Dolphins are highly sociable mammals that establish close links with other individuals of the same species and even with dolphins of other species sometimes. They seem to show empathic, cooperative, and altruistic behaviors.

Most species live in groups called pods composed of 2 to 30 dolphins as the number varies, but in some areas with abundant food, many pods can merge forming superpods with more than 1,000 members.

Dolphins depend on this interaction for hunting, mating and defending themselves. In some cases, these superpods include more than one species of cetaceans that seem to interact well together.

PODS, THE REASON

Why do dolphins group? They have several reasons to join, besides following a sample learned since they born. Small dolphin species gather into multi-member pods as a way to compensate for their size when facing predators.

In this sense, these groups provide protection to an animal that does not have large jaws or razor sharp teeth. When Dolphins are together, it is easier for them to survive if they cooperate with each other, either through communication or intimidating the predator if it is a large number of individuals.

DYNAMIC OF THEIR SOCIAL STRUCTURES

It seems that dolphins are free spirits. Studying the dynamic of the social composition of the pods, scientists discovered that when dolphins belong to a group, nothing binds them to it in a matter of space and time, this means that they can move freely to different pods that are in their vicinity, then the movement of members is continuous.

This type of social network is flat and open, and scientists found no evidence of a rigid, closed or semi-closed structure, so dolphins do not have permanent “membership” in any pod.

These open associations are another indication of their high intelligence since these actions require a lot of brain capacity. Likewise, the hydrodynamic shape of their body supports the need to move continuously between several groups of different environments.

Even though pods do not lack social hierarchy, this depends on the species. For example, bottlenose dolphins (Tursiops truncatus) establish dominance biting, chasing and striking their tails or fins against the surface of the water. The marks of teeth remain in the skin of the dolphins and are practically in all the species meaning that confrontations are also part of their life. That is why, when they want to demonstrate “who rules here,” they may not be so charming as usual but more aggressive than we think.

On the other hand, the composition and structure of the groups depend on certain circumstances: age, sex, family ties, reproductive condition and even the history of associations. Studies on the behavior of dolphins indicate that dolphins can have preferences for meeting with particular individuals and that they can be remembered and recognized after experiencing extended periods of separation. Amazing, right?

Dolphin social structure.

TYPES OF PODS

The characteristics of the groups differ according to the number of members and the circumstances mentioned above. Dolphins do not behave the same when they change from one pod to another.

There are three types of pods:

Nursery groups (mothers-offspring).
A calf stays with its mother from birth up to a few years after weaning. Usually, the mother’s bond with her son is very close and continues until the young dolphin is 6 or 8 years old. Since offspring are vulnerable, the females with calves join and form groups where they help each other to feed and protect their offspring. If a young female gets pregnant, she can return to her natal pod to give birth and care for her calf along with her female relatives, forming a multigenerational group.

The males usually do not get close to these groups.

Juvenile pods.
When reaching a certain age, both males and females leave their breeding group and join with other young dolphins, but curiously, they go to the group of their mothers occasionally for a while and then return to their youth group.

Two male dolphins can stay together for 10, 15 or 20 consecutive years.

The members of these groups are engaged in socializing with others and establishing a preamble to mating. Genres, however, are not intimately related for extended periods of time and once a female becomes pregnant, she joins the nursery group.

Adult males.
The structure of the male pods is very complex and similar to a human male group, you will see why.

Often males are related to 2 or 3 individuals of the same gender and create partnerships for cooperation purposes. Two male dolphins can stay together for 10, 15 or 20 consecutive years. The smaller groups have the objective of cooperating to ensure the mating of the others with a specific female. The larger groups make alliances with other herds of males to defend themselves but also to compete. They continue moving from pod to pod throughout their lives.

INTERNAL SOCIAL STRUCTURE

Males are dominant in all groups, but there is no evidence of strong social bonds between them and females. An example of social interaction and their high intelligence is the regular playing activities they perform. Juvenile and adult dolphins often chase each other and toss items such as seaweed back and forth.

Most experts believe that the social relationships formed by dolphins are long lasting.

Dolphins often have close body contact with other dolphins through rubbing, petting, and even hitting each other.

COMMUNICATION, THE GROUND FOR SOCIALIZATION.

Dolphins communicate with their pods usually through whistles. Each dolphin has a unique whistle that identifies it with other members of its group. If an individual is in distress, it uses a particular sound that indicates help is needed, so the pod responds quickly.

SOCIAL ACTIVITY BEYOND LIMITS.

Although it would be normal that dolphins socialize only with their kind, the interest of some species of dolphins to interact with humans is evident. In the wild, dolphins are extremely curious, and they will often engage in contact with people if a chance comes up. In captivity, dolphins are very attached to the people that usually interact with them, like trainers or researchers.

