Brief Communication: Molar development and crown areas in earlyAustralopithecus

Authors

  • Rodrigo S. Lacruz,

    Corresponding author
    1. Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, CA 90033
    • University of Southern California, Center for Craniofacial Molecular Biology, 2250 Alcazar St., CSA 103, Los Angeles, CA 90033, USA
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  • Fernando V. Ramirez Rozzi,

    1. UPR 2147 CNRS, 44 rue de l'Amiral Mouchez, Paris 75014, France
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  • Bernard A. Wood,

    1. Center for the Advanced Study of Hominid Paleobiology, George Washington University, Washington, DC 20052
    2. Department of Anthropology, George Washington University, Washington, DC 20052
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  • Timothy G. Bromage

    1. Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY 10010
    2. Department of Basic Science and Craniofacial Biology, New York University College of Dentistry, New York, NY 10010
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Abstract

Recent studies suggest that the hypodigms representing the two earliest Australopithecus (Au. anamensis and Au. afarensis) form an ancestor-descendant lineage. Understanding the details of this possible transition is important comparative evidence for assessing the likelihood of other examples of ancestor-descendant lineages within the hominin clade. To this end we have analyzed crown and cusp base areas of high resolution replicas of the mandibular molars of Au. anamensis (Allia Bay and Kanapoi sites) and those of Au. afarensis (Hadar, Laetoli, and Maka). We found no statistically significant differences in crown areas between these hypodigms although the mean of M1 crowns was smaller in Au. anamensis, being the smallest of any Australopithecus species sampled to date. Intraspecies comparison of the areas of mesial cusps for each molar type using Wilcoxon signed rank test showed no differences for Au. anamensis. Significant differences were found between the protoconid and metaconid of Au. afarensis M2s and M3s. Furthermore, the area formed by the posterior cusps as a whole relative to the anterior cusps showed significant differences in Au. afarensis M1s and in Au. anamensis M2s but no differences were noted for M3s of either taxon. Developmental information derived from microstructural details in enamel shows that M1 crown formation in Au. anamensis is similar to Pan and shorter than in H. sapiens. Taken together, these data suggests that the overall trend in the Au. anamensis-Au. afarensis transition may have involved a moderate increase in M1 crown areas with relative expansion of distal cusps. Am J Phys Anthropol , 2012. © 2012 Wiley Periodicals, Inc.

Ancillary