A thagomizer is a term coined in 1982 by cartoonist Gary Larson in his comic The Far Side to refer to the tail spikes of stegosaurian dinosaurs. These spikes are believed to have been a defensive measure against predators. The arrangement of spikes originally had no distinct name; the term thagomizer was, and thereafter became, gradually adopted as an informal term occasionally used within scientific circles, research, and education.
The term was picked up initially by Ken Carpenter, a paleontologist at the Denver Museum of Nature and Science, who used the term when describing a fossil at the Society of Vertebrate Paleontology Annual Meeting in 1993. Thagomizer has since been adopted as an informal anatomical term, and is used by the Smithsonian Institution, the Dinosaur National Monument, the book The Complete Dinosaur and the BBC documentary series Planet Dinosaur.
As stegosaurs and humans did not exist in the same era, Gary Larson suggests in The Prehistory of the Far Side that “there should be cartoon confessionals where we could go and say things like, ‘Father, I have sinned – I have drawn dinosaurs and hominids together in the same cartoon.’”