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A History Of Life On Earth: The Cenozoic Era

Updated on September 29, 2012

The Cenozoic Era

The mass extinction event that occurred 65 million years ago marks the start of the Cenozoic or ‘recent’ era, sometimes referred to as the Tertiary (third) era. The extinction event killed any animal that was larger than a crocodile, including virtually all of the dinosaurs. Those small animals that survived through to the Cenozoic era found themselves in a very different world. This era is also marked by the increasing separation of the continents and the formation of their own unique plants and animals.

The Dinosaurs Legacy

Not all the dinosaurs died out 65 million years. Feathered varieties known otherwise as birds survived, with some evolving into monsters such as Gastornis.
Not all the dinosaurs died out 65 million years. Feathered varieties known otherwise as birds survived, with some evolving into monsters such as Gastornis. | Source

Palaeocene Epoch: 65-55 Million Years Ago

The Palaeocene epoch began with a devastated, burnt out world, still reeling from the impact of a giant asteroid, but the plants were quick to recover. Within just 100,000 years there were thick jungles and swamps covering much of the world; even the Polar Regions were covered in dense forests. Animals that survived the extinction event remained small so that they could move among the trees. The largest animals in this period were a lingering legacy of the recently departed dinosaurs; while giants like Tyrannosaurus had gone for good, a vicious feathered cousin called Gastornis assumed the role of top predator, and at 7 feet tall, it was by far the largest animal of its day. It roamed widely through the jungles of Europe and North America, preying mostly on small mammals.

Speaking of mammals, the demise of the dinosaurs saw the mammals begin to expand and move into new environmental niches. Then, at the end of the Palaeocene epoch, some 55 million years ago, there was an explosion in mammalian variety. The ancestors of many modern mammalian groups appeared for the first time, including all the hoofed animals, elephants, rodents, primates, bats, early whales and sea cows. The mammals were unwittingly beginning to assert their domination of the planet.

Life in the Eocene

A depiction of the flora and fauna of North America during the Eocene.
A depiction of the flora and fauna of North America during the Eocene. | Source

The Walking Whale

The semi aquatic Ambulocetus was the forerunner of all modern cetaceans (whales, dolphins and porpoises).
The semi aquatic Ambulocetus was the forerunner of all modern cetaceans (whales, dolphins and porpoises). | Source

Eocene Epoch: 55-34 Million Years Ago

At the start of the Eocene, much of the Earth was still covered in thick jungle. High global temperatures created a hothouse planet. Living on the forest floor were small mammals, such as the small horse Propalaeotherium, and the hopping insectivore Leptictidium. Living in the trees was Godinotia, one of the earliest primates and a possible human ancestor. In Asia meanwhile lived a bizarre creature called Ambulocetus, an early form of whale that could still walk, albeit awkwardly on land.

Then, around 43 million years ago, the climate became cooler and drier. The dense jungles were replaced by woodlands and dusty plains. These more open conditions allowed the mammals to grow bigger.

Asia was home to giant brontotheres, which at first glance may have resembled rhinos, but were only distantly related. There were also massive carnivores such as Andrewsarchus. In the warm seas, the descendants of Ambulocetus had evolved into the first recognisable whales, while the African coasts, which at the time were covered in lush mangroves, provided home for an early form of elephant, Moeritherium, and the bizarre horned beast, Arsinotherium. Its horn was so large that it actually partially obscured its vision.

Around 36 million years ago, the isolated continent of Antarctica settled over the South Pole and started to freeze, causing huge ice sheets to form over its landmass. As a consequence, the world’s climate and oceans began to cool, disrupting the global weather and radically changing rainfall patterns. Many animals couldn't cope with these changes, and in only a few million years a fifth of all life on Earth became extinct. This small extinction event is sometimes called La Grande Coupure or ‘The Great Cut’.

