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Sunday, 21 December 2014

Taking in the festive air with an azhdarchid pterosaur

An azhdarchid pterosaur takes off in a festively-coloured woodland, because it's Christmas. Prints are available
I was recently thrilled to have the above image featured on the front cover of The Anatomical Record, its depiction of a freshly launched azhdarchid pterosaur tying in with the first paper of the issue. And yes, the colours are deliberately festive, because the Anatomical Record adopts a Christmas theme for its December issues, hence the deep reds and greens of my image. There's two stories I briefly want to tell about this: one about the paper it accompanies, and the other about the art itself.

The paper

My art accompanies the work of Nick Geist and his team on the respiratory mechanism of large pterodactyloid pterosaurs (Geist et al. 2014). Lung ventilation in pterosaurs is an interesting topic. The torso skeleton of many pterodactyloids is locked up pretty tightly thanks to their vertebrae fusing together, their scapulocoracoids being tightly braced between their sterna and backbones and a series of robust, mostly immobile ribs. How were their lungs or air sacs inflated within such a rigid skeleton? Because this configuration isn't a million miles from the torso skeletons of some birds, some authors (Claessens et al. 2009) have suggested that pterosaurs may have breathed in basically avian manner: muscles anchoring to small ribs set between the sternum and larger thoracic ribs move the sternum up and down, pumping air around the body in the process.

This has been accepted fairly widely for the last five years, but now Geist et al. (2014) have presented an alternative argument. They suggest that pterosaur sternal ribs are ill suited for anchoring such muscles because they are very slender - we might even call them fragile - and often entirely cartilaginous, the latter observation borne out by their poor representation in fossil record. Indeed, large portions of the pterosaur chest seem cartilaginous and rarely preserved - the bony sterna of many species (Dorygnathus and Scaphognathus spring to mind) are tiny, and cannot possibly have supported the flight musculature indicated by their powerful shoulders and forelimbs. There must have been large cartilage extensions to these in life. Moreover, in many respects pterosaur torso construction resembles those of crocodilians more than birds, such as the manner with which the thoracic ribs articulate with the vertebrae and the essentially vertical orientation of the ribs themselves. This configuration does not permit the rib rotation required to move the sternum in respiration, and actually adds further rigidity to the anterior pterosaur torso. A bird-like respiratory mechanic may be unlikely for pterosaurs then.

So how were pterosaurs breathing, then? Perhaps the only part of their bodies which wasn't locked up tight and permitted the expansion and contraction required for breathing was their bellies. Behind the sternum sits a suite mobile bones: the belly ribs (gastralia) and the prepubes, a pair of paddle-shaped bones articulated with the pelvis, along with a few 'floating' sternal ribs. Perhaps, like crocodiles, but unlike birds, pterosaurs used this region of their body to control the pressure in their lungs. Crocodiles use contraction of their abdominal muscles to move a large, body-spanning liver forward to compress their lungs, while relaxation of their abdominal wall then allows the liver to retract and the lungs to expand, bringing in their next breath. It seems this action accounts for about 65% of air moved in and out of their lungs, with the rest coming from costal - rib - movements. Given that it seems only pterosaur bellies were flexible enough to inflict substantial changes on body volume, it is not inconceivable to think they used a similar 'belly-pump' (or extracostal pump) as their principle means of controlling air flow into their lungs.

What does this mean for pterosaur lung structure overall? It's well known that pterosaur skeletons and bodies were pneumatised to the same extent, if not more, than avian dinosaurs, prompting suggestions that pterosaurs also had solid avian-like lungs and similar unidirectional flow-through pulmonary mechanics (Claessens et al. 2009). Do the observations of Geist et al. (2014) refute this? Well, not really, but they don't support them, either. As Geist et al. point out: we really don't know anything concrete about pterosaur lung structure, and it's actually pretty hard to tell anything about them from bones alone. A bird-like lung may have been present in pterosaurs and would certainly be consistent with extensive skeletal pneumaticity. However, we need to be careful about exclusively linking extensive pneumaticity with bird-like respiratory organs: flying fish, which of course have no lungs at all, also have pneumatised skeletons thanks to outgrowths of their swim bladders (Geist et al. 2014). Moreover, our uncertainty is not helped by a general lack of knowledge about reptile lungs. This year has seen several revelations about the lungs of extant reptiles being more complex, and sometimes more avian-like, than previously thought. We might need a better handle on reptile lung diversity, and the phylogenetic distribution of different lung structures within Sauropsida, before we start making inferences about the lungs of long extinct reptile lineages. In sum, while the avian-like pterosaur lung remains a viable hypothesis, it's not the only option on the table. We might be able to gain insights into how the body cavity of pterosaurs was manipulated to move air in and out, but their precise lung anatomy remains largely mysterious (Geist et al. 2014). There's a lot more we could say about this, but you'll have to track down the full paper for further details.

The cover image

Festivodactylus in situ.

There's a bit of a story behind the cover artwork for this paper too. It's hardly the stuff of novels but, given that 2014 has been another year in which palaeoart plagiarism and working practices have been a hot topic, it's nice to share a happier, positive story about a palaeoartwork for a change.

This cover has been a long time coming, with Nick asking me for potential cover art for the paper at the end of last year. I duly obliged by lending the flying Anhanguera from my book. Nothing much happened while the paper was crunched through the publication mill, until in November the cover art arrived. Looked like I was due for the December issue, which, as noted above, Anatomical Record always jazzes up with festive colours - green, red and white. This involved tweaking the colours of my original art to meet these, as well as some stretching and cropping to fit the AR cover format. Without going into details, I wasn't really happy with the results. Uh oh. Pessimist I am, I foresaw the worst. I stress that these expectations weren't because of previous experience of working with Nick or AR, but my experiences with other clients and agencies. Protesting about art use normally leads to Bad Things: unhappily forced compromises, loss of commissions, or having to fix 'problems' without pay. When writing back to Nick and AR with my concerns, I pretty much expected the whole cover project to fall apart. I pitched, without optimism, the idea of doing another image, for a fee, to replace the modified one. Despite linking to the 'State of the Palaeoart' article I helped pen this year to substantiate my request for payment, I was expecting the same old response: lack of money, thanks but no-thanks.

To my complete surprise, Nick, his colleagues and AR were on board with everything. The 'palaeoart situation' was new to them all, but I - we, the palaeoart community - had their sympathy. Within a day, AR had been able to put things on hold for a week while I drafted a new image to their specifications and size, Nick and his team rapidly found a generous payment for the work at short notice, and we all ended up with a product we were happy with.

I mention all this for two reasons. Firstly, Nick, his team and AR deserve accolade for being so refreshingly cool and respectful of palaeoartistry. Secondly, independent palaeoartistry can seem a most hopeless industry at times: we get ripped off by everyone from toy companies and movie makers to museums and publishers; our marketplace is mainly structured around exploitation of individuals, and sympathy or assistance from those in the position to change this can be hard to find. But, as this case shows, it's not all hopeless. Increasing awareness of the issues facing palaeoartistry does help rectify them, change can happen, and we have more supporters than we know. I'm optimistic that eventually we'll all have more stories like this one than the negative situations currently reported so frequently.

Best to you all for the festive period, see you all in 2015!

References


  • Claessens, L. P., O'Connor, P. M., & Unwin, D. M. (2009). Respiratory evolution facilitated the origin of pterosaur flight and aerial gigantism. PloS one, 4(2), e4497.
  • Geist, N. R., Hillenius, W. J., Frey, E., Jones, T. D., & Elgin, R. A. (2013). Breathing in a box: Constraints on lung ventilation in giant pterosaurs. The Anatomical Record, 297, 2233-2253.

Friday, 5 December 2014

Overcooking Aucasaurus garridoi

Aucasaurus made a note in its diary after this. Simply said: "Bugger". Prints are available.
This week I've been mostly rendering an abelisaurid, the theropod group best known for short-faced, short-armed taxa such as Carnotaurus, and famous for occupying many predatory niches in southern continents while tryannosaurids occupied the north. This 'common knowledge' is only mostly true however: abelisaurids did spread to at least Europe in the uppermost Cretaceous, and represent the largest predatory dinosaurs on the continent at that time. We need not overstate that significance however: uppermost Cretaceous Europe was a topsy-turvy world where all theropods were rather small, and top-dog predator duties were likely filled by terrestrially-stalking, quarter-tonne azhdarchid pterosaurs. It seems even evolution likes a good Htichcockian-twist every now and then.

In southern continents, abelisaurids remained medium-to-large sized predators. It was one of these, the Campanian, Patagonian species Aucasaurus garridoi that Felix Bridel asked me to paint as one of my £100 palaeoart commissions. Aucasaurus is one of the best known abelsisaurids, the holotype skeleton presenting an almost complete osteology of this c. 5 m long animal, and is considered a 'derived' member of the abelisaur clan. Its anatomy is almost as unusual as that of its close relative Carnotaurus. Like other abelisaurids, the general bauplan of Aucasaurus was that of a small head, tiny arms and relatively gracile torso strapped to a robust, probably powerfully muscled hindlimbs and tail. The peculiar anatomy of derived abelisaurid proximal tail vertebrae created huge spaces for hindlimb muscle-anchorage and likely betrays tremendous sprinting power (Persons and Currie 2011). Perhaps this explains the strange upper-body anatomy of abelisaurids: their gracile bodies and reduced extremities may represent pressures to keep weight down and speeds high. Long term readers may reconcile some components of this functional complex with another group of dinosaurs, the ornithischian clade Dryosauridae, which also married a powerful set of legs with a svelte upper body.

