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).

My Home, The Sauropod - Part I: Getting Filthy

The idea of an organism playing host to a multitude of other organisms is well known, and is something which most of us are familiar with - even if it's only through catching headlice at school or pushing a worming tablet down a cat's throat. On a smaller scale, there are gut bacteria, some of which perform an important role in keeping the digestive tract healthy. Others are less helpful, as those who frequent dodgy kebab shops will testify - if they're still alive. And it's not all restricted to Animalia, with trees being well-studied examples of a complex ecosystem centred around an individual.

It's not just about parasitism. Sharks, large fish, turtles and whales are often seen with a posse of remora, unusual fish with a sucker-like organ on top of the head, allowing them to hitch a ride. They take advantage of a steady food supply, in the form of particles of food dropped by the host animal, sloughed skin and faeces, but they also help keep the host healthy by consuming parasites which may attempt to adhere to its surface. In return, the host doesn't (always) eat them. On land, large mammals may be parasitised by blood-sucking invertebrates, but these, in turn, may be preyed upon by birds, which the larger mammals are big enough to bear the weight of - and the additional irritation. So, there's a constant battle being enacted on and in many animals, by other organisms, and often this affects the way these animals look and behave. A consideration of how parasites, symbiotes and associated organisms interacted in ancient settings may steer palaeoart in the direction of increased accuracy. It may also result in depictions which look rather different to what we're used to. After all, nature isn't always a tidy place.

Now, portraying these kinds of interactions probably drops this type of speculative palaeoart somewhere in the All Yesterdays camp. Of course, it's only 'speculative' with regard to how one might decide to show those interactions; they undoubtedly happened, but fossilised remains of those interactions are exceedingly rare. And not all of those interactions will be targeted encounters between a parasite or symbiote, and host, and this is what I have attempted to show in the following sketches.

Sauropods represent an interesting branch of Dinosauria, and include the largest terrestrial animals ever to walk the earth. The idea of these keystone species forming some sort of walking ecosystem is an attractive one, as they no doubt carried a contingent of parasites which may have attracted animals which predate those parasites. In addition, they may have provided a perch for flying reptiles and insects, and a surface for non-parasitic organisms to grow on. It's probably also not unreasonable to imagine some sauropods accumulating leaf litter and a twigs, especially if one restores certain species with a row of spines and other ornamentation, as some palaeontologists and artists do. It's hard to imagine sauropods successfully ridding themselves of all the material which rains down on them from the forest canopies under which they must have spent some time. That's not to say an apatosaur would never have dislodged accumulated forest junk from its back, but it would probably have found cleaning itself with any kind of precision difficult.

An apatosaurine sauropod, sketched up quickly and based on Scott Hartman's 'Apatosaurus' excelsus skeletal illustration. The dorsal spines form a trap for falling leaf and branch material, whilst the mosaic of scales and osteoderms provides a surface on which lichen fragments and diaspores adhere.  (Copyright © 2015 Gareth Monger)

That probably looks like a lot of twigs and branches, but these are long-lived animals which may have spent a long time in wooded environments. A smooth-backed sauropod probably won't accumulate twigs in any appreciable quantity, but you might expect to see a bit of lichen growth, especially on those surfaces which see little abrasion from rubbing against trees and other surfaces, or areas of skin which experience minimal flexing. A sauropod might look rather colourful - and different - if adorned with a collection of brightly-coloured lichens, dried on leaves, and small branches. And different populations of a single species might look different, depending on the differences in the vegetation of their respective home-ranges.

An apatosaurine sauropod, as viewed from above, wandering through a pine forest. Dead twigs and branches constantly rain down onto the forest floor, with some inevitably landing on passing sauropods. Reference photo: SV-POW! (Copyright © 2015 Gareth Monger)

For the fans of wild speculation, it might be fun to imagine that certain sauropods used a pile of vegetation in sexual displays, with those male sauropods carrying the largest pile of woody compost most likely to attract a female. Behaviour is one aspect of palaeoart which is wide open to ideas. You've only to look at extant animals' courtship displays to realise that from the future skeletal remains of, say, the bird of paradise, you'd never come close to guessing how they go about impressing a potential mate. There's every reason to think that some non-avian dinosaurs could have been at least as weird. And for palaeoartists, that's where a little imagination can prove useful.

Next up: some more thoughts on Yi qi...   ...and maybe something quick on Stegosaurus.

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.