Since the first stegosaurus was uncovered during the “Bone Wars” in 1877, the purpose and layout of the plates on its back have been hotly contested debates. The name stegosaurus, meaning “roofed lizard”, relates to the first theory of the arrangement of the plates - as a wide shield over the back of the dinosaur. Scientists today mostly agree that this theory is unlikely to be true, and that the plates more than likely stood upright in the dinosaur’s skin. The function of the plates is still something that remains debated to this day.

Hot Plates

While blood vessels don’t fossilize, the traces of their paths remain. By taking sections of the plates, scientists have noted that there were many of these paths for blood vessels and nerves along the out layers. Having blood vessels so close to the outer surface can be useful for cooling off or heating up, acting as a way for stegosaurus to remain comfortable in a changeable climate. Mammals like elephants and hares use their vessel-rich, large ears for the same function. The structure of stegosaurus plates is like the osteoderms of crocodiles, who also use these little bones to help them cool down.

Decked out with decoration

Blood vessels close to the surface of the plates could also have had a different purpose – display! By engorging the vessels with blood, the keratin covering of stegosaurus’ plates could have changed colour. This would have been useful for several reasons, from attracting mates to threatening rivals. Scientists have also discovered more recently that stegosaurus plates vary widely in size and shape, which would have been useful for recognising your own species, determining gender, or even advertising strength and health to attract a mate.

A deterrent or a defence?

Another theory is that the plates were a defence mechanism. Large, bony structures (especially osteoderms, like those on Gastonia) are a tried-and-true method of defence that has stood the test of time, and perhaps stegosaurus’ adapted osteoderms are no different. In the 1980s it was even suggested that because the plates were only embedded in the skin and not attached to the skeleton that they may have been slightly movable. This would have made it difficult for a large predator such as Allosaurus to find an exposed area to attack. However, most plates have a rounded edge, rather than coming to a point, and this “loose” nature of their arrangement may have made them too weak to fend off a determined attacker.

All in One?

It’s also possible that the plates had multiple functions! Perhaps the stegosaurus was a jack of all trades, using its plates to indicate good health, attract mates, and fend off predators and rivals with a mix of movement and display.

We may never know for sure, but based on the evidence, what do you think?