Megafauna

The term megafauna (Ancient Greek megas "large" + New Latin fauna "animal") has two distinct meanings in the biological sciences. The less commonly found meaning is of any animal which can be seen with the unaided eye, in contrast to microfauna - however, the standard term for this category is macrofauna rather than megafauna. The more commonly found meaning, discussed in this article, is of "giant", "very large" or "large" animals — although there is no universal definition of a minimum size.

In practice the most common usage encountered in academic and popular writing describes land animals roughly larger than a human which are not (solely) domesticated. The term is especially associated with the Pleistocene megafauna — the giant and very large land animals considered archetypical of the last ice age such as mammoths.^[1] It is also commonly used for the largest wild land animals surviving today, especially elephants, giraffes, hippopotamuses, rhinoceroses, moose, condors, etc.

Other common uses are for giant aquatic species, especially whales, any larger wild or domesticated land animals such as larger antelope and cattle, and dinosaurs and other extinct giant reptilians.

Some technical definitions of size however go down to as small as 40–45 kg (88–99 lb)^[2]^[3] and thus encompass a great many animals commonly regarded as not especially large, such as goats and (larger) domestic dogs.

The term is also sometimes applied to animals (usually extinct) of great size relative to a more common or surviving type of the animal, for example the 1 m (3.28 ft) dragonflies of the Carboniferous age.

Ecological strategy of megafauna

Megafauna — in the sense of the largest mammals and birds — are generally K-strategists, with great longevity, slow population growth rates, low death rates, and few or no natural predators capable of killing adults. These characteristics, although not exclusive to such megafauna, make them highly vulnerable to human over-exploitation.

Megafaunal mass extinctions

A well-known mass extinction of megafauna, the Pleistocene-Holocene extinction event, occurred at the end of the last ice age glacial period, and wiped out many giant ice age animals such as mammoths. However, this extinction pulse near the end of the Pleistocene was just one of a number of such megafaunal extinction pulses that have occurred during the last 50,000 years over much of the Earth's surface, with Africa and southern Asia being largely spared. Outside of Eurasia, these megafaunal extinctions followed a distinctive landmass-by-landmass pattern that closely parallels the spread of humans into previously uninhabited regions of the world, and which shows no correlation with climate.^[4] Australia was struck first around 50,000 years ago, followed by the Americas 13,000 years ago, the Antilles 6000 years ago, Madagascar 2000 years ago, New Zealand 500 years ago, and more isolated islands subsequently.

A number of other mass extinctions occurred earlier in Earth's geologic history, in which some or all of the megafauna of the time also died out. Famously, in the Cretaceous–Tertiary extinction event the dinosaurs and most other giant reptilians were eliminated. However, the earlier mass extinctions were more global and not so selective for megafauna; e.g., many other species, including plants, marine invertebrates and plankton went extinct along with the dinosaurs. Thus, the earlier events must have been caused by more generalized types of disturbances to the biosphere.

Examples of megafauna

The following are some of the animals often considered as megafauna (in the sense of the "large animal" definition):

Elephants - The largest living mammals on land. The African Bush Elephant - Loxodonta africana - can reach a length of about 16 feet and a weight of 7 6/8 tons. Extinct species of elephants are termed mammoths (Mammuthus); mastodons (Mammut) are distantly related extinct proboscideans.
Whales, dolphins, and porpoises are marine mammals. The Blue Whale - Balaenoptera musculus - is the largest known animal that has ever lived. This species is a baleen whale. The Sperm Whale - Physeter macrocephalus is considered the largest toothed whale. The Orca is the largest dolphin.
Rhinoceroses are odd-toed ungulates with horns made of keratin; a material the same as hair.
A hippopotamus is a large aquatic even-toed ungulate.
Giraffes are considered the tallest land mammals.
The glyptodonts were a group of large, heavily armored animals related to living armadillos. Most became extinct during the Pleistocene.
Mammals of the ground sloth family were usually slow, terrestrial animals, related to the modern tree sloth. They too became extinct in Pleistocene times. The largest genera were Megatherium and Eremotherium.
Seals, sea lions, and walruses are marine carnivores that have specialized in swimming. The Southern Elephant Seal is one of the largest, having a length of around 10 feet.
Bears are large carnivorous mammals. The Polar Bear - Ursus maritimus - has a body weight of 1,500 pounds.
Big cats include mammals like the Tiger - Panthera tigris - and Lion - Panthera leo. These felids are distinguished by morphological features which enable them to roar. Extinct big cat species include the Saber tooth tiger - Smilodon and American Lion - Panthera leo atrox.
Bovine mammals often grow to large sizes, like the Water buffalo, Bison, and Gaur; often weighing over 1,000 pounds.
A ratite is a very diverse group of flightless birds, the largest were probably the Moa, growing to heights of 11 feet, taller than the largest living bird, the Ostrich - Struthio camelus.
Alligators and crocodiles are large aquatic reptiles. The largest, the saltwater crocodile Crocodylus porosus, grows to a weight of 1,700 pounds.
Some creatures living in the deep oceans have grown to large sizes. This includes the giant squid and the colossal squid, both (although rarely seen in the wild) have been reported to grow very large.