Prehistoric Earth was a terrifying place, with giant, fearsome creatures roaming an equally deadly world of erupting volcanoes and primordial swamps. Survival could be counted in minutes, with a deadly predator hiding behind every enormous Jurassic fern.
Click through this gallery for our ranking of the scariest extinct creatures we'll never have to face...
It is the sheer size of the megatherium that makes it scary. This giant ground sloth lived in South America until about 10,000 years ago and reached heights of up to 20 feet (6m) when standing.
In modern representations it looks like a much larger version of a normal sloth, and fossils from Argentina have provided glimpses into the details of its slow-moving life and unique adaptations for its herbivorous diet.
Pteranodon, a genus of pterosaurs, soared the skies over North America around 90-100 million years ago, terrifying the prehistoric world with their wingspans of 23 feet (7m) or more. Their closest living relatives are birds, and fossils found in Kansas reveal much about their flight mechanics and lifestyle – and what an intimidating sight they must have been.
Diprotodon, the largest known marsupial, lived in Australia from about 1.6 million to 46,000 years ago. Its fossils, discovered widely across Australia, show its significant presence in Pleistocene (Ice Age) megafauna.
It is said to have resembled a giant wombat, which is not terrifying in itself. But the fact that it could grow as large as a rhinoceros is.
Quetzalcoatlus, one of the largest known flying animals, lived around 70-65 million years ago. With a wingspan exceeding 30 feet (9m), it soared over what is now North America.
Quetzalcoatlus fossils, especially those found in Texas, reveal that it more than equalled the large birds of today in its flying prowess.
Triceratops lived in North America about 68-66 million years ago. This herbivorous dinosaur had a large bony frill and three facial horns, growing up to 30 feet (9m) long.
Similar to modern rhinoceroses in behaviour, you wouldn't want to be in their path if they were startled or angered. Triceratops fossils offer a window into the herbivorous life of the late Cretaceous period.
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The Irish elk, or megaloceros giganteus, lived across Eurasia from about 400,000 to 8,000 years ago. Known for its enormous antlers, which could span up to 12 feet (4m), it resembled modern deer but was much larger.
Fossils, especially those preserved by peat bogs, highlight its impressive size and the potentially deadly nature of its magnificent antlers.
The moa, native to New Zealand, became extinct around AD 1400. These flightless birds, related to modern-day kiwis, were some of the largest birds ever to exist, with some species reaching heights of 12 feet (4m) and boasting claws that were large and deadly.
Overhunting by early Polynesian settlers and habitat destruction led to their rapid extinction.
The Tasmanian tiger, or thylacine, was a carnivorous marsupial native to Tasmania, Australia and New Guinea. It resembled a large dog with stripes and existed until the 1930s.
Related to modern marsupials like the Tasmanian devil, the thylacine's decline was due to hunting, disease and habitat loss.
This massive wild cattle species, which once roamed across Europe, Asia, and North Africa, is considered to be the wild ancestor of modern domestic cattle. Standing over six feet (1.8m) tall at the shoulders, it played a crucial role in ancient cultures and mythology.
Hunted extensively for its meat and targeted as a symbol of strength in medieval hunts, the aurochs gradually disappeared. Like with modern cattle, early humans underestimated just how deadly this majestic creature could be.
Living between 286 and 270 million years ago, dimetrodon inhabited swampy regions of North America and Europe. Measuring about 12 feet (4m) long, this predator featured a sail-like spine on its back.
Although it predates dinosaurs and mammals, it has no modern relatives. Its sail is believed to have played a role in regulating body temperature as it stampeded through the prehistoric world.
Also known as the Falkland Islands fox or warrah, this wolf was the only native land mammal on the Falkland Islands. Isolated from mainland predators, it evolved into a unique canid species.
Hunted by settlers for its fur and considered a threat to livestock, the population quickly declined. The last known specimen was killed in 1876, making the Falkland Islands wolf the first known canid species to be driven to extinction by humans.
The woolly mammoth lived from 400,000 to 4,000 years ago across Europe, Asia and North America. Similar in size to modern elephants, it was covered in long, shaggy hair to withstand the Ice Age's frigid temperatures. It was its sheer size and fearsome tusks that made the woolly mammoth such a formidable foe.
Fossils of these creatures are often found in Siberian permafrost, revealing well-preserved specimens. Modern elephants are their closest living relatives.
