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Stegosaurus is one of the most widely recognizable dinosaurs, mainly thanks to its distinctive appearance. The trait that stands out most of all is, perhaps, its tail spikes and plates on its back that have intrigued humanity for over a century now. Why did stegosaurus have spikes?
Stegosaurus had spikes on their tails for fighting predators. The plates on their back likely also served this function, as well as attracted females while scaring off other male stegosauruses. They were also possibly used for temperature regulation.
In this article, I will dive more into the reasons why the stegosauruses had tail spikes and plates on their backs. We’ll look into the theories that exist on the matter and discuss each of them and to what extent they might be actually true. View our best dinosaur gifts including the Stegosaurus.
While many refer to the two rows of bony formations on the stegosaurus’s back as spikes, that is not exactly correct. Though they look pointy and sharp, they are quite different from spikes and have a name of their own.
What is considered to be the spikes on a stegosaurus’s back are actually plates called scutes. They were made of osteoderms, a structure of skin and bone common for reptiles; it is, for instance, the tissue of crocodile’s skin. While scutes were bony, they also had blood vessels.
However, stegosaurus had spikes, too: they were located on the dinosaur’s tail. When it was first discovered in the 1870s, scientists believed the stegosaurus had eight tail spikes, a dangerous weapon against powerful enemies. However, it is proved today that there were only four spikes on its tail and seventeen to twenty-two scutes aligned in two rows along its spine.
Scientists have proposed numerous hypotheses regarding the purpose of the spikes and plates of the Stegosaurus. While they are pretty positive that tail spikes were used for defense, the plates were likely there for a combination of reasons. Let’s discuss those reasons in more detail.
The stegosaurus probably used both tale spikes and spine plates to defend itself against other animals, primarily Allosaurus. It was likely the main purpose of the spikes, while plates were there for safeguarding only in part.
Thagomizer, which is what stegosaurus’s tail is called, is big and powerful, and the spikes it carries present a threat to possible attackers. That is why the general assumption was that thagomizer was used for defense, yet for a long time, there was no substantial evidence for this theory.
However, in 2005, proof was found. A closer observation of stegosaurus remains showed that some tips of the spikes were broken, and the bone was also deformed. Another piece of evidence, and probably the most impressive one of all, came from studying remains of Allosaurus.
The remains in question also had a modified bone with a small hole in it. One might think it could be a bite, but there was no indication of teeth being the cause of the damage. A tale spike of the stegosaurus, however, was exactly the same in diameter and fit perfectly into the picture.
And what about the spine plates? Well, they could have been used for defense as well since they were sharp and positioned in a way that made it easy to point them against the predator. However, it is not likely they were quite effective as an actual weapon.
It is more probable that the scutes served a passive defensive function. They made the stegosaurus visually larger, which could potentially scare predators away. The fact that many people mistake the plates for spikes, it is likely attackers could get a similar impression and reconsider getting into a fight with the stegosaurus.
Another popular hypothesis about the purpose of spine plates stated that they were used for regulating temperature. As I’ve mentioned, the plates were mottled with blood vessels, which is partially why they could have participated in thermoregulation.
It is assumed that stegosauruses were cold-blooded like other vegetarian dinosaur species. The theory essentially suggests that the plates located on the back gathered sunlight during the day, and the accumulated heat kept the stegosaurus warm during the night.
While this idea is often cited and has been a pretty popular explanation of the purpose of stegosaurus scutes, there is not much evidence to support it. Had thermoregulation been the primary function of the plates, other dinosaur species of the same natural habitat, size, and habits, would’ve probably developed similar organs.
Indeed, nothing about the plates indicates they existed to regulate body temperature. However, there is also no strong argument against this theory that would let us toss it aside altogether.
This is why scientists today generally agree that thermoregulation processes could be one of the functions plates performed, but it was likely not their primary purpose.
From what we currently know about stegosaurus, it is likely their spine plates existed mainly for display. They signified belonging to the group, intimidated other male stegosauruses, and attracted females for mating.
‘Species recognition,’ a term that essentially means recognizing possible mates, is a concept the scientists are pretty divided on. Some find it a plausible explanation for various evolutional adaptations, while others are skeptical about it. Still, it could be one of the functions stegosaurus plates served.
It is rather probable that the plates were seen as attractive by females. Much like peacock tales, they could be a product of sexual selection, meaning that the stegosauruses with bigger plates were more likely to be chosen for mating.
The size and sharpness of the plates also probably intimidated other male stegosauruses. Potential contestants for a mate could reconsider shooting their shot if the size of their rival’s plates gave an impression they were not to be messed with.
To sum up, we can be positive that the tail spikes of stegosaurus were used for self-defense. The spine plates, however, likely served multiple purposes, the main one being attracting mates and scaring away possible rivals. Other functions could be intimidating predators and thermoregulation.