Felix wanted to incorporate the notion that Aucasaurus and similar species were probably fast runners into his commission, but not in a conventional way. While recent research has hinted that abelisaurids were likely fast, they were likely not as agile as other taxa. Bulging abelisaurid hindlimb muscles may have created a lot of power, but they also kept the tail base rather immobile (Persons and Currie 2011). In tight turns, the tail probably fairly ineffective for adjusting gravity centres or resisting turning inertia. Felix wanted his Aucasaurus image to reflect this, showing a predator which had overcooked its pursuit of a more nimble prey item and lost balance altogether. I was more than happy to oblige: watching animals for any length of time reveals they are just as clumsy as we are, but we seldom see palaeoart reflecting this. Perhaps the only exception is predators being thwacked by the weapons of their prey, which I guess sort of reflects a clumsiness, but it's not quite the same level of slapstick as an animal slipping over.

My brief working time with Felix was a lot of fun: it was clear from our first few emails that we had a similar idea in mind and the image came together quickly. I posted my progress of the image up on Twitter and, as you can see below, the basics of the image weren't altered from the start. Efforts were made to show the Aucasaurus mid-slip: deep enough into the fall for some immediate reaction to show, but early enough that the limbs and dust still have to settle. To my mind, the animal's right leg flew out from beneath it when attempting a tight left-turn, leaving it to gaze off-canvas at whatever prey item it was pursuing.


That final Tweet did indeed feature the finished version (also seen at top), which is now being printed and packaged for delivery (click here if you would like your own copy). As usual, there's a lot more to say, but I'll have to end there. Before I go, a few nods are needed as goes sources for the picture: Scott Hartman's Aucasaurus skeletal was an important reference, as was the Coria et al. (2002) description of the Aucasaurus holotype. The notion that abelisaurid arms were used as display structures (termed 'pom pom arms' by @Blackmudpuppy) isn't new: All Yesterdays (Conway et al. 2012) explored that first.

References


  • Conway, J., Kosemen, C. M., & Naish, D. (2012). All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals. Irregular Books.
  • Coria, R. A., Chiappe, L. M., & Dingus, L. (2002). A new close relative of Carnotaurus sastrei Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia. Journal of Vertebrate Paleontology, 22(2), 460-465.
  • Persons IV, W. S., & Currie, P. J. (2011). Dinosaur speed demon: the caudal musculature of Carnotaurus sastrei and implications for the evolution of South American abelisaurids. PloS one, 6(10), e25763.

Friday, 28 November 2014

You won't believe how interesting the Mesozoic mammaliaform Morganucodon watsoni actually is!

Morganucodon watsoni forage for insects and spiders at night among Carboniferous limestones in early Mesozoic Wales. Empty, torn webs suggest they're having a good night, while forest fires burn in the background. Prints are available.
Vertebrate palaeontology textbooks always devote a good chunk of space to morganucodonts, a clade of Triassic-Jurassic Mammaliaformes representing some of the first wholly 'mammal-like' synapsids. Even folks largely uninterested in Mesozoic synapsids will be familiar with two morganucodonts - the Triassic, South African Megazostrodon and the widely-spread Triassic-Jurassic Laurasian genus Morganucodon - because they have become the quintessential 'Mesozoic mammal': small, shrew-like creatures which scurried around the feet of reptiles. Their lack of unusual proportions or adaptations for specialist lifestyles has probably played a part in Mesozoic mammaliaforms being considered a bit boring compared to their dinosaur contemporaries (sorry, mammal palaeontologists), a feat not helped by a deficit of new, particularly interesting artwork of them. Morganucodont representations in palaeoart are frequently quite 'diagrammatic' with 'generic' early Mesozoic backgrounds, animals in lateral or anterolateral aspect to show off their anatomy and daylight settings, despite frequent discussion about their possible/likely nocturnal habits.

Recently, I was asked to produce a reconstruction of Morganucodon watsoni for some friends (above). Being better versed in reptiles than mammals, I had to undertake a fair bit of research to bring myself up to speed on morganucodont anatomy and evolution. Turns out that reputation for being dull is entirely unwarranted: Morganucodon, its relatives, and the world they inhabited are really fascinating. Indeed, they should be bona fide fossil celebrities: Morganucodon and Megazostrodon were the first Mesozoic mammaliaforms known from anything like complete remains (albeit lots of fragments for the former, rather than a single complete specimen) instead of mere teeth and jaws. Their discovery in the mid-20th century can be seen as the start of a new era of understanding of Mesozoic mammaliaform life, and a forerunner of our now rapidly expanding knowledge of Mesozoic mammal diversity.

Initially, I wanted to write a long, detailed post about this painting and the animals it depicts, but that just won't be happening this side of 2015. But, dammit, Morganucodon is too cool to ignore completely or short-change with a 'picture of the day' post, so here's a quick-fire, from-the-hip summary of the research behind the work.

We'll start with the setting. Fossils of M. watsoni occur in British Triassic/lower Jurassic 'fissure fills' cropping out around Bristol and south Wales. These deposits represent ancient infills of caves carved into much older Carboniferous limestones, which are perhaps best known for yielding the sauropodomorph Thecodontosaurus. Fissure fill outcrops occur in multiple quarries across the southern UK and are frequently rich in fossil material, but the mammaliaforms are rare components of the fauna constrained to just a few localities. Dating the fissure fills is not easy because they contain few fossils useful for dating. Some quarries are reliably set at the Rhaetian, but they are probably not all of the same age: some may be as young as the earliest Jurassic. These include sites which contain M. watsoni fossils, which is why different texts give slightly different ages for this animal.

The upper Triassic/lower Jurassic of Europe would be an ideal holiday location for many. The desert landmass of Pangaea was in the process of breaking up, and Europe - including the southern UK - was in the process of being flooded by shallow seas. By the time M. watsoni appeared, Britain's only landmasses were small, low-lying, forested islands which, in terms of climate and general topography, would have resembled those of the Caribbean. Burned plant remains in the fissure fills indicate that the forested inlands of these islands burned on occasion, the remnants of forest fires being washed into coastal limestone caves by storms and floods. We can identify the fissure fill caves as coastal because they contain marine fossils along with terrestrial and freshwater species. It's on these limestones that I set this painting, a deliberate move to avoid another cycad-filled 'semi-arid' Triassic scene.

The island home of M. watsoni was ruled by reptiles - but not necessarily the ones you expect. Although dinosaurs were common, represented by both sauropodomorphs and theropods, the most abundant and diverse reptile group were sphenodonts. These guys deserve their own posts and paintings one day, their Mesozoic run being far more than just spreading tuatara clones across the world. Anyway, the decaying body of one of these - Planocephalosaurus - can be seen in the foreground of the painting above. As these indicate, the sphenodonts contemporary with M. watsoni weren't huge, but they still likely gave the resident mammaliaforms a hard time in competing for similar food resources. It's interesting to ponder how these animals carved up their respective ecologies to avoid direct competition with one another.

Scientists predict that, if Morganucodon were alive today, the sight of them would make grown women leap on their chairs, clutching the skirt tails in fear. 
What of Morganucodon itself? The skeleton of M. watsoni is small (about 10 cm nose to tail base) and extremely mammal-like, with differences limited to fine anatomical details. For instance, the composition of the Moranucodon jaw-joint isn't a simple as those of true mammals, the scapula is a little bit 'reptile-like', and (according to some sources, anyway), there may have been some degree of bowing to the fore- and hindlimbs when walking or standing. This doesn't necessarily indicate sprawling limbs, but they may not have been as neatly tucked under the body as those of other mammals. Because morganucodont skeletons are so similar to those of true mammals, it seems likely that many aspects of our basic soft-tissue anatomy were established by this point of synapsid evolution - ear pinnae, fur, loose skin and so on. Direct evidence for these are currently lacking in morganucodonts, but there is indirect evidence for fur from the relatively large Morganucodon brain. Although not as large as those of later mammals, Morganucodon endocasts were expanded beyond a typical 'reptilian' condition, and much of this reflects an enlarged neocortex. This part of the brain processes sensory information, and it may be that the covering mammaliaform bodies with pressure-sensitive hairs promoted this development. I find this observation quite interesting because other lineages with fuzzy bodies - bird-like dinosaurs and pterosaurs - have also developed expanded brains and enhanced abilities to process sensory information. These enlargements are often attributed to enhanced balance and coordination, but might they also be related to the developed of sensitive fuzzy hides, as is assumed for mammals?

