles, squeaks, crunches, clicks and some similar to screams. From a general perspective, the sounds can be burst-pulsed or frequency modulated. Sometimes a separation of a burst of clicks to the previous ones is made when used for echolocation and not precisely for communication between the members of a pod.

Dolphins produce frequency modulated sounds by changing the tone while emitting them, that is, it can go up or down. Pure whistles, squeaks, and squeals are frequency modulated sound. Bottlenose dolphins have a “signature whistle,” well differentiated from other sounds, which identifies a particular dolphin from the others.

On the contrary, the burst-pulsed sounds are brief, emitted successively and at regular intervals. In this category are clicks and bursts produced when the cetacean emits clicks remarkably fast.

DOLPHIN COMMUNICATION PROCESS

Dolphins produce sounds from the vibrations of an air sac in their respiratory cavities. They lack vocal cords, so they are unable to make emissions with them.

Production and emission.
When the air enters through the blowhole the nasal air sacs swell and Some structures of the nasal passages, called phonic lips, open and close continuously, making vibrate the surrounding tissues, generating sound waves.

The waves group in bundles in the melon and the dolphin directs them forward. Then the sound waves bounce back when they find objects in their path.

Reception.
Part of the signal bounces back and returns to the dolphin as an echo. It may seem strange, but the bones of the lower jaw are the principal areas of reception of sounds. From there they travel to the inner ear and then to the auditory centers of the brain.

Interpretation.
The brain receives the returned sound waves in the form of nerve impulses, and the dolphin can interpret the echo.

One of the primary uses of sounds by dolphins is for echolocation, which is an ability of Odontoceti cetaceans, based on the emission of sounds and the interpretation of their echo.

DO DOLPHINS HAVE LANGUAGE?

Whether or not dolphins have language is a matter for debate unless and until we humans figure out how to speak to them. But evidence is mounting that dolphins may indeed have a language.

There is a lot of research on dolphin vocabulary that indicates they communicate with at least as much sophistication as the higher apes. They have a lexicon of danger sounds, food sounds, seeking sounds, and sometimes they put these sounds together in a reasonably sophisticated fashion. There is evidence that they may greet one another by name because they utter unique sounds when meeting other dolphins.

DOLPHINS AND MAN-MADE SONAR

Dolphins are incredibly good at distinguishing their echolocation sounds even in very noisy underwater environments. It has also been found, though, that some noisy locations confuse dolphins.

Beaching is probably the most tragic thing that we can see: a pod of dolphins that have apparently killed themselves by swimming onto a beach and lodging themselves there.

Why do dolphins do this? The most accepted theory is that something confuses their echolocation, taking them to the beach instead of the open ocean. Some autopsies of beached dolphin bodies show a very high percentage of damaged hearing, suggesting that a powerful sound may have blown out their hearing.

Although dolphins see quite well, without their hearing sense, they are disoriented and blinded. And when one dolphin beaches itself, the others are at risk because they will try to help it.

References

https://dolphins.org/acoustics

http://biol.wwu.edu/mbel/media/pdfs/AquatMamm2004_30.pdf

https://www.uaeh.edu.mx/scige/boletin/prepa3/n1/r2.html

Janik, Vincent; Laela Sayigh (7 May 2013). “Communication in bottlenose dolphins: 50 years of signature whistle research”. Journal of Comparative Physiology.

Dolphin Mysteries: Unlocking the Secrets of Communication. Yale University Press. 2008.

Denise L. Herzing. Dolphin Communication and Cognition: Past, Present, and Future. MIT Press, 2015.

Along with human beings, dolphins belong to a group of creatures considered to be intelligent. The intellect of these cetaceans is not superior to the human’s, although some scientists believe that the intelligence of dolphins is different and the comparison in human terms is not fair.

THE BRAIN AS THE CENTER.

Dolphins have larger brains than humans and a complex neocortex.

When it comes to comparing the brain sizes of living creatures, it is done assessing the ratio between brain size and body size. The dolphin case is exceptional. They have brains larger than those of humans and a highly complex neocortex ( the type of cerebral cortex in charge of processes associated with reasoning and consciousness).

The fact that dolphins have a larger brain than other mammals is still an issue. Some theories state that is the result of the need for sound detection and processing, and to a superior intelligence.

