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.

Saturday, 6 September 2014

Hey Dreadnoughtus, not so close

I try to avoid hopping on the bandwagons following new discoveries - few internet experiences are more tiresome than seeing social media and inboxes swollen with discussions and pictures of the same new fossil species (tyrannosaurids, for some reason, do this more than anything else). Of course, some new discoveries are just too cool to pass up: Dreadnoughtus schrani Lacovara et al., 2014 is one of them. Not only does it have a fantastically marketable and charismatic name entirely befitting one of the largest land animals to ever exist (take that, naysayers), but the sheer amount of data published on it is really first class (Lacovara et al. 2014) and the fossil is truly spectacular. If you've not done so, check out the Dreadnoughtus description and supplementary material: there's everything from measurements and photographs to interactive 3D scans of every bone for you to look at in fine detail (or spin around like crazy while giggling, if you're comfortable enough with your maturity). And before you can say 'paywall', this is all freely-available, open access information. It's not just a great paper for those interested in sauropods or dinosaurs, but also an important reference point for those interested in the evolution of extreme animal anatomies and gigantism.

How the world met Dreadnoughtus schrani in palaeoart. Left, restoration by Jennifer Hall; right, Mark A. Klingler. Images from the Dreadnoughtus media release hosted at the Drexel News Blog.
I found one aspect of the very good, super-comprehensive and fittingly giant media release for Dreadnoughtus rather unusual, however: the artwork. For a media story principally being sold on the size of a dinosaur, the two 'official' pieces of Dreadnoughtus artwork by Mark A. Klingler and Jennifer Hall (above) have - what seem to me at least - some odd choices as goes composition and posture which might undermine the awesome size of Dreadnoughtus. I'm not saying the images are bad or 'wrong': there's lots of lovely detail and atmosphere in both (note the neat sauropod and titanosaur characteristics like the lack of manual claws, the concave posterior surface of the hand etc.), and this is not a dig at the artists, who have definitely earned the wide success of the Dreadnoughtus press campaign. My problem - and I hope this comes across as the constructive criticism it's intended as - is that I'm a bit underwhelmed by the sense of scale, which I'd say is pretty important for artwork of this animal. To be fair, conveying extinct animal size in art is never straightforward, but peculiar compositional choices in each image prohibit my being fooled into thinking I'm looking at truly giant animals. For example, both position the animals in the foreground, filling the canvas with as much Dreadnoughtus hide as possible. I can understand why - it says "it's so big we can barely contain it in the edges of these illustrations", but it also leaves little room for a point of size reference between us and the animals. It also forces the adoption of stooping postures and requires significant foreshortening to fit the animals into view, the former reducing their apparent size and the latter obscuring proportions we intuitively recognise as characteristic of large animals (e.g. the relatively small heads of large animals). Hall's illustration also sets the point of view at shoulder height so we're actually looking across and somewhat down at the subject animal - not necessarily what you might want to suggest this thing was bigger and taller than us. Both images feature trees immediately alongside their animals as a means of conveying scale, but I find the rest of the composition overpowers their effect. In all, while the other aspects of the images are effective, I'm just not sold on the size.

I find these decisions interesting because I think they represent a case of a modern palaeoart convention overruling 'classical' artistic approaches. Traditionally, artists use the same basic techniques for making subjects look big and important when placing them in a scene. They stress proportional extremes (including small head size - this even occurs in renditions of royal or divine human figures), use low points of view so that the the top of the subject clears the horizon line along with other elements in the composition, and place items to give an appropriate sense of scale. Positioning smaller items in the foreground can help the viewer find their position in the scene and ground their sense of size, but these need to be placed carefully: cluttered compositions tend to dwarf their subjects. A consequence of these methods is that giant subjects are often no closer than the mid-ground. An obvious exception to this are images with points of view positioned at the very base of a subject, looking up, so it looms above the viewer (below). This is a slightly different approach to the problem, though, almost treating the subject as the landscape rather than an entity within a background.

A cockroach-eye view of a titanosaur.
Palaeoart produced before the 1970s/1980s stuck to the classic rules of depicting giant animals: Zallinger, Knight, Burian et al. rarely deviated from 'standard' methods of conveying large size when drawing sauropods and other big extinct animals. The scientific transformation of dinosaurs into dynamic, active animals in the late 20th century also brought on a artistic shift where some artists abandoned 'classic' compositions in favour of more exciting, convention-defying and 'extreme' images. One consequence of this was some artists moving (frequently giant) animals closer to the foreground, turning them to face viewers and sometimes, through their body language, 'interacting' with those looking at them. The first seeds of this were probably sown by by the likes of Robert Bakker who, in many of his illustrations, fills every possible square inch with his animals to the point of using extreme postures - particularly arching backs and curving tails - to do so (e.g. illustrations in Bakker 1986). Bakker's works frequently lack the context of backgrounds however, leaving other artists to bring dynamically posed, big extinct animals closer and closer in landscaped works. I think Mark Hallett may have be particularly instrumental here, with works such as his famous 1984 'Dawn of a New Day', and the 1985 paintings 'Awakening of Hunger' and 'Ancient One' leaning towards, or perhaps even pioneering, an 'in your face' style of palaeoart where the subjects are looking at, sometimes menacing, their viewers (if anyone did this earlier, please let me know). Such artworks would become common in the 1990s, with Luis Rey famously combining these compositions with extremes of colour, perspective and pose to produce a style which has since been widely imitated. It's from such imagery that 'slasher' palaeoart arose, those images were animals are rushing, teeth and claws bared, at the viewer from within the painting.

