Information gathered over the centuries has helped us bring light to their evolutionary past which shows that these marine mammals originated from their land baring mammal ancestors and over the course of millions of years these animals evolved into the species we now know today as cetaceans or whales, dolphins and porpoises.
In fact even today there are several factors we can look at that help us identify their ancestral beginnings such as their need to breathe air, the bones in their fins which resemble the limbs of their land dwelling ancestors and the design of their spines which appear to be designed originally for running (not swimming).
There have also been a number of archaeological findings that have brought additional insights into the history of these marine mammals.
For ages the evolution of whales transforming from from land animals to sea creatures remained a mystery until a recent discovery in Pakistan as well as in other areas which revealed several different evolutionary cycles indicating the changes in their physiology from land animals into their current state as marine mammals.
From this gathered information cetaceans are believed to have evolved through several different forms of species over the course of millions of years as evolution continued to evolve these marine mammals as a way to adapt to anticipated threats in order to improve their survivability on earth.
This article will guide you through some of the most important stages in evolution for the cetacean species and educate you about their beginnings and how they ended up becoming the marine mammals they are today.
A small deer like creature that lived about 48 million years ago and resembles a small deer, but was only about the size of a raccoon.
The sister group of the (pakicetidae) indohyus share several characteristics with cetaceans (whales) including an unusual characteristic only found between the two species known as an Involucrum (A layer of new bone growth outside of existing bone).
Pakicetids are hoofed mammals that lived around 53 million years ago and are considered the earliest form of whale acnestory with indohyus being the closest sister family.
Pakicetids fossils were first discovered in pakistan in 1979 and appear not to have been designed for swimming due to their legs and short hands and feet.
Pakicetids teeth are also similar in shape and design of the fossil whale.
They had unusually thick bones which seem to have been a way to make it easy to float on water rather than swim underneath the ocean.
Ambulocetus natans lived about 48 million years ago and appear to have been amphibious resembling the appearance of a crocodile.
This species had long limbs and a tail (without flukes) and where able to travel on both land and water, however they where not particularly great at either.
It seems as though they hunted in ways very similar to modern-day crocodile and ate raparian prey and fish.
Remingtonocetids appear to have existed between 49 and 43 million years ago.
They had short legs as compared to the remingtonocetids and swam in shallow marine deposits.
This species did not ingest fresh water so they had little to no dependency on fresh water.
Protocetids existed around 48 to 35 million years ago and were considered to be the first whales to leave the Indian subcontinent and spread through all shallow subtropical oceans throughout the world.
Compared to the Remingtonocetids the protocetids nasals were much larger and located about halfway up the snout.
The eyes have grown increasingly lateral which may have been used to better detect prey underwater.
Some protocetids had short/long fore and hinde limbs which were most likely used for swimming, but didn’t really aid much in swimming in the ocean.
It is also believed that some protocetids even had flukes which resemble the flukes of modern whales.
Basilosauridae and Dorudontinae
Existed around 41 to 35 million years ago and lived entirely in the ocean.
Basilosauirds were as large as modern-day whales, but lacked certain characteristics such as the melon organ which allows modern whales to use echolocation effectively, and they had small brains which suggests that they may have been solitary creatures and not as social as modern whales are.
They also had very similar skeletal structures compared to modern-day whales and were fully recognizable as part of the whale species.
Despite their large size (some species may be up to 115 ft. long) most baleen whales are able to fully leap out of the water.
Some believe that leaping is a strategy used to attract female whales by showing athleticism.
Baleen whales have also developed two blowholes as compared to toothed whales which only have one.
Although the exact reason for this development is unknown some toothed whale species use the second blowhole to assist with echolocation.
Dolphins are often found in coastal waters, however some species may live further out to sea.
These marine mammals can be found swimming throughout all of the worlds major oceans around the world.
They can vary greatly in size and range anywhere from 4 to 30 ft.
The typical diet for the animals consists of fish, squid and various other crustaceans.
Species such as the killer whale may also consume a variety of marine mammals.
Currently there are around 40 known species of dolphins.
Dolphins generally get along well with humans and have even been trained by marina instructors and for used in military operations, however on rare occasions they have been known to attack people when they feel threatened or isolated.
- Wikipedia: Evolution of cetaceans
Over the course of millions of years whales, dolphins and porpoises have adapted from land dwelling animals to living exclusively in the ocean by developing a number of different evolutionary changes.
Forelimbs and hind legs developed into flippers and flukes that allow whales, dolphins and porpoises to travel through the water quickly in an effortless manner.
A dorsal fin developed on the back of some species in order to provide them with better stabilization when swimming through the water.
