Integration patterns of cheek teeth and ecomorphological evolution in grinding herbivores: The case of caviine rodents (Caviomorpha: Caviidae)

Abstract

Caviid rodents have peculiar craniomandibular specializations toward masticatory propalinal movements and grinding, in relation to a grass-rich diet. The aim of this study is to: (1) analyse the variation of cheek tooth shape in the Caviinae and, (2) quantify the covariation relations between caviine cheek teeth. For this purpose, we perform the first geometric morphometric analysis on cheek teeth of fossil and extant caviids, ancestral shape reconstructions and covariation analyses. Our results show that caviine dentition is strongly integrated with a higher covariation between teeth of the same row than between opposite teeth, differing from mammals with complex interlocking. Each series acts as a single functional unit integrated during grinding action obtained by mainly propalinal movements. However, p4 shows more plasticity, allowing its morphology to differentiate from the common pattern of molars. Morphologically homogeneous cheek tooth series are ancestral in crown caviids and highly marked in Cavia, while stronger morphological differences between tooth pieces are observed in Microcavia and Galea. These differences are probably driven by diet changes. The tendency towards alignment of main masticatory movements with the tooth row axes seems to be a key factor in understanding cheek tooth covariation patterns in this and other rodent clades.