Meeting Abstract

P3-197  Tuesday, Jan. 6 15:30  Quadrupedal to bipedal skeletal transformations inferred from a morphological and phylogenetic analysis of Dipodidae MOORE, T Y*; FIELD, D J; BIEWENER, A A; COOPER, K L; Harvard University; Yale University; Harvard University; Univ. of California, San Diego

Three desert-dwelling groups of rodents have independently acquired bipedal locomotion. The most diverse clade, Dipodidae, exhibits 8 distinct morphotypes across its extant taxa. This morphological diversity, interpreted within a novel phylogenetic framework, provides an unprecedented opportunity to study the transition from quadrupedal to bipedal locomotion in rodents. To identify traits associated with bipedality, we generated the first behaviorally relevant skeletal reconstructions of a bipedal jerboa (Jaculus jaculus) and a quadrupedal birch mouse (Sicista betulina). We then traced morphological transitions from quadrupedality to bipedality mapping characters from the 8 hindlimb morphotypes onto a molecular phylogeny of Dipodidae and estimating ancestral traits for each character within a Bayeseian framework. To compare jerboa limb proportions to those of other rodent ecomorphs, we performed a phylogenetic Principal Components Analysis using 38 species across Myomorpha. Our morphological data best fit a dual-optimum OU model, suggesting that although dipodid rodents experience different selective pressures from their quadrupedal relatives, they experience similar degrees of selection and drift as other members of Myomorpha. Combining functional morphological and phylogenetic comparative methods establishes testable hypotheses for the biomechanical advantages of bipedal locomotion and developmental mechanisms of skeletal transformation in response to changing selective pressures. Together, these data reveal fundamental insights into the repeated acquisition of bipedality across Myomorpha, one of the most conspicuous macroevolutionary patterns observed within rodents.