Meeting Abstract
The endemic rodents of Madagascar (Nesomyidae: Nesomyinae) compose a small radiation of remarkable morphological and ecological diversity, but the tempo and mode of their evolution is not well understood. We inferred a species-level phylogeny for the 28 recognized species of nesomyines and examined dental evolution within this phylogenetic context. We examined whether nesomyine rodents adhere to a developmental model of molar-size evolution derived from murine rodents (Kavanagh et al. 2007). This model plots the ratio of m2/m1 planar occlusal area by m3/m1 area, creating a simple system to evaluate dental morphospace. All extant muroid rodents examined to date follow the classic activation/inhibition pattern of molar development in which the anteriormost molar inhibits growth of successive molars resulting in m1 as the largest tooth and m3 as the smallest. Many other mammals follow the same pattern, but few have large m2s or m3s. Nesomyines diverge significantly from this pattern. Uniquely, we found that nesomyines encompass nearly as much variation in molar-size ratios as observed across all mammals. To examine tooth morphology in greater detail, we uCT-scanned nesomyine mandibles at 5-12 um resolution and calculated shape metrics of lower tooth rows that describe aspects of functional morphology. These metrics comprise a suite of 14 variables including orientation patch count (OPC), volumetric enamel:dentin ratios, occlusal surface descriptors, and vertical complexity measures. Based on a similar study of North American rodents, these tooth metrics predict trophic categories with high accuracy. We use this model to predict trophic categories for nesomyines. Using multivariate comparative methods, we estimate rates of evolution for these dental characters among lineages and over time to better characterize the nature of this radiation.
