Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comparative Study
. 2007 Apr 17;104(16):6568-72.
doi: 10.1073/pnas.0606454104. Epub 2007 Apr 10.

Gorilla-like anatomy on Australopithecus afarensis mandibles suggests Au. afarensis link to robust australopiths

Yoel Rak  1 , Avishag Ginzburg, Eli Geffen
Affiliations
Comparative Study

Gorilla-like anatomy on Australopithecus afarensis mandibles suggests Au. afarensis link to robust australopiths

Yoel Rak et al. Proc Natl Acad Sci U S A. .

Abstract

Mandibular ramus morphology on a recently discovered specimen of Australopithecus afarensis closely matches that of gorillas. This finding was unexpected given that chimpanzees are the closest living relatives of humans. Because modern humans, chimpanzees, orangutans, and many other primates share a ramal morphology that differs from that of gorillas, the gorilla anatomy must represent a unique condition, and its appearance in fossil hominins must represent an independently derived morphology. This particular morphology appears also in Australopithecus robustus. The presence of the morphology in both the latter and Au. afarensis and its absence in modern humans cast doubt on the role of Au. afarensis as a modern human ancestor. The ramal anatomy of the earlier Ardipithecus ramidus is virtually that of a chimpanzee, corroborating the proposed phylogenetic scenario.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Ramal morphology in Au. afarensis and extant primates. (Top) Left mandibular ramus and right mandibular ramus (horizontally flipped) of Au. afarensis specimen A. L. 822-1 and left mandibular ramus of a gorilla. (Middle) Left mandibular ramus of Au. afarensis MAK-VP 1/83 specimen; fragment of left mandibular ramus of Au. afarensis specimen A. L. 333-100; and mandibular ramus of Au. robustus specimen SK 23. (Bottom) Mandibular ramus of a chimpanzee, an orangutan, and H. sapiens. (Scale bar: 5 cm.) Note that the upper end of the ramus in all of the specimens above the white line resembles that of a gorilla (particularly in the shape of the coronoid, the great percentage that the coronoid base constitutes of the ramal width, the confined appearance of the mandibular notch, and the small percentage that the notch area constitutes of the ramal area). The limited reconstruction of the coronoid process on the left ramus of A. L. 822-1 is based on the corresponding preserved area on the right ramus and vice versa.
Fig. 2.
Fig. 2.
The mean contour of the superior margins of the left and right mandibular ramus in A. L. 822-1 compared with the mean contours of other primates. The A. L. 822-1 contour constitutes the border of the shaded area. Note that the contours fall into two distinct groups. Each contour was plotted with the posterior margin of the ramus vertically oriented. The tip of each condylar process lies at the upper left corner of the coordinate system (the zero point), and the anterior margin of the ramus lies at the far right, at the vertical line T. These contours do not express the posteriorly directed tip of the coronoid process (see Fig. 1) exhibited by A. L. 822-1 and many gorillas; the resolution of the grid does not capture the full extent of the tip's morphology.
Fig. 3.
Fig. 3.
Canonical scores of root 1 versus root 2. Individual scores are indicated by species-specific symbols, and group centroids are indicated by encircled species-specific abbreviations. Roots 1 and 2 account for 50.2% and 38.8% of the variance, respectively.
See this image and copyright information in PMC

References

    1. Afifi AA, Clark V. Computer-Aided Multivariate Analysis. New York: Chapman & Hall; 1995.
    1. Bernstein IH. Applied Multivariate Analysis. Berlin: Springer; 1988.
    1. White TD, Suwa G, Simpson S, Asfaw B. Am J Phys Anthropol. 2000;111:45–68. - PubMed
    1. White TD, Johanson DC. Am J Phys Anthropol. 1982;57:501–544.
    1. Kimbel WH, Rak Y, Johanson DC. The Skull of Australopithecus afarensis. Oxford: Oxford Univ Press; 2004.

Publication types