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).

Historic Image Problems: Stegosaurus

To the untrained eye it would easy to think of Stegosaurus as one of those dinosaurs which the palaeo crowd thinks it's got right.  What is there to get wrong?  It's an obligate quadruped with a tiny head. Its brain - the front one, obviously (duh!) - was the inspiration for the humble walnut. It was a design so successful that even modern domestic mammals stole it: "Stegosaurus's brain was the same size as that of a kitten." And what of its array of fancy dorsal plates? Two rows of huge, bony diamonds, which chipped Allosaurus's teeth, and warmed the animal on those slow-go mornings. Slow and stupid and lumbering, with an entrance for plants at one end and Gary Larson's greatest achievement at the other. This dated and stagnant image of Stegosaurus is one that it's struggled to shake off.

It's nineteen eighty-something, and this particular less-than-ten-year-old is moping around the house, cursing the extinction event that robbed him of the full-scale versions of the plastic figures he plays with every day.  Feathered (non-avian) dinosaurs aren't being harvested by Chinese farmers yet and speculation about a dinosaurian origin for birds is hardly ever mentioned in the books available to children. (To make matters worse, most of my books are hand-me-downs from well-meaning family and friends and are even more out-of-date than the brand-new ones that my parents occasionally get for me.) The local font of historical knowledge and artifacts, Wisbech Museum, holds a few scrappy dinosaur remains (though some much better marine reptile fossils), but its most important collection, for me, was a tray of Inpro dinosaur toys.

Hideous green blob, driving forwards with its head in the mud.
Not sure of the manufacturer. (Photograph: Gareth Monger)

Stegosaurus by Inpro. Smile, for gawdsake - there are children watching! (Photograph: Gareth Monger

It's fair to say that my earliest exposure to three-dimensional dinosaurs was through Inpro's toys. Anatomically they're what you'd expect of a small, inexpensive museum souvenir. Indeed, I've only ever seen the range available in museum gift shops. The range is a strange mix of static-posed, goofy-looking creatures, and slightly-more-dynamic animals, as if Inpro employed two sculptors - one who already liked dinosaurs and one who didn't know what they were until he clocked in or work that morning. Inpro's Stegosaurus sits neatly in the latter camp. Early film appearances, such as in 1933's King Kong, helped cement the animal's image in the public psyche; why would Inpro not meet the expectations of its customers?

Stegosaurus meets Westerners for the first time, quickly assumes the horizontal position. A scene from the ground-breaking King Kong, 1933. (Photograph: © Warner Bros.)

Stegosaurus does get better coverage in the popular palaeontology literature, but this rarely seems to have filtered back into pre-'90s toys or kids' books, or else we'd have seen more of those toys with alternative plate arrangements or speculative bipedality. It might ultimately have been proven wrong, but it would have at least shown less of a reliance on popular cultural examples which are themselves not necessarily the product of up-to-date scientific process. That's not to say it never happens, but examples are hard to find. (Suggested examples will be added!)

More-recent high profile media appearances include the original Walking With Dinosaurs series and Primeval but, oddly, film fans had to wait until the second installment of the Jurassic Park franchise before they were treated to an ILM Stegosaurus. I find that unusual if only because, when one asks just about anyone to list some dinosaurs, there are a handful of dinosaurian poster boys which nearly always get mentioned - and Stegosaurus is one of them. A minor deviation from the novel gave Triceratops some screen time instead. Inevitably, The Lost Word did show Stegosaurus doing the only thing it knew how to do, other than eating - attempting to thagomize another creature out of existence. To be fair, King Kong, Fantasia and Walking With Dinosaurs all featured angry stegs, too. Angry, angry stegs. 'Death Stegs'.

Left: A Stegosaurus takes on a generic Hollywood theropod, in this case an allosaur seemingly modeled on a tyrannosaur, in Fantasia (© Disney); Right: An Allosaurus interrupts a Stegosaurus in Walking With Dinosaurs, which subsequently murders a young Diplodocus (© BBC)

As far as dinosaurs go, Stegosaurus is pretty well known, from numerous remains representing several species from multiple localities. Despite this, many aspects of Stegosaurus's behaviour and biology remain poorly understood. When one considers how extant organisms possess structures which exhibit multifunctionality, it's easy to see why the dorsal plates and thagomizer may be hard to nail down to a single use. For example, feathers are insulatory, aerodynamic and display structures though one of more of those functions were probably secondary. Common suggestions for Stegosaurus's bizarre array of kite and spike-shaped osteoderms include armour, sexual displays, as warnings to would-be predators and deceptive displays where the individual appears much larger. Palaeontologists are yet to suggest that the plates make Stegosaurus harder for an Allosaurus to swallow.

Hard to swallow: The dangers of not growing massive, inflexible plating.
(Image: © Gareth Monger. NB: This is shoestring palaeoart. At eight quid an illustration, Mike Taylor was outside my budget.)

This week it was announced that a well-preserved Stegosaurus, nicknamed 'Sophie', was going to be the subject of an intensive study in order to improve palaeontology's understanding of the strange, platey beast. Prof. Paul Barrett at the Natural History Museum is leading a team which, having scanned the 80%-complete skeleton, will examine it digitally in order reveal some important aspects of the animal in life, such as its posture, feeding, nutritional demands, locomotion and how it may have used those crazy osteoderms. With luck, the new data will filter quickly into the palaeoart community and new, improved restorations will be seen in books and in the form of children's toys. If any dinosaur deserves that, surely it's Stegosaurus.