A Bizarre Beast

Arsinotherium lived in the mangrove swamps along the coast of what is now Egypt. Its horn was so large that it partially obstructed its vision.
Arsinotherium lived in the mangrove swamps along the coast of what is now Egypt. Its horn was so large that it partially obstructed its vision. | Source

Life in the Early Eocene

Life in the Late Eocene Oceans

Fauna of the Oligocene

A restoration of the fauna that lived in North America during the Oligocene, included the brontotheres (the lumbering beasts at the top of the picture).
A restoration of the fauna that lived in North America during the Oligocene, included the brontotheres (the lumbering beasts at the top of the picture). | Source

Oligocene Epoch: 34-24 Million Years Ago

The early Oligocene had a cool, dry climate, which gave rise to wide plains, scrublands and semi-desert. The climate change at the end of the Eocene saw the extinction of many of the more ancient mammal lineages. In their place came new species, including the direct ancestors to many modern mammals, such as the rhinos, horses, pigs, camels and rabbits.

The mammals continued to produce giants. Some such as Indricotherium became the largest land mammals ever and rivalled the dinosaurs in size, while others such as the Entelodon (a possible ancestor of modern pigs) and Hyaenodon (not related to modern hyenas) became formidable hunters. There were also the first true carnivores, such as the dog like Cynodictis.

As the continents continued to move about, South America and Australia became completely isolated from the rest of the world. Over the passage of time these island continents evolved their own unique fauna of marsupials and other bizarre creatures.

Around 25 million years ago, the first grasslands began to emerge in Asia. Until then, grasses had been an insignificant part of the landscape, but from that time onwards they grew to dominate large areas of the world, eventually covering one fifth of all dry land.

A Pig With an Attitude

Entelodon was a possible ancestor of modern pigs. It possessed small tusks which may have been used by males when fighting over mates.
Entelodon was a possible ancestor of modern pigs. It possessed small tusks which may have been used by males when fighting over mates. | Source

Life in the Oligocene

Fauna of the Miocene

A  restoration of the Miocene fauna in North America.
A restoration of the Miocene fauna in North America. | Source

Miocene Epoch: 24-5 Million Years Ago

The wet and dry seasons of the Miocene climate ensured that large areas of the planet became covered in vast grasslands. It is not easy for animals to digest tough and fibrous grass, so mammalian herbivores had to evolve new types of teeth and digestive systems to take advantage of its abundance.

As a consequence, the grasslands were home to early species of cow, deer and horse. Many of these started to form themselves into herds that would migrate with the changing seasons. Following these great herds were new types of fleet footed predators including cats and dogs.

Other animals preferred to keep browsing on the leaves of trees and bushes. Some grew quite large, such as the giant Deinotherium, with its weird downward facing tusks and the strange looking Chalicotherium that walked like a gorilla and yet was a close relative of modern horses.

The Miocene also saw the rise of mountain chains, such as the Alps, the Himalayas, the Andes and the Rockies. Some of these new mountains were high enough to disrupt the atmospheric air flow, and thus started to play a major role in global weather patterns.

The Great Faunal Interchange

The great faunal interchange saw both North and South America become home to new species of animal which migrated over the Isthmus of Panama.
The great faunal interchange saw both North and South America become home to new species of animal which migrated over the Isthmus of Panama. | Source

Pliocene Epoch: 5-1.8 Million Years Ago

In the Pliocene the world’s climate became more complicated. The planet became subdivided into many climatic regions, ranging from the freezing ice caps, through the wet temperate zones to the warmer tropics.

On every continent the open grasslands became filled with new grazing mammals and their associated predators. In Eastern and Southern Africa the dense woodlands gave way to open grasslands, encouraging our ancestors, early hominids such as Australopithecus to start coming down from the trees and spending more time on the ground.

Around 2.5 million years ago the South American continent, which had been isolated for nearly 30 million years, collided with North America. Powerful carnivores, such as Smilodon, moved south into Argentina, while gigantic southern oddities such as Doedicurus and Phorusrhacos moved north into the United States in an event known as the Great Faunal Interchange.

