Sunday, December 30, 2012

Papers via blogposts

Those keeping up with the pterosaurian literature will be aware that the latest issue of Acta Geologica Sinica has a set of papers resulting (at least in part) from the 2010 Beijing Flugsaurier meeting. (And while we’re on the subject, the 2013 meeting in Rio has extended abstract submissions till the 31st of January, so there’s still time to get them in). I’ve got a couple in there and while people might be more interested in the horribly flattened anuroganthid, I’m more keen to talk about the short review paper I produced.

The title, ‘Pterosaur Research: Recent Advances and a Future Revolution’, might sound familiar and indeed some of the content may too. That’s because it ultimately sprung out of a post that I had over on the Musings and also put up on This is a first for me at least, a paper that resulted pretty much directly from a blogpost.

At the time I’d been writing about rates of discovery of dinosaurs and pterosaurs and what that might mean for future discoveries. It occurred to me that actually the pterosaurs seemed to be going through something of a renaissance in the way that dinosaurs had in the 1970s. We were finding more and more of them, more papers were being published by more researchers, and more of the big questions were either being answered, or at least were being tackled in a rather more systematic way than they had before. It occurred to me that this was worth summarising and producing something more formal. The fact that the next Flugsaurier volume was due meant there was a most suitable venue available and discussions with various colleagues helped me develop the idea and push for it’s inclusion.

If you look back at the developments of the last 10 years or so in pterosaurs, it’s quite a remarkable and rapid progression. That’s not to overlook the huge amount of groundwork that had gone before and the efforts of previous generations, but even quite a few fundamentals that had occurred for dinosaurs decades ago are now being sorted out for pterosaurs. We now have inclusive phylogenies for pterosaurs, we’ve got a good idea of their soft tissue structures and especially the wing, some of the taxonomic and systematics issues of the past are being resolved, we’ve got a major transition in the form of Darwinopterus, cool new taxa like the boreopterids and chaoyangopterids turning up, detailed analyses of flight, take-off, mass estimates, muscle patterns, and skull shapes, we finally, finally, have eggs and we’re even getting serious on behaviour and ecology for analyses of head crests, growth and the like as well as looking at major evolutionary trends like diversification and distribution. We’re even getting attention from the public and serious attention with whole exhibits on pterosaurs, new books, and documentaries, and of course we now have the Flugsaurier meetings themselves, established and (hopefully) regular events that will help keep things ticking along.

So this paper attempts to summarise all of this and in effect provide a statement of the ‘state of the art’ – what do we know and how have we got there, but it is also supposed to be a bit of a celebration of the last decade of research and the gains made by the pterosaur research community. Those in the know will probably realise that the background to this has not been without a significant amount of strife, and while this is not mentioned in the paper, I think it only emphasises how much has been learned despite this limitation. I hope it also provides a sort of counter-point, but also a continuation of Peter Wellnhofer’s piece that kicked off the 2008 Flugsauriervolume. Peter wrote a review of the history of pterosaur research, but pretty much only took it up to the modern era, and with the galloping developments of the last few years, this should bring things more or less up to date.

The paper is available here (and indeed all of the latest papers are from AGS). Just click on the left hand set of the three series of Chinese characters at the bottom of the page and then add a .pdf suffix to the filename once it’s been saved.

Wednesday, December 12, 2012

LACM to Boston: G+ Hangout Interview

I recently did a G+ hangout interview with Lorena Barba's bio-aerial motion class out at Boston University.  I broadcasted from the Natural History Museum of Los Angeles County, along with Justin Hall.  Here's the link on YouTube:

This was our first go with the "On Air" feature, which automatically records the hangout and sends it to a personal YouTube channel.  I talked a lot about pterosaurs, as well as a bit about Microraptor.



Saturday, December 1, 2012

That pesky clearance problem

I have received quite a few questions over the last year or two about wing clearance during takeoff in pterosaurs.  This seems to be a sticking point for some, as evidenced by the problem rearing it's ugly head again with the recent Chatterjee et al. GSA conference spectacular (see earlier posts below).  It would seem prudent to lay out some of the issues surrounding this problem - or, more specifically, to explain why this isn't really such a huge problem after all.

Because of the way that flying animals scale, larger, long-winged species with greater flight speeds flap with lower amplitudes than smaller species (on average, that is).  Interestingly enough, this means that the amount of clearance required by large flyers is comparatively small, so long as they can get up a good bit of speed on takeoff.  To examine this issue more closely and quantitatively for giant pterosaurs, we can look at something call the Strouhal number.

Strouhal Number is a dimensionless parameter that describes the "gait" of a flapping flyer (or really, anything that is oscillating its propulsion system in a fluid).  As it turns out, because of vortex shedding efficiency constraints, animals are remarkably constrained with regards to their Str during cruising flight: it only varies from about 0.2 to 0.4 including everything from insects to large birds.  There is a great explanation of this number, and its application to flying animals, here (I've shared that link elsewhere to good effect).

Str for a flapping flyer can be calculated as the ratio of flapping amplitude to the product of frequency and velocity.  The largest pterosaurs probably flapped at a rate just over 1 hertz in cruising flight, and likely had minimum steady state speeds near 12 m/s and a cruising speed a good bit greater, say around 20 m/s or more. 

Now, during launch, the animal probably only gets up near steady state stall speed (incidentally, it doesn't have to, contrary to what you often read in basic biology textbooks), and the Str can rise above the 0.4 mark that we might expect during cruising.  Let's let the Str rise to 0.50 and constrain the launch velocity to the min steady state stall speed above.  That still gives us an amplitude for the very tip of the wing in Quetzalcoatlus of 5.6 meters.  Of that total arc, about 40% of it is upstroke, so that leaves a required glenoid height at the end of the launch phase of 3.4 meters or so.  Given that Quetzalcoatlus had a glenoid height of about 2.5 meters while standing, it turns out that very little leaping is required at all for sufficient clearance (less than 1 meter).  The animal still needs to jump, but nothing extraordinary is required.