Some species also grew to be some of the largest animals in existence.
The large size of these marine mammals helps deter would be predators from attacking them.
Ironically when it comes to predators the killer whale (the largest animal in the dolphin species) and the false killer whale (the third largest dolphin) are two of the only purely oceanic marine mammals known to hunt whales, dolphins and porpoises.
Aside from these marine mammals sharks are also known to occasionally attack small dolphins and porpoises.
In addition to deterring predators their large size also allows heat to be better distributed throughout the body while requiring fewer calories to do so.
The nostrils were moved to the top of the head in order to make it easier to breathe and the air passage and food passage are separated in order to allow these marine mammals to consume food underneath the water without accidentally ingesting water into their lungs.
Having nostrils on the top of their head also make it easier to take in air when resting near the surface of the water since they do not have to lift their head completely out of the water to breathe.
The brain advanced in order to allow whales, dolphins and porpoises to stay semi conscious when resting so that they never fall completely asleep in case they need to quickly take in oxygen or escape an attack from a potential predator.
Echolocation was developed to help these marine mammals navigate the water, hunt for prey and avoid predators during the night or in areas where light is non-existent.
By bouncing sounds off of nearby objects whales, dolphins and porpoises are able to listen to the echo that returns in order to determine the size, direction, angle, speed and density of the objects around them.
Thick layers of blubber were created to help them stay warm in cold/freezing environments and their lungs became better adapted at taking in oxygen allowing these marine mammals to take in as much as 90% of the oxygen they inhale, compared to humans that take in about 15% – 30% of the oxygen we inhale.
Highly developed respiratory systems and blood transportation systems were created to help move blood into vital organs and muscles when needed and allows these marine mammals to have more control over their oxygen supply so that they can hold their breath for longer periods of time.
As you can see from all of these evolutionary changes that have occurred over millions of years dolphins, porpoises and whales have adapted in a number of different ways to become adapted to living and thriving in the ocean and to give them an upper-hand against both predators and prey.
Why did cetaceans evolve into marine mammals instead of fish?
Unfortunately there is no clear answer to this question.
Despite evolving from land animals to marine mammals whales continue to share a number of characteristics that are more common with land mammals than fish.
This includes breathing air, being warm-blooded, giving birth and producing milk among other physiological characteristics.
If we look at the physiology of fish we can see that their physiology is very different from whales and other mammals.
Fish use gills to extract oxygen from the water, are cold-blooded, lay eggs and aren’t known for nurturing their young.
When it comes to evolution their is no clear or decided road map for how an animal will evolve.
Nature looks at the best possible adaptations during that time and slowly evolves in order to give each living animal the best opportunity for surviving.
Evolution requires energy and its possible that given the amount of time whales have been on earth the most important and immediate changes were to increase their size for better protection against predators and cold environments, develop a thick layer of blubber to protect their vital organs from freezing temperatures, move their nostrils (blowholes) to the top of their head in order to make breathing easier, evolve their hearing and develop echolocation to navigate in the dark and gain better insights into their environment, maintain a separate esophagus and trachea to improve their ability to hunt for food underwater while protecting their lungs and modify their limbs into flippers and flukes among other changes.
Given this time frame there may have not been enough evolutionary energy to transform these marine mammals into cold-blooded, gill baring, egg producing animals or maybe its just not in their evolutionary cards.
Its also possible that evolution hasn’t figured out how to change a marine mammal into a fish.
Maybe this sort of transformation means rewriting a marine mammals entire DNA.
For example fish can live tens of thousands of feet below the water.
Would it make sense for a whale to develop gills if it weren’t going to maintain a deep underwater existence where it had no choice but to develop a way to extract oxygen from the water, and if not is there any point in making a whale cold-blooded as it will likely never maintain these freezing and completely dark depths for extended periods of time?
All of these questions which remain unanswered is what makes evolution so unpredictable.
Anything that can affect an animals ability to survive can cause a shift in how that animal evolves, how it will develop ways to protect itself and how it will adapt to become a better hunter.
What about their evolutionary future?
Just as the choices of their evolutionary past remains a mystery trying to determine how they will evolve in the future will be just as difficult to determine if not more.
Evolution and mother nature do not follow a straight path or road-map and what may make since today may not make sense tomorrow as the world and every living thing within it seeks to evolve and improve its chances for survival on this earth.
Evolution is fascinating and takes many generations if not millions of years for large changes to be detected and those that are able to evolve quickly enough stand the best chances of survival on this earth.
If its alive it evolves and if it evolves it affects the evolution of everything around it.