Friday, 11 April 2014

Palaeoartworks, the case studies, part 1: Giant pterosaurs

If you're heading to Lyme Regis this weekend, or indeed at any point until May 4th, you should stop by the Town Mill: a dedicated gallery of palaeoart lies within. It contains more than just a bunch of pictures however, as it also endeavours to explain how palaeoart is done. A good palaeoartist restores long vanished skeletomuscular systems; knows how to fill anatomical gaps; gives a sense of size to alien-looking creatures, and constantly adapts to changing science to render their subjects more accurately. If they do their job well, viewers won't see how much (often considerable!) paper palaeoartists pull across the patchy, cracked fossil record. But how, specifically, are these illusions pulled off? And can we really be that confident about the results?

Some of the answers lie at my Lyme Regis gallery. Along with the paintings you'll find 'Palaeoart Case Studies', short explanations outlining the path from fossil to reconstruction. In each case, relevant fossil material is also provided to demonstrate how much - or little - artists have to work with. There's six of these in total, and I'll be sharing most or all of them here over the next few weeks. First up are the crowd-pleasing giant azhdarchid pterosaurs, animals which are so commonly reconstructed that we must know buttloads about their anatomy and proportions. Or do we? Read on to find out how confident, or not, pterosaur palaeoartists really are about reconstructions of giants like Arambourgiania philadelphiae, below.

Giant azhdarchid pterosaurs: iconic, famous, mysterious


Reconstruction of the giraffe-sized monster pterosaur Arambourgiania philadelphiae. The dirty secret is that 95% of what you see here is extrapolated from other animals.
Restorations of giant azhdarchid pterosaurs like Arambourgiania, Quetzalcoatlus and Hatzegopteryx are understandably common. What captures the imagination more than a giraffe-sized animal with wings spanning 10 m and a 2 m long head? All pterosaurs have an unusual air about them, but giant azhdarchids also have a majesty which is hard for artists to resist. Despite the common nature of their reconstructions however, giant azhdarchid fossils are not only very rare but also extremely fragmentary. No complete, or even near complete, fossils of giant azhdarchid skeletons are known, and a standard family kitchen table could hold the entire inventory of giant azhdarchid bones from around the world. Arambourgiania, for instance, is known from little else than the giant, tubular neck vertebra shown below. It stands to reason that these reconstructions are based largely on inference and educated guesswork, but are they simply products of imagination, or is there more to it?

Arambourgiania philadelphiae holotype vertebra, UJA VF1. From Martill et al. 1998. Scale bar represents 100 mm.

When attempting to restore the appearance of a poorly known fossil species, the first port of call is the anatomy of more completely known, close relatives - the closer the better. The best known azhdarchid species have 3 and 5 m wingspans, so were only a fraction of the size of their bigger cousins. With such a size difference, it is not sensible to assume that the larger animals were perfectly scaled-up versions of these smaller ones. Organisms rarely evolve different sizes without changing proportion somewhere. Bones of larger animals are often more robustly built than those of smaller ones, for instance, because bigger animals have greater masses to support. This is certainly true for giant azhdarchids, as is an disproportionate increase their neck lengths which correlates with size. Paying attention to seemingly trivial scaling details like this can make a tremendous difference to the accuracy of a reconstruction, especially when a lot of extrapolation is involved.

However, this is only half of the story about restoring giant azhdarchids, because deciding which animals are closely related among this group can be difficult. Not all azhdarchids were alike, and the interrelationships between them is unclear. In these muddy taxonomic waters, palaeoartists have to make some educated guesses. Whereas palaeontologists can admit that their data has limitations or that the relevant studies have not been done, palaeoartists have to stretch current data to finish their work. Artists restoring animals with poorly determined taxonomy like giant azhdarchids have to decide which other animals serve as the best models for their reconstructions, and this often involves some degree of intuition and opinion. Such palaeoartworks are especially vulnerable to being proved inaccurate when new data becomes available. Until then, the best reconstructions of these animals are simply those which use the most careful extrapolations and guesswork, and this should be borne in mind when looking at any reconstruction of a giant azhdarchid or other, poorly known fossil species.

Come back soon for the next case study!

Reference

  • Martill, D. M., Frey, E., Sadaqah, R. M., & Khoury, H. N. (1998). Discovery of the holotype of the giant pterosaur Titanopteryx philadelphiae ARAMBOURG 1959, and the status of Arambourgiania and Quetzalcoatlas. Neues Jahrbuch fur Geologie und Palaontologie Abhandlungen, 207, 57-76.

3 comments:

  1. They seem to be getting taller and scarier!

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  2. I seem to remember you saying that treating azdarchid body designs as interchangeable is a bad idea. Was this ever elaborated upon? And was actually made up on examples, or based on differences and common sense that wouldn't be immediately applicable to overall body design (I hope your following what that meant.). I seem to also remember someone saying Hatzegopteryx was more robust and "powerful" then other azdarchids, and your Arambourgiania always seem more gracile and tall then other giant azdarchids... but that's probably just me. Speaking of things I remember you saying, what is the current idea of Dubious Quetzocoatlus?

    Also, is that 95% refering to proportions gotten from other Azdarchids, or more speculative postures, coloration, etc based on modern animals?

    --Sean

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