The evolution of the whale has been long and varied. From land mammals to marine mammals, many adaptations were needed.
Whales evolved from early land mammals, adapting to life in the oceans by losing their hind-limbs, growing a flat tail, developing flippers, and streamlining their bodies.
In this article, we look at the whale’s evolution, how it adapted to life in the oceans, and where modern whales came from.
It is known that life began in the ocean as tiny single-cell organisms (bacteria) around 3.8-3.5 billion years ago.
In those 3.8-3.5 billion years, those very first bacteria have evolved billions of times into every animal and plant that has ever lived on planet earth, including ourselves.
One of the most exciting and intriguing evolutionary journeys includes that of the whale.
One of the key concepts of evolution is adaptation, closely accompanied by the Darwinian theory of Natural Selection. As environments and other species have changed and developed, individual species had to adapt to these changes. This was greatly attributed to the process of natural selection.
Those that were not fit or suited to the environment died off, while those that survived were able to pass on their genetic material. Over generations of repetition, some genes died out completely, while others became dominant. This, in turn, changed the characteristics of species, eventually creating new ones altogether.
There is still a lot that scientists do not know about the evolutionary progress of whales. Work has been ongoing on the fossil record, and genetics and molecular biologists have been working with live animals. We now have a much clearer picture than we ever had before.
It is believed that modern-day whales evolved from land-based animals about 55 million years ago. These land-based mammals are believed to be hoofed mammals, sharing a common ancestry with even-toed ungulates such as the cow and the deer.
Mesonychidae was a family of hoofed mammals that lived in Asia, Europe, and North America. These ranged from small dog-sized mammals to mammals as large as modern bears.
It is believed that the earliest whales evolved from the smaller members of this family. Some of these mammals had adapted to eating fish, and it is believed that they would feed around the shallow edges of water around the Tethys Sea. From feeding on fish, they then evolved to an amphibious nature.
These earliest amphibious Mesonychidae would have fur and been otter-like in moving around the water using all four limbs.
The tail would have become flat from beating the water, which would have led to the regression of the hind-limbs.
Evolution of Whales
Whales started their journey as all other organisms have, as single-celled bacteria.
An evolutionary picture of the whales can be broken down as follows:
- 3.8 billion years ago: The first single-celled organisms appeared (Bacteria)
- 3 billion years ago: Viruses (also single-celled organisms) became present
- 2 billion years ago: Eukaryotic cells are present. These are cells that contain organelles, or tiny organ-like structures
- 1.5 billion years ago: Eukaryotic cells evolved three ways. These cells evolved into the ancestors of plants, animals, and fungi
- 900 million years ago: The first multicellular structures became present 800 million years ago: The animal strain of organisms undergoes its first split and continues into basic marine organisms such as sponges
- 540 million years ago: The first chordates or animals with backbones are present
- 530 million years ago: The first true vertebrate or boned organism is present
- 500 million years ago: Animals first started exploring the land
- 417 million years ago: Lungfish became present. Lungfish are the first organisms to breathe both on land and in the water with both lungs and gills
- 397 million years ago: The first tetrapods or four-legged species are present
- 340 million years ago: Amphibians branch off from the other tetrapods
- 310 million years ago: The remaining tetrapods split into what will be reptiles, birds and dinosaurs, and mammals
- 200 million years ago: A mass extinction occurred and warm-blooded proto-mammals developed
- 140 million years ago: Placental mammals also known as eutherians are present
- 105-85 million years ago: The placental mammals split into four major groups, including laurasiatheres, which will contain the whale species.
- 65 million years ago: The greatest extinction event so far wipes out the dinosaurs providing more potential for mammals to colonize the planet
- 50 million years ago: Artiodactyls pakicitus, a mammal, resembling a wolf and tapir mix with cloven hooves begins evolving into what we know as whales
- 47 million years ago: Early forms of whales live in shallow seas, returning to land to mate and give birth
- 35-45 million years ago: The first fully aquatic whale is present (Basilosaurus)
Modern-day whales are believed to have moved into the oceans around the Tethys Sea, now the Mediterranean Sea and Asia.