Two South American Oddities From the Pliocene

Phorusrhacos titanis was a giant, flightless predatory bird that was the top predator in South America until the arrival of sabre-toothed cats in the Pliocene.
Phorusrhacos titanis was a giant, flightless predatory bird that was the top predator in South America until the arrival of sabre-toothed cats in the Pliocene. | Source
The glyptodonts were giant relatives of the armadillo that were one of the few South American creatures to successfully colonise North America.
The glyptodonts were giant relatives of the armadillo that were one of the few South American creatures to successfully colonise North America. | Source

How our Ancestors Lived During the Pliocene

Life in South America During the Pilocene

Life in the Ice Age

As a response to the extreme cold of the ice age , many mammals either became larger or grew large fur coats such as the woolly mammoth.
As a response to the extreme cold of the ice age , many mammals either became larger or grew large fur coats such as the woolly mammoth. | Source

The Humans That Became Extinct

Neanderthals were a very successful species of human that became extinct shortly after the arrival of modern humans 30,000 years ago.
Neanderthals were a very successful species of human that became extinct shortly after the arrival of modern humans 30,000 years ago. | Source

When Man Lived Alongside Mammoths

Pleistocene Epoch: 1.8 Million Years Ago- Present

The start of the Pleistocene saw the world plunged into a full ice age. Throughout the entire epoch, the Earth’s climate alternated between colder and warmer phases. The colder phases would last around 40,000 years, during which glaciers and ice sheets would spread across the continents. In the north, the great Arctic ice cap expanded as far south as London and New York. In between these cold phases, the climate became milder and warmer; in these so called interglacial periods, the ice caps receded and the sea levels rose.

Animals such as the woolly mammoth and the woolly rhino evolved thick fur coats and a layer of fat to help them live in the colder regions. Around them were herds of deer, horses and bison that were be hunted by giant versions of the modern lion, called the cave lion. Around 180,000 years these ice age herbivores were also hunted by two species of human; us and our close cousins, the Neanderthals.

The increasing severity of the ice age and the extreme climate swings put many large animals under a great deal of pressure, but it was overhunting by us that ultimately caused their extinction. The last glacial period ended some 10,000 years ago bringing about an interglacial that we are still living through today. Some scientists classify the last 10,000 years as a new global epoch, the Holocene, while others have pushed for it to be known as the Anthropocene, on account of the fact that this current interglacial has seen Homo sapiens assume dominance over the planet. This was achieved by changing our lifestyle, by ceasing hunting and gathering, and starting to settle down into fixed communities that supported themselves by growing crops and domesticating animals. These small communities soon grew into towns, and then cities. Within just a few thousand years, the human population has expanded exponentially, creating a global society based on advanced technology. In the process, many animal species with which humans shared the planet came under tremendous ecological pressure. As a result, we are living through, and contributing to, what scientists would describe as a mass extinction event. What happens next is whether we like it or not, very much up to us.

Clear and Present Danger

In just a few thousand years, humans, through the development of agriculture have transformed virtually the entire planet, putting tremendous on the planet's living systems. The future, to a degree is very much in our hands.
In just a few thousand years, humans, through the development of agriculture have transformed virtually the entire planet, putting tremendous on the planet's living systems. The future, to a degree is very much in our hands. | Source

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    • profile image

      KDuBarry03 4 years ago

      Wow, you definitely put a great deal of research into this. Definitely learned a lot from this hub. Great job! Just tweeted and voted up.

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Thanks very much Keith, yes it took me quite a while to put this hub. So I really appreciate your feedback. Thanks for popping by.

    • mperrottet profile image

      Margaret Perrottet 4 years ago from Pennsauken, NJ

      Let's hope that we wake up in time to halt the harmful effect that we are having on our environment and on the creatures that share this beautiful planet with us. This is an amazing series, with so much information. I really learned so much, and I'll probably read through the series again. You've put so much time into writing the series - and it shows. Voted up+++!

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Thanks so much Margaret, I can't tell you how satisfied I was when I wrote this last hub. Its amazing to contemplate the journey that life has taken so far. But what fascinates me more is the future of life, I have no doubt that it will survive anything we throw at it. But I do wonder what the planet will be like in the far future, say 10 million, or 100 million years. Hmmm...there's an idea for a hub. Thanks for popping by.

    • cvanthul profile image

      cvanthul 4 years ago from Florida

      I'll echo the previoud commemts. Such a large amount of information and wee-written. Thanks for putting all this together.

