Discover the Biggest Stegosaurus Ever Found

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Written by Erica Scassellati

Published: September 20, 2023

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Despite their prevalence in pop culture, the Stegosaurus was not a well-known or understood creature for quite some time. At first, scientists had to work with tiny bone fragments to build their understanding of the Stegosaurus. Today a nearly complete Stegosaurus skeleton is on display in London, but this specimen was actually on the smaller side. So just how big can a stegosaurus grow?

Species Overview

Stegosaurus lived during the late Jurassic Period, around 155-145 million years ago. These herbivorous creatures grew to an average length of about 6.5 meters (21 feet) according to Britannica.

However, they can also be much larger. Though the Stegosaurus was huge by today’s standards, it was much smaller than some of the species of its time, such as the Apatosaurus.

This species contained a spiked tail and a pattern of bony plates on its back. It had forelimbs shorter than its hind limbs and short, broad feet. Stegasaurus is also known for having a very small head compared to its body. This creature is sometimes even known as the “dumbest dinosaur” due to its walnut-sized brain.

“Some dinosaurs have very well-developed areas of the brain that indicate excellent sight or smell, but stegosaurs don’t really seem to have those,” Susannah Maidment, a paleontologist at the Natural History Museum in London told BBC Science Focus.

Still, Maidment did note that those features probably weren’t as important for herbivores like the Stegosaurus. “They were obviously smart enough to do what was needed,” she added.

For a time, scientists believed that the Stegosaurus possessed two brains. This misconception was due to an enlarged space around the creature’s hip. Today, it is believed that the sacral cavity stored glycogen, not a second brain.

A stegosaurus model stands on a cliff at nighttime.



had a very small head and brain, but it probably wasn’t as dumb as its reputation indicates.

Bony Plates

The Stegosaurus is known for its distinctive bony plates, yet scientists are still trying to explain the purpose of this feature.

Earlier theories proposed that the plates served to protect the creature’s backbone and spinal cord. However, new discoveries suggest that the plates aided in thermoregulation by releasing body heat or collecting heat like a solar panel.

Stegosaurus are also sexually dimorphic. According to the University of Bristol, males had larger, wider plates while female Stegosaurus plates were longer. In males, the plates may have played a role in attracting a potential mate.

Stegosaurus Have Three Recognized Species

There are three universally recognized species of Stegosaurus: S. stenops, S. ungulatus, and S. sulcatus. The largest of the Stegosaurus species was S. ungulatus, which measured up to 9 meters (30 feet) in length and weighed up to 7 metric tons.

Despite this, when you picture a “typical” Stegosaurus, you’re probably thinking of S. stenops. This species makes up the majority of mostly complete Stegosaurus specimens.

According to the Philip J. Currie Dinosaur Museum, S. stenops had broad, blunt-tipped plates on its back, while the tail spikes were round in cross-section. In contrast, S. ungulatus had narrower, more pointed plates.

What Is the Biggest Stegosaurus Species Ever Found?

Stegosaurus ungulatus is the biggest of its species, yet there are currently more intact S. stenops artifacts. Since most specimens of S. ungulatus are not very complete, it’s difficult to say which is the largest among them. Here’s a look at some of the most notable remains of S. ungulatus.

Wyoming Specimen

In 1879 fossils were discovered at Como Bluff, Wyoming in Quarry 12, near Robber’s Roost. According to the Global Biodiversity Information Facility, these remains were the first to be called Stegosaurus ungulatus, though it is possible they were actually Stegosaurus armatus.

However, S. armatus has since been replaced as the representative for its genus by S. stenops, writes London’s Natural History Museum. Othniel Charles Marsh granted S. ungulatus its name, which translates to “hoofed roof lizard.”

Portugal Specimen

In 2007, scientists unearthed new Stegosaurus ungulatus fossils in Portugal, near the city of Batalha. According to NBC News, these fossils included a tooth and parts of the animal’s spinal column and leg bones.

The discovery was especially noteworthy because it was the first time any species of Stegosaurus was found outside of North America. The findings point to the idea that Stegosaurus likely crossed land bridges connecting North America, Europe, and Africa that appeared when sea levels were low.

Stegosaurus dinosaur footprint with slide mark in fluvial sandstone from the Jurassic of Colorado, USA (public display, Morrison Natural History Museum, Morrison, Colorado, USA).



dinosaur footprint was found in fluvial sandstone and is now on display at the Morrison Natural History Museum in Morrison, Colorado.

Carnegie Museum of Natural History

Another notable S. ungulatus species display is located at the Carnegie Museum of Natural History in Pittsburgh, Pennslyvania. Scientists uncovered the creatures’ remains between 1920 and 1922 from Dinosaur National Monument near Jensen, Utah. According to National Park Services, the display shows the Stegosaurus with staggered plates down its back, as they likely would have been in real life.

Nebraska State Museum in Lincoln

A final notable S. ungulatus species is on display at the Nebraska State Museum in Lincoln. Allosaurus Roar writes that this Stegosaurus is displayed in a manner that is out of date considering new knowledge about how these creatures lived and walked. However, it’s rare to find any remains on display from S. ungulatus, so the specimen is still impressive.

Bone Wars

The discovery of the first S. ungulatus specimen coincides with the dinosaur “Bone Wars,” which took place from 1877 to 1892. During this time, two paleontologists, (the aforementioned Othniel Charles Marsh and Edward Drinker Cope) had an intense rivalry around finding the best and most numerous dinosaur fossils.

The Bone Wars led to a number of scientific discoveries. Unfortunately, the rivalry also resulted in theft, bribery, spying, and the destruction of fossils and fossil sites, says ThoughtCo. Marsh and Cope remained bitter rivals to the end. The pair stooped to trashing each other’s reputations and trying to undermine each other’s research.

Cope even requested that scientists dissect his head after his death to determine if his brain was bigger than Marsh’s brain. Thankfully this request was not carried out.

The Most Complete Stegosaurus Helps Scientists Understand the Species

It’s worth noting that even today, Stegosaurus is somewhat shrouded in mystery and it’s hard to say exactly just how big these creatures could grow.

“Although they are iconic, stegosaurs are quite poorly known as fossils,” Dr. Maidment told BBC Science Focus. The Natural History Museum in London holds one of the most complete Stegosaurus skeletons ever found.

“Before [the NHM] specimen was discovered, we didn’t have a specimen that preserved all of the plates and spines in the correct place along the back, so we didn’t know how many there were,” Maidment continued.

Stegosaurus in Forest

The most complete


skeleton is located at the London Natural History Museum and is 85% intact.

“We didn’t even know how many vertebrae there were in the back or tail – so we could really only guess how long stegosaurs were.”

The specimen in question has been on display at the Natural History Museum in London since 2014. This creature, affectionately nicknamed “Sophie” only reached about 3 meters tall (9.8 feet) and 5.6 meters long (18.4 feet) from head to tail, according to CBC News.

Though Sophie might be the most intact skeleton, she was also a rather small Stegosaurus — likely only a young adult at the time of her death.

Sophie weighed about 1,600 kilograms (3,527 pounds) and had a similar body mass as a small rhinoceros. This specimen dates back to the Jurassic Period and was discovered in 2003 at Red Canyon Ranch in Wyoming. Sophie is the most complete Stegosaurus skeleton and is 85% intact.

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About the Author

Erica is a writer at A-Z Animals where her primary focus is on history, food, and travel. Erica has over 3 years of experience as a content writer and holds a Bachelor of Arts in English from the University of Missouri-Kansas City, which she earned in 2018. A resident of Kansas City, Erica enjoys exploring her home town and traveling around the world to learn about different cultures and try new food.

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