Monday, 21 April 2014

Palaeoartworks, the case studies, part 2: Feathered dinosaurs and tiny Crocodyliformes

It's time for part 2 of our 'Palaeoart Case Studies' series, this time featuring two subjects: the tiny Cretaceous crocodyliform Koumpiodontosuchus and the probable Lower Cretaceous troodontid Yaverlandia bitholus. Unlike our last subject in this series, giant pterosaurs, neither of these animals is huge. Koumpiodontosuchus is particularly diminutive with an estimated adult length of 600 mm long. Presenting the scale of an animal accurate is important for good palaeoart, as it's not only an important factor in the animal's biology and ecology, but also an integral part of it's character. Small animals present palaeoartists with a particular challenge because many folks hold the preconception that all extinct animals were large. For diagrammatic images, simply adding a person, modern animal or familiar object next to our creature shows its size, but this cannot work when rendering scenes that took place millions before familiar entities appeared. How do palaeoartists get around this? Read on to find out.

Yaverlandia represents the result of a recent palaeoart success story. After many years of trying, it seems palaeoartists have finally got the hang of recreating convincing-looking feathered dinosaurs. How did they do this? In short, by abandoning the need to show all dinosaurs as scaly reptiles and embracing the birdiness inherent to many species (or, to flip this around, realising that many traits unique to modern birds were common to many of their dinosaur ancestors). But what does this mean for the way we reconstruct troodontids and other feathered dinosaurs? Again, the answers are below.

This series of case studies is in aid of my art gallery in Lyme Regis, running until May 4th, at the Town Mill. Full details here.

Koumpiodontosuchus: a tiny, button-toothed crocodyliform

Reconstruction of the tiny Wealden bernissartid Koumpiodontosuchus aprosdokitii. Hopefully, you can see that it's not a large animal without having to think about it too much, but why is that?
The size of extinct animals a favourite topic of palaeontology aficionados, and presenting it accurately is an important goal for palaoartists. Although we often think of extinct species as very large animals, most were not giants. The skull of the tiny Cretaceous crocodyliform Koumpiodontosuchus show below, for instance, belonged to an adult individual that, in life, was about 600 mm long. But how can palaeoartists express a sense of animal size - big or small - without the use of modern objects, animals or people for reference?

Some general trends of animal appearance can be useful in conveying size in extinct species. These probably aren’t features that most of us think about when observing animals, but they provide palaoartistists with some tricks to give a sense of scale to their subject matter without using other objects or animals for scale. Generally speaking, facial features - particularly the eyes - of larger creatures are relatively smaller than those of more diminutive animals. The limb bones of larger animals are more robust and, as they approach the extremities, are proportionally shorter. Smaller animals often have less conspicuous muscle contours than larger animals, particularly if they have a fluffy covering and, in being lighter, smaller creatures are frequently more sprightly and ‘weightless’ than larger ones.

Animal proportions only give a very general sense of scale, however. To give a more precise measure, palaeoartists often juxtapose relatively familiar species alongside their subjects. The use of ‘background’ animals, or different varieties of plants, are useful in this respect. Even if the audience is not very familiar with these background entities, their proportions in relation to the subject gives an impression of scale. This can work in inverse, too: bigger animals or plants, shown in low contrast at a distance, can help reinforce the size of smaller subjects. Crafty consideration of point of view can also help: does the subject need a very low, tight point of view to be seen, or does a wider frame capture it more adequately? Again, these are not necessarily factors that we consider when viewing animals or artwork of them, but they are essential considerations for palaeoartists attempting to reconstruct not only the anatomy and lifestyle of their subject, but also their size and physical presence.

Yaverlandia: Britain's most bird-like dinosaur

Two Yaverlandia investigate a termite-riddent tree stump in Lower Cretaceous Britain. As with many other dinosaurs, their depiction here as very bird-like creatures is the result of palaeoartists having to completely overhaul the way feathered dinosaurs are rendered. 
Known only from skull caps, Yaverlandia bitholus is one of Britain’s lesser known dinosaurs. Found in Lower Cretaceous Wessex Formation cliffs close to its namesake, the Isle of Wight coastal village of Yaverland, it was thought for a long time to represent a member of the bone-headed dinosaur group Pachycephalosauridae. Recently, it has been reinterpreted as Britain’s first troodontid, an omnivorous theropod dinosaur closely related to birds and familiar carnivores like Troodon, Velociraptor and Deinonychus. Troodontids were big brained, nimble animals and most were rather small. Yaverlandia was no exception, with a tentative length estimate of about 2 m. 

Any restoration of Yaverlandia and its kin has to incorporate data on dinosaur feathering, details of which have only been available in earnest for the last 20 years or so. The uptake of feathered dinosaurs among palaeoartists has been variable. Some restrict them to specific regions of the body, while others provide smatterings of feathers across primarily scaly skin. Increasing numbers of artists restore these animals as very bird-like however, with feathers across their entire bodies including their heads, tails and legs. Fossil evidence is clearly in line with this latter approach. Bird-like dinosaurs, including troodontids, have been discovered with extensive feathering that covers their not only their torsos necks, heads and tails, but even sometimes their legs and toes. 

These discoveries have given palaeoartists a lot to think about when restoring the appearance of bird-like dinosaur species. Feathers are complex, three-dimensional structures which alter the body profile of their owners. They plump the appearance of the body and smooth contours of the animal’s profile. Thus, if a dinosaur has complex feathers, we can no longer simply restore their musculoskeletal system and wrap skin over it, as often done in the past. What’s more, palaeoartists have to think carefully about the way feathered dinosaur arms and hands are rendered, because their feather configuration is similarly complex modern bird wings: feathers erupt from the tip of the second finger to the elbow, with feathers of the shoulders covering the ‘gap’ between forelimb and body feathering. 

These ‘new look’ dinosaurs are more bird-like than ever, and evidence is mounting that feathers appeared much earlier in dinosaur evolution than classically realised. It is even quite probable that Tyrannosaurus was feathered. This is disheartening to some who ‘prefer’ the appearance of scaly dinosaurs, and many still erroneously render troodontids and their kin with scaly hides. Wholly feathered restorations of such dinosaurs are without doubt factually accurate renditions however, and entirely uncontroversial among scientists. 

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.

Monday, 7 April 2014

Palaeoartworks: a palaeoart gallery at Lyme Regis, April 7th - May 4th



As folks who follow me on Facebook and Twitter will have gathered, recent weeks have been spent not-so-secretly gearing up for my very own palaeoart gallery in the UK's spiritual home of palaeontology, Lyme Regis. Today, we're finally ready to go public: Palaeoartworks, as it's ended up being known, is now open.

Panoramic view of Palaeoartworks in near entirety. Image courtesy Georgia Maclean-Henry.
Palaeoartworks can be found in the Town Mill Malthouse, part of the Town Mill complex in the heart of Lyme Regis (map) and, from today (April 7th), is open every day until May 4th (including the Easter holidays). Admission is free, from 10.30am to 4.30pm daily.

The gallery is part of the famous Lyme Regis Fossil Festival, an annual event celebrating palaeontology and natural history with fossil stalls, outreach events, and public lectures by leading palaeontologists. The festival, now in its 9th year, will be running across the Early May Bank Holiday (Friday - Sunday, 3rd-4th May). I'll be present at the gallery for its final weekend, and it would be great to meet some readers if you find yourself in Lyme Regis for the festival. There may even - for the first time ever - be prints available to buy.

