A lower jaw bone, found in the Afar region of Ethiopia, represents the earliest known remains of the genus Homo. The early hominid to whom the jaw belonged lived between 2.8 and 2.75 million years ago according to researchers.

The international team of anthropologists and geoscientists also dated other fossils in the area to between 2.84 and 2.58 million years ago. The additional fossils will help to reconstruct the environment where the individual lived.

“The record of hominin evolution between 3 and 2.5 million years ago is poorly documented in surface outcrops, particularly in Afar, Ethiopia,” said Erin N. DiMaggio, research associate in the department of geosciences, Penn State in a statement.

Hominini, the group of primates that include Homo sapiens and of which we are the only known remaining member. It represents the branch of the evolutionary tree that occurred after the split from chimpanzees.

“In spite of a lot of searching, fossils on the Homo lineage older than 2 million years ago are very rare. To have a glimpse of the very earliest phase of our lineage’s evolution is particularly exciting,” said Brian A. Villmoare of the University of Nevada, Las Vegas

Due to the age of the fossils, direct dating is impossible. Instead, geologists used a variety of methods to date the age of the rock in which the fossils were found.

The Ledi-Geraru fossil mandible was dated by examining layers of volcanic ash using the argon40 argon39 dating. The method measures argon isotopes to determine the age of the volcanic eruption that deposited them.

“We are confident in the age of LD 350-1. We used multiple dating methods including radiometric analysis of volcanic ash layers, and all show that the hominin fossil is 2.8 to 2.75 million years old,” said DiMaggio, lead author on the paper which appears in the current online issue of Science Express.

The area where the remains were found is part of the East African Rift System. The area undergoes tectonic extension or stretching of the crust. That extension buried the rocks and then allowed them to be exposed through erosion.

In the Ledi-Geraru area, faults have broken the rock and exposed slices of the areas history. By dating the areas above and below the fossils, geologist can establish a range of dates.

Other fossils in the area belonged to prehistoric antelope, elephants, crocodiles, fish and a type of hippopotamus. All of them fall within the 2.84 and 2.54 million years ago.

According to Kaye E. Reed, University Professor, Institute of Human Origins, Arizona State University the fossils suggest that the area was primarily mixed grasslands and shrub lands with trees lining rivers and wetlands. It was likely similar to the current Kalahari or Serengeti Plains.

Many researchers have suggested that a period of global climate change about 2.8 million years ago forced evolutionary changes in a variety of animals.

“We can see the 2.8 million-year-old aridity signal in the Ledi-Geraru faunal community. 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,” said Reed.

The discovery was made in the same are of Ethiopia as the famed po afarensis “Lucy“, which dates to 3.2 million years ago. This new find, dates from between 200 million and 700 million years after that, during a period of climate change. So, although there isn’t a direct link yet, a picture starts to take shape of the earliest part of the hominid family tree.