The fossilised remains of a crocodile that ruled the oceans 140 million years ago have been discovered in Patagonia.
The giant crocodile was a fearsome predator (Image: National Geographic)
Scientists have nicknamed the creature Godzilla, because of its dinosaur-like snout and jagged teeth.
The US-Argentine team of researchers believes the animal was a ferocious predator, feeding on other marine reptiles and large sea creatures.
The species is formally known as Dakosaurus andiniensis and has been unveiled in the journal Science.
Unlike modern crocodiles, it lived entirely in the water, and had fins instead of legs. It measured 4m (13ft) from nose to tail and its jaws alone were a third of a metre (1ft) long.
Crocodiles became widespread during the Cretaceous Period (146 to 65 million years ago).
Other marine crocodiles alive then had long, slim snouts and needle-like teeth, which they used to catch small fish and molluscs. But this creature had a dinosaur-like snout and large, serrated teeth.
"These sorts of features are also present in carnivorous dinosaurs like Tyrannosaurus rex," said co-researcher Diego Pol, of Ohio State University in Columbus, US.
"It shows a really unexpected morphology that nobody thought could be present in a marine crocodile."
Palaeontologist Zulma Gasparini, of the National University of La Plata, Argentina, first came across a "Godzilla" specimen in 1996 in the Neuquen Basin, once a deep tropical bay of the Pacific Ocean.
But it was little more than a fragment and provided few clues to the creature's nature and habits.
Prof Zulma Gasparini and the skull (Image: Marta Fernandez)
However, two further specimens have recently been discovered, including a complete fossilised skull.
Computer analysis of the bones shows D. andiniensis belongs on the family tree of crocodiles. Scientists believe it evolved a different feeding strategy from its contemporaries.
The shape and size of its jaws and teeth suggest it hunted large marine vertebrates such as the giant marine reptile, Ichthyosaurus, rather than small fish.