Matthew Jordan Ravosa
Title: Associate Professor
Research area: Function, development and evolution of the mammalian skull and masticatory complex
Degree: Ph.D., 1989, Biological Anthropology, Northwestern University
Voice: 312.503.0492
Fax: 312.503.7912
e-mail: m-ravosa@northwestern.edu

Detailed research description:                                                                                            

My research program concerns the evolutionary morphology of the mammalian skull and masticatory apparatus, focusing in particular on major adaptive transformations across and within higher-level clades.  To this end, I employ comparative, ontogenetic and experimental analyses so as to increase our empirical and theoretical understanding of the biomechanical, ecological, developmental and allometric influences on important craniomandibular character states and character complexes.

Given the importance of transverse mandibular and occlusal forces in the evolution of anthropoid symphyseal fusion, we recently analyzed the relations among occlusal orientation, jaw kinematics and symphyseal fusion in selenodont artiodactyls.  Related analyses of symphyseal fusion and the scaling of jaw proportions in living and fossil carnivorans, as well as marsupials, indicate an emerging pattern common to a variety of mammalian clades whereby larger-bodied sister taxa show increased fusion and greater mandibular cross-sectional robusticity due to an emphasis on more ductile and/or brittle foods.

            Another project focuses on the ontogenetic and interspecific patterning of orbital orientation in strepsirhine and anthropoid primates.  Such an approach is vital as hypotheses about size and scaling are inherently concerned with ontogenetic patterns of structural covariation and how such intrinsic relations are expressed across taxa, i.e., what limits or directs the occupation of morphospace.  In doing so, it tests an influential model regarding the functional link between increased orbital convergence and orbital frontation and the evolution of the anthropoid postorbital septum, a feature unique among all vertebrates. 

Additional research tests a longstanding hypothesis that a nocturnal visual predation strategy and relatively larger brains in basal euprimates required more anteriorly and vertically positioned orbits, and this is related to the derived presence of the euprimate postorbital bar.  By coupling paleontological and neontological evidence from mammalian analogs with in vivo bone strain from the circumorbital region and evaluating this evidence allometrically, we identified a suite of functional and structural factors unique to small skull sizes that characterize basal euprimates.  Such evidence is critical for emphasizing the role of encephalization on circumorbital form and for revising our knowledge of euprimate origins. 

Ongoing comparative work on lemurs and slow lorises shows that, while variation in skull form between larger and smaller sister taxa is due to the differential extension of shared growth allometries, such ontogenetic scaling may not characterize the mandible due to taxic variation in dietary properties.  Although indriid skull proportions are ontogenetically scaled, jaw-adductor in-lever arms in the smallest genus (Avahi) differ from other taxa.  This is linked to the positive scaling of in-lever arm length during indriid cranial growth, such that in-lever proportions for avahis are uncoupled from this ancestral pattern to facilitate the production of comparable bite forces at small sizes (necessary for a clade-wide emphasis on folivory).  These findings highlight why one should assess the functional basis of allometric patterns in phyletic size variants as well as the adaptive basis for the lack of allometric concordance in a feature. 

Collaborative research on Malagasy sifakas offers a rare example where body-size differentiation and heterochronic changes can be linked to ecogeographic factors.  Propithecus diadema develops larger adult size primarily by growing at a faster rate, but not for a longer duration, than P. tattersalli and P. verreauxi.  On one hand, the less-seasonal rainforest environs of P. diadema impose greater selective pressures for larger size than the dry-forest or semi-arid climates of its two sister taxa.  On the other, as smaller sifakas are located in the east, west and northeast, this implies that adult size is set by dry-season constraints on food quality and distribution.  That ontogenetic scaling occurs via differences in growth rate also appears related to ecogeographic variation in resource seasonality and juvenile mortality risk.

Recently hosted the first international conference on Primate Origins and Adaptations.  Science (295, 613-615) : New Fossils and a Glimpse of Evolution

Representative publications:

Ravosa, M.J. & Savakova, D.G. (2003) Euprimate origins: The eyes have it. Proceedings of the National Academy of Sciences, USA in press.

Ravosa, M.J. & Hogue, A.S. (2003) Function and fusion of the mandibular symphysis in mammals: A comparative and experimental perspective. In C.F. Ross & R.F. Kay (Eds.): Anthropoid Evolution. New Directions. New York: Kluwer Academic/Plenum Publishers, in press. 

Ravosa, M.J., Savakova, D.G., Noble, V.E., Johnson, K.R. & Hylander, W.L. (2003) Primate origins and the function of the circumorbital region: What’s load got to do with it? In M.J. Ravosa & M. Dagosto (Eds.): Primate Origins and Adaptations. New York: Kluwer Academic/Plenum Publishers, in press. 

Ravosa, M.J. & Vinyard, C.J. (2002) On the interface between ontogeny and function. In J.M. Plavcan, R.F. Kay, W.L. Jungers & C.P. van Schaik (Eds.): Reconstructing Behavior in the Primate Fossil Record. New York: Plenum Press, pp. 73-111. 

Hogue, A.S. & Ravosa, M.J. (2001) Transverse masticatory movements, occlusal orientation, and symphyseal fusion in selenodont artiodactyls. Journal of Morphology 249:221-241.