Attitudes towards these foreground-emphasised, perspective heavy images are often divisive among palaeoart aficionados - some love them, others hate them. Fans of such works point out their utility for outreach, in that they're relatively novel, different, fun and striking, while detractors note their distortion of proportion, not to mention that many look, well, silly (I've argued elsewhere that this may have negatively skewed public perception of feathered dinosaurs). The most relevant common complaint to our discussion is that they lose all sense of scale, essentially for all the reasons listed above: unfamiliar proportions, a lack of foreground space to place 'scaling' elements, and often the loss of height associated with moving the anatomy into a position where it can all be seen behind the head (for many infamous examples, see Brusatte and Benton's enormous book Dinosaurs (2008)). Whatever your opinion, we can't deny their success and influence. such images are now a standard palaeoart convention, particularly in children's books, and have been used to showcase virtually any prehistoric animal you can think of. In this respect, the arching, frame-filling Dreadnoughtus images released last week are just following this now familiar palaeoart convention.

Thing is, I'm not sure if this practise works for all palaeoart, and especially in images where conveying size and anatomical details are important. Of course, the ultimate success of a composition is a matter of taste, and there is no actual 'right' or 'wrong' to palaeoart so long as it obeys basic laws of anatomy. But here's the beef: palaeoartworks often have a purpose - very commonly to convey the anatomy and size of a new species - but 'full frame' animal compositions are probably the worst composition to demonstrate these attributes, for reasons discussed above. Moreover, and fundamentally related to the goal of palaeoart being realistic portraiture of extinct species - how do we rationalise the adoption of the contorted postures required to fit the animals into frame? Why would these animals be condensing themselves into such weird shapes? And what do these poses look like from other angles? Wouldn't they look, at best, a bit odd? For me, seeing a restored animal in an unconventional, maybe even biomechanically implausible pose so it can take up more of the canvas is jarring, a reminder than I'm looking at an reconstructed animal rather than one an artist saw with their own eyes.


For art where proportions and a sense of scale is important, pushing our subjects back to the tried and tested middle distance would alleviate these problems, without jeopardising their excitement. Palaeoart was just as inspirational and exciting to audiences before we started rendering animals right under our viewer's noses, after all. Ultimately, while there's nothing inherently 'wrong' with any composition in palaeoart, some compositions suit certain scenes and animals more than others, and some are definitely more informative and educational than others. 'Full frame' compositions certainly have their place within palaeoart, but they're probably more limiting artistically and educationally than the alternatives.

I'll leave you with my own take on Dreadnoughtus, a quick painting done as the end result of my spate of fanboyism on Thursday night. And if you like sauropods, stay tuned, because there's more on the way...

The mighty Late Cretaceous titanosaur Dreadnoughtus schrani, making a mockery of two abelisaurids just by existing. Abelisaurids aren't known from the same formation as Dreadnoughtus, but are the most likely theropods to have occurred there given their abundance in the other Late Cretaceous South America. These are loosely based on Aucasaurus.

Update: 07/09/2014, well past bedtime

Not many moments after posting this, arty chum Jon Davies (@SovanJedi) responded with an image on Twitter which sums up the few thousand words above into one image:

It's funny because it's true.

References

  • Bakker, R. T. (1986). The Dinosaur Heresies. London, Penguin.
  • Brusatte, S. and Benton, M. J. (2008). Dinosaurs. Quercus.
  • Lacovara, K. J., Lamanna, M. C, Ibiricu, L. M., Poole, J. C., Schroeter, E. R., Ullmann, P. V., Voegele, K. K., Boles, Z. M., Carter, A. M., Fowler, E. K., Egerton, V. M., Moyer, A. E., Coughenour, C. L., Schein, J. P., Harris, J. D., Martínez, R. D., and Novas, F. E. (2014). A gigantic, exceptionally complete titanosaurian sauropod dinosaur from Southern Patagonia, Argentina. Scientific Reports. 4, 6196; DOI:10.1038/srep06196.

Monday, 1 September 2014

The accuracy of palaeoart and the 'new' Spinosaurus

Spinosaurus, big and small versions, poking about a stream in Cretaceous Morocco. Someone's about to ask if these chaps should have humps or sails - head to Palaeontology Online for my thoughts on this, and read on for why it doesn't resemble the (in?)famous National Geographic thumbnail.
Corking news, all: I've got a new article out at Palaeontology Online on the accuracy of palaeoart, explaining how confident - or not - we can be about different aspects of extinct animal appearance. It features two new bits of palaeoart, a Spinosaurus and a bizarre - but not implausible - reconstruction of Camarasaurus. The former started life as a simple illustration to make a point about reconstructing fatty tissues (including camel-like humps) in fossil animals, but I thought it warranted some elaboration: the painting above is the result.

The goal of the Palaeontology Online piece is not another 'how to?' guide to palaeoart, but a piece specifically targeted at those who want to know how accurate our restorations are. I've attempted to outline the reliability of standard palaeoart methods including phylogenetic bracketing, restoring musculoskeletal systems, placing fatty tissues, choosing integument types and, of course, deciding on colours and patterns. Note that the few years of optimism we've had for restoring fossil colour using melanosomes are over, because several new studies have highlighted numerous concerns with this technique: more on that at Palaeontology Online. All Yesterdays gets further mainstreamification, as does the mysterious, unexplained 'Support Original Palaeoart' logo (more on that in due time), and there's some philosophising over the goal of palaeoartists: are we actually bothered about 'the truth', or more concerned with making plausible art in line with fossil and biological evidence? OK, that's enough signposting for now: point your browser this way for the full piece, and be sure to leave any feedback below.

Just a quick note on the Spinosaurus illustrations here and in the article: they are not based on the thumbnail image of a unusual Spinosaurus skeleton at the National Geographic website, despite this spawning much excitement, umpteen new spinosaur renditions and revisions to Spinosaurus illustrations all over the Web. As stressed at Palaeontology Online, palaeoart is a scientific process requiring verified and trustworthy data. We have no idea how reliable the radical National Geographic depiction of Spinosaurus is because no information about the mount has been made public, and the image itself is tiny: it's silly to think there's enough resolution there to understand its anatomy. Moreover, there's enough counter-intuitive and weird morphology in that tiny photo to justify waiting for the data behind the mount to be published so it's accuracy can be evaluated. I'm not saying it's wrong, but I am joining the chorus of bona fide theropod experts in suggesting restraint against adopting it as the 'definitive new look' for Spinosaurus until we know more about it. The reconstructions here and at Palaeontology Online are based on Scott Hartman's skeletal: the appearance of the juveniles is speculative.