References

William F. Perrin, Bernd Würsig, J.G.M. ‘Hans’ Thewissen. Encyclopedia of Marine Mammals. Academic Press, 2009.

Karen Pryor, Kenneth S. Norris. Dolphin Societies: Discoveries and Puzzles. University of California Press, 1998.

https://link.springer.com/chapter/10.1007/978-1-4757-9909-5_7#page-1

http://www.cbmwc.org/wp-content/uploads/2012/01/Social-structure-of-bottlenose-dolphins-in-Cardigan-Bay-by-Cally-Barnes.pdf

]]> https://www.dolphins-world.com/dolphin-predators/ Thu, 27 Apr 2017 05:34:08 +0000 http://www.dolphins-world.com/?p=123 Dolphins have an exceptionally high-fat content, which makes them and other cetaceans an excellent source of nutrition for predators who stalk throughout the ocean. However, dolphins are more trouble than it’s worth and most predators learn to avoid dolphin pods, including sharks.

Dolphins will circle protectively around the weak members of the pod, and viciously attack anything that approaches in a threatening manner. And they can kill sharks. Most predators take one look, and then just swim away.

Like any animal, dolphins are sometimes victims to other species that seek to feed on them or get some other benefit from their body. But besides humans and other aquatic animals, they have a small number of natural enemies. In fact, some species do not have any.

In fact, the natural predators of dolphins kill very few specimens compared to the deaths of those predators who do not belong to their aquatic environment.

PREDATORS IN THEIR NATURAL HABITAT

Orcas (Orcinus orca) and large sharks dispute the title of “The most dangerous predator of dolphins,” and is that both, with their size and other physical characteristics and, of course, their natural need to feed on meat, find dolphins attractive.

Killer whales.
For some species, this mammal is the most deadly predator, and it is also a dolphin! Orcas feed on a wide variety of fish, mollusks, and crustaceans, but if they find a dolphin, they do not hesitate to grab it and feed on it. They usually catch the smallest individuals, the small species or the young.

Sharks.
It is common that sharks kill dolphins. Usually we hear that sharks are the mortal enemies of dolphins, but in reality, this is only because of their feeding instinct and not a particular “hate” or antagonism towards dolphins.

The smallest species are a common prey of bull sharks (Carcharhinus leucas), dusky sharks (Carcharhinus obscurus), tiger sharks (Galeocerdo cuvier) and great white sharks (Carcharodon carcharias). The most vulnerable dolphins are usually young and calves.

In some regions, sharks are the most dangerous group of predators that dolphins have to face, such as on the east coast of the United States. Sharks have species preferences; For example, bottlenose dolphins (Tursiops truncatus) are the favorite of the sharks mentioned above.

Killer whale – Apex predator.

Some researchers suspect that the attacks on dolphins do not always intend to kill for food, but only to defend what they consider their territory. However, scars on the skin of dolphins indicate that bites are evidence that sharks strike from below and behind the dolphins.

A surprising fact for many people, regarding the relationship between dolphins and sharks, is that they can tolerate each other perfectly in the same area and feed on the same bank of fish. Sometimes they completely ignore each other despite being a few meters apart.

But dolphins also defend themselves. Although they usually avoid sharks or flee from them, if necessary, they show aggression and show their most powerful defense system: The pod! When the group is together and alerted, sharks prefer to go away and avoid the pod which can quickly kill him.

Bottlenose dolphins sometimes attack these predators by striking their bodies with the caudal fins (tails). However, this defensive behavior is not very common with sharks.

THE MOST DANGEROUS PREDATOR

As with most species today, their most dangerous threat is the man. Sometimes, humans kill dolphins not because they are a source of food, but because they prey on the same fish species than humans. Therefore, many fishers have killed dolphins only because they are a competition for the fish.

In some countries, people eat cetaceans, including dolphins. In Japan, the meat of some species is seen as a delicacy and can cost up to $25 USD a pound.

In Peru and some other Latin American countries where the fish is becoming scarce due to overfishing or environmental conditions such as El Niño, desperate fishers have turned to catch dolphins and porpoises to sell them in fish markets.

Even more, there are some countries like the Faroe Islands, where killing and eating cetaceans, including dolphins, is a longstanding cultural tradition.

The presence of humans on Earth does not give dolphins many possibilities to survive. In the dynamic predator-prey, one side has to die so the other lives, but what happens when it is not about survival, but about business?

Without a doubt, humans are the biggest predator of dolphins. Their commercial activities endanger the life of these cetaceans directly and indirectly. Let’s look at some:

Dolphin Hunting.

The highest numbers of dolphin killings are in Asia, Africa, and South America. Dolphin meat is consumed in several parts of the world even though it is suspected to have high concentrations of mercury. Thousands of dolphins die every year, and the annual slaughter in Japan is infamously known. Sadly, dolphins put little or no resistance when massacred by humans.

