Researchers discovered what is believed to be the earliest-known fossil from the Homo genus, pushing the beginnings of human history back to 2.8 million years ago.
The lower jaw fossil was discovered in Ethiopia, and suggests the Homo lineage is about 400,000 years older than we thought it was, Arizona State University reported. Researchers have been searching for this type of fossil for decades, but samples from the time interval between 2.5 and three million years ago have remained essentially elusive.
The findings provide the first clues of changes in teeth and jaws of Homo specimens only 200,000 years after Australopithecus afarensis ("Lucy") walked the Earth. The fossilized jaw boasted advanced features such as symmetrical premolars and slim molars, distinguishing it from what would be seen in the ape-like Australopithecu. The primitive sloping shape of the jaw links it to a "Lucy-like ancestor."
"The Ledi jaw helps narrow the evolutionary gap between Australopithecus and early Homo," said William H. Kimbel, director of ASU's Institute of Human Origins. "It's an excellent case of a transitional fossil in a critical time period in human evolution."
The researchers believe periods of global climate change 2.8 billion years ago prompted species to pop up or go extinct, including the appearance of Homo.
"We can see the 2.8 million year aridity signal in the Ledi-Geraru faunal community," said research team co-leader Kaye Reed, "but it's still too soon to say that this means climate change is responsible for the origin of Homo. We need a larger sample of hominin fossils, and that's why we continue to come to the Ledi-Geraru area to search."
The findings were published in a recent edition of the journal Nature and was part of The Ledi-Geraru Research Project in the Institute of Human Origins (IHO) at Arizona State University.