Coming soon (probably): exciting news from the world of sauropods!

UPDATE (02/09/14): Like buses, it seems palaeoart articles all arrive at the same time. Head to Tetrapod Zoology for Darren Naish's detailed article on the changing life appearance of dinosaurs.

Friday, 22 August 2014

Scleromochlus taylori: more than just 'the early ornithodiran'

The Triassic ornithodiran Scleromochlus taylori depicted as a nocturnal desert-specialist with filamentous insulation, fuzzy feet for purchase on drifting sands and a saltatorial means of locomotion. 

Like actors with one famous character, fossil taxa can become typecast to specific ‘roles’ in palaeontological discussions. One fact of their palaeobiological significance is entrenched so deeply that they are seldom mentioned outside of this context. Examples include Archaeopteryx as the first bird, Mei as the cute sleeping dinosaur, and Darwinopterus as the bridge between major stages of pterosaur evolution. Packaging these animals into simple factoids obscures much of their other interesting palaeobiology, so we rarely hear about their other remarkable features.

Step forth Scleromochlus taylori, a small Triassic archosaur from the Upper Triassic (Late Carnian) of Scotland. For 100 years Scleromochlus has been implicated as a relative of pterosaurs (e.g. Huene 1914; Padian 1984; Gauthier 1986; Sereno 1991; Bennett 1996; Hone and Benton 2008; Brusatte et al. 2010, Nesbitt 2010) or, at very least, an ornithodiran representing a very early stage of stem-bird evolution (Benton 1999; Hone and Benton 2008).* This is about all we ever hear about Scleromochlus, however: nothing more than a milestone in the evolution of pterosaurs or dinosaurs. I'm guilty of it too: in my own book, Pterosaurs (Witton 2013), Scleromochlus just formed an anchor for discussing ornithodiran evolution. Undoubtedly, this needs correcting: Scleromochlus is a unique and interesting animal in its own right, and one fully worthy of detailed discussion. To relieve my shame, I'm going to attempt such a discussion here. Just for fun, I'm going to write it in the same style as a Pterosaurs chapter.

*You can't mention Scleromochlus on the internet without someone pointing out that its status as an ornithodrian has not been tested in analyses containing non-archosaur archosauromorphs. This is true enough, but - at least within the current limits of testing - its ornithodiran status is not controversial, having been recovered in at least six different analyses (e.g. Gauthier 1986; Sereno 1991; Bennett 1996; Hone and Benton 2008; Brusatte et al. 2010) and sharing several unique characteristics with Pterosauria (Padian 1984). Hence, we're following convention here.

Select line drawings of Scleromochlus taylori fossils from Benton (1999). There are two specimens here, showing dorsal and ventral views. The specimen on the right is the holotype, and the left shows two associated individuals. Note the banded scales crossing the vertebrae of the larger individual.
Although represented by at least seven specimens from the Lossiemouth Sandstone Formation, no Scleromochlus is well preserved (Benton 1999). Most specimens comprise shallow sediment molds rather than actual bones, and none are complete. But we should consider ourselves lucky we know of this animal at all: the delicate, 180 mm long bodies of Scleromochlus occur in sandstone deposits representing an ancient, wind-blown desert with 20 m high dunes. Such deposits are often devoid of fossil remains, but the Lossiemouth Sandstones actually preserve a diverse reptile fauna (Benton and Walker 1985). Still, it’s remarkable that the tiny bones of these reptiles preserved at all in these harsh conditions and in relatively coarse (fine - medium) sands - the grains preserving Scleromochlus are each as large as Scleromochlus teeth. As is typical of Lossiemouth Sandstone specimens, most Scleromochlus fossils are more-or-less articulated and many appear to have been crouching at death. With little indication of sun-cracking or scavenging, their remains clearly represent animals which were buried alive or buried shortly after death, probably by sandstorms or dune collapses (Benton and Walker 1985). Although likely complete when buried, no specimens have survived intact to the present. Cross-scaling elements from different specimens has permitted a reasonable insight into Scleromochlus anatomy all the same (Benton 1999). Some details remain murky however, and disagreement persists over precise bone lengths and skull bone attitudes (Sereno 1991, Benton 1999; Padian 2008). This is perhaps expected, given that Scleromochlus remains are interpreted via low-angle light and plaster or plastic peels of the skeleton molds. Bennett (1996) sums up working on Scleromochlus as "low-angle illumination [is used] to examine and interpret molds and peels, but in my experience a considerable amount of imagination is necessary as well".

Anatomy

Specific details aside, palaeontologists are happy to say that the basic bauplan of Scleromochlus resembles a small lizard with enormous hindlimbs (below). The skull has a low lateral profile but is rather triangular in dorsal aspect, with a blunt muzzle and widened posterior. So far as can be seen, the orbit is by far the largest opening in the skull, making the reduced nares look even smaller by comparison. The temporal fenestrae - as illustrated by Benton (1999) - are fairly sized, although their full margins aren't clear in any specimen. These sit above a posteriorly lengthened retroarticular process on an otherwise fairly unremarkable lower jaw. Each jaw seems to house 15/16 teeth, which are apparently isodont and - so far as can be seen - relatively small and lanceolate. The lizard-like visage of Scleromochlus is further enhanced by its short neck, which contrasts with later ornithodirans. The tail appears rather short too, being about as long as the snout-vent length.