Bycatch.

Tragically, the largest group of dolphins killed by man are those killed by accident or incidentally during large-scale fishing operations. Dolphins and other cetaceans that swim into these nets following fish, become entangled and drown when they can’t reach the surface to breathe or tear off parts of their body in their struggles to escape.

Dolphins die when incidentally caught by gillnets and trawl nets, without the intention to hunt these cetaceans.

Fishers have found that tuna swim beneath dolphins in high numbers, so they get caught when nets are deployed to catch tuna. Though the surviving dolphins are released, estimations indicate that at least 30 million dolphins have been killed in this way since the observations began in the 1960s.

Reduction of the habitat.

The construction of structures and the contamination reduces the number of healthy habitats turning some of them unsuitable. Intimately linked to pollution.

Pollution.

Every day millions of gallons of polluted water, toxic substances such as pesticides, heavy metals, plastic trash and hundreds of other hazardous materials are released into the ocean and the rivers. Their habitat becomes contaminated and causes illness and death. Especially, river dolphins are dangerously threatened by pollution because most of the rivers where the five river dolphin species live have high concentrations of pollutants.

Unintentional deaths.

Other unfortunate accidents are also deaths by collision against propellers or any other parts of boats.

References

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

https://seaworld.org/en/animal-info/animal-infobooks/killer-whale/diet-and-eating-habits

http://www.tandfonline.com/doi/abs/10.1080/13880291003705145

]]> https://www.dolphins-world.com/dolphin-physiology/ Thu, 27 Apr 2017 05:27:25 +0000 http://www.dolphins-world.com/?p=129 HOW CAN MAMMALS SURVIVE IN THE OCEAN?

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

HOW TO BECOME A DOLPHIN AND NOT DIE IN THE ATTEMPT?

The reproductive habits of dolphins are not defined exclusively by the need to perpetuate the species. Like humans, these cetaceans mate for pleasure with individuals of the opposite sex, of the same genus or even a different species to their own, so talking about reproductive habits in strict terms does not apply to dolphins. Some researchers think that their recreational sexuality has social purposes.

When mating with the intention to produce offspring, their habits are varied. The age of sexual maturity depends on the geographical region they inhabit, the genus and the species, but most dolphins reach sexual maturity between five and eight years of age. Males take longer and can be sexually mature at the age of 11. Occasionally they begin to have sexual contact before they can reproduce.

Now, how do dolphins breed?

Most dolphins reach sexual maturity between 5 and eight years of age.

1. CONDITIONS.

Before copulation, the necessary conditions must exist to take place. Sometimes sexual maturity is not relevant, but so is the receptivity of females. The mating season of bottlenose dolphins and other species lasts during the whole year although in some areas of the world more sexual contact may occur during the spring and autumn months.

The age of maturity for dolphins varies significantly among species. For females, the age can range from 5 to 13 and for males, it is often much later with the range being from 9 to 14 years of age.

Dolphin offspring.

Females can be receptive during the 365 days fo the year, and like males, they have several partners in the same season. Dolphins are not very direct; this means that before mating they strive to get the attention of the opposite sex by manifesting a well-identified courting process.

They can begin the contact by chasing each other and giving very soft bites to the partner. His eyes take on a languid look, and the dominant individual floats softly under the body of the passive dolphin. At the moment before the mating, the male touches the female and after that, they mate joining their bellies. However, other species are aggressive and bite or scratch their partner.

The act is brief and lasts for a few seconds although it can be repeated several times in a short time interval.

Males can be very aggressive towards each other when it comes to the right to mate. They make sounds to warn each other off, and they may collide their bodies against each other. The use of the fluke is very common when it comes to males trying to show their strength.

The males can be very aggressive with females that aren’t very responsive to the advances, but if she is receptive to the male, then he seems to be more relaxed. There can be plenty of touching and interacting with a pair of dolphins before mating takes place. The pair will likely engage in mating several times over a period of a few days.

2. BABY ON BOARD.

The pregnant female has a gestation period according to its species. The most usual time is between 11 and 12 months. Incredibly, the gestation of an orca lasts about 17 months, more or less. For all other species, it is in that given range, and even location can play a role in when the offspring will be born. In some regions, the birth period coincides with the nurturing season for the calves.

It is very rare for twins to be born, but there are a few cases. Almost all births though are singles, and it is quite an amazing experience.

3. NEXT TO MOM.

When a female feels she will deliver her calf, she tends to move away from her pod and separates herself to an area near the water surface to facilitate the first breath of her calf.

