Ancient Human Ancestors Faced Fearsome Horned Crocodile

Charles Q. Choi

Date: 23 February 2010 Time: 03:00 PM ET

A newfound horned crocodile may have been the largest predator encountered by our ancestors in Africa, researchers now suggest.

Scientists have even found bones from members of the human lineage bearing tooth marks from this reptile, whose scientific name, Crocodylus anthropophagus, means "man-eating crocodile."

This predator, which lived some 1.84 million years ago, possessed a deep snout that would have made it look more robust than modern crocodiles. It also had prominent triangular horns.

"They would have been visible mostly from the side as projections behind the eye," said researcher Christopher Brochu, a vertebrate paleontologist at the University of Iowa. "If you looked at them from the front, you would have seen ridges projecting upwards."

A couple of living species of crocodile have similar horns, such as the Cuban and Siamese crocodiles. "Males will use these in mating season to show off," Brochu explained. "While submerged they kind of tip their head forward, showing off the prominence of their horns to females."

Scientists found a partial skull and skeleton of the crocodile at Olduvai Gorge in the Serengeti Plains of Tanzania in 2007. Past research there famously unearthed numerous fossils of extinct human species and their stone tools, strengthening the argument that our lineage originated in Africa.

Fossil leg and foot bones of at least two hominids from Olduvai bear crocodilian tooth marks, and came from roughly the same time as the newfound horned carnivore and within roughly 300 feet (100 meters) from where the reptile's skeleton was discovered.

"I can't guarantee these crocodiles were killing people, but they were certainly biting them," Brochu said. "Our ancestors would have had to be cautious close to the water, because the water's edge at Olduvai Gorge would have been a very dangerous place."

Crocodiles may have been common predators of hominids, the scientists noted. Larger crocodiles would be capable of consuming our ancestors completely, leaving no trace.

"It was probably as large as a modern Nile crocodile, one of the largest living crocodilians at between 18 to 20 feet," Brochu said. "One thing to bear in mind was that while these crocodiles are not necessarily bigger than the ones today, hominids back then were smaller than we are today, so the crocodiles would have been relatively quite a bit larger."

Crocodiles have a reputation for being living fossils that do not change over time, "and that's just wrong," Brochu added. "If you go back five to 10, 15 million years ago, there were more species of crocodile alive then than there are now, and the general assumption that once we entered the Quaternary period, the ice ages, crocodile diversity dropped. This fossil existed during the Quaternary, so it indicated crocodile diversity remained somewhat higher than expected."

Brochu and his colleagues detailed their findings online Feb. 23 in the journal PLoS ONE.