The giant fossil was excavated between 2021 and 2023 in Harding County, South Dakota.
The strange creature dubbed the "Witch Croc", shows the "weirdness" of life at the dawn of the dinosaur age.
It has been named Nagatitan chaiyaphumensis.
In total, only around 11 specimens of this kind have ever been recorded.
Its skull, broad and triangular in shape, had a pointed beak resembling that of parrots.
"It has been like solving an ancient murder mystery, with metatarsal evidence."
The species honors one of South Korea’s most beloved characters, Dooly the Little Dinosaur.
The poodle-sized reptile that lived over 200 million years ago was among creatures that had features similar to dinosaurs it lived beside.
The "miniscule" new fossil was discovered 500 miles south in Colorado’s Denver Basin.
Horned dinosaurs probably used their noses not just for smelling but also to help control temperature and moisture.