Pterosaur books to know and love, part 3: Pterosaur Trouble

Pterosaur Trouble cover image, by D. Loxton and Jim W. W. Smith, courtesy of Kids Can Press.

What's this? A review of a children's story book on Pterosaur.Net? Isn't this site about pterosaur science, with specimen numbers, refutable hypotheses and that sort of thing? Relax, dear reader: this review is about pterosaur science, and specifically how it can be presented well to even very young audiences without dumbing down, compromising illustration quality or making up nonsensical stories about the past.

Pterosaur Trouble, penned and illustrated by Daniel Loxton, with some illustrative assistance from Jim W. W. Smith, is a recently published work of 'palaeofiction' aimed at 4-7 year olds. It's the second in the Kids Can Press 'Tales of Prehistoric Life' series, following the 2011 Ankylosaur Attack. The short story sees a 10 m span Quetzalcoatlus halting its long journey across Late Cretaceous Canada in search of food, but runs into a vicious pack of Saurornitholestes instead. Along the way, we see various other fauna expected in a story set in the latest Cretaceous North America, including a couple of tyrannosaurs and a herd of Triceratops. As may be expected for a book aimed squarely at young children, the pages are kept largely free of text and only a single page, a final 'information page' on Quetzalcoatlus and Saurornitholestes, has a significant amount of text. The story is thus mostly told through its illustrations, which is what we'll focus on first.

Pterosaur Trouble spread, featuring Quetzalcoatlus and some noisy dinosaurs, by D. Loxton and Jim W. W. Smith, courtesy of Kids Can Press.

Virtual reality
The illustrations of Pterosaur Trouble are entirely rendered through CG animal models composited into photographed backgrounds (Loxton speaks at length about his illustration process in an interview over at the CSI blog). This sort of illustration has become commonplace in children's books on prehistoric life, and, it must be said, has generated some pretty awful bits of art. Sadly, there's probably more bad bits of CG palaeoart around than good ones, and this may create low expectations for Pterosaur Trouble's illustrations. Happily, Pterosaur Trouble dodges the problems of  obviously photoshopped backgrounds and plastic-looking, poorly composited creatures to create images which look pretty convincing (as you can see for yourself with the spreads throughout this blog). I'm not sure that they're 100% photorealistic, which is clearly the effect being sought, but they're pretty durned near. And not in that creepy, Polar Express sort of way, either. I think my 7 year old self would be pretty convinced that I was looking at some photographs. Special mention should go to the little details embedded into some scenes. Feathers float through the air from attacking Saurornitholestes, water splashes reveal the trajectories of the animals making them and reflections are seen in still water.

A chief issue with many pieces of CG palaeoart is inaccurate portrayal of the animals themselves. Pterosaur Trouble largely avoids this problem too, suggesting the mind of Darren Naish, who's listed as the scientific consultant for the book, has been put to good use. The animals look, more or less, pretty good and can be identified as the species they're meant to represent. The basic proportions and appearances of the animals are fairly close to the mark, and I get the feeling that real effort was made to render animals which would satisfy fully fledged palaeontologists as much as children. Again, there are lots of little details to appreciate. The Quetzalcoatlus beak has a chipped and rough appearance reminiscent of the beak of a marabou stork, the back of its neck has relatively long pycnofibres (as indicated by some specimens of Pterodactylus - see Frey and Martill 1998) and the primary feathers of the Sauronitholestes forelimb seem to attach to digit II (on correctly orientated hands, no less). The poses of the animals are also well chosen. There's a much appreciated deficit of roaring and hyperdynamic postures, and the points of view are sensibly placed so that we can clearly see the action, but the animals never look strange and distorted.

Pterosaur Trouble spread, showing Quetzalcoatlus in some Top Gun valley action, by D. Loxton and Jim W. W. Smith, courtesy of Kids Can Press.

As may be expected, I do have a few niggles. The faces and anterior neck regions of the star animals are devoid of fluff, a trope which I wish would politely clear off. Well known fossils of both dromaeosaurs and pterosaurs show that their necks and faces bore filamentous integuments, and we should reflect this in our reconstructions (Sharov 1971; Xu et al. 1999). The Saurornitholestes forelimbs could do with some more feather groups, and both star animals show some slight shrink wrapping on their heads. The uropatagium of the pterosaur attaches to the tail, which has never been found in any pterosaur specimen despite its prevalence in artistic reconstructions, and eye of the Quetzalcoatlus is set way too high in the skull (see my Quetzalcoatlus sp. skull reconstruction, below). Perhaps most glaringly, the wing finger of the pterosaur does not fold up against the body when the animal is grounded. These, and a few other nitpicks didn't really irk me that much however, probably because the overall illustration quality is pretty good and I enjoyed the other components of the book.

