In the previous article on the 58th Symposium on Vertebrate Palaeontology and Comparative Anatomy (SVPCA), held in Cambridge, UK, I discussed some of the work that was presented on stem-tetrapods and sauropods. This time round, we look at more Mesozoic stuff - pterosaurs in particular - before getting on to Cenozoic mammals.
Steve Sweetman presented the first outing of a new miniscule maniraptoran theropod that he and I have been working on. When it gets published, nothing will ever be the same again (massive hyperbole fully intended: Steve's talk was more to do with salamanders, anurans and lizards). Having mentioned lepidosaurs, Neil Curtis (et al.) and Marc Jones (et al.) presented some great analyses of skull function in Sphenodon.
Mesozoic marine reptiles weren't tremendously well represented, but Mark Evans and Roger Benson's new look at Lias Group plesiosaurian diversity was pretty neat: here was yet another study showing that Lias plesiosaurian diversity was higher than previously thought. It seems that Thalassiodracon hawkinsi is not, after all, the only small-bodied plesiosaurian in the Lias assemblage. Mark Purnell and Nia Roderick used microtextural analysis to show that the big pliosaur Simolestes was most likely not a cephalopod specialist as has been suggested, but that it wasn't much different in diet from Liopleurodon.
Morganucodontids, Australasian spinosaurids, ornithischian hindlimb and pelvic musculature and the distribution of pneumaticity in theropods formed the focus of other Mesozoic talks. Michael Pittman illustrated the morphological changes that occurred during maniraptoran evolution as tails changed in shape and flexibility.
David Norman discussed his views on British iguanodontian taxonomy: he accepts the validity of Mantellisaurus but doesn't regard Dollodon as distinct [adjacent Mantellisaurus reconstruction by Steveoc86, from wikipedia]. Furthermore, he reiterated his opinion that the Old Roar Quarry iguanodontian is referable to Barilium dawsoni (Norman 2010). I find this hard to believe because (despite extensive reconstruction of the right ilium) the former has a peculiar, sinuous dorsal iliac margin that makes it look quite different from the B. dawsoni holotype ilium (there are other differences as well - like taller neural spines in the Old Roar Quarry specimen - but it's not clear how significant they are. Norman says that the sinuous iliac margin is due to post-mortem deformation [UPDATE: I'm going to backtrack here. New observations lead me to think that he's right]). Anyway, what with the recent naming of Owenodon and Kukufeldia, it's clear that the once lamented wastebasket status of Iguanodon sensu lato (Naish & Martill 2008) is finally being resolved. What was meant to be one genus lasting for something like 30 million years is turning out to be at least five distinct 'genera', none of which were around for more than five million years. Incidentally, the Old Roar Quarry iguanodontian is of special interest (to me!) because of its claimed link to the Piltdown hoax (Naish 2008).
The stuff on pterosaurs you've all been waiting for
Few SVPCA talks on pterosaurs might be predicted given the very recent Flugsaurier 2010: Third International Symposium on Pterosaurs meeting in Beijing, but there were one or two revelations nonetheless. Dave Unwin's talk was pretty incredible: a new Darwinopterus specimen is preserved in direct association with an egg (the egg is positioned as if just emerging from the pelvis, an event that almost certainly happened post-mortem). The Darwinopterus specimen concerned lacks a cranial crest (unlike other individuals of the same species), allowing us to make confident conclusions about sexual dimorphism in this (and other?) pterosaurs. At this point I will resist the urge to say any more.
Colin Palmer gave a very interesting talk on the flight position of pterosaur wings. Due to the position of the centre of gravity, he had to get flying pterosaurs to hold their wings in a 'swept forward' posture, quite different from that traditionally imagined. At the moment I'm sceptical, because it would create a very 'pointed' wing-tip somewhat different from what seems to be present in preserved soft tissues. But let's not forget that not all pterosaurs are the same, and that what might apply to ornithocheirids does not necessarily follow for, say, rhamphorhynchids or anurognathids or whatever.