The ability to process external stimuli depends on the anatomy of the brain and the dolphin’s experiences, which are the interactions and perception of the world. To do this, dolphins have highly developed senses and high intelligence.

DEVELOPED SENSES

Like humans, dolphins are entirely dependent on their senses for survival in their environment, but the difference with Homo sapiens lies in a sixth sense useful for feeding.

Sight.
Most dolphin species have a very sharp vision in and out of the water thanks to the eyes that can move independently, and to the curvature of the eyeball. Their visual range is 180°, so they can see forward, backward and sideways, but they can not look up, and this explains why they are seen chasing prey swimming in a position with the back downward.

The retina of their eyes has rod cells and cones cells. This feature suggests that they cannot distinguish colors, but so far this has not been confirmed, and most think that they can only differentiate shades of gray.

However, not all dolphins species can see. River dolphins do not enjoy the same sense of their saltwater relatives and, either they have weak vision, or they are blind, as it is the case of the Indus dolphin (Platanista gangetica minor). This lack of vision is because the suspended sediments in the river waters that reduce the sunlight, therefore, the river dolphins do no need to look at their surroundings. However, they do have the other senses.

Smell.
This sense is not very developed. Dolphins lack olfactory nerves and lobes. Therefore this sense is inexistent or very limited.

Hearing.
Dolphins do not have external ears, but they have small holes on each side of the head, which conduct to the inner ear. They have 2 to 3 times more cells in the ear than humans, and thus they can detect low-frequency and high-frequency sound waves as well as the tone of sounds.

The lower jaw captures sound waves underwater. It might sound strange because it has no holes to listen to, but it drives the sounds into the ear through a cavity filled with fat. Their teeth also play an important role since they are a kind of antennas that receive the sounds.

+ River dolphins do not have the sense of sight like their saltwater relatives, and even may be blind.

Taste.
There is not much data about this sense, but it is present in dolphins because they show clear preferences for particular types of food. Their habit of testing the water functions as a sensor for the presence of objects or prey that are not in their mouth.

Bottlenose dolphins identify four basic flavors: sweet, salty, bitter and sour. The ability to taste goes beyond the preference of the food: it could be useful for the orientation, reproduction, and location of other dolphins.

Touch.
The skin of dolphins is very sensitive due to a large number of nerve endings they have below it, mostly around the snout, pectoral flippers, and genitals.

They are very susceptible to the water flowing through their body and use their sense of touch in social and sexual contexts.

Dolphins also have a highly developed sense of touch due to the nerve endings in their skin. The nerves seem to be more sensitive around the snout and the pectoral fins, but their entire body is very sensitive.

Echolocation or biosonar.
This sense works emitting high-frequency sounds (200,000 cycles per second) through a specialized organ called “the melon.” The sounds bounce back when they find an object, like prey, and return to the dolphin in as an echo. The teeth pick up the returning sound, and it is drawn to the auditory nerve and then to the brain through the lower jaw. The use of echolocation gives dolphins the possibility of knowing the shape, size, weight and density of the object and even to identify some species or dangers.

Dolphin senses are paramount to the overall survival of the dolphin. They use the information collected through them to interpret and to determine how to act or protect themselves.

References

https://seaworld.org/en/animal-info/animal-infobooks

Ronald Schusterman, J. A. Thomas, F. G. Wood. Dolphin Cognition and Behavior: A Comparative Approach. Psychology Press, 2013.

Denise L. Herzing. Dolphin Communication and Cognition: Past, Present, and Future. MIT Press, 2015.

https://en.wikipedia.org/wiki/Dolphin#Senses

Echolocation is a process that permits dolphins to send out sound waves that when they hit an object, are bounced back, allowing them to identify the location, shape, and size of such object.

The amount of time it takes for the sound waves to come back help them to determine the distance, as it takes longer the sound waves to return when there is more distance between the dolphin and that given object.

The first person to look at echolocation thoroughly and to document the findings was Jacque-Yves Cousteau. He wrote about it in a book published in 1953 called The Silent World.

Echolocation or biosonar is the ability of some animals to locate objects through sound waves, that is, sounds. Many animals, including odontocete cetaceans and some bats, make use of echolocation to orient themselves and detect prey.