Skull reconstruction of Quetzalcoatlus sp., based on Kellner and Langston (1996). Note the ventrally displaced orbit, well below the top half of the skull. From Witton (2013).

Text me
The images of Pterosaur Trouble are embellished with short passages of text on each page which provide details on the accompanying image. The text scores highly for avoiding anthropomorphising its animals too much, a major pitfall of much 'palaeofiction' . Instead, we have the actions of the animals being described more than their emotional states, often with neat bits of information sneaked into the same sentences. For instance, Quetzalocatlus is described as 'a giraffe-sized giant landing as a gently as a dragonfly' at one point. In one sentence we're given a sense of the size, mass and flight capabilities of this animal, and all in concise and evocative language that a 4 year-old could understand. The text is pretty on the ball scientifically, too. Pycnofibres, pterosaur 'fuzz', are described as 'hairlike fibers' rather than feathers or fur. The azhdarchid is said to eat 'anything that walked or slithered', which sounds like a reference to the terrestrial stalking hypothesis of Witton and Naish (2008) to me, and the animal vocalisations are the clicks, coos and chatters of an avian-like syrinx rather than the snarls, roars and bellows of a mammalian larynx. Given that many children's books on prehistoric life simply rehash information from other, sometimes much older children's books on the same topic, or else make mistaken claims that simply aren't true, it's refreshing to see Pterosaur Trouble presenting these new ideas to young audiences.

Pterosaur Trouble spread, showing Quetzalcoatlus apparently approaching Isla Nublar, by D. Loxton and Jim W. W. Smith, courtesy of Kids Can Press.

The story itself has one foot in the science camp, too. The overall premise was inspired by a Saurornitholestes tooth left in a large azhdarchid tibiotarsus, an indication that this dinosaur once ingested pterosaur meat (Currie and Jacobsen 1995). Whether the dromaeosaur actually attacked and killed the azhdarchid in that case is debatable, and I do agree with Currie and Jacobsen (1995) that the body size difference between the dinosaur and pterosaur suggests scavenging activities rather than predation. However, we're all aware that remarkable and unexpected feats of predation can occur in modern animals, such as lions attacking fully grown elephants and adult giraffes, so we can't rule out the occurrence of similar events in the Mesozoic. Happily, Pterosaur Trouble acknowledges this ambiguity on its final page along with a host of other factoids on its star animals. (Anyone interested in the logistics of dromaeosaur predation on pterosaurs should check out this post and its comments at Dave Hone's Archosaur Musings, which go into some detail on these issues.)

I couldn't feel like I've reviewed this book fairly without mentioning one particular part of its story, which may serve as an excellent case study as for how well put together this little book is. At one pivotal moment, the Quetzalcoatlus has to escape its dinosaur attackers, leading to it quad launching into the air while carrying a couple of dinosaurs. How cool is that? This one moment in the story, and its accompanying spread, is an awesome hat-trick of splendidness. Firstly, it reaffirms that Loxton has really been paying attention to the cutting edge of pterosaur research. Pterosaur quad launch is still a fairly fresh idea that, as a fully fledged hypothesis, was proposed as recently as 2008 (Habib 2008). Secondly, it features a simply terrific (and convincing) reconstruction of an azhdarchid mid-launch (below), with dromaeosaurs being cast from the launching pterosaur like feathery rodeo cowboys. Thirdly, it completely disregards the idea of pterosaur as weak, flimsy fliers, showing its star animal breaking free of its attackers and taking off despite being weighed down with unintended passengers. This is yet another nod to new research which indicates that giant azhdarchid humeri were extremely strong, and capable of launching animals far in excess of their estimated body weights (Witton and Habib 2010). As someone with a direct hand in this research, it's great to see these ideas being picked up here. Finally, the fact that a children's book is featuring quad launch makes me feel very warm inside, as a generation of people can now grow up with quad-launch in mind whenever they think of pterosaur takeoff. Wait, that's four things, which is one more than a hat-trick, right? Whatever: I don't do football.