Fossils recovered show an animal called Archaeoceti, thought to be the first sub-order of cetaceans, existed in the estuaries of the Tethys Sea. Archaeoceti originally had four limbs but adapted to an aquatic way of life.
Adaptations To Marine Life
There were many adaptations to living in the sea that these mammals did not have while on land. Evolution is required by evolution to adapt to where the animal lives.
Whales would not be able to rely on their four limbs to walk, so they would need a new way of moving. They would also need to cope with the water instead of the air surrounding their bodies. They would also need to be able to adapt to finding and catching prey and need to be able to breathe while in the oceans.
To efficiently breathe while in the oceans, whales still needed a way to breathe air. The nostrils located at the front moved to the tops of their heads, forming the blowholes we now know.
To be able to find and catch prey, the jaws and teeth had to change. The upper jaw became longer and broader to accommodate prey, and the teeth changed from carnivores’ teeth, which have different sets of teeth. The new teeth were all the same, indicating the move to homodont teeth.
Changes to the skull were needed to accommodate the melon on top of their head in front of the braincase. The melon houses fatty deposits that are used to focus sound, helping whales to use echolocation.
The whale’s body had to become more streamlined to swim through the oceans, with a long body, which made it easier to push through the dense water.
To be able to propel itself forward efficiently, the tail evolved into a paddle. The fore-limbs also changed, evolving into small paddles on each side of the body, allowing the whale to turn.
The back limbs were no longer needed, and these are still there. However, they are much smaller than they were and are essentially buried in the whale’s blubber and muscle.
Dorsal fins also evolved on the whale’s top side, although not all whales still have this. Whales that still have dorsal fins use them to regulate their temperatures, and the lack of a dorsal fin can be attributed to different ocean conditions. Beluga whales use their dorsal fin to break through thin ice to breathe.
The primary food of baleen whales is plankton, and these whales developed a way of catching many of these at one time. Baleen whales developed baleen, which they use to gulp in huge amounts of water and plankton, sieving these through fiber-like sheets before expelling the water.
The kidneys and the eyes would have had to adapt to the amount of salt in the oceans, and the ears would have to change to hear underwater. The nose would have had to adapt to develop nasal plugs to close the nostrils when diving underwater.
The loss of hair apparent on modern whales would have happened over time, and blubber would develop to insulate them from the cold of the depths.
What Were The Earliest Whales?
Protocetids, some of the most primitive of the archaeocetes, possessed features that distinguished them as cetaceans. These early mammals had varied teeth, including teeth for catching and for cutting.
Pakicetus, a fossil from 50-53 million years ago, found in Pakistan, is the most primitive Protecetid. The skull is small, indicating the recent one from being a land mammal, although it does have an ear bone adapted for hearing underwater.
Protocetus from 50 million years ago has adapted further. Although it still has a small head, it has separated eyes, a blowhole behind the tip of the slender upper jaw, and a longer braincase.
One of the earliest examples of relatives to the whale is the family of Basilosauridae. These were huge animals, with sizes up to 21 meters long. Although they were whale-like, they had a small head with varied teeth and a flexible neck.
Basilosauridae is best known from a fossil from 38-45 million years ago. This shows enlarged sinuses in the skull along with cheek teeth that have multiple cusps. These features can also be seen in both the early toothed and baleen whales, suggesting that whales evolved from Basilosaurus.
Basilosauridae had also developed pectoral fins, regressed the hind limbs, and had the paddle-like tail to swim efficiently.
Archaeocetes survived into the Eocene period and possibly into the later Oligocene period, but they would have died out at least 25 million years ago.
