Tetrapod Zoology

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On to more of my thoughts about the outstanding Wellnhofer pterosaur meeting, held at the Bayerische Staatssammlung für Paläontologie und Geologie (Bavarian State Palaeontological Collection – BSPG) in Munich last week. For part I go here, and for initial thoughts on what a neat conference it was go here. For those of you wondering (and for those of you that know that the pterosaur meeting was the third of three conferences I attended during August and September 2007), my plan is to talk about all three conferences, but in reverse order. Once I finish talking about pterosaurs, I’ll do SVPCA, and after that I’ll say at least something about the cryptozoology conference. Other things may well get in the way, of course.

Anyway: again, I’m not reviewing (or even mentioning) everything that happened, just covering the areas that caught my personal attention. Thanks to Mark, I got hold of additional photos from the meeting today, so expect lots of serious images; no more posing with cocktails (though you never know). Here we go…

Two talks – by Leon Claessens and Pat O’Connor – looked at pterosaur physiology and pneumaticity. Leon showed that, while pterosaurs exhibited a reduction of those skeletal components that permit costal ventilation of the lungs, the sternum and its associated structures must have been capable of a significant amount of dorsoventral excursion, and the prepubes probably helped with this too. The bottom line is that pterosaurs evolved an efficient avian-style flow-through pulmonary system long long prior to the appearance of birds. For those of you reading this that don’t know pterosaurs well, I should point out that the evidence for avian-style skeletal pneumatisation in pterosaurs is very robust and based on excellent evidence; for a review see Bonde & Christiansen (2001, 2003). Basal pterosaurs appear not to have been pneumatic, but rhamphorhynchids and pterodactyloids clearly were.

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Pat O’Connor showed that skeletal pneumaticity in pterosaurs strongly parallels that present in birds, and that large taxa in both clades exhibit similar styles of skeletal pneumaticity not seen in their small relatives. Pterosaurs were probably able to pneumatise distal skeletal elements (such as wing finger phalanges) via the opportunistic invasion of diverticula from a subcutaneous air-sac that may have extended across part of the forelimb skeleton. As a very excited Dave Martill pointed out after Pat’s talk, there may indeed be direct evidence for the presence of this air-sac from some preserved pieces of pterosaur wing membrane: in addition to layers containing aktinofibrils and blood vessels, pterosaur wing membranes have also been reported to contain a ‘spongy’ layer that has been inferred to have been mostly air-filled (Frey et al. 2003). Might this ‘air-filled’ layer correspond to a subcutaneous air-sac? [I don't have any images showing Leon or Pat, so above is a pic of me giving my talk on European Lower Cretaceous pterosaurs].

One area of palaeobiological speculation that surprised me slightly was the inference from a few pterosaur workers that Tapejara (and related taxa) was frugivorous, or at least herbivorous: though don’t get me wrong, I’m familiar with the history of this idea in the literature (I just didn’t think that it was still taken that seriously). This idea was initially proposed by Wellnhofer & Kellner (1991) in their description of T. wellnhoferi, and later discussed (Fleming & Lipps 1991) by biologists interested in the role that Mesozoic vertebrates must have played in ancient endozoochory (the transport of plant seeds in an animal’s gut). It has also been viewed in a favourable light by Dave Unwin (2006). In an effort to determine the diet of Tapejara, Hanneke Meijer and colleagues used morphometric analyses to compare the inferred bite strength and other details of Tapejara with those of extant birds. I didn’t exactly follow the logic behind the application of these various tests (to be honest I never do), but the outcome was that Tapejara is about similar enough to extant herbivorous birds to have practised a similar lifestyle. Well, maybe.

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Pterosaur skull evolution was also looked at by Michael Fastnacht and Jesús Marugan-Lobón. Michael’s talk employed the principles of construction morphology, and among other things he argued that certain phylogenetic pathways were not available once a certain construction had evolved. I have a minor comment on this, which is that phylogenies indicate that ‘impossible’ reversals can indeed happen in evolution: certain marsupial tree frogs have apparently re-evolved both a tadpole phase and a lower jaw dentition, biphasic life history has re-evolved in some plethodontid salamanders from direct-developing ancestors, some stick insects have re-evolved wings from wingless ancestors, egg-laying in some squamates has evolved from viviparous ancestors, and some people think that limbed snakes re-evolved their limbs from limbless ancestors, for example. I am therefore cautious about claims that such events as, for example, the re-evolution of teeth from edentulous ancestors cannot happen. They probably can, actually [adjacent photo is me with Ursula Göhlich, and the Wellnhofer Pteranodon model in the background. God I look awful].

