thagomizers

A thagomizer is the informal name for the set of elongated, pointed tail spikes at the end of the tail in stegosaurian dinosaurs, most famously in Stegosaurus. The spikes are attached to the tail vertebrae and arranged in a way that creates a distinctive cluster or “spear” at the tail tip. The exact number, length, and curvature of the spikes varied among stegosaurs, but the feature is a defining hallmark of the group.

Etymology and usage: The term originated as a joke in The Far Side cartoon by Gary Larson, published in 1988, in which a caveperson points to a stegosaur’s tail and proclaims “Now this is a thagomizer.” Since then the name has been widely adopted in popular science and museum contexts, and it is commonly used in paleontological discussions, though it is not always an official anatomical term.

Function and interpretation: Thagomizers are generally interpreted as a defensive adaptation, capable of delivering powerful tail strikes to deter predators. Biomechanical analyses support the idea that the tail could generate significant force, making the spikes an effective deterrent. Some researchers also consider the spikes to have served display or signaling roles within species, though defense remains the primary interpretation.

Distribution and notes: Thagomizers are associated with stegosaurids, particularly Stegosaurus, and are observed in fossil specimens where preservation allows tail-tip morphology. While not every specimen preserves the tail end, the thagomizer is widely recognized as a characteristic feature of this group and a popular example of dinosaur weaponry in science communication.