Numerous paleontologists have suggested that the total abundance (or biomass) of animals has increased substantially over the course of the past 550 million years, perhaps driven by gradual or episodic increases in nutrient supply and food availability. We have been working to quantify short-term and long-term changes in animal abundance and food requirements. Our work on short-term changes has focused on changes in fossil abundance across the end-Permian mass extinction as part of field studies in south China, Turkey, and Japan. This work involves careful quantification of the abundance of skeletal, non-skeletal, and diagenetic phases across lithofacies and depositional environments in areas of known sediment accumulation rate. Our work on long-term changes in animal abundance and energy demand has focused on using gastropod size and abundance data, along with physiological scaling principles and constraints from studies of living gastropod species, to study changes in energy demand of gastropods over the past 250 My.