The recent discovery of a 3.8m-year-old cranium (skull without the lower jaw) is the hottest topic of conversation among palaeoanthropologists right now. But fossils are found all the time, so why is the cranium of this small, old man so important? It turns out the discovery is changing our view of how early hominin species evolved – and how they led to humans. To understand how, let’s start at the beginning.

In 1995, researchers found several partial jaws, isolated teeth and limb bones in Kenya, dated between 4.2m and 3.9m years old, 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 local language. A number of additional specimens were then found in Ethiopia, thought to belong to the same species.

The primitive features of A. anamensis have led to the widespread view that this species is the ancestor of Australopithecus afarensis, a younger hominin from Tanzania, Ethiopia and perhaps Kenya, dated between 3.8m and 3m years old. The most iconic fossil of A. afarensis is probably the partial skeleton known as Lucy, which was for a long time viewed as the oldest known human ancestor.The authors discovered several new morphological features in the MRD cranium that are conventionally considered to be characteristic of younger species on the human lineage. The depth of the palate, for example, exceeds that of all known A. anamensis and A. afarensis specimens, and even is among the deepest palates of later Australopithecus species. This challenges the long and widely-held view that Lucy’s species evolved gradually from A. anamensis without branching of the evolutionary line – a process known as anagenesis.The newly discovered cranium, nicknamed “MRD” after its collection number MRD-VP-1/1, shows many similarities to the already existing A. anamensis specimens, an

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