Ingestion of Fossil Seashells, Stones and Small Mammal Bones by Gravid Gopher Tortoises (Gopherus polyphemus) in South Florida

Abstract

Instances of vertebrates supplementing their diets through the ingestion of gastroliths have been observed or documented in numerous organisms, including birds, crocodiles and dinosaurs. Although not uncommon, this behavior can be motivated by a wide range of factors that include endoparasite removal, stomach cleaning, or calcium supplementation during eggshell formation. As plant-based diets are often mineral deficient, the use of gastroliths as calcium supplements may play an important role in the reproductive biology of egg-laying herbivorous reptiles. Whereas gravid females of some species of herbivorous reptiles have been shown to seek out calcareous gastroliths, the occurrence or prevalence of gastroliths in gravid females remains unknown for many species. Using field observations and radiographs, we studied patterns of gastrolith ingestion by adult female gopher tortoises (Gopherus polyphemus), a herbivorous species of testudinoid turtles. Gastroliths documented included fossil seashells, calcareous stones and carnivore feces containing vertebrate bones. The prevalence of gastroliths was significantly different between gravid and non-gravid tortoises. We suggest this behavior is a means of supplementing calcium intake during eggshell formation and may play a part in the female reproductive biology of this species.