Stegosaurus: The Armored Giant of the Late Jurassic

Stegosaurus: The Armored Giant of the Late Jurassic

The Stegosaurus, a well-known dinosaur that resonates with a sense of awe and wonder, is one that has captured the imagination of many. This herbivorous, four-legged, armored dinosaur from the Late Jurassic period is characterized by its distinctive kite-shaped upright plates along its back and spikes on its tail.

Stegosaurus fossils have been found in the western United States and in Portugal, dating back to between 155.7 to 93.5 million years ago. This broad geographical and temporal range is impressive among dinosaurs. With its unique combination of broad, upright plates and tail tipped with spikes, this is one of the most recognizable kinds of dinosaurs.

Stegosaurus Key Facts

Stegosaurus PronunciationSTEG-oh-SORE-us
Meaning of NameRoof-lizard’
Type SpeciesStegosaurus stenops
When it Lived155.7 to 93.5 MYA
PeriodLate Jurassic
EpochLate/Upper Kimmeridgian to Early/Lower Cenomanian 
Length23.0 ft
Height15.1 ft
Weight3.8 tons
MobilityMoved on all four
First Discovery1876 by Marshall Parker Felch
Location of First FindColorado
First Described1877 by Othniel Charles Marsh
HolotypeYPM 1850

Stegosaurus Origins, Taxonomy and Timeline

Life reconstruction of Stegosaurus, showcasing its distinctive double row of large, bony plates along its back and the spiked tail known as a thagomizer. The dinosaur is depicted in a walking stance, with a greyish-brown body and darker plates. This illustration highlights the unique features of Stegosaurus, a well-known species from the Late Jurassic period.
Fred Wierum, CC BY-SA 4.0, via Wikimedia Commons

The Stegosaurus has a name that carries a meaning as distinctive as the dinosaur itself. Derived from the Greek words ‘stegos’ meaning ‘roof’ and ‘sauros’ meaning ‘lizard’, the name is a nod to the large, flat bony plates that adorned its back. People described these plates as flat, giving the dinosaur the appearance of a gigantic, walking roof.

In the taxonomy of dinosaurs, it is classified under the Order Ornithischia–known for their bird-like hip structure. It’s part of the Stegosauria group, in the family Stegosauridae. We know this group of herbivorous dinosaurs for their array of plates and spikes. The genus Stegosaurus is further divided into several species, with the type species Stegosaurus stenops being the most well-known and well-preserved.

The timeline takes place during the Late Jurassic period, specifically spanning from the Late Kimmeridgian to Early Tithonian stages. This was a time when the earth was warm and the continents as we know them today were still forming. This herbivore roamed the earth alongside other iconic dinosaurs, leaving behind a legacy that continues to fascinate us today.

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Discovery & Fossil Evidence

This dinosaur first stepped into the limelight in 1877 when it was finally described by renowned paleontologist O.C. Marsh. This was after its fossils were discovered by 1876 by Marshall Parker Felch. The initial discovery was made in Morrison, Colorado and the dinosaur was aptly named Stegosaurus armatus, or ‘armored roof lizard’. This holotype specimen, YPM 1850, is housed at the Yale Peabody Museum. This specimen was considered unfit as the type specimen for a well-known dinosaur like the Stegosaurus, so it was eventually replaced by S. stenops. 

Skeletal mount of Stegosaurus on display in a museum. The skeleton features the iconic double row of bony plates along its back and a spiked tail. The dinosaur is shown in a standing position, providing a detailed view of its anatomy and size. Museum visitors can be seen in the background, highlighting the educational display of this well-known Late Jurassic dinosaur.
Thomas Quine, CC BY 2.0, via Wikimedia Commons

Researchers have unearthed numerous fossils since that initial discovery, not just in Colorado, but also in other parts of the United States such as Wyoming, Utah, and Montana. Interestingly, findings of Stegosaurus fossils have extended across the Atlantic to Portugal, suggesting a broader geographic distribution of these dinosaurs than initially assumed.

