What You Can Learn From Bones: The Proximal Femur

There is an interesting article in HOMO – Journal of Comparative Human Biology on the proximal femur. The article, Geometric morphometric analyses of hominid proximal femora: Taxonomic and phylogenetic considerations, looked at whether one can separate extant hominids into different taxa using geometric morphometrics and whether one could distinguish Homo from Australopithecus and Paranthropus.

The study digitized 20 landmarks on the proximal femur from recent humans (n=82), chimpanzees (n=16), gorillas (n=20), and casts of fossil hominins (n=6, included are A. L. 288-1, KNM-ER 1472, KNM-ER 1481, KNM-WT 15000, SK 82, and SK 97). The landmarks are pictured below:

The data was then analyzed using both Procustes analysis and principal components analysis. What did the researchers find? Here is a scatter plot of the first two principle components (I apologize for the poor quality I had trouble extracting them):

PC1 and PC2

:

Note that principal component one separates Homo and the fossil hominins from extant apes. Principal component two clearly separates chimps from gorillas. Biologically, low PC1 scores indicate a large head, long neck, and short greater trochanter. High scores indicate a small head, short neck, and tall greater trochanter. Low PC2 scores indicate cranially projecting greater trochanters with a deep trochanteric fossa. Below is a scatter plot of PC3 and PC4:

PC3 and PC4

PC3 is governed primarily by neck shaft angle and doesn’t segrate any of the groups. PC4, governed by neck length and breadth, greater trochanter height, and lesser trochanter position, separates all early hominins from recent Homo.

To summarize, there are distinct differences in proximal morphology between chimps, gorillas and recent humans. There are also differences in proximal femur morphology between the apes and fossil hominins (i.e. Australopithecus, Paranthropus, and early Homo). There are some differences between fossil hominins and recent humans – although there is some overlap as well. At this point cluster analysis was used which succeeded in separating Australopithecus from Paranthropus and both of these from Homo. All of this has some interesting implications for our ability to assign isolated femora to the generic level. An additional implication concerns the impact on certain creationist arguments concerning the taxonomic status of the australopithecines. Specifically, the claim that australopithecines were just bipedal apes. This study demonstrates that there are specific morphological differences between the femora of apes and australopithecines – differences that are large enough to allow us to distinguish between the two.

Literature Cited

Holliday, Hutchinson, Morrow, and Livesay (2010) Geometric Morphometric analysis of hominid proximal femora: Taxonomic and phylogenetic considerations. Homo – Journal of Comparative Human Biology 61:3-15

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6 Responses

  1. The earlier publication by the late Elizabeth Harmon is worth a look if you like the Holliday et al. paper:

    “The Shape of the Early Hominin Proximal Femur”
    HARMON Elizabeth H.
    Abstract:
    Postcranial skeletal variation among Plio-Pleistocene hominins has implications for taxonomy and locomotor adaptation. Although sample size constraints make interspecific comparisons difficult, postcranial differences between Australopithecus afarensis and Australopithecus africanus have been reported (McHenry and Berger: J Hum Evol 35 [1998] 1-22; Richmond et al.: J Hum Evol 43 [2002] 529-548; Green et al.: J Hum Evol 52 [2007] 187-200). Additional evidence indicates that the early members of the genus Homo show morphology like recent humans (e.g., Walker and Leakey: The Nariokotome Homo erectus skeleton. Cambridge: Harvard, 1993). Using a larger fossil sample than previous studies and novel methods, the early hominin proximal femur is newly examined to determine whether new data alter the current view of femoral evolution and inform the issue of interspecific morphological variation among australopiths. Two- and three-dimensional data are collected from large samples of recent humans, Pan, Gorilla, and Pongo and original fossil femora of Australopithecus, Paranthropus, and femora of African fossil Homo. The size-adjusted shape data are analyzed using principal components, thin plate spline analysis, and canonical variate analysis to assess shape variation. The results indicate that femora of fossil Homo are most similar to modern humans but share a low neck-shaft angle (NSA) with australopiths. Australopiths as a group have ape-like greater trochanter morphology. A. afarensis differs from P. robustus and A. africanus in attributes of the neck and NSA. However, interspecific femoral variation is low and australopiths are generally morphologically similar. Although the differences are not dramatic, when considered in combination with other postcranial evidence, the adaptive differences among australopiths in craniodental morphology may have parallels in the postcranium.

    American Journal of Physical Anthropology (2009) vol. 139, no2, pp. 154-171

  2. I wasn’t able to find a copy freely available on the web. She does have a similar paper in the Journal of Anatomy (which is freely available) and One in the Journal of Human Evolution that focuses on Australopithecus afarensis which looks interesting. Richmond and Jungers also had a paper along similar lines in Science a few years ago.

  3. The AJPA paper uses the same 3-D coordinate-based morphometric methods as the J. Anatomy paper, but adds in the proximal femora of fossil hominins. I couldn’t find a freebie pdf through Google Scholar, but the J. Anatomy article is available there. The A. afarensis paper was more about relative variation and extreme sexual dimorphism in that species.

  4. [...] Afarensis has a nice post up explaining how the genus Homo and extinct hominids can be distinguished from other living apes AND [...]

  5. This seems to support generic level status for Paranthropus.

  6. Yes, somewhat

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