Stegosaurus

Overview

Stegosaurus stenops was a large, quadrupedal herbivorous dinosaur that lived during the Late Jurassic, primarily in what is now North America. Weighing around 5 tons and reaching ~30 ft in length, Stegosaurus is easily recognized by the double rows of distinctive, alternating plates along its back and spiked tail (often called a thagomizer).

Despite its size, Stegosaurus had a relatively small head and likely browsed on low-growing vegetation such as ferns and cycads. Recent studies suggest that the plates might have served multiple purposes, including display, thermoregulation, or species recognition.

Quick Facts

Diet

Ferns, cycads, mosses (Herbivore)

Speed

~5–7 mph (est.)

Weight

~5 tons

Length

~30 ft (~9 m)

Bite Force

~300 psi (estimated)

Discovery & Significance

Stegosaurus was first described by paleontologist Othniel Charles Marsh in 1877. Fossils have been recovered largely from the Morrison Formation, a Late Jurassic sedimentary deposit rich in dinosaur remains. Marsh initially believed the plates lay flat on the back like roofing tiles (hence the name “Stegosaurus,” meaning “roofed lizard”), but further finds revealed the alternating, upright arrangement.

The spiked tail of Stegosaurus, consisting of two pairs of large spikes, is a potent defensive weapon often called a thagomizer. Paleopathological evidence suggests these spikes inflicted lethal wounds on potential predators, underscoring Stegosaurus’s ability to defend itself effectively against apex predators like Allosaurus.

Stegosaurus vs. Other Thyreophorans

More Details

At first glance, Stegosaurus might appear as a walking fortress from the Late Jurassic, covered in large, upright plates and armed with formidable tail spikes. Yet those plates, which could exceed half a meter in height, functioned as more than just defense. Scientists have debated whether the plates were used to regulate body temperature, to signal to others of the same species, or to deter predators by making the dinosaur appear larger. The tail spikes, often called a “thagomizer,” almost certainly had a defensive role, as fossils show injuries and scars consistent with a powerful tail strike. Stegosaurus remains are typically found in the Morrison Formation of western North America, where it lived approximately 155 to 145 million years ago. Fossil evidence places it in the same environment as giant sauropods such as Apatosaurus and Diplodocus, and carnivores like Allosaurus, which may have preyed upon unwary or juvenile stegosaurs. Though it grew to about seven and a half meters long and weighed up to five metric tons, its head was strikingly small, suggesting that its brain did not occupy much of its large body mass. Its mouth likely featured a beak for cropping low vegetation, implying a diet that relied heavily on ferns, cycads, and other ground-level plants. The genus is divided into multiple recognized species, including Stegosaurus stenops, S. ungulatus, and S. sulcatus, each with slight variations in armor arrangement and skeletal proportions. Early scientists incorrectly thought that the plates lay flat across the back like shingles on a roof (hence the name “roofed lizard”), but more complete skeletons later showed they were arranged in two alternating rows. Visitors to museums can still see composite skeletons reflecting these ideas as curators have updated older mounts to fit the new science. Even now, new finds and research continue to refine our understanding of Stegosaurus, an iconic dinosaur whose distinctive silhouette—broad back plates and spiked tail—captures the imaginations of paleontologists and the public alike.

References & Further Reading