Because art of Mesozoic mammals scurrying about at night is so rare, I wanted to capture this in my painting. The evidence for nocturnal activity in Mesozoic mammaliaforms is not as strong as you might think - it's largely based on the (questionable?) assumption that reptiles forced early mammals into nocturnal niches and the abundance of small nocturnal mammals in the modern day - but what the heck: it makes for a fun picture. It seems nocturnal mammals are often equipped with tremendous sets of whiskers, so I put similar features on my Morganucodon to help them find their way around, They may not be 'true' whiskers, in the sense of derived, mobile whiskers of modern mammals, but it doesn't seem unreasonable to imagine long, stiffened sensory hairs of some kind developing rapidly once fur was attained.

And... blast it, I'm out of time. So many other things to say, but they'll have to wait for another time. Coming soon: various theropods, festive pterosaurs, er... and probably other things too!

Friday, 14 November 2014

Of tiny tyrants and Triassic big-heads: Tyrannosaurus rex and Garjainia madiba

This week sees two new pictures of mine being 'released' in one way or another. Much as I'd like to go into lots of detail about each, that realistically isn't going to happen anytime soon. I'm going to attempt a sort of 'picture[s] of the day'-style writing. I'm sure I can do it... right?

Chidumebi Browne's resting Tyrannosaurus teens

Two young adult old male (left) and female Tyrannosaurus on a break from pillaging and destroying the Cretaceous, distracted by a group of ruffian moths. Concept and animal colouration by Chidumebi Browne. Prints are available.
First up is one of my '£100 palaeoart offers', painted for Chidumebi Browne. Featuring Tyrannosaurus, which needs no introduction as an dinosaur most famous for antisocial tendencies, Chidumebi wanted a more relaxed approach to tyrant dinosaur art. The concept called for Tyrannosaurus at the smaller end of their size scale, settling on individuals approximating the size of the 'Jane' specimen - about half the length of a fully-grown animal. There were also requests for contrasting blue and red colours on a male and female. I was happy to oblige, seeing as some degree of dimorphism is defensible for dinosaurs even at on half their full-grown size. Like mammals and non-avian reptiles, Mesozoic dinosaurs hit sexual maturity well before attaining fully ossified, completely grown skeletons and, for Tyrannosaurus, specimens in their early teens were probably reproductively active. In that sense, some features related to sexual behaviour might be expected in 'teenage' animals. Such individuals - better considered very young adults rather than large children - look rather different to their super-size contemporaries with their longer legs and more gracile build. Some of that is obscured here by the extensive feathering covering both animals (if you look very closely, you can just make out the arms of the sitting male), but their long legs at least show through.

The concept called for a a series of moths catching the attention of the male tyrant: initially one was ordered but, even at half-size, Tyrannosaurus is pretty big, so a few more were added to make them more conspicuous. My initial thought was to use butterflies rather than moths for the role of the lepidopterans, but I was surprised to learn that butterflies don't appear in the fossil record until well after the K/Pg event. Moths have a fair, if not especially extensive Mesozoic record, so they seemed a safer bet. They certainly add an air of tranquility to the scene not featured in a lot of theropod art: well done to Chidumebi for an excellent idea.

There'll be more output from the '£100 palaeoart offers' soon, although note that the offer is now full - over-full, in fact. There's some great ideas which I'm hoping to do justice to, so thanks to all who got their orders in - the offer sold out very quickly. If you didn't manage to get something to me on time, prints are still available - wittonprints@gmail.com is the address to contact for them.

Gower et al.'s Garjainia madiba: yes, the head is that big 

Gargainia madiba sp. nov., South Africa's newest erythrosuchid. From Gower et al. 2014.

Art number 2 is a life restoration of a new species of Early Triassic stem-archosaur, the erythrosuchid Garjainia madiba, described by David Gower and colleagues in this week's PLoS ONE. Unearthed in South Africa and named for Nelson Mandela ("Mr Mandela was known affectionately as 'Madiba'" - Gower et al. 2014), G. madiba has been making surprising ripples on Twitter and Facebook because of its rather enormous head. I say surprising because, for an erythroshucid, G. madiba is fairly typically proportioned - so far as anyone can tell, anyway. We don't have anything like a complete skeleton for G. madiba, although many aspects of its anatomy are represented in fragmentary specimens. It is currently distinguished from its relatives by fine anatomical details, perhaps the most notable being its large postorbital and jugal bosses of unknown function (best seen in the reconstructed anterior aspect, above). The discovery of more substantial G. madiba fossils may reveal more obvious distinction from other erythrosuchids, but, for the time being, the best we can do reconstruction-wise is show G. prima with a madiba upgrade package. Still, given how similar the two Garjainia species seem to be, this does not seem unreasonable.

Restoring Garjainia was a lot of fun because it forced a 'back to basics' approach to the artwork where David Gower, Richard Butler and I spent a lot of time discussing proportions, muscle distribution and posture. Many fossil animals - dinosaurs, pterosaurs, etc. - have been restored so often that the basic foundations of their anatomy are very well known, but this is not so for Garjainia and other erythrosuchids. A personal revelation to come from this process was evidence for enlarged areas of axial musculature on erythrosuchid skeletons, indicated by the rather tall neural spines of their necks and backs. This might give some insight into how their large heads were supported: a particularly well-developed, strong set of axial muscles. The posterior faces of their skulls are also wide and robust, providing space sufficient to anchor powerful neck muscles. But erythrosuchid anatomy was likely not held together only by brute strength: there's also some clever biological engineering at work. Like many archosauriforms with huge-looking heads, their skulls are more gracile and lightweight than they first appear, actually being fairly narrow for much of their length and riddled with fenestrae. We tried to show the former in our anterior aspect reconstruction: note how slender the snout of the animal is compared to the cheek region. The result is a head which is undeniably large, but probably much more manageable than it first seems.

For a lot more on Garjainia and other erythrosuchids, including the life restoration in situ, full descriptions of G. madiba anatomy and revisions to the diagnosis of the group, Gower et al. (2014) can be read here (hurrah for open access!). Thanks to David and Richard for bringing me on board, and congrats to them on the paper.

Coming soon: small, brown Mesozoic mammialiaforms! Yes, they are exciting. Really.

Reference

  • Gower, D.J., Hancox, P.J., Botha-Brink, J., Sennikov, A.G., & Butler, R.J. (2014) A New Species of Garjainia Ochev, 1958 (Diapsida: Archosauriformes: Erythrosuchidae) from the Early Triassic of South Africa. PLoS ONE 9(11): e111154. doi:10.1371/journal.pone.0111154

Friday, 7 November 2014

Prints, custom palaeoart, and antisocial Triceratops

Hey now - look at this: there's a way to buy high-quality prints of my artwork, and it's dead simple. Drop me an email at wittonprints@gmail.com with your requirements, pay off the invoice, and wait for your prints to arrive - hopefully within a week or so of order confirmation. Prices, sizes and all are discussed over here. Added 02/2015: visit my print store!

To celebrate this occasion, I'm also offering a limited number of über-cheap palaeoart commissions for private clients:


Yep - your own palaeoartwork, a print and delivery for just £100, which is a stupidly cheap price for original artwork. Full details (including a few important conditions) are here (edit 02/2015: not any more!). As you may expect, I can't sustain working at that price for long. For that reason, there's only five of these deals being offered, and at time of writing, three of these deals have been taken. If you want in, don't delay. Don't despair if you miss this deal but would still like your own commission: drop me a line and we might be able to work something out.

Finally, because things have been a bit quiet about here for the last month or so, here's something to fill the void: a monochrome bristly Triceratops horridus, the dromaeosaur Acheroraptor temertyorum, and an interaction inspired by the wise, yellow philosophy of The Simpsons.

"...and like people, some [animals] are just jerks."

Apologies for yet another short post. Coming soon (when I'm allowed to publish them): Mammaliaformes! Heaps of pterosaurs! Deinonychus! Diminutive tyrannosaurines! And perhaps other subjects too!

Sunday, 19 October 2014

Dorygnathus tweets its way through development

For various - and mostly good - reasons, there's not been much chance for blogging of late, but the upside is that I have a lot of new art, discussion and science to share in the near future. In the interests of not completely abandoning the blog in the interim, here's a series of Tweets posted over the last two days documenting work on a painting of the Early Jurassic pterosaur Dorygnathus banthensis. I can't say too much about the painting at this stage, because it's earmarked for an upcoming project and its context will be best explained there. Still, there's no harm in leaving a few notes about the restoration and painting process, so here goes...

The initial digital sketch, complete with Kevin Padian's (2008) Dorygnathus skeletal reconstruction in the top corner for basic guidance. Padian's (2008) work was my principle reference here, and is probably the go-to paper for all things Dorygnathus. Those of you who know a bit about pterosaur research may be aware that Kevin was the main, and rather vocal, proponent of pterosaur bipedality in the 1980s and 1990s, so may be surprised to see his name attached to a quadrupedal pterosaur skeletal. Kevin is now on board with the consensus view that pterosaurs were primarily or exclusively quadrupedal animals, although he still argues that bipedality was essential for rapid terrestrial locomotion. I don't really agree with him, but that discussion will have to wait for another time.
A little rotation of the underlying sketch, some basic outlines of the background complete the overall composition. I've had this image knocking about my brain for about a week now, and think the layout is a fairly good approximation of what I've been imagining. This painting has a message to deliver about the sprawling posture of the animal, and I think this composition demonstrates that well enough. There is a lot of compelling anatomical evidence that Dorygnathus and many other non-pterodactyloids could not adopt erect forelimb postures, which is partly why they're considered inferior terrestrial animals to pterodactyloids. But is that the case for all non-pterodactyloids? I'm saying nothing else at this stage, other than that this painting has a contrasting sister image.

