THE EVOLUTION OF HYLOBATID POSITIONAL BEHAVIOR AND POSTCRANIAL OSTEOLOGY

Author

Matthew Gerard Nowak, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2024

Degree Name

Doctor of Philosophy

Department

Anthropology

First Advisor

Ford, Susan

Abstract

A comparative understanding of the patterns and processes of hominoid evolution is critical for determining the evolutionary trajectories of our own species. Several traits, including the development of relatively large-body size, a torso-orthograde (or upright; TO) -Bauplan, and suspensory adaptations are often considered key adaptations within the Hominoidea. Unfortunately, comparisons of the neontological and paleontological records have resulted in divergent theories regarding the origin of these traits, with one extreme advocating their homologous origins and the other for rampant homoplasy. It is argued here that a key factor that has continued to limit our understanding of hominoid and human evolution is the underutilization of hylobatids within comparative studies. The Hylobatidae are an extremely successful radiation of moderate-sized primates from the superfamily Hominoidea. The extant hylobatid family currently comprises four genera and 20 species spanning 11 countries in East, South, and Southeast Asia, with three known extinct genera from China and potentially one from India. Hylobatids are the smallest of the extant apes yet size-variable and are among the most orthograde/suspensory. Nevertheless, their natural variation is often condensed into a single observation point in comparative studies. As such, the goal of this dissertation is to document the variation in positional behavior and postcranial osteology among hylobatids, utilizing an ecological morphological framework, and to integrate this detailed evaluation with previous neontological and paleontological studies. Several interrelated studies are presented within this dissertation, including a new comparative look at hylobatid postcranial osteology and several new studies of hylobatid positional behavior from the wild. These investigations shed light on the adaptive niche of hylobatids and provide insights into the evolutionary processes that shaped this uniquely successful hominoid family. Moreover, the new results presented here allow for a more critical understanding of hominoid evolution and facilitate the synchronization of the neontological and paleontological records. In doing so, this study provides support to the theory that hylobatids and hominids have developed their body size regimes, TO-Bauplan, suspensory morphological adaptions, and accompanying TO-positional behavioral repertoire independently.