Australopithecus anamensis

Phylogenetic Discussion

Post Crania

The anamensis species seems to have been an obligate biped, as shown by the tibia and a hallux bone recovered. The tibia has concave condyles of approximately the same area, while the lateral condyle is larger and flat (in chimpanzees one of the condyles is convex, and the medial is larger). The shaft of the tibia is straight and there is less space between the tibia and fibula than there is found in chimps (Ward et al, 1999).

Dental

Shows stronger adaptations to powerful chewing forces than that of A. ramidus or A. afarensis. Post canine teeth are larger than A. ramidus, as well as covered with thicker enamel. It has an elongated, posteriorly angled mandibular symphysis, a shallow palate, and vertical maxillary canine roots (Leakey et al, 1995). The upper molars are broader across the mesial side with thicker enamel. Some evidence that might link it to A. ramidus includes: deciduous molars that are elongated with thin enamel, straight and parallel tooth rows, and a relatively small P4 – smaller than the P3 (which is rare in hominids). Some features that distinguish it from A afarensis include: bigger and less posteriorly inclined upper canine root, more sloping lingual sides of upper molars (subtle), and a more retreated mandibular symphysis (Ward et al, 1999).

Conclusion

All of these traits can lead to a discussion of the place of A. anamensis in the hominid lineage. With accurate dates placing it from 4.2-3.9 ma and the similar but more primitive anatomy of anamensis relative to afarensis, make it a good candidate for a precursor to afarensis. Whether anamensis is a precursor species or simply part or a highly variable population through time is a matter of some debate.