Lets look at some of the biggest species who walked on our planet millions and millions of years ago.

Megalodon sharks

You may have heard reports that there are massive sharks prowling the oceans, three times as long as a great white and 30 times as heavy. Relax: they’re long since extinct.They were called Megalodon, and no one is quite sure how big they were. Like all sharks, its skeleton was made of cartilage rather than bone, and so did not fossilize well. As a result, we only have teeth and a few bits and pieces of vertebrae to go on. Recent estimates put it at 16-20 meters (52-65ft) long. That is significantly bigger than the largest fish alive today, whale sharks, which only reach 12.6 metres (41ft).

Titanoboa cerrejonensis

Around 60 million years ago, shortly after the demise of the dinosaurs, a snake evolved that was twice as long as the biggest modern snakes.Titanoboa cerrejonensis was 14.6m (48ft) long, and weighed in at more than a tonne. It was described in 2009, after fossilised vertebrae and skulls were found in a coal mine in Colombia.Believed to be a distant relative of the anaconda and boa constrictor, T. cerrejonensis crushed its prey to death. Its victims may have included crocodiles.Snakes rely on external heat to survive as they cannot regulate their own body temperature. T. cerrejonensis may only have reached its great size because Earth was warmer when it evolved.


What would an elephant-sized hamster crossed with a bear look like? Pretty odd, and perhaps a bit like Megatherium.This genus included the largest of the giant ground sloths, which lived mostly in South America from 5 million to 11,000 years ago.While not quite as big as dinosaurs or woolly mammoths, these impressive beasts were still among the biggest land animals. They were up to 6m (20ft) long.They were part of a group that includes modern tree sloths, armadillos and anteaters.Megatherium had had extremely robust skeletons. They were apparently built for strength and stability, but not speed.They also had long arms and large claws. Most scientists believe they used these to reach up into trees and grab leaves and bark that were out of reach for smaller animals.

Jaekelopterus rhenaniae

Jaekelopterus rhenaniae is an arachnophobe’s ultimate nightmare. At 2.5m long, this giant ‘sea scorpion’ has a claim to the title of largest arthropod ever to have lived.Its common name is misleading. They weren’t true scorpions, and probably scuttled about in lakes and rivers rather than the ocean. J. rhenaniae lived about 390 million years ago and spent its time chopping up fish.It was described in 2008, after a spiked claw measuring 46cm was found in a quarry in Prüm, Germany. This was all that remained of the animal. However, the ratio between claw and body size is pretty constant in sea scorpions, so researchers were able to estimate that J. rhenaniae was 233-259cm long.

Sarcosuchus imperator

It’s not just insects that have downsized over the years. Palaeontologists on a dinosaur hunt in Niger in 1997 were amazed to encounter fossilised crocodile jaw bones as long as a human.They had stumbled upon the most complete specimen to date of Sarcosuchus imperator, a prehistoric giant that hunted in the broad rivers of tropical northern Africa 110 million years ago.Also known as ‘SuperCroc’, it grew as long as 12m and weighed about 8 tons. That’s twice as long and four times as heavy as the largest of today’s crocodiles. It probably ate small dinosaurs as well as fish.It had a narrow jaw 1.8m long, containing more than 100 teeth, plus vertically tilting eye sockets and a large bony protrusion on the tip of its snout. It would have resembled the critically endangered gharials of modern India and Nepal.Despite its nickname, S. imperator wasn’t a direct ancestor of the 23 species of modern crocodilians. It belonged to an extinct reptilian family called the pholidosaurs.

Sarcosuchus imperator, also known as 'SuperCroc' (Credit: Sergey Skleznev/Alamy)