So, what can you expect from the gallery? Hopefully, there's a wide enough range of restorations to keep most tastes happy: dinosaurs, pterosaurs, Crocodyliformes, invertebrates, marine reptiles, even some fish. These are organised into are three collections. The first is dedicated to palaeoart of the Wealden Supergroup, a sequence of Lower Cretaceous sediments found throughout south-east England with an intensely studied palaeobiota and palaeoenvironment. Regular readers will know that I've been publishing a lot of Wealden artwork recently - enough, it seems, to fill the wall of a gallery - and my favourites are now on display.

Ever see a man make a gallery out of Wealden palaeoart? Yes, once.
The second set comprises - big surprise here - pterosaurs, the Mesozoic flying reptiles which need no introduction to anyone reading this (but if you need an introduction, consider this). A lot of the pterosaur imagery is reproduced from my book, but there's also some rarely seen or entirely new stuff here too. Efforts were made to show pterosaurs at their most diverse and interesting: you'll see them swimming, climbing, assaulting little dinosaurs, imitating famous film posters, and all sorts of stuff.

Partial shot of the 'Pterosaur' collection. There's a lot more to see in the gallery itself.
The last collection doesn't really have a theme, instead just being a suite of pieces I especially like: mating tyrannosaurs, fuzzy pachyrhinosaurs, noir-inspired palaeoart and so on. This section also features a video of art for which there was no space, including several brand new pieces and modified versions of older artwork. All of the art in the collection was produced in the last three years.

Miscellaneous palaeoart things: paintings, a discussion of ammonite palaeoart, and a scrolling movie of artwork. 
If pictures say 1000 words, there's at least 40,000 words on display at my Palaeoartworks. That, however, wasn't quite verbose enough for me, so you'll also find general introductions to the principle art subjects and several 'Palaeoart Case Studies': plinths showcasing fossil specimens behind select reconstructions and some explanation of how palaeoartists use these in their work. There's six of these in total, detailing the different approaches palaeoartists can take to fossil reconstruction, how sometimes we have to look beyond fossils of one particular species to obtain data, and how confident we can be about the resultant restorations. I'll share some of these brief bits of text online over the next few weeks.

So that's Palaeoartworks, then. Coming off the back of a post where the status of the palaeoart industry was not shown in a particularly good light (head here for the full article), it's nice to be writing about an event which pushes palaeoart to the fore. We need more events like this. Overall, I'm really happy with the gallery and hope you enjoy it too - remember to sign my guest book so I know you've visited!

A few acknowledgements

Naturally, there are a lot of people to thank here. Hats off to Kimberly Clarke for inviting my work down to Lyme Regis and organising the gallery space; Philip Clayton for helping organise and install the gallery; University of Portsmouth for sponsoring my printing costs and supplying in-house printing services; Gary Blackwell of Dinosaur Isle and Steve Sweetman for supplying a cast of Koumpiodontosuchus. A huge thanks to palaeoartist and Maximum cassowary-wrangler Gareth 'GaffaMondo' Monger, who provided top-quality printing and framing under tight deadlines (is there any other type?) - Granthams prints come highly recommended. Southsea Gallery virtually saved the show at the last moment. Finally, as usual, thanks to Georgia Maclean-Henry for help and support throughout the entire organisation and installation process. It's totally her fault if the pictures are wonky, though.

Friday, 4 April 2014

Can palaeoart prevent the over-commercialisation of fossils?

If money was no object, would you buy a sauropod skeleton, or artwork of one? A question to ponder while these Lower Cretaceous rebbachisaurids and 'Angloposeidon' look for water in this desiccating Wealden lake.
The greatest threat to 21st century palaeontology is the inflating commercialisation of fossils. At least, this the view put forward in a recent article by Kenshu Shimada and colleagues (2014), and I don't disagree with them. While the commercialisation of fossils is not inherently wrong, the explosion in auctioning spectacular fossil specimens, often at prices which are well beyond the reach of the scientific institutions, presents many concerns for palaeontological science. This is more than just jealousy from poor palaeontological institutions: it causes illegal plundering of fossil specimens, locality vandalism and loss of specimen provenance, robbing fossils of almost all scientific worth. Some legitimate scientists are involved in this game, either selling, lending their interpretation to auction lots, or publishing details of privately-owned fossils in peer reviewed literature. The latter, even when done with the best intentions (e.g. Sereno et al. 2009; Tischlinger and Frey 2013) panders to the private fossil market, sending a signal that scientists will accept and make-do with this new status quo. Even museums are getting in on the act, toying with the idea of selling off historically-valuable specimens for funding. At auction, commercial dealers often mislead buyers with scientific over-advertisement to increase lot appeal, making claims which have not been substantiated by genuine scientific investigation. The result has been years of debate over the legalities, economy and ethics of fossil commercialisation, with little evidence of a balance between those wanting to profit from and privatise fossils, and those who want them publicly preserved, studied and shared.

Desperate times call for desperate measures, and maybe a radical approach is needed to help settle these debates. Such an idea was pushed forward by Shimada et al. (2014), who proposed that commercialising palaeoart may be a viable alternative to selling spectacular fossils. This is not quite the first time this idea has been mentioned, although I think it's the first time it's been mentioned in print. Shimada et al. do not dwell on the point too long, merely stating that:
"...suggestions have also been made that, similar to the annual meetings of the SVP, our paleontological community can perhaps promote the sales of fossil replicas and 'paleo arts' (e.g., paintings and 3-D models of extinct organisms) as acceptable alternatives [to real fossil specimens]." Shimada et al. 2014, p. 3
Intuitively, this seems like a good idea. Combining the lucrative art market with palaeontology should allow collectors to own fossil-related wares without loss of scientifically-important specimens. Palaeoartists would make money, more specimens would end up in academic institutions, and collectors would obtain rare and valuable items - everyone seems to win in this arrangement. As someone with some experience of working within the palaeoart industry however, I'm not convinced that this plan could be executed in the foreseeable future, nor that it provides a solution to the problems of over-commercialising fossils. There seem to be three problems here: 1) original palaeoart and fossil specimens are not as readily interchanged as some may think; 2) our art is not seen as particularly interesting or varied to wider audiences, and 3) the palaeoart community is simply not in shape to offer the high-value, desirable art required for this bid, and will not be until it receives a lot more support from the scientific community at large.

Tarbosaurus specimen made famous - or more rightly infamous - when put up for auction in 2012. It was ultimately repatriated to Mongolia after palaeontologists pointed out the illegal nature of its exportation from its native country. Image from (shudder) the Daily Mail.

1. Palaeoart cannot compete with genuine fossils for aesthetic appeal or as a status symbol

As with any material item, the ownership of fossils is pursued because of academic interest, the collector mindset of owning unique objects, admiration of the natural beauty and the attainment of status. Fossil specimens, particularly large and spectacular ones, not only meet these criteria but exceed them. They're extremely rare. They cost lots of money to buy and maintain. And they're amazing. Looking at a fossil reminds us of unfathomable depths of time and evolution, and the very limits of our human experience. You don't have to know anything about fossils or palaeontology to be awed by them: their mystery, impressiveness, rarity and worth is obvious to anyone. It's little wonder that fossils can be sold at auction for large sums of money: they're immensely charismatic objects, and make major statements about the taste and wealth of their buyers.

If we intend on replacing fossils with palaeoartworks at auction, the latter needs to replace this appeal. Unfortunately, even the best-executed, most accurate, or most famous palaeoartworks can't inspire the same interest and awe as fossils themselves. That's not because palaeoartists are bad at their jobs, but because fossils and palaeoart are completely different entities. Fossils are natural objects obtained by chance and perseverance, and palaeoart is a human-derived statement about palaeontological science. It seems naive to expect rich buyers to turn from fossils to fossil-related artwork when the two have such different cultural statuses, and I think we are misunderstanding the people buying fossils if we think we can simply swap one for the other. We should probably abandon any hope of palaeoart being fossil substitutes, and realise that we need to sell palaeoart on its own merits.

