Most people know that the blue whale is the largest animal in the world and the African elephant is the largest land animal.

You may know that the blue whale is the largest animal that ever lived on Earth.

But did you know about the whole slew of other amazing and unusual giants that once appeared on our planet?

Find out about some of these king-sized creatures:

Paraceratherium, the Largest Land Mammal

Paraceratherium was about 18 feet tall (from ground to shoulder) and about 25 feet long (not including its tail). Its skull was between 4 and 7 feet long. Estimates of its weight range from 8 to 20 tons.

The largest land mammal to ever live on Earth, Paraceratherium was as big as a large dinosaur and four times as large as a modern elephant.

The name Paraceratherium is Greek for "like a horned animal" - a reference to the fact that it was like a rhinoceros, but hornless.

It lived in Asia between 37 million and 23 million years ago.

Fossils of Paraceratherium have been found in Pakistan, India, Kazakhstan, China and Mongolia.

Paraceratherium is also known as Baluchitherium (sometimes spelled Baluchiterium), for the province of Baluchistan in Pakistan, where fossils were first discovered.

Yet another name for Paraceratherium is Indricotherium. This name comes from a legendary Russian creature known as the Indrik, who ruled all the other animals on Earth.

Paraceratherium was related to the rhinoceroses, but had no horns.

It was an ungulate (a mammal with hoofs). It belonged to the order Perissodactyla - odd-toed ungulates - which also includes modern rhinoceroses and horses.

Paraceratherium shared some characteristics with rhinos and horses. Its body looked like that of a large horse, and it had three toes on each foot, like a rhinoceros.

It was herbivorous.

It had long legs and a long, flexible neck - similar to a giraffe's neck - which allowed it to reach leaves and twigs in trees. It had strong, flexible upper lips, similar to those of a modern rhino, and two large front teeth that resembled tusks. It used its lips to grab onto vegetation and then tore it off with its front teeth.

When Paraceratherium was alive, its habitat consisted of subtropical forests.

Scientists believe that Paraceratherium may have become extinct when the Indian subcontinent collided with Asia, causing the Himalayas to rise up. This caused the Earth to become dryer and cooler, which may have caused the plants that Paraceratherium ate to become extinct.

Gigantopithecus, the Largest Ape

Gigantopithecus blacki was 3 meters (9.8 ft) tall and weighed up to 540 kilograms (1,200 lb). Two to three times larger than a gorilla, it was the largest ape to ever walk the Earth.

This huge creature lived around what are now China, India and Vietnam. It was incredibly strong, and its massive bulk kept it safe from local predators, tigers, leopards and black bears.

Gigantopithecus blacki lived between 300,000 to 1 million years ago and ate the tough grasses found in South East Asian forests. Climate change and scarcity of resources may have caused its extinction.

It has often been claimed by people who research and search for hidden animals from local and ancient legends that a type of Gigantopithecus blacki are the source of tales regarding creatures such as Bigfoot and the Yeti.

Arctodus, the Largest Bear

Arctodus simus, known as the short-faced or bulldog bear, weighed up to 2500 pounds and stood up to 4 meters (13 feet) tall on its hind legs. When it stood on all fours, its head would have been on a level with the head of a 6 foot tall person.

It lived in North America, wandering between Canada, California and Central Mexico, between 800,000 and 12,500 years ago and was the largest carnivore living on Earth at that time.

Arctodus simus was an obligate carnivore, meaning that it ate only meat, and did not rely on any vegetation for nutrition. Scientific studies of remains have shown this to be true, finding no evidence that the creature ever ate any vegetation and that it must have consumed around 16kg (35 pounds) of flesh per day to survive.

It was strong enough to kill a buffalo and may have fed on horses and antelopes as well.

Arctodus may have become extinct because its prey died out, because of competition from smaller brown bears that came to North America from Europe and because it was hunted by humans.

Daeodon, the Largest Pig

Daeodon shoshonensis, which could reach up to 2.1 meters (7 feet) tall, was the largest pig-like animal to live on Earth.

It lived in North America between 18 and 25 million years ago.

Daeodon shoshonensis was a member of the Entelodont family, a group of animals that are related to modern pigs and hogs.

They had bulky bodies, short legs and long muzzles, as well as bony lumps on the sides of their heads, which might have been used in competition between males. These lumps were similar to those in modern warthogs.

The Entelodonts were omnivores. They lived in the plains and forests of North America, where they hunted for live animals, scavenged and ate plants.

Daeodon shoshonensis would have fed on the ancestors of modern horses and camels. Its skull was a meter long, and its strong jaws were full of teeth that could slice flesh and splinter bone.
This animal used to be called Dinohyus - "terrible hog".

Brontornis, the Largest Carnivorous Bird

Brontornis burmeisteri, the largest carnivorous bird that ever lived on Earth, lived in South America between 23 and 25 million years ago.

It was 3 meters (10 feet) tall and weighed 400 kilograms (880 pounds).

Brontornis had a large, strong beak and huge claws.

According to current scientific knowledge, Brontornis burmeisteri is the third heaviest bird ever to have lived on Earth.

In its own environment and time it was the largest land predator.

