Size, shape, and asymmetry in fossil hominins: the status of the LB1 cranium based on 3D morphometric analyses

Karen L. Baab, Kieran P. McNulty

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72 Scopus citations

Abstract

The unique set of morphological characteristics of the Liang Bua hominins (Homo floresiensis) has been attributed to explanations as diverse as insular dwarfism and pathological microcephaly. This study examined the relationship between cranial size and shape across a range of hominin and African ape species to test whether or not cranial morphology of LB1 is consistent with the basic pattern of static allometry present in these various taxa. Correlations between size and 3D cranial shape were explored using principal components analysis in shape space and in Procrustes form space. Additionally, patterns of static allometry within both modern humans and Plio-Pleistocene hominins were used to simulate the expected cranial shapes of each group at the size of LB1. These hypothetical specimens were compared to LB1 both visually and statistically. Results of most analyses indicated that LB1 best fits predictions for a small specimen of fossil Homo but not for a small modern human. This was especially true for analyses of neurocranial landmarks. Results from the whole cranium were less clear about the specific affinities of LB1, but, importantly, demonstrated that aspects of facial morphology associated with smaller size converge on modern human morphology. This suggests that facial similarities between LB1 and anatomically modern humans may not be indicative of a close relationship. Landmark data collected from this study were also used to test the degree of cranial asymmetry in LB1. These comparisons indicated that the cranium is fairly asymmetrical, but within the range of asymmetry exhibited by modern humans and all extant African ape species. Compared to other fossil specimens, the degree of asymmetry in LB1 is moderate and readily explained by the taphonomic processes to which all fossils are subject. Taken together, these findings suggest that H. floresiensis was most likely the diminutive descendant of a species of archaic Homo, although the details of this evolutionary history remain obscure.

Original languageEnglish (US)
Pages (from-to)608-622
Number of pages15
JournalJournal of Human Evolution
Volume57
Issue number5
DOIs
StatePublished - Nov 2009

Bibliographical note

Funding Information:
The authors appreciate the assistance of the following individuals in the preparation of this manuscript: Peter Brown, Eric Delson, Ryan Raaum, Steve Frost, Will Harcourt-Smith, and Jim Rohlf. We also thank Tony Djubiantono and ARKANAS for access to the Liang Bua material, and Mike Morwood and William Jungers for inviting us to contribute to this special volume on the Liang Bua hominins. We thank Steven Leigh, William Jungers, Adam Gordon, and Katerina Harvati for their comments on this manuscript. We gratefully acknowledge the curators and staff of the American Museum of Natural History, Aristotle University of Thessaloniki, Duckworth Collection at the University of Cambridge, Gadja Mada University, Humboldt University Museum, LIPI, Musée de L'Homme, Musée Royal de l'Afrique Centrale, National Museums of Ethiopia, National Museums of Kenya, National Museum of Tanzania, COSTECH, Natural History Museum, Museum of Comparative Zoology, Peabody Museum at Harvard University, Powell-Cotton Museum, University of Cape Town, and the Institut de Paléontologie Humaine for allowing us access to fossil and comparative samples. Grant support was provided by NSF (BCS 04-24262, DGE 03-33415, and DBI 96-02234), the L.S.B. Leakey Foundation, and the Sigma Xi Foundation. This is NYCEP morphometrics contribution number 28.

Keywords

  • Asymmetry
  • Geometric morphometrics
  • Homo floresiensis
  • Liang Bua
  • Static allometry

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