Megafauna

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This article is about large land animals. For naked-eye-visible bottom-dwelling animals, see Macrobenthos.

In terrestrial zoology, megafauna (Ancient Greek megas "large" + New Latin fauna "animal") are "giant", "very large" or "large" animals. Their original and most common definition is 100 lb, often rounded in the metric system to 40 or 45 kg.^[1]^[2] This thus includes many species not popularly thought of as overly large, such as white-tailed deer and red kangaroo.

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.^[3] It is also commonly used for the largest extant wild land animals, 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.

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.

[edit] 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.

[edit] 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 woolly mammoths, in the Americas and northern Eurasia. However, this extinction pulse near the end of the Pleistocene was just one of a series of 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]^[5] Australia was struck first around 50,000 years ago, followed by the Solomon Islands 30,000 years ago, the Americas 13,000 years ago, Cyprus 9000 years ago, the Antilles 6000 years ago, New Caledonia 3000 years ago, Madagascar 2000 years ago, New Zealand 800 years ago, the Mascarenes 400 years ago, and the Commander Islands 250 years ago. Actually, nearly all of the world's isolated islands could furnish examples of extinctions occurring shortly after the arrival of Homo sapiens. (Most of these islands, such as the Hawaiian Islands, never had terrestrial megafauna, so their extinct fauna were smaller.)

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; i.e., many species of other types, 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.