Like any art, selling palaeoart is dependent on it being a fashionable commodity, culturally significant enough that it seems worth spending money on. Working against palaeoart in this regard is its real lack of status outside of the (largely online) palaeontology community. Palaeoart processes and credibility are poorly understood among the public and its most revered practitioners are entirely unheard of. It seems mostly considered a branch of dry scientific illustration, anonymous visual manifestations of what palaeontologists are imagining at a given time. Other times, palaeoart is seen as art for children, or pseudo-fantasy work with a similar target demographic to science fiction and fantasy media. In short, palaeoart is neither considered fashionable or culturally significant, and is not likely to appeal to the rich companies and celebrities who buy spectacular fossils at auction. The fact that master palaeoartists frequently find it difficult to auction their work at worthwhile prices lends credence to this idea. Sales of high-value palaeoart will not happen until we can demonstrate its cultural significance to people outside of palaeontology, and that's going to be an uphill struggle.

2. Palaeoart is probably too stylistically and compositionally homogenous to appeal to wider audiences

Because some art is sold on the strength of its style or composition, palaeoart may make some headway in the high-stakes open market so long as it offers a range of styles and subjects, with varied compositions and themes. Currently, palaeoart offers quite the opposite however, as it's compositionally and stylistically rather homogenous. Only rarely do palaeoartists deviate from realistic-ish portraits of animals, or animals in landscapes, to more stylistic or abstract waters. To my knowledge, this has never been done for significant financial gain. And yes, while palaeoartists do differ stylistically, it's a marginal difference compared to the spectrum in other branches of art. It's little surprise that palaeoart has entered a deconstructionist phase in recent years because its practitioners have noticed how repetitive and trope-filled a lot of palaeoart is (Conway et al. 2013). From a marketing point of view, this is dangerous territory. It's easy to imagine that many will take the attitude that 'once you've seen one piece of palaeoart, you've seen it all', and if its general style or compositions are not to taste, there's little chance of it being bought. We must remember that our objective here is to make palaeoart appeal as widely as possible, and not only to palaeontologists and dinosaur fans.

Those of us who know palaeoart may argue that it is continually changing and developing, and subject to fashions and trends as much as other artworks. These are mostly related to the methods of reconstruction and changes in science however, which are subtle to the point of near-undetectability for lay audiences. Palaeoartists and palaeoart fans may consider the publication of All Yesterdays (Conway et al. 2013) a recent landmark in palaeoart methodology, but for the uninitiated, it's just an excuse to draw extinct animals in different postures or with slightly tweaked anatomy. In short, unless potential buyers are up on palaeontological and palaeoart history - and most aren't - this significance of palaeoartworks will be missed. Our current lack of artistic diversity may be a real problem for those wanting to make palaeoart a valuable commodity.

Misty the Diplodocus, auctioned last year in the UK for £400,000. Image by Luke MacGregor/Reuters, from here.

3. Palaeoart needs support to develop the culture required for commercialisation

The points made above highlight palaeoart's biggest problem: it basically lacks context and culture outside of a tiny community. There's no way we can take this little industry to auction and expect it to compete with awesome fossils. There may be ways we can alter this, but it might require a significant overhaul of the way palaeoartists work with scientists, educators and the media. To be honest, palaeoartists are presently treated quite awfully with little public promotion, a resulting lack of public identity and an infamously poor and unreliable economy. This condition describes the 'major players' or 'masters' of palaeoart as well as its lesser-known or new, fledgling artists. We need to change this if we want palaeoart to step into the world of high-value auctions.

How might we go about this? Firstly, it is time that artists were obviously and publicly credited for their work. In other industries, artist names are essentially brands. Artwork is frequently valued because of who produced it rather than the art itself. In most off-line activities, palaeoartist accreditations are difficult to spot or, worse, allocated to faceless institutions or companies. This is even so in richly illustrated palaeontology books, where artists are treated as secondary importance to authors. This may be why palaeoart is often only seen as an extension of science: funny as it sounds, we rarely acknowledge palaeoartist roles in producing palaeoart. As long as we largely deny exposure and name-recognition to palaeoartists, no-one will pay top dollar for their work. Perhaps we should start prominently naming artists who make significant contributions to palaeontological projects - galleries, articles and books - to start building their reputations. With time, artist association may pay off commercially, lending 'brand recognition', credence or quality to the projects they work on. People could start to follow palaeoartist careers in the way we can musicians and actors and, when their original work comes up for sale, potential buyers will have some concept of its significance to the artist as well as wider scientific culture.

We also need to stamp out the idea that all palaeoart, and palaeoartists, are interchangeable. Not only is it highly detimental to palaeoartworks, but it cripples the industry as a whole. Book publishers, outreach coordinators and even major museums regularly have in-house artists directly copy palaeoartworks rather than using original work. Sometimes, the shamelessness of these acts is unbelievable. The reasons for this are normally to do with money and desire for 'in house' styling. This is a disaster for multiple reasons. From an outreach perspective, plagiarising artists often misunderstand their subjects and make mistakes: we fail in our goal of conveying palaeontology accurately. More broadly, these acts are questionable ethically and legally, they dilute the importance and impact of original work, are insulting to the original artists, and ultimately reduce the market value of palaeoartworks. I can't think of another artistic medium which allows this. Radio stations didn't play cover versions of Beatles songs because they don't want to pay royalties. Book publishers do not force artists to re-draw the Mona Lisa so it matches their house styles. They herald the art for what it is, its significance, and the hard work of the people behind it. By allowing palaeoart to be copied so liberally, we send the message that the artists are unimportant, which means their work is also worthless and undesirable.

The sort of crap palaeoartists have to put up with all the time. One is an original image considered shocking and thought provoking when first published, the other is a direct knock-off, produced for profit by a renowned palaeoart plagiarist. The institution hiring the latter has since taken the offending image, and others of similar derivation, out of circulation. 
This has to change if palaeoart is to develop any real sense of culture. After all, if the palaeontological community does not respect its artists, how can we expect wider audiences to? We need to stop employing individuals who repeatedly rip off other people's work and, if asked, palaeoartists themselves should refuse outright to rip-off the art of their colleagues. Authors, exhibition developers, publishers, and educators should employ genuine palaeoartists rather than knock-off illustrators, and obtain the education to know when 'historically important' images are more appropriate than new ones. We cannot have culture without a sense of history, after all. Some folks within the palaeontological community already strive to do this, often against the tide of publisher might. Palaeoartists do also sometimes get treated well by publishers, even being featured in well publicised, high quality books celebrating their art (e.g. White 2012). Unfortunately, these are exceptional instances in the palaeontological community, when they should be normal. I don't doubt this proposal will require more money to obtain original artwork for projects rather than second-rate copies, but the investment might pay off: better treatment and more business for palaeoartists; higher quality work for the products concerned; and more marketability for both. This would be a major step towards offering palaeoart as a replacement for fossil specimens.