The fossils provide a wealth of information about this fascinating dinosaur. From the distinctive plates and spikes to the smaller bones of the skeleton, each fossil find adds another piece to the puzzle and helps us understand the life and times of the Stegosaurus.

Stegosaurus Size and Description

This genus of herbivorous, four-legged, armored dinosaurs from the Late Jurassic is characterized by the distinctive kite-shaped upright plates along their backs and spikes on their tails. They were large, heavily built, herbivorous quadrupeds with rounded backs, short fore limbs, long hind limbs, and tails held high in the air. Their distinctive combination of broad, upright plates and tail tipped with spikes makes the Stegosaurus one of the most recognizable kinds of dinosaurs.

Size and Weight of Type Species

Size comparison chart of two Stegosaurus species: Stegosaurus ungulatus and Stegosaurus stenops. The chart shows the different lengths and heights of the two species, with a human silhouette included for scale. Stegosaurus ungulatus is depicted in orange and Stegosaurus stenops in green, highlighting the differences in their plate arrangements and body proportions.
KoprX, CC BY-SA 4.0, via Wikimedia Commons

One species, Stegosaurus ungulatus, is one of the largest known of all the stegosaurians, reaching 7 metres (23 ft) in length and 3.8 metric tons (4.2 short tons) in body mass. Some large individuals may have reached 7.5 m (25 ft) in length and 5.0–5.3 metric tons (5.5–5.8 short tons) in body mass. The quadrupedal Stegosaurus is one of the most easily identifiable dinosaur genera due to the distinctive double row of kite-shaped plates rising vertically along the rounded back and the two pairs of long spikes extending horizontally near the end of the tail. S. stenops reached 6.5 m (21.3 ft) in length and 3.5 metric tons (3.9 short tons) in body mass. 

Stegosaurus Games

If you want to test your knowledge about Stegosaurus, here is a fun quiz you can play. Don’t worry if you don’t get all questions right, it is a learning opportunity! Have fun!

Don’t forget to try our other games as well!

The Dinosaur in Detail

The Stegosaurus has some unique features that set it apart from other dinosaurs. Its broad, upright plates and tail tipped with spikes are not only distinctive but also reflect the dinosaur’s adaptability and survival instincts. Primarily, the Stegosaurus may have used the plates for display and secondarily for thermoregulatory functions, implying a complex social or behavioral life. Most likely, it used the spikes on its tail for defense against predators. This indicates that the Stegosaurus was not a passive herbivore but an active participant in its ecosystem.

It also had a relatively low brain-to-body mass ratio, which has been the subject of much discussion and study. Despite its large size, the brain of the Stegosaurus was no larger than that of a dog. This has contributed to the popular idea that dinosaurs, or at least the Stegosaurus, were not particularly intelligent. However, recent studies suggest that brain size is not necessarily a measure of intelligence and the Stegosaurus, like other dinosaurs, may have been more intelligent than previously thought.

Notable specimens, such as the “Sophie” specimen at the Natural History Museum in London, have contributed greatly to our understanding of this dinosaur. With 85 percent of the skeleton preserved, “Sophie” is the most complete Stegosaurus skeleton ever found. This specimen has allowed scientists to make more accurate reconstructions and to gain new insights into its biology and behavior.

The Stegosaurus in its Natural Habitat

Illustration of Stegosaurus ungulatus, a species of Stegosaurus, showing its distinctive features including the alternating double row of plates along its back and the spikes on its tail known as the thagomizer. The dinosaur is colored in shades of green and brown with yellow plates.
Slate Weasel, Public domain, via Wikimedia Commons

This herbivorous dinosaur lived during the Late Jurassic period. Researchers have found the Stegosaurus in the western half of North America, then known as Laramidia, and in the westernmost part of Europe. At that time, a semi-arid environment with distinct wet and dry seasons shaped the landscape. Ferns, horsetails, and gymnosperms such as conifers, ginkgoes, and cycads dominated this terrain. The Stegosaurus, with its low-slung head and beak, showed excellent adaptation for consuming these low-lying plants.