The immense, sometimes bizarre sail-like cranial crests of some pterosaurs (see, for example, Tapejara navigans shown at the very top of the article) have led to suggestions from the start that these organs might – or even must – have had some sort of aerodynamic effect. Ross Elgin and colleagues have actually tested this, using scale models and wind tunnels. A paper on this is due to appear soon, and the bottom line is that crests have no significant aerodynamic effect, either positive or negative. Dave Unwin provided a good review of what we know about pterosaur wing membranes based on the fossil evidence. As Tet Zoo regulars will know (see the ver 1 article here), fossils show – like it or not – that pterosaur patagia, preserved across a wide and representative diversity of taxa, were mostly extensive, incorporating the hindlimb down to the shin or ankle.

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However… (moving now away from Dave’s talk).. there are apparently good aerodynamic reasons to think that this configuration didn’t apply to all pterosaurs, and that oceanic soarers in particular (like some ornithocheiroids) may have benefited from a narrow-chord wing. Pterosaurs are highly controversial animals, and it’s interesting that, even now, the extent of the patagia remains one of the most debated issues in the field. Certainly it was the most debated thing I heard about, and toward the end of the conference I had lost count of how many times I’d heard the same discussion (albeit going on among different people). Maybe I spent too much time hanging out with Mike Habib and John Conway, both of whom generally favour narrow-chord wings [adjacent Conway pic of Anhanguera from his excellent palaeo.pterus.net site], and Mike’s argument in particular comes from his understanding of avian wing aerodynamics. I know nothing of aerodynamics and am sceptical of the idea of favouring a theoretical model over fossil evidence – I also harbour the naïve suspicion that organisms are not necessarily optimally ‘designed’, nor do they have to work in a way that makes most sense to us – but I can see that these arguments have merit and that we should remain open-minded.

And that’s not all, lots more to come in part III. It will be posted soonish.

Refs – -

Bonde, N. & Christiansen, P. 2001. Aspects of the detailed anatomy of Rhamphorhynchus. In Two Hundred Years of Pterosaurs, A Symposium on the Anatomy, Evolution, Palaeobiology and Environments of Mesozoic Flying Reptiles. Strata Série 1 11, 29-31.

- . & Christiansen, P. 2003. The detailed anatomy of Rhamphorhynchus: axial pneumaticity and its implications. In Buffetaut, E. & Mazin, J.-M. (eds) Evolution and Palaeobiology of Pterosaurs. Geological Society Special Publication 217. The Geological Society of London, pp. 217-232.

Fleming, T. H. & Lipps, K. R. 1991. Angiosperm endozoochory: were pterosaurs Cretaceous seed dispersers? The American Naturalist 138, 1058-1065.

Frey, E., Tischlinger, H., Buchy, M.-C. & Martill, D. M. 2003. New specimens of Pterosauria (Reptilia) with soft parts with implications for pterosaurian anatomy and locomotion. In Buffetaut, E. & Mazin, J.-M. (eds) Evolution and Palaeobiology of Pterosaurs. Geological Society Special Publication 217. The Geological Society of London, pp. 233-266.

Unwin, D. 2006. The Pterosaurs from Deep Time. Pi Press, New York.

Wellnhofer, P. & Kellner, A. W. A. 1991. The skull of Tapejara wellnhoferi Kellner (Reptilia, Pterosauria) from the Lower Cretaceous Santana Formation of the Araripe Basin, northeastern Brazil. Mitt. Bayer. Staatsslg. Paläont. Hist. Geol. 31, 89-106.

Comments

  1. #1 David Marjanovi?
    September 20, 2007

    Yep, almost all frogs lack teeth in the lower jaw, and the few exceptions are all highly nested in the tree and widely dispersed there. We are quite obviously looking at reversals here.

    There’s also an anecdote about a beetle larva an entomologist who’s currently based in Vienna found some time after a forest fire… the beetle taxon in question was supposed to have lost larval legs tens of Ma ago. Looks like they are only switched off, and the switch denatures in heat…

  2. #2 Zach Miller
    September 20, 2007

    Seriously, Darren, if that fabled Triassic pterosaur doesn’t have a fifth finger or a lizard head or lacks an antorbital fenestrae or something, you know, equally mind-blowing, then all this anticipation isn’t worth it! WHY DO YOU MAKE ME WAIT?!?

