Sunday, April 4, 2010

Actinopatagia percussion and sketchy speculation


I’ve been enjoying the previously unreported sonic qualities pterosaur wings a lot this week. Thanks to the need to paint some fibreglass pterosaur wing membranes and a newfound obsession with the heavy beats of Florence and the Machine, I’ve been smacking out tunes with paintbrushes on the folded wings of our giant male azhdarchid model, tastefully named Bamofo, all week. Hit them hard enough with a paint-slopped brush and they make a noise unlike that of a walloped bass drum, albeit one that splashes paint everywhere and renders the artist and workshop looking like a Jackson Pollock canvas. With the amount of paint I find on the walls, floor and my hands, arms, shoulders, chest, neck and face after a particularly enthusiastic rendition of Dog Days Are Over, I’m surprised any colour has made it onto the model at all. Seriously: given my choice of using blue shading on Bamafo’s leading wing edges, a good day at work means I could easily pass as an extra in Braveheart.

To date, there’s not been any indication that any pterosaurs lost these impromptu percussion devices, nor scaled back their wing anatomy enough to assume that, winged or not, they had abandoned flight. Accordingly, I’m not aware of many – if any – pterosaurologists who consider that any known pterosaur was secondarily flightless. Unlike theropod dinosaurs, which seem to have developed and lost flight numerous times in their evolutionary history, it seems that all pterosaurs - even the biggest 250 kg jobbies - were able to takeoff and fly about with minimal fuss (Marden 1994; Habib 2008). Buffetaut et al. (2002) raised the possibility that the giant azhdarchid Hatzegopteryx may have been flightless, but ruled it out on grounds that the holotype humerus bears the same volant characteristics as it’s smaller brethren. Sato et al. (2009) suggested that pterosaurs spanning more than 5.1 m and massing more than 41 kg would be incapable of flight, thereby grounding a good number of forms including many long-winged, tiny legged ornithocheiroids. Without going into too much detail, this work is quite problematic and I’m pretty sure these conclusions have not been accepted by the pterosaur community: a rebuttal paper, penned by Mike Habib and myself, is under review, and Ross Elgin has posted similarly-minded comments on the Dragons of the Air blog. I suggested that mass and wingspan of Dimorphodon may have combined to produce a relatively ineffective flier that only took to the air to cover ground quickly or escape predation (Witton 2008): this could be taken as a suggestion that dimorphodontids were moving towards abandoning flight, but there’s no reason to assume that it had been totally lost.

Despite this, the subject of flightless pterosaurs has been brought up in informal circles a number of times: along with numerous discussions of the topic on blogs and the Dinosaur Mailing List, flightless pterosaurs have appeared on Tet Zoo here (along with being discussed in the comments of several other Tet Zoo posts) and were famously depicted as giraffe-like critters in The New Dinosaurs by Dixon (1988). In such discussions, it seems generally accepted that there’s no reason why pterosaurs shouldn’t have abandoned flight given the right selection pressures: as long as they could find enough to eat, reach suitable areas for reproducing and, by whatever means, achieve relief from predators, the terrestrial abilities of pterosaurs were probably sufficient to let them hang up their wings and let them become fully terrestrialised again. I’m in full agreement with this and, here, want to share some old speculations (drawn at the end of 2008) of flightless pterosaurs, complete with horrible, unimaginative Latin and Greek names. The drawings are a bit crude, but I’ve not had time to spruce them up – nor will I in the foreseeable future. Unlike most speculative flightless pterosaur creations, though, I haven’t just picked on azhdarchids: although they may have been more terrestrially proficient than other pterosaurs (Witton and Naish 2008), I’m sure other clades would be equally capable of abandoning flight. As such, some of imaginings here would not necessarily post-date the known pterosaur record: many would have existed side-by-side with flying (and Mesozoic) pterosaurs.

