The dinosaur most famous for having prominent spikes on its tail belongs to the Stegosauria, a group of armored, herbivorous dinosaurs. This distinctive feature, a series of elongated spikes at the end of the tail, was a formidable biological weapon protecting these animals from large predators. The genus Stegosaurus is the most famous member of this lineage, and its tail weapon is one of the most recognizable features in paleontology.
Identifying the Dinosaur with the Spiked Tail
The Stegosaurus, a large, four-legged herbivore, is the most famous dinosaur with tail spikes. It lived during the Late Jurassic period, approximately 155 to 145 million years ago. This dinosaur is classified within the family Stegosauridae and is instantly recognizable by the double row of kite-shaped plates along its back.
The typical Stegosaurus species, such as S. stenops, possessed four long, bony spikes near the tail’s end, serving as a powerful deterrent against predators like Allosaurus. This spiky tail was a characteristic shared by many relatives within the Stegosauria clade. Other spiked-tail dinosaurs include Kentrosaurus from Tanzania and Dacentrurus from Europe.
It is important to distinguish this feature from the massive, bony tail club of the Ankylosaurs, which belonged to a separate group of armored dinosaurs. The Ankylosaur tail club was a blunt, heavy weapon used for crushing impact, whereas the Stegosaur’s tail spikes were slender, sharp projections designed for piercing and stabbing. The tail of the Stegosaurus lacked the ossified tendons found in many other ornithischian dinosaurs, which allowed it to be far more flexible and maneuverable for swinging its spiked weapon.
The Anatomy of the Tail Spikes
The arrangement of spikes on the end of a Stegosaur’s tail is informally named the Thagomizer. This term, coined in a 1982 Far Side comic strip by Gary Larson, has been adopted by paleontologists and is widely used in scientific contexts. The Thagomizer is composed of highly modified dermal armor, known as osteoderms, which are bony plates embedded in the skin, similar to those found in crocodiles.
In the most well-studied species, Stegosaurus stenops, the Thagomizer typically consisted of two pairs of spikes, totaling four projections. Each spike measured between 60 to 90 centimeters (2 to 3 feet) long. These spikes were covered in a layer of keratin, the tough protein that forms human fingernails and horns in modern animals, making the sharp tips durable and capable of inflicting serious damage.
The spikes projected backward and outward from the tail, not vertically, as they are sometimes mistakenly depicted. This horizontal or slightly angled placement maximized the weapon’s reach and effectiveness when the dinosaur swung its tail from side to side. The positioning and composition of these keratin-tipped osteoderms confirm the structure was built for robust physical interaction.
Evidence of Defensive Use
Scientific analysis confirms the Thagomizer was actively used as a defensive weapon against predators. The Stegosaurus tail was highly muscular and flexible, allowing the animal to swing its weapon with significant force. Researchers estimate that powerful tail muscles could accelerate the spikes to strike with enough pressure to puncture tough dinosaur hide and pierce bone.
The most concrete proof of combat comes from the fossil record, specifically from a damaged vertebra of the large predatory dinosaur Allosaurus. This tail bone shows a partially healed puncture wound that perfectly matches the size and spacing of a Stegosaurus tail spike, demonstrating a successful defensive strike that the predator survived. Further supporting this function is the discovery of trauma-related damage to the Thagomizer spikes themselves on Stegosaurus fossils.
Broken and healed spikes found on some Stegosaur specimens indicate the weapons were frequently used. While some paleontologists suggest the spikes may have also been used for display, mechanical analysis and direct evidence of puncture wounds on predators establish the Thagomizer’s primary purpose. It was a high-impact solution to a predator problem.