Brain size and shape diversification in a highly diverse South American clade of rodents (Echimyidae): a geometric morphometric and comparative phylogenetic approach

Abstract

Brain morphological variation is analysed through virtual endocasts in a highly diversified clade of caviomorph rodents belonging to the family Echimyidae. Diversification in brain size and shape is explored through geometric morphometrics and comparative phylogenetic analyses. The results indicate that brain shape is largely independent of general size and reveal different trends in brain size and shape. Fossorial Euryzygomatominae, arboreal Echimyini and the semi-aquatic Myocastorini Myocastor show high encephalization; the former with a greater contribution from the olfactory bulb and petrosal lobe, and the latter two with a larger surface area of neocortex. The Euryzygomatomyinae and Myocastorini of terrestrial habits show low encephalization with a low contribution of the neocortex. Phylogenetic comparative analyses suggest that endocranial morphological evolution would have been influenced by both phylogeny and locomotor habits. The concurrence of the best fit of the Ornstein–Uhlenbeck model and the significant phylogenetic signal in the datasets suggests the involvement of constraints on morphological diversification within the major clades, as expected under phylogenetic conservatism. This could be explained by an early establishment of a particular endocranial morphology in each major clade, which would have been maintained with relatively little change.