    On the patagium issue, I’m afraid it’s something we’ll never know for sure. It’s entirely probable that various pterosaur clades DID have differing patagium structures. We can’t take two taxa (Rhamphorhynchus and Pterodacyl) and apply their patagiums to the entire spectrum of the Pterosauria. I’m quite certain, though future fossil evidence may contradict this, that pterosaurs who led different lifestyles had different patagium constructions.

  3. #3 Darren Naish
    September 21, 2007

    Zach: I’m not making you wait on purpose I promise, I’m just trying to go through things in order. The wait will be over when part III is published later today.

    As for the patagia issue, you’re right that there may always be room for doubt. However, we already have a fairly representative collection of specimens that have patagia preserved (note: far more than just Rhamphorhynchus and Pterodactylus!!), and – the way things are going – it is conceivable that we will eventually end up with a truly compelling data set that extends across pterosaur diversity.

  4. #4 Dave Hone
    September 21, 2007

    I already think the patagium argument / collection is fairly compelling. We have a lot of data and it all comes out to approximately the same shape & structure. True, there was doubtless variation, but pterosaurs are remarkably conservative in some ways and wingshape appears to be one of them.
    In terms of having a basic understanding of the wing shape, attachement and structure, pterosaurs were (within reason) very similar across the board. Blanket statements might be pushing the boundaries, but they serve as useful starting points on a subject like this and are broadly true.

  5. #5 Mike Habib
    September 21, 2007

    Ah yes, the wing attachment debate [insert evil grin]. To be fair, after seeing the wide range of specimens with soft tissue while in Munich, I too have come to the conclusion that the inboard wing probably had a hindlimb attachment in many (if not most) taxa, which I mentioned to David Hone. Of course, I also suspect that this attachment may have been lost in pelagic taxa.

    In any case, it is quite possible to have a fairly narrow wing for most of the span, and a broad attachment inboard, which looks fairly well supported as best I can tell. The resulting wing morphology performs a bit differently from a ‘total’ narrow wing, but not greatly.

  6. #6 Zach Miller
    September 21, 2007

    Okay, new question about the patagium:

    In rhamphorhynchoids, does the hind patagium connect the ankles to the tail, or the the ankles together, and the tail is completely separated from the hind patagium (I know there’s a better term, but my Pterosaurs of Deep Time is at home)? I’ve seen it both ways.

    ALSO, when a pterosaur folded its fourth finger back when grounded, could somebody explain the orientation of the finger to the body? That’s a problem I often run into when trying to reconstruct a walking pterosaur.

  7. #7 Nick
    September 21, 2007

    Darren–

    Just a heads-up: a mouse-over of the image of Tapejara(?) navigans above might give away more information than you intended.

  8. #8 Randy Irmis
    September 22, 2007

    Or maybe the flow-through avian-style lung evolved in basal ornithodirans once, and then invaded the skeleton multiple times…[here's the point where Matt Wedel is supposed to get my back]

  9. #9 Hanneke Meijer
    September 23, 2007

    Hi Darren
    Chapeau for your extensive write-up of the Flugsaurier meeting in Munich. For me, it was an inspiring and fascinating conference and I finally was able to see the faces accompanying the names in the literature.
    From your blog, I get the impression that your interpretation of my talk is somewhat misunderstood. Wellnhofer and Kellner suggested, in their 1991 article, that Tapejara wellnhoferi might have been able to crack seeds with their beak. Seed cracking is just one way of being herbivorous. To investigate this suggestion by Wellnhofer and Kellner, we compared aspects of the skull (it goes a little bit too far to go into all of that here) between Tapejara and several feeding types of birds. As it turned out, the orientation of the quadratum with regard to the ventral skull base does not comply with that seen in typical seedcracking birds such as parrots and finches. In contrast, is more similar to that in birds that ‘pull or push’ on their food items, such as geese and probers. Sofar, our results reject the suggestion by Wellnhofer and Kellner that Tapejara was able of cracking hard objects with its beak. We therefore suggest that it either ate softer plant items, or possible even probed for food items such as small insects. However, our results are very preliminary and there are many more things to take into account to fully understand pterosaur feeding habits.
    I hope that the take home message of my talk has become a little bit more clear now.
    Best, Hanneke Meijer

    [from Darren: thanks Hanneke for the clarification and further information; my apologies for misinterpreting the content of your talk. Maybe I should have taken better notes!]

  10. #10 DDeden
    September 24, 2007

    The mental anguish siren just went off in my head when I read “marsupial tree frogs”… will have to reset the alarm now.

    I assume the young are deposited in a pouch or skinfold or something.

    The photo at top shows what? an egg? I saw no description.

  11. #11 Darren Naish
    September 24, 2007

    The mental anguish siren just went off in my head when I read “marsupial tree frogs”… will have to reset the alarm now.