Azhdarchid pterosaurs are all the rage these days, ever since those Witton and Naish guys published that excellent paper (Witton & Naish 2008) [one of many newspaper articles shown in image above: look for typos. Image directly above - an adapted version of a Mark Witton piece - from The Paleochick's Digs]. The inferred strong terrestriality of azhdarchids, combined with the more realistic mass estimates that are now kicking around (Witton 2008), means that the possibility of azhdarchid flightlessness has recently been speculated about on a few occasions. While Witton (and Naish) favour a mass for big azhdarchids of 250 kg or so, Don Henderson recently proposed c. 540 kg for Quetzalcoatlus northropi, and therefore suggested that Q. northropi might have been flightless (Henderson 2010). This formed the topic of his talk. In my opinion it's good to see someone else being highly critical of the absurdly low masses that have traditionally been given to pterosaurs large and small. With regard to the 70 kg apparently regarded as likely for Quetzalcoatlus by many authors, Don said "I would love to know what they've been smoking" (with the 'they' being the pterosaur workers, not the pterosaurs).
While most of us tend to assume that flightlessness for azhdarchids is contradicted by what we know of their skeletons, the fact remains that Q. northropi is very poorly known, perhaps allowing the possibility that it had reduced wings. However, the overall robustness and muscle attachment sites of the humerus are, I should think, still indicative of flight ability. I also think that the c. 540 kg mass estimate is too high: Don based his computational model on an incorrect template, but he knows this and is working to test things further. We might come back to this subject again.
Where the desmostylians are
Cenozoic mammal talks included those on rodent cranial anatomy, Oligocene sirenian diversity and the mechanics of gulp-feeding in mysticetes.
Vera Weisbecker (with Anjali Goswami) looked at brain size across marsupials and placentals: comparisons show convincingly that marsupials are NOT consistently smaller-brained than same-sized placentals. The idea that they are results from skewing by primates. Interestingly, marsupial brain size is not correlated with basal metabolic rate (in contrast to placentals) but seems more to do with extended lactation. This work (which looked at brain size and development in birds too) has just been published in PNAS (Weisbecker & Goswami 2010).
Desmostylians - a neat and bizarre group of afrotherian mammals that really should be covered on Tet Zoo some time - were the subject of Shoji Hayashi et al.'s talk. As everybody knows, the lifestyle, diet and even appearance of desmostylians has been controversial. At one extreme, some authors have interpreted them as terrestrial quadrupeds that foraged on exposed shores. At the other, some have regarded them as pinniped-like marine animals that only visited land for resting and basking. Thin-sections and CT scans from the ribs and limb bones of diverse desmostylian taxa show that they are not all alike: some exhibited osteosclerosis or pachy-osteosclerosis and most likely relied on static buoyancy in shallow water, while one (Desmostylus) exhibited osteoporotic bones and likely used dynamic buoyancy in deep water. Desmostylus may thus have been a pelagic, deep-water animal, in contrast to the other taxa (though it's only fair to note here that this is in contradiction to conclusions drawn from isotope analysis: Clementz et al. (2003)). Oh, and if you want to know the story behind the orange cartoon character used at the very top, I recommend you visit this article at The Aquatic Amniote.
So, neat stuff. Loads more happened and I'd love to talk about it, but time is a real factor. I hope you enjoyed this quick look at (some of) the edited highlights. If you want to know more, the abstracts from the meeting are online at the SVPCA site here. Oh, and those of you who have previously seen this photo (humans included are Stephanie Pierce, Lionel Hautier, John Conway, Mathew Wedel, Michael P. Taylor, Stig Walsh, Robert Nicholls and Julia Molnar)...
... and want to know what everyone is gawping at.. well, here is the answer. It's John Conway's Jehol Biota zoom scene...
For previous articles on azhdarchids (flightless or not) and other pterosaurs see...
- The Wellnhofer pterosaur meeting, part I
- It could look a giraffe in the eyes
- The Wellnhofer pterosaur meeting, part II
- The Wellnhofer pterosaur meeting, part III
- Terrestrial stalking azhdarchids, the paper
- Shemhazai and other flightless pterosaurs
- Come back Lank, (nearly) all is forgiven
- Pterosaurs breathed in bird-like fashion and had inflatable air sacs in their wings
- Darwinopterus, the remarkable transitional pterosaur
- Giant pterosaurs invade London, Summer 2010
- Pterosaurs, err, indoors (the Summer 2010 exhibition)
Such plesiosaurs as Thalassiodracon and Simolestes have previously been discussed here...
