Typically, pictures that I draw are posted on this here medium pretty quickly after they’re finished, sometimes in such a flurry of activity that I later feel the urge to remove them, finish them properly, and upload them again. Not so with this image: this one has been lurking on my hard drive since April, waiting for an embargo lifted only hours ago before it could be revealed to the rest of the world. Yes folks, I’m pleased to announce that this is another press release image drawn to illustrate the findings of a brand spanking new scientific paper. Although my pictures are slowly trickling into other publications, this is only the second picture I’ve drawn to order. It accompanies a new paper in PLoS Biology (synopsis here) that presents findings of biomechanical and anatomical research that suggests pterosaurs could not skim-feed in the manner of the skimming bird, Rynchops. This idea is pretty entrenched in pterosaur literature and certainly needed some serious testing given that, as we’ll find out in a minute, it’s quite a bold claim that should’ve raised eyebrows a long time ago. As such, it was only relatively recently that Stuart Humphries of the University of Sheffield, Richard Bonser (University of Reading) and Dave Martill (University of Portsmouth) finally addressed the issue head on. I should point out that these chaps were not alone in their studies: there’s one more author on this paper, too. It might be early hours of the day, but please pop the corks from the Champagne and raise your glasses to toast what for me is a most momentous day: Mark P. Witton is now, officially, joint author of a technical, peer-reviewed publication. What’s more, I can proudly proclaim a reasonable chunk of the manuscript was researched and penned by myself, so my name has not been stuck on there to commemorate my making of coffee whilst real scientists did the hard work. Furthermore, PloS Biology has the highest readership of any biology journal in the world and several press agencies have been in contact with me and the rest of the team to write their own pieces on it, so it’s not turning out to be a bad entry into the world of technical publications. Time will tell how far our story runs, but for the time being, words fail to really sum up just how excited this makes me. I suppose, in case you can’t tell, it will suffice to say that I am very, very happy about this.
But that’s enough self indulgence: what of the paper itself? Well, the story of this project has a bit of a prologue, beginning way back in 2002 with the publication of the pterosaur Thalassodromeus. This enormous Brazilian pterosaur has a peculiar, apparently laterally compressed jaw that was suggestive to its describers of a ‘skimming’ lifestyle. ‘Skimming’ is a highly specialised foraging technique employed by a group of birds imaginatively titled ‘skimmers’, or Rynchops in scientific circles. Skimmers feed by flying extraordinarily close to the water surface with their lower jaws (mandibles) trawling through the water to catch any prey items they may strike. They tend to do this in shallow waters around marshes and estuaries to concentrate their prey into a shallower water column, and you can expect a skimmer to snag a morsel of food every five minutes or so. This feeding method is pretty much unique to skimmers, with only the closely related terns showing any other skimming behaviour on occasion. You may justifiably wonder why this is, and the apparent answer is that skimming is more difficult than it looks. In order to compensate for the tremendous drag and impact forces that occur in skim-feeding, Rynchops has evolved a hyper-thin, knife-like mandible for cutting through the water, additional bracing around the jaw joint to prevent jaw disarticulation during skimming impacts and ultra-robust neck anatomy for the same purpose. Bear in mind that catching relatively small prey on constitutes a proportion of skimming impacts: skimmers also snag submerged obstacles and substrata that can wipe them out of the air and snap their beaks. For this reason, skimmers have extra-long extensions of their mandibular beaks formed from quickly regenerating soft tissues to allow snapping of their bill tips. As feeding strategies go then, skimming is up there with eating McDonalds food in not being for the faint hearted.
It is perhaps surprising, then, that the workers behind Thalassodromeus should have proposed skimming as a lifestyle for their sexy new pterosaur. In fact, these chaps went as far as to name their beast ‘ocean runner’ in Latin in reference to its supposed lifestyle. A look into the history of pterosaur research reveals that this was only the latest in a long line of proposed pterosaurian skimmers: as early as 1912, folk were proposing that Rhamphorhynchus was a skimmer, with Pteranodon, ornithocheirids, dsungaripterids and even the giant azhdarchids all postulated as skimmers by the turn of the millennium. Thalassodromeus, therefore, was merely one more form on the skimming bonfire, but one that, with a supposedly-knife like mandibular tip, was far more likely than the other postulated skimmers. However, the skimming hypothesis already smells a rotten here: as animals become bigger and heavier, flight becomes more costly. Some of these proposed skimmers were huge – could they really provide enough muscle to, erm… muscle their way against all those skimming forces?