Reconstructed skeleton of Scleromochlus taylori from Witton (2013), a modified version of the skeletal in Benton (1999).

The limbs of Scleromochlus are where a lizard-like visage starts to unstick. The forelimb bones are long and slender, and capped with tiny hands. The fingers are poorly known, but the tiny metacarpals suggest they were rather diminutive and unlikely of any use for standing or walking, a hypothesis supported by the dichotomy in fore- and hindlimb length. Even less lizard-like are the hindlimbs, which are extremely long - about half the length of the entire animal - and end with a narrow foot with tightly bound metatarsals. Both the forelimbs and pelvis appear relatively small compared to the legs, though neither is atypically small for the length of the animal. The fifth toe appears to have been lost, the only remnant being a short, pointed metatarsal. Scleromochlus hindlimb arthrology betrays a parasagittal posture akin to that of dinosaurs and pterosaurs - the suite of characteristics associated with this is one clue that Scleromochlus is closely related to these clades (Bennett 1996; Benton 1999; Hone and Benton 2008).

Thin, transversely-banded scutes(?) covered the dorsal surface of the Scleromochlus torso, extending from at least the shoulders to the posterior pelvic region (indicated in the fossil illustrations, above). These indicate that Scleromochlus was at least partly scaled, although whether this represents the entire integument is not clear. It is increasingly apparent that scraps of fossil skin do not tell whole stories about ornithodiran integuments, as more and more specimens with extensive skin preservation present 'mosaics' of scales, naked skin and various kinds of filaments (demonstrated in pterosaurs, theropods and ornithischians; e.g. Bakhurina and Unwin 1994; Chiappe and Göhlich 2010; Godefroit et al. 2014). Scleromochlus may have been covered in scales, but it is equally likely that it had fuzz-like filaments in places. There are several reasons for this. Firstly, it belongs within a phylogenetic bracket where filaments are the ancestral condition or, at very least, scales were prone to developing filamentous morphologies. Secondly, virtually all models of archosaur evolution recover Scleromochlus as sister taxon to a fuzzy clade - pterosaurs, so there is good 'phylogenetic proximity' for fuzz. Thirdly, insulating integuments are common - if not ubiquitous - in small, active (see below) desert-dwelling animals. Thus, while the overall  integument of Scleromochlus remains mysterious, a mosaic of filaments and scales is not an unreasonable suggestion. In the reconstruction here, Scleromochlus is shown as rather fuzzy all over (see below for rationale), with filaments poking through its scaly back as they do on opossum tails and armadillo hide.

Please provide your own 'boing' sound effects.

Locomotion

Scleromochlus has long been recognised as a sprightly, cursorial or saltatorial biped because of its elongate, parasagittal hindlimbs (e.g. Woodward 1907; Huene 1914, Walker 1961; Padian 1984; Benton and Walker 1985; Benton 1999; Witton 2013). It has also been considered an arboreal glider with Sharovipteryx-like hindlimb membranes, as well as an aquatic diver, but few obvious adaptations to these lifestyles are found on its skeleton (Benton and Walker 1985). Cursorial features of Scleromochlus include lengthening of the distal hindlimb, reduction of the lateral pedal digits and narrowing of the metatarsal, and it is generally considered to have assumed a digitigrade stance, at least when moving at speed. Several features indicate that Scleromochlus was a saltator rather than a running creature: a relatively small but strong pelvis, short trunk skeleton, and a pronounced intercondylar groove at the end of the femur, which likely reflects a large quadriceps femoris tendon (Benton and Walker 1985). Saltation is an energy-efficient means of locomotion which has frequently evolved in desert-living species - extant examples include desert rodents, jerboas and kangaroos - and Scleromochlus has been favourably compared with such animals on several occasions (Walker 1961; Benton and Walker 1985; Benton 1999). Saltation may seem unusual means for a reptile to move, but other Triassic ornithodirans may have also locomoted in this way (Sereno and Arcucci 1994). Indeed, the powerful leaping and bounding abilities of early ornithodirans has been tied to the evolution of pterosaur flight (Bennett 1997; Witton 2013). 

Lifestyle and palaeoecology

It is difficult to say exactly what Scleromochlus ate because its teeth are poorly known, but a generalised diet of insects and other small prey seems mostly likely given the shape of its teeth and jaws (Benton and Walker 1985; Benton 1999). The wide skull and enlarged retroarticular process may have provided space for large and powerful jaw muscles, allowing Scleromochlus to make short work of tough insect carapaces. The association of crouching, articulated Scleromochlus skeletons (see line drawings, above), along with the recovery of multiple specimens (actually 5% of the Lossiemouth Sandstone fauna - Benton and Walker 1985), hints at some degree gregarious behaviour. It is difficult to imagine how the two associated individuals shown above were preserved in such a way unless they were alongside each other when they died - huddled together against whatever catastrophe buried them. Was coupling or group living 'normal' behaviour in Scleromochlus? Statistically, the odds of rare fossil specimens like those of Scleromochlus preserving unusual, 'one in a million' types of behaviour are low, so we might take the co-preservation of two animals as being representative of 'average' or typical behaviour in this species.

For those of you now weeping about tiny, panicked pairs of Scleromochlus dying in huddled balls of fear, here's a speculative reconstruction baby Scleromochlus to cheer you up. Using back of the envelope calculations of lizard egg mass and size, I predict this gangly hatchling was 50-60 mm long. The image is deliberately displayed at this size to stress the tiny proportions: on my 'standard issue' laptop screen, it's about life-size. Click to embiggen.

