April 4, 2022 Scott Kraus

Stegosaurus is a Stegosaurid from the Late Jurassic Era

Stegosaurus, pronounced STEG-o-SAWR-us, was named by Othniel Marsh in 1877. The name means “roof lizard” or “plated lizard” after the distinctive plates sticking out of it’s back. It is an armored stegosaurid dinosaur that lived during the Late Jurassic era about 150 to 155 million years ago. Specimens of Stegosaurus fossils have been found in North America, Europe, and Africa. Marsh originally considered Stegosaurus to be bipedal because of its short forelimbs, but he later changed his mind and decided it must be quadrupedal after taking into account the massive build of the dinosaur.

Quick Facts

What did Stegosaurus look like?

The stegosaurus has one of the most recognizable silhouettes of any dinosaur.  Its twin rows of bony plates running along the spine make the look of this dinosaur unmistakable.  Whether these plates were used for protection, display or temperature regulation is still under debate.  But we do know that the Stegosaurus had exactly 17 of these plates on its back, and each plate could be up to 2 feet tall and 2 feet wide.  If you saw one in real life, you would also probably notice the menacing tail this creature had.  The four spikes on stegosaurus’ tail were held high above the height of an average human.  And at sizes reaching up to 30 feet long, you would be glad that this giant doesn’t bite.

Stegosaurus was a powerfully built herbivore

The quadrupedal, or four-legged, herbivore was well adapted to the environment it lived in.  It held its head low to the ground. Supported by a short and sturdy neck, the head of the stegosaurus was elongated and chiseled.  Riding on two short forelimbs and two much longer and more powerful hindquarters, the stegosaurus must have been quite a sight. The stegosaurus was a massive animal too, with adults estimated to weigh up to 5 metric tons.

Physical Attributes

Most of the inquiry into the life of the stegosaurus revolves around the plates it wore along its spine.  These plates, which always numbered 17, were not attached directly to the skeleton of the animal.  The plates were composed of one large hardened scale that was a part of its skin.  It has been found that the plates were also grooved to allow blood to flow around the scales, possibly for display when threatened or for the relegation of body heat.  It has been theorized that the plates would not be carried upright against the creatures back for normal activity.  The plates lack sufficient width to remain in this posture without continuous muscle exertion from the animal. The largest of the plates were located directly above the animal’s hip.

What were the tail spikes of a stegosaurus used for?

Whether the tail spikes were used for combat or display has also undergone recent scrutiny.  Early indicators pointed to the spikes being too weak to sustain fighting blows.  The arrangement of the spikes were also incorrectly placed by early paleontologists, and the new model of horizontally opposed spikes supports the theory that they were used for combat.  The scientific community seems to be leaning toward this view.  Remains of the predator animal, allosaurus, with wounds approximately matching the puncture marks of a stegosaurus spine lend provide further evidence to that theory.  Also, as the tail was not limited by the usually ossified (fused) tendons, it had a much greater range of motion and flexibility.  The unusually proportioned hind legs may have also been used to quickly and deftly maneuver the animal while attacking with its tail.

Did Stegosaurus Have a Second Brain?

The relatively small head, when compared to the total body size, has also been the cause for some study.  The very low brain mass to body mass ratio has led some to speculate that the unknown cavity located in the posterior of the tail could have housed a brain-like structure, used to control the mechanics of walking and tail posture.  This theory is under debate, however, and it has also been suggested that the chamber was used to store glycerin, which is an adaption for blood regulation found in birds.

What did Stegosaurus eat?

Scientists believe that the low lying head was used to graze on the brush and plant matter close to the ground.  It has been speculated that the stegosaurus may have been able to support its weight on its back legs enabling it to graze foliage at much higher levels than the neck and head posture would suggest. It did not eat grass however, as grass didn’t evolve until much later than the late Jurassic period.  The bite force of stegosaurus teeth has been calculated to reach levels capable of biting through smaller branches and twigs. However, jaw movement was limited. While it was greater than tooth grinding dinosaurs – where movement to chew food is a mortar and pestle-like grinding action, it was not enough for eating more than soft plant matter and twigs.

How did Stegosaurus move?

Stegosaurus walked slowly compared to other dinosaurs, at a maximum speed of only about 5 mph.  Because of the awkward arrangement of short forelimbs and long hindquarters, the natural gait of the animal was shortened artificially.  If the hindquarters moved at the natural range of motion, the stegosaurus would trip over itself.  These same hindquarters would however, help the stegosaurus move its giant tail nimbly.  And the short forelimbs would act as stabilizers planted into the ground.  It is interesting to note that most dinosaurs, including stegosaurus were adapted to walk on their toes, called digitigrade. Humans on the other hand, walk on their palms, called plantigrade.

Stegosaurus Probably Moved in Groups

Matthew Mossbrucker, a scientist of Morrison Natural History Museum in Colorado, discovered Stegosaurus tracks indicating that Stegosaurus lived in herds representing multiple age groups of the dinosaur. One set of tracks show four to five baby stegosaurus moving together in the same direction. Another set shows a young stegosaurus track with an adult track imprinted over it. Herd movement would have provided the dinosaurs, particularly the young, extra protection from predators.

History and Discovery of Stegosaurus

The first remains of the stegosaurus, were found by paleontologist Othniel Charles Marsh in 1877. They were uncovered in Colorado, United States. At first, Marsh thought the bones were from a new species of aquatic animal similar to a turtle. This idea was behind the name “roof lizard”, as he believed the plates lay flat over the animal’s back like roofing tiles. Several subspecies of stegosaurus were also located in Wyoming and Utah. In 1886, the best known species of Stegosaurus: the Stegosaurus stenops, which means “narrow-faced roof lizard” was collected by Marshal Felch at Garden Park in Colorado. Othniel Marsh named it in 1887. These remains included a complete and fully articulated skeleton. It had the distinctive large, broad plates and four spikes on its tail. Othniel Marsh said, about the Stegosaurus, “The series of vertical plates which extended above the neck, along the back, and over two-thirds of the tail,is a most remarkable feature, which could not have been anticipated, and would hardly have been credited had not the plates themselves been found in position.”

Historical Significance of Stegosaurus

Thanks to its charming and unique shape, Stegosaurus is one of the most popular of all dinosaurs. The state of Colorado even declared it as their State Dinosaur in 1982. It is especially well represented among cartoons and children toys. The Stegosaurus is probably at least partially responsible for making many future paleontologists and dinosaur lovers!