The process of evolution of dolphins gave them this ability that allowed them to survive in the aquatic environment. In water, the sound waves travel 4.5 times faster than in the air, so echolocation is the perfect resource that facilitates their survival.

WHY DOLPHINS USE ECHOLOCATION?

Dolphins need echolocation to navigate, locate prey, hunt, protect themselves from predators in murky waters or where there is no sunlight and to communicate. In fact, in deep dark waters, their sense of sight is almost nil, but they do not need it because they can detect and chase fast prey through the emission of sounds.

Most odontocete cetaceans can emit very high-frequency sounds. In this sense, the frequencies vary according to the species, but there are general characteristics in all dolphins. For example, they always communicate with low-frequency signals, which include whistling or chirping; But they emit high frequencies when using echolocation. The sounds vary according to the circumstances and the purpose.

Dolphins need echolocation to navigate, locate prey, hunt, and protect themselves.

HOW DO ECHOLOCATION WORKS?

First, is necessary to know that dolphins are devoid of vocal cords, so they do not have a “voice” like that of humans. Instead, they generate sounds through other internal structures.

Step number 1: Generate sounds.

Dolphins produce sounds from the nasal air sacs, the blowhole, the larynx, the lungs, and the melon; This latter is an organ located in the upper inner area of ​​the head filled with low-density lipids.

First, the dolphin opens the blowhole to make an inhalation and the nasal air sacs swell as the air enters the lungs. Then the dolphin exhales: the air resonates in the nasal sacs and comes out with pressure through the blowhole. Vibrations occur in the larynx, and the nasal air sacs deflate.

For echolocation, dolphins emit ultrasounds called “clicks” by pushing air between the phonic lips of the nasal passages. When these lips open and close, the surrounding tissues vibrate and produce sound waves.

The passage of air through the respiratory cavities generates the sounds.

Step number 2: Amplify sounds.

The Dolphins have an organ in the head, called melon, that allows the transmission of the sound waves.

The melon concentrates the pulsations that the dolphin emits and sends them forward. The primary “function” of this organ is to group sounds into beams and produce and amplify the resonance.

Once the emission is released forward, the sound waves bounce back in the objects that are in the water.

Step number 3: Reception and interpretation of sounds.

A part of the signal bounces back in the objects and returns as an echo to the dolphin. Their brain receives the sound waves in the form of nerve impulses, and the dolphin can interpret this echo.

The receiver of the returning sound waves is in the lower jaw, and the teeth of dolphins work like antennas to receive the signals. It is a very complex adaptation vital for their survival.

The intensity, pitch, and time that it takes the echo to return to the dolphin provide information about the target, such as its size, shape, composition, position, distance, and direction. Based on this, the dolphin builds an image of its environment and the object.

Echolocation has been studied in bottlenose dolphins (Tursiops truncatus), although there are still underlying aspects that are not entirely understood. For now, scientists see echolocation as a learning opportunity to create new communication technologies in some areas of human life.

DOLPHIN ECHOLOCATION

What is known is that dolphins have the ability through echolocation to emit sounds with a frequency of 120 kHz and humans, with excellent hearing, can hear sounds with frequencies ranging from 20 Hz to 20 kHz. Even dogs and cats that have amazing hearing capabilities do not compare to dolphins. Dogs hear up to 45 kHz, and cats up to 65 kHz.

However, high-frequency sounds don’t travel very far in the water while Low-frequency sounds have more energy and can reach greater distances. Most of the time, dolphins will get the best results with echolocation when the object is from 16 to 656 feet from them.

Excessive noise in the environment should be upsetting for dolphins and can cause them to lose their hearing over time. It can also disorient them and disrupt their navigation systems.

References

Kathleen Dudzinski, Toni Frohoff. Dolphin Mysteries: Unlocking the Secrets of Communication. Yale University Press, 2014.

Jeanette A. Thomas, Cynthia F. Moss, Marianne Vater. Echolocation in Bats and Dolphins. University of Chicago Press, 2004

Whitlow W.L. Au. The Sonar of Dolphins. Springer Science & Business Media, 2012.

https://link.springer.com/chapter/10.1007/978-1-4612-1150-1_9#page-1

https://seaworld.org/en/animal-info/animal-infobooks/bottlenose-dolphins/communication-and-echolocation

The overall anatomy of the dolphin is designed to survive in the water. All dolphins have similar anatomical and morphological characteristics; this means that all species have some features that do not differ widely between species.

