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The thagomizer, or tail spikes, is an arrangement of four to ten spikes on the tails of particular dinosaurs of the clade Stegosauria, of which Stegosaurus stenops is the most familiar. The tail arrangement is believed to have been a defensive weapon against predators.^[1]

The term "thagomizer" was coined by Gary Larson in a 1982 Far Side comic strip, in which a group of cavemen in a faux-modern lecture hall are taught by their caveman professor that the spikes were named for "the late Thag Simmons". The term was picked up initially by Ken Carpenter, a palaeontologist at the Denver Museum of Nature and Science, who used the term when describing a fossil at the Society of Vertebrate Paleontology in 1993.^[2]

Thagomizer has since been adopted as an informal anatomical term, appearing, for example, on the website of the Smithsonian Institution.^[3] The term has been used in displays at Dinosaur National Monument in Utah, in the book The Complete Dinosaur, and in the stegosaur display at the Smithsonian Institution.^[2] As of 2007, however, the term does not appear to have been published in a peer-reviewed scientific journal.^[4]

The fate of Thag Simmons notwithstanding, stegosaurs and humans did not coexist in the same era. In The Prehistory of the Far Side, Gary Larson suggests 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".^[5]

Contents 1 Paleobiology 2 See also 2.1 Other scientific terms first used in comedy 3 References

There has been debate about whether the tail spikes were used for display only, as posited by Gilmore in 1914 ^[6] or used as a weapon. Robert Bakker noted the tail was likely to have been much more flexible than those of other dinosaurs as it lacked ossified tendons, thus lending credence to the idea of the tail as a weapon. He also observed that Stegosaurus could have manoeuvred its rear easily by keeping its large hindlimbs stationary and pushing off with its very powerfully muscled but short forelimbs, allowing it to swivel deftly to deal with attack.^[7]

More recently, a study of tail spikes, by McWhinney et al.,^[8] showed a high incidence of trauma-related damage. This supports the theory that the spikes were used in combat.

Stegosaurus stenops had four dermal spikes, each about 60-90 cm (2 to 3 feet) long. Discoveries of articulated stegosaur armor show that, at least in some species, these spikes protruded horizontally from the tail, not vertically as is often depicted. Initially, Marsh described S. armatus as having eight spikes in its tail, unlike S. stenops. However, recent research re-examined this and concluded this species also had four.^{[9] [10]}

• Stegosaurus, tail spikes
• Strigiphilus garylarsoni

• Horrendous Space Kablooie
• Flange of baboons