A flightless bird, like modern-day emus and ostriches, it could run as fast as a cheetah and shatter bone with its kicks.

This predatory bird fed on ancient relatives of the armadillo, which were as large as small cars.

People think Brontornis probably hid in wait for its prey and then pounced on it after chasing it for a short while. It was probably too large to chase down prey for any great distance, so it was more like to hide form its victims and then attack them by surprise, crushing them quickly with its heavy mass and claws then dragging their bodies away to a safe place to be eaten.

Titanoboa, the Largest Snake

Titanoboa cerrejonensis, which lived in Colombia between 50 and 60 million years ago, was the largest snake that ever lived on Earth.

It had a body as thick as a man's waist and was strong enough to kill a crocodile.

Titanboa often reached 13 meters (43 feet) long and weighed over 1100 kilograms (2400 pounds).

The largest snakes that are alive today are Python reticulatus, which grows to about 9 meters (30 feet) long and the anacondas, which are about 7.5 meters (25 feet) long.

Fossilized remains of 28 Titanoboa cerrejonensis were discovered in Colombia in 2009. Scientists believe that this means that the climate of the tropics at that time must have been warmer than previously thought. The warmer climate would have allowed these cold-blooded animals to grow much larger than modern snakes.

Sarcosuchus, the Largest Crocodile

Sarcosuchus imperator, the largest crocodile ever to live on Earth, was 12 meters (39 feet) long and weighed 10 tons.

Its jaws, which were larger than a human being, contained 132 conical teeth that pointed backward.

A row of bony plates, known as osteoderms, ran down its back. They were up to 1 meter (3 feet) long.

It was large enough and strong enough to feed on dinosaurs, crushing them, dragging them into the water and drowning them.

Sarcosuchus lived in Sub-Saharan Africa 110 million years ago, during the Cretaceous period.

Archelon, the Largest Turtle

Archelon ischyros, the largest sea turtle that ever lived on Earth, weighed more than two tons. This is over one third more than the weight of a modern African elephant.

The largest Archelon fossil, which was discovered in the 1970s, was more than 4 meters (13 feet) long and 5 meters (16 feet) wide.

Archelon lived in North America 74 million years ago, during the Late Cretaceous period. A marine animal, it lived during a time when most of central North America was covered by a shallow sea.

It did not have a solid shell like modern turtles. Instead, it had a leathery or bony carapace that was supported by a skeletal framework.

With its strong, hooked beak, it could bite through the shells of crustaceans and crush squid.

It also had a pointed skull that was more narrow-shaped skull than that of a modern turtle.

It is thought that Archelon had a lifespan of around 100 years, a little shorter than that of modern sea turtles.

We don't know much about Archelon because very few fossils have been discovered. Scientiest think they brumated (Brumation is a type of dormancy in reptiles similar to hibernation in mammals) at the bottom of the ocane and often died during brumation. This makes their fossils hard to find.

Beelzebufo, the Largest Frog

Beelzebufo ampinga, the largest frog that ever lived on Earth, weighed 4 kilograms (9 pounds) and was 40 centimeters (16 inches) long.

It lived 70 million years ago, in Madagascar.

In comparison, the goliath frog, the largest known species of frog alive today, measures up to 32 centimeters (12.5 inches) long.

The closest living relatives of Beelzebufo are the horned toads of South America. The largest of these are 15 centimeters (6 inches) long.

Beelzebufo probably lived on dry land, in arid environments. It probably ambushed its prey, which may have been very large. Beelzebufo may have eaten young dinosaurs.

Dunkleosteus, the Largest Fish

At 10 meters (33 feet) long, Dunkleosteus terrelli, which lived about 400 million years ago, was the Earth's largest fish of all time. This giant vertebrate weighed up to 4 tons.

It could bite with a force of 5000 newtons (1100 pounds) in 1/15 of a second. The speed with which it opened its jaws would have created a current that drew fish into its mouth

The teeth of Dunkleosteus were self-sharpening.

Dunkleosteus belonged to a class of ancient prehistoric fish called Placoderms. These fish had heavy armor, and therefore probably could not swim very fast. The Placoderms were some of the earliest fishes with jaws. They also may have been among the first vertebrates to reproduce by internal fertilization.

Arthropleura, the Earth's Largest Land Invertebrate

At 2 meters long, Arthropleura was the largest invertebrate ever to live on land.

It lived in Scotland and North America between 280 and 340 million years ago, during the Carboniferous period.

Arthropleura resembled a millipede, and had 30 pairs of legs.

Fossilized footprints show that it moved quickly along the floors of ancient forests, stretching its body to increase the length of its stride. Some scientists think it may have been able to move around underwater.

The body of Arthropleura was wide and flat, with heavy armor.

Its diet was omnivorous. It hunted for small animals and ate rotting leaves as well.

When Arthropleura lived on Earth, the oxygen content of the atmosphere was high, and there were no large vertebrate predators living on land. This enabled Arthropleura to evolve to a larger size than modern invertebrates.

At the beginning of the Permian period, the climate began drying out and rainforests were destroyed. This lowered the level of oxygen in the atmosphere, causing giant arthropods, such as Arthropleura, to become extinct.