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The Cenozoic Era, also known as the ''Age of Mammals', is Earth's current geological era, representing the last 66 million years. The era is characterised by the dominance of mammals, insects, birds, and angiosperms (flowering plants). During this time, mammals proliferated from a few small, simple forms into a diverse collection of terrestrial, marine, and flying animals. Australia, in particular, saw the arrival and diversification of marsupials, which became the dominant group of mammals on the continent. The Cenozoic Era also witnessed significant changes in Australia's geography, climate, and vegetation, shaping the evolution of its animal life.
| Characteristics | Values |
|---|---|
| Name | Cenozoic Era |
| Other Names | Cænozoic, Caenozoic, Cainozoic, Kainozoic, Age of Mammals |
| Time Period | Last 66 million years |
| Preceding Era | Mesozoic |
| Animals | Mammals, marsupials, monotremes, birds, snakes, rhinoceroses, primates, penguins, pelicans, ducks, gulls, alligators, horses, dogs, cats, pigs, camels, monkeys |
| Size of Animals | Some mammals grew very large |
| Number of Species | High diversity of species |
| Geological Events | Collision with Southeast Asia, Circum-Antarctic Current, global cooling |
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What You'll Learn
Marsupials
In Australia, marsupials thrived and evolved into diverse forms, including the Diprotodon, a genus of giant wombats that rivalled mastodons in size. Marsupials such as the grey cuscus and the brushtail possum were introduced to nearby islands of Australia, particularly New Zealand, over 10,000 years ago.
Today, about 70% of the 334 extant marsupial species are found in Australia, Tasmania, New Guinea, and nearby islands. Marsupials played a significant role in the country's ecosystem, with some growing to massive sizes. The Thylacoleo carnifex, or marsupial lion, was the largest known carnivorous mammal in prehistoric Australia, comparable in size to female placental lions and tigers. Other large marsupials included the giant koala, Phascolarctos stirtoni, and the Simosthenurus occidentalis, a leaf-eating kangaroo.
The arrival of humans and the use of fire may have contributed to the extinction of some marsupial species, known as megafauna, around 50,000 to 45,000 years ago. However, rock art in the Kimberley region and Arnhem Land depicts a marsupial lion and other extinct creatures, preserving their memory.
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Monotremes
During the Cenozoic Era, Australia was still attached to Antarctica as part of the southern supercontinent Gondwana. This landmass began to break up around 164 to 145 million years ago during the Late Jurassic, and Australia continued to move away from Antarctica during the Cenozoic Era. By the beginning of the Oligocene Epoch, about 34 million years ago, the ocean between Australia and Antarctica was wide enough to allow the unimpeded flow of the Circum-Antarctic Current, resulting in a global cooling event.
The Cenozoic Era was a period of significant geological activity in Australia. The Eastern Highlands, a low plateau, rose about 90 million years ago, and parts of the Great Western Plateau rose even earlier during the Paleozoic. The riverine plains of southeastern Australia, inherited from former sea and lake basins, were made fertile by carefully managed irrigation. The arid zone expanded, and giant forebears of the Holocene marsupial animals became extinct.
While monotremes are now only found in Australia and New Guinea, fossil evidence suggests that they once lived in South America as well. A tooth discovered in Argentina, dated to 63-61 million years ago, belonged to an extinct species of platypus known as the Patagonian platypus. However, monotremes did not survive in South America, and the reason why they did not use the land connection to leave Australia remains a mystery.
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Reptiles
The Cenozoic Era, which began 66 million years ago, is considered the ''Age of Mammals'' due to the proliferation of mammals during this period. However, reptiles also persisted and evolved during this era, after the extinction of large Mesozoic reptiles like dinosaurs.
During the Eocene Epoch of the Cenozoic, which ranged from 56 million years to 33.9 million years ago, the climate was warm and moist. This epoch marked the end of large reptiles as dominant life forms, with the previous epoch, the Paleocene, experiencing a sudden global warming event. The exact cause of this temperature increase is unknown but may be attributed to the release of carbon dioxide and methane into the oceans and atmosphere.
