Thyreophora means “shield bearers”. This group of four-legged, plant-eating dinosaurs is made up of two different types – the stegosaurs and the ankylosaurs. Stegosaurs had large, vertical bony plates on their backs and spikes on their tails, while ankylosaurs had backs that were covered in bony scales called “osteoderms” that protected them like a suit of armor. Both groups of these large dinosaurs developed defensive measures to protect them from large predatory dinosaurs that shared their habitat.
Stegosaurs lived in the Jurassic Period, from around 170 to 125 million years ago. They were characterized by their very small heads, the spikes on their tails, and the rows of plates (or sometimes spines) that ran down their backs. By far the most popular stegosaur was Stegosaurus, the dinosaur for which the group is named. This dinosaur likely used its tail spikes to fend off attacks from meat eaters like Allosaurus and Ceratosaurus. Paleontologists have found leg bones from some of these predators that seem to show damage from stegosaur spikes.
The row of vertically flattened plates on the backs of Stegosaurus has long been a topic of debate, both in their function as well as how they were arranged. They were originally thought to have laid flat on the back, like armor. Then, it was believed that they ran down the back in a single row. Later, scientists theorized that the plates were arranged in two rows along the back. Originally it was believed that these rows were symmetrical, which the plates arranged side by side. However, skeletons have been discovered that appear to show the plates were staggered; where there’s a space in one row, there’s a plate on the other side.
But what were they used for? Long ago, when it was believed that dinosaurs were cold-blooded and unable to generate heat in their bodies, it was thought that the plates could help with regulating the dinosaur’s body temperature. Author W.H. Ballou proposed that Stegosaurus could use its plates like wings, flapping them up and down to help it leap and glide across cliffs. This idea was discredited and ignored by most serious paleontologists. Today, scientists believe they were more likely used for display, to help male stegosaurs impress females, or to help different stegosaurs identify each other.
The other group in Thyreophora are called ankylosaurs. These armored dinosaurs are further divided into two groups: the ankylosaurids and the nodosaurids. What’s the difference? Ankylosaurids were wider and featured bony clubs at the end of their tails. Nodosaurids, meanwhile, lacked these clubs, but often had large spikes protruding from their bodies that helped to protect them in addition to their bony armor.
Ankylosaurs first appeared in the Jurassic Period, around 170 million years ago, but were more common in the Cretaceous Period. The group is named for Ankylosaurus, one of the most popular ankylosaurids, that lived alongside Tyrannosaurus Rex and Triceratops, and died out in the mass extinction event around 66 million years ago that was responsible for the deaths of all non-bird dinosaurs.
The purpose of the bony tail club of Ankylosaurus and its relatives is a bit of a mystery, like the plates of Stegosaurus. Many believe the dinosaurs used it like stegosaur tail spikes, as a weapon that could break the bones of attacking dinosaurs like T. Rex. However, baby ankylosaurids lacked the tail club, and it’s believed that it grew slowly as the animals matured. The fact that babies didn’t have the clubs, despite being the most vulnerable to predators, has led to another theory: that adult ankylosaurids used the clubs to fight among their own kind, particularly males fighting with each other to impress females.
Nodosaurids, such as Sauropelta, lacked these tail clubs, but still had more than enough protection from predators. Large and fearsome spikes projected from Sauropelta’s shoulders and its back was covered with armor plating. Dinosaurs like Acrocanthosaurus and Deinonychus (a relative of Velociraptor) were likely its main threats.
Another nodosaurid, Borealopelta, is one of the most remarkable dinosaurs ever discovered. Its remains were amazingly well preserved, with skin and soft tissue that showed how the animal looked in life. Scientists were also able to determine its coloration from preserved cellular structures and discovered that it was reddish brown.
Thyreophorans are often called the tanks of the dinosaur world. With their spikes, clubs and bony plates, these formidable dinosaurs were more than ready for anything their prehistoric habitat could throw at them.
Click on the images above to buy any of the toys shown, or check out these other awesome Thyreophoran dinosaur toys!
Great Dinos Stegosaurus - a great large size toy meant for small hands
Dinos TOOB - featuring Stegosaurus and Ankylorsaurus miniature figures
Dino Fun Pack - featuring Stegosaurus Good Luck Mini figure