Apterigulo
Found in Early Jurassic forests (and decorating the top of this post), this metre-long bundle of fluff has ancestry lying with dimorphodontids: continual development of their large heads and hindlimbs (these attributes already make genuine dimorphodontids quite heavy for their size [Brower and Veinus 1981; Witton 2008] but retention of short wings rendered some members of this clade capable of only the most limited burst of flight, and, eventually, even this ability was lost. While the terrestrial ability of basal pterosaurs has generally been considered to be poor at best, this loss of flight didn’t leave Apterigulo and it’s kind up the proverbial locomotory creek: although the limbs are somewhat sprawled like it’s ancestors (see Unwin 1988), Apterigulo can move like dynamite with saltating, or rather bounding, around like a giant, reptilian squirrel. While this method of locomotion doesn’t permit Apterigulo to run marathons, it gives it a neat burst of speed over short distances and, what’s more, it could happily chase you up a tree: the exaggeration of its massive appendages and claws make it even more proficient at climbing than its ancestors (Unwin 1988). The skull, teeth and neck have become more robust and powerfully muscled, giving what was ancestrally a nasty bite even more force. Being derived from a flighted ancestor also gives Apterigulo an unusually strong but lightweight skeleton: this not only facilitates quicker movement, but means it’s capable of considerable rough and tumble. It uses these attributes to ambush and chase vertebrates across a range of size classes, mainly eating smaller forms but occasionally subduing prey of equal or even larger size. Burrowing dinosaurs are particular favourites: with its massive bulk blocking the burrow entrance, the experience is akin to being stuck in a train carriage with a hungry tiger. Once subdued, the carcasses of big animals are dragged into the treetops to keep them out of reach of other carnivores but, if their carrion is threatened before this can happen, little Apterigulo will stand firm against even the biggest scavengers. It would not, therefore, be an ideal house pet.


Caprajarids
At some point in the middle Cretaceous, some tapejarid populations began to favour the herbivorous side of their omnivorous diet so much that their guts required some development, including the expansion of their gizzard (it’s likely all pterosaurs had a gizzard of some kind – Reily et al. 2001) to house bulkier quantities of gastroliths. Their beaks became more robust with rounded tips and sharp tomia, making them suitable for cropping all manner of vegetation before their guts began the real processing procedure. Living in relatively bleak environments that excluded the existence of large dinosaur herbivores ensured that movement over harsh, craggy terrain was a constant issue, but the retention of the large foot pads of their ancestors (Frey et al. 2003) ensured good traction on even perilous slopes. Their pycnofibres – or fuzz – grew particularly long and shaggy to withstand the cool nights and winds of such environments and gregarious living ensured protection from the large azhdarchids that occasionally preyed upon the smaller individuals. Living in such groups encouraged the development of even more elaborate cranial crests than those of their flying ancestors as males sought breeding rights over the females. Free of aerodynamic considerations, male caprajarids went to town with bifurcating (males and females of this sort can be seen above), spiralling and even horn-like crests. If these visual displays could not sort out competition between males, violent shoving, punching and biting matches, often conducted whilst balanced on their hindlimbs, would take place.


Jacanazhdarchines
While the big azhdarchids were denizens of the open plains, smaller, more basal variants kept to the forests. One clade of these forest forms lost their ability to fly in the Late Cretaceous and, while some flightless developed into seriously lanky limbed, sloth- or monkey-like arboreal forms, others began to specialise in foraging around ponds and streams, these being obvious sources of all manner of foodstuffs. The smallest forms, the jacanazhdarchines (above), were only 20 cm in length and defied the reduction of foot size and non-flight fingers seen in their larger cousins (Hwang et al. 2002) and instead developed large, weight spreading appendages that made movement across soft substrata easy. The bulk of the flight apparatus was lost comparatively recently in these forms and, although the wing membranes were lost, the wing finger was retained and served as an additional weight spreading devices. The limbs were also lengthened, facilitating movement through deeper water and, when splayed, distributing their weight over an even larger area. With such weight spreading abilities and such small size, jacanazhdarchines could be entirely supported by even flimsy vegetation growing over water bodies and, with a turn of speed, could literally walk on water. The already hypertrophied azhdarchid rostrum was elongated further for swishing through the water in search of food, though the fused pterosaur skull and poor gaping ability of such a long rostrum means that their probing abilities were limited, however.