Pterosaur Trouble spread, showing Quetzalcoatlus quad launching into awesomeness while shaking off some feathery vermin. Image by D. Loxton and Jim W. W. Smith, provided by M. Cornell

So, in sum...
While I can't claim any great expertise in children's books on prehistory, I've seen enough attempts to bring extinct species to popular audiences to know that I often find more things to dislike than praise. Because it uses up to date science, high quality illustrations and some clever text, Pterosaur Trouble is a fantastic little book that should greatly please and educate any little pterosaurologists you may know. I'll go so far as to say that Pterosaur Trouble is a terrific example of how to make a popular book on prehistoric animals both exciting and scientifically sound, an accolade that is all the more remarkable when you consider that a part of its targeted demographic is still learning to read. As a final recommendation, I could see myself reading a copy of this to my own kids, should I ever have them, without any muttering or wry comments. And if it can please a bitter old thing like me, then it must be doing something right.

If you're after a copy of Pterosaur Trouble, check out the Kids Can Press website, or log onto Amazon. The first book in the series, Ankylosaur Attack, is being published again by Franklin Watts in August, 2013 under ISBN: 9781445119427.

References

• Currie, P. J. and Jacobsen, A. R. 1995. An azhdarchid pterosaur eaten by a velociraptorine theropod. Canadian Journal of Earth Sciences, 32, 922-925.
• Frey, E. and Martill, D. M. 1998. Soft tissue preservation in a specimen of Pterodactylus kochi (Wagner) from the Upper Jurassic of Germany. Neuhes Jahrbuch für Geologie und Paläontologie, Abhandlugen, 210, 421-441.
• Habib, M.B. 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana, B28, 161-168.
• Kellner, A. W. A. and Langston, W. Jr. 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from Late Cretaceous sediments of Big Bend National Park. Journal of Vertebrate Paleontology, 16, 222-231.
• Sharov, A. G. 1971. [New flying Mesozoic reptiles from Kazahstan and Kirgizija]. Transactions of the Paleontological Institute, Academy of Sciences, USSR, 130, 104-113. [In Russian]
• Witton, M. P. 2013. Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press, 336 pp. In press.
• Witton, M. P. and Habib, M. B. 2010. On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness. PLoS ONE, 5, e13982.
• Witton, M. P. and Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE, 3, e2271.
• Xu, X., Wang, X. L., and Wu, X. C. 1999. A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China. Nature, 401, 262-266.

Can you identify this cast?

Some of you may know that I've been trying to track down all manner of 'missing' Solnhofen pterosaurs. All kinds of specimens have been sold off over the years and are in collections all over the world. Many of these are 'known' to curators and visitors, but they don't realise that the material has never been described in the literature and is not readily known to the scientific (or at least pterosaur) community. If any of you do know of pterosaurs languishing in collections that have not been described, do please let me know in the comments.

The flip-side of this, is that things turn up that need to be identified. The other day Matthew Parkes, a curator in Dublin, e-mailed with with this photo. It's a plaster cast of a pterodactyloid pterosaur from the Solnhofen and labeled as being Pterodactylus longicollum (which has only just got a new generic name of Ardeadactylus). This seemes reasonable, the unusually long and tube-like cervical centra of this taxon are visible at the upper left part of this cast and the size and gross proportions are about right (even if few details are visible). However, Matthew wanted to know what original specimen this could be a cast *of* and that's where I'm stuck. I've seen most Ardedactylus specimens and don't recognise it, and I've checked through my extensive collection of photos and papers of all manner of Solnhofen material and can't find a match.

The records in Dublin show that it has been in their catalogue since 1891, so it's at least this old and probably rather older. The catalogue suggest it may be figured as a plate in von Meyer's 1854 Neues Jarbuch paper, but I don't have, and can't find, a copy. Matthew suspects it may be a lost specimen and in which case, this may be the only remainder. Of course if we can work out which it pertains to, we can check at the original institute, but the first step eludes us. So, anyone recognise it? Has it been spotted in Frankfurt or Haarlem? Or is there a figure in some obscure Wellnhofer paper I've missed?

Any help is welcome, and I'm still on the lookout for other Solnhofen pterosaurs, so please let me know of any you've spotted. Thanks and good hunting.

 

A new Romanian azhdarchid in PLOS ONE

Posted on behalf of Darren:

A new azhdarchid pterosaur – a member of that highly distinctive, long-necked, long-skulled Cretaceous clade most famous for the gigantic Quetzalcoatlus northropi – has just been described by Mátyás Vremir (Transylvanian Museum Society at Cluj-Napoca), Alex Kellner (Museu Nacional in Rio de Janeiro), Darren Naish and Gareth Dyke (both of the University of Southampton). The new animal is from the Upper Cretaceous Sebeş Formation of the Transylvanian Basin in Romania and is named Eurazhdarcho langendorfensis (Vremir et al. 2013). Based on a partial neck and partial right wing found in close association (and hence definitely coming from the same individual), it can be recognised as a new species thanks to various details of its cervical vertebrae.