At this time, the two current suborders that we know today were around. These two, Odontoceti (toothed whales) and Mysticeti (baleen whales), completely took over from Archaeocetes, although it is unknown why Archaeocetes died out.
It is believed that Archaeocetes became extinct due to a global mass extinction thought to have affected many groups of organisms. However, it could also be that the rocks needed to find later specimens of Archaeocetes have not been found in the oceans yet.
Most fossils are found in shallow waters, but it could be that Archaeocetes evolved to swim in deeper waters. Kekenodon is the last fossil of Archaeocetes from about 30 million years ago.
When Did Todays Whales Evolve?
Approximately 25 million years ago, at the end of the Oligocene era, many toothed whales lived in the oceans across the world. None of these were the same as the whales that we have living today, but these had evolved further from the earlier whales.
The modern killer whale is believed to have evolved from a shark-toothed dolphin around at this time. Squalodontidae is believed to have a similar lifestyle to the killer whale.
Modern sperm whales evolved from Physeteridae, a sperm whale around at the time, while beaked whales evolved during the Miocene period, ranging from 25 to 5 million years ago.
During the Miocene period, it is thought that all modern families of whales were now established, although there are gaps in the fossil record. Belugas, narwhals, and porpoises are some of the marine mammals that are unclear due to the fossil records.
The gray whale is the only modern Eschrichtiidae species, and fossil records only go back 100,000 years for this animal with no real differences to the modern animal. It is believed that Eschrichtiidae evolved along a separate branch from other whales.
Blue whales, humpback whales, and other Balaenopteridae family members evolved from Cetotheriidae, which is now extinct. These two coexisted in the oceans for approximately 7 million years. Cetotheriidae had about 50 species of whales at its most successful period.
Many of this family made several adaptations, including a longer skull and baleen in its mouth. At this time, the jaws became more flexible to allow a wider gulp allowing easier access to large amounts of plankton.
Although gaps in the fossil record make their origin hard to determine, right whales appeared around this time. Some fossils have also been found back as far as 25 million years ago.
Why Did Whales Return To The Sea?
It may seem strange for an animal that has adapted to living on land to return to the sea, but the ancestors of today’s whales from 50 million years ago had good cause.
At this particular time, the land was becoming more populated, and so the animals that were present needed new food sources. The ocean was rich in the required nutrients, and whales were then separated into two new groups, baleen whales and toothed whales.
Scientists agree that moving back into the water allowed today’s whales to reach the colossal sizes that they grow by removing the restraints of gravity.
The low gravity of water causes less strain to the bones. This almost eliminates size as a constraint with the largest whale living today, the blue whale (Balaenoptera musculus).
Measuring in at 30 meters (100 feet) in length and weighing 181 tonnes, the blue whale is the largest animal to have ever lived. They are also the loudest, with their cry outweighing that of a jet plane.
One of the most mysterious animals that live in our greatly unexplored oceans is whales. The evolutionary story of the whale is one that has confused scientists for years.
It had been difficult to understand why an animal that had evolved to live in a terrestrial manner would then head back into the water, but it seems that food was the main motivator. This behavior would lead to the first whales evolving around fifty million years ago.
References And Further Reading
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Marshall, M. 2009, Timeline: The Evolution of Life, NewScientist, retrieved 29/01/20, <https://www.newscientist.com/article/dn17453-timeline-the-evolution-of-life/>
Australian Academy of Science 2018, The Origins of Life on Earth, Australian Academy of Science, retrieved 29/01/20, <https://www.science.org.au/curious/space-time/origins-life-earth>
Parry, W. 2013, How Whales Ancestors Left Land Behind, LiveScience, retrieved 29/01/20, <https://www.livescience.com/28075-how-whales-ancestors-left-land.html>
PBS 2020, Going Aquatic: Cetacean Evolution, PBS, retrieved 29/01/20, <https://www.pbs.org/wnet/nature/ocean-giants-going-aquatic-cetacean-evolution/7577/>
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