A lot more detail by the end of day one. The eye was shrunk to fit the orbit a little better, and the animal now looks generally larger as a result. This is good: Doryngathus is about 1.8 m across the wings, so needs to look seagull-sized. The basics of the colour scheme are added now too. There's a lot of evidence that rhamphorhynchines* like Dorygnathus were seabird like in their habits, so it makes sense to use common seabird colours - whites, greys, blacks and - here. There's a butt-tonne more detail here than I'm used to working with, the result of a big upgrade to my painting hardware and software. A graphics tablet built this decade? Imagine that!

*I don't really agree with Bennett's (2014) proposal that Dorygnathus is a scaphognathinid/ine/whatever. Ah, non-pterodactyloid pterosaur taxonomy: what a mess.

Lots of laminae - fine scaling bedding - in the rock here. Got to put that training into sedimentology to use somewhere.

Nearly there by this stage. Note the similar dip-direction on the rocks jutting out into the sea. Their angle means we can have a few splashy waves here and there, which is nice, and you could map the geology of this bay quite effectively. Because if you had a time machine and visited the Jurassic, mapping grey rocks would totally be the thing to do.

And done. The only real differences between the last two images are some tidier shading, a few background Dorygnathus and some splats of guano on the hero rock. I've long thought that locations supporting lots of pterosaurs would literally be a bit crappy, but never put it into art until now. I expect their guano looked a lot like that of birds and other reptiles: a mix of white, pasty stuff and darker gunge. Nice.

OK, time at the blog. Sorry for the short post, but I may have some good news soon for anyone interested in buying prints of my stuff - just in time for Christmas! I'll leave you with a larger version of the image than the low-res versions afforded by Twitter.

Dorygnathus banthensis at the coast, surrounded by the filth of its contemporaries.


Reference

  • Bennett, S. C. (2014). A new specimen of the pterosaur Scaphognathus crassirostris, with comments on constraint of cervical vertebrae number in pterosaurs. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 271(3), 327-348.
  • Padian, K. (2008). The Early Jurassic pterosaur Dorygnathus banthensis (Theodori 1830). Special Papers in Palaeontology 80: 1-64.

Monday, 29 September 2014

'Support Original Palaeoart': we take it to the mainstream

The industry of reconstructing extinct animals in illustration, sculpture and animation - we all know it as 'palaeoart' - is a paradoxical place. One the one hand, there is more demand for palaeoart than there ever has been, increasing recognition of the role of palaeoart as a scientific and outreach tool and, because of the internet, more interesting and thought-provoking palaeoart being produced than ever before. This would make it seem that palaeoartistry is a flourishing, economically viable and interesting place to work within. On the other hand, much of our widely published, well-paid and/or high profile palaeoart work is rife with plagiarism, is creatively stagnant, has limited commercial appeal and presents gross inaccuracies to the fossils it is meant to represent. Given the elevated public influence and larger economy of these high profile artworks, it might be argued that this less interesting, ethically-questionable and scientifically dubious side of palaeoart overrides the independent sphere as the current 'status quo' within the palaeoart industry.

These issues are not new: since at least the late 1990s, artists and palaeoart aficionados - including well known artists like like Bob Walters, Tess Kissinger and Gregory Paul - have made noises about generally poor working practises in palaeoart and called for change - sometimes in radical ways. However, most of this commentary has been published in esoteric online venues with limited prospects for reaching those involved in palaeoart production. Moreover, because these discussions have taken place in online forums, mailing lists and blogs rather than more 'officious' venues such as magazines or journals, they may be largely discredited or ignored by those who only have time for 'real' literature appearing in mainstream venues. This is a genuine and relevant problem: many scientists - including individuals involved with the production of palaeoart - see little value in the online palaeontological community or the opinions it expresses.

Today, Darren Naish, John Conway and I are attempting to bring the problems within the palaeoart industry into the light via an open-access commentary piece at Palaeontologia Electronica. We hope that by publishing this piece at a respected online venue that it will be more visible and credible to the academics and financiers involved in palaeoart production, and help stimulate the discussion needed for changes desired for years. Much of what we cover in our article will be familiar to regular denizens of the online palaeontological community. We outline why we think palaeoart is important (its long history, importance to science and the millions dollar industries it underpins); what we think is sour with modern working practices (that copied, objectively inaccurate art forms the majority of high profile/commercially produced art, while truly original and progressive artists are overlooked and sometimes deliberately ignored) and what we think can be done about these issues (artists being more circumspect about their trade; palaeontologists being more prudent in their consultancy roles; and art patrons improving their knowledge of and financial approach to palaeoartistry). There's a lot more to say on each of these issues, but I do not want to simply rewrite our article here: head to PE or download the pdf version for more details. There are a few comments and questions I want to nip in the bud, however:

The money issue

Yeah, we suggest artists take a firmer line about their costs. Cue comments about dictating industry workings, comparison to infamous 2011 Greg Paul palaeoart debate, etc. But look at what we say carefully: we encourage artists to be more realistic with their costs beyond a certain career stage, and we give no opinion on what their art should cost. We suggest working standards will improve if folks who've proven their palaeoart mettle, and are 'getting serious' with their palaeoartistry, appreciate that their work is worth something. Of course it is: it takes hours or days or research and labour to make. We should be proud of that, and not undervaluing it. Ultimately, palaeoart will continue to be treated as a disposable commodity - a point we make time and again - until the collective producing it makes it worth something to those buying it. There's a lot more to say on this point, so please read what we say over at PE before leaping to the comments box below.

So, palaeoartists need to be cold, heartless businessmen now, right?

No: we just arguing that there needs to be greater respect all round for the palaeoart trade. Like any industry, there will always be room for personal favours, 'mates rates' and that sort of thing, but these should be exceptions, not the standard. We're not asking for people to be inhuman, or trying to take the enjoyment out of producing palaeoart, only for standard business practises to be more routinely applied to palaeoart production and financing.

You guys are hypocrites. You've asked for/given free art, for instance, and been involved with products featuring awful palaeoart

Yep. Like all human beings, we're a mess of hypocrisy and mixed-messages, and we fully admit to being associated with behaviour which we suggest is detrimental to palaeoartdom. However, we can also honestly say that we try to implement our 'best practises' where we can. Darren, for instance, pushes for using independent artists wherever he can in his books and articles, and fights for payment for image use. Both John and Darren (along with Memo Koseman) have been important voices in the call for more interesting palaeoart with the publication of All Yesterdays (Conway et al. 2012). John has also outlined earnings for his art and explained how, realistically, art needs to be costed to make a living from it. Given the cultural taboo associated with declaring earnings and salaries, that's a bold but important set of figures to release to the public. Along with John and Darren, I do my best to promote excellent palaeoart, work genuinely hard in my consultancy roles, and endeavour to strike realistic costs with my patrons (it's been a long time since I've done art for free, for instance). We're not always successful in these bids, but we push hard wherever we can for the better standards we would like.

I don't see a recommendation for any 'good' palaeoartists in the article. Who do you recommend?

We each have our favourite artists - modern artists who do great work, past artists who broke new ground and so forth - but we have deliberately avoided promoting any services in the PE piece, including our own. The only artwork featured therein are a few incontrovertibly classic pieces of vintage palaeoart or modern works used to make specific points (e.g. John's reptile cat from All Yesterdays, which we use to mirror the inaccuracies present in many modern palaeoartworks). We want people thinking more about what makes palaeoart good and bad, and using their own research to make informed decisions about palaeoart services. Stating who we think are the 'best' artists conflicts with that message.

So what can we do?

Regular visitors to this blog or related works may have seen this image knocking about in various posts:

From Witton et al. (2014).

This is actually a figure from our article, and is our way of making it easy for you - a member of the palaeoblogosphere - to promote this cause. The three elements listed along the bottom touch on the cornerstones of our arguments:
  1. Accuracy: adherence of palaeoart to fossil and biological data; realistic depictions of contemporary palaeontological hypotheses; excellency in consultancy
  2. Creativity: ending of the widespread issue of palaeoart plagiarism and the production of meme-worthy art; promotion and appreciation of artwork and individuals who bring new perspectives and insights to the depiction of extinct animals
  3. History: appreciation of palaeoart as a 200 year old institution with its own important fashions, movements and individuals; realisation that the 'when, where and who' of palaeoartworks are as important as the artworks themselves
We want our graphic on blogs, articles, videos and even conference presentations as a means of promoting these issues as widely as possible. Remember that the whole reason for writing the Palaeontologia Electronica piece was to break these issues out into the wider world. The way to do that is through promotion in as many places as possible. We want it Facebooked, Tweeted, blogged, Tumblr'd and whaever else you can do on social media. We want it on respected, widely-read websites so those who don't frequent the depths of the palaeoblogosphere can't avoid it. We want SVP 2014 audiences seeing this in so many presentations that Berlin erupts with discussion of 'what's with all those palaeoart logos?'. However you do it, we're simply asking for a bit of a fuss. Ultimately, we want this widespread enough that the folks involved in palaeoart production can't ignore it, and will hopefully start thinking about palaeoartistry and its practitioners with the respect they deserve.