Speculative reconstruction of Eurazhdarcho langendorfensis 

(in quad launching pose), by Mark Witton.

 Scale bar = 500 mm. From Vremir et al. (2013).

Eurazhdarcho was a small azhdarchid, with an estimated wingspan of about 3 m. As discussed in the paper – and also at theTetrapod Zoology article on the new species – Eurazhdarcho is yet another azhdarchid discovered in a terrestrial, continental sort of environment: it provides more support for the view of azhdarchid behaviour and ecology that Mark Witton and I put forward in 2008 (Witton & Naish 2008). What’s also interesting is that Eurazhdarcho seemingly lived alongside a gigantic species (probably Hatzegopteryx thambema) that would have had a wingspan of 10-11 m. What does this mean for azhdarchid ecology? Does it show that different azhdarchid species were sharing habitats and occupying distinct ecological niches? These issues and more are covered at Tetrapod Zoology and also in the paper. The paper is in PLOS ONE so is freely available to anyone (linked below).

Some geological units reveal evidence of two or even three sympatric azhdarchid species. Diagram produced by Mark Witton and map used with kind permission of Ron Blakey, Colorado Plateau Geosystems, Inc; from Vremir et al. (2013).

Vremir, M.,Kellner, A. W. A., Naish. D. & Dyke, G. J. 2013. A newazhdarchid pterosaur from the Late Cretaceous of the Transylvanian Basin,Romania: implications for azhdarchid diversity and distribution. PLoSONE 8(1): e54268. doi:10.1371/journal.pone.0054268

Witton, M. P. & Naish, D. 2008. A reappraisal ofazhdarchid pterosaur functional morphology and paleoecology. PLoS ONE 3(5): e2271. doi:10.1371/journal.pone.0002271

2012 Reach roundup for Pterosaur.net

Well we're well into 2013 now, so time to do a quick summary of the team's contribution to pterosaur research over the last 12 months or so. As usual, there's a good selection of material here covering new species and finds, reviews and summaries, ecology and behaviour and evolutionary studies. I maintain its important in the light of, shall we say, 'competing' sites on pterosaurs, that we show our activity in the scientific literature and the fact that we present our work publicly and put it through peer review (and those who work on pterosaurs will be well aware just how brutal this field in particular can be when it comes to reviews).

As this is a general sort of update post, I thought I'd put up a reminder that the 2013 Flugsaurier meeting in Rio has extended the deadline till the 31st of Jan, so you still have another week to get in your abstracts.On a very different note, I'm appealing for funds to support research into tyrannosaurs (not very pterosaur-y, but very outreach related) so if you can spare a few bucks or just have the time to tweet and blog this, please spread the word.

..............................

Habib M. in press. Constraining the Air Giants: Limits on size in flying animals as an example of constraint-based biomechanical theories of form. Biological Theory: Special Volume (X): XXX-XXX

Habib M. 2012. Mesozoic speed demons: flight performance of anurognathid pterosaurs
2012. ASB Annual Meeting, Gainesville

Hone, D.W.E. 2012. A new specimen of the pterosaur Rhamphorhynchus. Historical Biology, 24: 581-585. (This has been online since 2010 but is only now in print).

Hone, D.W.E. 2012. Pterosaur research: recent advances and a future revolution. Acta Geologica Sinica, 86: 1366-1376.

Hone, D.W.E., Naish, D. & Cuthill, I.C. 2012. Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia, 45: 139-156.

Hone, D.W.E., Tischlinger, H., Frey, E. & Röper, M. 2012. A new non-pterodactyloid pterosaur from the Late Jurassic of Southern Germany. PLoS ONE, 7: e39312, 18p.

Hone, D.W.E., Tsuhiji, T., Watabe, M. & Tsogbataar, K. 2012. Pterosaurs as a food source for small dromaeosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology, 331: 27-30.

Hyder, E., Witton, M. P. and Martill, D. M. 2012. Evolution of the pterosaur pelvis. Acta Palaeontologica Polonica. [in press]

Naish, D., Simpson, M., & Dyke, G.J. 2012. A small-bodied azhdarchoid pterosaur from the Isle of Wight (UK): its implications for pterosaur phylogeny, anatomy, diversity and distribution. SVPCA (Oxford).

Knell, R., Naish, D., Tompkins, J.L. & Hone, D.W.E. 2012. Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution, in press. (Not directly pterosaurian, but they do get a big mention and it includes an illustration by Mark too).