- Voracious snub-nosed robber
- Sea Dragons of Avalon: a 2009 seminar
- Sea Dragons of Avalon, an Arthurian adventure (part I)
- An Arthurian adventure, part II: more fossil marine reptiles than are good for your health
And for more on iguanodontians, see...
Refs - -
Clementz, M. T., Hoppe, K. A. & Koch, P. L. 2003. A paleoecological paradox: the habitat and dietary preferences of the extinct tethythere Desmostylus, inferred from stable isotope analysis. Paleobiology 29, 506-519.
Henderson, D. (2010). Pterosaur body mass estimates from three-dimensional mathematical slicing Journal of Vertebrate Paleontology, 30 (3), 768-785 DOI: 10.1080/02724631003758334
Naish, D. 2008. Conan-Doyle [sic], Piltdown, and the dinosaur in the well: obscure Wealden dinosaurs and the stories behind them. In Moody, R., Buffetaut, E., Martill, D. & Naish, D. (eds) Dinosaurs and Other Extinct Saurians: A Historical Perspective. Abstracts of Meeting Held on the 6-7 May 2008. Geological Society of London, London, pp. 8-9.
- . & Martill, D. M. 2008. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: Ornithischia. Journal of the Geological Society, London 165, 613-623.
Norman D. B. 2010. A taxonomy of iguanodontian (Dinosauria: Ornithopoda) from the lower Wealden Group (Cretaceous: Valanginian) of southern England. Zootaxa 2489, 47-66.
Weisbecker, V. & Goswami, A. 2010. Brain size, life history, and metabolism at the marsupial/placental dichotomy. Proceedings of the National Academy of Sciences 107, 16216-16221.
Witton, M. P. 2008. A new approach to determining pterosaur body mass and its implications for pterosaur flight. Zitteliana B28, 143-158.
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I've talked to Colin at some length about his wing configuration, and I think there are some points to be made. He rejects the notion that actinofibrils would have been able to take the compressive load necessary to support a roach (a projection of membrane posterior to a straight trailing edge). I agree with him, these things were like hairs, which have virtually no compressive strength. That means that the Greg Paul styley wing with their curve in the trailing edge toward the wingtip were very unlikely, they'd flutter like crazy.
I think there are a few things that mitigate the pointy-wing look that sort of appeared in his drawing. The terminal phalanx would have curved quite a bit, but that's variable among individuals and he showed very little. Second, he didn't include in his drawing (though he probably should have) the small projection of the membrane posterior to the tip of the terminal phalanx.
Jim Cunningham, at least, agrees that the wings would be held further forward than you normally see in flight. I suspect this part of it is dead right.
I'm going to do some paintings of Colin's configuration and see how it pans out, looks wise.
Ueno and Kohno I believe have a isotope paper in prep on Japanese Desmostylians, so hopefully we will soon have more answers to whether Desmostylus itself was pelagic.
There really is no excuse, Darren: you've got to get around to writing a post, or perhaps a series of posts, on desmostylids. They are woefully underappreciated.
Question for anyone that actually saw the talk: Were desmostylian bones of similar ontogenetic stage used (and just as important: were they actually the same bone)? Because if not, then that's a major problem for paleohistology.
I'm quite surprised at the osteoporotic bone in Desmostylus, although the work of Clementz et al. (as mentioned) suggest quite shallower (if not a lagoonal or estuarine environment) for these guys (at least California fossils), if I recall correctly.
weren't desmostylans related to manatees? Also, get a load of what that Metro article calls pterosaurs!
Yes, Desmostylians + Sirenia + Proboscidea form a clade called the Tethytheria (I'm not sure what the current consensus is on this group).
Its not the typos that I'd worry about with Metro, its the utter mangling of the paper. First they call them dinosaurs, then they suggest they dived like gulls. And you can't see it in your screencap, but they also called them birds.
Awesome video.
How good is the evidence for that, actually?
Of course, so are temnospondyls.
Morphological support for the inclusion of Desmostylians within Paenungulata and within Tethytheria seems quite solid, although whether they were more related to Sirenians or to Proboscideans might still be debated.
Also it's good to remember that their are two families of desmostylians, and from published and unpublished ecological work I have seen they probably had quite different life styles.
