Cenozoic Era “The age of mammals”

Background The total life span of the earth from the time of its

origin is called geological time.

The available evidence indicates that age of earth is 5000 million(5 billion) years .

Geologists have divided the geographical time into different divisions based on the different types of fossils available in the different strata of the earth.

Each division has its own duration and feature and it differs from other divisions.

Major divisions are called eras.The eras are divided into periods and the periods into epochs.

The eras,periods and epochs of the geological time are arranged in an orderly manner and this arrangement is called geological time scale.

Cenozoic Era (65 million years ago to present)

The KT Event set the stage for the Cenozoic Era that began 65 million years ago. As the dinosaurs perished at the end of the Cretaceous, the mammals took center stage. It is represented upto present.It is called “Age of Mammals”.

Even as mammals increased in numbers and diversity, so too did the birds, reptiles, fish, insects, trees, grasses, and other forms of life. Species changed as the epochs of the Cenozoic Era rolled by, with the mammals eventually becoming the largest land animals of the Era, as the dinosaurs had been during the Mesozoic.

Flowering plants strongly influenced the evolution of both birds and herbivores throughout the Cenozoic era by providing a rich abundance of food.

Those that could adapt to the changes in the environment survived; those that could not were doomed to extinction.

The era is divided into 3 periods(Paleogene,Neogene,Quaternary) and 7 epochs.

Outline of cenozoic era

TERRESTRIAL AND AQUATIC LIFE 

Terrestrial Life During the Paleogene PeriodMammals.

Mammals didn't suddenly appear on the at the start of the Paleogene period; primitive mammals dated back as far as the Triassic period, 230 million years ago. In the absence of dinosaurs, though, mammals were free to radiate into a variety of open ecological niches. During the Paleocene and Eocene epochs, mammals still tended to be fairly small, but had already started evolving along definite lines: the Paleogene is when you can find the earliest ancestors of whales, elephants, hoofed mammals.

By the Oligocene epoch, at least some mammals had begun to grow to respectable sizes, though they weren't nearly as impressive as their descendants of the ensuing Neogene period.

Birds. During the early part of the Paleogene period, birds, and not mammals, were the dominant land animals on earth . One early evolutionary trend was toward large, flightless, predatory birds like Gastornis, which superficially resembled meat-eating dinosaurs, but subsequent eons saw the appearance of more diverse flying species, which were similar in many respects to modern birds.

Reptiles. Although dinosaurs and marine reptiles had gone completely extinct by the start of the Paleogene period, the same wasn't true for their close relative the crocodiles, which not only managed to survive the K/T Extinction but actually flourished in its aftermath. The deepest roots of snake and turtle evolution can be located in the later Paleogene, and small, inoffensive lizards evolved.

Plant Life :Flowering plants, which had already made an appearance toward the end of the Cretaceous period, continued to flourish during the Paleogene. The gradual cooling of the earth's climate paved the way for vast deciduous forests, mostly on the northern continents, with jungles and rain forests increasingly restricted to equatorial regions. Toward the end of the Paleogene period, the first grasses appeared, which would have a significant impact on animal life during the ensuing Neogene period, spurring the evolution of both prehistoric horses and the saber-toothed cats that preyed on them.

Marine Life :

Not only the dinosaurs went extinct 65 million years ago; so did their vicious marine cousins, the mosasaurs, along with the last remaining plesiosaurs and pliosaurs. This sudden vacuum at the top of the aquatic food chain naturally spurred the evolution of sharks (which had already been around for hundreds of millions of years, though in smaller sizes). Mammals had yet to venture fully into the water, but the earliest, land-dwelling ancestors of whales survived the Paleogene landscape, most notably in central Asia.  

Terrestrial Life During the Neogene Period

Mammals. Global climate trends, combined with the spread of newly evolved grasses, made the Neogene period the golden age of open prairies and savannahs. These extensive grasslands spurred the evolution of even- and odd-toed ungulates, including prehistoric horses and camels (especially in North America), as well as deer, pigs and rhinoceroses.

During the later Neogene, the interconnections between Eurasia, Africa, and North and South America set the stage for a confusing network of species interchanges, resulting (for example) in the near extinction of South America's Australia-like megafauna.

Birds. While birds never quite matched the size of their distant mammalian cousins, some of the flying and flightless species of the Neogene period were truly enormous (for example, the airborne Argentavis and Osteodontornis both exceeded 50 pounds.) The end of the Neogene marked the extinction of most of the flightless, predatory birds of South America and Australia, the last ones being wiped out by the end Pleistocene.

 Argentavis osteodontornis

Reptiles. A large part of the Neogene period was dominated by gigantic crocodiles, which still never quite managed to match the size of their Cretaceous forebears. This 20-million-year span also witnessed the continuing evolution of prehistoric snakes and (especially) prehistoric urtles, the latter of which began to reach truly impressive proportions by the start of the Pleistocene epoch.

