Meeting Abstract

P1.119  Saturday, Jan. 4 15:30  A comparative analysis of sciurid feeding systems with a focus on the functional morphology and biomechanics of the enigmatic Bornean tufted ground squirrel Rheithrosciurus macrotis KRENTZEL, D; Univeristy of Chicago dkrentzel@uchicago.edu

The sources of selection that produce dramatic phenotypes and novel specializations can be difficult to determine. Distinguishing the forces of competitive exclusion, evolutionary arms races between predator and prey, and other mechanisms requires an integrative approach. Rheithrosciurus macrotis, a large sciurine ground squirrel endemic to Borneo, is an enigmatic species with a highly derived zygomasseteric system among the relatively conservative squirrel family, Sciuridae. A recent landmark-based morphometric analysis of mandibles across sciurids found R. macrotis to be a major outlier in the phylomorphospace. R. macrotis was the furthest diverged in terms of allometry, and also had the highest estimated mechanical advantages for most of the muscles in feeding system. It has been reported that R. macrotis feeds on the seeds of Mezzettia parviflora, characterized by extreme hardness and toughness, supposedly at the intersection between the most durable material properties and ability to germinate for this seed. The authors reported that it would be incredibly strenuous for R. macrotis to feed on M. parviflora seeds. However, their maximum bite force estimation was based solely on expected bite force given the squirrel’s body size. Here, we reassess the functional morphological parameters of R. macrotis crania and include this cranial data in a comparative analysis of sciurids, with a particular focus on the attachment sites for the masseteric musculature.