Obviously, there are differences in skin color, shape, size and weight but it is relatively easy to recognize that a particular animal observed is a dolphin. However, it is common to confuse porpoises with dolphins, and this is because their external appearance is very similar and both are cetaceans closely related. The difference is that porpoises are smaller animals and have rounder snouts than dolphins.

Their size can range from one extreme to the next. Some of the smaller ones are about 4 feet in length, and others measure as long as 30 feet. Some of them weigh about 90 pounds while others tip the scale around 11 tons.

The coloring of dolphins is mainly grayish blue, brownish or black and white. They have a very sensitive skin, which can get easily harmed if hit by rough surfaces. However, they can recover pretty fast from severe injuries, including shark bites because they have a rapid healing process even for deep wounds.

Their skin feels like rubber, and they don’t have any sweat glands. Part of this though could be due to the thickness of the skin of a dolphin. The epidermis, which is the outer layer of skin, is from 10 to 20 times thicker than that of other terrestrial mammals. The skin will peel and flake off for new skin cells to replace the older ones.

The bone structure of a dolphin.

Dolphins have a streamlined body designed to swim very fast, even for extended periods of time. The tail of a dolphin has two parts called flukes, and they use them to propel their body through the water, using their pectoral flippers to swim in a given direction.

Dolphins have a blowhole at the top of their head, and they must come to the surface for air. Some of them need to breathe several times a minute, and some species only have to get air twice per hour. They also have a large brain, the second largest for mammals in comparison to their body size, only after humans. Their brain is very complex, and research shows it to be more advanced than that of other animals.

What anatomical features characterize a dolphin? Let’s see:

GENERAL FEATURES

– Weight and size.

Dolphins vary in weight and size. There are small species as the Maui dolphin, which measures on average 1.7 meters in length and weighs about 50 kilograms, and there are large species that reach 5 to 8 meters in length like the Orca (Orcinus orca) which, by the way, is the largest and heaviest extant dolphin.

– Skin color.

The skin of dolphins feels soft to the touch although it has a thick epidermis covered with a thin layer of cornified cells. Despite this, it is extremely sensitive due to a large number of nerve endings it has on the exterior. Given this fragility, it damages very easy with any contact of a rough surface and even human fingernails, but if this happens, the healing process is fast and develops a dark scar in the tissue, which later turns white.

Beneath the skin, there is a thick layer of fat that dolphins use as an energy reserve in periods of food shortage, as an insulation to prevent heat loss in cold environments and as a resource that helps maintain the hydrodynamic shape of their body.

Most species have a gray or bluish color on the dorsal area and white or light gray in the ventral area. This coloration is particularly useful for camouflage because if you see a dolphin from above, its dark skin is confused with the ocean floor while when seeing it from below, the color of its belly is similar to the ocean surface, brightened by the sunlight.

However, not all species have the same color pattern described above. The Amazon river dolphin (Inia geoffrensis) has a pink color on its skin, therefore is known as the “pink dolphin.” Also, some species have stripes or spots of different sizes, colors, and shapes.

Skeleton.

The bone structure of dolphins is lighter than that of terrestrial mammals as it has to withstand less weight in the water. Dolphins have an adjustable rib cage, thanks to which they can swim in low-pressure environments without suffering damage. The neck is rather short because the seven cervical vertebrae are fused together.

The skeleton still retains vestiges of a terrestrial life, like a pair of floating bones under the backbone that should have been a pelvis.

On the other hand, the body of the dolphins is fusiform and hydrodynamic, perfectly adapted to life in the water. It has three main parts, head, trunk and tail, which include other elements.

External anatomy of a common dolphin.

Head

Brain.
The brain of these cetaceans is large, and its mass is slightly greater than that of humans. It is 15-60 times bigger than the brain of a shark of similar size.

Eyes.
Located on each side of the head, they provide a broad field of view and are very sensitive despite the inability to identify colors. They can move independently of one another, but they are not able to look directly up or down.

Ears.
Dolphins do not have external ears, but they have small openings behind the eyes, which lead to an ear canal.

Blowhole.
It is the orifice located at the top of the head that serves to breathe and to make sounds. It has a kind of muscular membrane that prevents water from entering the body when the dolphin is submerged.