      Don't recall the name of the special right off but Discovery aired a look at Earth's future a few years ago. The special went through climate changes and what kinds of animals may exist in 10 million years or so. Very interesting.

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Hi cvanthul, I recall that special too. I think it was called 'The Future is Wild' all I can remember is that they speculated that in 100 million years, the largest land animal will have evolved from tortoises, and in 200 million years, squid will have invaded dry land, with some evolving human like intelligence, it sounds far fetched, but its plausible. Thanks for popping by and following.

    • NateB11 profile image

      Nathan Bernardo 4 years ago from California, United States of America

      Those strange creatures of this era are fascinatingly bizarre. Also interesting are the changes in environment, leading to different evolutionary developments in the animals. In addition, the climate changes are interesting to observe, as are the various extinctions including what is happening today. Humans certainly have developed something incredible technologically; it is true what we do with all of this that we've developed is up to us.

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Hi Nate, in the case of some of the creatures, bizarre is an understatement. While it is true that what happens next is very much up to us; nature could still take it out of our hands in the form of a supervolcano or a virus- you just never know. Thanks for popping by.

    • cvanthul profile image

      cvanthul 4 years ago from Florida

      That's the one! Yes, sounds far-fetched but if you'd asked the dinosaurs 70 million years ago, they probably wouldn't think they'd be extinct and a bipedal ape-like creature would have built everything we have. You never know what can happen.

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Yes you're right cvanthul, you never know what will happen, that's why I love natural history so much, its so unpredictable, it ensures that life is always interesting.

    • suzettenaples profile image

      Suzette Walker 4 years ago from Taos, NM

      These articles you write on the prehistoric ages are so interesting and thought provoking. We can see over the millions of years how the earth has changed because of weather, flora, fauna, climate etc. We should be learning from history, but I don't know if the lessons are sinking in today or not. I enjoy these articles because we only briefly touched on this in school and I have learned much from your articles. Thanks for sharing your knowledge with us! One more thing, it is interesting to see the evolution of these animals!

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Hi Suzette, thanks very much for the comments. It is indeed very interesting, which is why I so thoroughly enjoyed putting these all together. Too often I hear phrases such as 'since the dawn of time' applied to us. But in reality, in geological terms we've only just arrived. I didn't really learn much about prehistory in school either, but that was because I went to a Catholic school; so most of my knowledge is self taught. Anyway, I appreciate you taking the time to stop by Suzette. Thank you.

    • Greensleeves Hubs profile image

      Greensleeves Hubs 4 years ago from Essex, UK

      Excellent summary of the life which has existed between the time of the dinosaurs and the present day, and the climate and geographical changes which have brought it about. The videos from 'Walking with Beasts' obviously help to bring these animals to life, and the artists impressions also help.

      JKenny, another in your series on prehistoric life which deserves to be widely read - every paragraph will bring information which will be new to the majority of readers.

      Voted up and shared. Alun.

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Thanks very much Alun. Personally I think the story of life is truly the greatest story ever told, because there are so many factors along the way that could have wiped life out completely. But yet here we are today. Speculating about the future is also fun, who knows what life will be like in the far future.

    • samowhamo profile image

      samowhamo 4 years ago

      Very interesting and well written. Speaking of the Cenozoic my next article is going to be about the La Brea Tar Pits and I am thinking about making some of my articles longer I didn't before because I was not sure if how long I could make them.

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Hi Sam, make them as long as you want, the longer the better. Some of my recent articles are around 4000 words long. The La Brea Tar Pits is a fascinating fossil site, maybe you could write about all of the different creatures that have been found there.

    • samowhamo profile image

      samowhamo 4 years ago

      Thank you JKenny. I am not going to write about all of them because there are 650 species found in them and I can't name all the ones I was originally going to name both would take to long (and I am kind of on a schedule I am trying to get to my 20th article before new years day because my 20th one is going to be special) so I am only going to name 11 species but I will also write about some other things on exhibit there.

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      PINKTANNA 4 years ago

      hmmm.. this is good

    • JKenny profile image
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      James Kenny 4 years ago from Birmingham, England

      Thank you very much.

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