I propose a species-level analysis of Middle Cambrian Ptychagnostidae (Trilobita, Agnostida) in order to test hypotheses relating microevolutionary attributes of species to macroevolutionary pattern within this clade. Specifically, I aim to measure phenotypic variability and document the geographic and stratigraphic ranges of all species of Ptychagnostidae based on literature, museum, and field collections. The role of these attributes in determining the number of descendants of a species will be assessed in the context of a phylogeny constructed using the cladogram of Westrop et al. (1996) and the stratigraphic occurrence of taxa. A literature-based database is currently being constructed, yet robust measures of phenotypic variability require large samples of specimens available in museum collections and supplemented by additional field collections. The proposed project will build upon extensive prior research on Middle Cambrian Ptychagnostidae and will specifically address the hypotheses that: 1) levels of phenotypic variability and the geographic and stratigraphic range of a species are correlated with the number of descendants produced by a species, and 2) the distribution of species of Ptychagnostidae within a morphospace should be constant in order to avoid competition while minimizing evolutionary differentiation. The evaluation of these hypotheses has great significance for understanding both the evolutionary dynamics of the Ptychagnostidae and the tempo and mode of evolution during the Cambrian radiation of marine invertebrates and during other intervals of Earth history.
