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Age of Animals

Quaternary Period, 2.588 MYA - present

Quaternary Period
  • During this period four Ice Ages, separated by warmer interglacial periods, covered the northern land areas. As the ice slowly advanced and retreated, the climate zones and their mammal faunas moved across the continents via the Bering region and Panama Isthmus. An unexplained feature of this period was the appearance of giant representatives of nearly every order of mammals, from platypus, kangaroo and lemur, to deer, beaver, edentate and unusually large elephant. However between 40,000 and 5,000 years ago many of the world's largest mammals died out as shown in Figure 17a. Most of them weight 90 lbs or more. The smaller animals such as mice and shrews almost all survived. Irrespective to the cause of extinction (there are many speculations such as climate change and slaughtered by humans),
  • Figure 17a Quaternary Period Extinction [view large image]

    large animals have the disadvantages that its smaller size of population is more vulnerable and they have a much slower rate of reproduction taking years to give birth.

    The woolly mammoths lived from the Pliocene epoch around 5 MYA to about 4,000 years ago in Africa, Europe, Asia, and North America (see "Mammoth" by Wikipedia for more detail). They were plentiful before the onset of the ice ages 45,000 years ago (see the illustration in "Geological and Biological Evolutions"). Most populations in the mainland disappeared around 10,000 years ago after the end of the ice ages. A few lingered on in the Wrangel Island (Figure 17b,c) and finally died out some 4,000 years ago.
    Death of the Woolly Mammoths Close examination of their genome shows that it was riddled with deletions and an abundance of stop codons (for stopping mRNA transcription). In particular, the mutated genes are related to smell, urinary proteins, and translucent fur (Figure 17b,b). The meltdown was caused by small population, which permits bad mutations to rack up, since there was no competition. Such observation is very important for the preservation of modern species on the brink of extinction.

    Figure 17b Death of the Woolly Mammoths [view large image]

    (see a BBC documentary on "Woolly Mammoth Died Out", also see the 2017 article on "Dying woolly Mammoths" in Nature).
    Thus, starting from some lifeless molecules in deep sea hydrothermal vents, life has evolved to some 10 million species today. Figure 20 shows the biodiversity horizontally, while the vertical scale indicates the important events during the last 4.5 billion years. Biodiversity is not static; it is a system in constant evolution, from a species, as well as from an individual organism point of view. The average half-life of a species is estimated at between one and four million years, and 99% of the species that have ever lived on earth are today extinct. It is not distributed evenly on earth either. It is consistently richer in the tropics. As one approaches polar regions one finds larger and larger populations of fewer and fewer species. Flora and fauna vary depending on climate, altitude, soils and the presence of other species. At present, the number of species estimated to have gone extinct as a result of human activities is still far smaller than are observed during the major mass extinctions of the
    Evolution Idyllic Scenery geological past. However, it has been argued that the present rate of extinction is sufficient to create a major mass extinction in less than 100 years. Others dispute this and suggest that the present rate of extinctions could be sustained for many thousands of years before the loss of biodiversity matches the more than 20% losses seen in past global extinction events. Figure 21 is an artist's impression of an idyllic scenery at the dawn of civilization.

    Figure 20 Diversity of species [view large image]

    Figure 21 Idyllic Scenery before the Mad Rush [view large image]

    2A 2006 report exonerates humans from slaughtering the large mammals. It is found that although mammoths and horses became extinct, animals such as the wapiti, bison and moose survived and thrived, suggesting that the faunal change was a function of ecological and vegetational change rather than human-induced "overkill".

    See "Anatomy of Animals" in the special topics for more information about the living animals, which has branched and evolved from their ancestors to the present-day forms and structures.

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