TY - JOUR
T1 - Ontogenetic patterns of sexual dimorphism in the cranium of Bornean orang-utans (Pongo pygmaeus pygmaeus)
AU - Masterson, Thomas J.
AU - Leutenegger, Walter
N1 - Funding Information:
We thank Professor Dr G. Ziegelmayer for permission to study the SELENKA collection of orang-utan crania. We also thank Dr Matthew Ravosa and Anne Gomez for inviting us to participate in their symposium and to contribute to this special issue of the Journal qf Human Evolution. Dr Brian Shea’s comments on earlier manuscripts are greatly appreciated, as well as comments from three anonymous reviewers and Dr Care1 van Schaik’s insights that helped to improve this manuscript. Special thanks go to Dr Luci Kohn for her many helpful discussions and comments throughout the duration of this project. This research was supported by a Senior Professor Fulbright Award and a grant from the Graduate School, University of Wisconsin-Madison to W.L.
PY - 1992/7
Y1 - 1992/7
N2 - Ontogenetic patterns of cranial sexual dimorphism in a large sample of the Bornean orang-utan (Pongo pygmaeus pygmaeus) are investigated by means of univariate, bivariate and multivariate statistical analyses. Univariate analyses of 21 linear dimensions reveal that starting at the mid-juvenile stage there is a strong tendency for an increase in number and strength of significant sex differences, all in favor of males. Significant sex differences in the viscero-cranium, reflecting stronger prognathism in males, emerge before those in the neurocranium. Two major growth allometry patterns emerge from bivariate analyses. Ontogenetic scaling is present in 10 dimensions. It is particularly strong in the neurocranium directly associated with brain size, the orbital region and the dental arcade. The heterochronic process of time hypermorphosis is most likely responsible for this pattern. The second growth pattern reflects a departure from ontogenetic scaling with males exhibiting significantly steeper slopes than females. This occurs in 10 cranial dimensions associated with secondary sexual character development: prognathism, canine size and cheek pad area. We suggest that the heterochronic process of acceleration underlies this growth pattern. Principal components analyses reveal two major multidimensional patterns of cranial sexual dimorphism. First, sexual differences at age groups 2 and 3 are primarily the result of differences in principal component II scores, reflecting mainly shape-related differences. Second, age groups 5, 6 and 7 show a trend of stronger size-related shape differences with increasing age in the allometry vector along with decreasing differences in principal component II scores. Age group 4 shows a combination of both patterns. Sexual rather than ecological selection best explains the underlying selective regime of the ontogenetic patterns of cranial sexual dimorphism in orang-utans. Our morphometric analyses clearly corroborate the conclusions of behavioral ecologists in support of the sexual selection theory.
AB - Ontogenetic patterns of cranial sexual dimorphism in a large sample of the Bornean orang-utan (Pongo pygmaeus pygmaeus) are investigated by means of univariate, bivariate and multivariate statistical analyses. Univariate analyses of 21 linear dimensions reveal that starting at the mid-juvenile stage there is a strong tendency for an increase in number and strength of significant sex differences, all in favor of males. Significant sex differences in the viscero-cranium, reflecting stronger prognathism in males, emerge before those in the neurocranium. Two major growth allometry patterns emerge from bivariate analyses. Ontogenetic scaling is present in 10 dimensions. It is particularly strong in the neurocranium directly associated with brain size, the orbital region and the dental arcade. The heterochronic process of time hypermorphosis is most likely responsible for this pattern. The second growth pattern reflects a departure from ontogenetic scaling with males exhibiting significantly steeper slopes than females. This occurs in 10 cranial dimensions associated with secondary sexual character development: prognathism, canine size and cheek pad area. We suggest that the heterochronic process of acceleration underlies this growth pattern. Principal components analyses reveal two major multidimensional patterns of cranial sexual dimorphism. First, sexual differences at age groups 2 and 3 are primarily the result of differences in principal component II scores, reflecting mainly shape-related differences. Second, age groups 5, 6 and 7 show a trend of stronger size-related shape differences with increasing age in the allometry vector along with decreasing differences in principal component II scores. Age group 4 shows a combination of both patterns. Sexual rather than ecological selection best explains the underlying selective regime of the ontogenetic patterns of cranial sexual dimorphism in orang-utans. Our morphometric analyses clearly corroborate the conclusions of behavioral ecologists in support of the sexual selection theory.
KW - Pongo pygmaeus pygmaeus
KW - allometry
KW - heterochrony
KW - sexual dimorphism
KW - sexual selection
UR - http://www.scopus.com/inward/record.url?scp=0002314019&partnerID=8YFLogxK
U2 - 10.1016/0047-2484(92)90041-7
DO - 10.1016/0047-2484(92)90041-7
M3 - Article
AN - SCOPUS:0002314019
SN - 0047-2484
VL - 23
SP - 3
EP - 26
JO - Journal of Human Evolution
JF - Journal of Human Evolution
IS - 1
ER -