Doctoral Dissertation Improvement: Extant Island Dwarf Mammals as Models for Insular Dwarfing in Pleistocene Hominids

Derived, species-level reduction in body size (dwarfing) of isolated populations has occurred in many mammals and may have even affected some of our hominid relatives. Common postcranial correlates of island dwarfing have been documented, yet there are few detailed studies of how the form of the skull and its many integrated components are affected. This project will examine museum specimens of several island species that have reduced body size compared to their ancestors in order to characterize differences in size and shape of the skull. Craniofacial morphology of several endemic primate species will be quantified using multiple size and shape metrics, including methods from 3D geometric morphometrics, and compared to closely-related mainland primates. Regression analyses will account for phylogeny when appropriate. In addition, an example of island dwarfing in carnivores will provide a non-primate comparative case. The aims of these interspecies comparisons are threefold. First, the study will define the changes in craniofacial form associated with island dwarfing in a sample of extant primate species. Second, it will identify any commonalities among the island dwarf populations relative to their mainland counterparts by testing for differences in shape, size, and degree of encephalization. The null hypothesis in each case will be the allometrically-predicted condition (for a given body size) based on previous studies of the taxonomic group in question. Finally, the project will use the findings of aims 1 and 2 to shed light on the interpretation of the Flores hominid remains exhibiting apparently unexpected craniofacial proportions. The quantitative characterization of skull shape in known cases of island dwarfing will lend needed insight into the mechanisms of this process and its possible effects on an extinct member of the hominid lineage.

Although evolutionary oddities such as dwarf mammoths and giant rodents have always interested researchers, they have recently risen to prominence since the remains of a small-bodied, small-brained human were recovered on the island of Flores in Indonesia. The suggestion that an isolated population of the ancient humans may have been subject to island dwarfing has renewed scientific interest in this curious evolutionary process. This project addresses one of the many unanswered questions related to dwarfing: How does skull shape respond to a significant reduction in body size, particularly in an animal for which brain size is presumably so important? This research will contribute to our understanding of basic mechanisms of evolution, with implications for human history and for the conservation ecology of endangered island species today.