Megafauna is the name scientists give to the largest animals on Earth, from blue whales and elephants today to the mammoths and giant sloths of the Ice Age. In geological terms, it was not long ago that giant animals roamed every continent, and most of the biggest vanished within the last 50,000 years. The story is also about people, because human arrival keeps turning up alongside the disappearances.
How Big Does An Animal Have To Be To Count As Megafauna
Definitions use weight, and the common line is surprisingly low. One widely used definition counts any animal heavier than about 40 kg as megafauna.1PubMed Central. Origins of the Apple: The Role of Megafaunal Mutualism in the Domestication of Malus and Rosaceous Trees That is roughly the weight of a medium-to-large dog, so an adult deer, a wolf or a person would technically qualify.
Some researchers set a much higher bar, such as 1,000 kg, for the very largest plant-eaters. That picks out only a handful of living land animals, including elephants, rhinos and hippos, so the same word can describe a long list or a very short one.
The definition shifts with who is using it. Paleontologists often use 40 kg when comparing Ice Age animals across continents. Conservation scientists, meanwhile, may name the largest species within each animal group, so fish, birds and reptiles each have their own giants and creatures like giant salamanders and sturgeon get counted.2Conservation Letters. Are we eating the world’s megafauna to extinction? By that method, researchers count 362 living megafauna species across mammals, bony fish, sharks and rays, amphibians, birds and reptiles.3Conservation Letters. Are we eating the world’s megafauna to extinction? A 40 kg fish and a 40 kg mammal live very different lives, so one number can mislead.
The word describes size, not age. Many people meet it in Ice Age museum exhibits and assume it means prehistoric, but living whales and elephants are megafauna too, along with whale sharks, giraffes, crocodiles, ostriches and Komodo dragons.
The Prehistoric Giants
The Americas were full of giants, especially sloths. Giant sloths lived across South, Central and North America and some Caribbean islands until the end of the last Ice Age.4Land. A Tale of Two Continents (and a Few Islands): Ecology and Distribution of Late Pleistocene Sloths At least 27 different groups of these sloths existed then, in habitats from Patagonia to Cuba.5Land. A Tale of Two Continents (and a Few Islands): Ecology and Distribution of Late Pleistocene Sloths Some grew as big as elephants, which is why they dominate museum displays. South America also had armadillo relatives the size of cars. New fossils from across the continent keep adding species and filling in how these animals lived.6Journal of Quaternary Science. Giants beasts updated: A review of new knowledge about the South American megafauna
Birds and island animals reached giant sizes too. Terror birds, flightless predators up to about 3 m tall, are among the most famous extinct giants.7The Extinctions. The Last Terror Birds: A review of Phorusrhacids and their Plio-Pleistocene occurrences New Zealand had nine species of moa, giant flightless birds, the largest taller than a person. Madagascar had giant lemurs and elephant birds that survived until about 1,000 years ago.8Cambridge Prisms: Extinction. Patterns of late Holocene and historical extinctions on Madagascar Islands could also shrink animals, producing pygmy mammoths, dwarf elephants and dwarf hippos.9Wikipedia. Foster’s rule – Wikipedia
North America had mammoths, mastodons, sabre-toothed cats and giant beavers. Europe and Asia had woolly rhinos, cave bears and giant deer. Australia had wombat relatives the size of a car and giant kangaroos. Many of these overlapped with early humans.
Some of these losses are also surprisingly recent. The moa and Madagascar’s giants vanished within roughly the last thousand years, after the pyramids were built and during the Middle Ages.
Why Animals Evolve To Be So Big
Large size helps animals compete and defend themselves.10Biological Journal of the Linnean Society. The evolution of gigantism on temperate seashores Bigger animals can also move faster, dig more effectively or catch larger prey.11Stanford News. What Is Megafauna? From Prehistoric Giants to Today Whether a group grows large depends on how much food is available and how often extinctions clear the way.12Biological Journal of the Linnean Society. The evolution of gigantism on temperate seashores On small islands with little food, the same species can evolve to become much smaller.13Wikipedia. Foster’s rule – Wikipedia
Whales show what food supply allows. The biggest animals ever, baleen whales, got huge by filter-feeding on dense swarms of tiny prey like krill.14PubMed. Why whales are big but not bigger: Physiological drivers and ecological limits in the age of ocean giants Toothed whales that catch one prey at a time are held back by how many large prey exist.15PubMed. Why whales are big but not bigger: Physiological drivers and ecological limits in the age of ocean giants Baleen whales only became giants in the last few million years, as ocean food became more seasonal and concentrated.16PubMed Central. Independent evolution of baleen whale gigantism linked to Plio-Pleistocene ocean dynamics Heat sets a limit as well: the largest animals move slower than mid-sized ones because they risk overheating.17PubMed Central. The travel speeds of large animals are limited by their heat-dissipation capacities Nothing on land grows as large as a blue whale: water supports body weight, while land animals need massive legs, and land food is spread out rather than concentrated in swarms.
