Sharks are intimidating enough without the thought there could be super-sized beasts out there.But meet the Megalodon.
This particular species lived 23 million years ago and is closely related to the great white shark - but could reach up to 59ft long. That's 10x the size of a T-Rex. They prayed on large things, probably whales, and their teeth and jaws were built for grabbing and breaking bones. Oh, and they also swam very fast. Fossils of the species have been found in Europe, Africa, America and Australia.
Pulmonoscorpius
This is a giant species of scorpion, which thankfully doesn't roam the earth any more. But it did use to live a little bit closer to home than the intimidating mega-shark, with fossils found in West Lothian, Scotland. This guy was 70cm long and bigger than the average domestic pet cat, using its tail to catch and kill its prey. Also, it had very large eyes in comparison to its modern-day counterparts, meaning it probably hunted out its victims in the daytime.
Ornimegalonyx
Owls might not strike you like the most terrifying creature on the planet, but think about how you'd feel like a rodent running away from their super sharp claws. And now imagine if that owl was over three foot tall, weighed over 20lbs and could kill prey up weighing to 70lbs. It's said to have had very long legs in proportion to its body, which meant it could run very fast too. On the plus side, it did have quite small wings.
Anthropornis nordenskjoeldi
Another animal which might not seem like the most terrifying but would most definitely be if you came face to face with it is a giant six-foot, 200lbs penguin.
These were found off the coast of Antarctica and also New Zealand, living 33-45 million years ago. The regular emperor penguin is around four-foot high. And the weight of this giant, 6foot penguin meant it could charge and bowl over pretty much anything in its way.
Sarcosuchus imperator
Back to another absolutely terrifying and giant animal - a massive crocodile.Literally a giant, it weighed around eight tonnes and was twice as long as a regular croc.Because of its giant size and the fact it lived 12 million years ago, its prey would include dinosaurs living around the same area.
Paraceratherium
This massive rhino could grow up to 16ft tall and weighed a hefty 20,000 tonnes.It's one of the largest land mammals to have ever existed.They are described as having "pillar-like" legs to support all their heft - they were approximately five ft long, which is only three inches shorter than the full height of an average woman today.Despite how terrifying they sound, they mainly ate leaves and shrubs.Their extinction was probably caused by climate change and a lack of food rather than one big catastrophic event that wiped them all out.
Megatherium
A giant sloth the size of an elephant just roaming around planet earth - what could be more unnerving (or cute, depending which way you want to look at it). They lived in South America and only a few land mammals exceeded their giant size. They could be up to 20ft tall, weighing up to four tonnes. These sloths had longer front legs than back legs and long claws similar to the smaller species we know today.
