Australopithecus anamensis represents an early member of the human evolutionary tree, existing approximately 4.2 to 3.8 million years ago. The discovery of its skull provided significant information about this ancient species, offering direct insights into the physical characteristics and evolutionary relationships of early hominins.
Unearthing the Skull
The discovery of the nearly complete Australopithecus anamensis skull, known as MRD-VP-1/1 or “MRD,” occurred in 2016 in the Miro Dora locality of the Woranso-Mille site in the Afar region of Ethiopia. A local Afar pastoralist, Ali Bereino, initially spotted the face and upper jaw while building a goat pen. Paleoanthropologist Yohannes Haile-Selassie and his team soon found the braincase, and subsequent excavation recovered additional pieces.
The skull, dated to about 3.8 million years old, provides a detailed look at the species’ cranial anatomy, previously known primarily from isolated jaw fragments and teeth. Its location, just 35 miles from the Hadar area where “Lucy” was found, and the geological context, including volcanic layers, allowed researchers to precisely date the find and understand the ancient environment.
Distinctive Skull Characteristics
The MRD skull of Australopithecus anamensis showcases a blend of ancient and more advanced features, distinguishing it from both earlier ape-like ancestors and later hominins. The face is noticeably protruding, a primitive trait known as prognathism. The braincase, estimated at about 365-370 cubic centimeters, is relatively small, even smaller than that of Australopithecus afarensis.
The skull also exhibits considerable post-orbit constriction, where it narrows significantly behind the eye sockets. Its jaws are ape-like with a U-shaped dental arcade, where cheek teeth rows are nearly parallel. The upper canine teeth are relatively large and pointed, although shorter than those found in earlier ape-like forms. However, the molars are robust with thick enamel and low cusps, a feature shared with later hominins.
Evolutionary Insights
The discovery of the MRD skull provided new understanding of Australopithecus anamensis’s place in the hominin family tree. Before this find, A. anamensis was widely considered the direct ancestor of Australopithecus afarensis, with a linear evolutionary progression. However, the 3.8-million-year age of the MRD skull revealed a significant temporal overlap of at least 100,000 years with A. afarensis.
This overlap challenges the idea of a simple linear progression, suggesting a more complex, branching evolutionary pattern. While A. anamensis is still considered ancestral to A. afarensis, the coexistence implies that a portion of the A. anamensis population continued to exist after A. afarensis branched off. The skull’s mosaic of primitive and derived features provides a clearer anatomical transition from earlier hominins, like Ardipithecus ramidus, towards later species, including Australopithecus afarensis.
Lifestyle and Environment
Inferences about the lifestyle and environment of Australopithecus anamensis are drawn from the skull’s characteristics and associated fossil evidence. The robust teeth with thick enamel suggest a diet that included tough, abrasive foods, possibly alongside fruits and nuts. This dental morphology indicates adaptation to processing a variety of plant materials. Microwear patterns on their molars show long striations, similar to modern gorillas, suggesting a diet primarily of C3 resources (fruits and tender greens) with some C4-derived resources.
While the skull itself doesn’t directly reveal locomotion, other A. anamensis fossils, such as elements of the knee and tibia, indicate habitual bipedalism. However, features like long forearms and wrist bone characteristics suggest they likely retained capabilities for tree climbing, perhaps for foraging or avoiding predators. The environment where A. anamensis fossils have been found, including the Woranso-Mille and Kanapoi sites, suggests a diverse landscape of woodlands, bushlands, and grasslands, often near ancient lakes or rivers. This mosaic environment would have supported a varied diet and allowed for both terrestrial and arboreal activities.