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Related Experiment Videos

Relative cheek-tooth size in Australopithecus.

H M McHenry

    American Journal of Physical Anthropology
    |July 1, 1984
    PubMed
    Summary

    Australopithecus species had significantly larger cheek teeth relative to body size than modern humans, a trait termed megadontia. This megadontia decreased over time in the Homo lineage, marking a key evolutionary transition.

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    Area of Science:

    • Paleoanthropology
    • Human Evolution
    • Comparative Anatomy

    Background:

    • Cheek-tooth megadontia was a defining trait of early hominins, alongside bipedalism and small brains.
    • Australopithecus afarensis presents a unique case with postcanine tooth area similar to Homo habilis, prompting further investigation into relative tooth size.

    Observation:

    • Australopithecus species exhibit megadontia, possessing cheek teeth 1.7 to 2.3 times larger than expected for their body size compared to modern hominoids.
    • Analysis of associated skeletons confirms this, with Australopithecus afarensis teeth 2.8 times larger than expected, and Australopithecus africanus and Australopithecus robustus over twice the expected size.

    Findings:

    • A clear trend of increasing megadontia is observed from Australopithecus afarensis through Australopithecus boisei, indicated by strong positive allometry.
    • Conversely, the Homo lineage (Homo habilis to Homo sapiens) shows strong negative allometry, signifying a substantial reduction in relative posterior tooth size.

    Implications:

    • The evolutionary shift from Australopithecus to Homo involved a significant decrease in relative cheek-tooth size.
    • This transition likely occurred between 2.5 and 2.0 million years ago, possibly from an Australopithecus africanus-like ancestor to Homo habilis.

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