They usually have one offspring, and the first thing that comes out of the mother’s body is the dolphin’s tail. A calf is born measuring between 90 and 120 centimeters and weighing approximately 18 kilograms. Immediately the mother pushes her baby to the surface to obtain oxygen.

Mother with her calf.

The newborn has dark skin and lighter bands that run through his torso called fetal bands that disappear after several weeks. Both the dorsal fin and the pectoral flippers are very soft but harden over time; The dorsal fin stiffens a few hours after birth.

The young can weigh 23 to 65 pounds at birth. They will consume milk from their mother for one year to 3 years being introduced to fish and squid though when they are around four months of age. The fat in the mother’s milk helps them to grow very quickly.

The calves are coordinated to swim, they have their eyes open, and their senses are fully alert.

At the same time, other dolphins of the pod keep close to the offspring and the mother. When the pod is in movement, the young are at the center of it, with protection all around to help them have the best chance of survival.

4.- A LONG LIFE.

Dolphins can stay up to 4-8 years with their mother.

The behavior of females with their offspring is different according to each mother. Some are comfortable allowing their calf swimming almost freely, but others are more “overprotective.” Very much like human mothers. If a child is healthy the mother is calm, and her behavior is normal, but if her offspring have health problems, she behaves abnormally.

During the first days of life, a baby is nursed every 20 minutes during the 24 hours and usually follows its mother when swimming. Breastfeeding lasts for 2-3 years, but Dolphins can stay up to 4-8 years with their mother, often helped by some other female.

After being fully weaned, the males will leave the pod and join another one while the females may live in the same pod as their mother for their entire life.

A mature dolphin will usually only have one calf every 3 to 6 years. This slow rate of reproduction is one of the common problems that makes it hard to increase the numbers of any species of dolphin.

Dolphins can have a long life under natural conditions. According to the species, its longevity is between 20 and 80-90 years.

References

Slooten, Elisabeth. Age, growth, and reproduction in Hector’s dolphins. Canadian Journal of Zoology, 1991.

https://dolphins.org/maternity

Silva Jr, J.; Silva, F.; Sazima, I. “Rest, nurture, sex, release, and play: diurnal underwater behaviour of the spinner dolphin at Fernando de Noronha Archipelago, SW Atlantic – Mating behaviour”.

Richard C. Connor, Michael R. Heithaus. Complex social structure, alliance stability and mating access in a bottlenose dolphin ‘super-alliance’. 2001.

FROM DAY TO NIGHT.

Most dolphins are active during the 24 hours, both day and night although they are mainly active during the morning and afternoon. Everything they do during the day depends on the conditions of their habitat, the season of the year (breeding season, mating, etc.), the time of the day and the physiological conditions of their bodies.

SLEEPING BEHAVIOR.

There was a general uncertainty about the way dolphins sleep, but after several studies, it became evident that they do sleep but not the way humans do. Since they need some degree of consciousness to reach the surface and breathe, they keep one cerebral hemisphere active while the other rests. However, dolphins in captivity have an entirely different resting behavior than wild dolphins as they keep their blowhole off the water and do not respond to light stimuli, apparently having a deeper sleep, perhaps because they are not concerned about predators in their tanks that could threaten them.

One unusual behavior is when they do a sort of “a cough,” throwing their food out.

The case of the Indus river dolphin (Platanista gangetica minor) is particular because of its habitat; the river full of dangerous materials, muddy waters and strong currents, allow this dolphin to rest only 4-60 minutes in short bursts throughout the day.

TRAVEL BEHAVIOR.

Some species move from one place to another in an almost straight direction. They can travel alone or in the company of other individuals, swimming on the surface of the water to save the energy produced by the friction of the water on the submerged body, to orient themselves better or to get rid of the parasites in their skin. If they are resting, they group tightly and surface often to breathe.

FEEDING BEHAVIOR.

The feeding activities can be carried out individually or in groups, cooperating with each other to capture larger prey and having less energy expenditure. One unusual behavior is when they do a sort of “a cough,” throwing their food out.

The dolphins of Shark Bay, Australia, have demonstrated to the astonished researchers that they have traits of a culture development, understanding this as a set of knowledge, ideas, beliefs, customs, and practices learned in a society and transmitted from generation to generation. This conclusion was the result of watching these cetaceans protecting their “snout” from rough surfaces with marine sponges, and later their offspring also did this; a behavior that was not inherited but transmitted from parents to their offspring.

LET’S PLAY!

Dolphins are very curious and enjoy playing with objects and other dolphins. They jump up to 4.9 meters above the surface of the water falling on their backs or with their belly down. They often follow the waves of the stern or the bow of boats.

They jump up to 4.9 meters above the surface of the water.