That's enough from me on this: head to Palaeontologia Electronica for more. Again, if you agree with what we're saying, please help us promote this widely and, if you're in the lucky position to be influencing palaeoart projects, please consider what we're saying here especially carefully.

References

  • Conway, J., Kosemen, C. M., & Naish, D. (2012). All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals. Irregular Books.
  • Witton, M. P., Naish, D. and Conway, J. (2014). State of the Palaeoart. Palaeontologia Electronica Vol. 17, Issue 3; 5E: 10p;

Friday, 26 September 2014

Does Deinonychus really have one of the most powerful bites of all dinosaurs?

Quick sketch of Deinonychus antirrhopus with expanded, bone-puncturing jaw muscles, a requirement of having a bite as strong as a modern alligator. Say what? Read on...
There's a part in Michael Crichton's Jurassic Park novel where Velociraptor attempt to bite through bars to reach a people-shaped lunch. Presumably, they're meant to give readers something to rally behind seeing as one person in the line of fire is Ian Sodding Malcolm - I'd be chewing through steel too if it meant we could enjoy a few moments without another preachy monologue. Crichton describes them as hyena-like in their ability to bite through steel, delivering thousands of pounds of pressure per square inch and gnawing their way through thick metal bars in 15 minutes.

Dromaeosaurids biting through steel bars - heck, any animal biting through steel bars, including hyenas - intuitively sounds like crazy talk*. But was Crichton at least right about the strong bites of dromaeosaurids? I've been doing some investigating on dromaeosaur jaw muscles for a new palaeoart commission, but I've come unstuck. Here's why.

*Is there any substance to claims about modern animals biting through steel? Given that tooth enamel is only very slightly harder than straight steel, I wonder how long teeth would last when gnawing through anything but the thinnest metal sheet.

Recently, Gignac et al. (2010) presented a suite of bite marks on Tenontosaurus bones argued to show Deinonychus as capable of deeply puncturing bone with powerful bites. The tooth gouges match those of large Deinonychus in many aspects (bite mark size, shape, correspondence with dental arcade) and broken teeth associated with the same Tenontosaurus corroborate suggestions that Deinonychus fed from the carcass. Other teeth, not from Deinonychus, were also at the site, but their owner does not seem to have left any other obvious traces. Experiments with modern cow bones suggest Deinonychus needed a whopping 8200 N to puncture Tenontosaurus bones to the degree seen in the fossil remains. This value puts Deinonychus bites on par with those of adult alligators and leaves hyenas in the biomechanical dust. It also grants Deinonychus one of the highest estimated bite forces of any dinosaur, even greater than animals of much larger size. The tooth marks only match the largest known Deinonychus individuals, possibly indicating that juveniles were incapable of delivering such bite forces. Because Deinonychus puncture wounds are rare, Gignac et al. argue that puncturing bones was not common in Deinonychus, and that their powerful bites were primarily used for aggressive behaviours instead.

Bitemarks in the radius of Tenontosaurus specimen FMNH PR 2261, below, compared to the dental arcade of Deinonychus antirrhopus, above. This is one of many pathologies on FMNH PR 2261, almost all of which have been attributed to Deinonychus feeding behaviour. From Gignac et al. 2010.

For artists, Gignac et al.'s paper has important implications. Generating 8000 N of bite force requires a lot of muscle, so we might predict that Deinonychus jaws had the same swollen jaw muscles of modern crocodiles to generate all those bone-smashing newtons. This is at odds with other reconstructions of Deinonychus, where the jaw muscles do not atypically alter the contours of the face. I don't know how visible expanded, crocodile-like jaw muscles would be on deeply feathered maniraptorans, but reconstructions with sparse or naked faces would certainly need to take this on board. I've had a quick play about with this concept in the conservatively feathered Deinonychus above.

Problem is, Gignac et al.'s conclusions are not uncontested. Biomechanical assessments of Deinonychus jaws have found they were mechanically weak and ill-suited to delivering powerful bites (Therrien et al. 2005; Sakamoto 2010; Fowler et al. 2011). Therrien et al. (2005) estimated Deinonychus bite force at a relatively wimpy 15.7% of alligator jaw power, which Gignac et al. translate into 1450 N. This isn't unimpressive - as strong as that of a 30 kg wolf - but a far cry from an alligator-like bite, and certainly deflates our reconstructed jaw muscles to their traditional size. On the face of it, I certainly find the arguments for weak jaws more convincing. Hyenas and alligators have robust, wide and solidly-built skulls with generous room for jaw muscle placement, whereas the skull of Deinonychus is full of holes, is relatively narrow and slender, and with comparatively little room spaces jaw for muscles.

So, what to do? Jaws with relatively small muscles have been the norm in Deinonychus palaeoart since its discovery, but is it time we changed that? Were their jaws actually visibly and powerfully muscled as inferred by their trace feeding evidence, or is there something missing here? Is it significant that lower estimates of their bite forces match those of animals which can also puncture bone (wolves - see Haynes 1982)? If anyone has anything to add, please let me know...

References

  • Fowler, D. W., Freedman, E. A., Scannella, J. B., & Kambic, R. E. (2011). The predatory ecology of Deinonychus and the origin of flapping in birds. PLoS One, 6(12), e28964.
  • Gignac, P. M., Makovicky, P. J., Erickson, G. M., & Walsh, R. P. (2010). A description of Deinonychus antirrhopus bite marks and estimates of bite force using tooth indentation simulations. Journal of Vertebrate Paleontology, 30(4), 1169-1177.
  • Haynes, G. (1982). Utilization and skeletal disturbances of North American prey carcasses. Arctic, 266-281.
  • Sakamoto, M. (2010). Jaw biomechanics and the evolution of biting performance in theropod dinosaurs. Proceedings of the Royal Society B: Biological Sciences, 277(1698), 3327-3333.
  • Therrien, F., Henderson, D. M., & Ruff, C. B. (2005). Bite me: biomechanical models of theropod mandibles and implications for feeding behavior. The carnivorous dinosaurs, 179-237.

Monday, 22 September 2014

The Spinosaurus hindlimb controversy: a detailed response from the authors

No-one with an interest in Mesozoic reptiles will have missed the week of controversy following Ibrahim et al.'s (2014) new reconstruction of Spinosaurus. The most important debate has focused on the allegedly reduced Spinosaurus hindlimbs, which are integral to the proposed locomotor and lifestyle hypotheses proposed for the 'new look' animal, but also difficult to reconcile with presented data. Scott Hartman, who's no stranger to producing high-quality skeletal reconstructions, blew this whistle first when he found the reconstructed proportions of the Spinosaurus neotype specimen - a series of vertebrae and hindlimb elements - were questionably scaled against measurements of the bones themselves. Lead author of the Spinosaurus study, Nizar Ibrahim, publicly responded and suggested that the measuring landmarks Scott used in comparing vertebral and hindlimb elements may be wrong. When reviewing the controversy before the weekend, I attempted my own scaling effort, using Nizar's suggested landmarks, but ended up replicating Scott's results almost exactly. I concluded "[s]omething - the original measurements of the specimen or the reconstruction - just doesn't add up, and I suspect the latter, as I figure someone would have owned up to and corrected simple numerical errors in the paper by now."

It turns out that I've got to eat a few of those words. Following my post, Nizar opened a chain of correspondence where I directly asked about these scaling issues. Nizar's response was bringing his coauthor Simone Maganuco into our chat, who had taken the time to demonstrate and describe how the restored vertebral and hindlimb lengths match the dimensions reported in the paper. In his screenshot and email, Simone provided an enlarged view of the restored Spinosaurus trunk and took the time to explain where he thought the alleged scaling errors came from. Appreciating their interest to a wide audience, Simone has kindly allowed me to reproduce his screengrab and email here.

Image courtesy Nizar Ibrahim and Simone Maganuco, used with permission.
Dear Mark,

It is nice to be in touch with you. I am writing to comment briefly on my photoshop image, forwarded by Nizar a couple of hours ago.

I hope it is the key to understand the misunderstanding about the measurements, so I would be really glad to know your opinion about it.

I have tried to replicate the coefficients for scaling obtained by you and Scott Hartman and here is my line of reasoning.

Look at the vertebra D8 in my photoshop image. For convenience, we can focus our attention on the D8 on the left.

The yellow line is 18 "units" (and matches our measurements in the table) but if you include the posteriormost margin of the slanted posterior face and the condyle you have nearly 23 units.

23:18=X:71 where 18 and 71 are also the measurements in cm in the table of the Science paper; 23 units is the length of the whole vertebra in the drawing; and X should be the length of the ilium to match the length of the vertebra in the drawing, if one assumes that the whole vertebra - and not the yellow line - is 18 units, i.e., if one thinks  we used different landmarks and measured the maximum length of the centrum.

