Skull of humankind’s oldest-known ancestor discovered

The Guardian – By Hannah Devlin/Science correspondent – Wed 28 Aug 2019

Iconic’ finding of 3.8m-year-old fossil in Ethiopia casts doubt on previous evolutionary theory.

The face of the oldest species that unambiguously sits on the human evolutionary tree has been revealed for the first time by the discovery of a 3.8 million-year-old skull in Ethiopia.

The fossil belongs to an ancient hominin, Australopithecus anamensis, believed to be the direct ancestor of the famous “Lucy” species, Australopithecus afarensis. It dates back to a time when our ancestors were emerging from the trees to walk on two legs, but still had distinctly ape-like protruding faces, powerful jaws and small brains, and is the oldest-known member of the Australopithecus group.

While Lucy became celebrated in studies of human evolution, her direct predecessor has remained a shadowy trace on the record, with only a handful of teeth, some limb bones and a few fragments of skull to provide clues about appearance and lifestyle.

The latest specimen, a remarkably complete adult male skull casually named MRD, changes this.

The skull shows that MRD had a small brain – about a quarter of the size of a modern human – but was already losing some of its ape-like features. Its canines are smaller than those seen in even earlier fossils and it is already developing the powerful jaw and prominent cheekbones seen in Lucy and the famous Mrs Ples fossil (another later member of the Australopithecus group), which scientists think helped them chew tough food during dry seasons when less vegetation was available.

The dating of the skull also reveals that Anamensis and its descendent species, Lucy, coexisted for a period of at least 100,000 years. This discovery challenges the long-held notion of linear evolution, in which one species disappears and is replaced by a new one. Anamensis, which now spans from 4.2 million to 3.8 million years ago, is still thought to be Lucy’s ancestor, but continued to hang around after the Lucy group branched off from the parent lineage. Geological evidence suggests the landscape would have featured extremely steep hills, volcanoes, lava flows and rifts that could easily have isolated populations, allowing them to diverge.

Divergent groups may have later crossed paths and competed for food and territory.

Read entire article here

Posted by Teri Perticone

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