Prehistoric Earth was a lot more dangerous than it is today.
If you ever travel several million years into the past, you’ll probably have a hard time staying alive.
Little wonder most of these monsters had to die off before the small defenseless mammals could evolve into their present-day forms.
In this article, we list 15 scary extinct animals that could kill you in an instant if they were still alive today.
|Name Meaning||Giant boa|
|Era||Cenozoic – Paleogene Period|
|Classification||Squamata, Serpentes & Boidae|
|Length||12-15 meters (39-49 feet)|
|Weight||1,135–1,135 kilograms (2,500–2,500 pounds)|
Snakes are already among the scariest animals around today.
It’s why the Anaconda movie has a reputation as one of the most iconic adventure horror movies ever made.
But even the biggest snake today is nothing compared to the massive Titanoboa—a monster snake that lived in South America during the Paleocene Epoch.
It grew to a length of up to 14.3 meters (47 feet) and had a mass of about 730 to 1,135 kilograms (1,610–2,500 pounds).
For context, the largest snake today, the green anaconda, weighs just 550 pounds and is just a little over five meters (16.4 feet) long.
The Titanoboa evolved after the dinosaurs and took over as the largest land predator of Paleocene South America.
|Name Meaning||References German Paleontologist Otto Jaekel and the Greek word “pteron,” which means wing or fin.|
|Era||Paleozoic – Silurian Period|
|Classification||Eurypterida, Pterygotioidea, Pterygotidae|
|Height||6 meters (20 feet)|
|Length||2.5 meters (8.2 feet)|
|Weight||272 kg (600 pounds)|
Jaekelopterus is a type of predatory eurypterid, a group of predatory arthropods also known as sea scorpions.
Eurypterids are not actual scorpions.
Their name only refers to their superficial resemblance to modern scorpions.
Jaekelopterus is the largest member of this group, and it also holds the title of the largest arthropod ever discovered, with a maximum length of about 8.5 feet.
It had giant claws that were up to 45.5 centimeters (17.9 inches) long and was an apex predator in its ecosystem.
It was an active and agile predator capable of picking out prey in the water with its well-developed eyes.
This spiky marine monster was probably capable of venturing out of the water occasionally and could snag you up from the water’s edge with its giant claws if you stood close enough.
|Name Meaning||Spined lizard|
|Era||Mesozoic — Cretaceous Period|
|Classification||Dinosauria, Saurischia & Theropoda|
|Height||4 to 5 meters (13 to 16 feet)|
|Length||12 to 18 meters (39 to 59 feet)|
|Weight||6 to 12 tons (13,000 to 26,000 pounds)|
The Spinosaurus was arguably the largest carnivorous dinosaur to have ever lived.
But the scariest thing about this dinosaur wasn’t even its size.
It’s the fact that it could sneak up on you from the water or ambush you on land if it wanted to.
Spinosaurus is one of the few semi-aquatic dinosaurs.
Like the dorsal fin of the great white shark, the only thing that might give this dinosaur away is the giant sail on its back.
As if the Spinosaurus wasn’t scary enough, this dinosaur was featured in Jurassic Park III in a scene where it killed a massive T. rex.
Although a showdown between both dinosaurs is unlikely in real life (they both lived in different locations), watching one of the most ferocious dinosaurs ever get killed is probably one of the scariest sights ever.
|Name Meaning||Terrible Crocodile|
|Era||Mesozoic – Late Cretaceous|
|Classification||Reptilia, Crocodilia & Alligatoroidea|
|Length||10-12 meters (33-39 feet)|
|Weight||8–10 tons (16,000–20,000 pounds)|
Deinosuchus is another prehistoric monster that preyed on dinosaurs.
As part of its rich carnivorous diet, this massive crocodile ancestor probably fed on hadrosaurid dinosaurs that shared the same habitat with it in Late Cretaceous North America.
Scientists know this because they’ve found tooth marks that resemble that of the Deinosuchus on numerous dinosaur bones.
Deinosuchus is unlike any other crocodile you have ever seen.
It grew to an average length of about 10.6 meters (35 feet) in total length.
For context, the largest crocodile species around today, the saltwater crocodile, grows to an average length of about 23 feet (7 meters).
Deinosuchus hunted large terrestrial prey by ambushing them at the water’s edge, pulling them into the water until they drowned.
|Name Meaning||Jointed Ribs|
|Era||Paleozoic- Late Carboniferous|
|Classification||Diplopoda, Arthropleurida, Arthropleuridae|
|Length||2.5 meters (8.2 feet)|
|Weight||49 metric tons (108,027 lbs)|
|Location||North America and Europe|
Creepy crawlies with numerous legs, such as the millipedes, are among the scariest arthropods today.
If you’re scared of them, you’ll probably find the idea of a 2.6 meters (8 feet) long version of the millipede even more disturbing.
