Jennifer Wilber is an author and freelance writer from Ohio. She holds a B.A. in creative writing and English.
Stegosaurus: Beloved, but Misunderstood
Stegosaurus is one of the most well-recognized dinosaurs of the Late Jurassic period. It commonly appears in television shows, movies, and video games. Stegosaurus is a favorite dinosaur of children and adults alike. Despite being a familiar dinosaur in pop culture, there are many things that most people don’t know about these gentle prehistoric giants. There have been many controversies and misconceptions about this dinosaur within the paleontological community since it was first discovered. As paleontologists continue to make new discoveries, we are beginning to learn much more about these magnificent creatures.
The Brain of Stegosaurus was the Size of a Dog’s
Though Stegosaurus could grow to 9 m (29.5 ft) in length and weigh 5.3–7 metric tons (5.8–7.7 short tons), it’s brain was extremely tiny by comparison. Stegosaurus’s brain only grew up to 80 g (2.8 oz), about the size of that of a modern-day dog. Though most dinosaurs had small brains relative to their overall body size, Stegosaurus’s brain was exceptionally small by comparison. Though much about the actual brain anatomy of Stegosaurus is unknown, the brain itself was small even by dinosaur standards. This minuscule brain size was well-suited to a creature with a slow, herbivorous lifestyle and limited behavioral complexity.
Paleontologists Once Thought Stegosaurus Had an Extra Brain in its Butt
American Paleontologist Othniel Charles Marsh, the researcher responsible for first identifying Stegosaurus in 1887, once proposed that Stegosaurus had extra gray matter located in a cavity nears its hind quarters. Soon after first identifying Stegosaurus, Marsh noted a large canal in the hip region of the creature’s spinal cord, which he believed could have accommodated a structure up to 20 times larger than its tiny brain. This led to a misconception that dinosaurs like Stegosaurus had a "second brain" located in the tail. Paleontologists believed that this “second brain” may have been responsible for controlling the animal’s reflexes in the rear portion of the body. This "brain" was theorized to have given a Stegosaurus a temporary boost when under threat by predators. This theory of an extra brain in its butt was quickly discredited.
The Spiked Tail of Stegosaurus is Called a “Thagomizer,” and Was Named by a Comic Artist
The term “thagomizer,” referring to the spikes at the end of Stegosaurus’s tail, was coined by Far Side creator Gary Larson. In 1982, a Far Side comic depicted a group of cavemen, presumably in a class learning about Stegosaurus. The professor caveman points to the sharp spikes at the end of Stegosaurus’s tail and says, "Now this end is called the thagomizer... after the late Thag Simmons." The word "thagomizer" has been used by paleontologists to refer to this part of the Stegosaurus ever since.
Stegosaurus Ate Small Rocks to Help it Digest its Food
Like many herbivorous (plant-eating) dinosaurs of the Mesozoic Era, Stegosaurus may have intentionally swallowed small rocks called as gastroliths to help it digest tough plant matter in its enormous stomach. Stegosaurus had to eat hundreds of pounds of vegetation every day to survive and to maintain its cold-blooded metabolism.
Stegosaurus’s Diet Consisted Mainly of Twigs and Foliage
Though Stegosaurus was an herbivore, its teeth and jaws were very different from other herbivorous ornithischian dinosaurs of the time. Most other ornithischian dinosaurs possessed teeth capable of grinding plant material and a jaw structure capable of movements other than the up-and-down movements that Stegosaurus was capable of. While most ornithischians had sturdy jaws and grinding teeth, Stegosaurus had small, peg-shaped teeth and its unusual jaws were probably only capable of up-down movements while chewing food. Stegosaurus probably ate mainly small twigs and foliage, as it would have been unable to handle digesting larger parts of plants.
A clade of mainly herbivorous dinosaurs which had a pelvic structure similar to birds. Stegosaurus belonged to this clade.
Stegosaurus’s Plates Were Likely Used for Display and Temperature Control, Not Defense
The most recognizable features of Stegosaurus are the plates on its back. These plates were actually highly modified scales, much like those seen in crocodiles and many lizards today. These plates were not directly attached to the Stegosaurus’s skeleton, but instead arose directly from its skin. The exact arrangement and placement of the plates on Stegosaurus’s back may have varied between species. Othniel Charles Marsh originally suggested that the plates functioned as a form of armor to protect Stegosaurus from predators, but later researchers suggested that the plates were too fragile and ill-placed to be used for this purpose. It is possible that these plates functioned to make the creature appear larger to potential predators, or were used to attract mates, though male and female Stegosauruses seem to have had the same type of plates. Now, most researchers believe that the plates were mainly used to help the creature to regulate its body temperature. The plates have been found to contain blood vessels running through grooves. The air flowing around the plates may have helped to cool the animal’s blood.
Stegosaurus Was Initially Believed to be an Aquatic Turtle-like Animal
When Othniel Charles Marsh first identified Stegosaurus in 1877, he initially believed it to be an aquatic turtle-like animal. He named the creature Stegosaurus, which means “roofed lizard” because of his original misunderstanding of the nature of the animal’s plates. Marsh’s original belief was that the plates lay flat over the animal's back, overlapping like shingles or tiles on a roof.
Stegosaurus was Originally Thought to be Bipedal, Due to its Comically Short Forelimbs
Othniel Charles Marsh originally believed Stegosaurus to be bipedal, like Tyrannosaurus rex, due to the relative shortness of the creature’s front legs compared to its back legs. Some scientists today still argue that Stegosaurus may have occasionally been capable of standing upright on its hind legs, using its tail to form a tripod for balance, when threatened by a predator or to reach higher-hanging food sources. Most people agree, however, that this was likely not the case.
Stegosaurus Could Only Run up to 5 Miles Per Hour
Analysis of the size and nature of Stegosaurus’s legs reveal the creature could likely only travel at a maximum speed of up to 5 miles per hour, though speeds of 3.7–4.3 mph were likely more common. Stegosaurus had short forelimbs in relation to its hind legs. To further slow down this animal, within the hind limbs, the lower section (comprising the tibia and fibula) was short compared to its femur. Because of the unusual proportions of its front and hind legs, Stegosaurus could not walk very fast. The stride of its back legs at greater speeds would have likely overtaken the front legs, causing the dinosaur to stumble and trip as a result.
There are only Three Universally Recognized Species of Stegosaurus
Though there were many different species of Stegosaurus initially described upon its discovery, many of these earlier identified Stegosaurus species have since been invalidated or been considered synonymous with earlier named species. The currently recognized Stegosaurus species are: Stegosaurus ungulates ("hoofed roof lizard"); Stegosaurus stenops ("narrow-faced roof lizard"); and Stegosaurus sulcatus ("furrowed roof lizard"). Stegosaurus stenops is the most well-known species of Stegosaurus.
|Species Name||Meaning||Year Discovered||Distinguishing Characteristics|
"hoofed roof lizard"
longest species, longer hind limbs, proportionately smaller and more pointed plates with wide bases and narrow tips, several paired spine-like plates before the tail spikes
"narrow-faced roof lizard"
best known species, large, broad plates in an alternating double row, and rounded tail plates
"furrowed roof lizard"
large, furrowed spikes with very large bases
Stegosaurus: New Discoveries Ahead
We have learned much about Stegosaurus since it was first discovered. Many of the original theories and assumptions about this dinosaur have since proven to be incorrect. As paleontologists continue to research this amazing creature, new discoveries are sure to be uncovered, shedding new light on this prehistoric marvel.
© 2018 Jennifer Wilber