The likely saltatorial locomotion of Scleromochlus may not be their only adaptation to desert life. Their metatarals are rather flattened posteriorly (Benton and Walker 1985), permitting sitting or squatting on plantigrade feet without sinking into sand. Their nares are small, and flanges from the back of the skull cover the tympanic region (the location of the ear opening), both adaptations common among modern xerocoles to prevent moisture loss and minimise irritation from wind-blown sands (Benton and Walker 1985). Their orbits, by contrast, are very large, and may reflect another common response to desert life - nocturnality. Tiny animals like Scleromochlus rapidly overheat under a desert sun, but foraging at night negates that risk. Of course, desert temperatures plummet once the sun sets, but a layer of filaments (if present) may have countered this. Perhaps groups of Scleromochlus spent their days under shelter - rocks or vegetation - before venturing out at night to forage for insects. This strategy also helps avoid predators, of which the Lossiemouth Sandstone Formation has its fair share: early dinosaurs and nimble pseudosuchians are likely predators of Scleromochlus (Benton and Walker 1985). Hypothetical filaments of Scleromochlus may have had further uses in desert life, including enhancing their grip - and therefore agility - on sandy substrates, as seen in some modern saltatorial desert species. Likewise, covering or filling nose and ear openings with long scales or fur is another feature common to desert species, enhancing resistance to evaporation and airborne sand. The desert habitat of this early ornithodiran presents several intriguing reasons for the development of filamentous structures, which is obviously of interest when considering the origins of fuzz in Ornithodira more broadly.

And that, in a way, brings us full circle: back to considering Scleromochlus anatomy in the context of wider Ornithodira. Still, I'm sure we can all agree Scleromochlus is actually a very interesting animal in its own right, and definitely worthy of escaping typecasting as 'the early ornithodiran'.

References

  • Bakhurina, N. N., & Unwin, D. M. (1995). A preliminary report on the evidence for ‘hair’in Sordes pilosus, an Upper Jurassic Pterosaur from Middle Asia. In Sixth Symp. Mesozoic Terrestrial Ecosystems and Biota, Short Papers (pp. 79-82).
  • Benton, M. J. (1999). Scleromochlus taylori and the origin of dinosaurs and pterosaurs. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 354(1388), 1423-1446.
  • Benton, M. J., & Walker, A. D. (1985). Palaeoecology, taphonomy, and dating of Permo-Triassic reptiles from Elgin, north-east Scotland. Palaeontology, 28(2), 207-234.
  • Bennett, S. C. (1996). The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoological Journal of the Linnean Society, 118(3), 261-308.
  • Bennett, S. C. (1997). The arboreal leaping theory of the origin of pterosaur flight. Historical Biology, 12(3-4), 265-290.
  • Brusatte, S. L., Benton, M. J., Lloyd, G. T., Ruta, M., & Wang, S. C. (2010). Macroevolutionary patterns in the evolutionary radiation of archosaurs (Tetrapoda: Diapsida). Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 101(3-4), 367-382.
  • Chiappe, L. M., & Göhlich, U. B. (2010). Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 258(3), 257-296.
  • Gauthier, J. A. (1986). Saurischian monophyly and the origin of birds. In Padian, K. The Origin of Birds and the Evolution of Flight, Memoirs of the California Academy of Sciences 8. California Academy of Sciences, 1–55. 
  • Godefroit, P., Sinitsa, S. M., Dhouailly, D., Bolotsky, Y. L., Sizov, A. V., McNamara, M. E., ... & Spagna, P. (2014). A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. Science, 345(6195), 451-455.
  • Hone, D. W., & Benton, M. J. (2007). An evaluation of the phylogenetic relationships of the pterosaurs among archosauromorph reptiles. Journal of Systematic Palaeontology, 5(4), 465-469.
  • Huene, F. von. (1914) Beiträge zur Geschichte der Archosaurier. Geologische und palaeontologische Abhandlungen, N.F., 13, 1-53.
  • Nesbitt, S. J. (2011). The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History, 1-292.
  • Padian, K. (1984). The origin of pterosaurs. In Third Symposium on Mesozoic Terrestrial Ecosystems: Short Papers (pp. 163-166).
  • Padian, K. (2008). Were pterosaur ancestors bipedal or quadrupedal?: Morphometric, functional, and phylogenetic considerations. Zitteliana, B28, 21-33.
  • Sereno, P. C. (1991). Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology Memoir 2, 11, 1-53.
  • Sereno, P. C., & Arcucci, A. B. (1994). Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis, gen. nov. Journal of Vertebrate Paleontology, 14(1), 53-73.
  • Walker, A. D. (1961). Triassic reptiles from the Elgin area: Stagonolepis, Dasygnathus and their allies. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 103-204.
  • Witton, M. P. (2013). Pterosaurs: natural history, evolution, anatomy. Princeton University Press.
  • Woodward, A. S. (1907). On a new dinosaurian reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society, 63(1-4), 140-NP.

Wednesday, 13 August 2014

Lies, damned lies, and 'Thalassodromeus sebesensis'

Yesterday, a huge team of authors called out the science behind 'Thalassodromeus sebesensis', an alleged new pterosaur species 40 million years and thousands of miles out of time and space (Grellet-Tinner and Codrea 2014). As with many outlandish palaeontological claims, the evidence behind 'T. sebesensis' really falls apart rapidly under scrutiny, principally because the alleged pterosaur remains actually represent an unremarkable piece of turtle plastron (Dyke et al. 2014).

A, the plastron of the fossil Romanian turtle Kallokibotion magnificum, compared with B, the alleged holotype 'cranial crest' of 'Thalassodromeus sebesensis'. For further details, see yesterday's post.
Since then, the response to our comment has been published (Codrea and Grellet-Tinner 2014). I'll admit to being surprised that Codrea and Grellet-Tinner maintain the specimen as a pterosaur, and consider the arguments raised against our points as weak, hypocritical and problematic, but whatever: the two arguments are now out, and the palaeontological community can judge for themselves. CT scanning is apparently planned for the specimen (Codrea and Grellet-Tinner 2014), which should put 'T. sebesensis' to bed once and for all.