Lü, J-C. & Hone, D.W.E. 2012. A new Chinese anurognathid pterosaur and the evolution of pterosaurian tail lengths. Acta Geologica Sinica, 86: 1317-1325.

Martill, D. M., Sweetman, S. and Witton, M. P. 2012. Pterosaurs of the Wealden. Palaeontological Association Field Guide to Wealden fossils.

Steel, L. 2012. The pterosaur collections at the Natural History Museum, London, UK: an overview and list of specimens, with description of recent curatorial developments. Acta Geologica Sinica, 86: 1340-1355.

Witton, M. P. 2012. New insights into the skull of Istiodactylus latidens (Ornithocheiroidea, Pterodactyloidea). PLoS ONE, 7, e33170.

Guest Post. Dragon Tails: What Pterosaurs Teach Us about Velociraptor

As part of the flurry of new papers in the Flugsaurier 2012 paper pseudo-volume, Scott Persons has a paper out looking at the remarkable convergences between various dromaeosaurs and a number of rhamphorhynchoid pterosaurs. Here in a guest piece he takes us over this project. - Dave.

An Unexpected Tail

Last week, like a growing 149 million dollars’ worth of other holiday movie goers, I took three hours out of my yuletide respite to make an epic trek across sidewalks long and public transportation foul to my local cinema and saw “The Hobbit: An Unexpected Journey”. I was particularly keen to see how the special effects wizards of Weta Workshop would depict the story’s big bad: Smaug, the dragon. Naturally, since The Hobbit has been broken up into a trilogy, Peter Jackson decided not to fully unveil Smaug, and I’ll have to wait until the sequel. But there was a surprise appearance by a Megaloceros (the “broad antlered” or “Irish Elk”), and Jackson did give the audience a dragon teaser. We got to see a smoke-obscured silhouette here, a clawed foot there, and . . . the tail. 

I’m a PhD student of paleontology at the University of Alberta and, with the help of my supervisor Dr. Phil Currie, I’ve dissected, excavated, measured, photographed, and digitally sculpted the tails of many creatures, ancient and modern. To me, Smaug has an interesting tail. Unlike a crocodile or a dragon from the isle of Komodo, he did not drag his tail behind him. Rather, the Tolkienian drake carried it raised above the ground -- a caudal posture that I suspect shows the influence of dinosaur paleontology on the animators. The tail was very flexible and muscular enough to casually toss aside a group of armored castle-defenders and to do collateral damage to the medieval architecture.

Swooping out of the sky, Smaug’s fiery breath and wrecking-ball tail deal a one-two punch to a stone tower.

That brings me to a fun, blatantly whimsical, and entirely inconsequential thought problem: if the monsters of Middle-earth were not spontaneously generated from Uruk-hai pits and human imaginations, but instead were products of biological evolution, what sort of tail would a dragon most likely have? It’s a silly question, but at least twice in the history of our own planet, reptilian beasts have taken on dragon-like form, and both times their tails have followed remarkably convergent evolutionary paths.

Tail of a Revolution

It can be argued that, of all the dinosaurs ever dug, none have been more scientifically important than Deinonychus. Deinonychus is a kind of dromaeosaurid (meaning that it belongs to a group of carnivorous dinosaurs commonly known, because the group includes the iconic Velociraptor, as “raptors”).  The 1969 study of Deinonychus by Professor John Ostrom documented a wealth of anatomical features previously unseen, or at least unrecognized, in any other dinosaur. Many of these features seemed to imply a high metabolic rate, an active lifestyle, and an ancestral relationship with modern birds. Deinonychus was the catalyst that began the “dinosaur renaissance” or “dinosaur revolution” (a paleontological paradigm shift that has affected how we think about, and approach learning about, a great deal more of prehistory than just dinosaurs -- including pterosaurs). Among the unusual anatomy of Deinonychus was its tail.

The skeleton of a tail is an extension of the spinal column and, in a dinosaur, the tail skeleton is composed of three major kinds of bones. First and foremost, are the interlocking vertebrae, which protect the spinal nerves and sport upwards-projecting neural spines, to which epaxial muscles attach. Then, there are the caudal ribs (or simply “transverse processes” – there is controversy over the proper terminology), which fuse to the vertebrae and project outwards (perpendicular to the long axis of the tail) and also provided anchorage for tail muscles. Last, but certainly not least, are the chevrons. Despite the fact, or perhaps a little bit because of the fact, that these tail bones have received little descriptive or collecting priority from other researchers, I positively love chevrons. They are elegantly shaped, usually resembling capital Y’s, are important for tail muscle function, and (contrary to historic assumption) are useful in identifying taxonomic and evolutionary relationships.  In the tails of both dinosaurs and pterosaurs, chevrons are positioned in between sequential pairs of vertebrae and project downwards.

