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.

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/

There are many studies out there that compare the size of brains from one living thing to the next. What has been found is that the size of the brain for a human and a dolphin are almost the same. This is based on information that shows the evolution of the cetacean brain over a period of more than 47 million years!

Such studies have given experts information about the large size of the brain for toothed whales. Some of these species have abilities that have only previously been seen to exist in some of the Great Apes as well as humans. Now they have also been observed with some of the species of dolphins.

Brain of Pacific white-sided dolphin / Author: Tranletuha.

There are studies that show dolphins have the ability to recognize who they are when they see their reflection in a mirror. They are also able to communicate using symbol based programs and through concepts that are abstract in nature. Some researchers believe that the large size of their brain is what allows such intelligence to occur.

Yet what continues to be a huge mystery to the experts is the evolution of the brain over time. One of the largest fossil studies that has ever been conducted has been done by Lori Marino has several of her colleagues from Emory University in Atlanta. The study spanned 4 years looking over various collections in different museums.

The team used 66 different fossilized cetacean skulls that they found. Using CT scans, they were able to document the size of each of the brains. They were also able to document the body mass through the bones found at the base of each skull.

This study also included looking at similar data already collected on 144 cetacean skulls. This resulted in a total of 210 samples being looked at, with 62 species and 37 different families being represented in that total of samples. Find the EQ, or Encephalization Quotient, of each one was the purpose of collecting such data.

If you aren’t familiar with EQ, it is a representation of the ratio of brain to body mass. The scale works like this:

Large brain size – EQ greater than 1

Average brain size = EQ of 1

Smaller than average brain size = EQ less than 1

The largest of all creatures is humans with an EQ of 7. There have been two significant points in the evolution of cetacean that the EQ showed a significant jump. The first dates back about 35 million years ago. There were dramatic changes to the EQ as well as to changes in body size.

There are studies that indicate the development of larger brains was the result of the evolution for echolocation. This is the use of high frequency sounds that can be picked up as they echo off of various objects. Then the animals are able to interpret a variety of information from that occurrence.

It is believed the second dramatic increase in brain size occurred about 15 million years ago in the Delphinoidea super family. This includes narwhales, belugas, dolphins, and porpoises. The information from fossil records suggests that these increases were significantly more than that of humans or great apes.

The findings of this study are believed to be one of the few that have helped us to gather such information from the fossil records. Such research is time consuming but it is also very important as well as interesting. If you are interested in reading more about the research this team has done, it will be in The Anatomical Record, December issue.

Source: http://dsc.discovery.com/news/briefs/20041108/dolphin.html

Wild Bottlenose dolphin

Did you know that dolphins swim up to five times faster than the best human Olympic swimmer? Many think that this is obvious, since they are aquatic animals; however, they are mammals like humans. This is the reason why they are doing experiments to measure their speed and energy usage. It should be noted that those studies do not threaten the lives of these beautiful aquatic mammals.

//www.youtube.com/watch?v=zp-Po76p5pw

Performing Bottlenose Dolphins

Adult bottlenose dolphins have a length ranging from 10 to 14 feet long and weight 330 to 440 pounds. The body length and weight vary according to the region where they live and the quality and availability of food. There are specimens up to 1,100 pounds, but they are not common.

The hole on the top of the dolphin is the blowhole.

Dolphins breathe by getting air through the blowhole, which can empty and refill the lungs of a dolphin in one-fifth of a second.

The blow is explosive and the air reach speeds of up to one hundred miles per hour.

A nerve mechanism alert the dolphin when the blowhole is out of the water, so it can blow out the air and breathe in again.

Strong muscles close the blowhole when dolphins dive into the water to avoid drowning.

This question is paramount because they are similar in the water and many times people confuses them. Even more, some people sometimes use the word dolphin and porpoise interchangeably. However, this is a mistake, as dolphins and porpoises are in fact different animals.

While both are mammals and nurse their calves similarly, both have lungs and breathe air; they have several significant differences.

Taxonomically both are cetaceans and members of the Odontoceti suborder, but they belong to different families. Porpoises are part of the Phocoenidae family while dolphins belong to the Dolphinae family.

Physically, porpoises are smaller than dolphins, reaching up to seven feet long while dolphins reach up to ten.

Porpoises have small rounded heads while most dolphin species have a round bulbous in the head.

The dorsal fin of porpoises is different than the dorsal fin of dolphins, while the former have a triangle shaped fin, the dolphin’s fin is slightly curved backward.

Regarding their behavior, porpoises are shy creatures, which usually do not approach boats while dolphins show less fear, approaching more often to people.

Bottlenose dolphins are probably one of the best-known species of animals. They have a length of around 10 to 14 feet and a streamlined body with a large fin at the top. Their skin is gray and smooth without long hair like most mammals.

Some look small, and others are much larger and heavier, since their range is between 150 and 650 kilograms, with males having larger body dimensions than women, so there is sexual dimorphism.

One of the characteristics of bottlenose dolphins is their thick and notorious snout that give them their odd colloquial name.

Other features of bottlenose dolphins are the flippers and their powerful caudal fin.