Melon.
It is a spherical organ located in front of the skull, used for echolocation. The rounded shape of this mass of adipose tissue is what gives dolphins the shape of their forehead.

Mouth.
Located in the front area of ​​the head, it has several teeth whose number varies according to the species, but they are around 80-100. The jaws are elongated and play a significant role in the sensory system of the dolphin.

Trunk

Dorsal fin.
It is on the top of the dolphin; they only have one dorsal fin that gives them stability when swimming, preventing them from spinning involuntarily in the water. There are a couple of species that lack this dorsal fin.

Flippers.
In the lower part of their body, dolphins have two pectoral flippers which are curved, useful for directing and controlling movements and speed when swimming.

Lungs.
Like all mammals, dolphins have lungs and breathe air. They are the organ of the respiratory system which process the air inhaled through the spiracle. Unlike humans that do it instinctively, dolphins breathe conscientiously.

The orca is the largest and heaviest dolphin.

Stomach.
It is just in the middle part of the body, and it has several sections.

Intestines.
Just as in other mammals, they serve to absorb nutrients from the food and remove the unused material from it.

Bladder.
It is nearly at the end of the trunk, and it is tiny.

Post-anal hump.
It is a protuberance in the lower part of the body only found in adult males.

Genitals.
Also in the inferior part of the body, the genitals of dolphins are hidden in slits. Males have two slits that conceal the penis and anus, while the females have only one that contains the vagina and anus, and two mammary slits on both sides of this one.

Tail

Peduncle.
It is the narrow section that connects the flukes with the rest of the body.

Caudal fin.
They function as a propellant when swimming. It moves from top to bottom and not from side to side as in the case of fish.

Flukes.
They are the two sections of the caudal fin.

OTHER ANATOMICAL ADAPTATIONS.

Sleeping.
Dolphins do sleep, but it may not appear that way when you observe them; This is because only one hemisphere of the brain will rest at a time. The other allows them to be alert for dangers and to reach the surface for breathing at regular intervals.

Another unique characteristic of the dolphin anatomy is that they don’t have hair covering their body; They may be born with a few hairs, but they lose them soon after being born.

References

https://dolphins.org/anatomy

http://www.sciencedirect.com/science/article/pii/0361923080902725

Cozzi, Huggenberger, Oelschläger. Anatomy of Dolphins: Insights into Body Structure and Function. Academic Press, 2016.

http://oceantoday.noaa.gov/dolphinanatomy/

Communication, strictly meaning, involves the transmission and feedback of coded messages. However, the complexity of the communication processes seems to be exclusive to the human race.

Despite this, it is clear that dolphins have a sophisticated communication system which is the reason for their success against their predators. In short, dolphins survive because they communicate with each other and this allows them to organize and cooperate to increase their probabilities of survival.

HOW DO DOLPHINS COMMUNICATE?

Dolphins communicate through the emission and reception of sounds; Each dolphin develops its distinctive sound since the first years of life. All individuals produce a unique sound, which is different to the others so they can fully identify each other.

Dolphins emit two types of vocal sounds: continuous tone and burst-pulsed sounds.

But, how do they produce these sounds? While dolphins are devoid of vocal cords, they emit sounds through their larynx, in the region of the nasal air sacs. These sounds do not mean that dolphins have a voice, but there is a tissue in the nasal area that has structures that project in the duct. When the air passes through that section, the tissue vibrates, and so the sound is produced.

Dolphins emit two types of vocal sounds: continuous tone and burst-pulsed sounds. The first type includes whistles, squeaks and some species of squeals. They are “frequency modulated sounds” because dolphins modify the tone of the sound, this is, it can rise and fall over time. The burst-pulsed sounds are recognized by the superposition of sound waves and refer to the “clicks,” produced successively at regular intervals.

WHERE, WHEN, WHAT

Different emissions, different context. Dolphins can make sounds to interact socially: when they separate from their peers, when they are excited, when alarmed or just when they feel happy. The sound depends on the situation. Lost dolphins have been observed to produce whistles frantically in an attempt to call their companions, and individuals of some species emit pulsating sounds if they become excited or angry; Apparently, this is intended to make known their emotional state to other dolphins.

