Skull morphology in herbivorous mammals: macropodids (Metatheria, Diprotodontia, Macropodidae) and caviids (Eutheria, Rodentia, Hystricomorpha) as a comparative study case

Abstract

Quantication of morphological diversity among herbivorous mammals and comparisonsbetween herbivorous marsupials and placentals are scarce. In this report we compared morphological variationof 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 ofcomparison, one pointed to a placental-marsupial dichotomy and another pointed to the intra-variationin each group. We also performed an analysis of modularity based on a likelihood approach in order toevaluate dierent modularity models and analyzing the intra- and inter-module correlation (i.e., morphologicalintegration). Beyond strong morphological dierences that split caviids and macropodids along the rst axesof the morphospaces of the cranium and mandible, they shared similar allometric shape changes, includingthe enlargement of muscular attachment areas and lengthening of the diastema. In both clades, the largestvalue of inter-module correlation (as a measure of modular integration) was found for the oral-nasal andorbit modules. We reported relatively low values of within-module correlation for the oral-nasal and molarmodules in macropodids while the opposite was recorded for caviids. Beyond the great dierences in cranialstructure, one of the factors that inuence the patterns of morphological variation and dierential integrationwas the processing of plant matter which seems to induce strong structural changes in both clades, in whichthe eciency of the masticatory apparatus is resolved in a similar way.Morfología cráneo-mandibular en mamíferos herbívoros: macropódidos (Metatheria, Diprotodontia, Macropodidae) y cávidos (Eutheria, Rodentia, Hystricomorpha) como un caso de estudio242 Mastozoología Neotropical, 26(2):241-254 Mendoza, 2019 http://www.sarem.org.ar – http://www.sbmz.org A. Álvarez and D. A. Flores. estuvieron relacionados con la ampliación de las áreas de fijación muscular y el alargamiento del diastema. Los módulos oral-nasal y orbital mostraron los valores más altos de correlación tanto en macropódidos como en cávidos. Se obtuvieron valores de correlación intramódulo relativamente bajos para los módulos oral-nasal y molar en macropódidos, mientras que se registró lo contrario para los cávidos. Más allá de las grandes diferencias en la estructura craneana, uno de los factores que influye en los patrones de variación morfológica e integración diferencial es el procesamiento de materia vegetal que parece inducir fuertes cambios estructurales que en ambos clados, en los que la efciencia del aparato masticatorio se resuelve de manera similar