From giant apes that may have crossed paths with our early ancestors, to sloths the size of small trucks, these prehistoric heavyweights reveal just how much evolution can reshape life over time.
Some vanished completely, leaving only fossils and legends behind. Others live on in smaller, humbler descendants – grazing in meadows, prowling savannahs or lazing in tropical treetops.
Here are 6 of the most extraordinary giants that once roamed the Earth – and the modern animals that trace their lineage back to them.
6 huge prehistoric ancestors of today's animals
Aurochs
All domestic cattle today are descended from aurochs – a wild bovid. Males and females differed greatly in size and weight, with the largest males tipping the scales at around 900kg, it was one of Europe’s heaviest land mammals. Males were probably black with a paler dorsal strip, while females were brown.
They were a woodland, woodland edge, grassland and wetland species. Extensive loss of woodlands and overhunting were the two main factors in their demise. By the 13th century, aurochs were only found in Poland, Lithuania and some parts of modern-day Bulgaria and Romania. And by the early 1600s, the last known herd was restricted to the Jaktorów Forest in Poland. They went extinct nearly 400 years ago when the last, lonely female died in the Polish forest.
Giant ground sloths
Prehistoric giant ground sloths once roamed the Americas. To defend themselves, ground sloths had long, sharp claws on the ends of several of their fingers: the 6m-long Eremotherium had four such claws, each nearly a foot in length.
They also had size on their side: with thick bones and even thicker joints, they could strike with a surprising amount of power. It’s unlikely that many predators went after a fully grown ground sloth – to do so would have meant certain death, especially if the predator found themselves on the receiving end of a well-timed slap.
Their immense bulk didn’t just help them ward off predators. Ground sloths also used their size – and their ability to stand on two legs – to reach vegetation that would have been out of reach to most other herbivores of the time.
The largest ground sloths, Megatherium, Lestodon and Eremotherium, were probably capable of reaching heights of up to 5.5m, which is about the height of an average residential street light.
The descendants of these giant ground sloths are still alive today, but they live exclusively in trees, aren’t nearly as large, and are only represented by six species – all of which are endemic to the tropical rainforests of Central and South America.
Gigantopithecus
Just one look at this 10-foot-tall primate and it’s clear how it has earned itself the nickname ‘the real life bigfoot’. Gigantopithecus lived in south China during the Pleistocene, inhabiting subtropical, evergreen forests. Only teeth and several jaw bones of this giant ape have been found so far, but from these researchers have been able to deduce its size, how it lived and maybe even how it died.
Like their closest living relatives, orangutans, Gigantopithecus were vegetarians and survived largely on a diet of leaves, tubers and fruits. We know this because of small stones, known as phytoliths, found on their teeth. A lot of these phytoliths come from fruits (figs in particular) and tell us that Gigantopithecus probably had a sweet tooth.
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Unlike orangutans, Gigantopithecus – the largest of which likely weighed 270kg – were unsuited for an arboreal lifestyle and almost certainly dwelt on the forest floor, as gorillas do today. In doing so, it’s possible they may have clashed with our ancestors, Homo erectus, who arrived in this part of the world roughly 800,000 years ago.
Cave lions
Today, lions are restricted to pockets of savannah in sub-Saharan Africa. In the Pleistocene, their extinct relatives cave lions lorded over territory that stretched all the way from the Iberian Peninsula to North America – and included the British Isles.
They were among the most successful predators that lived on the Mammoth Steppe: an icy tundra that covered large parts of the northern hemisphere for long periods during the Pleistocene. And it’s here, on the Mammoth Steppe, where they’d have run into our ancestors as the two competed for mammoths, mastodons and reindeer.
Cave lions (Panthera spelaea) are very closely related to modern lions (Panthera leo) and are thought to have only diverged from a common ancestor as recently as 500,000 years ago, making them as closely related as us (Homo sapiens) and neanderthals (Homo neanderthalensis). They were almost twice the size of modern lions, though, and males lacked shaggy manes.
Giant short-faced bear
It has long been theorised that this 950kg bear, which stalked the land bridge that once connected Russia to Alaska during the Pleistocene, may have prevented humans migrating into the Americas from Eurasia. This bear, appropriately named the giant short-faced bear (Arctodus simus), is widely considered the largest terrestrial carnivore ever – larger than a polar bear and almost twice the size of a grizzly bear.
While the giant short-faced bear may have weighed close to a tonne, it had a relatively slender build compared to many modern bears. This has sparked debate about its lifestyle, with some claiming it was a pursuit predator capable of running down prey at speeds of up to 31 miles per hour, and others suggesting it was a kleptoparasite: an animal that specialises in stealing kills from other predators.
Today the giant short-faced bear’s closest living relatives are the spectacled bears of South America, the only surviving members of its ancient lineage.
Arthropleura
At 2.5m in length, Arthropleura is widely considered the largest invertebrate to ever walk the Earth. This giant ancestor of today’s millipedes is not an insect but a myriapod – an adjacent yet distinct group of invertebrates (or rather arthropods) that includes millipedes and centipedes.
Arthropleura lived across Europe and North America for more than 50 million years between the Early Carboniferous and the Early Permian. Like many bugs, living and extinct, it was a detritivore that fed on pretty much any rotting biological material it came across, from dead trees to dead animals.