Sometimes bottlenose dolphins (Tursiops truncatus) produce a blast that invites other individuals to play, as a way of informing them that they are in a good mood and want to have fun with them. Very high pulsating sounds are used during aggressive encounters to call other dolphins, and others direct to the genital area of ​​females when males chase them and flee. Mothers often whistle their offspring for several days after birth.

Bottlenose dolphins distinguish different frequencies depending on what they want to communicate. Low-frequency sounds (0.25-50 kilohertz) are used to communicate in social situations while high frequencies serve in echolocation. Another case: during the aggressive persecutions of Indo-Pacific dolphins (Tursiops aduncus), they issue a kind of crunch that is called “pop” sound.

The human ear perceives successive clicks as a sound without interruption, but the truth is that they are short. We do not know much about the purpose of the different sound emissions and researchers are still working on sound-target identification.

SIGNALS WITHOUT “VOICE.”

Although dolphins rely primarily on sounds to exchange information, they also communicate through touch and body language:

Identification of body coloring patterns.
Stains, stripes, and specks may indicate to other dolphins the health status or the age of their companions. For example, the skin of the Atlantic spotted dolphin (Stenella frontalis) develops spots when it begins to get old, and the scars in the skin of the Risso dolphin (Grampus griseus) informs others of their combat skills and experience.

Postures.
The body positions convey the idea of ​​the dolphin’s mood. An S-shaped posture demonstrates anger or aggression and is a way of saying “do not mess with me now.” If they are in a fight, they can expand their pectoral fins and extend their jaws to look bigger and more dangerous.

Touch.
The skin of these cetaceans is very sensitive to the touch. If they are in a good mood, then they can make physical contact with the flippers by pressing them against the flippers of another dolphin.

Tail Slapping.
It is a vertical blow of the tail against the water surface that often indicates aggressiveness, but it can also express the desire to leave the area where they are or ask for attention.

Flipper Slapping.
It probably has the same goals as the blows on the surface with the tail, but in this case, Dolphins hit their flippers against their body or the water surface.

DOLPHIN LANGUAGE AND COMMUNICATION

Dolphins are almost constantly making one of two kinds of sounds: communicative or navigational. They produce these different sounds in a variety of ways.

Echolocation sounds are produced in their nasal passages just below their blowholes and are called clicks. Dolphins create these clicks sometimes in such rapid succession that they sound like buzzes or even quacks. These sounds are produced just behind the melon, an oily, slightly off-center lump on what you’d call the dolphin’s forehead, and the sound waves are focused forward through this organ.

Scientists are not entirely certain how the melon works, but it does seem to amplify, clarify and direct the dolphin’s echolocation sounds which allow dolphins to detect remarkably detailed information from the world around them. In one test, a dolphin found a marble-sized sphere at more than the length of a football field. Some scientists speculate that echolocation sounds may also be used to deliver an acoustic shock to small prey.

In the larynx, dolphins can produce high-pitched whistles and squeals which can rapidly change pitch. Whistles are single tones, with no vibrations that make them sound like buzzes. As far as scientists can tell, the whistles are a form of communication with other dolphins, and squeals are used to express alarm or sexual excitement.

DOLPHIN COMMUNICATION

Like some other animals, dolphins do have communication. But do they communicate linguistically? There’s some evidence for it. Dolphins tend to stay within their pods and may have trouble understanding “foreign” dolphins. In studies done on dolphins near Scotland, individuals appear to have names; or at least, other dolphins use specific and unique whistles only in the presence of certain other dolphins, as if calling them by name. Unlike any other animal besides humans, dolphins exhibit a tendency to take turns when vocalizing – making their communications sound like a conversation.

There have also been very basic linguistic studies of dolphin sound patterns. According to some studies, dolphin sounds follow the same basic patterns of all human-based language, from Morse code to Chinese.

References

https://dolphins.org/communication

Denise L. Herzing. Dolphin Communication and Cognition: Past, Present, and Future. MIT Press, 2015.

Thomas I. White. In Defense of Dolphins: The New Moral Frontier. John Wiley & Sons, 2007.

Roitblat, Herman, Nachtigall. Language and Communication: Comparative Perspectives. Psychology Press, 2013.

http://www.bbc.com/news/science-environment-23410137

https://seaworld.org/en/animal-info/animal-infobooks/bottlenose-dolphins/communication-and-echolocation