The goal of this project is to reconstruct the paleobiology of the extinct New World monkey Protopithecus brasiliensis, a little-studied fossil known from Brazilian cave sites and represented by a nearly complete skeleton. Protopithecus is linked phylogenetically with living howler monkeys (Alouatta); both share aspects of the howler's unusual cranial morphology, which is functionally related to its roaring vocalizations. A major part of this research will investigate the shape of the mandible and cranial base of howler monkeys in an effort to test the hypothesis that Protopithecus also had an enlarged hyoid bone. Measurements captured by laser scanning and 3D digitizing will be analyzed using the statistical approaches of geometric morphometrics. Another component of the project focuses on the postcranial skeleton to answer two separate but related questions: 1) Is there evidence to support a hypothesis that Protopithecus was a terrestrial quadruped? If so, it would be the only truly terrestrial New World primate, extant or extinct. 2) Did Protopithecus position its body in the same unique way that Alouatta does during howling bouts, leaving distinctive skeletal adaptations in the upper body? The intellectual merit of this project addresses a large gap in the evolutionary history of New World primates. Protopithecus is among the most complete non-hominin fossils and it can shed much light on the evolution of the larger, prehensile-tailed monkeys, which are poorly represented in the fossil record. The broader impacts of the project are several. The results will be of interest to the public since opportunities to derive evidence regarding social behaviors, in this case vocalizations, from fossilized skulls is rare and intuitively interesting. International collaborations will be advanced by working with researchers at the Brazilian museum that houses the Protopithecus fossils. This grant will also help to support a female graduate student working in the sciences.