These were the questions that Stu, Richard and Dave set out to answer. At this very early stage, I was still finishing my degree and the plans for the experiment were set out to my total ignorance. Hence, by the time I was first introduced to Stu and Richard (I knew Dave already, being my thesis supervisor and all) in the first few weeks of my PhD back in 2005, some trial runs of the experiment had already been run. Stu, Dave and Richard had come up with the idea of testing the skimming capabilities of pterosaurs by literally pulling mock-ups of their jaws through water down a 10 m flume tank housed at the University of Portsmouth. We had two pterosaur jaws to test, that of the purported skimmer Thalassodromeus, the non-skimmer Tupuxuara and the mandible of Rynchops for comparative purposes. The jaws were underslung from a trolley that ran along the top of the tank, itself pulled along by a motorised winch at the tank end operated by Stu. Gathering all our data was a stress sensor recording the forces experienced by a 3 mm thick aluminium bar connecting the jaw tip to the trolley during the towing. It all sounds pretty slick, and it was, save for the fact that 10 m was enough distance to get the jaws up to speeds of 25 kmph (or almost 16 mph for those who refuse to go Metric), but not enough to slow it down. Hence, some poor sod had to stand on a ladder to catch the screaming hell-banshee that was the skimming dolly or else it, and all the paraphernalia and models it was carrying, would shoot off the edge of the tank into a rather expensive disaster on the floor. The day I met the skimming team also marked the first day of testing, and Dave and I took it in turns to do act as catcher for the dolly. All was going relatively well, with good data recorded for Rynchops and Tupuxuara, and then, as I climbed the ladder for my turn, Thalassodromeus, the ocean runner itself, was loaded onto the trolley.
In all the press accompanying the publication of Thalassodromeus, one worker is recorded as saying it must’ve looked like a ‘vision of hell’. Well, hats off to him: he was right. There was something unerringly terrifying about the massive jaw tip of this thing hurtling towards you at great speed. Maybe it’s because there was water everywhere. The moment Thalassodromeus began to skim, the whole rig started shaking manically, throwing water about like a possessed jetski and drawing worried glances from the crew. Notching the speed higher, the rig became more unstable and, to everyone’s surprise, the aluminium bar was even bent on one run. This was replaced and, eventually, the time came to set max speed: 25 kmph. The catcher, a nervous looking PhD student, was braced and ready. At the other end of the flume, the pterosaur-cyborg beast glared at him, the water eerily calm before the violence that would follow. “You ready?” asked Stu, and I gulped my affirmative. The winch was pulled. Suddenly, the beast was roaring down the runway. The room echoed with the inhuman screaming of its wheels on the track. The jaw was convulsing madly. Water crashed over the tank walls. Then the screaming stopped with a loud bang: the Thalassodromeus was airborne; the whole rig arcing through the air and spiralling forward - only milliseconds seperated it from a watery grave. My clothes ripping against the metal tank and the waves pounding my body like Achilles in the River Scamander, I leapt forward and grabbed the plummeting contraption moments before it hit the water. We rushed the wounded rig from the flume to check its health: the aluminium bar was totally twisted, the electronics shot. The little blinking lights on the mechoreceptor faded to black. The rig lay dead in Richard’s arms. Stu called to the Heavens in anger. Dave cried. I was soaking wet. It was about then that we started wondering if ‘ocean runner’ was a name slightly too optimistic about the skimming capabilities of its owner. With testing brought to a dramatic but premature end for the day, we retired for back massages and herbal treatments from attractive Scandinavians to recover from the ordeal. Such is the life of courageous university researchers.