Aliazhdarcho
The pterosaur equivalent of putting a jet engine in a Land Rover, Aliazhdarcho (above) applied the powerful musculature, skeletal morphology and physiology of its azhdarchid ancestors to the sort of carnivory typically reserved for big, predatory theropods. The largest member of this clade was Aliazhdarcho, a 4 m tall monster with a deepened, robustly constructed metre-long head and stout limbs. This latter point is crucial to the hunting strategy of Aliazhdarcho: retaining the highly pneumatised skeleton of its ancestry means that it combined strength with lightness (despite its size, Aliazhdarcho weighed just under 500 kg), increasing the power/weight ratio and allowing the animal to move like the clappers during a sprint. The massive shoulder muscles that once propelled azhdarchids into the air were retained, but modified somewhat to prioritise grounded locomotion over aerial. The principle role of these muscles is a modified quadrupedal launch (Habib 2008) that, rather than being used for takeoff, provided a dynamite sprint start. With shoulder musculature used to high anaerobic loads, Aliazhdarcho was capable of moving at great speed for up to a minute before tiring, so ambushing it’s prey was the order of the day. Once within range, Aliazhdarcho would employ its long neck and head to strike its target prey, ramming or biting the haunches to prevent its escape and, ideally, tripping or crippling it. Once immobilised, the powerful jaws and deep, sharpened beak would remove chunks of meat from the dying animal, though the jaws weren’t quite strong enough to shatter bones. It would not, therefore, be a good idea to be a mid- to large-size animal in the same area as Aliazhdarcho: in short, wherever it was, you didn’t want to be.

And that’s it. Once again, that’s gone on far longer than I intended, but hey ho. Happy Easter to everyone and now, with the sun high in the sky, I’m heading off to my workshop. I just had a wicked idea involving our fake pterosaur fur and the bassline from David Bowie’s Stay.

References

  • Brower, J. C. and Venius, J. 1981. Allometry in pterosaurs. The University of Kansas Paleontological Contributions, 105, 1-32.
  • Buffetaut, E., Grigorescu, D. and Csiki, Z. 2002. A new giant pterosaur with a robust skull from the latest Cretaceous of Romania. Naturwissenschaften, 89, 180-184.
  • Dixon, D. 1988. The New Dinosaurs: An Alternative Evolution. Grafton Books, London, 120 pp.
  • Frey, E., Tischlinger, H., Buchy, M. C., and Martill, D. M. 2003. New specimens of pterosauria (Reptilia) with soft parts with implications for pterosaurian anatomy and locomotion. In: Buffetaut, E. and Mazin, J. M. (eds.) Evolution and Palaeobiology of Pterosaurs, Geological Society Special Publication, 217, 233-266.
  • Habib, M.B. 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana, B28, 161-168.
  • Hwang, K. G., Huh, M, Lockley, M. G., Unwin, D. M. and Wright, J. L. 2002. New pterosaur tracks (Pteraichnidae) from the Late Cretaceous Uhangri Formation, S. W. Korea. Geological Magazine, 139, 421-435.
  • Marden, J. H. 1994. From damselflies to pterosaurs: how burst and sustainable flight performance scale with size. American Journal of Physiology, 266, 1077-1084.
  • Reily, S. M., McBrayer, L. D. and White, T. D. 2001. Prey processing in amniotes: biomechanical and behavioural patterns of food reduction. Comparative Biochemistry and Physiology Part A, 128, 397-415.
  • Sato, K., Sakamoto, K., Watanuki, Y., Takahashi, A., Katsumata, N., Bost, C., and Weimerskirch, H. 2009. Scaling of soaring seabirds and implications for flight abilities of giant pterosaurs. PLoS ONE, 4, e5400.
  • Unwin, D. M. 1988. New remains of the pterosaur Dimorphodon (Pterosauria: Rhamphorhynchoidea) and the terrestrial ability of early pterosaurs. Modern Geology, 13, 57-68.
  • Witton, M. P. 2008. A new approach to determining pterosaur body mass and its implications for pterosaur flight. Zitteliana, B28, 143-159.
  • Witton, M. P. and Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE, 3, e2271.

4 comments:

  1. Hey, Mark.

    Can you email me, please?

    anzha lyu at gmail dot com.

    This is in reference to the XenoPermian project that Zach, Scott, and I are working on. I'd like a little guidance with respect to alternate pterosaur evolution in our scenario.

    If you have a moment, of course.

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  2. The Apterigulo actually looks kind of dejected at having lost his wings. :-)

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  3. These are some awesome speculative flightless pterosaurs. I especially like the one derived from dimorphodontids. If you don't like the name, why don't you call it Scuriobuteo (squirrel-hawk), Saltogulo, or Gulosalta (leaping wolverine).

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  4. Thanks. Your names are much nicer: I quite like Scuriobuteo. Most of mine were made up on the fly: hence their lack of intrigue and originality.

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