This post isn't really about that, though: it's about correcting a mistruth in Codrea and Grellet-Tinner's response. Their comment shows little decorum or professionalism, attempting to undermine our response with ad hominem potshots at some authors of Dyke et al. (2014), including criticism of their editorial skills and the taxonomic confusion surrounding specimens described by the authors. Moreover, they criticise us for not examining the specimen, UBB ODA-28, before publishing our response. They state that:
"...UBB ODA-28 is housed in an official and recognized Romanian institution, thus available for examinations to anyone interested. This includes Dyke’s July 2nd 2014 written request to examine UBB ODA-28, which was immediately granted, although, Dyke went on writing its hasty comment without examining UBB ODA-28."
Codrea and Grellet-Tinner, 2014, p. 3-4 (my emphasis)

Well, this isn't really true. Some of it is: Gareth Dyke did write to ask for permission to look at the specimen this year - specifically between July and September - but 'immediate' access was not granted. Rather, eventual access was promised following on-going studies, including CT scanning of the specimen, the dates of which was not disclosed. This is not, as Codrea and Grellet-Tinner describe, 'immediately' granting access, but nebulously promising access at an undetermined future date. 

This may not seem like a big deal, but our integrity is being questioned for having not seen the specimen, so we - the authors of Dyke et al. (2014) - think the record should be set straight. There's no doubt that examining specimens is the way forward in any research. But it was clear from Gareth's correspondence that accessing UBB ODA-28 was going to be difficult for the immediate future, and all the while the science behind 'T. sebesensis' remained extremely problematic and in need of swift rebuttal. Why? In short: none of us concerned with pterosaurs or European palaeontology want to deal with this outrageous, nonsensical claim in future publications. Hence, we fell back on using the published accounts of UBB ODA-28 to construct an argument against the pterosaur identification. Given that our authorship team has collectively amassed thousands of hours examining actual thalassodromid pterosaurs, as well as turtle plastrons, and how obvious the turtle affinities of the specimen are, this method seemed more than sufficient for the task at hand. Despite allegations from Codrea and Grellet-Tinner, these were not the actions of a team hastily assembling a rebuttal, but a collective of experienced individuals succinctly calling out obvious flaws in bad science.

So there we go: that's our side of that mistruth. Hopefully, that's the last we'll hear of 'T. sebesensis' around these parts, for there are much more interesting and exciting things to cover: palaeoart guides, Triassic fuzzy saltating xerocoles, dinosaur fat humps... all coming soon.

References

  • Codrea, V. A., & Grellet-Tinner, G. (2014). Reply to Comment by Dyke et al. on "Thalassodromeus sebesensis, an out of place and out of time Gondwanan tapejarid pterosaur" by Grellet-Tinner and Codrea (July 2014)"  Gondwana Research. IN PRESS
  • Dyke, G. J., Vremir, M., Brusatte, S., Bever, G., Buffetaut, E., Chapman, S., Csiki-Sava, Z, Kellner, A. W. A., Martin, E, Naish, D, Norell, M, Ősi, A, Pinheiro, F. L., Prondvai, E, Rabi, M, Rodrigues, T., Steel, L., Tong, H, Vila Nova B. C. & Witton, M. (2014). Thalassodromeus sebesensis-a new name for an old turtle. Comment on" Thalassodromeus sebesensis, an out of place and out of time Gondwanan tapejarid pterosaur", Grellet-Tinner and Codrea. Gondwana Research. IN PRESS.
  • Grellet-Tinner, G., & Codrea, V. A. (2014). Thalassodromeus sebesensis, an out of place and out of time Gondwanan tapejarid pterosaur. Gondwana Research. IN PRESS

Tuesday, 12 August 2014

'Thalassodromeus sebesensis': pterosaur out of time and space? Nope, just a misidentified chunk of turtle.

Thalassodromeus sethi after some worms. Note: not a turtle. From Witton (2013)
Today sees the publication of an article challenging an exciting claim made in recent pterosaurology (Grellet-Tinner and Codrea 2014). If you missed it, the article concerned identifies a thalassodromid pterosaur in uppermost Cretaceous rocks of Romania and the erects a new species, Thalassodromeus sebesensis Grellet-Tinner and Codrea, 2014. At the centre of this is ODA-28, an (alleged) fragmentary cranial crest only fully exposed on one surface. None of this may not sound like a big deal, except that other thalassodromids - including the alleged sister species, Thalassodromeus sethi - are only known from the Lower Cretaceous Araripe Group of Brazil. T. sebesensis thus is about 40 million years out of time and thousands of miles out of place, and also occurring when azhdarchid pterosaurs basically represent the entire diversity of Pterosauria (Grellet-Tinner and Codrea 2014). Suddenly, the routine act of naming of a new animal is rewriting our understanding of pterosaur evolution.

There's more. Despite having only a scraps of bone to work with, Grellet-Tinner and Codrea (2014) suggested the T. sebesensis crest anchored muscles to form a ‘sizeable fleshy crest’, acted as a rudder in flight, that it somehow highlighted co-evolution between Romanian pterosaurs and angiosperms, and ecological segregation between azhdarchids and thalassodromids. All of these ideas are pretty radical in one way or another, especially considering the fossil material they are based on.

Blah blah blah… extraordinary claims, extraordinary evidence etc. When T. sebesensis was published it raised the collective eyebrows of pterosaur workers for all the wrong reasons. ODA-28 has no obvious ties to Thalassodromidae (or Thalassodrominae, if that’s how you roll - see Witton 2009), Pterosauria, or even to a cranial crest. Today, I and 19(!) other authors have said this in print (Dyke et al. 2014), noting that ODA-28 lacks any pterosaurian synapomorphies or even features typical of the group. As anyone who has handled pterosaur fossils can attest, pterosaur remains are distinctive at gross and microscopic level, and ODA-28 lacks any features expected in pterosaur bone (e.g. extremely thin bone walls separated by trabeculae). Any resemblance to the Thalassodromeus sethi holotype is entirely superficial, and shared characters between the two specimens - notably the ‘fossae’ at the base of the ‘T. sebesensis’ crest - are really incomparable on detailed examination. A clear lack of symmetry in ODA-28 shows it is not a medial skeletal element either, and thus not the cranial crest of anything. In short, cancel the text-book revisions: the temporal and palaeobiogeographical anomaly of ‘Thalassodromeus sebesensis’ is just a fairly major misidentification of a scrappy fossil (Dyke et al. 2014).

