Research on the evolution of body size in the lab has grown out of observed shifts in maximum and mean size in gastropods and other higher taxa across the end-Permian mass extinction. Our goal is to use time-series of sizes in gastropods and other higher taxa to identify environmental and biological controls on body size evolution. Our current research efforts are focused on the Permian-Triassic and Triassic-Jurassic transitions. We are focused in particular on isolating the contributions of size-biased extinctions and originations and within-lineage size trends to overall shifts in the size distributions of higher taxa through geological time. Isolating these components allows us to better test hypothesized links between environmental change and evolutionary pattern.