Matthew J. Ravosa” Received 2 I February 1989 Revision received 9 September 1989 and accepted 10 February 1990 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Keq’word.r: Symphyseal Fusion, Masticatory Biomechanics, Allometr), Prosimians. Subfossil Lcmurs. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Structural allometry of the prosimian mandibular corpus and symphysis Experimental and comparative studies among primates suggest that symphyseal fusion and relatively large mandibular symphysis and corpus dimensions are often part of the same functional pattern (Hylander, 1977, 1979a.b, 1984, 1985, 1988; Beecher, 1977, 1979, 1983). To test this hypothesis further, the biomechanical scaling of corpus and symphysis dimensions was examined in prosimians and compared to anthropoids. Symphyseal fusion was similarly investigated in large-bodied Malagasy “subfossil” Icmurs. Dietary influences on prosimian corpus and symphysis proportions werr also considered, brcause leaf-eating positively all’ects the degree of symphyseal fusion (Bcecher, 1977, 1979, 1983; but see also Greaves, 1988) and mandibular robusticity (Hylander, 19790; Bouviel-. 1986a.h). Prosimian regression lines for mandibular corpus and symphysis measures are significantly transposed below those for anthropoids. Palaeopropithecus moximus, P. ingens. Hadropithecss slenognulhus, Archneolemur eduardri and A. majori display relatively robust symphysis and corpus dimensions, which appear to be related to large body size and folivor!-. .Ilegaludapis madagascariensi.c. .CI. grandidieri and M. edwudsi have more moderately positive residuals; thus symphyseal fusion appears more singularly the reSult of large siLe. Leaf-eating prosimians, such as indriids, do display relatively large corpora and symphyses. These data strongl) support previous predictions about structural and functional diffcrrnccs brtween the masticatory system of extant primate suborders (e.g., Hylander, 1979a; Brecher, 1977, 1979). Journal oJHuman Bz~oiution (1991) 20, 3-20 Introduction zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON Much attention has been devoted to historical and adaptive interpretations ofthe form and function of the primate masticatory apparatus. Experimectal data are particularly useful in documenting zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA in viuo patterns of stress and strain in the mandible during incision and unilateral mastication. When specific phylogenetic data are considered, it is possible to generate hypotheses about patterns of morphological and functional covariation among sister taxa. For example, work by Hylander (1979 a and Bouvier (1986a) demonstrates ) that certain differences in cross-sectional jaw morphology among Old World monkey subfamilies can be related to colobine folivory and the loading regimes associated with leaf- eating proclivities (also Hylander, 1977, 19798, 1984, 1985, 1988; Beecher, 1977, 1979, 1983; Bouvier, 19866). Compared to studies of anthropoid primates, however, similar analyses among prosimians are generally less common (but see Jablonski, 1986). This can be attributed in large part to a lack of adequate morphometric data to which one can compare available experimental data (e.g. Galago cmssicaudutus-Hylander, 1977, 19796). The purpose of this study is threefold; to investigate whether or not: (1) the presence/ absence of symphyseal fusion predictably influences subordinal differences in mandibular corpus and symphpseal scaling between anthropoids and extant prosimians; (2) the presence ofsymphyseal fusion * Current address: Drpt of Biological Anthropology iyr Anatomy. Duhc L!ni\crsity Medical Center. Box 3170, Durham, North (krolina 27710. U.S.A. 0047-2484/91/010003 + 18 $03.00/O 0 1991 Academic Press Limited