10 Facts About Stegosaurus, the Spiked, Plated Dinosaur

Stegosaurus eating plants

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Few people know much about stegosaurus beyond the fact that a) it had triangular plates on its back, b) it was dumber than the average dinosaur, and c) its plastic figurine looks really cool on an office desk. Below, you'll discover 10 fascinating facts about Stegosaurus, the popular plant-eater with the spiked tail and plated back. 

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Stegosaurus Had a Brain the Size of a Walnut


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Given its size, stegosaurus was equipped with an unusually small brain, comparable to that of a modern golden retriever — which gave it an extremely low "encephalization quotient," or EQ. How could a four-ton dinosaur possibly survive and thrive with so little gray matter? Well, as a general rule, any given animal only has to be slightly smarter than the food it eats (in stegosaurus' case, primitive ferns and cycads) and just alert enough to avoid predators—and by those standards, Stegosaurus was brainy enough to prosper in the wilds of late Jurassic North America.

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Paleontologists Once Thought Stegosaurus Had a Brain in its Butt

A Stegosaurus defending itself from an attacking Allosaurus.

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Early naturalists had a hard time wrapping their minds around the diminutive size of stegosaurus' brain. It was once proposed that this none-too-bright herbivore possessed supplementary grey matter located somewhere in its hip region, but contemporaries quickly soured on this "brain in the butt" theory when the fossil evidence proved unavailing.

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The Spiked Tail of Stegosaurus Is Called a "Thagomizer"


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Way back in 1982, a famous Far Side cartoon depicted a group of cavemen clustered around a picture of a stegosaurus tail; one of them points to the sharp spikes and says, "Now this end is called the thagomizer...after the late Thag Simmons." The word "thagomizer," coined by ​Far Side creator Gary Larson, has been used by paleontologists ever since.

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There's a Lot We Don't Know About Stegosaurus' Plates

stegosaurus at Jura Park

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The name stegosaurus means "roofed lizard," reflecting the belief of 19th-century paleontologists that this dinosaur's plates lay flat along its back, like a form of armor. Various reconstructions have been offered up since then, the most convincing of which has the plates alternating in parallel rows, pointy ends up, from this dinosaur's neck all the way down to its butt. As to why these structures evolved in the first place, that's still a mystery.

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Stegosaurus Supplemented its Diet with Small Rocks


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Like many plant-eating dinosaurs of the Mesozoic Era, stegosaurus intentionally swallowed small rocks (known as gastroliths) that helped mash up the tough vegetable matter in its enormous stomach; this quadruped would have had to eat hundreds of pounds of ferns and cycads every day to maintain its presumably cold-blooded metabolism. It's also possible that stegosaurus swallowed rocks because it had a brain the size of a walnut; who knows?

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Stegosaurus Was One of the Earliest Dinosaurs to Evolve Cheeks

stegosaurus at the Natural History Museum of Utah

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Although it was undoubtedly lacking in other respects, stegosaurus did possess one relatively advanced anatomical feature: extrapolating from the shape and arrangement of its teeth, experts believe this plant-eater may have possessed primitive cheeks. Why were cheeks so important? Well, they gave stegosaurus the ability to thoroughly chew and pre-digest its food before swallowing it and also allowed this dinosaur to pack away more vegetable matter than its non-cheeked competition.

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Stegosaurus Is the State Dinosaur of Colorado

stegosaurus at Carnegie Natural History Museum

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Back in 1982, the governor of Colorado signed a bill making Stegosaurus the official state dinosaur, after a two-year write-in campaign spearheaded by thousands of fourth-grade students. This is a bigger honor than you might think, considering the huge number of dinosaurs that have been discovered in Colorado, including Allosaurus, Apatosaurus, and Ornithomimus—but the selection of Stegosaurus was still (if you'll excuse the expression) a bit of a no-brainer.

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It Was Once Thought that Stegosaurus Walked on Two Legs


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Because it was discovered relatively early in paleontological history, stegosaurus has become the poster-lizard for wacky dinosaur theories. Early naturalists once thought this dinosaur was bipedal, like Tyrannosaurus Rex; even today, some experts argue that Stegosaurus may have been occasionally capable of rearing back on its two hind feet, especially when threatened by a hungry Allosaurus, though few people are convinced.

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Most Stegosaurs Hailed from Asia, Not North America


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Although it's by far the most famous, stegosaurus wasn't the only spiked, plated dinosaur of the late Jurassic period. The remains of these odd-looking reptiles have been discovered across the expanse of Europe and Asia, with the largest concentrations further east--hence the odd-sounding stegosaur genera ​Chialingosaurus, Chungkingosaurus, and Tuojiangosaurus. All in all, there are less than two dozen identified stegosaurs, making this one of the rarest types of dinosaur.

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Stegosaurus Was Closely Related to Ankylosaurus


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The stegosaurs of the late Jurassic period were cousins of the ankylosaurs (armored dinosaurs), which prospered tens of millions of years later, during the middle to late Cretaceous period. Both of these dinosaur families are grouped under the larger classification of "thyreophorans" (Greek for "shield bearers). Like Stegosaurus, Ankylosaurus was a low-slung, four-footed plant-eater—and, given its armor, even less appetizing in the eyes of ravenous raptors and tyrannosaurs.