 Cladistics is an exact method of arranging species based strictly on their evolutionary relationships, which are calculated by determining the evolutionary tree implying the least number of changes in their anatomical characteristics.In the 1980s, cladistic methodology was applied to dinosaur phylogeny for the first time by Jacques Gauthier and others, showing unequivocally that birds were a derived group of theropod dinosaurs.Early analyses suggested that dromaeosaurid theropods like "Deinonychus" were particularly closely related to birds, a result that has been corroborated many times since.