stylistic:tone, information:extraction
Thagomizer (tail spikes)

There has been debate about whether the tail spikes were only used for display, as posited by Gilmore in 1914, or used as a weapon. Robert Bakker noted the tail was likely to have been much more flexible than that of other dinosaurs, as it lacked ossified tendons, thus lending credence to the idea of the tail as a weapon. However, as Carpenter has noted, the plates overlap so many tail vertebrae, movement would be limited. Bakker also observed that Stegosaurus could have maneuvered its rear easily, by keeping its large hind limbs stationary and pushing off with its very powerfully muscled but short forelimbs, allowing it to swivel deftly to deal with attack.

More recently, a study of the tail spikes by McWhinney et al., which showed a high incidence of trauma-related damage, lends more weight to the position that the spikes were indeed used in combat. This study showed that 9.8% of Stegosaurus specimens examined had injuries to their tail spikes. Additional support for this idea was a punctured tail vertebra of an Allosaurus into which a tail spike fits perfectly. The damage shows that the spike entered at an angle from below and displaced a piece of the process upward, remodeled bone on the underside of the process shows that an infection developed.

S. stenops had four dermal spikes, each about 60–90 cm (2.0–3.0 ft) long. Discoveries of articulated stegosaur armor show, at least in some species, these spikes protruded horizontally from the tail, not vertically as is often depicted. Initially, Marsh described S. ungulatus as having eight spikes in its tail, unlike S. stenops. However, recent research re-examined this and concluded this species also had four.