[edit] Examples of megafauna

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

class Mammalia
- infraclass Metatheria
  - order Diprotodontia
    - The red kangaroo (Macropus rufus) is the largest living Australian mammal and marsupial at a weight of up to 85 kg (187 lb). However, its extinct relative, the giant short-faced kangaroo Procoptodon goliah reached 230 kg (510 lb), while extinct diprotodonts attained the largest size of any marsupial in history, up to an estimated 2,750 kg (6,060 lb).
- infraclass Eutheria
  - superorder Afrotheria
    - order Proboscidea
      - Elephants are the largest living land animals. They and their relatives arose in Africa, but until recently had a nearly worldwide distribution. The African bush elephant (Loxodonta africana) has reached shoulder heights up to 4.3 m (14 ft) and weights up to 13 tons. Among recently extinct proboscideans, mammoths (Mammuthus) were close relatives of elephants, while mastodons (Mammut) were much more distantly related.
    - order Sirenia
      - The largest sirenian at up to 1500 kg is the West Indian manatee (Trichechus manatus). Steller's sea cow (Hydrodamalis gigas) was probably around five times as massive, but unfortunately was exterminated by humans within 27 years of its discovery off the remote Commander Islands in 1741. In prehistoric times this sea cow also lived along the coasts of northeastern Asia and northwestern North America; it was apparently eliminated from these more accessible locations by aboriginal hunters.
  - superorder Xenarthra
    - order Cingulata
      - The glyptodonts were a group of large, heavily armored ankylosaur-like xenarthrans related to living armadillos. They originated in South America, invaded North America during the Great American Interchange, and went extinct at the end of the Pleistocene epoch.
    - order Pilosa
      - Ground sloths were another group of slow, terrestrial xenarthrans, related to modern tree sloths. They had a similar history, although they reached North America earlier, and spread farther north. The largest genera, Megatherium and Eremotherium, reached sizes comparable to elephants.
  - superorder Euarchontoglires
    - order Primates
      - The largest living primate, at up to 266 kg (586 lb), is the gorilla (Gorilla beringei and Gorilla gorilla). The extinct Malagasy sloth lemur Archaeoindris reached a similar size, while the extinct Gigantopithecus blacki of Southeast Asia is believed to have been several times larger.
    - order Rodentia
      - The extant capybara (Hydrochoerus hydrochaeris) of South America, the largest living rodent, weighs up to 65 kg (140 lb). Several recently extinct North American forms were larger; the capybara Neochoerus pinckneyi (another neotropic migrant) was about 40% heavier; the giant beaver (Castoroides ohioensis) was similar. The extinct blunt-toothed giant hutia (Amblyrhiza inundata) of several Caribbean islands may have been larger still. However, several million years ago South America harbored much more massive rodents. Phoberomys pattersoni, known from a nearly full skeleton, probably reached 700 kg (1,500 lb). Fragmentary remains suggest that Josephoartigasia monesi grew to upwards of 1,000 kg (2,200 lb).
  - superorder Laurasiatheria
    - order Carnivora
      - Big cats include the tiger (Panthera tigris) and lion (Panthera leo). Members of Panthera are distinguished by morphological features which enable them to roar. Extinct large felids include the saber-toothed cat (Smilodon) and American lion (Panthera leo atrox).
      - Bears are large carnivorans of the caniform suborder. The polar bear (Ursus maritimus) has a body weight of up to 680 kg (1,500 lb). The extinct giant short-faced bear of North America (Arctodus simus) was the largest mammalian land carnivore of the late Pleistocene, reaching 1136 kg (2500 lb).
      - Seals, sea lions, and walruses are amphibious marine carnivorans that evolved from bearlike ancestors. The southern elephant seal (Mirounga leonina) of Antarctic and subantarctic waters is the largest carnivoran of all time, with males (bulls) reaching a maximum length of 6–7 m (20–23 ft).
    - order Perissodactyla
      - Rhinoceroses are odd-toed ungulates with horns made of keratin, the same type of protein composing hair. Their extinct central Asian relatives the indricotherines were the largest terrestrial mammals of all time.
    - order Artiodactyla (or cladistically, Cetartiodactyla)
      - Giraffes (Giraffa camelopardalis) are the tallest living land animals, reaching heights of up to nearly 6 m (20 ft).
      - Bovine ungulates include the largest surviving land animals of Europe and North America. The water buffalo (Bubalis arnee), bison (Bison bison and B. bonasus), and gaur (Bos gaurus) can all grow to weights of over 900 kg (2,000 lb).
      - A hippopotamus (Hippopotamus amphibius) is a large semiaquatic even-toed ungulate; it and the pygmy hippo (Choeropsis liberiensis) are believed to be the closest extant relatives of cetaceans.
    - order Cetacea (or cladistically, Cetartiodactyla)
      - Whales, dolphins, and porpoises are marine mammals. The blue whale (Balaenoptera musculus) is the largest baleen whale and the largest animal that has ever lived. The sperm whale (Physeter macrocephalus) is the largest toothed whale, as well as the planet's loudest and brainiest animal (with a brain about five times as massive as a human's). The orca (Orcinus orca) is the largest dolphin.
class Aves (phylogenetically, a clade within Coelurosauria, a taxon within the order Saurischia; see below)
- order Struthioniformes
  - The ratites are an ancient and diverse group of flightless birds that are found on fragments of the former supercontinent Gondwana. The largest living bird, the Ostrich (Struthio camelus) was surpassed by the extinct elephant bird (Aepyornis maximus) of Madagascar, the heaviest of the group, and the extinct giant moa (Dinornis) of New Zealand, the tallest, growing to heights of 3.4 m (11 ft). The latter two are examples of island gigantism.
- order Anseriformes
  - Extinct dromornithids of Australia such as Dromornis may have exceeded the largest ratites in size. (Due to its small size for a continent and its isolation, Australia is sometimes viewed as the world's largest island; thus, these species could also be considered insular giants.)
class Reptilia (or cladistically, Sauropsida)
- order Crocodilia
  - Alligators and crocodiles are large semiaquatic reptiles, the largest of which, the saltwater crocodile (Crocodylus porosus), can grow to a weight of 1,360 kg (3,000 lb). Crocodilians' distant ancestors and their kin, the crurotarsans, dominated the world in the late Triassic, until an unexplained extinction event allowed dinosaurs to replace them.
- order Saurischia
  - Saurischian dinosaurs of the Jurassic and Cretaceous include sauropods, the longest (at up to 40 m or 130 ft) and most massive terrestrial animals known (Argentinosaurus reached 80-100 metric tonnes, or 90-110 tons), as well as theropods, the largest terrestrial carnivores (Spinosaurus grew to 7-9 tonnes).
- order Squamata
  - While the largest extant lizard, the Komodo dragon (Varanus komodoensis), another island giant, can reach 3 m (10 ft) in length, its extinct Australian relative Megalania may have reached more than twice that size. These monitor lizards' marine relatives, the mosasaurs, were apex predators in late Cretaceous seas.
  - The heaviest extant snake is considered to be the green anaconda (Eunectes murinus), while the reticulated python (Python reticulatus), at up to 8.7 m or more, is considered the longest. An extinct Australian Pliocene species of Liasis, the Bluff Downs giant python, reached 10 m, while the Paleocene Titanboa of South America reached lengths of 12-15 m and an estimated weight of about 1135 kilograms (2500 lb).
- order Testudines
  - The largest turtle is the marine leatherback turtle (Dermochelys coriacea), weighing up to 900 kg (2,000 lb). The largest terrestrial chelonians are the giant tortoises of the Galápagos Islands (Geochelone nigra) and Aldabra Atoll (G. gigantea), at up to 300 kg (660 lb).
class Actinopterygii
- order Tetraodontiformes
  - The largest extant bony fish is the ocean sunfish (Mola mola), whose average adult weight is 1,000 kg (2,200 lb). While phylogenetically a "bony fish", its skeleton is primarily cartilage (which is lighter than bone). It has a disk-shaped body, and propels itself with its long, thin dorsal and anal fins; it feeds primarily on jellyfish. In these three respects (as well as in its size and diving habits), it resembles a leatherback turtle.
class Chondrichthyes
- order Lamniformes
  - The largest living predatory fish, the great white shark (Carcharodon carcharias), reaches weights up to 2,240 kg (4,940 lb). Its extinct relative C. megalodon (the disputed genus being either Carcharodon or Carcharocles) was more than an order of magnitude larger, and is the largest predatory shark or fish of all time.
- order Orectolobiformes
  - The largest extant shark, cartilaginous fish, and fish overall is the whale shark (Rhincodon typus), which reaches weights in excess of 21.5 tonnes (47,000 lb). Like baleen whales, it is a filter feeder and primarily consumes plankton.
class Cephalopoda
- order Teuthida
  - A number of deep ocean creatures exhibit abyssal gigantism. These include the giant squid (Architeuthis) and colossal squid (Mesonychoteuthis hamiltoni); both (although rarely seen) are believed to attain lengths of 12 m (39 ft) or more. The latter is the world's largest invertebrate, and has the largest eyes of any animal. Both are preyed upon by sperm whales.