The basic parts of the tail skeleton shown on a duckbilled dinosaur.

At the start, the tail skeleton of Deinonychus appears normal. Just past the hips, the neural spines, caudal ribs, and chevrons all have a typical shape and they all project to a respectable extent. But, as the tail progresses towards the tip (and it doesn’t take long) things start to get weird. The neural spines, caudal ribs, and chevrons all shrink in, with the former two disappearing entirely . . . and then come the caudal rods. Both the vertebrae and chevrons abruptly develop pairs of elongated rods of bone that project towards the hips. These rods are slender, but very long (the longest easily overlap seven other sequential vertebrae), and they split, each becoming two still thinner rods. Together, rods of the vertebrae form a quiver that virtually encapsulates the dorsal (upper) portion of the tail, and together the rods of the chevrons do the same to the ventral (lower) portion.

Raptor tails are strange! Elongated vertebral rods form an upper quiver and elongated chevron rods form a lower quiver. Skeletal image of Velociraptor courtesy of Scott Hartman (www.skeletaldrawing.com

  Professor Ostrom was rightfully impressed by the caudal rods of Deinonychus, and he realized that such unusual structures must have evolved to serve some sort of unusual function. Ostrom’s best specimens of Deinonychus were preserved lying on their sides and their tails were straight as boards. Ostrom was also much taken with what he thought was the overall highly-athletic nature of the hindlimbs of Deinonychus, so he speculated that the caudal rods were adapted to aid in high-speed pursuit. His idea was that the rods must have stiffened the tail and allowed it to function like the balancing pole of a tightrope walker. This balancing tail, he reasoned, would have come in handy when turning while running or when leaping onto the back of some poor dinosaurian herbivore.

Enter the Sky Dragons

The tail of Deinonychus and its raptor relatives is bizarre, but it is not (as Professor Ostrom himself realized) unique. Among all known vertebrates, a similar tail anatomy has evolved in one other group. . . and now we come to why I have been allowed to spend so much time discussing dinosaurs on what is supposed to be a blog about pterosaurs.

While later and more advanced pterosaurs (like Pterodactylus) only had short, stubby tails, early pterosaurs had long ones. The caudal skeletons of these long-tailed pterosaurs (with the exceptions of the dimorphodontids and very primitive forms) are strikingly similar to that of Deinonychus. In the case of long-tailed pterosaurs, the function of the caudal rods has always seemed obvious. As flying animals, increased rigidity would have helped a tail to serve as a stabilizer or as a rudder.

Look familiar?  The tails of pterosaurs and dromaeosaurids are so similar that, in the fossil-forging black-markets of China, the tail of one is often used to “complete” a partial skeleton of the other. Skeletal image of Rhamphorhynchus courtesy of Scott Hartman (www.skeletaldrawing.com).

In Professor Ostrum’s description of Deinonychus, he expressed his interest in considering this striking example of convergent evolution in a later study. Regrettably, however, he never got around to it -- after all, he soon had a revolution on his hands.

Fleshing Out the Evidence

            A lot has changed since the dinosaur renaissance. For instance, we now know that caudal rods are characteristics of all dromaeosaurids (except the South American unenlagiine dromaeosaurids, which are odd-ducks in many regards). We know a lot more about the evolutionary history of caudal rods, in both dromaeosaurids and pterosaurs. We also know that the rods were not as stiff as Ostrom had thought. Consider the below images of a tail of a Bambiraptor and of a Velociraptor. Both are dromaeosaurids with caudal-rod bearing tails and both are fully articulated. Yet, both are preserved in a sinuous curve (or in the case of the Velociraptor, many sinuous curves).

The strongly curved tail of Bambiraptor.

Despite its caudal rods, this Velociraptor tail is preserved in a graceful S-shaped curve.

So, it turns out that caudal rods are flexible (not surprising when you think about how thin each rod was). But, if caudal rods permitted their tails to curve to such a degree, what good were they? Well, I suspect that the rods were very helpful in keeping the tails rigid. No, I am not talking in circles, and I don’t think that I am talking nonsense. The rigidity provided by the rods of dromaeosaurids was one-dimensional. I have been able to see a lot of dromaeosaurid tail fossils, and many specimens, like the two above, are curved laterally, but I have never seen one that shows articulated caudal rods bending strongly dorsoventrally (that is, up or down).