Most dolphins play chasing one another, using objects and passing them on to others for attention. They commonly make bubbles in the water and take the time to recreate themselves in the ocean. Occasionally, this playful behavior includes other species of dolphins and animals such as Risso dolphins (Grampus griseus), Pantropical spotted dolphins (Stenella attenuata), pilot whales (Globicephala) and humpback whales (Megaptera novaeangliae).

Other games are only fun for them; they have been seen catching birds and submerging them several meters down, without eating them later.

THIS BEHAVIOR IS NOT NICE …

The habitat of dolphins also has a lot of dangers. If they notice something unpleasant near the pod, they quickly react swimming to the surface, exhaling, striking the water with their tail and grouping very close to each other. Any external element that disturbs dolphins has negative consequences that include stress, wounds, abnormal migrations and even less reproductive success.

Adult males swim in the perimeter of the pod territory to monitor the environment and to communicate others the presence of danger if something happens. Usually, dolphins avoid sharks or flee if they are in the proximity, but there are cases in which these cetaceans have attacked and killed sharks.

Normally, dolphins avoid sharks or flee if they are near, but if necessary, they know how to defend from them.

FRIENDLY DOLPHINS

The sociability of dolphins is evident due to their continuous association with other dolphins of the same species and occasionally interactions even with other species of cetaceans and animals in general.

If there is something for which people recognize dolphins, it is because of its charming “personality.” Docile and friendly to the human presence, they are also close with their companions. They establish strong social ties, assist wounded dolphins, cooperate to feed themselves and survive, and even voluntarily approach divers and bathers. Did you know that there are unconfirmed reports of dolphins helping humans to fish and sometimes they even offer them fish, octopus, and squid as gifts?

References

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

Dr. Denise L. Herzing. Dolphin Diaries: My 25 Years with Spotted Dolphins in the Bahamas. St. Martin’s Press, 2011.

Karen Pryor, Kenneth S. Norris. Dolphin Societies: Discoveries and Puzzles. University of California Press, 1998.

http://sanctuaries.noaa.gov/dolphinsmart/pdfs/behavior_factsheet.pdf

The intelligence of dolphins is one of their most outstanding features. Among the thousands of members that the animal kingdom has, dolphins take one of the top places regarding intelligence.

The brain is the organ involved in the ability of understanding, reasoning, learning, and other cognitive processes. The dolphin’s brain is astonishingly complex, almost comparable to that of humans. And it is large related to their body. Through magnetic resonance imaging, their brains have been found to be 4-5 times bigger than those of other animals of similar sizes.

The bottlenose dolphin (Tursiops truncatus) is the second place in a list of species with a higher encephalization ratio (EQ), which compares the mass of the encephalon against its body size.

In addition to a developed neocortex, the cerebellum has more convolutions (turns of the brain surface) than that of other mammals. The connections between the neurological areas and the motor areas of the organ exhibit a great sensitivity to pain and a pronounced tendency to stress.

Some scientists claim that the social intelligence of these cetaceans competes with that of the great apes.

Most of their behaviors show the development of their brain and their ability to understand situations. They process information from their environment in a similar way to people, and some say that they can solve problems like humans. For example:

– Their forms of communication are complex, evolving and diverse.

– They are creative and playful animals. Their behavior is not mechanical or rigid; they seem to enjoy playing and look for the companionship of other individuals.

– Their empathy suggests that they experience emotions such as sadness or joy.

– They have an excellent learning ability; this is why they are highly requested animals for water parks, although the activities of these places are highly controversial.

– They can transmit learning to other generations of dolphins.
There have been cases where they use tools. For example, sponges to protect your snout from rough surfaces.

– The members of a pod collaborate with each other and sometimes with other species of animals.

Some scientists argue that the social intelligence of these cetaceans competes with that of the great apes because they can demonstrate empathy towards the companions and help them when they are injured or immobilized.

Signs of higher intelligence are related to self-awareness and dolphins are. Proof of this is that when they look in a mirror, they can recognize themselves and know that they are the ones in the mirror; This is a sign of the development of abstract thinking. Likewise, their learning ability is comparable to that of a 3-year-old child, according to cognitive psychologist Diana Reiss of the New York City University.

+ According to science, their ability to learn is comparable to that of a 3-year-old toddler.

INTELLIGENCE TESTS

Many other experiments on dolphins have proved their superior thinking ability compared with other animals and similar to that of humans:

– They respond positively to television, that is, show interest and curious attention to the moving images displayed on the device.

– They have been seen playing with inanimate objects that they find in their surroundings.

– They play with bubbles of water as they swim, and then take the time to observe their creations.

– They can solve complex problems and can imitate the actions of human beings. A dolphin named Tanner was blindfolded and told to imitate the actions of a trainer who was in the water. As the dolphin could not watch, emitted sounds and interpreted the sound waves to make replicas of the movements of the instructor.