The 'flying turtle': the holotype of 'T. sebesensis' compared with the plastron of the turtle Kallokibotion. A, NHMUK R4930, the lectotype plastron of Kallokibotion magnificum with the portion corresponding to ODA-28 outlined in black (photo supplied by S. Chapman, Natural History Museum, London); B) ODA-28 (modified from Grellet-Tinner and Codrea, 2014). Abbreviations: hypo, hypoplastron; hxc, hypoplastron-xiphiplastron suture; ihc, intra-hypoplastral suture; ib, inguinal buttress; ps, pubic scar; meso, mesoplastron; mhc, meso-hypoplastral contact; pll, posterolateral lip; xiphi, xiphiplastron. Scale bar for A equals 50 mm. From Dyke et al. (2014).

Is ODA-28 anything exciting at all? Well, not especially. The specimen is clearly a piece of turtle plastron, exactly matching the internal structure of the hypoplastron and xiphiplastron of the Maastrichtian, Romanian genus Kallokibotion (above, Dyke et al. 2014). The anatomy of Kallokibotion has been documented fairly thoroughly and known for about 100 years (e.g. Gaffney and Maylan 1992), allowing us to be confident in this identification. Ergo, 'T. sebesensis’ offers nothing other than new a piece of fossil turtle and a name for the Kallokibotion synonymy list.

In all, a bit of an anticlimax. How did our short paper end up with 20 authors? The response was started by experts in the terrestrial faunas of upper Cretaceous Romania, who asked me and the Natural History Museum’s Lorna Steel if we could contribute a few paragraphs targeting the flawed pterosaur identity of the specimen. While we were working, it emerged that pterosaur experts from Brazil were also planning a response. The editors of Gondwanan Research, who published Grellet-Tinner and Codrea (2014), understandably only wanted one response, so the two teams joined forces. By the time experts in turtles, Romanian fossils and pterosaurs were all on board, we ended up with a truly international background: the USA, UK, Brazil, Romania and France are all represented.

A final note: this is not the first time thalassodromids have been pulled to the top of the Cretaceous. Kellner (2004) and Martill and Naish (2006) argued that a partial skull and mandible from the Maastrichtian Javelina Formation of Texas represented a thalassodromid based on perceived similarities with the thalassodromid Tupuxuara. While others have argued against this idea (the mandible and premaxillary morphology are more similar to those of azhdarchids - Lü et al. 2008; Witton 2013) - these claims have not been met with a sledgehammer response because the suggestions are not unreasonable. Sure, I don’t think the Javelina material in question is thalassodromid, but I can see why others might. ‘T. sebesensis’ has been swiftly rebutted by a crowd of experts because the underlying science is so clearly bogus that all concerned with pterosaur and Romanian palaeontology wanted it’s impact nipped in the bud. A response from Grellet-Tinner and Codrea will be published soon, so we'll see what they make of our rebuttal. To end on a high: there are exciting pterosaur remains coming out of Romania, and some of them are in the review/publication system already. Hopefully, we'll have some news on these out soon.

References

  • Dyke, G. J., Vremir, M., Brusatte, S., Bever, G., Buffetaut, E., Chapman, S., Csiki-Sava, Z, Kellner, A. W. A., Martin, E, Naish, D, Norell, M, Ősi, A, Pinheiro, F. L., Prondvai, E, Rabi, M, Rodrigues, T., Steel, L., Tong, H, Vila Nova B. C. & Witton, M. (2014). Thalassodromeus sebesensis-a new name for an old turtle. Comment on" Thalassodromeus sebesensis, an out of place and out of time Gondwanan tapejarid pterosaur", Grellet-Tinner and Codrea. Gondwana Research. IN PRESS.
  • Gaffney, E. S., & Meylan, P. A. (1992). The Transylvanian turtle, Kallokibotion, a primitive cryptodire of Cretaceous Age. American Museum novitates; no. 3040.
  • Grellet-Tinner, G., & Codrea, V. A. (2014). Thalassodromeus sebesensis, an out of place and out of time Gondwanan tapejarid pterosaur. Gondwana Research.
  • Kellner, A. W. A. (2004). New information on the Tapejaridae (Pterosauria, Pterodactyloidea) and discussion of the relationships of this clade. Ameghiniana, 41, 521-534.
  • Lü, J., Unwin, D. M., Xu, L., & Zhang, X. (2008). A new azhdarchoid pterosaur from the Lower Cretaceous of China and its implications for pterosaur phylogeny and evolution. Naturwissenschaften, 95(9), 891-897.
  • Martill, D. M., & Naish, D. (2006). Cranial crest development in the azhdarchoid pterosaur Tupuxuara, with a review of the genus and tapejarid monophyly. Palaeontology, 49(4), 925-941.
  • Witton, M. P. (2009). A new species of Tupuxuara (Thalassodromidae, Azhdarchoidea) from the Lower Cretaceous Santana Formation of Brazil, with a note on the nomenclature of Thalassodromidae. Cretaceous Research, 30(5), 1293-1300.
  • Witton, M. P. (2013). Pterosaurs: natural history, evolution, anatomy. Princeton University Press.

Friday, 25 July 2014

"Think Batman x Iron Man": how pterosaurs are inspiring the next generation of aircraft

Admit it, whatever you drive to work seems a little less adequate now.

