The skull of the dwarf crocodile is around 110 million years old and was found alongside lots of other important dinosaur relics.
Top dinosaur hunter Dr Paul Sereno has showed off some of the remains in America, and said some of the finds could kick-start a "new era in dinosaur discovery".
They've also found evidence of another new dinosaur, which they've called Nigersaurus, because it was found in the country of Niger in Africa.
The Nigersaurus had a mouth shaped like a Cheshire cat with up to 1,000 teeth. Experts think it was a sauropod - a plant-eater with a long neck and feet.