Arthropleura is considered one of the largest arthropods to have ever evolved.
It lived in North America and Europe during the Carboniferous Period, about 345 to 290 million years ago.
So what did a 110-pound Arthropleura feed on?
Experts think it was probably herbivorous, meaning it was probably not as scary as it looks.
This is only speculatory, and there’s a chance Arthropleura killed the small prey animals that were alive in its ecosystem.
|Name Meaning||Named after Uruguayan national hero José Artigas|
|Era||Cenozoic — Neogene|
|Classification||Mammalia, Rodentia, Dinomyidae|
|Height||1.5 meters (4.9 feet)|
|Length||2.6 meters (8.5 feet)|
|Weight||58 kg (130 lbs)|
Imagine a rat as big as a beef cow.
That’s exactly what you get with the Josephoartigasia.
The largest rodent today is the capybara, and it only weighs about 130 pounds, several times smaller than the Josephoartigasia.
This giant rodent weighed over a thousand pounds and had a full body length of about 262.8 centimeters (8 feet 7 inches).
Josephoartigasia had a massive skull with a bite force that would have rivaled some of the biggest crocodiles today.
Fortunately, like its modern relatives, this giant rodent had no interest in eating flesh. It lived in a lush estuary environment and preyed on plant materials.
|Era||Paleozoic — Carboniferous Period|
|Classification||Odonatoptera, Meganisoptera, Meganeuridae|
|Length (Wingspan)||70 centimeters (28 inches)|
|Location||Europe and North America|
Dragonflies today are tiny insects that you can easily swat away with your hand.
If their ancient ancestors from the Carboniferous Period were still alive, you’d probably run away in fear if you saw one.
Meganeura holds the spot for the largest flying insect ever found.
It looked every bit like its modern relatives but was significantly bigger.
This insect had a wingspan of about 65 centimeters (25.6 inches) to over 70 centimeters (28 inches).
This giant dragonfly was so big that experts think it may have suffered from overheating during flight.
Meganeura lived in open habitats and was adapted to an insectivorous diet.
It was capable of snatching flying insects in midair.
Meganeura had huge eyes, effective for spotting prey efficiently.
|Name Meaning||Giant Tooth|
|Era||Cenozoic – Neogene|
|Classification||Chondrichthyes, Lamniformes, Otodontidae|
|Length||15-18 meters (50-60 feet)|
|Weight||50-100 tons (110,000-220,000 pounds)|
The main antagonist in the 1975 blockbuster movie, “Jaws,” is the great white shark.
Many people still get scared when they think of the bloody scenes from that movie, but the great white would have been anything but great if it swam in the same oceans as the Megalodon.
This prehistoric shark was bigger than any other shark known so far and was also the biggest fish known to man.
Megalodon lived during the Pliocene, about 2.6 million years before the first Jaws movies came out.
This shark grew to lengths of about 14.2 to 20.3 meters (47–67 feet).
For context, the largest great shark today is a paltry six meters (20 feet) long fish.
Megalodon had massive jaws lined with rows of teeth up to seven inches long.
This dentition makes it possible for the Megalodon to feed on large, fleshy prey like whales and dolphins.
|Name Meaning||Knife tooth|
|Era||Cenozoic – Quarternary|
|Classification||Carnivora, Feliformia, Felidae|
|Height||1 meter (3.3 feet)|
|Length||1.5 to 2.5 meters (5 to 8 feet)|
|Weight||160 to 280 kilograms (350–620 lbs)|
|Location||North America and South America|
The upper canine teeth of big cats are one of the scariest things about them.
Of all the living felids, tigers have the longest canines, reaching a maximum length of about three inches.
Now imagine a big cat with exceptionally long and curved canine teeth that reached a length of up seven inches. That’s exactly what the Smilodon looks like.
The saber-toothed cat’s intimidating teeth were not just there to strike fear in your heart.
They were sharp like daggers and designed as precise killing weapons.
The carnivore lived during a period when mammals grew to massive sizes and were built to take down large prey like the Bison antiquus and Camelops.
|Name Meaning||Inner Horn|
|Era||Paleozoic — Late Ordovician|
|Classification||Nautiloidea, Endocerida, Endoceratidae|
|Length||3 to 6 meters (10 to 20 feet)|
|Weight||250 to 1000 kg (551 to 2204 lbs)|
|Location||North America, Europe, and Asia|
Endoceras was a giant predatory nautiloid that lived during the Ordovician Period.
It is a member of the cephalopod class, which means it is distantly related to squids and octopuses.
Endoceras are bigger than present-day nautiloids.
It is characterized by a long, cone-shaped shell that could grow up to 5.7 meters (19 feet) long.
The animal itself was probably about half this length, but it had long, slender tentacles that could squeeze prey to death and pull them in towards its mouth.