Huge bodies bring another puzzle. More body cells should mean more chances for cancer, yet elephants rarely get it. They carry at least 20 copies of a cancer-blocking gene, where humans have one pair, and damaged elephant cells tend to self-destruct rather than risk faulty repair. This helps explain how giant animals live long lives.
What Killed The Ice Age Giants
The global evidence points strongly at humans. Explanations that include human spread beat every climate-only explanation when matched against where and when extinctions happened.18Anthropocene. Megafauna extinctions in the late-Quaternary are linked to human range expansion, not climate change Across five landmasses, though, the best fit combines human arrival with climate.19PubMed Central. Quantitative global analysis of the role of climate and people in explaining late Quaternary megafaunal extinctions
Specific places show how the two combined. In Patagonia, giants died out in a short burst about 12,300 years ago, 1,000 to 3,000 years after people arrived.20PubMed Central. Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation The extinctions waited until human presence and a warming climate coincided, in both North and South America.21PubMed Central. Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation In New Zealand, moa vanished within little more than 200 years of human settlement.22Journal of Geometry and Physics. A high-precision chronology for the rapid extinction of New Zealand moa (Aves, Dinornithiformes) People did not single out the biggest moa species; all disappeared together.23Journal of Geometry and Physics. A high-precision chronology for the rapid extinction of New Zealand moa (Aves, Dinornithiformes) Madagascar’s giants had survived many past droughts but collapsed when farming and herding spread during a drying period.24PubMed Central. A multimillennial climatic context for the megafaunal extinctions in Madagascar and Mascarene Islands
Hunting mattered, but so did burning, land clearing and livestock. Slow-breeding giants could disappear even under modest hunting pressure, and climate stress could weaken populations before people pushed them over. Timing varies by continent because people arrived at different times.
Islands lost their giants especially fast. Island animals had never met humans and were unafraid, and small areas meant nowhere to retreat. New Zealand and Madagascar were settled late, so their losses are well dated.
Africa still has elephants and giraffes, probably because animals there evolved alongside humans for a very long time. They may have gradually become wary of people.
Why Losing Big Animals Changes The Whole Landscape
Some fruits still wait for animals that no longer exist. Large fleshy fruits usually evolved to be eaten and spread by large mammals.25PubMed Central. Origins of the Apple: The Role of Megafaunal Mutualism in the Domestication of Malus and Rosaceous Trees Many big-fruited plants, including squashes and some trees, likely relied on now-extinct giants to spread their seeds.26PubMed Central. Origins of the Apple: The Role of Megafaunal Mutualism in the Domestication of Malus and Rosaceous Trees Giant fruit-eaters let plants grow seeds bigger than smaller animals could carry.27PubMed Central. Seed Dispersal Anachronisms: Rethinking the Fruits Extinct Megafauna Ate Some living trees are therefore “ghosts” of a lost partnership, like an endangered Chilean tree whose fruit matches what extinct herbivores ate.28PubMed Central. Anachronic Fruit Traits and Natural History Suggest Extinct Megafauna Herbivores as the Dispersers of an Endangered Tree
Avocados, osage oranges and honey locust pods are suspected examples. Their large seeds have few living animals to spread them, so the fruit can fall and rot under the parent tree. Humans and livestock may now partly fill the old role.
Scientists spot these cases by looking for a mismatch: a plant makes large, sweet, fleshy fruit with big seeds, yet no living local animal eats it and carries the seeds away. They then check whether the fruit’s size and traits match what extinct giants ate, and whether fossil dung or bones of such animals turn up in the same region. It is a well-supported idea but a hypothesis for each plant, since some fruits may simply be spread by other animals or water.
Big grazers also shaped vegetation and soil. Extinct megafauna once kept many landscapes open, with a patchwork of grassland and woodland rich in species.29PubMed Central. Ecological consequences of Late Quaternary extinctions of megafauna After they vanished, many of these places grew into denser, more uniform vegetation.30PubMed Central. Ecological consequences of Late Quaternary extinctions of megafauna The loss of the Ice Age mammoth steppe giants was one of the main drivers of plant change there.31PubMed Central. Potential plant extinctions with the loss of the Pleistocene mammoth steppe Digging and trampling animals loosen soil and help water soak in.32Soil Science. Burrowing Through the Literature: The Impact of Soil-Disturbing Vertebrates on Physical and Chemical Properties of Soil Living elephants push over trees and keep savanna open, their dung carries seeds kilometres away, and the trails and water holes they dig help other species.