The warm and moist conditions of the Eocene allowed for the presence of alligators within the Arctic Circle. However, by the end of this epoch, temperatures dropped drastically, leading to the formation of glaciers in Antarctica and the replacement of subtropical forests with temperate forests. The cooling trend that began during the Late Cretaceous continued into the Cenozoic, resulting in the restriction of tropical climates to the equator.
The Cenozoic Era, also known as the age of savannas, witnessed the emergence of grasslands and an increase in the body size of mammals. The diversification of flowering plants, which began in the Mesozoic, continued into the Cenozoic, replacing conifers and other gymnosperms. Grasses played a significant role in shaping the evolution of birds and mammals that fed on them.
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Birds
The Cenozoic Era, also known as the Age of Mammals, represents the last 66 million years of Earth's history. It was characterised by the dominance of mammals, insects, birds and angiosperms (flowering plants). The Cenozoic is the era when the continents moved into their current positions, with Australia-New Guinea eventually colliding with Southeast Asia.
During the Cenozoic, birds diversified rapidly, with some flightless birds growing larger than humans. These species are sometimes referred to as "terror birds", and were formidable predators. The ranges of many Cenozoic bird clades were governed by latitude and temperature and have contracted over the course of this era as the world cooled.
The earliest known bird, Archaeopteryx lithographica, lived 150 million years ago during the Jurassic Period. It lived alongside flying reptiles called pterosaurs. During the Jurassic, Africa, South America, Australia, and Antarctica remained united as part of the supercontinent Gondwana. Over the following 84 million years, a large number of primitive bird species, equipped with teeth, hand claws, and long bony tails, appeared.
In Australia, the term megafauna refers to the megafauna present during the Pleistocene Epoch. Most of these species became extinct during the latter half of the Pleistocene, as part of the broader global Late Quaternary extinction event. The roles of human and climatic factors in their extinction are contested.
One of these megafauna birds was Genyornis newtoni, a flightless bird that became extinct in Australia. Chemical analysis of fragments of its eggshells revealed scorch marks consistent with cooking in human-made fires, indicating the first direct evidence of human contribution to the extinction of a species of Australian megafauna. Another bird, Dynatoaetus gaffae, was the largest bird of prey in Australia, second only to the Haast's eagle of New Zealand.
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Insects
The Cenozoic Era, also known as the Age of Mammals, is the current geological era and has been ongoing for the last 66 million years. It is characterised by the dominance of mammals, insects, birds, and angiosperms (flowering plants).
During the Eocene Epoch, for example, fossil insects have been remarkably preserved in the Rocky Mountains of Colorado. Insects from this epoch have also been found in the Green River Formation, which extends across Utah, Colorado, and Wyoming. The Green River Formation is known for its rich fossil deposits, including those of insects, plants, and fish.
Additionally, in the Pliocene Epoch, insect fossils have been discovered alongside those of molluscs, macroalgae, microfossils, shells, crabs, and porpoises in various localities. The study of these fossils provides valuable insights into the diversity and distribution of insect life during the Cenozoic Era.
The Cenozoic Era, with its diverse range of ecosystems and habitats, provided a variety of niches for insects to occupy and adapt to. The availability of flowering plants, which characterise this era, also played a crucial role in supporting insect populations and facilitating their ecological success.
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Frequently asked questions
The Cenozoic Era, also known as the Age of Mammals, represents the last 66 million years of Earth's history. It is characterised by the dominance of mammals, insects, birds and angiosperms (flowering plants).
Marsupials arrived in Australia around 50 million years ago and became the dominant group of mammals in the country. These included kangaroos, wombat-like mammals called diprotodons, and the American opossum. Another group of animals that developed during this time were monotremes, egg-laying mammals that nurse their young without teats, including the platypus and echidna.
During the Cenozoic Era, Australia was still joined to New Guinea and Tasmania by dry land. The climate was arid, with hot, dry summers and strong winds.
