Here is a pre-1923 drawing of Stegosaurus stenops, the most distintive of the Stegosaur family. The challenge for scientists is to make sense of the remains that they find which are essentially the solid parts of the animal which, in the case of the Stegosaur, included the twin plates running down the back and the spikes on the tail.

In the case of the Stegosaur several explanations have been proposed for the the plates running down the back and the spikes on the tail. Originally they were thought to be for protection. With the mindset of protection, little thought was given to the colour of the animal in general and the plates in particular. Colour depictions drew on the colour scheme of the dinosaurs living relatives, crocodiles. Thus were saw dinosaurs depicted as a brown-green colour as per the image below.

The structure of the plates, however, does not support their presence as a protective structure. They consist of a layer of dense bone surrounding a latticework of bone that would be like biting through a sandwich.

Kevin Padian, professor of integrative biology at the University of California, Berkeley proposes that analysis of stegosaur plates supports the idea that they were decorative and served no function other than to differentiate species, akin to birds' colorful feather ornamentation. He says

We cut up and compared the internal structures of stegosaur plates and the smaller scutes of their ancestors, and found that a functional explanation for these plates doesn't make sense for all the stegosaurs. So we think that they're more likely involved in some type of species recognition, as with many African antelopes - you have to be different from all animals in the area so you don't get mixed up with other species.

If this is the case then there is little likelihood that they were dull monochrome structures as typically depicted. With this new purpose in mind it makes much more sense for the plates to be much more distinctive,

The same applies for the plate strutures of triceratops.

The planes of the Jurassic period, about 210 to 144 million years ago, may have been a lot more colourful than we originally imagined.

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