Myology of the masticatory apparatus of herbivorous mammals and a novel classification for a better understanding of herbivore diversity.

This article focuses on the classification and evolutionary interpretation of masticatory muscle configurations in herbivorous mammals, based on a comprehensive quantitative analysis of muscle mass proportions and topography across 104 extant species (including rodents, ungulates, diprotodonts, and others) and four extinct taxa. The study identifies 15 distinct myological morphotypes through principal components and cluster analyses, revealing two main evolutionary pathways of herbivorous masticatory specialization that do not align with the traditional dichotomy of 'ungulate-grinding' versus 'rodent-gnawing' types. Rodents exhibit exceptional myological diversity, necessitating subdivision beyond previous classifications, while some extinct herbivores and extant taxa like wombats show convergences bridging rodent-like and ungulate-like morphotypes. The authors propose this refined morphotype scheme as a useful framework for selecting extant models in paleobiological reconstructions and for understanding the functional evolution of mammalian herbivory.