Size and shape variation in Australopithecus afarensis proximal femora

Area of Science:

• Paleoanthropology
• Primate anatomy
• Evolutionary biology

Background:

• Interpretations of size and shape variation in Australopithecus afarensis fossils have varied significantly.
• Previous studies suggested size variation exceeding extant hominoids or similar to modern humans.
• Shape variation has been described as both substantial and negligible.

Purpose of the Study:

• To analyze the proximal femur of Australopithecus afarensis to quantify size and shape variation.
• To compare this variation to extant hominoid samples for evolutionary context.

Main Methods:

• Analysis of seven well-preserved Australopithecus afarensis proximal femora.
• Use of comparative samples from Pan, Pongo, Gorilla, and Homo.
• Calculation of coefficient of variation (CV) for size variation and ratios for scale-free shape variables.
• Pairwise comparisons using Euclidean distance.

Main Results:

• Size variation in Australopithecus afarensis is comparable to gorillas and orangutans.
• Shape variation among Australopithecus afarensis is generally within the range of most extant hominoids.
• A few instances of excessive size and shape variation were noted, potentially due to temporal bias.

Conclusions:

• Proximal femur variation in Australopithecus afarensis suggests size variation similar to strongly sexually dimorphic apes.
• Shape variation is not extreme and falls within the typical range observed across hominoids.
• While generally consistent, some outliers warrant further investigation into potential causes like temporal variation.