POSITIONAL BEHAVIOR AND VERTEBRAL MORPHOLOGY IN ATELINES AND CEBINES

Atelines are of particular interest to primate evolutionary studies be cause they converge with hominoids in postcranial anatomy, including t he vertebral column. Currently, our understanding of ateline vertebral morphology is limited to mainly qualitative descriptions and function al interpretations based on general categories of positional behavior Even less is known about the vertebrae of other platyrrhines. This stu dy more closely examines vertebral form and function in atelines and c ebines by combining direct field observations of axial postures and mo vements, assessments of spinal loading regimes, and a detailed vertebr al morphometric analysis. Field observations (Corcovado, Costa Rica) o n Ateles geoffroyi, Alouatta palliata, Cebus capucinus, and Saimiri oe rstedii were quantified in conjunction with a morphometric analysis of ateline and cebine lumbar vertebrae. Hylobates was also included for comparison. Compared to Cebus and Saimiri, atelines engage more freque ntly in postures and locomotor behaviors that induce pronounced bendin g loads on the spine. All atelines share lumbar adaptations for resist ing bending, including ventrodorsally elongated vertebral bodies and p erpendicularly oriented transverse processes. Among atelines, lumbar r egion lengths and vertebral bodies are shortest in Ateles and Brachyte les, longest in Alouatta (resembling Cebus), and intermediate in Lagot hrix. Compared to Cebus and all atelines, Saimiri has a relatively lon ger lumbar region, longer and less ventrodorsally expanded vertebral b odies, and more ventrally oriented transverse processes. These feature s accentuate bending loads, but increase the sagittal flexibility requ ired for leaping. Vertebral convergence between hylobatids and ateline s is more readily interpretable as a product of shared spinal loading patterns than shared positional behaviors. (C) 1998 Wiley-Liss, Inc.