Giants also moved nutrients around the planet. Animals’ ability to spread nutrients across landscapes is now about 8% of what it was on land before the extinctions, and about 5% in oceans.33PubMed Central. Global nutrient transport in a world of giants Whales once lifted nutrients from deep water, seabirds and salmon carried them ashore, and land giants spread them inland.34PubMed Central. Global nutrient transport in a world of giants Losing large top animals has triggered chain reactions in oceans, forests and rivers worldwide.35PubMed. Trophic downgrading of planet Earth
Megafauna Today And Why They Are At Risk
Size itself raises extinction risk. Large animals breed slowly, so they recover from losses much more slowly than small ones.36PubMed. Ageing and the extinction of large animals In mammals, extinction risk jumps sharply above roughly 3 kg body weight.37PubMed. Multiple causes of high extinction risk in large mammal species Big species face both outside threats and their own slow life cycles, while small species mainly face outside threats.38PubMed. Multiple causes of high extinction risk in large mammal species When conditions change quickly, small fast-breeding species adapt far more easily.39PubMed. Ageing and the extinction of large animals
A large animal needs a lot of food and a large range, so shrinking or fragmenting habitat hits it harder than a small animal that can live on a small patch. Large animals are also more likely to come into conflict with people, whether by raiding crops, threatening livestock or being targeted for meat and trophies. And since they reach breeding age late and have few young, the animals people take most are the ones whose populations replace themselves most slowly.
A small population of giants is fragile. An elephant has one calf every four years or so, so losing a few adults can wipe out years of growth, and populations can’t bounce back after a bad year.
People are still the main threat. Human activities are harming the survival of megafauna across all six animal groups.40Conservation Letters. Are we eating the world’s megafauna to extinction? Hunting for meat is a major pressure on many of today’s giants.41Conservation Letters. Are we eating the world’s megafauna to extinction?
All rhino species are threatened, some reduced to a few individuals. Many large sharks and rays have declined steeply from fishing, and sturgeon, among the largest freshwater fish, are among the most endangered animal groups. Forest elephants and great apes face hunting and habitat loss.
Can We Bring Megafauna Back
Rewilding means returning large animals to landscapes so they can do the jobs lost giants once did.42Cambridge Prisms: Extinction. De-extinction beyond species: Restoring ecosystem functionality through large herbivore rewilding European projects aim to restore groups of large grazers, such as bison, wild horses and cattle.43Cambridge Prisms: Extinction. De-extinction beyond species: Restoring ecosystem functionality through large herbivore rewilding Abundant large animals are expected to boost seed spreading, nutrient cycling and varied vegetation.44PubMed. Trophic rewilding as a restoration approach under emerging novel biosphere conditions Non-native species can sometimes stand in for extinct ones in this role.45PubMed. Trophic rewilding as a restoration approach under emerging novel biosphere conditions
It differs from a zoo or safari park. The animals live in a landscape and shape it through grazing, trampling and dunging, rather than being kept for display or fed by staff. Success is measured by the effect on the ecosystem, such as more varied vegetation or more seed spreading, not by how many animals visitors can see. Managers usually still keep some control, such as fencing, health monitoring and limits on numbers, so projects range from lightly managed to hands-off.
European bison have been returned to forests in Poland, the Netherlands and the UK, and wild horses and cattle graze reserves to keep land open. These projects are often open to visitors.
De-extinction, meaning the use of genetic engineering to bring back extinct species such as the mammoth or Tasmanian tiger, raises bigger questions. Critics argue these projects move samples and money from places like Siberia and Kenya to wealthy labs while sidelining local communities.46Science as Culture. Mammoths and tigers and rhinos, oh my: mapping de-extinction species and networks
A recreated mammoth would really be an elephant with mammoth-like genes edited in. It would need an elephant mother or an artificial womb, and a few animals could not restore the herds that shaped the steppe.
How Early Humans Saw The Giants
Paintings of large animals appear in the earliest archaeological sites across the continents.47PubMed Central. Ice Age megafauna rock art in the Colombian Amazon? As people spread into new lands, giant animals shaped how they understood and claimed those places.48PubMed Central. Ice Age megafauna rock art in the Colombian Amazon? Cave art also tells us about ancient people’s minds and their relationship with animals now extinct.49Current Biology. Cave art reveals human nature
France’s Lascaux and Chauvet caves show horses, aurochs, mammoths and woolly rhinos, and rock art in the Colombian Amazon may depict Ice Age animals. Replica caves let visitors see the art without damaging it.
The paintings show which animals people noticed and chose to depict, a record of species present near the artists, sometimes in regions where they are now long gone. A painting does not prove that people hunted the animal or caused its extinction, since people also painted animals they feared, admired or had spiritual ties to. Dating the art is hard and often relies on pigments or the mineral crusts that formed over it, so ages are usually estimates.