The second day of testing (actually a number of weeks later) went by pretty smoothly, and it wasn’t long before we had enough data to call a halt to the testing and start work on the manuscript. It was about this time that the idea occurred to us that we should also check out pterosaur skulls – after all, if Rynchops is so specialised for its skimming lifestyle, we should see similar traces of specialisation in pterosaur skimmers, right? So, while Stu and Richard crunched the numbers obtained from our fluming exercises, I went to work looking into the skimming adaptations of a whole bunch of pterosaurs. First and foremost, the shapes of pterosaur bills: turns out that not one, even Thalassodromeus has a bill even remotely like the razor-thin bill of Rynchops. Granted, Thalassodromeus has a tapered upper margin on its mandible like those of skimmers, but its mandibular tip is still incredibly fat – with all the drag this would produce, it’s no surprise it shook itself to pieces in the flume. Jaw joints were next: any adaptations to withstanding impact forces? Uh, no. Pterosaur jaws are really pretty flimsy – more like those of non-skimming birds than the doubly reinforced jaw of Rynchops. Necks? Also nothing special, although Thalassodromeus and Tupuxuara score points for being more flexible than most. Long-necked azhdarchids, by contrast, would’ve snapped their necks the moment they skimmed anything with more resistance than snot, and that’s probably enough to shoot their skimming prospects down on its own. As it was, while I was buried in books the results from the number crunching came back: turns out that Thalassodromeus and Tupuxuara were on the wrong side of the graph to be skimmers, whilst Rynchops was comfortably the right neck of the woods – er, marsh – to skim happily (lucky for us, really – it’d be a bit embarrassing if we proved that skimmers couldn’t skim). What we’d found was basically a problem of scaling: the bigger pterosaurs, in association with their relatively broad jaw tips, appear to have had insufficient energetics to both flap their wings – even incorporating some gliding into the equation – and skim at the same time. Interestingly, our modelling suggests that skimming is even more energetically demanding than it appears for Rynchops, highlighting the necessity for that blade-like bill to reduce drag. Using the mandible of Tupuxuara as a model, Stu then played around with some bigger pterosaurs: the 6 m Pteranodon and 10 m Quetzalcoatlus, both of which have been postulated as skimmers at one point or another. Neither made the grade, especially when we (just to cover our backs) extended their mass estimates from ‘consensus figures’ to the highest published mass figures out there. Conversely, our model suggested that small pterosaurs might be able to skim with the right equipment, but, as no known pterosaurs appear satisfactorily geared in this respect, we feel pretty damn confident in saying that no pterosaurs were regular skimmers. In fact, based on their jaw morphology alone, I’ve been wondering how the idea gained any following in the first place. Why do people latch onto these ideas when all the evidence is to the contrary? How do these proposals ever get through peer review to begin with? Mind you, I’m sure lots of people would say the same thing about many of my proposed pterosaur ecologies, so I shouldn’t get too high on this soap box. I just figure that some ideas about ancient animals are a bit too larger than life and could really do with more thought before publication. This is not to criticise people coming up with new hypotheses of course – I just think that suggestions of this nature should be mulled over, researched and tested more before they’re released to the world, s’all. I’ll stop ranting now.
Even once we knew what we wanted to say, it took a long time to get this paper together. At one point, we had a pretty major re-write after several reviewers suggested the initial submission was overly brief. If one thing’s become apparent since I started all this academic stuff, it’s how long everything takes. Other projects turn up, personal commitments take you out of the loop for a while, silly pieces of bureaucracy suck your time away… It all conspires to push projects like this on and on, and it’s nearly been two years since the first run in the flume tank. Still, it’s all been worth it: a neat little paper that I hope will be well accepted, a place in a top journal, lots of press interest and the promise of being on Radio Four this Thursday (21:00, 26/07/07, pterosaur fans). Plus, and most happily for me I suppose, there’s another press image to put on my C.V. This was an interesting picture to draw, actually: there are pictures a-plenty of skimming pterosaurs, but we naturally didn’t want to show this as it conflicts with our findings. Problem is, how do you draw a pterosaur not skimming? All right, that has a rather obvious answer, but how can you show a pterosaur not skimming meaningfully? You know, to make the point that it can’t and all? The answer came to me from bitter personal experience: school discos. As anyone who’s ever met me will know, I am not really the dancing type. No, I can’t get funky for love nor money, and I’ve never been able to. Hence, while all the fun and excitement was going on at school dances, I tended to sit on the side, watching the spinning, dancing and twirling of my chums as I sucked on a Coke and waited for home time. Nothing quite says ‘I can’t dance’ more than a guy sitting on his own at the side of the dancehall, so I figured nothing would say ‘I can’t skim’ more than Thalassodromeus, the fallen wave-runner, sitting on a riverbank whilst Rynchops, having the time of his life, whizzes by in a skimming frenzy. Although I’m pretty happy with it, I’m especially glad that Rynchops has come out all right: it’s rare that I draw anything from modern times that you can directly compare the real McCoy, so the fact that it looks pretty Rynchops-like is a relief.
And on that note, I’ll finish. All that’s left is to thank Stu, Richard and Dave for inviting me in on the project and congratulate anyone still reading this marathon essay – this is the longest post on this site by a long way. As always, thanks for reading.