The differences between human intelligence and that of dolphins are that the former need to manipulate their environment, but dolphins do not, and that is why they concentrate their intellect in other things.

There are still many questions regarding dolphin intelligence. There are still many things to discover, but what is known so far is enough to say that these animals are very, very intelligent.

ARE DOLPHINS SMART? THE ONGOING DEBATE ABOUT DOLPHIN INTELLIGENCE

Most scientists refuse to take a firm stand on the intelligence level of dolphins, and although many will admit that dolphins seem to be intelligent creatures, it is not a proven fact. The biggest problem researchers are running into seems to be the actual definition of intelligence and the way to test it in animals.

If you were to step out into the street and ask the first ten people you see whether or not they believed dolphins were creatures of intelligence, 8 of 10 would probably say yes. If you ask two scientists the same question, you just may be opening up a debate that could last for hours.

Darwin’s theory bases intelligence on the ability of a species to recognize what it needs to survive, while others believe that the size and architecture of the brain, the capacity to communicate or the ability to solve problems are the indicators.

Another reason why the research is limited is that it is complicated and expensive to do it in the wild. Dolphins in captivity may respond differently based on their surroundings and are therefore may not be representative of the wild dolphin.

While most of us outside the scientific realm recognize that dolphins are intelligent, we do not know the intricacies of the dolphin’s brain. It has two hemispheres just like the human brain. However, theirs split into four lobes instead of three. The fourth hosts all of the senses, whereas in humans, they are in different parts. Some believe that having all of the senses in one lobe allow dolphins to make quick and often complicated judgments that are well beyond the scope of human ability.

When studying the neocortex, which is the outside surface of the brain responsible for perceptions, memories, and thoughts, dolphins have more convolutions than the most intelligent humans. Even more, dolphins may be able to use the hemispheres of their brain separately as they have different blood supplies.

Some researchers think that the size and complexity of the brain at birth is a better measure of intelligence. If that statement holds up, however, once more the dolphin comes out on top. The bottlenose dolphin has a brain mass at birth that is 42.5% of the brain mass of an adult. In contrast, human babies at birth have 28% of their adult counterparts. At 18 months, the brain mass of a bottlenose dolphin is 80% of the adults, while humans don’t achieve this level until the age of three or four.

While the research certainly makes it look like the dolphin may be the closest to our level of intelligence, it may be quite some time before this can be confirmed.

References

Richard C Connor. Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals. 2007.

Pilleri G, Gihr M, Purves P.E, Zbinden K, Kraus C 1976 On the behaviour, bioacoustics and functional morphology of the Indus river dolphin (Platanista indi Blyth, 1859).

Stephen Leatherwood, Randall R. Reeves. The Bottlenose Dolphin. Elsevier, 2012.

news.health.ufl.edu/2012/18591/multimedia/animal-airwaves/dolphins-dig-tools/

Dolphins are active predators that have a carnivorous diet. Their eating habits are flexible so that they can adapt perfectly to the habitat where they live.

Although they have small teeth, they do not use them to chew the food but only to hold the prey. What they do is, once the prey is in their control firmly hold by those teeth, they swallow it whole starting with the head. If the prey is a large animal, then they tear it by shaking or crushing their body so that it breaks into smaller pieces.

The stomach of these cetaceans has several compartments that make digestion a quick process. The daily total food intake varies according to the species, but they do not feed abundantly. For example, a bottlenose dolphin (Tursiops truncatus) consumes between 4 and 5 percent of its weight per day.

Dolphins spend plenty of time finding food every day, and some species can consume up to 30 pounds of fish per day as adults. They migrate and move long distances to find food, although if they have enough supply where they reside, and the temperature of the water is also acceptable, they probably won’t migrate.

Dolphins do not use their teeth to chew the food but only to hold the prey.

FAVORITE PREY

They consume a variety of bony fish, crustaceans, and cephalopods. Individuals living near the coast regularly feed on fish and benthic invertebrates, while those who stay in high seas prefer to eat squid and fish as well.

Specifically, their favorite prey includes:
– Atlantic mackerel
– Herring
– Mullet
– Cod
– Squid
– Octopus
– Shrimp

Orcas (Orcinus orca) are a separate case because their diet includes more than small fish. They are used to hunt other marine mammals such as walruses, sea lions, and seals, as well as penguins, sea birds, and even small baleen whales.

Some reports indicate that deep-sea fish remains have been found in the stomach of some dolphins, pointing out that they may be able to dive up to 500 meters deep to search for food.

HUNTING METHODS

Dolphins use various strategies to catch their food, but they are usually related to group hunting:

HERDING.