To be fair to the Metro journalist, 'azhdarchids' is spelled correctly (although it's miscapitalised in the figure caption).
Mike Habib and I have a paper, now well-over a year in the making, that addresses Don's half-tonne azhdarchids. We also presented our comments on his work in Flugsaurier 2010. It won't give a huge amount away to say that we retain our 250 kg maximum for a big, healthy azhdarchid, and find that Don's estimates, when corrected for, are actually very comparable with masses generated by people like Greg Paul and myself.
>Question for anyone that actually saw the talk: Were desmostylian bones of similar ontogenetic stage used (and just as important: were they actually the same bone)?
All specimens were sampled from same bone of adults.
Except for paleoparadoxia, we used their holotype.
So, you can check if our specimens are adult using published papers on desmostylus.
What, precisely, has been published presuming flightlessness on azhdarchid (or, really, any pterosaurs)? I understand that some old, old -- really old -- works in the 1800s have presumed it thinking their limbs too unlike that of bats or birds, but these are not current thinking. The presumption of "high" terrestriality and that of potentially inaccurate reconstructions of wings of some very large specimens do not seem to make much predictive capability in inferring a lack or reduced ability to fly.
Is the argument of "flightlessness in azhdarchids" merely rhetorical in leading into "useful regions of discussion," without having ever been seriously proposed by those with the means to actually test the options on a primary, rather than circumstantial, basis?
Jamie,
Flightless pterosaurs have seriously been proposed in recent pterosaur literature. Their existence is not based on anatomical characteristics however, but on flight models that cannot grant giant pterosaurs flight. Chatterjee and Templin (2004) started this trend when they found that they couldn't get a pterosaur massing over 70 kg into the air. Given that this is an entirely unfeasible mass estimate for things like Quetzalcoatlus northropi, this, in effect, renders big azhdarchids flightless in their estimations. They very nearly render things like Pteranodon flightless, too, if realistic masses are assumed.
Later, Sato et al. (2009) suggested that any pterosaurs over 41 kg and 5 m wingspans were flightless, an assumption derived from their work on soaring procellariiforms.
Finally, Henderson (2010) estimated the mass of Q. northropi at well over 500 kg with his digital geometric modelling. Much of Don's paper, in fact, is devoted to discussing the (alledgedly) heavy mass and flightlessness of Q. northropi. Our paper on all this should be out very soon (it's been accepted for publication; Mike and I are just finishing our final bif of tinkering).
There should be some prize for Impossible Ecology of the Year, given to paleontologists, science-fiction movies etc.
A flightless pterosaur in an environment inhabited by theropods would be eaten on the day one.
Unless somebody proves that pterosaurs were fast runners comparable to ostriches this idea has no chance.
Jerzy: is that necessarily true? I'm no expert, but that huge pointy beak seems like a decent weapon to me. Especially if the creatures had any tendency to be gregarious, I think a theropod would think twice before attacking them.
After all, even humans managed to survive long enough to invent firearms.
Has any research been conducted into how flightless pterosaur locomotion might work? If they were unencumbered by large flight membranes might it have been possible for them to have run on their hands in effect? It seems highly unlikely but . . .
Hominids had big brains, used tools, and above all could climb trees.
Azhdarchids - no teeth, stiff neck - would be easy meal.
Hominids, on the other hand, didn't have anything resembling a natural weapon. That's why they needed the tools in the first place.
Also, are trees really that safe when one of your main predators is leopards?
Wow, that Jehol Biota video is splendid. It beautifully underscores just how remarkably complex and multi-layered ecosystems are. The task of trying to rebuild how whole ancient ecosystems worked out using mere bone fossils, coprolytes, plant inprints, and other lucky bits of information eavesdropped from other fields of science suddenly is put in such daunting perspective. ...It's like trying to rebuild a sandcastle with the grains in their original positions after the sea has washed it away.
Goood luck with that, guys...
Stu of the Peak,
Pterosaur membranes can't have been that much of a hindrance in their locomotion: we have trackways of pterosaurs running and, to adopt all the positions they would have to for launching and landing, their proximal membranes had to be really quite elastic. What's more, there wouldn't really be much membrane at ground level to snag on vegetation or tread on once the membranes were folded up properly. Oh, look: here's my first shameless plug - buy my book next year to find out more.