Longer term, granting palaeoartists more fame, income and success can only have a positive outcome. Financially comfortable artists have more time to make art, which gives us more art to sell instead of fossils. Moreover, it allows time for experimentation. Palaeoart really needs this if we want it to float economically outside of the immediate palaeontological community. We need more stylised and abstract art in addition to more conventional scientific illustrations, or service to dinosaur fanboys. We can look to the popularity of modern animal artwork as a guide here: it's very popular, but also mostly stylised. Palaeoartists have little to offer in this area at the moment, and, if palaeoart is to really help push against over-commercialisation of fossils, we need fossil-based art which is as interesting and striking as the fossils themselves.

But will any of this ever happen?

The palaeoart industry has always been a bit of a slum to work in. Even Charles Knight, arguably the most famous palaeoartist ever, spent much of his career on sporadic contracts which made relatively little money (Milner 2012). There's no obvious sign that this is going to change either, or - from a strictly functional perspective - that it even has to. Palaeoart will probably always be around, its practitioners making the best they can from the opportunities that come their way. But this is not to say that perseverance alone makes it fit for high profile auctions as an antidote to over-commercialisation of fossils. There's very little palaeoart can do to develop itself, let alone take the brunt for another cause, until it is properly supported and respected by scientific and media communities, and we stop treating it as a near-worthless addendum to palaeontological science.

References


  • Conway, J., Kosemen, C. M. & Naish, D. (2012). All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals. Irregular Books.
  • Milner, R. (2012). Charles R. Knight: The Artist who Saw Through Time. Abrams.
  • Sereno, P. C., Tan, L., Brusatte, S. L., Kriegstein, H. J., Zhao, X., & Cloward, K. (2009). Tyrannosaurid skeletal design first evolved at small body size. Science, 326(5951), 418-422.
  • Shimada, K; Currie, P. J., Scott, E., & Sumida, S. S. (2014). The greatest challenge to 21st century paleontology: When commercialization of fossils threatens the science. Palaeontologia Electronica Vol. 17, Issue 1; 1E: 4 p;
  • Tischlinger, H. & Frey, E. (2014). A new pterosaur with mosaic characters of basal and pterodactyloid pterosauria from the Upper Kimmeridgian of Painten (Upper Palatinate, Germany). Archaeopteryx, 31: 1-13.
  • White, S. (2012). Dinosaur Art: the World’s Greatest Paleoart. Titan Books, London.

Tuesday, 11 March 2014

Episode 3: Bernissartids, the button-toothed Crocodyliformes

3/3 - this, ladies and gentlemen, is the end. At least, until the inevitable prequels where I'll ignore the canon of the expanded universe and do my best to tarnish everything you liked about the original trilogy.
Here we are then, the last instalment of the Wealden Crocodyliformes Trilogy. Following the posts on atoposaurids and goniopholidids, today we're going out with a bang by covering a newly described Wealden crocodyliform unleashed on the world this morning. The study was written up by my University of Portsmouth chums and colleagues Steve Sweetman, Ulysse Pedreira-Segade and Steven Vidovic (Sweetman et al. 2014), and Steve V. has covered some aspects of his involvement at his blog. The paper is open-access so, for the full skinny on the discovery, you should head here.

This most recently identified Wealden crocodyliform is among the most sophisticated and unusual of all Wealden crocs. Named Koumpiodontosuchus aprosdokitii, it is known from a well-preserved skull which was recovered in circumstances owing much to chance and good fortune (Sweetman et al. 2014). This animal is currently only known for certain from the Wessex Formation of the Isle of Wight, specifically from fossil-rich cliffs next to the seaside village of Yaverland, and the only known skull of it is broken in half. The posterior half was discovered in March 2011 by holidaying fossil hunters, who took it to the local dinosaur museum (Dinosaur Isle, of Sandown) to have it identified. Another family, on a fossil-hunting holiday three months later, then found the front half of the skull. They took this to the same museum where, by chance, the same museum staff who’d handled the first piece were on hand. It was realised that each piece belonged to the same specimen, and the first half was rapidly brought back to the museum to check the degree of articulation. Remarkably, the join between the broken pieces was near perfect – clearly neither chunk had been exposed to weathering effects very long before being discovered – and the entire skull could be seen. Each piece was then donated to the museum to allow its study. Given the chain of events and people involved in the discovery of Koumpiodontosuchus, it’s easy to imagine how only single halves of the skull might be known to science, or even neither. This is clearly yet another story which stresses the importance of amateur fossil hunters to Wealden fossil discoveries, and the benefits of responsible collecting.

Holotype skull and mandible of the button-toothed crocodyliform, Koumpiodontosuchus aprosdokitii. From Sweetman et al. 2014.

Button-toothed crocodiles in context

Koumpiodontosuchus is a member of Bernissartidae, a group named by Sweetman et al. (2014) which only contains two species: Koumpiodontosuchus and Bernissartia fagesii. The latter is a famous, small Jurassic and Cretaceous crocodyliform known from France, Denmark, Spain, Portugal and particularly Belgium, where a spectacular complete skeleton has been unearthed. Indeterminate species of Bernissartia also seem to occur in the Ashdown Formation of Hastings (Salisbury and Naish 2011), but this identification may eventually warrant reappraisal now that Koumpiodontosuchus has been discovered. Bernissartid remains are not new, some of the first material of these animals being documented in the 1850s and Bernissartia itself being named from Belgian fossils in the 1880s. Isolated teeth, likely referable to Koumpiodontosuchus, have been found in Wealden deposits since at least the 1970s (Buffetaut and Ford 1979), so were clearly present across the entire geographic and stratigraphic range of the Wealden Supergroup.

Bernissartia has long been a bit of an oddball among Crocodyliformes, possessing some unusual anatomy and being of uncertain placement in crocodyliform systematics. The discovery of Koumpiodontosuchus provided a bit of light on this front, suggesting that Bernissartia was part of a group containing at least one other similar species, and that they occupy an evolutionary place between atoposaurids and the goniopholidid + Eusuchia radiation. This position isn’t too surprising, as there are a number of features in bernissartids which link them to Eusuchia – see below. Bernissartidae is primarily defined by dental characteristics, with the most obvious one also being the namesake of Koumpiodontosuchus: “button-toothed crocodile” (if anyone wants a common name for these Crocodyliformes, this is the one to use). The posterior teeth of bernissartids are rather globose – wide, short and blunt – and distinctive compared to the dentitions of most other Crocodyliformes. It’s these teeth which, even in isolation, betrayed the presence of bernissartids in the Wealden well before the more substantial Koumpiodontosuchus fossil was discovered. Their other teeth are quite different to this, however. The mid-region dentition is rather conical in shape; ‘pseudocanines’ erupt about 25 % of the jaw length from the jaw tip, and conical teeth emerge procumbently from the jaw tips themselves. Koumpiodontosuchus has two large pseudocanines on its lower jaw, which erupt so close to each other that they share a single, enlarged tooth socket. Bernissartia, by contrast, only possesses one.

The new Wealden bernissartid Koumpiodontosuchus aprosdokitii foraging for molluscs. It's eating a mud snail, Viviparus cariniferus, while tiny (6 mm long) physid gastropods Prophysa crawl over pond scum in the lower left of the image. Dragonflies provide scale, while unnamed tetanurans (based on findings of Benson et al. 2009) prowl around the background. This reconstruction is featured in Sweetman et al. (2014).
Bernissartids packed this sophisticated dentition into relatively tiny jaws: these were not big crocodyliforms. Indeed, with body lengths of approximately 600 mm, bernissartids were probably the smallest crocodyliform species in the entire Wealden succession. Like goniopholidids, bernissartids bore osteoderm shields on their backs and bellies, but the dorsal series was rather more complex than those of other Wealden crocodyliforms. Rather than possessing two rows of interlocking osteoderms as we saw in goniopholidids and atoposaurids, bernissartids possess four rows of osteoderms along their backs. These comprise two sets of rectangular, double-keeled scutes along the midline, and laterally bordering square osteoderms with single keels (Salisbury and Frey 2001). None of these interlocked, and – based on what we’ve discussed for other Wealden Crocodyliformes – it’s worth considering what impact this had on bernissartid locomotion. Rather than supporting their trunks with scutes, it seems that bernissartids developed procoelus trunk vertebrae (that is, vertebrae with centra extending into the corpus of the vertebra behind) to support their bodies when walking (Salisbury and Frey 2001). This feature, along with their relatively complex osteoderms, is shared with eusuchians and are some of the reasons why these animals have classically been allied to these Crocodyliformes. Of further interest here is the biconvex nature of the first bernissartid tail vertebra – this has further implications for their locomotion, which we’ll get to below.