The value of X is 90.72  units.

90.72 /71  = 1.27 that is exactly the coefficient for pelvic girdle and hindlimb scaling suggested by Scott @ skeletaldrawing.com to resize the pelvis and the legs to match the size of the D8 vertebra measured with different landmarks (i.e., if 18 is considered the maximum length).

I can see that your coefficient is slightly lower, and I wonder if you have taken slightly lower measurements (it seems to be the case looking at the white lines in your test).

Do you think that this could be the explanation of  what happened?

In the paper, we thought it was better to measure the vertebrae from rim to rim (the rounded margins of the faces), excluding the condyle, and at the same dorsoventral height (because some vertebrae are like parallelograms). It is easier to compare anterior dorsals and posterior dorsals in this way, and it is easier also to compare the centra with those of some specimens not prepared three-dimensionally but preserving well-articulated vertebrae, i.e. specimens in which it is difficult to look at the anterior condyle.

As what concerns the femur, it must be taken into account that there is also a slight perspective effect, because in the digital model it points a bit laterally. i.e., it is not 100% parallel to the sagittal plane.

The misunderstandings generated by the comparison between the figure and the table clearly indicate that we had to indicate our landmarks in one extra figure, or dedicate a couple of lines to this into the text to satisfy the need to compare figure and measurements by people who want to test our skeletal reconstruction.

When I work with palaeoartists to prepare illustrations and flesh-models I also compare figures and measurements, so I can understand this need.

Sometimes there are figures that are not 100% in the view indicated in the caption (also because it is not easy to put a bone in plane!) and sometimes it is difficult to understand the landmarks used to take measurements. What if I were in your shoes? Who knows... but I can understand that the new look of Spinosaurus has unexpected proportions that leads to think that there is something wrong.

In the monograph everything will be more clear because the detailed figures will report measurements directly on the bones, permitting everybody to see the landmarks.

In the meantime, however, I think it is useful to clarify this aspect.

Best wishes,

Simone

--

So there we have it: the measurements, landmarks and an image where they can be measured accurately. The latter is especially important because dorsal vertebra 8 in the full restoration is rather small, and thus prone to measuring errors even when measuring landmarks are known. A slip of a few pixels may not seem like much but, because the bone is a tiny component of a huge reconstruction, such minor errors can throw a scaling calibration right off. These risks were identified in Scott's original posts, and it seems they have been borne out. Nevertheless, it is interesting that Scott and I - and others, according to some Facebook chat - found such similar results: this could be coincidence, or it might be that the published reconstruction lends itself to a erroneous interpretation. Either way, there is plenty of food for thought here as goes presentation and reading of reconstruction data. For the record, when attempting to replicate the scaling again, this time on the screenshot, I found my results matched measured values given in Ibrahim et al. (2014) within a few percent. My confidence in the published proportions is thus fully restored.

Hopefully this helps resolve the scaling controversy with the 'Spinosaurus reboot', and the result is much more confidence about the downright weird and remarkable anatomy of this genuinely unusual animal. Thanks to Nizar and Simone for taking the time to explain their work, and allowing me to post their response here.


Reference


  • Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., Zouhri, S. Myhrvold, N. & Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 1258750.

Saturday, 20 September 2014

The 'Spinosaurus reboot': sailing in stormy waters

UPDATE: 21/09/14: Following chats with Nizar Ibrahim and Simone Maganuco, it appears the Spinosaurus 2014 saga has another twist to take concerning the controversy over the revised hindlimb proportions. I'd rather write about it in a comprehensive fashion when I have the time (hopefully tomorrow) and am hoping to deliver some definitive, knock-out information from the authors which puts this controversy to bed. Bear this in mind before you read the following...

ANOTHER UPDATE: 22/09/2014: Read this.

Are depictions of Spinosaurus like this now redundant? Answer: who knows? After weeks of anticipation and teased images, the 'new look' Spinosaurus has met a sceptical reception from academics and the online palaeontology community, and they've not kept their opinions quiet.
One thing is clear a week after the 'Spinosaurus reboot' (a phrase coined by Mickey Mortimer) was revealed amidst a furore of academic and media swirl: Spinosaurus c. 2014 has not met the warmest reception from the palaeontological community. A sceptical tone, sometimes very openly so, can be seen in numerous articles from the first popular science write-ups to articles penned by professional palaeontologists. As we all know by now, the primary concerns centre around Ibrahim et al.'s (2014) new Spinosaurus aegyptiacus reconstruction, which Brian Switek describes as a 'hodgepodge [of] different dinosaurs... the new subadult skeleton, digital representations of the original and long-lost Spinosaurus bones, vertebrae and hands that may or may not belong to Spinosaurus, as well as replacement parts from an assortment of spinosaurs'. Allegations have been made that scaling errors are responsible for the unusual new bauplan rather than an unprecedented lifestyle, with the allegedly tiny legs being far more proportionate once the scaling problem is addressed. These undermine the credibility of the furthest reaching claims of the authors - theropod quadrupedality and a lifestyle/locomotory strategy akin to early whales. Two widely shared and commented blog articles on this topic over at Scott Hartman's Skeletaldrawing.com have cast enough doubt over the new reconstruction that the Spinosaurus 2014 authors publicly responded to the criticism, but the reply is really just a holding message. Other than pointing out well known problems of measuring images rather than fossils (which, to be honest, are unlikely to produce the large scaling problems levelled at the paper), the message is essentially 'all will be clear in an upcoming Spinosaurus monograph'*.

*For what it's worth, I took five minutes to measure up the new Spinosaurus skeletal restoration myself following Nizar Ibrahim's measuring instructions for dorsal vertebra 8, just to see if I could make head-or-tail of the debate. Differences in measuring landmarks were chalked up as being a potential problem, so I measured the ilium and femur blind to other methods, instead using whatever landmarks were most intuitive. For both the ilium and femur lengths, I arrived at almost identical scaling errors to Scott, and the legs should - according to the data in the paper - be c. 25-27% larger in the reconstruction. Something - the original measurements of the specimen or the reconstruction - just doesn't add up, and I suspect the latter, as I figure someone would have owned up to and corrected simple numerical errors in the paper by now. My working is below.

Independent test of the alleged hindlimb proportion issues in the new-look Spinosaurus. Skeletal reconstruction from Ibrahim et al. (2014); see Skeletaldrawing.com for the posts inspiring this test, especially this and this.
The controversy extends much further than just scaling, however. Across other articles, multiple issues have been raised including the incorporation of isolated spinosaur elements and other taxa to a single Spinosaurus reconstruction; whether all the material used in the reconstruction is of spinosaurid origin (e.g. this humerus); the likelihood for theropod quadrupedality (remember that we don't know anything concrete about Spinosaurus forelimbs: there is really nothing to suggest quadrupedality in this animal other than its alleged proportions); the authors taking too much credit for the 'semi-aquatic hypothesis'; the suitability of their journal choice and the somewhat ambiguous circumstances surrounding the provenance of the new material. And this is to say nothing of the extensive discussion on social media, much of which revolves around the same topics. This is not to say the Internet is hating on Ibrahim et al. (2014) - I think the pieces linked to here are balanced, reasoned critiques, not slanderous attacks - and, before anyone asks, I'm not saying I agree with, or even have opinions on a lot of these issues. The point here is that the 'Spinosaurus reboot' has experienced a very bumpy, almost slightly hostile landing.

The response to the Spinosaurus reboot is of some interest. Controversial, questionably-supported claims are made in palaeontology all the time, but they don't get the online palaeontology community anywhere near as riled as Spinosaurus has in the last seven days. Ibrahim et al. (2014) clearly hit a nerve, perhaps because they have inadvertently created a 'perfect storm' for scientific backlash.

At the heart of the storm is a data vacuum about Spinosaurus - an odd state to be in seeing as we're now meant to have a good idea what it looked like. The main discussion about Spinosaurus in the last week has been methodological: that is, trying to figure out how the new reconstruction has been put together. This is because the paper lacks essential details concerning how the 'hodgepodge' of spinosaur bits were scaled to size or identified as Spinosaurus aegyptiacus in the first place. In skipping these details readers are left guessing - and discussing - how the proportions were ascertained and whether they are trustworthy. That people would want to know this was predictable: you can't propose a radical notion like a famous theropod being a semi-aquatic quadruped, even converging on whale ancestors, without academics, enthusiasts and dinosaur nerds wanting to know more. While the paper does have plenty of good data, it lacks transparent methods and discussions where it counts, leading readers to make their own tests and discoveries. Lest we forget, people like talking about dinosaurs online at technical levels, and it's only natural that blogging software and social media is being fired up to discuss these revelations. It's quite likely that there'd be less fuss made if the paper stood on sounder methodological ground but, ultimately, controversy sells, in part because the continual uncovering of new information and scientific debate makes for good copy.

