When picturing prehistoric giants, many imagine a massive, plant-eating dinosaur adorned with striking back ornamentation. These creatures, often depicted with an imposing silhouette of plates and spikes, roamed ancient landscapes. Their distinctive features suggest a formidable presence in past ecosystems.
Identifying the Spiked Dinosaur
The dinosaur most famously recognized for its prominent back spikes and plates is the Stegosaurus. This large herbivore lived during the Late Jurassic period, between 155 and 145 million years ago, with fossils primarily discovered in the western United States and Portugal.
Stegosaurus was a substantial animal, reaching lengths of 21 to 30 feet (6.5 to 9 meters) and standing up to 13 feet (4 meters) tall, with an estimated weight of 5 to 7 metric tons. It walked on all four legs, with hind limbs significantly longer than its forelimbs, giving it a distinctive posture. As a herbivore, Stegosaurus primarily consumed low-lying vegetation such as ferns, conifers, and cycads, using its small, narrow head and beak-like mouth to snip plant material.
The Purpose of Stegosaurus’s Spikes and Plates
The two most striking features of Stegosaurus are the large, bony plates along its back and the sharp spikes on its tail. The plates, up to 17, kite-shaped or triangular, were arranged in two alternating rows along its neck, back, and tail. These plates were embedded in the skin, allowing flexibility. Scientists have proposed several theories for their function, including defense, display, and thermoregulation.
While early theories suggested the plates were for defense, their relatively thin structure and placement, leaving the flanks and belly exposed, make this less likely as a primary function. Current theories suggest they were used for display, to attract mates, signify species membership, or intimidate rivals. The presence of numerous blood vessels within the plates also supports thermoregulation, allowing the dinosaur to absorb or dissipate heat.
The sharp tail spikes, known as a “thagomizer,” are accepted to have been defensive weapons. Stegosaurus had four such spikes at the end of its tail, each 2 to 3 feet (60-90 cm) long. Evidence for their defensive use includes healed puncture wounds found on the tail vertebrae of predators like Allosaurus that match Stegosaurus spikes, and broken, yet healed, tips on many fossilized Stegosaurus tail spikes, indicating their use in combat. The lack of ossified tendons in the tail suggests it was flexible, allowing Stegosaurus to swing it effectively against attackers.
Other Dinosaurs with Defensive Features
Beyond Stegosaurus, many other dinosaurs developed unique defensive features. Armored dinosaurs were particularly well-equipped.
Ankylosaurus, a heavily armored dinosaur from the Late Cretaceous period, is renowned for its tank-like body and formidable tail club. Its entire body, including its head and eyelids, was covered in thick, bony plates called osteoderms, providing robust protection. The massive club at the end of its tail, formed by fused vertebrae, could deliver powerful blows capable of breaking bones, making it an effective weapon against large carnivores like Tyrannosaurus rex.
Another relative of Stegosaurus, Kentrosaurus, also displayed prominent spikes. This smaller stegosaur from the Late Jurassic had a double row of small plates on its neck and back that transitioned into elongated spikes towards its hips and tail. The longest spikes were on its tail, forming a thagomizer similar to Stegosaurus, which it used for defense by swinging its flexible tail. Triceratops, a ceratopsian dinosaur from the Late Cretaceous, possessed three facial horns and a large bony frill. While the exact functions of its horns and frill are debated, they played roles in defense against predators, such as Tyrannosaurus, and in intraspecific combat or display.