The discovery of a nearly intact skull in Ethiopia is the first to show the facial characteristics of a critically important species linked to early hominin evolution. At the same time, the 3.8-million-year-old fossil is further complicating our understanding of Australopithecus — the genus that likely gave rise to humans.

Before the rise of Homo there was Australopithecus, a genus that lived in Africa from between roughly 4 million and 2 million years ago. The first fossils of Australopithecus were discovered in South Africa 95 years ago, and the genus is now known to encompass at least five species: anamensis, afarensis, africanus, sediba and garhi.

It’s highly likely that one of these species — we still don’t know which one — spawned the Homo genus to which we belong. Frustratingly, the fossil record of these early hominins is exceptionally sparse, leading to tons of ambiguity on the matter.

Two new papers published today in Nature describe the discovery of nearly complete A. anamensis skull, signifying a critically important addition to the fossil record and the study of human origins. Previously, this species was only known from odd bits of teeth and jaw fragments, so this new cranium, uncovered at the Woranso-Mille site in the Afar region of Ethiopia, represents a major leap in our understanding of this early australopithecine.

“The new find fills [an] important gap and puts a face on this pivotal species,” Zeresenay Alemseged, a paleontologist at the University of Chicago, told Gizmodo. “The preservation is impressive and

major contribution to paleoanthropology,” said Alemseged, who was not affiliated with the new research.

The cranium, in addition to revealing facial characteristics, is shedding new light on the origin of Australopithecus and the species that followed. Importantly, at an estimated age of 3.8 million years old, A. anamensis likely lived alongside A. afarensis for around 100,000 years, according to the new research.

This unexpected overlap means some species within the Australopithecus genus didn’t evolve linearly, with one species tidily following another in an orderly fashion, a process known as anagenesis. Rather, this new discovery points to a different scenario, in which multiple species co-existed at the same time in a process known as cladogenesis. Evolution, as we’ve long known, is often messy and complicated.

In the first of the two Nature papers, paleoanthropologist Yohannes Haile-Selassie from the Cleveland Museum of Natural History and his colleagues presented their analysis of the fossil.

Dubbed MRD, the skull was discovered three years ago in Ethiopia around 55 kilometres north of Hadar, where the famous Lucy fossil was uncovered in 1974. Analysis of the fossil’s teeth and jaw allowed the researchers to assign the species as A. anamensis. The specimen was likely an adult male who reached an advanced age, as evidenced by his well-worn teeth. Analysis of the cranium revealed some surprising characteristics.

“MRD has a mix of primitive and derived [ancient] facial and cranial features that I didn’t expect to see on a single individual,” said Haile-Selassie in a press release.