Compounding this effect is the star of the show: Spinosaurus itself. By now, Spinosaurus has to be one of the most popular dinosaurs of all. It's the one widely known theropod to have a size advantage over Tyrannosaurus, has starred in a couple of big movies and documentaries, is undeniably cool looking, is a bit 'alternative' as dinosaurs go... for lots of reasons, it's a major dinosaur celebrity. Even among po-faced academics, the sheer size and unusual anatomy of Spinosaurs means most - probably even guys who work on brachiopods - find it a little bit more interesting than usual. Any publication on this animal is guaranteed a good amount of casual interest, but one where the animal is almost completely reinvented will send the online palaeontology community into overdrive. Did anyone else have to wait for the Science website to stop crashing when the embargo was lifted last week? I'd be interested to see how riled the internet palaeontology community got if someone questionably reconstructed a small ornithischian. For contrast, consider that the publication of another dinosaur with a radical lifestyle - the burrowing dinosaur Oryctodromeus - ruffled relatively few feathers when it was published, despite it's PR. I remember most discussion of it on the Dinosaur Mailing List concerning the formulation of its name.

Driving the storm is the considerable hype surrounding the paper, which bears little resemblance to traditional scientific press releases and is more akin to the launch of a summer blockbuster. 'Surrounding' is the right word, too, as tantalising glimpses of the new reconstruction were online weeks before the paper's release, foreshadowing the avalanche of 'official' art, articles, and videos which would follow. There are documentaries, a tie-in exhibition in Washington DC, press conferences and lectures. You'd think Spinosaurus and its wranglers were rock stars. I mean, can you name one other palaeontological PR event which needs dry ice?

The popular side of this release has been a resounding success, which - whatever you think of science being spun as a media event of this kind - is certainly well earned. In concert with National Geographic, Ibrahim et al. (2014) have put on a very slick, professional show with some wonderful art and graphics, and they've certainly made it difficult to miss. But publicity can be polarising, not to mention difficult to steer. It seems the PR for Spinosaurus 2014 has somewhat backfired in the palaeoblogosphere, the conspicuous, sensational nature of the story encouraging interested minds to investigate and test, and ultimately question the findings at the core of the hype. I expect the extensive publicity surrounding a widely-questioned paper also brings a faint sense of irritation to some, prompting them to advertise the fact that the conclusions are not as watertight as the documentaries, exhibition and magazine covers indicate. Whereas other studies with problematic conclusions would slip away into the literature to be discussed within the closed confines of scientific journals, Spinosaurus 2014 cannot hide easily: the advertising and publicity for this paper is keeping the controversy relevant and prompting more responses. I do wonder what National Geographic, presumably footing the bill for all this press work, are making of the frosty scientific response to Spinosaurus 2014.

Between the data vacuum of a radical new proposal, a megastar fossil animal and persistent reminders of a controversial study, it's hardly surprising that the online palaeo community has spent the week giving the Spinosaurus reboot a good grilling. What does the future hold? With the promise of a Spinosaurus monograph, we can be sure that there will be more discussion eventually, but, more realistically, the next major ripples will follow response papers. Some authors are already in talks about this and - given what's been demonstrated online already - there are strong cases to be made against the main hypothesis of the Spinosaurus reboot. Is a rebuttal article appropriate with another paper on the way? Yes, entirely, because we have to work with data which is available and test the hypotheses presented to us. In this case, the new-look Spinosaurus and the many implications made about its habits have been quickly questioned - deemed irreproducible, even - by a number of scientists, and this should be 'formalised' as a genuine concern about the initial paper. The upshot, of course, is that the eventual monograph will have to take this into account, which should make for a stronger publication, and hopefully an improved understanding of Spinosaurus itself.

I can't help think that there are a few causalities from the last week, not least being the good new data in Ibrahim et al. (2014), such as Spinosaurus weirdly tetradactyl feet, unusually short femur and dense bones (Ibrahim et al. 2014). What do these mean, in light of the hindlimb scaling controversy? Is the long first toe more to do with spreading weight than creating a flipper? Are the thickened bone walls more to do with relocating the centre of gravity than swimming? There are interesting discussions to be had there, but they've been overshadowed by other details. Also, scaling issues or not, I imagine the 'dachshund' Spinosaurus is here to stay for a while, so we can look forward to having to downplay confidence about the new reconstruction of Spinosaurus for the foreseeable future. It's very doubtful that the press will be interested in a story about the uncertainty over a new paper, nor is National Geographic likely to replace the legs on its Spinosaurus model with question marks. This is a constant bugbear of working within science of course: the media is interested in new and exciting discoveries, but has virtually zero attention span for scientific debate.

Finally, is there anything to learn from this? For me, the message is that while publicity is largely about presenting conclusions and results, we can't just assume our audiences are passive. Particularly if you're discussing a fan-favourite species (and let's face it, 'fans' here includes a good number of vertebrate palaeontologists), people remain just as interested in what you've done as what you conclude, and omitting those details leaves papers, and those associated with them, vulnerable to misunderstandings and criticism. As demonstrated this week, even the combined might of Spinosaurus and its PR campaign is not immune to this: when the world's largest theropod took a bite out of the Internet, it was bitten right back.

Reference


  • Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., Zouhri, S. Myhrvold, N. & Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 1258750.

Tuesday, 9 September 2014

The new African titanosaur which (almost) got away: Rukwatitan bisepultus

Rukwatitan bisepultus, a new titanosaurian sauropod from the Middle Cretaceous (Aptian/Cenomanian) of Tanzania. Why does this otherwise chirpy scene feature a dying Rukwatitan? Read on...
Hot on the heels of super titanosaur Dreadnoughtus comes another new Gondwanan titanosaur, Rukwatitan bisepultus Gorscak et al. 2014 (press release restoration, above). As indicated by the publication of two new sauropods in close succession, we live in a time where our knowledge of sauropods dinosaurs is expanding rapidly. This surge in interest and activity is perhaps less conspicuous than other expanding areas of palaeontology - sauropods don't grab the headlines as much as small, feathered theropods - but it's fair to say that the landscape of sauropodomorph research has changed considerably in the last two decades. This particularly applies to our appreciation of their diversity and distribution across space and time. Once, the sauropod story could came to a near-end in the upper Jurassic once diplodocids started to decline, but we now know that titanosauriforms kept the sauropod end up throughout the Cretaceous, being abundant, widely distributed and diverse until the end of the Mesozoic. They appear particularly important in South America, where something like 39 species have been recovered (Gorscak et al. 2014).

Schematic of known elements of Rukwatitan bisepultus. From Gorscak et al. 2014.
Rukwatitan bisepultus is not South American however, but African, specifically from the 'middle' Cretaceous (Albain-Cenomanian) Galula Formation of Tanzania. Africa's Mesozoic faunas remain poorly known and, as one of only four named sauropods from 'middle' Cretaceous Africa, as well as a component of relatively poorly-known sub-Saharan Cretaceous forms, Rukwatitan is a find. Thus far, Rukwatitan is the only named sauropod from the Galula Formation, but other Galula fossils record a 'typical' Gondwana fauna of gondwanatherian mammals, notosuchian crocodyliforms (including the carnivoran-immitating Pakasuchus, below) and osteoglossomorph fish, as well as indeterminate small theropods and turtles (Roberts et al. 2010). Rukwatitan can be seen as another component of a middle Cretaceous sub-Saharan sauropod assemblage, joining the roughly contemporaneous sauropods, Malawisaurus dixeyi and Karongasaurus gittelmani of Malawi, along with scrappy fossils which hint at additional species. Represented by an incomplete skeleton (above) and a referred humerus, Rukwatitan is a relatively small titanosaur, although its exact size is difficult to gauge. It is seemingly larger than the relatively completely known (and probably closely related, see below) Malawisaurus, Rukwatitan humeri being 20 and 28% larger than those of Malawisaurus. With Malawisaurus estimated at about 9 m long (not 16 m as indicated in Paul 2010! - see comments below), this puts Rukwatitan in a rough length ballpark of 10-12 m.

Rukwatitan is not my first artistic trip to ancient Galula: in 2010 I helped Patrick O'Connor et al. restore their unusual notosuchian crocodyliform, Pakasuchus kapilimai, famous for it's cat-like slicing dentition. The word on the palaeo grapevine is that there's a lot more to come in the world of African crocodyliforms. I'd like to have another crack at rendering these guys, so I'll be waiting by the phone if anyone wants me...
Titanosauria is an increasingly big group, so leaving Rukwatitan with this label doesn't tell us much about its relationships to other sauropods. A useful phylogenetic landmark within Titanosauria is Lithostrotia, the group of derived titanosaurs which includes many famous taxa: Saltasaurus, Opisthocoelicaudia, Alamosaurus, Nemegtosaurus and Malawisaurus. This clade also contains all known armoured titanosaurs, although armour is not ubiquitous across the group (D'Emic et al. 2009). Other titanosaurs form successive offshoots from the titanosaur evolutionary line leading to Lithostrotia, and it's among these that Gorscak et al. (2014) place Rukwatitan. It only just misses inclusion within Lithostrotia however, suggesting close evolutionary ties to basal members of this group, including the geographically and stratigraphically proximal Malawisaurus. This mirrors findings that some geographically proximal, middle Cretaceous sub-Saharan reptiles - most notably Crocodyliformes - are also closely related, and substantiates ideas that sub-Saharan faunas were evolving at a relatively local, as opposed to cosmopolitan, or even continental-scale level (O'Conner et al. 2006; Gorscak et al. 2014). Possible further evidence of sub-Saharan regions being biogeographically distinct in the mid-Cretaceous stems from an apparent absence of many north African dinosaur groups. Although titanosaurs occur across the continent, evidence of large theropods (spinosaurids and carcharodontosaurids), other sauropod groups (rebacchisaurids, non-titanosaurian titanosauriforms) and ornithopods is currently lacking in Albian-Cenomanian deposits south of the Sahara. Will these animals turn up in time? Perhaps, but the continental Cretaceous beds of Tanzania and Malawi are not new localities only now being exploited, but the sites of many years, even decades of fieldwork. If north African dinosaur groups were there, their fossils are remaining well hidden.

