"Our results demonstrate that skull shape correlates with feeding behaviour...with the only exception of the bushy-tailed olingo (B. gabbi) [herbivorous carnivorans] share a set of common traits in their craniodental anatomy...These features relate to the capacity to exert high bite forces...carnivorans that feed on fibrous plants have higher bite forces than those species of similar size that are specialized insectivores, omnivores, or even carnivores that take small prey. In fact, only those carnivores that prey upon ungulate prey much larger than themselves and those specialized in the consumption of vertebrate carrion (e.g. the wolverine, Gulo gulo) parallel the bite force of herbivorous carnivorans (Christiansen and Wroe, 2007)...We have identified a set of common functional traits in the carnivoran skull that allow specializing on an herbivorous diet. As a result, we identify these morphological traits as common adaptations towards herbivory in the carnivoran skull."
"extant [carnivoran] herbivores...compared to their ancestral [carnivorous] states...develop in their mandibles a larger coronoid, a deeper mandibular corpus, a longer distance between the articular condyle and the angular process, and a larger lower molar tooth row. In addition, their crania tend to be more brachycephalic and deeper, have a more developed upper molar tooth row and show the orbits more anteriorly placed. ... These features relate to the capacity to exert high bite forces and include a stoutly built mandible with a deep mandibular corpus, an enlarged coronoid and well-developed lower post-carnassial molars, as well as a deep brachycephalic cranium with well developed zygomatic arches, a short neurocranium and enlarged upper molars."
Figueirido, B., F. J. Serrano-Alarcón, G. J. Slater, and P. Palmqvist. 2010. Shape at the cross-roads: homoplasy and history in the evolution of the carnivoran skull towards herbivory. J. Evol. Biol. 23:2579–2594.