As a larger herbivore, it would have played an important role in the ecosystem by shaping the landscape through its feeding habits. It is likely that it had to eat a large amount of vegetation to sustain its large body and this would have had an impact on the vegetation of the area. It was also likely prey for large carnivorous dinosaurs such as the Allosaurus. This predator-prey relationship would have influenced the behavior and evolution of both species.

This was a slow-moving dinosaur, with a top speed estimated at around 5 mph. Despite its slow speed, it was not defenseless. The dinosaur could have used the spikes on its tail, called thagomizers, as a formidable weapon against predators. Additionally, evidence of a complex social life emerges from the presence of plates it possibly used for display.

It is possible that they lived in herds, as suggested by the discovery of several Stegosaurus fossils found together.

Interesting Points about Stegosaurus

  1. It had a brain that was very small relative to its body size, leading to the popular myth that it had a “second brain” in its tail to help control its hindquarters.
  2. They made the plates from bone, featuring a lattice-like structure, not solid. A layer of hardened keratin covered the outside.
  3. Colorado honors the many significant fossils found within its borders by designating this as the state dinosaur.
  4. It had a beak and no front teeth, suggesting that it was a selective eater that chose specific plants or parts of plants to eat.
  5. Books, movies, and toys often use its image as it’s easily one of the most recognizable dinosaurs.

Contemporary Dinosaurs

This dinosaur lived across millions of years and multiple continents and thus shared its world with an intriguing array of contemporaries. Among these were the Allosaurus, Apatosaurus, Diplodocus, and Camarasaurus, each contributing to the intricate dynamics of their shared environments. 

The predatory Allosaurus might have posed a significant threat to the Stegosaurus. Yet, the Stegosaurus was not defenseless. Its spiked tail was a natural deterrent that could have been a formidable weapon against the Allosaurus. This potential predator-prey relationship paints a vivid picture of the survival strategies these creatures might have employed, with the Stegosaurus using its natural defenses to counter the predatory instincts of the Allosaurus.

In contrast, the Apatosaurus, Diplodocus, and Camarasaurus, all herbivores like the Stegosaurus, likely had a different kind of relationship with our main dinosaur. They might have been competitors for the same plant resources, yet their differing body sizes and feeding heights could have allowed for resource partitioning. This would have reduced direct competition and promoted coexistence. The Stegosaurus, with its low-lying head, would have grazed on lower vegetation while the towering Apatosaurus, Diplodocus, and Camarasaurus could have reached the higher foliage.

In this complex ecosystem, the Stegosaurus and its contemporaries played out a delicate dance of survival. Their interactions, whether as potential prey and predator or as competitors for resources, shaped their existence and left an indelible mark on our understanding of prehistoric life. Through this exploration, we gain a deeper appreciation of the Stegosaurus–not just as an isolated creature but as an integral part of a rich and diverse prehistoric world.

List of All Dinosaurs

We have created a list of all dinosaurs we have covered here, sorted across the seven main groups of dinosaurs. We also include information about their type of diet, (omnivore, herbivore or carnivore) and the time they lived.

Frequently Asked Questions

What was the purpose of the plates on its back?

Primarily, they may have used the plates for display, and secondarily for thermoregulatory functions.

How did it defend itself?

It likely used the spikes on its tail, known as thagomizers, as a formidable weapon against predators.

What did this dinosaur eat? 

This was an herbivore and likely are low-lying plants such as ferns, horsetails, and gymnosperms.

Did the Stegosaurus live in herds?

It is possible that it lived in herds, as suggested by the discovery of several fossils found together.

How fast could it move?

This was a slow-moving dinosaur, with an estimated top speed estimated at around 5 mph.


Article last fact checked:Joey Arboleda, 06-13-2023

Featured Image Credit: Copyright (c)