Friday, 22 May 2015

Standing Tall: Stegosaurus

This blog was never conceived with the intention of filling it with speculative palaeoart, but it's as good a place as any to put it. Stegosaurus has had a fair bit of coverage in recent months, with the NHM's mount being used to estimate the animal's mass, and Saitta 2015 looking at apparent differences in individuals' plates to determine the animals' genders. Padian and Carpenter disagreed, and Theropoda looked at the health implications of stegosaurs dragging their tails (such as constipation).

Superb illustrations by John Conway and Mark Witton got me thinking about those plates. Palaeontologists have put forward various ideas regarding their purpose, the most popular of which being thermoregulatory aids, display structures and defensive structures. In nature, structures often have multiple functions, with secondary functions being unrelated to their primary function. Feathers, for example, probably developed initially for insulation, but could have been easly modified for use in display, either through behavioral means or by changes in pigmentation. Structural modification of the feather - and other key anatomical features - then endowed the owner with an aerodynamic advantage.

That's a long-winded way of suggesting that Stegosaurus's plates probably did not perform one single function. Some of that's already been touched on in this earlier post, but I'm keen on the idea that part of Stegosaurus's display is concerned with how tall an individual looks, i.e., how much vertical space it occupies, especially in the eyes of potential mates, conspecific rivals and would-be predators. With fuzziness now known to be present in (some) ornithischians, I'm happy to speculate that some stegosaurs may have used stiff fur or 'fuzz' as it's often called, to extend the margins of the dorsal plates. Many palaeoartists, palaeoillustrators and palaeontographers already restore those dorsal plates with a sizable soft-tissue (see comments) keratinous extension. An additional growth of stiff hairs as a light-weight projection could, in theory, increase the size of the plates' appearance. Compared to a bone-and-flesh plate, the hair component would be less demanding on the animal, given that once the hair as at the surface, it's a dead structure, and no longer requires a blood supply in order to maintain it.  Of course, if it's concerned with sexual display, it may be renewed seasonally, and shed after mating. This would get around the problem of it getting trashed through day-to-day activities, and filling up with dirt, mould and parasites - which nobody wants.
Stegosaurus stenops, displaying some serious fuzz. Not unlike a filthy old coconut husk. (Copyright © 2015 Gareth Monger)
Anyway, it's just a thought. And this post is supposed to be short and sweet, like the Holocene.

Next up: Yi qi (again).


  1. Hey Gareth. There's a stegosaur specimen that has part of the external keratinous sheath to one of its plates preserved. Reveals vertical corrugations.

    1. Thanks Darren. :) My bad for using 'soft tissue extensions' for the plate sheaths, when I meant 'not bone'. At the risk of sounding like I'm splitting hairs (sorry, awful unintentional pun - but pedantic is too strong a word) I was hoping the hairs would appear as originating somewhere near the base of the plates and following their contours. There are corrugations, but the whole affair is so ambiguous, what with hairs running parallel to them, that it's not really possible to make the details out.

  2. "Short and sweet, like the Holocene" -- What an ominous thought!