'' Some stegosaurs such as
Kentrosaurus do not have a distinct "thagomizer" consisting of two pairs of spikes, as in these species there is not clear differentiation between the last two pairs on the tail and the other tail
osteoderms, which are also spike-like, unlike the broad plate-like osteoderms on the back of
Stegosaurus. There has been debate about whether the thagomizer was used simply for display, as posited by
Gilmore in 1914, or used as a defensive weapon.
Robert Bakker noted that it is likely that the stegosaur tail was much more flexible than those of other
ornithischian dinosaurs because it lacked ossified tendons, thus lending credence to the idea of the thagomizer being a weapon. He also observed that
Stegosaurus could have maneuvered 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. In 2010, analysis of a digitized model of
Kentrosaurus aethiopicus showed that the tail could bring the thagomizer around to the sides of the dinosaur, possibly striking an attacker beside it. with a hole matching a thagomizer spine In 2001, a study of thagomizers by McWhinney et al. showed a high incidence of trauma-related damage. This too supports the theory that the principal function of the thagomizer was defense in combat. There is also evidence for a defense function in the form of an
Allosaurus tail vertebra with a partially healed puncture wound that fits a
Stegosaurus tail spike. This usage of the thagomizer would be similar to defensive behaviors in some extant lizards with tail spikes, such as the
giant girdled lizard. The species of stegosaur known as
Stegosaurus stenops had four dermal spikes, each about 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,
Othniel Charles 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. == Other uses ==