Stegosaurus was a genus of stegosaurid dinosaur that lived in North America during the Late Jurassic Period around 155–145 million years ago. It is the largest and most famous known member of the Stegosaurs, an aptly-named race of armored dinosaurs known for their bony plates and spikes.
Stegosaurus (meaning "roof lizard") is a genus of herbivorous, four-legged, armored dinosaur from the Late Jurassic, characterized by the distinctive kite-shaped upright plates along their backs and spikes on their tails. Fossils of the genus have been found in the western United States and in Portugal, where they are found in Kimmeridgian- to Tithonian-aged strata, dating to between 155-145 million years ago. Of the species that have been classified in the upper Morrison Formation of the western US, only three are universally recognized: S. stenops, S. ungulatus, and S. sulcatus. The remains of over 80 individual animals of this genus have been found. Stegosaurus would have lived alongside dinosaurs, such as Apatosaurus, Diplodocus, Camarasaurus, and Allosaurus, the latter of which may have preyed on it.
Stegosaurus were large, heavily built, herbivorous quadrupeds with rounded backs, short forelimbs, long hind limbs, and tails held high in the air. Due to their distinctive combination of broad, upright plates and tail tipped with spikes, Stegosaurus is one of the most recognizable kinds of dinosaurs. The function of this array of plates and spikes has been the subject of much speculation among scientists. Today, it is generally agreed that their spiked tails were most likely used for defense against predators, while their plates may have been used primarily for display, and secondarily for thermoregulatory functions. Stegosaurus had a relatively low brain-to-body mass ratio. It had a short neck and a small head, meaning it most likely ate low-lying bushes and shrubs. One species, Stegosaurus ungulatus, is one of the largest known of all the stegosaurians, with the largest known specimens measuring about 7.5 meters (25 feet) long and weighing over 5 metric tons (5.5 short tons).
Stegosaurus is one of many fauna in The Rite of Spring segment. It is unusually mixed in alongside species of the Permian, Triassic, Jurassic, and Cretaceous periods. When the Tyrannosaurus rex first makes its appearance, the Stegosaurus is shocked like the many of them. As the T. rex lunges for the herbivores, the Stegosaurus attempts an escape, but is slow in getting away from the dangerous predator and resorts to fighting the T. rex in an effort to save its own life. However, the battle comes to an end with the T. rex emerging victorious. The carnivore then proceeds to eat the fallen herbivore as the scene becomes quiet and fades to black.
Later, other Stegosaurus appear in the group of dinosaurs marching through the drought. Some are trapped in a muddy pit with Apatosaurus and Diplodocus then they are killed by heat exhaustion and attacked by a group of desperately hungry Ceratosaurus.
A Stegosaurus also appears in The Little Mermaid episode "Land of the Dinosaurs", along with Apatosaurus, Triceratops, and Tyrannosaurus rex. It is depicted as having sharp teeth and no beak unlike the real Stegosaurus, which has a beak and flat teeth in its jaws.
Stegosaurus was originally meant to appear in early drafts of The Good Dinosaur, but were eventually cut in the final film. However, the species was mentioned by Nash, where he tells his story about how he got his scars from thirteen outlaw Steggos.
Stegosaurus appears in both the Primeval World diorama on the Disneyland Railroad and in the Universe of Energy at Epcot. In both attractions, the fight with the Tyrannosaurus is recreated, although in Universe of Energy, the Tyrannosaurus is replaced by an Allosaurus.
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In Fantasia, Stegosaurus was depicted as a sluggish animal, with its legs sprawling and tail dragging along the ground. In real life, Stegosaurus had its legs tucked underneath its body and its tail held far off the ground.
Stegosaurus and its Stegosauridae relatives never coexisted with the Tyrannosaurus rex, as they lived during different time periods spanning millions of years apart. The carnivorous theropods of that time were instead the Allosaurus, Saurophaganax, Ceratosaurus, and Torvosaurus.
Stegosaurus has been found in both North America and Portugal; during the Jurassic era, Portugal was a large island off the coast of North America, which allowed larger dinosaurs to colonize it.
Despite its intelligent portrayal as a leader of a herd of herbivores, Stegosaurus has one of the smallest brains of any non-avian dinosaur proportionate to body size.
The tail spikes of Stegosaurus (also known as thagomizers) measure approximately one meter in length. Although its purpose is debated, evidence exists that they were used for defense. Fatal wounds have been found in Allosaurus skeletons that fit the tail spikes of Stegosaurus. This indicates that Stegosaurus' flexible tail was able to move its tail spikes quickly to defend itself from carnivores. The structures may have also served as a form of display for species differentiation.
Despite its great size, Stegosaurus' backplates were actually quite delicate; they were thin, full of blood vessels, and covered in keratin (found in nails and hair, as well as claws and horns). At one time, they were assumed to be used for warming up or cooling the animal down. They were probably more for display and species recognition than heat regulation or defense.
According to a 2014–2015 study with S. Mjosi specimens, the backplates of some Stegosaurs were found to be round. These were attributed to being a male trait. The stereotypical pointed plates of Stegosaurs that most people are familiar with may have been a predominantly female trait.
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