[edit] Gallery

[edit] Extinct megafauna

Jaekelopterus was a variety of sea scorpion.	Dunkleosteus was a gigantic, 10 m (33 ft) long prehistoric fish.	Dimetrodon and Eryops from the early Permian of North America.	Liopleurodon ferox (right) harassing Leedsichthys problematicus.
Several macronarian sauropods; from left to right Camarasaurus, Brachiosaurus, Giraffatitan, and Euhelopus.	Life restoration of Tyrannosaurus rex.	The teratorn Argentavis had an 8 m (26 ft) wingspan.	Carcharocles megalodon with the great white shark and a human for scale.
Titanis walleri, the only known North American terror bird.	Megatherium and two glyptodonts from the Pleistocene of South America.	The American lion became extinct about 10,000 years ago.	Haast's Eagle is the largest eagle known to have existed.
The thylacine was the largest carnivorous marsupial of modern times.

[edit] Living megafauna

The green anaconda can weigh up to 97.5 kg (215 lb).	African elephants are the largest living land animals.	The blue whale is the largest animal that ever lived.	Tigers are the biggest living cats.
The Ostrich is the heaviest living bird.	The orca is the largest dolphin.	The giant eland is the world's largest antelope.	The gorilla is the largest primate on the planet.
The saltwater crocodile is the largest living reptile.	Fish of the family Molidae are the largest bony fish.	Polar bears are the largest semi-aquatic carnivores.	The black rhinoceros grows up to 14 feet long.
The grizzly bear is the largest woodland carnivore.	The Nile perch is one of the largest freshwater fish.