The bit on palaeoecology

Ecologically, it seems that bernissartids had a preference for hard shelled prey. Their blunt posterior dentition has been labelled as ‘tribodont’ – literally meaning ‘crushing teeth’ – and, like slamming a couple of anvils together, are ideally shaped to crunch hard shells. Some confirmation of this idea is seen in the wear facets often seen on tribodont bernissartid teeth. Classically, their prey was largely considered to comprise molluscs such as the freshwater snails and clams populating Wealden streams and lakes (Buffetaut and Ford 1979). Recently, a broader diet has been postulated for bernissartids however, the logic being that hard shells are hardly restricted to molluscs even in freshwater settings (Sweetman et al. 2014). Insects and crayfish probably formed as much of their diet as molluscs, all of which were likely procured or extracted from soft-substrates with the procumbent anterior teeth. We should not forget the savage-looking pseudocanines of these animals however: these would be of little use against hard prey items, but may have allowed for spearing relatively soft-animals. Perhaps bernissartids are best viewed as rather opportunistic feeders, primarily taking hard-shelled prey but not turning their noses to other types of food when the opportunity arose.

If gastropods like this Wealden mud snail, Viviparus cariniferus, had nightmares, they contained bernissartids. 
Where was most of this prey caught? There is evidence that bernissartids were equally at home in water and on land. Their biconvex first tail vertebra suggests their tails were capable of considerable movement for providing burst propulsion through water and, unlike most other Wealden Crocodyliformes, their lack of interlocking osteoderms facilitated lateral trunk motion (Salisbury and Frey 2001). While compromising overall speed, this may have permitted greater amounts of manoeuvrability – ideal for pursing nimble, if relatively slow, aquatic arthropods. We’ve already mentioned that the reinforced trunk vertebrae of bernissartids would provide ample reinforcement for terrestrial locomotion, and their small size is relevant here as well. Like the small-bodied atoposaurids, and unlike the big goniopholidids, bernissartids had relatively small amounts of weight to lug around on land and could likely sustain long periods of terrestrial locomotion without tiring. It’s possible, therefore, that they found much of their prey on land as well as in water, perhaps enjoying the beetles, cockroaches and other tough-shelled terrestrial insects known to occur in Wealden deposits.

It’s worth pointing out that bernissartids may not be the only Wealden Crocodyliformes adapted for hard-shelled prey. The poorly known, 1.5 m long Wealden eusuchian Hylaeochampsa vectiana also has large posterior teeth ideal for smashing shelled prey (Clark and Norell 1992), although the dentitions of other hylaeochampsids are complex and it’s possible Hylaeochampsa had a very varied diet. As discussed for other Wealden Crocodyliformes, it’s likely that the size difference between the bernissartids and Hylaeochampsa would prevent too much overlap in prey preference: the latter may have been capable of eating large molluscs or even small armoured vertebrates, which were probably unavailable to bernissartids. There's lots more we could say here, but I'd best not - maybe Hylaeochampsa will warrant dedicated discussion at a later date.

The end

And I guess that's where we'll leave the Wealden Crocodyliformes for now. As alluded to above, there are other crocodyliform species and groups we could discuss, but they're generally less well known than the taxa we've covered across these posts and it would be difficult to discuss them in comparative depth. I hope you've enjoyed this series of themed posts and, if artwork of ancient Wealden animals is your thing, come back soon for a big announcement about an event related to just that.

References

  • Benson, R. B., Brusatte, S. L., Hutt, S., & Naish, D. (2009). A new large basal tetanuran (Dinosauria: Theropoda) from the Wessex Formation (Barremian) of the Isle of Wight, England. Journal of vertebrate Paleontology, 29(2), 612-615.
  • Buffetaut, E., & Ford, R. L. E. (1979). The crocodilian Bernissartia in the Wealden of the Isle of Wight. Palaeontology, 22(4), 905-912.
  • Clark, J. M., & Norell, M. (1992). The Early Cretaceous crocodylomorph Hylaeochampsa vectiana from the wealden of the Isle of Wight. American Museum novitates; no. 3032.
  • Salisbury, S. W. & Naish, D. (2011). Crocodilians. In Batten, D. J. (ed.) English Wealden Fossils. The Palaeontological Association (London), pp. 305-369.
  • Salisbury, S. W. & Frey, E. 2000. A biomechanical transformation model for the evolution of semi-spheroidal articulations between adjoining vertebral bodies in crocodilians. In Grigg, G. C., Seebacher, F. & Franklin, C. E. (eds) Crocodilian Biology and Evolution. Surry Beatty & Sons (Chipping Norton, Aus.), pp. 85-134.
  • Sweetman, S.C., Pedreira-Segade, U., & Vidovic, S. (2014) A new bernissartiid crocodyliform from the Lower Cretaceous Wessex Formation (Wealden Group, Barremian) of the Isle of Wight, southern England. Acta Palaeontologica Polonica (in press)

Monday, 10 March 2014

Episode 2: The Wealden River Masters, goniopholidid Crocodyliformes

Insert your own whoops, hollers,cheers, or discharging firearms here. 
Welcome to Episode 2 of the snappily-titled Wealden Crocodyliformes Trilogy!* We'll waste no time with introduction - read this if you haven't already - and dive straight into our second group, the goniopholidids. Much of the information herein is derived from Salisbury and Naish (2011) so, if in doubt, consult this tome for further details.

*Snappily titled? And it's about crocodiles...? Man, I'm so wasted on you guys.

Without question, the Wealden waterways were lorded over by a group of Crocodyliformes known as Goniopholididae. The namesake of this group, Goniopholis, is one of the more familiar Mesozoic crocodyliforms after famous taxa like Sarcosuchus and Deinosuchus, and is well known as a relatively ‘conventional’ crocodyliform compared to some of the other weirdo crocs doing the rounds in the Mesozoic. Goniopholidids are found throughout Jurassic and Cretaceous rocks in the Northern Hemisphere and are part of several famous fossil faunas, including being the best known crocodyliforms of the Wealden fauna. Miscellaneous goniopholidid teeth and scutes occur throughout the Wealden, and their existence has been known for a long time. Teeth ultimately attributed to indeterminate goniopholidids were found in Sussex during the 1820s by Gideon Mantell as part of the same collections of crocodile’ material which was later found to contain unappreciated early records of Wealden baryonychines.

