An international team has found a cranium fossil, in good conditions, from a 3.8 million year hominid from the area of Afar Region, in Ethiopia. This dating shows the cranium belongs to the species Australopithecus anamesis, ancestor of Australopithecus afarensis –a species that belongs to Lucy- and both species were contemporary, at least for 100,000 years. The findings contradict the idea of an anagenetic relation between both groups, through which a species disappears giving way to a new species in a lineal fashion.
Results were published in the journal Nature, one on the description of the fossil and another one on the geological context and age of it, a study in which the researcher Lluís Gilbert, from the Faculty of Earth Sciences of the University of Barcelona, took part. “The obtained data shows the fossil is 3.8 million years old. This puts the cranium in a period of time with a few fossils and helps us completing the puzzle of human evolution”, notes Gilbert.
The research study was carried out as part of the WORMILL project (Woranso-Mille), led by Yohannes Haile-Selassie, curator at the Museum of Natural History of Cleveland and adjunct professor at the Case Western Reserve University (United States), which has provided for fifteen years about 230 hominid fossils and discovered this cranium, identified as MRD-VP-1/1, in 2016.
The Australopithecus anamesis is the oldest member of the genus Australopithecus. This species was previously identified for its dentition and jaw fragments that dated from between 4.2 and 3.9 million years ago. The similarities with the dentition of the found fossil (MRD), enabled its identification as member of this species. Moreover, thanks to the almost complete state of the cranium, researchers found cranial and facial characteristics that had not been observed before. Some of these characteristics were shared with the descendant species A. afarensis, while others were more related to more primitive ancestral groups such as Ardipithecus and Sahelantropus.
Identifying a new fossiliferous area
According to Gilbert, “this discovery is only relevant within a geological and chronological context. Without this information the discovery has no value. Therefore, geology and the age of the cranium are essential to interpret the fossil in the context of human evolution”. The article on the geological aspects counts on the participation of fourteen researchers from different institutions that bring different data related to the age and environment of the place where the fossil lived.
The cranium was found in 2016 in a new fossiliferous area, which had not been studied before. The site is located in the palanteological area of Woranso-Mille in the Afar Region (Ethiopia). It is located at 550 km in the north-eastern area from the capital, Addis Ababa, and 55 km north from Hadar (where Lucy comes from).
At the moment, the Afar Region is a semi-dessert area, crossed by some rivers. This are is located in the northern area of the African Rift Valle, near a triple spot where three tectonic plaques separate. Therefore, its tectonic activity is high and there is active volcanism. The tectonic situation could be similar 3.8 million years ago, with a high presence of volcanic eruptions due the levels of ash, some of them over two meters of thickness.
The site is located in a remote area that requires crossing the River Mille, during the geological campaign in 2017 the rain made the river width go from 20 to 100 meters, making the geological work even harder, says the researchers. Preliminary observations allowed researchers determining the site had been formed in a delta in the River Mille.
In another campaign in 2018, many sedimentary and volcanic ash samples were taken, “these data enabled relating the extracts with volcanic ashes from other places and determining its approximate age”, notes Gilbert. New radiometric datings on volcanic ashes near the site together with paleomagnetic data, helped determining the precise age of the fossil. Also, pollen and diatomic samples, and biomarkers apart from the found fauna related to the cranium, “gave us an approximate idea of how plants and the environment were”, says the UB geologist.
Regarding the landscape where the MRD lived, researchers know there was a lake with a certain level of salinity and which was about between six and eight meters deep, fed by a river with a similar size to that of the current River Mille. There were forested areas, but other areas far from the water had an open and arid environment with bushes and a variable proportion of plants, perhaps similar to the current one. “The surroundings of the lake would offer many eating resources for individuals that walked in a biped way”.
Beverly Z. Saylor et al. “Age and context of mid-Pliocene hominin cranium from Woranso-Mille, Ethiopia“. Nature, August, 28 2019.
Yohannes Haile-Selassie et al. “A 3.8-million-year-old hominincranium from Woranso-Mille, Ethiopia” Nature, August, 28 2019.