The recent discovery of a 3.8-meter skull (lower jawbone) is currently the hottest talk among paleoanthropologists. But fossils are found again and again. Why is the skull of this little old man so important? It turns out that the discovery changes our view of the development of early hominin species – and how they have led to humans. To understand how, we start at the beginning.
In 1995, researchers in Kenya found several partial jaws, isolated teeth and limb bones that were between 4.2 and 3.9 meters in age, and assigned them to a brand new species: Australopithecus anamensis . All these fossils were found in sediments associated with an ancient lake – "anam", which means "lake" in the vernacular. In Ethiopia, a number of other specimens were found that are believed to belong to the same species.
The primitive features of A. Anamensis has led to the widespread view that this species is the ancestor of Australopithecus afarensis a younger hominin from Tanzania, Ethiopia and perhaps Kenya, between 3.8 and 3 m old. The most iconic fossil of A. afarensis is probably the partial skeleton known as Lucy, which was long considered to be the oldest known human ancestor. The authors discovered several new morphological features in the MRD skull that are traditionally regarded as characteristic of younger species on the island of human descent. The depth of the palate, for example, exceeds those of all the well-known A. anamensis and A. afarensis specimens and even belongs to the deepest palates of later Australopithecus species. This questions the long and widespread view that Lucy's species gradually evolved from A. Anamensis without branching of the evolutionary line ̵
Given that these modern features were already present in older species, the most likely scenario is that Lucy's species were created by evolutionary deviation from A. Anamensis – a process known as cladogenesis. However, it is not known exactly when A. afarensis diverged. Further proof of cladogenesis comes from a 3.9 m old frontal bone (part of the forehead) from Ethiopia, which was discovered in 1981. Its shape differs from that of MRD, suggesting that this fossil is likely to belong to A. afarensis .
If that is the case, we need to revise the human evolution timeline with A. Anamensis which occurred 4.2 to 3.8 million years ago, and A. afarensis from 3.9 to 3 m years ago. This would mean that both species overlapped for at least 100,000 years, which made A impossible. afarensis is said to have gradually evolved from a single ancestral group. In fact, it is becoming increasingly obvious that most species in our line of evolution are likely to have been created by diversion from existing groups.
The Human Line
The new discovery also questions the idea that Lucy's is the ancestor of all later species. Australopithecus Hominins that eventually led to humans.
The opposite disease – a low and arched cheekbone – is considered primitive and is shared among A. afarensis Ardipithecus ramidus (from 4.3 to 4.5 million years ago from Ethiopia, a monkey-like primitive hominin) and African monkeys. A vertically straight and steeply rising bulge of the cheekbone was traditionally considered to be a relatively modern feature. It was found in Australopithecus africanus (3.7 to 2.1 million years ago from southern Africa, by some as the direct ancestor of the homo-line and in the Paranethropus lineage (from 2.7 to 1.2 million years ago from southern and eastern Africa, not directly on our evolution line).
The crest of the MRD skull, which is surprisingly modern, now challenges that view. It also opens up the possibility that the longstanding idea of A. afarensis as the ancestor of all later Australopithecus groups could have been mistaken, and that instead A. anamensis which is the ancestor of these younger species. Which early hominin is the direct ancestor of man remains open.
This latest discovery has undoubtedly provided new insights into our evolutionary past, but also the complexity of relationships increased between early hominins. The middle Pliocene (5.3 to 2.6 million years ago) is crowded with many contemporary and geographically widespread species.
Clarifying the relationships between these species, safely characterizing their morphology and deciphering the complex and intricate history of hominin evolution is not an easy task. Specimens at each new site capture a different point along the evolution curve, but it is not easy to transform those results into stable and reliable branches of an evolution tree.
Other specimens from periods and geographic areas that are currently underrepresented in the US Fossils could help clarify these issues, but also turn anything we know into an upside down one.
Discoveries around the world in the last decade have led to a complete rethink in our evolutionary past. It shows that new fossils do not always support existing hypotheses and that we must be ready to change our minds and formulate new theories based on the evidence available.
By Hester Hanegraef, Doctoral in Anthropology, Museum of Natural History
This article has been republished from The Conversation as a Creative Commons license. Read the original article.