            That caudal rods provide mostly dorsoventral rigidity makes sense, if you consider the way the rods are arranged in their quivers. The rods are not haphazardly piled on top of one another; rather, they are tightly pressed against the vertebrae and chevrons and are neatly stacked vertically. In other words, the quivers were arranged to be thicker dorsoventrally than they were laterally.

Cross-section through the tail of Deinonychus showing the arrangement of the caudal rods. The arrangement of the rods made the tail harder to bend up-and-down than side-to-side.

A cylindrical tight-rope walker’s pole is the wrong analogue. Instead think of a meter stick, which may be bent with moderate force, but only perpendicular to its broadest plane.

It is now also possible to think a step further and consider the muscles of the tail. Let’s first try to do that in very general qualitative terms. Remember the quickly reduced neural spines, caudal ribs, and chevrons? Those all indicate that the caudal muscles of both dromaeosaurids and pterosaurs were substantially reduced.

To help consider the problem quantitatively, a technique I used was to create digital models of the tail skeleton of a Velociraptor and a Rhamphorhynchus (a pterosaur) and to sculpt the corresponding muscles over the skeletal models. The results of this modeling concur with the qualitative inference. In particular, raptors and pterosaurs were found to have very weak caudofemoral muscles (indeed, some pterosaurs may not have had caudofemoral muscles at all).

Digital reconstructions of the tail of Velociraptor, showing the tail and hip skeleton (A), the caudofemoral muscles (B), and the full muscle reconstruction (C).

Digital reconstructions of the tail of Rhamphorhynchus, showing the tail and hip skeleton (A), the caudofemoral muscles (B), and the full muscle reconstruction (C)

 These caudofemoral muscles merit special explanation. They are muscles found in the tails of reptiles and dinosaurs that are actually part of the hind limb system. They are the primary limb retractors and provide a major power boost when walking and running.

Again, these adaptations seem easy to explain in the tail of pterosaurs. If a tail is to serve as an inflight rudder, some lateral flexibility would be needed, but strong dorsoventral stiffness would have prevented the constant pull of gravity from deflecting the tail downwards and disrupting the body’s aerodynamic form, and all the better if this stiffness was obtained by the passive rigidity of bone, rather than the hard work of muscle. Reducing weight is always a benefit for flight, and, perhaps, particularly reducing posterior weight. What better posterior weight could a flying animal lose than that of a tail muscle whose primary function is in land-bound locomotion?

Thanks in large part to the work of pterosaur researcher Dr. Dalla Vecchia, we know that among the most primitive of pterosaurs (animals like Austriadactylus and Eudimorphodon) caudal rods had not yet evolved (though there are some anatomical signs that they were in the works). However, all these primitive forms already had clear possession of the power of flight. We can be certain (or about as certain as the fossil record ever permits) that, when the caudal rods of pterosaurs evolved, it was in the context of an aerial lifestyle.

To me the remarkable similarity in form between the tail skeletons and muscles of pterosaurs and dromaeosaurids indicates an equally strong similarity in function.  Is it possible then, that the tails of dromaeosaurids also evolved on the wing?

Feathered Dragons from the Orient

The little dromaeosaurid Microraptor has sparked something of its own dinosaur revolution. Microraptor is among the oldest and most primitive of the known dromaeosaurids. Buried in fine volcanic ash, specimens from the famous fossil beds of China have revealed that Microraptor had feathered wings on the fore and (oddly enough) on the hind limbs. It also had caudal rods. Whether or not Microraptor could truly fly or simply glide is a matter of current scientific debate, but the winged-raptor was clearly not a land-bound creature.

Microraptor has wings and caudal rods.

An older Chinese dinosaur, Anchiornis is a primitive member of the Deinonychosauria. Named in honor of Deinonychus, the group Deinonychosauria includes the dromaeosaurid and their close relatives the troodontids. Like Microraptor, Anchiornis had wings, but it lacked caudal rods. Thus, as with pterosaurs, it appears possible to bracket the evolution of the bizarre dromaeosaurid tail between two aerial genera.

Anchiornis has wings but not caudal rods.

Does all this mean that the tails of Deinonychus and Velociraptor indicate that these dinosaurs could fly? Certainty not. However, I do think it means that we should think of Deinonychus, Velociraptor, and other dromaeosaurids like Cretaceous ostriches. They are animals without the ability to fly or glide but who have inherited a few telltale anatomical feature that attest to their ancestor’s aerial life. (I am certainty not the first person to suggest this. Based on various other lines of anatomical evidence, many paleontologist, most prominently Greg Paul, have argued that dromaeosaurids were secondarily flightless.)

