A six-metre long crocodile with three sets of fangs - like wild boar tusks - roamed parts of northern Africa millions of years ago, researchers report.
While this fearsome creature hunted meat, not far away another newly found type of croc with a wide, flat snout like a pancake was fishing for food.
And a smaller, one-metre relative with buckteeth was chomping plants and grubs in the same region.
The three new species, along with new examples of two previously known ancient crocodiles, have been detailed by researchers Paul Sereno of the University of Chicago and Hans Larsson of McGill University in Montreal.
They spoke on Thursday at a news conference organised by the National Geographic Society, which sponsored the research.
"These species open a window on a croc world completely foreign to what was living on northern continents," Sereno said of the unusual animals that lived 100 million years ago on the southern continent known as Gondwana.
Hans Dieter Sues of the Smithsonian Institution's National Museum of Natural History said the discovery revises the ideas of what crocodile-type reptiles were like.
"It's a joy for anyone who is interested in ancient life to see," said Sues, an editor at ZooKeys, which published the findings.
The researchers suggest that these crocs could gallop across the landscape chasing prey and yet dive into water and swim.
"My African crocs appeared to have had both upright, agile legs for bounding overland and a versatile tail for paddling in water," Sereno wrote in an article for National Geographic magazine.
"Their amphibious talents in the past may be the key to understanding how they flourished in, and ultimately survived, the dinosaur era."
They were not racehorses, Sereno said, but they could move quickly.
Freshwater crocs in Australia manage to eat a few people every year and these would have been able to do as well, he said. However, there were no people around at the time.
The newly discovered species are:
- Kaprosuchus saharicus, nicknamed BoarCroc, found in Niger. BoarCroc was a six-metre long meat-eater with an armoured snout for ramming and three sets of dagger-shaped fangs for slicing.
The tusks stuck out above and below the jaw like a modern warthog, said Larsson. "This has never been seen before on any crocodile."
- Araripesuchus rattoides, which the researchers call RatCroc, found in Morocco. This one- metre croc was a plant- and grub-eater with a pair of buckteeth in the lower jaw that it used to dig for food.
- Laganosuchus thaumastos, or PancakeCroc, found in Niger and Morocco. Also six metres long, it was a squat fish-eater with a one-metre pancake-flat head and spike-shaped teeth on slender jaws. Sereno said it probably remained motionless for hours, its jaws open and waiting for prey.
In addition, the researchers found new fossils of two previously named species:
- Anatosuchus minor, DuckCroc, found in Niger, a one-metre fish-, frog- and grub-eater with a broad snout and Pinocchio-like nose. Special sensory areas on the snout end allowed it to root around on the shore and in shallow water for prey. Its closest relative is in Madagascar.
- Araripesuchus wegeneri, or DogCroc, found in Niger, a one-metre long mew plant- and grub-eater with a soft, doglike nose pointing forward.
Sereno has focused since 2000 on fossils in the Sahara Desert, his first find being Sarcosuchus imperator, a 12-metre long creature that would have weighed 7.2 tonnes and which he called SuperCroc.
The new findings are detailed in the journal ZooKeys as well as National Geographic magazine and a documentary film.
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