Plant Life:There were two major trends in plant life during the Neogene period. First, plunging global temperatures spurred the rise of massive deciduous forests, which replaced jungles and rain forests in high northern and southern latitudes. Second, the worldwide spread of grasses went hand-in-hand with the evolution of mammalian herbivores, culminating in today's familiar horses, cows, sheep, deer, and other grazing and ruminant animals.  

Marine Life During the Neogene Period

Although prehistoric whales started to evolve in the preceding Paleogene period, they didn't become exclusively marine creatures until the Neogene, which also witnessed the continuing evolution of the first pinnipeds (the mammalian family that includes seals and walruses) as well as prehistoric dolphins. Prehistoric sharks maintained their status at the top of the marine food chain; Megalodon, for example, had already appeared at the end of the Paleogene, and continued its dominance throughout the Neogene as well.

Outline of cenozoic era

Terrestrial life During the Pleistocene Epoch

Mammals. The dozen or so ice ages of the Pleistocene epoch destroyed megafauna mammals, the largest examples of which were simply unable to find enough food to sustain their populations. The wolly mammoth lived during this period.Conditions were especially severe in North and South America and Eurasia, where the late Pleistocene witnessed the extinction of Smilodon (the Saber-Toothed Tiger), the Giant Short-Faced Bear, Glyptodon (the Giant Armadillo) and Megatherium (the Giant Sloth). Camels disappeared from North America, as did horses, which were only reintroduced to this continent during historical times, by Spanish settlers.

Birds. During the Pleistocene epoch, bird species continued to flourish around the globe, inhabiting various ecological niches. Sadly, the giant, flightless birds of Australia and New Zealand, such as Dinornis (the Giant Moa) and Dromornis (the Thunder Bird), quickly succumbed to predation by human settlers. Some Pleistocene birds, like the Dodo and the Passenger Pigeon, managed to survive well into historical times..

Reptiles. As with birds, the big reptile story of the Pleistocene epoch was the extinction of oversized species in Australia and New Zealand, most notably the giant monitor lizard Megalania(which weighed up to two tons) and the giant turtle Meiolania (which "only" weighed half a ton). Like their cousins around the globe, these gigantic reptiles were doomed by a combination of climate change and predation by early humans

Plant Life During the Pleistocene Epoch

There were no major plant innovations during the Pleistocene epoch; rather, during these two million years, grasses and trees were at the mercy of intermittently plunging and rising temperatures. As during preceding epochs, tropical jungles and rain forests were confined to the equator, with deciduous forests and barren tundra and grasslands dominating northern and southern regions.

Marine Life During the Pleistocene Epoch

The Pleistocene epoch witnessed the final extinction of the giant shark Megalodon, which had been the top predator of the oceans for millions of years; otherwise, though, this was a relatively uneventful time in the evolution of fish, sharks and marine mammals. One notable pinniped that appeared on the scene during the Pleistocene was Hydrodamalis (aka Steller's Sea Cow), a 10-ton behemoth that only went extinct 200 years ago.Dugong

Dugong seal

Holocene epoch:- “the age of man”Plant and animal lifeAnimal and plant life have not changed much during the relatively short Holocene, but there have been major shifts in the distributions of plants and animals. A number of large animals including mammoths and mastodons, saber-toothed cats like Smilodon and Homotherium, and giant sloths disappeared in the late Pleistocene and early Holocene—especially in North America.

The Holocene extinction event is a name customarily given to the widespread, ongoing extinction of species during the modern Holocene epoch. The genera vary from mammoths to dodos, to species in the rainforest dying every year. Because some believe the rate of this extinction event is comparable to the "Big Five" mass extinctions, it is also known as the Sixth Extinction, although the actual numbers of extinct species are not yet similar to the major mass extinctions of the geologic past.

In broad usage, the Holocene extinction event includes the remarkable disappearance of large mammals, known as megafauna, by the end of the last ice age 9,000 to 13,000 years ago. Such disappearances have been considered as either a response to climate change, a result of the proliferation of modern humans, or both. Also, some scientists have considered the possibility of new diseases and super-viruses. These extinctions, occurring near the Pleistocene/Holocene boundary, are sometimes referred to as the Pleistocene extinction event, or Ice Age extinction event. The Ice Age extinction event is characterized by the extinction of many large mammals weighing more than 40 kg. Among the major megafauna exterminated about 9,000 to 15,000 years ago were the woolly mammoth, the woolly rhinoceros, the Irish elk, the cave lion, the cave bear, and saber-toothed cats.

woolly rhinoceros

Irish elk

cave bear

Within the past 2,000 years, a large number of species have become extinct in ways more clearly linked to human dispersal or activity.The observed rate of extinction has risen dramatically in the last 50 years. Only during these most recent parts of the extinction have plants also suffered large losses.Among the human activities currently considered as impacting extinctions are overhunting (either directly, or indirectly by decimation of prey populations), introduction of infectious diseases (perhaps carried by associated animals such as rats or birds), increased interspecific competition, habitat destruction. The destruction of large mammals could have had even wider impacts on the ecosystems of which they were part. 

Psychozoic era:Pertaining to the period of geological time characterized by the presence of human intelligence.

By:TEJAS KUMAR.S.K.