I also think it means that, when you imagine a flying dragon, be it a dinosaur, pterosaur, or thought problem fantasy, you should not envision it with a tail that limply streams behind it. The tail should be, most probably, held up; be capable of lateral, but not vertical, swishes; be muscularly reduced and light weight; be quite elegant and graceful; and, thus, not (I am afraid, Mr. Jackson) be of much use as a siege weapon.

Papers via blogposts

Those keeping up with the pterosaurian literature will be aware that the latest issue of Acta Geologica Sinica has a set of papers resulting (at least in part) from the 2010 Beijing Flugsaurier meeting. (And while we’re on the subject, the 2013 meeting in Rio has extended abstract submissions till the 31^st of January, so there’s still time to get them in). I’ve got a couple in there and while people might be more interested in the horribly flattened anuroganthid, I’m more keen to talk about the short review paper I produced.

The title, ‘Pterosaur Research: Recent Advances and a Future Revolution’, might sound familiar and indeed some of the content may too. That’s because it ultimately sprung out of a post that I had over on the Musings and also put up on Pterosaur.net. This is a first for me at least, a paper that resulted pretty much directly from a blogpost.

At the time I’d been writing about rates of discovery of dinosaurs and pterosaurs and what that might mean for future discoveries. It occurred to me that actually the pterosaurs seemed to be going through something of a renaissance in the way that dinosaurs had in the 1970s. We were finding more and more of them, more papers were being published by more researchers, and more of the big questions were either being answered, or at least were being tackled in a rather more systematic way than they had before. It occurred to me that this was worth summarising and producing something more formal. The fact that the next Flugsaurier volume was due meant there was a most suitable venue available and discussions with various colleagues helped me develop the idea and push for it’s inclusion.

If you look back at the developments of the last 10 years or so in pterosaurs, it’s quite a remarkable and rapid progression. That’s not to overlook the huge amount of groundwork that had gone before and the efforts of previous generations, but even quite a few fundamentals that had occurred for dinosaurs decades ago are now being sorted out for pterosaurs. We now have inclusive phylogenies for pterosaurs, we’ve got a good idea of their soft tissue structures and especially the wing, some of the taxonomic and systematics issues of the past are being resolved, we’ve got a major transition in the form of Darwinopterus, cool new taxa like the boreopterids and chaoyangopterids turning up, detailed analyses of flight, take-off, mass estimates, muscle patterns, and skull shapes, we finally, finally, have eggs and we’re even getting serious on behaviour and ecology for analyses of head crests, growth and the like as well as looking at major evolutionary trends like diversification and distribution. We’re even getting attention from the public and serious attention with whole exhibits on pterosaurs, new books, and documentaries, and of course we now have the Flugsaurier meetings themselves, established and (hopefully) regular events that will help keep things ticking along.

So this paper attempts to summarise all of this and in effect provide a statement of the ‘state of the art’ – what do we know and how have we got there, but it is also supposed to be a bit of a celebration of the last decade of research and the gains made by the pterosaur research community. Those in the know will probably realise that the background to this has not been without a significant amount of strife, and while this is not mentioned in the paper, I think it only emphasises how much has been learned despite this limitation. I hope it also provides a sort of counter-point, but also a continuation of Peter Wellnhofer’s piece that kicked off the 2008 Flugsauriervolume. Peter wrote a review of the history of pterosaur research, but pretty much only took it up to the modern era, and with the galloping developments of the last few years, this should bring things more or less up to date.

Hone, D.W.E. Pterosaur research: recent advances and a future revolution. Acta Geologica Sinica, 86: 1366-1376.

The paper is available here (and indeed all of the latest papers are from AGS). Just click on the left hand set of the three series of Chinese characters at the bottom of the page and then add a .pdf suffix to the filename once it’s been saved.

LACM to Boston: G+ Hangout Interview

I recently did a G+ hangout interview with Lorena Barba's bio-aerial motion class out at Boston University.  I broadcasted from the Natural History Museum of Los Angeles County, along with Justin Hall.  Here's the link on YouTube: https://www.youtube.com/watch?feature=player_embedded&v=Mt88TkOlD4g

This was our first go with the "On Air" feature, which automatically records the hangout and sends it to a personal YouTube channel.  I talked a lot about pterosaurs, as well as a bit about Microraptor.

Cheers,

--MH