Despite this long history, work on Wealden goniopoholids is still developing (Salisbury and Naish 2011). At one time, most Wealden goniopholid taxa were considered members of Goniopholis proper, the famous Owen-named genus of great historic significance. As with many 'classic' genera, Goniopholis is now appreciated to be a bit of a taxonomic mess and claims of 19 species are being scrutinised (e.g. Salisbury and Naish 2011; Andrade et al. 2012). Recent reviews have suggested that the Wealden goniopholidid assemblage contains a sole Goniopholis species from the Weald Sub-basin and two other genera from the Wessex Sub-basin, all known from good skull material and, in the latter instances, a series of articulated postcranial remains (Salisbury and Naish 2011). These named species include Goniopholis willetti from the Grinstead Clay Formation, Sussex; Anteophthalmosuchus hooleyi (below), from the Wessex and Vectis Formations of the Isle of Wight, and Vectisuchus leptognathus, also of the Wessex Formation (why Vectisuchus when it’s not found in the Vectis Formation? ‘Vectis’ is the Roman word for the Isle of Wight, so ‘Vectis’ frequently pops up in animal names from this part of the world). The latter was almost known from a complete skeleton, but a cliff fall during its collection rendered much of the hindlimb, pelvis and tail inaccessible. In spite of this incident, it’s still fair to say that this group has one of the better records among Wealden reptiles, and it might get even better. Fragmentary goniopholidid jaw fossils hint at further, unnamed species, but they are currently too poorly represented to warrant naming.

The Wealden goniopholidid Anteophthalmosuchus hooleyi takes advantage of a flooding river to hunt two stranded Hypsilophodon foxii. The big one is Using the Ballet to escape.

Goniopholidids vs. modern crocodilians, round 1: anatomy

What kind of Crocodyliformes were goniopholidids? Because these animals appear to resemble modern crocodiles in size, shape and probably lifestyle moreso than any other well-known Mesozoic Crocodyliformes, they are often reconstructed as ancient copies of large modern species like Nile or saltwater crocodiles (e.g. Karl et al. 2006 - see reconstruction here). This isn’t really the case, however: goniopholidids may look a little similar to modern crocodilians at first glance, but much of their anatomy is unconventional and their possible habits were likely rather different. If we compare these aspects directly, their differences will soon become apparent.

We’ll start with size. Here, it must be said, goniopholids are undoubtedly pretty similar to modern crocodilians. The largest Wealden goniopholidids – Anteophthalmosuchus and G. willetti - were large animals each attaining at least 3.5 m long. This is a pretty comparable size for many modern crocodiles, and may even seem a little on the small side compared to the 5 m+ lengths attained by some extant crocodilians. Don’t be fooled into thinking this makes Wealden goniopholids diminutive creatures, however: a 3.5 m long crocodyliform would somewhere around 200 kg in weight and stretch longer than your 3-seater sofa. These were undoubtedly big, bulky animals. Vectisuchus, by contrast, was a much smaller species, only attaining 1.2 m in length.

In fine anatomy, we start to see obvious differences between the ancient goniopholids and modern crocodilians. Goniopholidid backs were covered with two rows of rectangular osteoderms with interlocking pegs at their distal margins – they are much like the atoposaurids we met last time in this respect (Salisbury and Frey 2000). These are largely devoid of ornamentation with only slight keels along their dorsal surfaces. This configuration is rather different to the more complex and ornate osteoderm arrangements seen in modern crocodyliforms, and goniopholidid osteoderm shields would probably seem rather simple and inelegant by contrast. Also unlike modern crocs, goniopholid osteoderms do not extend far up the neck, perhaps because doing so would impair neck mobility (see below), and further osteoderms were found along their bellies. These were formed of hexagonal plates rather than long, rectangular ones however. Another key distinction between goniopholidids and modern crocodilians is found in their forelimbs. Most goniopholids have arms which are at least as long as their legs and many species - including Anteophthalmosuchus and Vectisuchus – have forelimbs which surpass the length of the hindlimb. This increased length is provided by relatively elongate humeri and wrist bones, and would give goniopholidids taller statures than those of all modern crocs, which are always shorter up front than behind. If we extending this comparison further, we’ll see that goniopholidid forelimb length is almost unique among all Crocdyliformes, being longer than virtually all of their relatives.

Like many modern crocodilians, goniopholidids possess the well-built, powerful skulls of formidable predators. There is also overlap in general skull shape with modern crocs too, with G. willetti and Vectisuchus having rather long, slender snouts which are narrower than the posterior regions of their jaws. By contrast, the skull of Anteophthalmosuchus belongs to a real bruiser; its jaws only gently converge from the enormous posterior region to form a chunky, roughly triangular skull with a rounded muzzle. Both skull types are equipped with goodly-sized, slightly recurved conical teeth which would not look out of place on modern crocodilians. Again however, there are differences in detailed anatomy. Of particular interest is the orbits of Anteophthalmosuchus, which only permitted forward vision rather than anterolateral as is usual for Crocodyliformes (its name, roughly meaning ‘forward-eye-crocodile’, reflects this - see Salisbury and Naish 2011). A similar condition is also seen in Vectisuchus, but it is not quite as well developed and seems to have arisen independently. Goniopholid skulls are also rather flatter than those of modern crocs, and have distinctly over-biting upper jaws. An unusual hollow in the cheek region, known as the maxillary depression, was also present, apparently representing an unusually large pressure-sensitive region of the goniopholidid face (Andrade 2009).
A house-proud Goniopholis willetti stands at the entrance to his burrow. Note his long arms, narrow jaws, and lack of a doormat.

Goniopholidids vs. modern crocodilians, round 2: habits

It may be expected that these similarities and differences between modern crocodilians and goniopholididis may translate to overlapping, but also slightly different lifestyles. Happily, because the anatomy of Wealden goniopholidids is well-documented, we can make some informed speculation as to how these animals may have lived and, indeed, this seems to be the case. The size and robust skeletons of G. willetti and Anteophthalmosuchus suggests that the ecological bucks of Wealden waterways stopped with them: occasional visits from spinosaurids aside, they were the largest predators in Wealden lakes and rivers and clearly well suited for tackling large prey items. We might imagine each as the apex predators of their respective waterways, taking small or medium-sized terrestrial animals, large fish and other aquatic reptiles as prey. This gives these animals a role much like those filled by several species of large crocodilians today. Smaller Vectisuchus, by contrast, probably ranked it in the mid-league of ancient Wealden ecosystems, probably capable of holding its own against most aquatic Wealden species but wanting to be wary of its larger cousins. Applying trends of snout shape and prey preference of modern crocodiles to Wealden goniopholidids suggests they likely differed in general prey preference: slender-snouted Vectisuchus and G. willietti probably took relatively smaller prey than the massively-jawed Anteophthalmosuchus. Through overall body size and jaw shape, these animals probably avoided stepping on each other’s ecological toes – at least Anteophthalmosuchus and Vectisuchus were contemporaries which probably practised niche partitioning (Salisbury and Naish 2011).

We might expect goniopholidids to exploit their large size in a similar way to modern crocodilians. Large modern crocodiles often focus their predation efforts to certain times of year when environmental conditions are favourable, such as times when rivers and lakes are in flood, when prey is particularly abundant, or at least the climate is more forgiving. Given how extreme the Wealden climate was - summer temperatures in some parts of the Wealden reached 36–40°C and experienced annual droughts (Sweetman and Insole 2010) – goniopholidids may have used similar strategies. As with big modern crocodilians, their large bodies hold ample reserves to wait out leaner or stressful times, and it’s possible that some goniopholidids waited out the long, hot Wealden summer in cooling pools or burrows (see image, above), while smaller crocs had fewer resources to fall back on and continued to exert themselves throughout hard times.

