Frogmouth Pterosaurs

I have (finally) some new material to post.  In addition to the new stuff, I've decided to post some of my past abstracts that might not have been easily accessible to everyone.  Here is my abstract from the GSA Northeast Conference in 2011.  I gave a platform talk on the biomechanics of anurognathids (some of you will already know that Mark Witton and I have a manuscript nearing completion on the topic, as well).

Functional Morphology of Anurognathid Pterosaurs
Anurognathid fossils include several exceptionally well-preserved specimens, some of which include extensive soft tissue preservation.  This exceptional amount of morphological information makes anurognathids prime candidates for functional biomechanical analysis.  Furthermore, anurognathids displayed a suite of unusual characteristics that make them of particular interest for functional study.  These traits included extensive pycnofiber coverings, fringed wing margins, shortened distal wings, shortened faces, and enlarged orbits. Prior authors have suggested that anurognathids were adapted to catching small insects on the wing.  I present a quantitative analysis that supports this general behavioral inference, and provides details regarding probable anurognathid locomotion. Results indicate that anurognathids were exceptionally maneuverable animals.

Bone strength analysis in Anurognathus ammoni reveals that each proximal wing was capable of supporting nearly 22 body weights of force.  The wing spar of A. ammoni was substantially stronger in bending than that of an average bird of the same size (residual of 0.72).  The calculated relative bone strength overlaps significantly with that of living birds that capture prey on the wing (p>0.92) but differs significantly from all other avian morphogroups (p<0.04).  Overall humeral robustness is similar between A. ammoni and megadermatid bats.

Anurognathid launch appears to have been particularly rapid and steep. Once airborne, anurognathid pterosaurs could likely generate high lift coefficients.  Leading edge structure in Jeholopterus suggests that anurognathids were capable of generating a leading edge vortex (LEV) as observed in some living bats and swifts.  Analysis of flapping efficiency suggests that the expansion of the proximal wing, coupled with reduction of the distal wing elements, would have increased flapping power at the cost of increased drag.  The proportions of the wing and details of the shoulder may be indicative of the ability to hover for brief intervals; power analysis also supports this conclusion. These results are consistent with reconstructions of anurognathids as highly maneuverable flyers, preferentially foraging in cluttered habitats on small aerial prey.
 

Microraptor: Odds and Ends

The top image on the left is from Hone et al. (2010) and shows the holotype of Microraptor gui under UV light.  The image below, by Mick Ellison, shows a life restoration of Microraptor, and was taken from here (note: the hindlimbs could not actually get into the position shown in the image; that was done to show off all of the airfoils at once for comparative purposes).   One of the key questions regarding flight in Microraptor is whether it evolved flight independently of avialans, or if it represents a morphology that was a more direct precursor to flight in birds proper.

One thing I noticed a few years back is that it seems that Microraptor had a different set of "solutions" to the problem of aero control, as compared to living birds.  I have since put some math to it, and the calculus bears out the intuition.  Myself, Justin Hall, David Hone, and Luis Chiappe are writing this up now (see earlier cryptic blog post), but Justin has given a couple of talks on the hindwing use recently and some of you out there know that that I have been murmuring about the tail being used in aero control.  All will be revealed in the full manuscript (WFTP moment) but I do think it is quite interesting that the aero control surfaces in Microraptor took advantage of pre-existing maniraptoran anatomy.  In other words, you don't have to do much to your average dromaeosaurid to get it into the air.

This is a potentially critical observation.  For one, it suggests that the origin of flight in dinosaurs may have been more simple than previously supposed.  It also suggests that flight control may have had more to do with the gains and losses of aerodynamically active morphology we see near the origin of birds than simple weight support.  I am sad to say that most paleontologists don't seem to have a particularly good grip on what lift actually is, how it is used, and how it is generated.  Many of my colleagues also seem to struggle with how drag fits into the whole scheme.  Of course, I have lots of gaps in my knowledge, too, so I can't go pointing fingers.  Nonetheless, I suspect that we are going to see a major overhaul of the models for dinosaur flight evolution in the year or two.

The Ellison image is associated with a recent paper by Li et al. (2012) in Science.  The authors favor display characteristics for some of the feathered morphology, particularly the tail fan.  I don't discount this function at all, but it should be noted that it doesn't take much to provide a decent stabilizer or control surface for a mid-sized flying animal, and display surfaces don't have to be aerodynamically useless or costly.  (Just to shore a common myth, that is not the same as saying that tail fans, crests, flaps, etc would act as rudders on flying animals.  As a general rule, rudder use does not work well for a non-fixed wing flyer.  Even fixed-wing aircraft do not initiate turns by using rudders; the rudder systems are for stabilization).

References
Hone DWE, Tischlinger H, Xu X, Zhang F (2010) The Extent of the Preserved Feathers on the Four-Winged Dinosaur Microraptor gui under Ultraviolet Light. PLoS ONE 5(2): e9223. doi:10.1371/journal.pone.0009223


Li Q, Gao KQ, Meng Q, Clarke JA, Shawkey MD, D'Alba L, Pei R, Ellison M, Norell MA, Vinther J. 2012. Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science 335 (6073): 1215-1219

Pterosaur Acrobatics

I received a fun message from David Hone of Archosaur Musings fame yesterday.  Here's the relevant bit:

"A biology teacher in Ireland tweeted me to ask if I thought a pterosaur could pull off a loop-the-loop or victory roll or similar. My guess was 'probably' especially something like and ornithocherid, but I thought you'd love it as a thought problem..."  -- David Hone

It's a fun idea to ponder.  The precise maneuvers available to fossil animals are can be difficult to work out with much confidence, but there are a few things that can be said with confidence:

- The most maneuverable pterosaurs were probably anurognathids, and they could certainly pull off a loop-the-loop or just about anything else you could want from a flying animal.  In fact, anurognathids were probably among the most agile flying animals of all time, right up there with living vesper bats, swifts, and the like.  I talked a bit about their abilities at Pterosaur.net here.  Mark Witton dealt with them more while debunking the vampire anurognathid concept here.

- For larger pterosaurs, things get a bit trickier, but the inertial problems would still be pretty minor.  The real question becomes whether the animals could handle multiple extra body weights of force on the wings.  Based on work I've done on pterosaur wing strength, as well as work by Colin Palmer, it seems that at least pterosaurs as large as Anhanguera (4-5 meter wingspan) could have handled major rolls or loops.  I have yet to check the numbers for something bigger, like Quetzalcoatlus northropi, but I might have to give it a shot.  I may post a more extensive conversation on it the idea at H2VP soon.