Spines, Sails, Plates & Horns – All About Dinosaur Defenses & Display

Many dinosaurs are known for the shocking array of spines, plates and sails adorning their bodies, and many more are distinguished by the horns sprouting from their heads. But why did dinosaurs develop such strange and unique adaptations? Nobody really knows for sure, but scientists do have some pretty good theories.

 

Spikes and Spines

There are many types of dinosaurs whose bodies featured fearsome spikes. Sometimes these existed along with other forms of protection, like the spikes on the neck and shoulders of the armor-plated Sauropelta, an ankylosaur. Other times they ran along the neck and back, as in the backward-curving spines of the sauropod Amargasaurus, as well as the forward-pointing spines on its recently discovered relative, Bajadasaurus. Spikes can also be found on the tails of Stegosaurus and its relatives, supplementing the plates along their backs (more on those later!).

 

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The neck spines of Amargasaurus...

...the shoulder spikes of Sauropelta...

...and the tail spikes of Stegosaurus

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So, why were these dinos covered in sharp spines? The most obvious theory is to defend themselves against predators. Spines and spikes like these occur much more commonly on plant-eating dinosaurs, which would have needed some way to protect themselves from meat-eating carnivores that might try to make them into a snack. Any predator trying to jump on the back of an Amargasaurus would get a nasty surprise, and a swing from a Stegosaurus’s tail could do major damage to any attacker. And, Sauropelta would have had to do little more than hunker down and let its spikes and armor take care of the rest.

These spikes and spines could also have been used in conflicts between other individuals of the same species, perhaps in a battle to impress a potential mate. This can be seen in modern animals such as deer, who battle each other with their antlers.

 

Sails and Fins

Sometimes, dinosaurs had spines sprouting from their backbones with an arrangement that suggests they were probably connected by a membrane when the animal was alive, creating a continuous “sail”. Dinosaurs like Spinosaurus and (to a much lesser extent) Acrocanthosaurus, were believed to possess these sails due to the tall spines jutting from their vertebrae.

One of the most famous prehistoric creatures to possess such a sail was not a dinosaur at all, though it is often incorrectly grouped with them. Dimetrodon was a pelycosaur, a group of animals that featured characteristics shared by both mammals and reptiles. It lived millions of years before the dinosaurs, and sported a very tall sail on its back.

 

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Spinosaurus, a sail-backed dinosaur...

...and Dimetrodon, a sail-backed pelycosaur

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Why did these dinosaurs and other prehistoric creatures have sails? Well, for a long time, scientists thought the sails must have been used to help control the animals’ temperature. It was thought that the large surface area of the sail would help to collect heat that would allow the animal to stay warm.

However more recently, scientists have largely moved away from this idea, especially as it became understood that dinosaurs and even animals as old as Dimetrodon were not necessarily the slow, lumbering cold-blooded creatures they were long thought to have been.

So why the sails? No one knows for sure, but the prevailing belief is that they were probably used for display purposes. They may have been vibrantly colored with unique patterns that could help the animal attract a mate. They may also have helped individuals of the same species tell each other apart.

 

Plates and Armor

Instead of spines or sails, some dinosaurs have rows of plates on their backs. We’ve already discussed the spikes on the tail of the Stegosaurus, but it was also covered with large hexagonal plates arranged in two rows along its back. What were these plates on the Stegosaurus used for? Scientists have proposed all kinds of ideas, including the regulation of body temperature, display, and defense, though no one knows the absolute truth of the matter. It has also been proposed that with the added height of the plates, the Stegosaurus could have looked larger and scarier as a method to ward off predators.

 

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The plates of Stegosaurus...

...and the armor and tail club of Ankylosaurus

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Some dinosaurs had large scale-like structures called osteoderms, arranged on their backs like a suit of armor. Crocodiles and alligators of today have similar structures, though those of the dinosaurs were much larger. The  Sauropelta, the ankylosaur with spines on its neck and shoulders, was also covered head-to-tail in armored osteoderms. The Ankylosaurus, a relative of the Sauropelta, was covered in bony armor as well. While it lacked spikes, it possessed a different type of weapon: a bony club at the end of its tail that it could use to smash the legs of attacking predators. While ankylosaurs are the most well-known dinosaurs to feature these tail clubs, they were also found on some other types of dinosaurs, including the sauropod Shunosaurus. Though unrelated, they possessed similar defensive traits. When similar features show up in two unrelated animals, it is known as "convergent evolution".

Armored ankylosaurs weren’t the only dinosaurs to possess osteoderms. They’ve been found on long-necked sauropods, including the Saltasaurus and Malawisaurus, and even on some carnivorous theropods, such as the Carnotaurus. In these cases, the osteoderms are much smaller than those found on ankylosaurs.

 

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The osteoderms of Malawisaurus...

...and Carnotaurus

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Horns and Frills

We’ve discussed dinosaurs with spikes on their necks, backs, shoulders, and tails. But ceratopsian dinosaurs possessed large spiked horns right on their faces, often above their brows, or sprouting from their noses like a rhinoceros, or both. In fact, the word “ceratopsian” means “horned face”. One of the most famous of these dinosaurs was the Triceratops.

Ceratopsians also possessed large shield-like frills on the backs of their heads. In some dinosaurs, such as the Styracosaurus, Einiosaurus and Diabloceratops, these frills featured spiky horns of their own in addition to those on the animal’s face.

 

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The horns and frill of Triceratops...

...Styracosaurus...

...and Regaliceratops

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What were these horns and frills used for? If you’ve been reading along, you can probably guess the most common theories. The horns are believed to have been used to defend against predators, and to aid in battles with one another. Triceratops’ skulls have been found with horns bearing healed wounds from Tyrannosaurus Rex teeth, so it’s known that the two dinosaurs engaged in combat, and that the horns could be used to protect the Triceratops.

How about the frills? The popular belief is that they were used to protect the ceratopsians’ vulnerable necks, from attacks by both predators and each other. They may also have been brightly colored and patterned, with such ornamentation used to scare off predators or impress potential mates.

During the hundreds of millions of years in which they were the dominant life form on Earth, dinosaurs developed a wide variety of unique structures and features. There are far too many to fit in a single blog post, and what we’ve discussed barely scratches the surface. In addition to that, new discoveries are helping to change and shape our understanding of dinosaurs every day. Who knows what we’ll discover next!  

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