Roy Caldwell and Hugh Dingle conducted research on mantis shrimp and other stomatopods, which focused on the evolution of agonistic behaviour and how it applies to the ecology of these organisms. Agonistic behaviour has co-evolved alongside biotic factors such as body morphology, competition both within the species and against other species, and the habitats that these shrimp inhabit. Stomatopods arose from leptostracan stock, as is indicated by fossil evidence, approximately 400 million years ago. Morphology of stomatopods is consistent with most malacostracans in that they have three main body segments: the cephalon, the thorax and the abdomen. The abdomen is made up of six segments, five of which possess a pair of pleopods, which are used for respiration and swimming.