Ceratosaurus was one of the biggest hunters of the Late Jurassic period (153-148 million years ago). Estimated to have been around 19.5-23 feet long (6-7m), it had a row of sharp horns on its head and a row of small, bony pieces of armour running along its back which were probably used to protect it from larger dinosaurs.
When ceratosaurus went on the attack it made use of its long, slender teeth which could be over 3.5 inches (9cm) in length making them particularly suitable for inflicting deep, slashing wounds in its prey.
Once thriving, with a large geographic range across Central Asia, the Caspian tiger was a formidable apex predator. Its demise began with the Russian colonisation of Turkestan during the late 19th century, when the tiger was systematically exterminated by the military, sports hunters and locals who were paid for tiger skins.
By the mid-20th century, habitat loss, hunting and agricultural expansion led to its demise. It was officially declared extinct in 2003.
While it probably wouldn’t kill you, the eight-foot-long (2.5m) arthropleura is not a creature you wanted to stumble upon during the Carboniferous period. As long as a modern car and tall enough to rear up and look you in the eye, the arthropleura remains the largest known land invertebrate of all time.
And while it fed on dead plant matter like the modern millipede, the scuttling of its undulating legs would have been disconcerting to say the least.
The Javan tiger, native to the Indonesian island of Java, was officially declared extinct in 2008. However, it had not been found in the wild for decades beforehand, its population driven to extinction by habitat loss and hunting. In August 2019, a local in West Java claimed to have glimpsed one.
A single hair was recovered from the scene, and DNA analysis in 2022 concluded that it belonged to a Javan tiger. Whether the Javan tiger actually still occurs in the wild needs to be confirmed by further genetic and field studies.
Mastodons roamed North and Central America from about 27 million to 10,000 years ago. These prehistoric relatives of elephants stood around 10 feet (3m) tall and were covered in long, shaggy hair.
Mastodons were akin to modern elephants but had distinct, blunt-tipped tusks and different molar shapes adapted for chewing leaves and branches. Numerous well-preserved mastodon skeletons have been unearthed in peat bogs and tar pits.
Dunkleosteus roamed the oceans around North America, Europe and Morocco from 358 to 382 million years ago. This giant fish grew up to 33 feet (10m) in length and had an armour-plated head, but lacked true teeth – instead boasting two long bony blades that could snap and crush its prey.
They ate sharks and were even cannibalistic. Experts believe Dunkleosteus may have been one of the earliest creatures to exist as male and female, meaning that pairs had to mate physically.
The American lion roamed North America during the Pleistocene epoch, from about 340,000 to 11,000 years ago. Larger than modern lions, it stood around four feet (1.3m) at the shoulder and weighed up to 450kg (1,000lbs).
Fossils, particularly from the La Brea Tar Pits in Los Angeles, reveal its similarities to today's big cats and its role as a top predator.
The helicoprion roamed the world’s oceans between 275 and 235 million years ago, hunting prey with its terrifying buzzsaw jaw. The curved, spiral-shaped jaw contained several hundred teeth and measured 18 inches (45cm) in diameter, with each tooth having a different function depending on its position.
The anterior teeth hooked and dragged prey into a helicoprion’s mouth, the middle teeth pierced and cut the prey, and the posterior teeth then pushed the captured prey into the oral cavity.
Looking not that dissimilar to the terrifying facehuggers in the Alien movies, jaekelopterus was a giant water scorpion that hunted along the shorelines of North America during the Silurian period, around 444 to 416 million years ago. At eight feet long (2.5m) it was the largest arthropod ever known and was equipped with multiple limbs – some with spikes, two with nasty looking pinchers.
With no known predators, it terrorised the seafloor for millions of years.
Therizinosaurus, who lived across Asia roughly 70 million years ago, had the largest claws of any land mammal ever known, a fact which has seen it nicknamed the Scythe Lizard. However, despite its intimidating nickname, Scythe Lizard was actually a herbivore and experts are uncertain what they used those ferocious looking claws for.
Some think they were used for raking vegetation into piles, others think they were for defence. Whatever the case, you wouldn’t want to risk being on the receiving end of a slap from this potentially vicious vegetarian.
Pterodactylus darkened the skies above Germany during the Late Jurassic period, its 3.3-foot (1m) wingspan casting a shadow over its terrified prey below. Technically, these creatures were winged reptiles, not dinosaurs.
