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The discovery of a mostly intact a 3.8 million year old fossil skull found buried within sandstone, from the Waranjo-Mille site in the Afar region of Ethiopia, was announced last week in Nature. Based on the size and shape of its canines, which has certain anatomical features that make it stand out from A. afarensis and other close relatives, the skull has been assigned a member of Australopithecus anamensis.

Yohannes Haile-Salassie poses in the field with the newly discovered skull. Photograph courtesy of the Cleveland Museum of Natural History
Yohannes Haile-Salassie poses in the field with the newly discovered skull. Photograph courtesy of the Cleveland Museum of Natural History

Before this discovery, we knew of this species only from its teeth and jaws. We did not have such a complete specimen in the fossil record. Remarkably, finding fossil skulls before 3.5 million years ago is remarkably rare.

The 3.8 million-year-old fossil skull of Australopithecus anamensis. Photograph courtesy of the Cleveland Museum of Natural History
The 3.8 million-year-old fossil skull of Australopithecus anamensis. Photograph courtesy of the Cleveland Museum of Natural History

We have thought A. anamensis and A. afarensis to be a chronospecies as A. anamensis‘ because it didn’t have many derived features. The broad cheeks and narrow face resemble Lucy, and the brain case is 365-370 cc in volume, was smaller than A. afarensis.

But now that we have a complete skull, we can now see that A. anamensis’ face has a surprising number of derived features, some of which are quite different from A. afarensis. These findings are described in detail in the original publication. In summary, A. anamensis and A. afarensis could actually be branches from a common ancestor,

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