The dinosaur's brow was also massively swollen, giving it a menacing glare.
The paleontologists speculate that this bony feature may have been used by Eocarcharia and related species in head-butting contests over mating rights.
Matt Lamanna, a dinosaur expert at the Carnegie Museum of Natural History in Pittsburgh was not involved in the research.
"[The head-butting] is an interesting idea that deserves further study," he said.
While head-butting between males is usually confined to plant-eating animals, such behavior has been suggested for a few other meat-eating theropods, Lamanna said.
Meanwhile the idea of a scavenging lifestyle for carnivores such as Kryptops is controversial, Lamanna said.
"If this thing had a fingernail-like covering all over its face, then maybe that was used to poke into carcasses, but I'd like to see more evidence for it," he said.
"This is why studying the Southern [Hemisphere] theropods is so much fun—we're still learning so much about them," Lamanna added.
The newly revealed species give important insights into the southern-dwelling dinosaurs that rose to the top of the food chain during the Cretaceous period, 144 to 65 million years ago.
Kryptops represents one of the earliest known abelisaurids, a group that was also found in South America and India, the researchers said.
Eocarcharia was a carcharodontosaurid, a family that gave rise to some of the largest southern predatory dinosaurs, matching or exceeding Tyrannosaurus rex in size.
"What we've found are primitive members of the two groups of megacarnivorous dinosaurs that ruled the southern continents for 50 million years," study co-author Brusatte said.
"For those of us [who] work on dinosaur evolution, finding these very old and primitive species is kind of like a paleoanthropologist finding a Neandertal," he said.
The two new dinosaurs—along with an even bigger predator, the fish-eating, sail-backed Suchomimus—represent a trio of meat-eating lineages that became dominant in Africa and possibly other southern landmasses, Sereno said.
"For some 20 to 25 million years, these would have been the three big ones you'd have had to watch out for if you'd gone down there," Sereno said.
Strange Prey The creatures likely targeted other large African dinosaurs such as the strange, long-necked plant-eater Nigersaurus, which had a muzzle resembling a vacuum cleaner.
Around this time Africa was breaking free of Gondwana, the huge southern supercontinent that also included South America, the researchers said.
This makes the discovery of a primitive abelisaurid like Kryptops highly significant, the Carnegie Museum's Lamanna said.
"Kryptops shows that abelisaurid origins may have predated the separation of most major Gondwanan continents," he said.
"Therefore the group may have been able to spread around Gondwana before it broke apart."
While abelisaurids are known from most former Gondwanan landmasses, it isn't known whether different geographical groups evolved while the supercontinent was still joined, Lamanna added.
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