There are just a handful of animals that have barely revolved from their original form since they first appeared on earth. If we were to list these animals in a ranking formation, one particular reptile is worth mentioning and will most likely take the lead. Am referring to the crocodiles.
Crocodiles along with pterosaurs and dinosaurs were among the offshoot of archosaurs, the ruling lizards of the early Jurrasic to middle triassic periods some 65 million years ago. As you already know, every known animal from that period has either gone extinct or revolved to several different species scattered around the earth. The crocodile chose to remain the same till date. The only major difference discovered from today's crocodiles and those of the jurrasic period are the shape and musculature of their jaws, which tend to be more deadly, as well as their relatively splayed limbs-as opposed to the straight locked in legs of those from the jurrasic period. Asides this, nothing else has changed in the crocodile, it's brain is still as small as the size of a golf ball. Or perhaps, the brain size is the reason why it's unable to revolve. No matter it's reason for not evolving much, the crocodile takes the lead on this subject as it's over 65million years old.