    You’ve never heard of marsupial tree frogs? You need to get out more :)

    The image at top is the skull of the Brazilian azhdarchoid ‘Tapejara’ navigans: it has a whacking great sail-like crest on the top of its skull (only the base of which has been caught in the photo). The big opening in the middle of the image is the nasoantorbital fenestra: the orbit is posterior to this (to the left). The pointed tip of the bill is at bottom right; I hope you can make sense of this.

  12. #12 DDeden
    September 24, 2007

    Yes, thanks Darren, now I see. Sort of. Not egg. Head. Simple.
    (Nothing pre-miocene makes much sense to me, including flying reptilian protogiraffids.) Reversals? Yes indeed, though never quite identical.

    Subcutaneous air sacs, interesting. My research indicates that early hominoid laryngeal air sacs allowed vertical floating, which paved the way for the loss of the tail and the vertical posture and locomotion amongst extant apes (sacs reduced in upland gibbons), apiths (seen in Lucy and Selam) and man (reduced to laryngocoels found in 2% of humans, due to SC fat and diving/backfloating).

  13. #13 Darren Naish
    September 24, 2007

    You’re not friends with Francois de Sarre are you? :)

  14. #14 David Marjanovi?
    September 25, 2007

    Yes, thanks Darren, now I see. Sort of. Not egg. Head. Simple.

    The skull is the dark part, not the light part.

    I think the rock filling the nasantorbital fenestra is what you see as an egg. The shape fits sort of. (At its right lower “corner” there was the nostril in the living animal.) The opening left of that is the right eye socket.

    My research indicates

    Have you published any of it? If not, it doesn’t make much sense to talk about it, because we can’t evaluate it if we can’t read it.

  15. #15 Matt Wedel
    September 25, 2007

    [here's the point where Matt Wedel is supposed to get my back]

    I’m on it!

    The storefront was in that condition when we got here, officer. I’ve never seen that woman before in my life. And besides, she said she was a licensed masseuse. That? No, that’s baby powder. I’ve, uh, got a rash.

    Or did you mean about the air sacs?

  16. #16 DDeden
    September 25, 2007

    Mr. De Sarre’s ideas are imaginative but seem to defy natural selection. I haven’t met him. (I had to google his name.)

    I think proconsul or close kin was ancestral to hominids.

    DN: “..the opportunistic invasion of diverticula from a subcutaneous air-sac that may have extended across part of the forelimb skeleton”

    My link to air sacs, was considering whether they started in hominoids due to improved vocalization (but small gibbons lack them), flotation (walruses), retained from gliding pneumatization (early arboreal primate gliding (flying squirrel like) mixed frugivore/insectivores (parallel to bat split) that eventually became brachiators due to dense lianas) or something else. Life jackets seem most likely, since the further from water the smaller they get AFAIK, except in chubby back-floating Homo sapiens. (More at paleoanthropology/yahoo group re. gibbon-human shared traits)

    Re. the egg-head, I couldn’t find the feet or wings, that’s why.

  17. #17 DDeden
    September 25, 2007

    DM: Have you published any of it?

    Not officially. However, briefly, for TZ, IMO our ancestors 35ma – 75,000 yrs ago generally lived in strong association with sea level pocket beaches surrounded by cliffs (previously gnawed by Tethyan waves into a sawblade pattern) on continental and island coasts (eg. Iran, Afar); intermittently radiating inland/outward (apes, apiths, Hs with dugouts) during changing sea levels & climate changes. This ecotype fits with virtually all information I have found on ancient ancestors.
    DDeden

  18. #18 Graham King
    March 24, 2008

    Re teeth, life-stages, behaviours, etc, I see no problem with them being absent for a generation or so (or much longer), then reappearing. To ‘lose’ them their total genetic information need not be deleted, just a genetic switch (Hox or something) be tripped ‘off’… then later ‘on’ again… whether by mutation or methylation or whatever. I have even read/heard that the gene that triggers eye development in the mouse works to trigger a Drosophila eye when substituted there (I don’t think I dreamt it?) – ie a gene that effectively says “grow EYE (as detailed elsewhere)”.
    Some people reportedly grow a third set of teeth, it would be interesting to know the mechanism.

  19. #19 johannes
    May 26, 2009

    > Pterosaur skull evolution was also looked at by Michael
    > Fastnacht

    Who, according to the German media – and I mean quality papers like Spiegel, not tabloids – has been charged with murder for allegedely slaying a goth chick with a frying pan :-(.

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