Integrating Fossil and Extant Data on the Evolution of Primate and Non‐Primate Mammal Orbit Orientation

Abstract

Orbit orientation is important for visual field construction in mammals. It is hypothesized that orbit convergence and binocular visual field overlap are part of an innovative character complex that is linked to the adaptive origin of primates. Tests of this hypothesis have relied on orbit orientation and ecological data from extant mammals. However, a thorough investigation of primate orbit orientation 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. Extant taxa include primates, scandentians, and dermopterans. Fossils examined here include several omomyiform, adapiform, and early anthropoid taxa as well as several plesiadapiformes, a possible outgroup to primates. Results demonstrate that alternate cladistic tree topologies lead 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, some reversals must have occurred. Support: Leakey Foundation