Department of Clinical Anatomy and Osteopathic Principles, Rocky Vista University, Parker, Colorado, USA.
Am J Phys Anthropol. 2021 Nov;176(3):402-421. doi: 10.1002/ajpa.24398. Epub 2021 Aug 28.
The presence of sexual dimorphism in the birth canals of anthropoid primates is well documented, and birth canal dimorphism tends to be especially robust among species that give birth to relatively large neonates. However, it is less clear whether birth canal dimorphism is accompanied by dimorphism in parts of the pelvis not directly under selection for birth, particularly including bi-iliac breadth, biactetabular breadth, lengths of the ischium and ilium, and 3D shape. This study investigates the patterns of dimorphism among anthropoid primates in those parts of the pelvis which do not directly contribute to the bony birth canal, here termed the non-obstetric pelvis.
3D landmark data were collected on the bony pelves of 899 anthropoid primates. Specifically, landmark data were collected on parts of the pelvis not thought to be directly involved in selection for parturition, including portions of the posterior and superior ilium, acetabulum, and lateral ischium. Principal components analysis and Euclidean distance matrix analysis were used to ascertain sexual dimorphism in pelvic sizes and shapes within each species.
Results show that dimorphism in non-obstetric pelvic size and shape exists across anthropoids, just as is seen in the birth canal. However, the magnitude of dimorphism in non-obstetric pelvic shape tends to be greater among anthropoid species that give birth to relatively large neonates compared with those birthing smaller neonates relative to maternal pelvic size.
Though all anthropoids included in the study show some degree of sexual dimorphism in non-obstetric pelvic size and/or shape, species which give birth to large neonates relative to maternal pelvic size have the highest levels of dimorphism in pelvic shape. Moreover, the magnitude of dimorphism in certain parts of the non-obstetric pelvis mirrors patterns seen in the birth canal. The results of this study are promising for ascertaining pelvic dimorphism and relative neonate size in fossil primates, particularly in fragmentary remains which do not preserve a complete bony birth canal.
类人猿的生殖道存在性别二态性，这已得到充分证实，而在分娩相对较大的新生儿的物种中，生殖道二态性往往特别明显。然而，骨盆中不受分娩选择直接影响的部分（特别是包括双髂宽、双髋臼宽、坐骨和髂骨长度以及 3D 形状）是否存在二态性，这一点还不太清楚。本研究调查了类人猿中骨盆不受分娩直接影响的部分（称为非产科骨盆）的二态性模式。
收集了 899 种类人猿的骨盆 3D 标志数据。具体来说，收集了骨盆不受分娩选择直接影响的部分的标志数据，包括髂骨后、上部分、髋臼和坐骨外侧部分。主成分分析和欧几里得距离矩阵分析用于确定每个物种中骨盆大小和形状的性别二态性。
结果表明，非产科骨盆大小和形状的二态性存在于类人猿中，就像在生殖道中一样。然而，与分娩相对较小新生儿的物种相比，分娩相对较大新生儿的物种的非产科骨盆形状的二态性幅度往往更大，相对于母体骨盆大小而言。
尽管研究中包括的所有类人猿在非产科骨盆大小和/或形状上都表现出一定程度的性别二态性，但相对于母体骨盆大小分娩较大新生儿的物种在骨盆形状上具有最高水平的二态性。此外，非产科骨盆某些部分的二态性幅度反映了在生殖道中看到的模式。本研究结果有望确定化石灵长类动物的骨盆二态性和相对新生儿大小，特别是在不保留完整骨性生殖道的零碎遗骸中。
