SKULL MORPHOLOGY IN HERBIVOROUS MAMMALS: MACROPODIDS (METATHERIA, DIPROTODONTIA, MACROPODIDAE) AND CAVIIDS (EUTHERIA, RODENTIA, HYSTRICOMORPHA) AS A COMPARATIVE STUDY CASE.

Quantification of morphological diversity among herbivorous mammals and comparisons between herbivorous marsupials and placentals are scarce. In this report we compared morphological variation of the skull and mandible in three representatives of caviid rodents and three species of macropodid marsupials, whose size is comparable, using three-dimensional geometric morphometrics. We applied two levels of comparison, one pointed to a placental-marsupial dichotomy and another pointed to the intra-variation in each group. We also performed an analysis of modularity based on a likelihood approach in order to evaluate different modularity models and analyzing the intra- and inter-module correlation (i.e., morphological integration). Beyond strong morphological differences that split caviids and macropodids along the first axes of the morphospaces of the cranium and mandible, they shared similar allometric shape changes, including the enlargement of muscular attachment areas and lengthening of the diastema. In both clades, the largest value of inter-module correlation (as a measure of modular integration) was found for the oral-nasal and orbit modules. We reported relatively low values of within-module correlation for the oral-nasal and molar modules in macropodids while the opposite was recorded for caviids. Beyond the great differences in cranial structure, one of the factors that influence the patterns of morphological variation and differential integration was the processing of plant matter which seems to induce strong structural changes in both clades, in which the efficiency of the masticatory apparatus is resolved in a similar way. [ABSTRACT FROM AUTHOR]