As for bounding locomotion, I mentioned this very possibility in my talk at Flugsauier 2010. I reckon we generally underestimate pterosaur terrestrial abilities: several authors have commented that pterosaur hindlimbs are adapted for leaping, and we have seen how strong their forelimbs are through the Cunningham/Habib quadrupedal launch hypothesis. If you buy these ideas and bear in mind that pterodactyloids generally seem walk with erect or erect-ish limbs, bounding doesn't seem an unreasonable method of locomotion (though variable limb proportions in different taxa will undoubtedly affect bounding efficiency/likelihood).
Shoji,
Good to hear it! I only asked because I know of dinosaur paleontologists who have committed some serious atrocities while doing paleohistology. Normally, mammal paleontologists hold themselves to a higher standard. Sounds like you have some really interesting results for an enigmatic and totally bizarre group of marine mammals!
Naraoia:
In the Pleistocene, a huge and apparently flightless - and, thus, terrestrial - marabou/adjutant stork lived on the island of Flores, Indonesia. It was able to evolve and survive there in spite of the presence of Komodo dragons (and 'hobbits').
Jerzy:
Patas monkeys don't have particularly big brains (by anthropoid standards), they don't use tools, and, while they can climb trees they do seem to much prefer staying on the ground.
In fact, patas monkeys are just the kind of animals that one wouldn't expect to have evolved in the first place - what are the odds that a forest-living, arboreal guenon monkey would ever successfully adapt to a life on the predator-infested* African savannah? And yet, the ancestors of Erythrocebus patas clearly did beat those odds. Why couldn't some pterosaurs, in their day, have done that as well?
* And, as Naraoia said, some of those predators do climb trees too.
> There really is no excuse, Darren: you've got to get around to
> writing a post, or perhaps a series of posts, on desmostylids. They
> are woefully underappreciated.
Except, for some reason, in Japan; but, judging by the picture between the flightless azdharchid and the iguanodont skeleton, desmostylians in Japanese popular culture are bipedal hippos wielding lightsabers.
> Don Henderson recently proposed c. 540 kg for Quetzalcoatlus
> northropi, and therefore suggested that Q. northropi might have been
> flightless (Henderson 2010)
This would nicely fill the huge gap between 100kg *Palaeosaniwa* and the multi-ton tyrannosaurs.
They are famously fast runners, though.
The multi-ton adult tyrannosaurs...
David:
The modern patas monkeys are, yes. Their vervet-like ancestors, however, almost certainly weren't. But that didn't stop them from leaving the safety of the trees.
Minor comment on patas monkeys: they aren't the only guenons with strong terrestrial adaptations, members of the lhoesti group have them too (the taxa most often known as Cercopithecus lhoesti and C. preussi). C. aethiops has what might be regarded as 'incipient' terrestrial postcranial features (e.g., long cuboid and tall, narrow talar head). While some authors have argued that terrestriality evolved three times independently within guenons, molecular phylogenies and skull characters indicates monophyly of this terrestrial group (Tosi et al. 2004, Sargis et al. 2008 and references cited in both). If the patas is part of Cercopithecus, the taxonomy has to be changed: Sargis et al. (2008) dealt with this by using Chlorocebus for the terrestrial clade.
Refs - -
Sargis, E. J., Terranova, C. J. & Gebo, D. L. 2008. Evolutionary morphology of the guenon postcranium and its taxonomic implications. In Sargis, E. J. & Dagosto, M. (eds) Mammalian Evolutionary Morphology: A Tribute to Frederick S. Szalay. Springer, pp. 361-372.
Tosi, A. J., Melnick, D. J. & Disotell, T. R. 2004. Sex chromosome phylogenetics indicate a single transition to terrestriality in the guenons (tribe Cercopithecini). Journal of Human Evolution 46, 223-237.
The Flores stork is only know to be either poor flyer or flightless. Flores and other islands are impoverished ecosystems without terrestrial carnivorous mammals. Komodo dragon, crocodile or a giant skink is unable for sustained running.
This exactly is my point. Quetzalcoatlus and other known pterosaurs come from deposits from continents having theropods. You are free to speculate about hypothetical Mesozoic islands without predatory dinosaurs and hypothetical flightless pterosaurs there.
