Meeting Abstract

P3.41  Jan. 6  Evolution of orbit orientation and binocular vision in primates and other euarchontans. HEESY, C.P.; Midwestern Univ. metacephalon@gmail.com

Orbit orientation is a critical component of visual field construction in primates as well as in other mammals. It has been hypothesized that orbit convergence (the degree to which the orbits face in the same direction) and its relationship with binocular visual field overlap is the cornerstone of an innovative character complex that is linked to the adaptive origin of primates. Tests of this hypothesis have primarily relied on orbit orientation and ecological data from extant primates and other mammals. Investigating the functional and adaptive significance of primate orbit orientation, however, requires the integration of extant and fossil data to reconstruct the sequence of transformations that led to the evolution of the primate circumorbital morphotype. This study combines orbit orientation data on extant and fossil taxa with methods of phylogenetic character reconstruction to analyze the sequence of orbit orientation evolution in primates and other euarchontans (tree shrews and dermopterans). Extant taxa include primates, scandentians (tree shrews), and dermopterans (�flying lemurs�). Fossils examined here include several omomyiform, adapiform, and early anthropoid taxa as well as several plesiadapiformes, one possible outgroup to primates. Results demonstrate that using alternate cladistic tree topologies advocated by various workers leads to different reconstructed sequences of orbit evolution. If plesiadapiformes are the outgroup to primates, then several reversals or reductions in orbit convergence relative to other archontans occurred prior to the origin of primates. However, under any advocated phylogeny, several reversals must have occurred in some taxa, such as the diurnal tree shrews. In general, the magnitude of character change in orbit orientation is greatest if plesiadapiformes are accepted as the outgroup to primates.