In the scientific journal Acta Palaeontologica Polonica, paleontologist Paul Sereno and co-author Stephen Brusatte named one Kryptops palaios, or "old hidden face," because of a horny covering over its face.
The other, they named Eocarcharia dinops, or "fierce-eyed dawn shark," for its razor-sharp teeth and bony brow.
Both were about 25 feet long and stood 7 feet high at the hip. Kryptops had a short snout with teeth better for gnawing, leading the scientists to believe he was more of a scavenger.
Eocarcharia's brow was so pronounced that Sereno thinks it was used for head-butting rivals to win over potential mates.
"The only thing I can think of is they were smacking each other with it," Sereno said.
The creatures lived at a time when land bridges connected Africa to India and even Antarctica, which was then a temperate home to dinosaurs. But Africa later became isolated and its dinosaurs followed unique evolutionary paths scientists have just begun to uncover.
"This is an important slice in geological time, and we don't yet fully comprehend how dinosaurs on the southern continents were evolving then," said Peter Makovicky, curator of dinosaurs at the Field Museum, who was not part of the Chicago team.
Makovicky called the new discoveries "an important data point toward a deeper understanding of what happened."
Sereno's group found both new species during a 2000 expedition to the Niger desert. They found bones from about a dozen new species, and stumbled across one of the richest archaeological sites that's been found in the region.
"We have not released even half of all that we found there," Sereno said.
Earlier this week, researchers led by Xiaolin Wang of the Chinese Academy of Science, reported their - a tree dwelling dinosaur about the size of a modern sparrow.