About patas monkeys, baboons etc. They didn't become unable to climb, they climb trees and rocks to escape predators, including every evening. It is not a talk about where they spend most of the active time. There are plenty of flying birds which spend 99.9% of the time on the ground, but they are strong fliers during 0.1% of the time when they escape running predators. This is not a model for a flightless pterosaur.
Perhaps unlike Jerzy, I do think that a giant flightless azhdarchid might be able to look after itself in a continental environment, even when there are big theropods around. After all, (1) azhdarchids were not slow or immobile, on-going work (much of which has yet to be published, sorry) indicates that they could bound or even gallop, and they were conceivably capable of out-running giant theropods, and (2) they were hardly defenceless - a pointed bill more than 1.5-2 m long is a pretty formidable jabbing weapon, probably sufficient to defend against small theropods and maybe some big ones.
However... what about babies, juveniles, sub-adults etc? Well, maybe they got eaten a lot, and maybe azhdarchids were r-selected and produced huge clutches. But maybe adults (or groups of adults) defended them. Maybe they were volant, and it's only adults that were flightless.
I'm not defending the flightlessness hypothesis - as I said above, I think it's erroneous and has come about because of a computational error (see Mark Witton's comment # 14). But I wouldn't be so quick to assume that the hypothesis is a non-starter, even for a continental azhdarchid living alongside big theropods.
Sorry to not comment on the article proper but only on the video: what is that absolutely adorable flying creature? Excuse my utter cluelessness, but is it actually mammalian (as suggested by the snout and whiskers)? Teh cute!!!
Jerzy:
But if the Flores marabou was flightless, it must have nested on the ground. And, as eggs can't run away, we must consider the possibility, unlikely though it might seem, that the adult birds were, in fact, able to keep the Komodo dragons at bay.
There were no large carnivorous mammals in the Cretaceous either. And since when is sustained running the only way of catching prey? Cats are highly efficient predatory mammals that are incapable of 'sustained' running.
For that matter, do you know for a fact, Jerzy, exactly how Cretaceous theropods hunted and whether all/some/any of them were even capable of sustained running?
(For the record: Like Darren, I am not 'defending' the idea that large pterosaurs were flightless. But I do not dismiss it out of hand either. Evidence has been presented, in the form of technical, peer-reviewed papers. And if that evidence is somehow flawed or incorrect - as it well might be - that must be demonstrated by using the scientific method. Only science can refute science.)
Kris, the flying creature is a Jeholopterus (well that's the logical conclusion for a Jehol panorama). Which is actually a tiny kind of pterosaur! There's enough indications that pterosaurs did have hairy coverings ... I don't know about whiskers though!
Darren, I would be interested in your pterosaur running work. I however guess that the speed was impressive by comparison with the idea of sprawled, crawling pterosaurs and not against the running bipedal theropod.
Among others, these plantigrade feet don't suggest high speeds. I think it is more like storks and pigeons, who walk around for hours, but for speed immediately spread wings.
Darren, you say you are sceptical of my conclusions about forward sweep. As I showed (albeit very briefly), posterior curvature on the distal wing phalanges gives rise to a caudal wing tip shape, which has worthwhile aerodynamic characteristics (reduced induced drag and less chance of tip stall.) So no problem with pointy tips.
But more fundamentally, if Don is correct with his centre of mass (CG) estimates, the wings must be further forward than conventionally drawn since centre of pressure (CP) and CG must be coincident. That is as basic to flight mechanics as Darwin is to evolution. Clearly there is some leeway in the estimation of CP position, but all aero data points to it being around 30% of chord. Given that, how else can we reconstruct a wing?
Colin: good points, well made :)
Jerzy,
I don't think anyone has ever estimated the speed of any ground-moving pterosaurs, running or otherwise. They must be able to generate substantial speeds in bounding, though: they're using the same equipment to bound that would be employed in surpassing their stall speeds in takeoff, after all. There haven't been any mimimum flight speed estimates of realistically-massed pterosaurs published, but the hyperlight (16 kg, 7 m span) Bramwell and Whitfield Pteranodon cruises at something like 20 mph. Hence, the flight speed of a heavier, 40 - 50 kg Pteranodon would be much greater, suggesting a launching Pteranodon has surpass 20 mph to take off. We have to assume, therefore, that a forelimb-propelled bound would give each leap the potential to hit such speeds (though, while possible, I think the bounding abilities of ornithocheiroids would be limited myself).