Endoceras also had a hard keratinous beak that could bite into the body of hard-bodied prey.
Given the size and likely strength of its tentacles, this tentacled monster is the largest cephalopod in the fossil record and was one of the apex predators during the Ordovician Period.
|Name Meaning||Great Wanderer|
|Era||Cenozoic – Quarternary|
|Classification||Reptilia, Squamata, & Varanidae|
|Length||3–7 meters (10–23 feet)|
|Weight||97–1,940 kg (214–4,277 lb)|
Imagine a 4,000-pound lizard, capable of crushing prey in its massive jaws and delivering a bite full of toxic venom.
What you have is the Megalania, the largest terrestrial lizard to have ever existed.
Megalania grew to a maximum length of about seven meters.
It was one of the apex predators in Australia until about 50,000 years ago.
Megalania fed on medium- to large-sized animals, including mammals and other reptiles in its habitat.
|Name Meaning||Giant Ape|
|Era||Cenozoic – Quarternary|
|Classification||Primates, Haplorhini, & Simiiformes|
|Height||9 to 10 feet (2.7 to 3 meters)|
|Weight||200–300 kg (441–661 pounds)|
If King Kong was a real animal, the only giant ape that would have come close to it in size is the Gigantopithecus.
The fictional giant ape was about 18 feet (5.5 meters) tall.
While the real-life Gigantopithecus was only 3.7 meters (12 feet) tall, it is still larger than any other living or extinct species of hominids today.
Gigantopithecus was about twice the size of a gorilla and weighed roughly 660 pounds.
This massive ape inspires legends of the mysterious sasquatch or bigfoot.
Like modern apes, the Gigantopithecus survived on a plant-based diet.
But that wouldn’t stop it from crushing you to death with its massive jaws if you ever strayed into its territory.
|Name Meaning||Rag Thief|
|Era||Cenozoic – Paleogene|
|Classification||Cariamae, Phorusrhacidae, & Phorusrhacinae.|
|Height||2.5 to 3 meters (8 to 10 feet)|
|Weight||30 kilograms (290 lb)|
The nickname “terror birds” sounds scarier than the genus name Phorusrhacos, and it’s the perfect name to describe this group of monstrous birds that ruled as the apex predators of South America during the Cenozoic Era.
Terror birds stood at a height of about 2.7 meters (8.8 feet), almost the same size as a male ostrich but had an even more formidable appearance.
The most intimidating part of the terror bird’s appearance was its huge skull which ended in a hooked beak that could tear through flesh easily.
The Phorusrhacos’ beak was also effective for stabbing prey.
The terror birds had three-toed feet, each toe armed with a sharp claw for dismembering prey.
Terror birds ate any animal smaller than them, so if you were alive during the Cenozoic, you’d probably be on the menu too.
|Name Meaning||Derived from the biblical sea monster “Leviathan”|
|Era||Cenozoic – Neogene|
|Classification||Artiodactyla, Cetacea, Physeteroidea|
|Height||6 meters (20 feet)|
|Length||13 to 17 meters (42 to 56 feet)|
|Weight||30 to 50 tons (66,000 to 110,000 pounds)|
Livyatan is named after the biblical sea monster, which should give you an idea of just how scary this monstrous whale was.
It is a type of extinct sperm whale, about the same size as modern sperm whales—13.5 to 17.5 meters long.
But unlike modern whales that are mostly filter feeders, the Livyatan lived up to its name as a real-life sea monster.
It was one of the largest predators to have ever lived, with monstrous teeth that were as long as 36.2 centimeters (1.19 feet).
Livyatan had the largest biting teeth of any known animal.
It is often described as the ‘killer whale of the Miocene,” hunting whales, sharks, dolphins, and other large marine vertebrates for food.
|Name Meaning||Giant piranha|
|Era||Cenozoic — Miocene|
|Classification||Actinopterygii, Characiformes, Serrasalmidae|
|Length||0.7–1 meter (2.2–3 feet)|
|Weight||10 kg (22 lbs)|
|Location||Argentina (South America)|
The movie Piranha featured a mutated strain of ferocious Amazonian piranhas eating anything and anyone in their way.
The Megapiranha is the real-life version of the toothy monsters in the movie.
It was alive during the Late Miocene about eight to 10 million years ago and was significantly bigger than present-day piranhas.
The Megapiranha’s jaws feature seven premaxillary teeth arranged in a zig-zag pattern in its jaws.
The sharp, triangular-shaped teeth of this marine predator may have been strong enough to bite into the shell of turtles and other large marine animals.
Jerry Young is a self-proclaimed prehistoric animal nerd. He has been fascinated with these ancient creatures for as long as he can remember, and his passion for them continues to this day. With his extensive knowledge and love for prehistoric animals, he is the perfect fit for Gage Beasley Prehistoric.