Pterosaurophile Mike Habib was recently featured in a Scientific American article about the utility of pterosaur research. Let's face it, as cool as pterosaurs are, it can be hard to justify research into them when the world is faced with real problems like climate change, overpopulation, an enormous biodiversity crisis and Michael Bay movies. But Mike's interest in pterosaurs principally concerns biomechanics, quantifying the mechanical properties of pterosaur anatomy and seeing what it was capable of, and this sometimes allows transference of their evolutionary solutions to our own technological problems. Among other things, pterosaur biomechanics might be applied to some big projects: developing unmanned vehicles - including some which may explore other planets - and developing wind-stable fabrics. The latter may not sound very exciting, but wind-resistant fabrics are essential in all sorts of extreme activities, from exploring remote corners of the world (think tents), lightweight aircraft (parachutes, hang gliders, etc.) and extreme sports (wingsuits).

But that's small fry compared to one idea mentioned in the article. As part of an international team - including myself - pterosaurs may be launching air travel in a whole new direction. The manner in which pterosaurs took off - so called quadrupedal launch - offers a solution to a problem faced thousands of times around the globe each day: launching aircraft into the air as effectively as possible. As we all know, three lines of evidence point to pterosaurs launching quadrupedally, with most effort coming from their forelimbs. 1) animals launch using from their 'default' gait, and pterosaurs were quadrupeds; 2) pterosaur forelimbs are much more developed than their hindlimbs, whereas the opposite is true in hindlimb launchers and, 3) above a certain size, pterosaur hindlimb bones would actually fail in launch (Habib 2008, 2013; Witton and Habib 2010). These point to a powerful, quadrupdal launch mechanic which permitted even the largest, 200-250kg pterosaurs to take to the skies from a standing start, while birds - with their hindlimb launches - are seemingly capped at 70-80kg.

It's not only large birds which look enviously on pterosaurs. Most of our own aircraft require runways for takeoff. Vehicles which can take off without runways, like helicopters, are constrained to large size because of their power requirements and required wingspans. All aircraft launches require lots of fuel, and lots of space. It's unsurprising, then, that quad-launching giant pterosaurs have attracted the attention of engineers, as they clearly evolved a method of launch which is not only space and fuel-efficient, but also incredibly powerful. Practical results are undoubtedly years away, but the notion of a small, solo-pilot aircraft being capable of quad-launch and powered flight is realistic enough that we're seeking money for a project to test the waters. The concept we have in mind resembles a suit more than a plane - as Mike put it on Twitter, "think Batman x Iron Man" - alluding to concepts of the craft being controlled by a person strapped within the chassis, sort of like wearing a multi-million dollar pterosaur costume.

A visual history of pterosaur-inspired flying machines. 1, Ernst Stromer, 1913, basic glider model of Rhamphorhynchus wing membranes; 2, Hankin and Watson, 1914, a model based on their pioneering studies of Pteranodon flight (Hankin and Watson 1914); 3, Erich von Holst, 1957, a rubber band powered, wing flapping Rhamphorhynchus glider; 4, Cherrie Bramwell and George Whitfield, 1974, 7m wingspan Pteranodon glider based on their seminal 1974 paper; 5, Bramwell and Whitfield, 1984, half scale 4.5m wingspan Pteranodon made for the BBC; 6, Paul MacReady, 1984-85, 5 m span Quetzalcoatlus remote controlled, computer balanced glider (see MacCready 1985); 7, Margot Gerritsen, 2005, scaled Anhanguera with fully articulated wings built for National Geographic; 8, Matt Wilkinson, Rodger Highfield, and Vivian Bock, 2007, wind tunnel model of Anhanguera used to test Wilkinson’s hypotheses on pteroid orientation, 9, PteroFlight, our new project looking into pterosaur wing performance and its applications. Image compiled by Iain McCreary, used with permission.

What might such a thing look like? Sadly, it's not going to look like the thing at the top of this post. What you've got there is food for thought rendered by someone who's aircraft design skills boils down to watching science fiction movies, and who's engineering protocols are determined by Cool Points. It takes the idea of a 'pterosaur exoskeleton' to an extreme definition, right down to the limb proportions, wing folding and ability to walk about on all fours. Undeniably cool looking, just not very practical. But technologies and ideas taken to an extreme in this painting actually do exist. Augmentation of human frames with robotic exoskeletons is an intensive area of research and already employed to aid physically disabled people, as well as boosting the carrying strength of ground troops. Computers capable of flying deliberately unstable and responsive aircraft -manned or unmanned - are widely utilised. Large, controllable pterosaur-inspired vehicles with moving, adaptable wings have been researched for 100 years (above) and achieved flight (albeit not launch) on numerous occasions, with recent models featuring automatic computer control. The basic elements of this project - essentially a computer-supported, pterosaur-inspired lightweight flying exoskeleton - are at the far end of known technological spectra, not fantasy and hokum.

Of course, we're not going to see pterosaur-inspired suits catapulting people skywards tomorrow. Some serious research and developmental work is required before we see anything like a working concept or even - if we're honest - if it's possible at all. At this stage, however, this ultimate application of pterosaur research is not being ruled out. In other words, keep watching the skies - and check out Mike's Scientific American feature for more details.

References

  • Bramwell, C. D., & Whitfield, G. R. (1974). Biomechanics of PteranodonPhilosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 503-581.
  • Habib, M. B. (2008). Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana, 159-166.
  • Habib, M. (2013). Constraining the air giants: limits on size in flying animals as an example of constraint-based biomechanical theories of form. Biological Theory8(3), 245-252.
  • Hankin, E. H., & Watson, D. M. S. (1914). On the flight of pterodactyls. Aeronautical journal, 324-335.
  • MacCready Jr, P. B. (1985). The great pterodactyl project. Engineering and Science49(2), 18-24.
  • Witton, M. P., & Habib, M. B. (2010). On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness. PloS one5(11), e13982.