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Stegosaurus was a herbivorous dinosaur that lived in the late Jurassic period, around 153 million years ago. It was an enormous beast, 30’ (9.1 m) from head to tail and weighing in at a robust 6,800 lbs (3,084 kg). But could it change color?
A Stegosaurus could change color, but only certain parts, such as the scutes (large keratin-covered osteoderms) on its back. These scutes were covered with a membrane that shifted from pink to bright red depending on the animal’s circumstances.
Although the mighty Stegosaurus has been extinct for millions of years, we're still discovering fascinating information about this dinosaur, including its ability to change color. Read on to discover how and why Stegosauruses could change the color of their spiny scutes.
Unlike animals with chromatophores, like octopi, chameleons, and cuttlefish, which can change the color of their entire body, the Stegosaurus's color-changing ability was likely limited to its scutes.
Unless you're a herpetologist (someone who studies reptiles and amphibians), you might not be familiar with this unique body part.
A scute is essentially a hardened, bone-like scale. Stegosauruses had rounded triangular osteoderms, or calcium-rich plates, lining their spines, which were covered in scutes. These scale-like formations were likely made of roughened keratin.
Notably, this is the same material that human fingernails and hair are made of. However, the keratin found on a Stegosaurus's spinal plates was much thicker. It was likely more like a turtle shell than a strand of hair.
This dinosaur's keratin-rich scutes might have also been quite colorful, ranging from a bright pink to a deep red.
Sadly, little is known about the purpose or coloration of these hardened scales. But because scutes covered the spiny plates along the Stegosaurus's back, we can at least assume they had some sort of protective quality.
They might have even protected the Stegosaurus during a fight with other dinosaurs, much like a turtle or other hard-shelled creatures.
The purpose or function of a Stegosaurus's plates and color-changing scutes is highly debated within the palaeontological community.
Some of the most common theories include the following:
The thermoregulation theory is the most hotly debated (pun intended). But most paleontologists agree that the Stegosaurus's colorful plates didn't fulfill a protective purpose, as their location makes them challenging to use as a means of defense.
A hungry Allosaurus, for example, could have easily disemboweled a Stegosaurus using its razor-sharp claws and teeth. At worst, the scutes and spinal plates would have proven tough to chew.
The predominant theory is those colorful Stegosaurus scutes helped these dinosaurs recognize one another. As a result, they might have been "display" features with few practical applications.
Still, because the Stegosaurus went extinct before the start of the Cretaceous period (about145 million years ago), it's impossible to confirm or refute these theories. That said, we can make a few informed and educated guesses about why Stegosaurus scutes changed color.
There are two prevailing theories regarding the Stegosaurus's color-changing scutes. For example, paleontologists have posited that these "mood ring" back plates changed color to do the following:
Determining the veracity of these two theorized purposes is challenging, as these animals have been extinct for about 150 million years. However, many modern animals have color-changing abilities to communicate, attract mates, and frighten potential predators.
By analyzing modern animals, particularly reptiles, we might be able to discover the reasons why the Stegosaurus had color-changing scutes.
To understand how the Stegosaurus could have used color-changing scutes to attract mates, we must look to modern reptiles that utilize color changes during mating.
Like many bird species, some reptiles, particularly males, develop brightly colored patches of skin to help themselves stand out and attract a mate. In some cases, the role is reversed, with females being the colorful ones.
Take the spiny-footed lizard (Acanthodactylus erythrurus), for example.
Sexually mature female spiny-footed lizards have bright red tails that turn white after they've ovulated. Male spiny-footed lizards seem to prefer pre-ovulation females and their red tails, indicating that coloration plays a significant role in mating success for this species.
However, the male peacock has bright tail feathers, while the female peacock is a dingy brown, which keeps them hidden better. As an evolutionary mechanism, this is meant to protect the species, as it’s usually the female who protects the eggs and their young.
Although we can't confirm that colorful Stegosaurus scutes fulfilled a similar function, it's not out of the question.
Still, flashing eye-catching colors to attract mates can be both a blessing and a curse, as bright colors are attractive to both mates and predators. So, if Stegosaurus scutes did change color to entice potential mates, they might have also drawn the ire of hungry predators.
But funnily enough, the brightly-colored scutes might have acted as a visual deterrent that helped ward away carnivorous dinosaurs.
Even though bright colors make an animal more visible, potentially making it more prone to attacks, eye-catching hues can also intimidate potential predators. Many poisonous species of frogs and snakes have brightly colored exteriors that act as a warning to would-be predators.
Although Stegosauruses had few innate defenses, primarily using their stubby spiked tail to repel attackers, their color-changing scutes might have served as secondary defense systems.
If these plates suddenly became much darker or lighter when a Stegosaurus felt threatened, predatory dinosaurs might have interpreted this color change as a warning of a deadly counterattack.
Like modern amphibians, some Jurassic-period dinosaurs might have developed brightly colored body parts to tell others they were poisonous. Stegosauruses might have evolved to resemble poisonous dinosaurs, thus repelling potential predators.
