Indeed dolphins and all cetaceans like whales and porpoises evolved from animals that lived, reproduced and died on land. In fact, their closest relative alive is the hippopotamus, which in turn also relates them to the artiodactyls.

The common ancestor of dolphins and hippos is an animal called Pakicetus that roamed the Earth about 50 million years ago. Pakicetus had a four-leg functional anatomy, elongated snout, flexible neck and a very long tail, morphology that laid the foundation for the subsequent appearance of cetaceans.

Millions of years later, creatures like Ambulocetus and Kutchicetus emerged with body characteristics increasingly adapted to the marine world.

While the former is the commonly accepted theory, others suggest that cetaceans descend from the Mesonikia, prehistoric animals that lived on Earth about 55 million years ago. Its appearance was similar to that of a tiger, and the evolutionary change began while searching for food in the disappeared sea of ​​Thetis.

The explanations about the evolution of dolphins are:

One. The scarcity of food on land forced some coastal populations to venture into the ocean for food, which gradually adapted their anatomy to their new habitat.

Two. The other theory has to do with the climatic changes of the era, which forced them to enter the water to get a convenient place with satisfactory temperature and abundant food.

Visible evidence.

Several indicators confirm that dolphins evolved from terrestrial animals, and these are the most evident:

1. They have a robust bone structure rather than a cartilaginous skeleton like sharks or fish.

2. They are mammals because they feed their young with breast milk from the mother.

3. Dolphins breathe air like us. They can not breathe underwater like fish because they have lungs instead of gills.

4. Dolphins have vestigial bones that once were legs and pelvic bones where they were attached.

5. These cetaceans are warm-blooded.

Even that some scientists still debate about the dolphin ancestors and their relation with other species, there are enough probes to confirm that these cetaceans undoubtedly descend from terrestrial animals.

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 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

]]> https://www.dolphins-world.com/the-law-of-brevity-and-dolphin-communication/ Wed, 23 Apr 2014 19:20:28 +0000 http://www.dolphins-world.com/?p=2064 Dolphin Communication

Every living thing has a method of communication, and it is fascinating to explore the depths of it. For example, humans use short words the most. Some of the most commonly used words are I, a, and the. This is a means of being efficient in communication, and dolphins are believed to follow similar types of patterns in their communication efforts as well.

This is referred to as the Law of Brevity, and it has become a very interesting and valuable area of study. It has been able to show that evolution plays a key role in communication in both humans and animals. Such studies also show animals are more capable of effective communication than humans once gave them credit for.

One person that has been involved in such studies is David Lusseau, a Behavioral Ecologist at the University of Aberdeen in Scotland. He believes that the Law of Brevity tells us a great deal about ourselves. It also explains many of the levels of complexity in the world regarding communication. There are still unknown factors though such as if it is limited or if there are so many ways to reach it that it is limitless.

The desire of Lusseau to learn more about the complexities of communication systems led him and to study dolphins along with a colleague, Ramon Ferrer-i-Cancho. They chose to study dolphins due to the fact that they are distanced from humans on the tree of evolution. Approximately 65 million years ago they split from humans, and they have brains that are designed different from those of humans.

Studies show that dolphins have the ability to use about 30 different nonverbal behaviors that allow them to effective communicate. However, we don’t have all the information to really understand the messages being sent all the time. For example, a dolphin that does a side flip or several of them is sending a message to the rest of the group. Are they telling them to follow the hierarchy within the group or is there another message from this movement?

To get the most out of the research efforts, all of the 30 behaviors were broken down individually into behavioral units. A flip equals 2 units while a head butt equals 4 units. There were hundreds of hours invested in observing and analyzing the dolphins. This included very simple behaviors as well as those that are quite complex.

The Law of Brevity is exhibited in all human languages, and it is evident in these observations of the dolphins too. Basically, when you have more to say, finding a shorter way to communicate it will save you time and deliver the message faster. At the same time, the listener is able to use less effort to understand that message being said to them. This all improves communicate results.

This type of study with the dolphins is just the tip of the iceberg. Many scientists including Brenda McCowan of the University of California have the theory that there are plenty of other types of animals that use the Law of Brevity as well. She believes that there are various systems in place when it comes to communicate that are structured in a manner that works for that type of animal.

As more data is compiled and analyzed, it shows that humans aren’t unique when it comes to communication and the Law of Brevity. McCowan encourages us to be open to the idea and to think about how it affects our relationships with animals in the world. It can help us to see how animals fit into society differently than we imagined before.

Source: http://dsc.discovery.com/news/2009/08/11/dolphin-language.html

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