Wednesday, April 25, 2012

It’s dumb, it’s awesome, it’s… Our lives with pterosaurs, part 2

If you’re wondering what’s going on here, or if you’re looking at the right blog, it’s probably because you haven’t read this yet. And yes, we are stooping this low.

 
Pterosaurs in the modern day! What would it be like if some pterosaurs survived the K/T extinction to coexist amongst our modern biota and in modern environments? Such are the questions we're attempting to answer here. Just to remind you, the only pterosaurs under direct scrutiny in these posts are azhdarchids and nyctosaurids as they seem to be the only pterosaur lineages that were present at the terminal Cretaceous. We spent a lot of the last post discussing how we may try to exploit pterosaurs for our own benefit, and in this concluding post we’re going to consider how we may succeed at coexisting with wild pterosaur populations. (Adjacent image: when stork-like animals go wrong)

NOTE: The Blogger upload system has been a real pig this evening, and formatting this post has been nothing short of a nightmare. Apologies in advance for any choppy bits of text or other issues. I have tried to correct errors as I go, but please let me know if I've missed any. 

Meeting the neighbours

Humanity would probably bump into wild pterosaurs fairly often. Azhdarchid pterosaurs, in particular, achieved very wide distributions in the Cretaceous, being absent only from Antarctica (Witton and Naish 2008; Ösi et al. 2011; see map, above, for the distribution of azhdarchid fossils. From my Ph.D. thesis). Azhdarchid fossils show very strong ties to terrestrial environments,either being preserved in continental freshwater deposits and, when they do occur in marine sediments, they tend to be components of mixed terrestrial/marine biotas (adjacent graph is a sexier version of the same data presented in Witton and Naish [2008] on this topic. I’ve not updated it with new data since then, but the statistics will not have changed significantly to my knowledge). Their distribution across the globe suggests they were versatile animals capable of living in different habitats and climates, and their palaeoenvironmental signature hints that they would preferentially frequent terrestrial settings. Modern azhdarchids, then, may be fairly familiar sights to us if they were around today.


We may even find that some single azhdarchid species were found all over the globe. Some of the recent findings on their flight ability are rather arresting, with the 10 m span giants seemingly capable of flight speeds exceeding 100 kph (62 mph; Witton and Habib 2010). Mike Habib's recent SVP talk suggests that they could remain aloft long enough to travel almost halfway round the world in one sitting (Habib 2010) and, to paraphrase him directly, (imagine this being said VERY LOUDLY for full effect. Those who know Mike will understand why), geographic boundaries would mean nothing to these guys. This may mean that the sort of provincialism we see in some modern fliers may not apply to these forms and, indeed, cautionary words on the implications of this have been said with regard to azhdarchid systematics.

We may not find ourselves quite so acquainted with nyctosaurids, however. Their fossils are generally rarer than those of azhdarchids and, to my knowledge, largely constrained the Americas. Their rarity is of particular interest because Nyctosaurus, perhaps the best known of all nyctosaurids, occurs in the Smoky Hill Formation of Kansas, a deposit that has also supplied over 1000 Pteranodon specimens since 1872. I’m not sure how many Nyctosaurus specimens there are around the world, but I get the impression that it may be dozens, not hundreds or thousands (please let me know otherwise if I’m wrong, though). Assuming that this does not reflect other sampling or preservational biases, it seems that nyctosaurids were simply rather rare animals. Their remains, unlike those of azhdarchids, are also found exclusively in deep marine deposits, suggesting they spent much of their time away from land. Nyctosaurid anatomy agrees with their lack of landlubber status: the loss of the three, small manual digits used in walking and embarrassingly small legs do not suggest proficient terrestrial abilities. By contrast, the development of ossified tendons in the forearms of some nyctosaurid specimens (Bennett 2003; Frey et al. 2006) suggests that they put tremendous, continuous strain on their wings, and the wings themselves are super-long and probably very glide-efficient. The impression one gets, then, is of highly volant creatures that probably spent almost their entire lives in the skies over seas and oceans, so perhaps only sailors and fishermen would regularly see them if they were alive today.