When a pod of these cetaceans locates a school of fish large enough, they start to surround their prey to reduce the area of ​​dispersion. Imagine a compact group of thousands of fish going from side to side to avoid a set of predators. When the prey is already disoriented, the dolphins take turns entering the fish school from below and begin feeding themselves. Some others stay on the outer perimeter to avoid the fish to disperse.

Herding is one of the most common methods of feeding that they use; This involves a pod working as a unit to get a school of fish to curl up into a tight ball. Then, they take turns to rush through and plow the center of that ball, eating all they can in the process.

CORRALING.

Other times, a pod goes to the coasts or the sandbanks to facilitate their task as these areas offer a great variety of fish and it is easier to catch them. Dolphins sometimes corral fish in shallow waters so they cannot escape.

Dolphins learned to feed following fishing vessels. Bottlenose dolphins are the species that practices this more often, and it involves following trawl nets to feed on discarded fish and or those thrown back into the water by the fishers.

They do not always hunt in groups. If necessary, dolphins also look for food individually. Orcas and other species herd their prey to the coasts or places where they will not escape and sometimes wait patiently until the victim makes a mistake and can catch them. There are some videos of orcas practically getting half of their body on the sand to the catch seals that feel safe in the seashore, in a move that has to be perfectly coordinated with the ocean waves.

Sometimes dolphins beat the prey with their tails until they come out of the water and they catch them in the air with their mouths.

Recently a particular behavior was discovered in bottlenose dolphins that inhabit the west of Australia: when looking for food in rocky areas, females protect their snout using a marine sponge; Just when they intend to swallow the prey they release the sponge and eat. This unusual but sophisticated behavior is exclusive to females and their offspring.

OTHER DOLPHIN FEEDING METHODS.

The concept of cooperative feeding involves driving the schools of fish to the shallow areas of the water. Sometimes, this is to the coast, or it could be to some natural barrier or even a subgroup of the dolphins making such function. Other species drive prey into muddy banks so that they can simply catch them.

There are certain species of dolphins that use their flukes to stun their prey hitting them, and while the victims are still disoriented, they will feed on them.

What is fascinating too is that in some locations the dolphins have learned to help the fishermen drive the fish into their nets. The payoff for dolphins is that they get to feed on the leftover fish that get out of the nets.

Large pods use circular cooperative feeding. They divide into subgroups and then form circles surrounding schools of fish this way and continue to reduce the overall size of that circle before they take part in consuming them.

Something very similar is the crossing cooperative feeding; This involves dolphins moving in a cross pattern with groups of them swimming in different directions, allowing the fish to be in the middle of the routes that dolphins have created. Such strategy is usually a good one to use around rocky shores and in shallow areas of small bays.

Dolphins are intelligent, so they have the option to create different methods that fit their feeding needs. They have been seen mixing two or more of the mentioned feeding strategies into one session to get results. The ability to create such variations with ease and to build new formations is fascinating. The level of cooperation it takes among the dolphins in the pod is also noted.

FEEDING DOLPHINS?

When meeting dolphins, either in aquariums or in areas that these cetaceans visit, humans can provide them with food, but this action is not good for them.

Researchers point out that the fact that dolphins get quickly accustomed to being fed causing them to lose their natural hunting ability. If you visit an area with ​​dolphins, do not feed them!

References

bioexpedition.com/dolphin-feeding/

Animals, a visual encyclopedia. Smithsonian. Dorling Kindersley, 2012.

Alan Rauch. Dolphin. Reaktion Books, 2013

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

]]> https://www.dolphins-world.com/dolphin-evolution/ Wed, 26 Apr 2017 05:34:08 +0000 http://www.dolphins-world.com/?p=54 A DOLPHIN STORY

The initial presence of dolphins on the Earth dates back millions of years. It is hard to believe, but scientists think that the earliest ancestors of dolphins were not marine creatures. They were terrestrial animals that today seem to have little in common with dolphins.

The fossil records indicate that the origin of all members of the modern order Cetacea is the order Artiodactyla, a group whose members are terrestrial mammals being their closest living relatives those belonging to the family Hippopotamidae (Hippopotamuses). Artiodactyls have two fused fingers, and the tip of their legs are called hooves.

Many signs prove that dolphins have terrestrial origins. They need to come to the surface of the water to get air is one factor. Their bones strongly resemble the limbs of many animals that live on land. Dolphins have spines that move vertically, and this is a characteristic mainly found in animals that can run on land. When you look at the movements of fish, their spines move horizontally.

The process of evolution can be very slow, and it allows living creatures to develop an anatomy that is structured to thrive in their environment.

The size and the shape of the skull have changed over time too. It has become larger which is an indication that the development of the fat pad in the lower jaw emerged. It extends to the middle ear, and this helps dolphins to be able to hear as well as to use the process of echolocation.

What is interesting though is that unlike many other mammals, they didn’t change to being herbivores. Instead, they continued to be carnivorous in the water as they would have been on land.

