In an examination of mammal body mass changes over time, the maximum increase possible in a given time interval was found to scale with the interval length raised to the 0.25 power.
One observation that has been made about the evolution of larger body size is that rapid rates of increase that are often seen over relatively short time intervals are not sustainable over much longer time periods.
These characteristics, although not exclusive to such megafauna, make them vulnerable to human overexploitation, in part because of their slow population recovery rates. Megafauna – in the sense of the largest mammals and birds – are generally K-strategists, with high longevity, slow population growth rates, low mortality rates, and (at least for the largest) few or no natural predators capable of killing adults. 3.2 Consequences of depletion of megafauna.The term megafauna is very rarely used to describe invertebrates, though it has occasionally been used for some species of invertebrates such as Coconut Crabs and Japanese spider crabs, as well as extinct invertebrates that were much larger than all similar invertebrate species alive today, for example the 1 m (3 ft) dragonflies of the Carboniferous period. Other common uses are for giant aquatic species, especially whales, as well as any of the larger wild or domesticated land animals such as larger antelope, deer, horse and cattle, as well as dinosaurs and other extinct giant reptilians. Megafauna are also categorized by the order of animals that they belong to, which are mammals, birds, reptiles, amphibians, fish, and invertebrates. Megafaunal species may be categorized according to their dietary type: megaherbivores (e.g., elephants), megacarnivores (e.g., lions), and, more rarely, megaomnivores (e.g., bears). Wild equines are another example of megafauna, but their current ranges are largely restricted to the old world, specifically Africa and Asia. Of these five categories of large herbivores, only bovines are presently found outside of Africa and southern Asia, but all the others were formerly more wide-ranging, with their ranges and populations continually shrinking and decreasing over time. Among living animals, the term megafauna is most commonly used for the largest extant terrestrial mammals, which includes (but is not limited to) elephants, giraffes, hippopotamuses, rhinoceroses, and large bovines. The term is especially associated with the Pleistocene megafauna – the land animals often larger than modern counterparts considered archetypical of the last ice age, such as mammoths, the majority of which in northern Eurasia, the Americas and Australia became extinct within the last forty thousand years. In practice, the most common usage encountered in academic and popular writing describes land mammals roughly larger than a human that are not (solely) domesticated. The first of these include many species not popularly thought of as overly large, and being the only few large animals left in a given range/area, such as white-tailed deer, thomson's gazelle, and red kangaroo. The most common thresholds used are weight over 45 kilograms (100 lb) (i.e., having a mass comparable to or larger than a human) or over a tonne, 1,000 kilograms (2,205 lb) (i.e., having a mass comparable to or larger than an ox). In terrestrial zoology, the megafauna (from Greek μέγας megas "large" and New Latin fauna "animal life") comprises the large or giant animals of an area, habitat, or geological period, extinct and/or extant. The African bush elephant, Earth's largest extant land animal
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