Beyond these generally favourable comparisons however, many aspects of goniopholidid anatomy hint at different habits to modern crocodilians. For instance, the development of goniopholidid maxillary depressions likely represent enlargements of sensory organs present in modern crocodilians used to detect prey at the water/air interface (Andrade 2009). All else being equal, does this indicate that goniopholids were more routinely grabbing prey at the water surface rather than diving for food or living generalist lifestyles? In other instances, it’s not clear what significance goniopholidid anatomical quirks may have. It’s difficult not to wonder why some Wealden goniopholidids possess entirely forward-facing eyes, for instance, and if this was related to feeding. Ordinarily, increased amounts of forward vision are associated with development of binocular vision and heightened abilities to judge distances. Might that mean predation techniques were unusual in some goniopholidids, involving chases, or carefully judged lunges and strikes at prey?

The preferred habitats and locomotory methods of goniopholidids are also worth pondering. There is some evidence that larger Wealden goniopholidids were mostly confined to a semi-aquatic existence, as their interlocking osteoderms likely strengthened their backs and improved terrestrial competency (as it does for atoposaurids and several other type of ancient crocodyliform), but their sheer weight likely impeded terrestrial locomotion over sustained periods (Salisbury and Frey 2000). The same is true of large modern crocodiles: here, reinforced vertebral joints perform a similar job to osteoderm bracing but still fail to facilitate effective, fast terrestrial locomotion for long periods. Larger crocodilians therefore spend much of their time in water, and certainly find most of their food there. If so, this makes the atypically long forelimbs of goniopholidids all the more interesting. Often, development of relatively equate limb lengths in quadrupeds is considered a sign of good terrestrial proficiency, betraying a well-balanced animal with effective carriage and equal gait efficiency in both limb sets. But how can this apply to large, heavy goniopholidids if they weren’t walking very much? Doubtless, an increased forelimb stride length was useful on occasions when large goniopholidids did leave the water, but why develop these features if much of their lives were spent in deep water? Did these animals ‘walk’ along river beds more than other Crocodyliformes? Was this trait even important for big adults? Perhaps smaller or juvenile goniopholidids took advantage of long forelimbs before they outgrew real terrestrial proficiency, spending more time on land before becoming more thoroughly aquatic at larger sizes. We could speculate all night about the intriguing possibilities here: Crocodyliformes are sophisticated creatures which do a lot more than eat, sleep and wander about: they also dig burrows, construct nests, climb onto trees and rocks, and are very sociable. Could their long forelimbs be related to these behaviours? Vertical size is seemingly more intimidating to modern Crocodyliformes than girth (Farlow and Dodson 1975) - might long arms and a tall stature have incurred social significance for goniopholidids? It’s not inconceivable that the long arms of goniopholidids were influenced by these activities rather than just locomotion, and I suspect an investigation into the evolution and functionality of their forelimbs would yield some very interesting results.

The outcome

In sum, then, it seems that we need to be cautious when thinking of goniopholidids as 'conventional' Crocodyliformes or simply forebears of modern crocodiles. Many aspects of their anatomy are not only different from those of modern crocodiles, but actually downright odd, and likely impacted on their habits and lifestyles significantly. Palaeoartists - bear all this in mind the next time you set out to draw your goniopholidids skulking in the background of your dinosaur artwork.

For the concluding post in the Wealden Crocodyliformes Trilogy, we're going out with a bang and an exciting new discovery - and it's not very far off now. Stay tuned!

References

  • Andrade, M. B. (2009). Solving a century-old mystery: the structure and function of the maxillary depressions of Goniopholis (Crocodylomorpha, Neosuchia). In Journal of Vertebrate Paleontology (Vol. 29, pp. 54A-55A). 
  • Andrade, M. B. de, Edmonds, R., Benton, M. J., & Schouten, R. (2011). A new Berriasian species of Goniopholis (Mesoeucrocodylia, Neosuchia) from England, and a review of the genus. Zoological Journal of the Linnean Society, 163(s1), S66-S108.
  • Farlow, J. O., & Dodson, P. (1975). The behavioral significance of frill and horn morphology in ceratopsian dinosaurs. Evolution, 353-361.
  • Karl, H. V., Gröning, E., Brauckmann, C., Schwarz, D, & Knötschke, N. (2006). The Late Jurassic crocodiles of the Langenberg near Oker, Lower Saxony (Germany), and description of related materials (with remarks on the history of quarrying the “Langenberg Limestone” and “Obernkirchen Sandstone”). Clausthaler Geowissenschaften, 5, 59-77.
  • Salisbury, S. W. & Frey, E. 2000. A biomechanical transformation model for the evolution of semi-spheroidal articulations between adjoining vertebral bodies in crocodilians. In Grigg, G. C., Seebacher, F. & Franklin, C. E. (eds) Crocodilian Biology and Evolution. Surry Beatty & Sons (Chipping Norton, Aus.), pp. 85-134.
  • Salisbury, S. W. & Naish, D. (2011). Crocodilians. In Batten, D. J. (ed.) English Wealden Fossils. The Palaeontological Association (London), pp. 305-369.
  • Sweetman, S. C., & Insole, A. N. (2010). The plant debris beds of the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern England: their genesis and palaeontological significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 292(3), 409-424.

Thursday, 13 February 2014

Episode 1: Diminutive, adaptable atoposaurids

There's only one rule in successful advertising: if you can't use sex, use Star Wars. Background borrowed from NASA, text generated by Fontmeme.
Welcome to The Wealden Crocodyliformes Trilogy! As in, three whole posts dedicated to the major types of Wealden Crocodyliformes! Yeah! Woot! Let's all have a pear!

Right, let's back up a bit. Hopefully, it’s well known that modern crocodilians represent only a tiny fraction of crocodile-line archosaur diversity. Crocodyliformes, the major group of crocodile-like archosaurs which ultimately begat our modern crocodile fauna, was ancestrally much more morphologically and ecologically diverse than its modern representatives. This is true to the point that the common labelling of crocodilians as ‘living fossils’ is only true in a very loose sense. Superficially crocodile-like Crocodyliformes have certainly been around for well over 100 million years, but even some of their close relatives were very different beasts. Despite this - hopefully – widely known fact, reconstructions of ancient Crocodyliformes, or even articles about them, are not exactly commonplace. Running through the major types of crocodyliform once found in Lower Cretaceous Britain, specifically those from the Wealden Supergroup, gives an opportunity to at least scratch the surface of Mesozoic crocodyliform diversity. Wealden Crocodyliformes are diverse, with 11 species identified in a recent review (Salisbury and Naish 2011). As with many Wealden groups, the long research history of these animals (Wealden crocodyliform teeth were first found in the 1820s) does not mean they have been 'done' by palaeontologists - there remains much to learn about Wealden crocodylomorph palaeobiology. Indeed, at some point in this trilogy, we'll cover a cool, new and in-press discovery - more on that later, as I've already said too much.

A key point to note in each of these articles is the major anatomical differences these animals have from modern crocodiles, meaning that not only their lifestyle but also appearance would contrast from anything we associate with Crocodyliformes today. This is despite the Wealden Crocodyliformes not, by any stretch of the imagination, representing the most 'extreme' bauplans offered up by the croc-line archosaurs. This message should ring particularly loudly for artists who simply place modern crocs in the Mesozoic (a crime I'm as guilty of as anyone). All right, enough preamble already – let’s meet our first subject, the resourceful, tiny atoposaurid crocodyliform, Theriosuchus.