However, considering the fact that Stegosauruses went extinct long before the mass extinction of the dinosaurs (about65 million years ago), the potential defensive applications of their scutes were probably lackluster at best and entirely ineffective at worst.
But understanding why Stegosaurus scutes changed color is only part of the puzzle. Knowing how they changed color might offer a little more insight.
Although we have a few theories outlining the reasons why the Stegosaurus changed color, how Stegosaurus scutes changed color is far more mysterious. After all, there’s no direct evidence of this phenomenon.
However, paleontologists and zoologists have proposed a few theories.
Some paleontologists theorize that the scutes may have contained specialized pigments that could change color in response to heat or light, similar to how some modern animals like chameleons change color in response to environmental temperature changes.
This could have allowed the Stegosaurus to communicate temperature-related dangers to other individuals.
But a color change related to temperature might have also been a purely biological response. Rising temperatures might have caused an increase in blood flow to the scutes. This color change is seen in humans who get overheated.
When a person gets too hot, their blood vessels dilate, and when this happens, the skin becomes flushed. The same response might have existed in Stegosauruses.
Another possibility is that the scutes may have changed color as the animal aged or grew. Some animals, such as reptiles and birds, change color as they grow and mature.
The same may have been true for Stegosaurus.
The bright scutes along the spine of a Stegosaurus might have changed color, becoming darker or lighter, as the animal reached sexual maturity. You can think of this as similar to how a child's hair might become darker as they age.
Essentially, a Stegosaurus going through puberty might have experienced an increase in pigment production that altered the color of the keratin-covered osteoderms on its back.
It’s also possible that the scutes may have changed color due to injury, disease, or stress. Some animals, such as chameleons, can change skin color in response to changes in their health or emotional state.
Consequently, we cannot rule out this trait for Stegosaurus.
Additionally, it's thought that the scutes along the Stegosaurus spine were connected to the animal's circulatory system. If a Stegosaurus experienced extreme blood loss, the scutes might have changed color in response to this change in blood flow, potentially becoming paler.
Still, it's difficult to say how Stegosaurus scutes changed their color. Due to a lack of biological specimens, scholars have few reference points to help them understand this phenomenon.
We don't know for certain what color Stegosaurus was, as this information isn't preserved in the fossil record. After all, fossilization transforms biological tissues like skin and bone into hard rock.
However, we have a few theories.
One possibility is that Stegosaurus may have been a brown or grey color, similar to the color of many modern reptiles. This theory is based on the fact that Stegosaurus was a reptile, and therefore, it might have had a similar coloration to modern-day reptiles.
Another possibility is that the Stegosaurus may have been a colorful animal with eye-catching patterns or markings on its skin or scales. But this theory doesn't only apply to the Stegosaurus, but all dinosaurs.
In fact, the Stegosaurus might have had feathers.
Many species of dinosaurs had colorful feathers the way birds do today. Still, many feathered dinosaurs were theropods. These meat-eating dinosaurs were known for being capable predators.
But Stegosauruses were herbivores, and they don't belong to the theropod group. So it's unlikely that the Stegosaurus was feathered, though it's not impossible. It's also worth mentioning that the Stegosaurus existed for millions of years.
Consequently, it likely enjoyed several morphological changes before going extinct.
Early Stegosauruses and those walking the Earth during the late Jurassic might have looked very different from one another, just as modern humans (Homo sapiens) and ancient humans look drastically different.
Picking and choosing its battles, the Stegosaurus sometimes had to make a run for it.
But running wasn't the best defense because Stegosaurus dinosaurs couldn’t run fast. Their top speed was about five miles per hour (8 km per hour). Usain Bolt wouldn’t be impressed.
There are several reasons Stegosaurus may not have been able to run fast.
One possibility is that the animal's anatomy may not have been well-suited for running. Stegosaurus had a relatively large body and a short, thick neck, which would have made it difficult for the animal to maintain its balance at high speeds.
In addition, Stegosaurus had a long, heavy tail that would have made it difficult for the animal to maneuver quickly.
Another factor that may have limited the Stegosaurus' speed is its diet. As a herbivorous dinosaur, Stegosaurus would have needed to graze on plants to survive, which would have required the animal to spend a lot of time searching for food, leaving little time for running.
In any case, paleontologists don’t feel the Stegosaurus was built for speed. Had you been alive during its time, you might have driven one to the grocery store, but the race track would have been out of bounds.
The Stegosaurus has been extinct for 150 million years. Owing to this, what we know about Stegosaurus is limited to theories and a handful of fossilized remains. Still, we know that the Stegosaurus had color-changing scutes (keratin-covered osteoderms) along its spine.
These scutes may have changed color to attract mates or ward off predators.
Stegosaurus scutes might have also changed color in response to heat or injury. Additionally, sexual maturity might have played a role in causing these spiny plates to change color. But until well-preserved Stegosaurus scutes are unearthed, we may never know for sure!