And despite what the movies would have us believe, they were not strong enough to carry off cavemen. Instead, they used their razor sharp teeth to feast on carcasses, baby dinosaurs, eggs, fish and other small marine life.
Mosasaurus lived around 70 million years ago in the Late Cretaceous period. This marine reptile could grow up to 56 feet (17m) long and had a robust body and powerful jaws, similar to modern monitor lizards.
Fossils, primarily found in Europe and North America, showcase its adaptation to marine life and its role as a top predator in ancient seas.
Reaching around 43 feet (13m) in length and weighing over 1.25 tonnes, the titanoboa is the largest snake ever known. This mega-snake slithered through South America during the Paleocene epoch 66 to 56 million years ago, and was so big it could swallow a crocodile whole.
The first fossilised skeleton of a titanoboa was discovered in Cerrejón coal mine in Colombia in 2004, with palaeontologists noting that its vertebrae were similar to today’s anacondas and boas – just much, much bigger.
The largest and deadliest raptor that ever lived, Utahraptor was around 23 feet (7m) in length and 5.5 feet (1.7m) tall. Not only were its jaws lined with serrated teeth, but it also had 10 inch-long (25cm), sickle-shaped claws attached to its second toes.
Utahraptor used these fearsome weapons to rip open the bellies and necks of its prey before moving in to feast.
This giant prehistoric crocodilian was the king of the rivers and swamps of modern-day Africa and South America about 112 million years ago. Measuring around 40 feet (12m), its head alone was six feet long (1.8m), with jaws that could clamp down with over nine tonnes of bite force – a stronger bite than a T-rex.
Its size made it a formidable predator, but it was remarkably adaptable too, and able to bring down beasts even larger than itself.
The gigantopithecus was the largest ape ever to have lived, and rampaged through what is now southern China as recently as 100,000 years ago. Standing nearly 10 feet tall (3m) and weighing up to 300kg (660lbs), the apes struggled to meet their calorific needs when the climate abruptly changed during the last ice age and they drifted into extinction.
Or did they? Cryptozoologists have enjoyed remarking on their uncanny resemblance to legendary creatures like the Yeti and Bigfoot.
Deinonychus means ‘terrible claw’, and the five-inch (13cm) sickle-like talons they had on each of their feet were indeed deadly. Combined with their blinding speed and unusually large brains, these claws saw the deinonychus terrorise the Early Cretaceous period 146 to 100 million years ago.
Little wonder then that Steven Spielberg modelled the terrifying raptors in Jurassic Park on these formidable and ruthless killers.
During the Late Cretaceous period in what is now Argentina, one beast ruled them all – the giganotosaurus or 'great southern lizard'. At 43 feet long (13m), giganotosaurus was bigger than the T-rex. And while its jaws did not have the crushing power of its fearsome counterpart, its razor-sharp teeth were perfect for slicing and dicing its prey.
In fact, palaeontologists believe that the giganotosaurus hunted by inflicting slicing wounds instead of biting, allowing it to bring down large herbivores it wouldn’t have been able to get its mouth around.
Smilodon, commonly known as the sabre-toothed cat, lived in the Americas from 2.5 million to 10,000 years ago. Weighing up to 280kg (620lbs), it had long, curved, sabre-like canines. Smilodon resembles modern big cats, like lions and tigers, but is distinct for its powerful forelimbs and elongated fangs.
Many fossils have been discovered in the La Brea Tar Pits in Los Angeles, providing significant insight into this fierce predator's life.
That's right: it's the Meg! Megalodon was a giant shark that lived from 23 to 3.6 million years ago and inhabited warm oceans worldwide. Reaching lengths of up to 60 feet (18m), it preyed on whales and large fish.
Bearing a resemblance to those of the modern great white shark, megalodon teeth, often the size of a human hand, are frequently found in marine sediments, ominous relics of this enormous predator.
Every five-year-old’s favourite dinosaur, and our pick for the world's scariest extinct creature, the T-rex is dubbed 'the king of the dinosaurs' and roamed the Earth around 66 million years ago. This predator dominated the food chain and is remembered for its massive size, powerful jaws and tiny arms.
The T-rex is believed to have faced extinction during the Cretaceous-Paleogene event, possibly due to climate change or a catastrophic asteroid impact, long before any humans had to face down its terrifying teeth.
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