If you want to kiss the sky Better learn how to kneel (On your knees, boy)

By jiminy, there are a lot of fat people around nowadays. Apparently, one in five people in Britain are clinically obese: a worrying figure, but nowhere near as harrowing as the one in three obese people that offset the planet’s gravity in the U.S. I’m nowhere near being lumped into this category and, to be honest, I never want to be: not that I have a problem with other people carrying a few spare tires, you understand, but obvious health defects suggest that my scrawny build is preferable to the more spherical builds that can be seen roaming around my local high street. However, I do have cause to wonder whether obesity is as common as it’s reported to be: go shopping in any outlet store and the only sizes left of anything are extra-large and extra-extra-large. Having never really grown into a suit bought many years ago when I was still a lanky adolescent, I’ve spent the last few days hunting down a new suit that acknowledges my still-lanky adult build and, to my dismay, hardly any shops carry suits with jackets with 38 inch-chest sizes and 30 inch-wasited trousers. No, only extravagantly proportioned individuals to reap the benefits of discount shopping, leaving me a frustrated and suit-less individual. Thing is, it appears that none of these big people go the shops to buy this stuff: where are they all? Just where are these fabulously dressed supersized individuals that should exist if so many huge people are around? If obesity is rising, this is clearly an influential factor: all the small people are trying to gain enough mass to fit discount threads from the outlet stores.

It turns out that the sizes of some pterosaurs have been over-exaggerated, too. Some folk may be aware that some initital wingspan estimates for Quetzalcoatlus were well over 20 m, and a certain member of my research group would no doubt like to forget claims of a 25 m span pterosaur leaked a few years back (note that rationale and reason have tempered both claims: Quetzalcoatlus probably spanned around 10 m or so, and the footprints and ‘wing finger’ of the Gargantuadactylus [my term, not theirs] turned out to be bogus). Even wingspans for everyone’s favourite pterosaur, Pteranodon, have been overhyped at one stage: a bigass skull belonging to an older Pteranodon species than the pointy-crested form we’re used to was suggested to represent a Pteranodon spanning 10 m across its wings. In actuality, this robustly skulled form (P. sternbergi) was probably the same size as other big Pteranodon, spanning 6 – 7 m. Thing is, in an eerie echo of my rigorously tested fashion-based conclusions on overstating obesity, it turns out that most Pteranodon weren’t that big at all. Oh no: most were considerably smaller, and the explanation reveals a surprising amount of detail about the lifestyle of a long dead animal.

We’ve known about Pteranodon for well over a century – the first remains were found in the chalk deposits of Kansas back in 1870 by expeditions outfitted by the famous American palaeontologist, Othniel Marsh. In the years between then and now, well over a thousand specimens of this animal have been recovered and, subsequently, despite the fact that every Pteranodon fossil is squashed to wafer-thin proportions, we have enough specimens to form a pretty comprehensive idea about skeletal anatomy and gross proportions. Aside from its enormous, toothless jaws and striking headcrest, Pteranodon gained notoriety as the first truly giant pterosaur, an animal capable of competing with the wingspans of the aircraft being developed contemporaneously and pebble-dashing the size records held by pterosaurs from English Weald deposits. Pteranodon’s size attracted the attention of numerous aeronautical researchers trying to figure out how such an oversize animal could fly, and, as a brief aside, a consensus seems to have emerged that it represents an ultra-efficient dynamic soarer, cruising over the Western Interior Seaway that once divided the North American continent hundreds of kilometres from the shoreline. From a nice bolus of regurgitated gut content we know made its living by eating comparatively tiny fish, so, for once, the idea of a pterosaur mirroring the lifestyles of seabirds is sound. Finally.

Getting back to size, the notion of Pteranodon being a 7 m span giant has become entrenched in pretty much any piece of popular pterosaurs literature, so why should we start to doubt it now? The man to ask is Chris Bennett, the chap who we owe most of our modern understanding of Pteranodon to. Bennett has toured the globe in a quest to scrutinise, measure and identify every Pteranodon specimen available and left nothing but a trail of categorised and identified pterosaur bones in his wake. Such an analysis revealed a pretty startling fact: all specimens of Pteranodon can be neatly placed into one of two groups predominately differentiated by their size. The larger of the two groups (66 % of our Pteranodon specimens) contains the smallest individuals - forms with wingspans of no more than 4 m. All right, this is still much larger than any modern bird, but for a pterosaur, and a Late Cretaceous pterosaur at that (the Late Cretaceous is when pterosaur size really went nuts), 4 m is a very average wingspan. The other 33 % of our Pteranodon samples attained spans of 6 – 7 m, values far more familiar to those reading The Big Boys General Guide to Pterosaurs. Now, this could of course reflect different growth stages - year classes, perhaps - but close examination of Pteranodon bone texture reveals that our entire sample represents adult or close-as-dammit-adult specimens. Yes, dear friends: the plot thickens by the minute.

Not so close examination reveals that further details distinguish these groups: the smaller animals have much shorter headcrests than their larger counterparts, structures that can be as long as the jaw itself in particularly well-endowed individuals. The jaw tips follow a similar narrative: the big guys have prominently developed upper-jaws that end in blunted tips and overbite the lower by some margin, whereas the smaller have more equable upper and lower jaw lengths. Away from the skull, one further difference is found in the pelvis: relatively speaking, the small Pteranodon have deeper, broader pelvic canals than their oversize counterparts. These differences are not so marked in the ever-so-slightly-immature Pteranodon specimens and, apart from these differences in headgear and pelvises, the skeletons of each morph are essentially identical. Now, the lazy and boring explanation for all this is ever-so-slight speciation of Pteranodon species, but a far more interesting and plausible conclusion can be drawn: Pteranodon was sexually dimorphic.

