A creature which lived six million years ago and which lacked sharp canines for fighting might be the first pre-human to branch off the ape line, says a US-led scientific team.
Ardipithecus kadabba, a short, small-brained hominid, did not have the long teeth found in chimpanzees.
The shape of the teeth gives clues to human origins
The researchers believe this feature and the animal's age means it was possibly the first species after the evolutionary split in the lineage that led to modern chimpanzees and humans.
The study, led by the Cleveland Museum of Natural History in Ohio, is reported in the journal science.
Between 1997 and 2000, Yohannes Haile-Selassie and colleagues recovered 11 hominid specimens from at least five individuals who lived in a wooded environment in Ethiopia between five and six million years ago.
In a 2001 report, these bones and teeth were assigned to a subspecies of another known pre-human, Ardipithecus ramidus. But further excavation work has recovered six additional teeth - including an upper canine, premolars from both upper and lower jaws and upper molars - belonging to different individuals.
This has prompted Dr Haile-Selassie's team to reclassify all the specimens - dated to be between 5.54 and 5.77 million years old - into their own species group, A. kadabba.
"The teeth not only revealed dental evolution in the earliest hominids, but they also helped to differentiate the earlier and later species of the genus Ardipithecus," Dr Haile-Selassie said.
Genetic studies have suggested a common ancestor for modern apes and humans may have existed about six million years ago.
Two other recent hominid finds in Africa, Orrorin tugenensis in Chad, and
Sahelanthropus tchadensis in Kenya, are said to be slightly older than the creature described by Dr Haile-Selaisse's team.
The curator and head of physical anthropology at the Cleveland Museum of Natural History suggested further fossil finds could indicate all three species actually belong to the Ardipithecus genus.