Giving Rukwatitan a tighter address within Titanosauria helps us flesh out a rough projection of its bauplan with a little phylogenetic bracketing. The neck was probably relatively long compared to the tail, evidenced by phylogenetic neighbours and proportions of the preserved vertebrae (note that the schematic above is probably a little wimpy on the neck end of things). It's limbs were likely robust and relatively equally sized, and it's skin probably lacked osteoderms. A short, deep skull seems likely because Rukwatitan is bracketed by short-faced Titanosauriformes, but note that the bracket here is quite loose thanks to the deficit of sauropod skull material. We leant heavily on the well-known anatomy of Malawisaurus for our reconstruction (Gomani 2005), including Scott Hartman's skeletal.

style="font-style: italic;">Rukwatitan: river victim

Quarry map of the Rukwatitan holotype specimen, looking at the cross-section of the quarry stratigraphy rather than a 'birds eye view' of a specimen spread over a single horizon. Note the distribution of the skeleton over two layers, the mudstones (representing overbank deposits - the riverbank) and sandstones (fluvial deposits - the river channel). From Gorscak et al. 2014.
The Rukwatitan type specimen has a story to tell beyond representing a new species and carving up African dinosaur biogeography: it has an unusual taphonomic history. The taphonomic agents removing bones from ancient carcasses destined to fossilise are largely anonymous: scavenging, decay and physical processes all have their part to play, but which processes affect specific specimens is often anyone's guess. This is not so with the Rukwatitan holotype: taphonomy, foul destroyer of data and frustrater of palaeontologists everywhere, has been caught with it's pants down.

Unusually for a fossil of any kind, the Rukwatitan holotype is spread over two sedimentary horizons: a layer of fine clays and muds, which represent an ancient overbank deposit (the fine sediments laid down by floodwaters in the area alongside a river), and an irregularly bedded sandstone horizon (an erosive river channel deposited over the hardened muds). We can interpret this story as beginning with a Rukwatitan carcass lying alongside a river, having finally come to rest on it's left side, indicated by the left elements of the skeleton being preserved lowest in the sequence. Clearly, the left side of the animal was buried first. The semi-articulated nature of the remains indicate that the carcass was in reasonable shape while this was happening: there was probably still soft-tissues holding it together. How completely it was buried is not clear, but it was left long enough for those soft-tissues to at least rot and weaken, if not disappear entirely. We know this because the carcass was not left buried indefinitely: a river channel scoured through the muds burying the Rukwatitan and began removing pieces of the carcass either wholesale, or by breaking the bones to pieces. The Galula Formation is essentially a large river braidplain where large (hundred of metres wide, and c. 10 m deep), relatively straight rivers would frequently change course to rework their environment (Roberts et al. 2010). Even though preserved soils and root-systems indicate that the riverbanks were bound together by plants (presumably doing well in the sub-tropical climate - Roberts et al. 2010), it seems that they were no match for these large, ephemeral rivers, and the remains of ancient bank collapses were visible alongside the in situ Rukwatitan remains. Now exposed to a torrent of water, the carcass lost many smaller bones (these are absent in the holotype) and larger bones were being disassembled. If left unabated, this Rukwatitan would have probably been eroded completely, but the river channel was particularly short lived and rapidly filled with sand. Indeed, the high energy phase of the channel incision didn't last too long at all, as many larger bones were only transported metres downstream, and their broken margins still fit the elements left in the mudstones, indicating limited exposure on the newly formed riverbed. This left us with a good chunk of titanosaur to find, but Gorscak et al. (2014) think another 'river attack' - this time the River Namba - scoured more material away in recent years. The Rukwatitan species name, bisepultus, means 'twice buried', a reference to the holotype being a veteran of erosive and re-burial processes.

If you're moved by the story of Rukwatitan specimen RRBP 07409 and want to know how you can help dinosaurs who've suffered river attacks, please contact me for details of charities and fundraising events.

We wanted to include a nod to this taphonomic story in our press artwork, which is why there's a dying or recently dead Rukwatitan at the base of the image. The cause of death for the Rukwatitan holotype is unknown, but we wanted to include some live sauropods, so it seemed sensible to attribute the death to 'natural causes' rather than an environmental catastrophe or predatory species. For fun, I included a few lesions around the mouth of the dying individual as hints of a trichomonosis-like infection, the same protozoan known to infect birds and other theropod dinosaurs to erode their bones and inflame their upper digestive tracts, leading to death from starvation (Wolff et al. 2009). Would sauropods be vulnerable to this infection? Possibly: trichomonosis leaves lesions in the lower jaw of it's victims which, to a pathologist, are quite characteristic. These lesions haven't been found in any sauropods to my knowledge, but similar ones have been found in other ornithodirans - pterosaurs (Wolff, pers. comm. in Witton 2013) - suggesting many members of this group were vulnerable to this protozoan. It's speculative, sure, but I figured it was a fun nod to other recent dinosaur research.

And finally, a request

We're just about done here, but one last point to make. Between this post, the last, and featuring more new sauropod art over at Palaeontology Online, I've developed a real hankering for a good sauropod book. You know, a readable, fully referenced overview of their history of study, anatomy, palaeoecology, biomechanics, evolutionary history and diversity (so, nothing major then). I'm quite serious here: they're an awesome, popular group of animals, fully deserved of their own semi-technical overview, ideally with lots of images to showcase their anatomy and habits. I'm sure this idea has sufficient legs to interest a major publisher. I lack the expertise to write it, so this is my attempt to plant a seed in the minds of those who can. For what's it's worth, I'd gladly help illustrate it: sauropods are fantastic fun to draw, and it'd be terrific to bring the diversity of this group to life in artwork.

I leave you with this image, which was drafted in response to Eric Gorscak's comments about the Rukwatitan press image: "Other than the lack of laser beams, I think it is looking fantastic!" Not wanting to disappoint, I duly complied...

Oh no, what caption to use? 'Pods of War? 'Podageddon? DinosAWESOME? Too... many... puns...

References

  • D'Emic, M. D., Wilson, J. A., & Chatterjee, S. (2009). The titanosaur (Dinosauria: Sauropoda) osteoderm record: review and first definitive specimen from India. Journal of Vertebrate Paleontology, 29(1), 165-177.
  • Gomani, E. M. (2005). Sauropod Dinosaurs from the Early Cretaceous of Malawi, Africa, Palaeontologia Electronica Vol. 8, Issue 1, 27A: 37p.
  • Gorscak, E., O'Connor, P. M., Stevens, N. J. & Roberts, E. M. (2014). The basal titanosaurian Rukwatitan bisepultus (Dinosauria, Sauropoda) from the middle Cretaceous Galula Formation, Rukwa Rift Basin, southwestern Tanzania. Journal of Vertebrate Paleontology. In press.
  • Paul, G. S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press.
  • O’Connor, P. M., Gottfried, M. D., Stevens, N. J., Roberts, E. M., Ngasala, S., Kapilima, S., & Chami, R. (2006). A new vertebrate fauna from the Cretaceous Red Sandstone Group, Rukwa Rift Basin, southwestern Tanzania. Journal of African Earth Sciences, 44(3), 277-288.
  • O’Connor, P. M., Sertich, J. J., Stevens, N. J., Roberts, E. M., Gottfried, M. D., Hieronymus, T. L., Jinnah, Z. A., Ridgely, R., Ngasala, S. E. & Temba, J. (2010). The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana. Nature, 466(7307), 748-751.
  • Roberts, E. M., O’Connor, P. M., Stevens, N. J., Gottfried, M. D., Jinnah, Z. A., Ngasala, S., Choh, A. M. & Armstrong, R. A. (2010). Sedimentology and depositional environments of the Red Sandstone Group, Rukwa Rift Basin, southwestern Tanzania: New insight into Cretaceous and Paleogene terrestrial ecosystems and tectonics in sub-equatorial Africa. Journal of African Earth Sciences, 57(3), 179-212.
  • Witton, M. P. (2013). Pterosaurs: natural history, evolution, anatomy. Princeton University Press.
  • Wolff, E. D., Salisbury, S. W., Horner, J. R., & Varricchio, D. J. (2009). Common avian infection plagued the tyrant dinosaurs. PloS one, 4(9), e7288.