<P> The Quaternary spans from 2.58 million years ago to present day, and is the shortest geological period in the Phanerozoic Eon . It features modern animals, and dramatic changes in the climate . It is divided into two epochs: the Pleistocene and the Holocene . </P> <P> The Pleistocene lasted from 2.58 million to 11,700 years ago . This epoch was marked by ice ages as a result of the cooling trend that started in the Mid-Eocene . There were at least four separate glaciation periods marked by the advance of ice caps as far south as 40 degrees N latitude in mountainous areas . Meanwhile, Africa experienced a trend of desiccation which resulted in the creation of the Sahara, Namib, and Kalahari deserts . Many animals evolved including mammoths, giant ground sloths, dire wolves, saber - toothed cats, and most famously Homo sapiens . 100,000 years ago marked the end of one of the worst droughts of Africa, and led to the expansion of primitive man . As the Pleistocene drew to a close, a major extinction wiped out much of the world's megafauna, including some of the hominid species, such as Neanderthals . All the continents were affected, but Africa to a lesser extent . That continent retains many large animals, such as hippos . </P> <P> The Holocene began 11,700 years ago and lasts until to present day . All recorded history and "the history of the world" lies within the boundaries of the Holocene epoch . Human activity is blamed for a mass extinction that began roughly 10,000 years ago, though the species becoming extinct have only been recorded since the Industrial Revolution . This is sometimes referred to as the "Sixth Extinction". More than 322 species have become extinct due to human activity since the Industrial Revolution . </P> <P> It has been demonstrated that changes in biodiversity through the Phanerozoic correlate much better with the hyperbolic model (widely used in demography and macrosociology) than with exponential and logistic models (traditionally used in population biology and extensively applied to fossil biodiversity as well). The latter models imply that changes in diversity are guided by a first - order positive feedback (more ancestors, more descendants) or a negative feedback that arises from resource limitation, or both . The hyperbolic model implies a second - order positive feedback . The hyperbolic pattern of the human population growth arises from a second - order positive feedback, caused by the interaction of the population size and the rate of technological growth . The character of biodiversity growth in the Phanerozoic Eon can be similarly accounted for by a feedback between the diversity and community structure complexity . It is suggested that the similarity between the curves of biodiversity and human population probably comes from the fact that both are derived from the superposition on the hyperbolic trend of cyclical and random dynamics . </P>

Which of the following is not one of the eras within the phanerozoic eon