From all the reptile species alive in nowadays, crocodiles and alligators are probably the ones that changed the least from their prehistoric ancestors of the late Cretaceous epoch, more than 65 million years ago.
Together with the dinosaurs and pterosaurs, crocodiles are an offshoot branch of the archosaurs group, known as the "ruling lizards" of the earlier to middle Triassic period.
But these earlier crocodiles that lived in the Triassic and Jurassic periods showed some very distinct and unique features far from the aquatic carnivores we know today.
The earliest crocodile ancestors were small, terrestrial, two-legged sprinters, with some of them being probably vegetarians, and had their nostrils located on the top of the head rather than the tip of the snout.
There are several candidates for the honor of being considered the "first crocodile", among them are Erpetosuchus and Doswellia, but these early archosaurs evolutionary relationships still remain uncertain and subject to change.
Only in the Mesozoic Era did these ancient crocodiles begin show the 3 main characteristics that we associate to crocodiles today, their sleek body with stubby legs and a marine lifestyle.
About 200 million years ago in the start of the Jurassic period, the ancient crocodiles had for the most part abandoned their earlier terrestrial lifestyles.
By this time we begin to see the adaptations and traits that characterize modern crocodile and alligator species, like long bodies with splayed limbs and a narrow, flat, tooth filled snout with very powerful jaws.
Since most ancient crocodiles like their modern counterparts ambushed dinosaurs and other creatures that ventured too close to the water, these were great evolutionary adaptations.
But there were still some differences for instance paleontologists believe that Stomatosuchus subsisted on plankton and krill, just like a modern grey whale does.
Well into the middle of the Cretaceous period, around 100 million years ago, crocodiles begun developing enormous sizes, imitating their dinosaur cousins. They weren't alone since other reptiles also begin grew to gigantic sizes like the Titanoboa, a giant snake believed to be 49 feet long and weighing over 2,500 lb.
The Cretaceous crocodile "king" was the giant Sarcosuchus, known as "SuperCroc", which reached about 40 feet in length and weighed an astonishing 10 tons. But there were other big crocodiles like the only slightly smaller Deinosuchus, the "Terrible crocodile" with an estimated size of 10 to 12 meters.
Modern crocodiles and alligators have changed very little from their prehistoric ancestors, this goes to show how extremely well adapted to their environment these reptiles were, and their descendents still are.
These amazing prehistoric crocodiles were indeed impressive their ability, as a group, to survive the K/T Extinction Event that wiped the dinosaurs off the face of the earth demonstrates it.
It's up to us to preserve their legacy in the form of the modern crocodiles like the saltwater crocodile or the american alligator, it would be a shame if these crocodilians go extinct on our watch.
Facts about crocodiles for kids
Where crocodiles live
Where do alligators live
Alligator facts for kids
Did you know?
There only are 2 different species of alligators found in the world.