Other pterosaurs, and particularly azhdarchids, were proportionally heavier than ornithocheiroids and have limb proportions more suitable for bounding. Because of their need to hit greater launch speeds, the largest azhdarchids would have a standing leap capable of hitting some serious speed and, chained together, I imagine a bounding azhdarchid could move pretty damn quick in a straight line.
Just seen the video - wonderful!
@Mark, Darren
One (of many) problem is structure of pterosaur limb bones, which are described as extremely honeycombed. This is not what I would expect from animal running for extended periods of time.
About bounding... I am not sure what exactly you mean by bounding. Could you give a model of a modern animal propelling itself by bounding, and compare a pterosaur skeleton to it? Do you expect eg. very flexible backbone in pterosaurs, like in hares and monkeys? Is it like hopping of hares, except that front legs generate more power? Then pterosaur trackways show nothing like that.
Jerzy,
Pterosaur bones are ridiculously strong against bending and torsion. Their bone diameters are huge: a 250 kg azhdarchid has a humeral diaphysis width comparable to that of a 2 tonne hippo (although hollowing the pterosaur bone out does weaken it a bit, but not enormously: shaft diameter is a more critical factor against bending than shaft density). Pterosaurs were, overall, amazingly strong for their body masses, reptilian sports cars with honking V8 engines and lightweight, carbon fibre bodywork. In my mind at least, there's no problem finding the strength or integrity necesary for bounding in the pterosaur skeleton.
As for the bounding mechanism, it's perhaps best demonstrated in the modern day by things like vampire bats (though it would be somewhat different, I imagine, in pterosaurs):
http://www.youtube.com/watch?v=ukIZRD1mzLg
Bounding is a gait, of course, that pterosaurs were only secondarily adapted for (hence no flexibility in the spine, plantigrade feet and whatnot), but seems biomechanically possible. A scenario where a pterosaur needed to move quickly but couldn't fly is easy to imagine, too (e.g. hunting terrestrial prey, foraging in a constrained or cluttered area). And yes, I concede that no pterosaur tracks show this form of locomotion, but we're citing negative evidence to rule it out based on this alone.
Mark Witton, you wrote (please noting the spelling of my name as I note yours):
To fully get this, I noted that each of these three primary studies are inarguably interesting, but have been superceded by the following. Thank you for citing these works, and how your own follow up used [1] to support it, as well as earlier work based solely on circumstantial data. Only [1,2] actually assess the aerodynamic qualities of azhdarchids while in flight. Work leading by Mike Habib and others implies azhdarchids have a launch system that could only work if they were flighted.
[1,2], unlike the Henderson work, extrapolate a mass/flight component to assessing pterosaur volancy; both of these put Pteranodon longiceps in danger of being flightless, if not unable to achieve steady flight entirely, despite it being found virtually exclusively in marine environments (along with a few other terrestrial Niobrara organisms).
I am sure your follow-up will note that azhdarchids could likely fly, and that they, being not birds, would have done some things to their ability to fly that, like bats, underscore that they are not birds. Treating them like birds, as [1,2] do, and Henderson's purportedly too-extreme mass estimate, implies that the large azhdarchids are being mismodeled, or that the assumptions made on them are wrong. If so, then using them to support terrestriality and near-flightlessness (or its achievement) seems a tad misleading, as in the disucssion in [3] where the support for terrestriality was not contradicted by the flaws implied in the work used to support the theory.
For the record, as a scientist, I do not hold that any pterosaurs are automatically flighted or not. I am sure Mark and Darren do not either (although I cannot prove, nor use, such a belief, in my arguments). Data seems to imply that there are no actual flightless pterosaurs, of which azhdarchids seem the likeliest to get there, yet they seem to have flighted capabilities. This also has NOTHING to do with the skimming/terrestrial-stalking argument.
I just want to underscore this: pterosaurs are not birds. Using one as the analogue for the other, in any way, shortchanges primary collection of data and its extrapolation to the fossil record. It presupposes, almost certainly, a sense of "archetyping," which is a primitive and categorical proposition.
