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They are among the most famous and the most recognizably bizarre of all dinosaurs. This episode, we discuss the fossil record, evolutionary history, and many morphological mysteries surrounding Stegosaurs.
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The Plated Dinosaurs
Few dinosaurs are as instantly recognizable as Stegosaurus, with its unique profile, short front arms, small head, and massive back plates. In fact, these features are common to a group called stegosaurs, the plated dinosaurs. These quadrupedal herbivores lived all over the world from the Middle Jurassic to the Early Cretaceous.
Top left: Tuojiangosaurus by Paleocolour, CC BY-SA 4.0
Top right: The (relatively) small Huayangosaurus by Nobu Tamura, CC BY 3.0
Bottom left: Long-necked Miragaia by Nobu Tamura, CC BY 3.0
Bottom right: The famous Stegosaurus by Fred Wierum, CC BY-SA 4.0
These dino images are not all to scale with each other!
Stegosaurs, like their cousins the ankylosaurs, carried around characteristic body armor. In stegosaurs, this armor includes rows of plates and/or spines along the back, two pairs of spikes at the tip of the tail, and sometimes spikes sticking out of the shoulders.
Right: Other stegosaurs like Kentrosaurus had spikes along their backs and on their shoulders. Photo by LoKiLeCh, CC BY 3.0
A Unique Suit of Armor
For well over a century, paleontologists have puzzled over the function of the back plates of stegosaurs. It might be that they served some form of defense, and it might be that they had some role in regulating body temperature, and it seems very likely that they were display features not unlike the elaborate headgear seen on other animals.
Image by Tim Evanson, CC BY-SA 2.0
Less puzzling are the spikes at the end of stegosaur tails. This apparatus – four sideways-pointing spikes on a stiff tail – is called a thagomizer thanks to a Far Side cartoon. Like the tails of ankylosaurs, stegosaur tails were formidable weapons. There are even fossils of predators like Allosaurus with injuries seemingly induced by the mighty swing of a thagomizer.
Top: Thagomizer at the end of Kentrosaurus‘ tail. Image by FunkMonk, CC BY-SA 3.0
Bottom: An isolated thagomizer. Image by Kevmin, CC BY-SA 4.0
Learn More
Stegosaurs, an overview (technical, open access)
Stegosaurus, an overview
Stegosaurus Plate Debate (Smithsonian Magazine, 2012)
The Stegosaurus Plate Controversy (Tetrapod Zoology, 2016)
The Double Dinosaur Brain Myth
About Thagomizers:
Watch Out for That Thagomizer! (2011)
Kentrosaurus Had a Formidable Swing (2011)
Allosaurus Died From wStegosaur Spike to the Crotch, Wyoming Fossil Shows (2017)
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If you enjoyed this topic and want more like it, check out these related episodes:
- Episode 21 – Dinosaurs, an Introduction
- Episode 69 – Ankylosaurs
- Episode 87 – Ceratopsians (Horned Dinosaurs)
- Episode 101 – Sauropods
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