Garbage monsters
In developed countries where little or no primary habitats remains, our modern azhdarchids may spend much of their times in rural areas, as this is probably the closest approximation of their natural habitat, and would, perhaps, provide the largest amount of live prey. The feeding habits of azhdarchids have been controversial since they were identified in the 1970s, but, in what is probably the only thorough exploration of their feeding habits to date, Darren Naish and I concluded that they were most likely ‘terrestrial stalkers’, long-legged predators of relatively small animals sought out in sparsely vegetated settings (Witton and Naish 2008). This idea may not be unfamiliar to many of you: not only have Darren and I waxed lyrical about it repeatedly in various blogs and lectures, but it’s now been immortalised on on TV and even in excellent, excellent comic book format (you can also download the full paper for free). Accordingly, I won’t go into details here, but, for the uninitiated, the seemingly proficient terrestrial abilities and long jaws and neck of azhdarchids seem well suited for hunting small game on land and, often, poorly adapted for anything else. The bulk of modern azhdarchid diets may not be too dissimilar to their Mesozoic ancestors, as these ancient forms were likely to primarily dine on small reptiles, amphibians and mammals that would appear, superficially at least, not too different from their modern representatives. Of course, modern azhdarchid diets would lack a certain non-avian dinosaur flavour, and that would presumably be substituted by various mammal species.

Azhdarchid jaws are generalised enough that we cannot rule out some ocassional bouts of scavenging, and it would be silly to ignore the importance of carrion feeding to some modern azhdarchid analogous, the ‘giant’ storks. Some of these birds – particularly the larger Leptoptilos species (e.g. the adjutant and marabou storks) – frequently forage on carrion (Kahl 1987) and, because we humans are disgusting slobs who do not dispose of our garbage properly, they have expanded their taste for lousy food to leftovers on rubbish tips. Other, more familiar birds are also keen rubbish raiders: I’m sure we’ve all seen local crows and gulls riffling through bins or splitting open refuse sacs. I see no reason why azhdarchids would not develop the same behaviours, so we may find some of them colonising urban areas and living off our waste. Perhaps this would mean that some modern azhdarchid species would be fairly resistant to the current global species decline, as the route to evolutionary success nowadays seems to mostly revolve around living off our garbage (well, it is the only resource we’re not running out of). (Image, above, shows said exploitation of waste in action)

If wild azhdarchids did take foot in urban settings, encounters with them may be a little daunting for human residents. As we discussed in the last post, pterosaurs seem to have increased their average body size over time, so later forms were much larger than the earlier. Perhaps we’d feel fairly confident stopping smaller (2.5 m span) animals from spreading rubbish all over our driveways, but would we feel the same about 4, 7 or 10 m span animals? Perhaps not. Plus, did I mention that these pterosaurs may have been gregarious? Several azhdarchid localities have yielded associated azhdarchid skeletons (Lawson 1975; Cai and Wei 1994) or very abundant azhdarchid remains (Nessov 1984; Ösi et al. 2005), suggesting that they were at least tolerant of each other, or perhaps even hanging around in little groups. All told, in this hypothetical world of pterosaurs, we’d probably need to seriously rethink our philosophy on garbage disposal. Probably best to keep the cat in, too.

They can eat my trash, so long as they don’t eat me
Speaking of modern pterosaur diets, an enormous elephant in the room needs to be acknowledged: would we be on the menu? This is a legitimate question, and not because we’re used to Tinseltown pterosaurs having a taste for human meat. Some azhdarchids were so enormous that they could consume people-sized prey (by which, I mean small adults, not just children). We don’t have particularly extensive fossils of giant azhdarchids to test this with, but we do have a key component for answering this question: a giant pterosaur skull fragment comprising the jaw joint and some bones from the roof of the mouth (shown on the left, in ventral view, in the image below). This belongs to the 10 m span Hatzegopteryx, one of the largest azhdarchids known, and is notable for its unusually robust construction of stout bony struts and enormous jaw condyles. By doubling its width we can attain minimum estimate of the complete jaw width, revealing a staggering maw 500 mm across (Buffetaut et al. 2002, 2003). (Image, below, shows the mirrored Hatzegopteryx jaw skull element. The ventral braincase and posterior jaw region of Thalassodromeus is shown for comparison and to scale. Thalassodromeus, by the way, has a jaw of 160 mm width and 700 - 800 mm long. Hatzegopteryx was mucking huge).



