Fascinating Animals

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The Age of the Mammals from 65 million years ago (mya)


65 milion years ago (mya) the Cenozoic Era began in the time-scale of geological units.  Each Era is divided into Periods of time, and each Period of the Cenozoic Era is divided into Epochs of time.   Please click on the link below for a diagram of the Periods and Epochs in the Cenozoic Era, and for important information about the rise of the Mammals.  This link below shows that the last Ice Age ended 10,000 years ago and the time period (epoch) since then is called the Holocene Epoch.  There has been a series of “ice ages” over billions of years, with the “Great Ice Age” occurring during the Pleistocene Epoch of the Cenozoic Era, 1.8 million to 10,000 years ago.


The dinosaurs had become extinct and now it was the Age of the Mammals, arising in the Palaeocene Epoch of the Cenozoic Era, 65 to 55 mya; with the modern line of human beings (from the genus Homo) developing 1.6 mya to 2 mya.  During the Pleistocene Epoch of the Cenozoic Era, there were four completely separate glacial advances in North America.  The advances were separated by long intervals of ice withdrawal, sufficient to permit the previously occupied area covered by ice to be reoccupied by plants and animals.   Glaciation severely affected life on the earth.   Animal and plant life was forced out of vast portions of the land covered by continental ice sheets. Large-scale migrations must have taken place as the ice sheets grew and climatic changes occurred.

Click here to see some wonderful preserved skeletons of some of the “mega-fauna” (large mammals) of the Pleisotcene Epoch (1.8 mya to 10,000 years ago).

Mammals are part of the Phylum, Chordata, the group of vertebrates (animals with backbones) to which human beings belong. Mammals are distinguished from all other animals by their mammary glands, glands that produce milk to feed the young. Mammals are also unique in having hair, although it may be scant. They are warm-blooded and air-breathing, and all but the whales and sirenians, or sea cows, have four limbs.

Mammals appeared on the earth long before the extinction of the dinosaurs. They originated in the early Jurassic Period of the Mesozoic Era about 200 million years ago. Please click on the link below to see a Table showing all the Eras, including the Mesozoic and the Cenozoic Eras. (Note: you will see the Table shows the tradionally accepted view of the Cenozoic Era divided into the Quaternary and Tertiary periods, but some people divide this Era into 3 periods, as in the first link above in this post).


It was only after the dinosaurs disappeared 65 million years ago, that the mammals began their great diversification and became the dominant land animals. Within 10 million years, there were mammals of all kinds living in many different habitats on land, in the sea and in the air. With dinosaurs gone, mammals could exploit the planet’s resources themselves.

The most spectacular event in Cenozoic Era terrestrial environments has been the diversification and rise to dominance of the mammals. From only a few groups of small mammals in the late Cretaceous Period of the Mesozoic Era that lived in the undergrowth and hid from the dinosaurs, more than 20 orders of mammals evolved rapidly and were established by the early Eocene Epoch of the Cenozoic Era. Although there is some evidence that this adaptive radiation event began well before the end of the Cretaceous Period of the Mesozoic Era, rates of speciation accelerated during the Paleocene and Eocene Epochs of the Cenzoic Era.

Some of them were very large, and those weighing more than about 100 pounds are referred to as the Megafauna. Most of these species are extinct (no longer living).

The current continents emerged during the Cenozoic era, and the initial tropical conditions were replaced by a colder drier climate, possibly caused by the Himalayan uplift. The appearance of grass meant the rise of grazing mammals, and the cooler drier world allowed modern mammalian groups to evolve, along with other lineages now extinct and a few archaic hold-overs.

Among the newcomers were the anthropoid apes that culminated in the Australopithecine hominids of Africa (Australopithecus).  About five million years ago, some African anthropoids started to walk upright. Decreasing temperatures and a polar landmass of Antarctica resulted in a new Ice Age. This era saw the rise of Man (Homo erectus, Neanderthal man and Cro Magnon man) over 1.8 mya, and the rise of the use of stone tools and fire, and the extinction of much megafauna. The rise of human civilization and human activities transformed the globe, but at the cost of some environmental destruction.

An infra-order of the sub-order Haplorhini of the Order Primates is Anthropoidea (or the Anthropoids), which consists of the Simian primates ( i.e. human beings, monkeys, marmosets, tarsiers, tamarins and apes).

Hominids” are any of the modern or extinct bipedal (two legged) primates of the Family Hominidae (including all species of the genera Homo and Australopithecus).

The Great Apes  (gorillas, chimps and orang-utans) and human beings (Homo sapiens) that walk upright are called Hominids.

The first known hominid group is called Australopithecus, meaning ‘southern anthropoid‘, and lived up to a million years ago.

Click   here   for a Chart giving more information about the Anthropoids.  Click here to see what Simians are.  To find out more about Australopithecus and listen to how it is pronounced, go to this website    here.    A timeline showing the evolution of Homo sapiens (human beings) from the Australopithecus species can be found    here.

Saber-toothed Cat

The Megafauna of the Cenozoic included fascinating beasts like

Auroch                (the giant cattle ancestor)

Castoroides        (the Giant Beaver)

Coelodonta         (the Woolly Rhino)

Mammoths        (like Manfred, in the movie “Ice Age”)

Mastodons        (long horned woolly mammoth-like creature)

Megaloceros    (the giant deer)

Smilodon          (the biggest saber-toothed “cat” of them all – wrongly called “saber-toothed tiger”)


Although elephants, rhinoceroses and assorted large mammals are still with us today, most of the world’s megafauna died off anywhere from 50,000 to 2,000 years ago, an extended demise known as the Quaternary Extinction Event.

Scientists point to two main culprits: first, the global plunge in temperatures caused by the last Ice Age, in which many large animals starved to death (herbivores or plant eater from lack of their usual plants, carnivores or meat eaters from lack of their usual herbivores), and second, the rise of the most dangerous mammals of them all – humans.

Megafauna collapse led to major ecological changes and helped create the vegetation we recognise today.

Click here to see a list of pre-historic Mammals, from A – Z.

Today, there are about 5,000 species of living (extant) Mammal species, divided or arranged into 26 Orders.   The Orders include the Primates (apes, lemurs, monkey, human beings).

Click here to see a list of these living Mammals.    This post here explains about how living organisms are classifed, according to taxonomy.

An early horse – Mesohippus celer







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