Third upper molar enlargement in sigmodontine rodents (Cricetidae): Morphological disparity and evolutionary convergence

Abstract

We studied the enlargement of the upper third molar (M3), with respect to the upper second molar in sigmodontine rodents, the largest subfamily of living cricetids. M3 is enlarged in extant and extinct members of at least six tribes (Andinomyini, Euneomyini, Oryzomyini, Phyllotini, Reithrodontini and Sigmodontini), all of them also sharing hypsodonty, planate crowns and overall dental simplification in the context of Sigmodontinae. Enlargement is expressed in four ways, including simplification or modest complication of occlusal design on a single plane. M3 enlargement in sigmodontines is primarily associated with increasing herbivory rather than strictly with phylogeny, and thus presents a classic example of evolutionary convergence.