We should remind ourselves at this point that we’re a) talking about the minimum width here, so there's possibly room for a little more expansion; and b) these are, so far as we can tell, animals capable of flight, and yet had skull widths that many large dinosaurs would be jealous of. As with many pterosaurs, the asymmetrical nature of the jaw condyle would deflect the lower jaw laterally when opened so that much of the 500 mm jaw width could be used for swallowing food. The posterior palatal region is also highly vaulted, so there is additional swallowing space in the dorsal region oral cavity, too. Combine this with the likelihood of a large gulf between the mandibular rami occupied by distensible gular pouch (known from several exceptionally-preserved pterosaur specimens), and it seems more than likely that Hatzegopteryx could fit a person into its throat.
After that, of course, you’d need to be moved down the long neck, a length up to 3 m if we assume that the giants had necks of comparable proportions to those of smaller azhdarchids. Unfortunately for us, we have good evidence that pterosaur throat tissues were highly elastic and capable of encompassing large prey, so we may slip through an azhdarchid oesophagus without issue. The preservation of a recently-devoured fish in a complete juvenile Rhamphorhynchus specimen reveals just how large some pterosaur prey items were, and how stretchy their throats must have been to accommodate it (see detail of the trunk region of this specimen, below. After Wellnhofer 1975). The specimen in question was preserved in the process of digesting a fish that – as preserved – occupies 60 per cent of its trunk length, but may have been even larger as the anterior end had already been partially digested (Wellnhofer 1975). Pterosaurs, then, may have had small bodies, but they weren't afraid of packing their meals in. Our previous discussions on how giant pterosaurs could support our weight in flight have obvious connotations here, too: if one could support our weight externally, there seems little reason to suggest they couldn’t internally. We may fill their bellies, but we wouldn't impede their locomotion in doing so.

The outlook isn’t looking promising for us, then. Larger members of the populace may be a bit too massive to comfortably digest, but leaner or smaller folks may well be at risk. In any case, giant azhdarchids would be best avoided. If we did encounter one, would our chances of being eaten be high? Perhaps it would depend on context of engagement. On open ground, the 2.5 m long limbs and powerful muscles of giant azhdarchids would almost certainly chase us down and, hey, let’s not forget: they can fly. It's hard to outrun an animal that can fly fast enough to get a speeding ticket on most roads. We may be safe if we could get to cover or a cluttered setting, as the giant azhdarchid bauplan is hardly suited to moving through narrow confines or probing crevices. Without that, though, I don’t fancy our chances. Azhdarchids of this sort may be quite difficult to deal with too, short of simply killing them. Troublesome bears or cats can be moved far enough away from populous areas that they won’t bother people again, but we’d be hard pressed to stop relocated azhdarchids from simply flying back to wherever we caught them. The more I think about it, the more it seems that large azhdarchids would actually be quite a dilemma for us, and one that would probably see most of them being shot. All told, maybe it’s best for us all that they're extinct.

On that bombshell, then, I think that’s enough of this craziness for the time being. Hopefully, someone, somewhere, will have taken something useful from these posts and, if nothing else, we finally have a picture of a cowboy quad-launching a giant pterosaur. With that, I think my work here, and perhaps the respectable portion of my career, is finished. 