Neat things come in small packages
Our fist Wealden crocodyliform is a far cry from the role of large, voracious apex predator we often think of when crocodiles are mentioned. At only 550 mm long, Theriosuchus was tiny compared to most Wealden Crocodyliformes and likely risked predation from even moderately-sized contemporary predators. Theriosuchus is a long lived genus known across Europe and Asia from Late Jurassic – Late Cretaceous deposits and several species are known. Wealden fossils of this animal – a partial skull from the Wessex Formation and isolated teeth from the Ashdown and Wadhurst Clay Formations of East Sussex – are too fragmentary to refer to any existing species, or permit identification of a Wealden-specific one. For the time being then, the Wealden Theriosuchus is simply referred to as Theriosuchus sp.
The Lower Cretaceous, Wealden atoposaurid, Theriosuchus sp., prancing about in pursuit of locusts. 
Theriosuchus belongs to Atoposauridae, a group of neosuchian Crocodyliformes which are seem closely related to the group containing modern crocs, Eusuchia. Atoposaurids possess several 'derived' eusuchian features in their nasal and vertebral regions, hinting at a possible close relationship with this group (fun fact: classic 'eusuchian' features actually evolve repeatedly in ancient Crocodyliformes, which can confound taxonomic assessments of fragmentary fossil crocodyliform material - more on this later). The most distinguishing feature of atoposaurids is their size. Even when fully grown, no atoposaur exceeds one metre in length. They are correspondingly sometimes labelled as 'dwarf’ species, but this label is not an entirely accurate. So-called ‘dwarf’ species are not uncommon (elephants, deer, many lizards and crocodilians are just some lineages containing 'famous' dwarfs) but - by definition - they must be descended from closely related, larger relatives. All currently known atoposaurs are small, so they cannot be said to have reduced their size from their ancestral condition. Thus, they are not true ‘dwarf’ Crocodyliformes, just small ones.

Although unquestionably crocodile-like, the life appearance of Theriosuchus probably wasn't strongly comparable with any modern animal. Broadly, atoposaurids recall attributes of crocodiles and long-legged lizards, but their relatively svelte skeletons and long limbs are also vaguely reminiscent of some small mammals. Their skulls are rather low and short, thanks to an unusually abbreviated and broad snout which tapers into a rounded muzzle. Unlike many Crocodyliformes, atoposaur nasal openings remain separated and placed on the lateral margins of the snout tip, rather than being combined into a single opening on the upper snout surface. Their eye sockets are proportionally large but an opening in the skull above and behind the eye, the upper temporal fenestra, is rather reduced. This suggests that at least some of their jaw muscles were not as large as the famously enormous jaw muscles of modern crocodiles. Atoposaurid body proportions are rather typical of Crocodyliformes with short necks, tubular trunks and a tail of moderate length, but the limbs of Theriosuchus and most other atoposaurids are rather longer and more gracile than we've come to expect from croc-line archosaurs (this is not universal across the group: other atoposaurids have rather squatter limb proportions). Two rows of square or rectangular, keeled osteoderms extended along the neck, back and tail, becoming slightly more prominent on the tail. Most are pretty flat, so atoposaurid backs would look considerably less ornate than those of modern crocodilians. In Theriosuchus at least, the dorsal osteoderms possess ‘peg and groove’ joints which locked each osteoderm into its neighbour, forming a relatively immobile bony sheet along the back. This feature is not common to all atoposaurids, but is found in some other Crocodyliformes - albeit not modern ones. It's thought that this locking mechanism provided more than just reinforcement of  the armour along the animals back, also helping to resist bending and twisting movements in the torso when the animal walked or ran. Additional osteoderms occur beneath the tail and neck.

Theriosuchus pusillus, one of the best known members of this genus, from the lower Cretaceous Lulworth Formation, UK. Image from Owen (1878), borrowed from Wikimedia Commons.
Like many Crocodyliformes, the teeth of Theriosuchus are deceptively complex. The teeth lining the jaw tip are rather conical with slight striations and carinae, while those behind become rather lance-shaped - longer than wide, with a pointed apex. The carinae of these teeth are rather coarser than those at the jaw tip. In some Theriosuchus species, the teeth at the back of the mouth are compressed into blade-like structures with particularly coarse serrations. Two peaks in tooth size can be seen in atoposaurid jaws, the first occurring with a large conical tooth which forms a ‘psuedocanine’, and the second (smaller) peak among the anterior lance-like dentition. A notch in the side of the upper jaw means that the ‘pseudocanines’ were probably visible even when the mouth was closed. Put together, the dentition of Theriosuchus was multifunctional and ideally suited to processing soft prey items: the anterior teeth could pierce and stab; the lance-shaped teeth could crush and cut, and the blade-like teeth (if present) could shear and rip into soft-food.

Raccoon-crocs?
The dentition of Theriosuchus suggest that, like other atoposaurids, it may have been primarily carnivorous, likely foraging for small vertebrates, arthropods and carrion. As in modern crocodiles, their diverse teeth may have also permitted ingestion of nutritious plant matter. Unlike modern crocodiles however, several features of atoposaurid anatomy suggest they found much of their prey away from aquatic settings. Relatively long limbs increased their stride distances, allowing for potentially rapid locomotion, while their interlocked osteoderms likely reduced the strain of walking and running on the trunk skeleton. The latter is likely true of all Crocodyliformes with interlocking osteoderms, but Theriosuchus was also a small, lightweight creature, thus reducing strain on its trunk even further when walking. Put together, the combination of small body size and a reinforced back may have allowed Theriosuchus to sustain long periods of walking and running compared to other Crocodyliformes. The general rarity of atoposaurid fossils compared to those of other Crocodyliformes - both in the Wealden and elsewhere - lends some support to this idea: animals which spend a lot of time in water generally have a higher preservation potential than those which don’t, simply because their remains are that much closer to environments where sediments are likely to accumulate and bury them.

Aquatic behaviour for Theriosuchus cannot ruled out, however. While the osteoderm bracing system likely limited their torso flexibility - thus somewhat impeding the ability for rapid and manoeuvrable swimming - the retention of a powerful, flexible tail and low body shape probably still permitted fair swimming performance. Thus, it is quite possible that terrestrial food sources were supplemented with diminutive fish and other small aquatic prey from time to time. Atoposaurids like Theriosuchus may be best regarded as very adaptable, generalised species which, if we were forced to crowbar them into a modern niche, may be most equivalent to small, semiaquatic mammalian carnivorans – raccoons, otters and so forth. Their generalised diet means that Theriosuchus probably competed for food with lizards and amphibians more than their fellow Crocodyliformes, and perhaps their ability to forage on land and in water, in concert with low body sizes, gave Theriosuchus an edge in a crowded Wealden ecosystem filled with many aquatic and terrestrial predators. Thus, while many Wealden animals were probably relatively restricted to specific foraging habitats and prey types, Theriosuchus could forage freely in both settings, resourcefully enjoying whatever morsels it could wrap its tiny jaws around.

The crocodyliformes we'll meet in the next instalment of The Wealden Crocodyliformes Trilogy are not quite as ecologically generalised as Theriosuchus - aspects of their size, dentition or proportions dictate that they had to commit to at least some lifestyle specifics. To see what they are, and how they fit more broadly into Wealden palaeoecology, you'll have to come back for Episode 2...

References

  • Owen, R. (1879). Monograph on the fossil Reptilia of the Wealden and Purbeck Formations. Supplement IX, Crocodilia (Goniopholis, Brachydectes, Nannosuchus, Theriosuchus, and Nuthetes)". Palaeontographical Society of London Monograph 33: 1–19.
  • Salisbury, S. W. & Naish, D. (2011). Crocodilians. In: Batten, D. J. (ed.) English Wealden Fossils. The Palaeontological Association (London), pp. 305-369.