The nostrils later evolved into blowholes, so they spend less energy when reaching the surface of the water to breathe. The movement of the ears closer to the eyes is also part of the evolution process. Those changes over time helped them survive in the water.

The body of actual dolphins does show two small pelvic bones that are rod shaped. These limbs aren’t on the outside, but they are vestigial legs.

The most direct link of the first cetaceans in the line of the artiodactyls is with the extinct taxonomic family Raoellidae, whose members lived during the early and middle Eocene in China, Pakistan, India, and Mongolia. They were hoofed mammals looking for their food walking near bodies of water.

Scientists believe that the oldest ancestors of dolphins were land animals and not aquatic.

In 1983 the fossil of an animal that the scientists named Pakicetus was discovered in Pakistan. The bones were of an elementally terrestrial mammal believed to have been an archaic cetacean because although it could remain on land, it also ventured into shallow waters. The pakicetidae family, these first cetaceans, appeared about 50 million years ago during the Eocene.

They had four legs and hooves such as camels and horses. We know now that the bone structure of the flippers of dolphins is similar to that of the extremities of mammals, with five phalanges and joints. Thus, the family pakicetidae was a transition link between the exclusively terrestrial mammals and the aquatic as they started to spend more and more time in the water.

Another theory suggests that modern cetaceans have their origin in mesonychids (Mesonychid family), a group of carnivorous ungulate mammals with teeth similar to whales and also related to artiodactyls that lived 55 million years ago and began to inhabit shallow water regions due to shortages of food supplies on land and climate changes.

After that, the following 15 million years the archaic cetaceans continued developing evolutionary modifications to adapt to life at sea. They still had paws and depended on the land to raise their offspring, but they were looking for their food in the ocean. The family of the Archaeoceti (Family Archaeoceti) to which the Pakicetus belonged, evolved from the Mesonickids and lasted until the Eocene-Oligocene, becoming increasingly aquatic members.

In the late Eocene, 38-45 million years ago, basilosaurids (Basilosauridae Family) appeared and lived, fully aquatic archaeocytes whose limbs were more elongated resembling the flippers. The base of their skull enlarged as it happens with modern whales and their hind legs were already atrophied; Possibly only used during mating.

Cetaceans with beards (Mysticeti) and toothed (Odontoceti) separated from a common ancestor about 35 million years ago. Since the early Miocene, the Odontoceti species developed echolocation as they have now.

Sometime about 12-15 million years ago, the first Dolphins of the Delphinidae family appeared. Among the first dolphins were Kentriodon and Hadrodelphis, belonging to the Kentriodontidae family and inhabitants of the ocean during the late Oligocene and Miocene.

Genetic studies show the current relationship of cetaceans to the Hippopotamidae family, which extends from the early Miocene.

12-15 million years ago, the first Dolphins of the Delphinidae family appeared.

FAMOUS ANCESTORS

Some dolphin ancestors are here below. However, they are cetaceans in general, and they are not specifically dolphins.

Simocetus rayi.
This species was present in the Oligocene, 30-34 million years ago in the northern Pacific Ocean. It had a length of 2 or 3 meters, and perhaps its head housed a small melon. Its snout was curved downward, and it had a blowhole positioned forward and lacked dental alveoli (divisions of alveolar bone) in the incisors. Its diet consisted mainly of mollusks and crustaceans.

Waipatia maerewhenua.
This species existed 24-26 million years ago in the southeast Pacific Ocean. It was about 3 meters long and resembled modern river dolphins because of its long snout and heterodont dentition (with multiple dental forms).

Zygophyseter varolai.
It inhabited the Earth during the Miocene 8.4-10.5 million years ago in what is now the Mediterranean Sea. Its length was between 6.5 and 7 meters and physically resembled a sperm whale although this cetacean had long teeth. Its feeding habits were comparable to those of the extant Orcas or killer whales (Orcinus orca).

Messapicetus.
A genus of odontocete cetaceans that lived 9-13 million years ago during the Miocene period. It measured between 3 and 5 meters in length, and its aspect was very similar to the present dolphins. Their cranial features indicate that they probably used echolocation and possessed a melon. They fed on fish and squid.

MODERN DOLPHINS

Dolphins with current physical characteristics appeared on the planet only about 5 million years ago. In fact, bottlenose dolphins (Tursiops truncatus) saw the Earth initially 2-5 million years ago. Since then there have been no drastic changes in their morphology, although there have been adaptations related to its distribution, habitat and food availability.

References

https://dolphins.org/physiology

https://en.wikipedia.org/wiki/Evolution_of_cetaceans

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

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1088639/

http://evolution.berkeley.edu/evolibrary/article/evograms_03

]]>