References
  • Bennett, S. C. 2003b.  New crested specimens of the Late Cretaceous pterosaur Nyctosaurus. Palaeontologische Zeitschrift, 77, 61-75.
  • 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.
  • Buffetaut, E., Grigorescu, D. and Csiki, Z. 2003. Giant azhdarchid pterosaurs from the terminal Cretaceous of Transylvania (western Romania). In: Buffetaut, E. and Mazin, J. M. (eds.) Evolution and Palaeobiology of Pterosaurs, Geological Society Special Publication, 217, 91-104.
  • Cai, Z. and Wei, F. 1994. Zhejiangopterus linhaiensis (Pterosauria) from the Upper Cretaceous of Linhai, Zhejiang, China. Vertebrata PalAsiatica, 32, 181-194.
  • Frey, E., Buchy, M. C., Stinnesbeck, W., González, A. G. and Stefano, A. 2006. Muzquizopteryx coahuilensis, n.g., n. sp., a nyctosaurid pterosaur with soft tissue preservation from the Coniacian (Late Cretaceous) of northeast Mexico (Coahuila). Oryctos, 6, 19-40.
  • Habib, M. B. 2010. 10,000 miles: maximum range and soaring efficiency of azhdarchid pterosaurs. Journal of Paleontology, 30, 99A-100A.
  • Kahl, M. P. 1987. An overview of the storks of the world. Colonial Waterbirds, 10, 131-134.
  • Lawson, D. A. 1975. Pterosaur from the Latest Cretaceous of West Texas: discovery of the largest flying creature. Science, 185, 947-948.
  • Nessov, L. A. 1984. Pterosaurs and birds of the Late Cretaceous of Central Asia. Paläontologische Zeitschrift, 1, 47-57.
  • Ősi, A., Weishampel, D. B. and Jianu, C. M. 2005. First evidence of azhdarchid pterosaurs from the Late Cretaceous of Hungary. Acta Palaeontologica Polonica, 50, 777-787.
  • Ősi, A.,Buffetaut, E. and Prondvai, E. 2011. New pterosaurian remains from the Late Cretaceous (Santonian) of Hungary (Iharkút, Csehbánya Formation). Cretaceous Research, 32, 4556-463.
  • Wellnhofer, P. 1975. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Palaeontographica A, 148, 1-33, 132-186, 149, 1-30.
  • Witton, M. P. and Habib, M. B. 2010. On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness. PLoS ONE. 5, e13982.
  • Witton, M. P. and Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE, 3, e2271.

7 comments:

  1. Mark,

    That was a fun ride! With your paleontology career done, though, you can fall back on art. Artists are notoriously prosperous, eh.

    Two things. My reaction to the realization of how big that Hatz jaw was was 'Holy shit!' I mean, I always have that pic of Hatz with you and the giraffe in mind, but had thought we'd just be too big for one to swallow, so that's pretty, hmmm, horrifying.

    Second, what is this "excellent, excellent comic book format" in which giant stalking azhdarchids are immortalized?

    And just in case you're really worried, this series of posts isn't nearly as goofy as 'birds are not dinosaurs'.

    Mike

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  2. Thanks for the nice words, Mike. This was the first time I've digitially reconstructed the Hatzegopteryx jaw pieces and, yes, my reaction was similar.

    For more on the comic depiction of azhdarchid terrestrial stalking, stay tuned. All will be revealed shortly.

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  3. You ought to engage in a bit of speculative bio here! If they make it across the KT/KPg boundary, having something that large and aggressive running around is going to have profound implications for mammalian evolution.

    That'd be a post for another time...

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  4. "imagine this being said VERY LOUDLY for full effect. Those who know Mike will understand why"

    Grin. Yeah, I liked that part. Shocking, I know.

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  5. Would civilisation even exist with pterosaurs eating us?

    That said, I think the largest azdarchids would become extinct via anthropogenic influence, just like our teratorns. Only the smaller species would have any chances of survival.

    By the way, would our plight of island habitats destroy nyctosaurs? Or, since pterosaurs had thin egg shells, the possibility of ovovivipary would save nyctosaurs from introduced pests?

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  6. Mostly off-topic, but I just wanted to say I've been able to acquire a miniature Hatzegopteryx (like this one. I'm quite happy with it :).

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  7. The mention of how huge azhdarchid geographical ranges were (and would be in this scenario) would make conservation efforts difficult if not impossible. Assuming of course that some of the larger species if not domesticated would certainly become endangered quite quickly. Eating our livestock if not us in general.

    Of course we could keep a few in caged enclosures in zoos and things like we do with Condors and such nowadays. And it seems that most azhdarchids were quite comfortable on the ground, maybe they wouldn't mind too much.

    Speaking of which, would it be possible to "clip" pterosaur wings somehow so they can't fly? I've heard bats can fly with quite a bit of their wing membranes gone, and do they grow back if a hole was torn in them?

    If it were possible, I suppose we could keep a flock of flight-incapable azhdarchids in somewhere like the San Diego Wild Animal Park and let them run around and eat little animals.

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