Pubic symphyseal synostosis and sexual dimorphism of the pelvis in Presbytis cristata and Presbytis rubicunda

Document Type

Article

Publication Date

8-1-1993

Abstract

This study examines the relationship between public symphyseal synostosis and sexual dimorphism of the pelvis in two sympatric species of Presbytis-P. cristata and P. rubicunda. Whereas no specimen of P. cristata shows fusion of the interpubic joint, a high percentage of female (43.8%) and male (83.3%)P. rubicunda have a fused public symphysis. As females of both species are similar in body size, they are predicted to give birth to similarly sized newborns. Based on comparison with other anthropoids, the percentage dimorphism in the ischiopubic index in P. cristata and P. rubicuda suggests selection on pelvic capacity in relation to obstetrics. In species characterized by cephalopelvic constriction (i.e., the size of the fetal cranium closely approximates the capacity of the maternal birth canal), successful birth seems possible only by a hormonally induced increase in pelvic joint mobility during delivery. However, fusion of the interpubic joint obviates pelvic joint mobility. Consequently, this study tests the hypothesis that P. rubicunda shows obstetric adaptations of the pelvis that are not found in P. cristata. The results show that pelvic capacity is larger in females than males in both P. cristata and P. rubicunda; the sexual difference is most pronounced at the inlet. Moreover, the pattern of pelvic dimorphism is nearly identical between the species. When females of the two species are compared, P. rubicunda evidences a shorter distance between the sacroiliac and hip joints and a wider bituberous diameter. The former is related to interspecific differences in locomotion, and the latter is associated with obstetrics. © 1993 Plenum Publishing Corporation.

Publication Source (Journal or Book title)

International Journal of Primatology

Number

674

First Page

637

Last Page

654

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