I don’t know about you, but I think everything about this is unbelievably cool. Firstly, the very fact that we have enough data to deduce that Pteranodon was dimorphic is pretty amazing in the first place, but we can also make a damned good stab at figuring our which morph represents which gender. To do this, we need to investigate their reproductive business ends. Guys don’t really have to do much when it comes to reproduction – in fact, our reproductive gear requires very little muscle anchorage at all. Hence, a male Pteranodon would only really need a narrow pelvic canal to house the last vestiges of its guts and little else. By contrast, a female Pteranodon would have to lay eggs, requiring a broader pelvic canal to facilitate their passage. Seeing as we see relatively broad canals in the smaller morphs, we can make the assumption that the big Pteranodon are male, and the smaller ones female. With that sorted, we can make some comparisons with modern animals and draw some basic conclusions about Pteranodon mating behaviour based on the conventions of dimorphism demonstrated by modern forms. Neat.

Focusing on the males, then: what makes a male Pteranodon? Large body size and showy headgear, apparently. It turns out that there is actually a lot of variation in crest and jawtip shape and size: some males had straight crests when others were crescent-shaped, and some jaws were relatively pointed when others were blunt. The fact that immature specimens don’t have the headgear of fully-grown males tells us that they were only useful in adulthood, so we can hypothesise that they had some role in reproductive behaviour, the only behavioural category reserved for adults alone. Male Pteranodon may have flaunted their crests and jaws around in competition with each other for sexual resources and we might infer that, if competitive structures and competition intensity were as closely related as they are in modern animals, the large size of the display gear in Pteranodon indicates short, intense periods of inter-male competition. Furthermore, we (or, at least, I) might go so far as to speculate that their relatively massive proportions indicate that some contests came to physical bouts of strength, possibly explaining some of the injuries riddling various Pteranodon specimens. Furthermore, we can postulate that male Pteranodon were promiscuous buggers: strongly dimorphic animals tend to be polygamous, or, in other words, will happily have relations with multiple partners. We can imagine male Pteranodon competing with each other for harems of females or, alternatively, competing continuously until a cute little lady came over, quickly having his way with her, then returning to the fray to grab more attention while she flies off to develop and lay her eggs. Female Pteranodon, by contrast, have it relatively easy: with promiscuous males battling each other for access to their eggs, all they have to do is wait for the victor to see off his competition and await the delivery of the highest-quality Pteranodon sperm going - hence their smaller body size and lack of ornamentation.

Of course, a lot of this borders on speculation, but it is informed speculation based on some pretty solid observations on modern animals. Sure, we can never be sure that we’re totally correct in our interpretation, but the fact that we can make informed inferences about mating behaviour in any animal that’s been dead 80 million years is pretty remarkable on its own. If nothing else, it demonstrates how generalisations of fact – even something as simple as the size of an animal - can hide some pretty amazing details. Hopefully, the picture I’ve drawn above of a big Pteranodon sternbergi and his harem captures some of these points. Everything about the male is meant to reflect his competitive lifestyle: not only is he astoundingly big compared to his fairer sexed counterparts with a metre-long, robust skull, but he also bears an imposing dark integument to intimidate his rivals. Note that when standing he would be much taller than shown here: the picture shows him rising from lying down in the fashion demonstrated by long-limbed mammals: pushing off with his wrists and onto his back legs. This guy is meant to be quite old, too: hence the shocks of grey hair. I wanted to make him look like the last critter on Earth you would ever want to pick a fight with: I like to think the whole reason he’s standing up isn’t to run away from the impending storm approaching from the right, but rather to go show that storm who’s boss. Comparatively, the females are slender skulled, delicately built and lightly coloured: their colouring matches the functional constraints of their seabird-like ecology far more than the male’s. A few other details are included here: notice the absence of cliffs on this section of the Western Interior Seaway shoreline. Cliffs are often cited as necessary for pterosaur take off and, ironically, studies on Pteranodon are often the rationale behind such claims. Well, guess what, buddy: we don’t have any evidence of cliffs along the Western Interior Seaway (at least, not along the eastern side), so that argument may be flawed. Notice that there’s shingle on the mudrock, too. Ever see a pterosaur on a shingle beach? Me neither. So I thought I’d paint it. You know, just for kicks.

Anyway, this is already too long. Thanks to all those who’ve already commented and said nice things about the picture – most appreciated. Incidentally, this picture has been drawn to feature in a top-secret project being worked on by the yuppies of the pterosaur world. Along with myself, it involves he likes of internet palaeontologists David Hone, Darren Naish and John Conway: Darren's Tetrapod Zoology (just celebrating it's second birthday, dontcha know) may well be known to lots of regular readers, but less well known may be Dave's (and, um, the University of Bristol's) Dinobase, a collection of all sorts of information on everyone's favourite Mesozoic reptiles. Be sure to check out the forum on this site, too: many of Dave's deepest neuroses can be found therein. Finally, John's artwork and projects are a must for anyone who wants to understand pterosaur anatomy and see amazing images of pterosaurs and some other ancient beasties. Right, that should do for now. Until next time, so long…