[1] Chatterjee, S. and Templin, J., 2004. Posture, locomotion and paleoecology of pterosaurs. Geological Society of America Special Publication: 376, 1-64.
[2] Sato, K., Sakamoto, K.Q., Watanuki, Y., Takahashi, A., Katsumata, N., Bost, C-A., Weimerskirch, H. 2009. Scaling of Soaring Seabirds and Implications for Flight Abilities of Giant Pterosaurs. PLoS One 4:1-6.
[3]Witton, M. P. & Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE 3(5): e2271
Jaime (apologies for the typo above),
I agree with your comment 100 per cent (well, aside from azhdarchids being the most likely pterosaurs to become flightless: I found Dimorphodon to be closer to this condition in my analysis of pterosaur wing ecomorphology). We discuss many of your points in our paper and yes, though we're working with fragments, we find that the most parsimonious interpretation of giant azhdarchid anatomy is that they could fly.
Belatedly, further comments on marabou storks and patas monkeys that may or may not be pertinent to a discussion about flightlessness in pterosaurs...
Re-citing Naraoia:
I realise that the following is extremely anecdotal information, but it's perhaps still worth mentioning here. Alfred Brehm, the famous German 19th century zoologist, spent many years in Africa; while there, he kept a large collection of live animals of various kinds. Among them was a lioness, which
(Text from the 1895 English translation of Brehm's Life of Animals.)
The relevance, if any, of that passage to a discussion about hypothetical flightless pterosaurs is that toothless doesn't equal defenceless...
As a slight aside: Apart from the giant Flores Leptoptilos mentioned earlier, there are other huge marabous known from the fossil record. The Pliocene Leptoptilos falconeri is the largest of them; Louchart et al. (2005) estimate it to have been about 2 m in height and about 20 kg in weight (the largest extant marabous weigh about 9 kg). L. falconeri differed in its body proportions from the modern species in that it had relatively smaller forelimbs - implying that it was a poorer flier than the extant marabous (though Louchart et al. do not go so far as to suggest that it was actually flightless). But reduced flight capabilities didn't prevent L. falconeri from colonising both Africa and Asia (and possibly Europe too; a huge marabou very similar to L. falconeri is known from Pliocene deposits of the Ukraine).
Jerzy:
No, it isn't, but it is an example of a (non-island-living) tetrapod lineage that has abandoned a highly specialised ecological niche and managed to adapt to a dramatically different one. In that sense - if in no other - it's analogous to a hypothetical secondarily flightless pterosaur.
Patas monkeys, by the way, seem to be paying a high price for their terrestrial adaptations. They seem to suffer higher adult mortality than most other primates, and, interestingly, they appear to have taken small steps towards evolving a somewhat more r-selected life history. Patas monkeys reproduce more often and at an earlier age than other similar-sized primates, which presumably is an evolutionary response to an increased predation pressure (Isbell et al., 2009).
Finally, this is probably very old news to many if not most Tet Zoo regulars, but, as it hasn't been brought up in this discussion thread yet, I might mention that there is some direct fossil evidence that azhdarchids did, in fact, occasionally end up as theropod food. Currie & Jacobsen (1995) described azhdarchid bones that contained dromaeosaurid tooth marks, as well as an imbedded, broken tooth tip. (As the authors note, however, it's possible and perhaps even likely that this represents a case of scavenging rather than actual predation.)
References:
Currie, P.J. & Jacobsen, A.R. 1995. An azhdarchid pterosaur eaten by a velociraptorine theropod. Canadian Journal of Earth Sciences 32, 922-925.
Isbell, L.A., Young, T.P., Jaffe, K.E., Carlson, A.A. & Chancellor, R.L. 2009. Demography and life histories of sympatric patas monkeys, Erythrocebus patas, and vervets, Cercopithecus aethiops, in Laikipia, Kenya. International Journal of Primatology 30, 103-124.
Louchart, A., Vignaud, P., Likius, A., Brunet, M. & White, T.D. 2005. A large extinct marabou stork in African Pliocene hominid sites, and a review of the fossil species of Leptoptilos. Acta Palaeontologica Polonica 50, 549-563.
Dartian | September 24, 2010 4:08 AM:
Marabou/adjutant storks and Komodo dragons? With jaws that bite and claws that catch? What manxome foes!