I assume you’re here for the Tetrapod Zoology. If so, you’ll have been excited and intrigued by one of 2013’s best tetrapod-themed books: Mark Witton’s Pterosaurs, an enormous, lavishly illustrated encyclopedia of all things pterosaur. Scholarly but highly readable, fully referenced throughout, and featuring hundreds of excellent photos, diagrams and beautiful, colour life restorations, this volume is a must-own, whatever your interest in pterosaurs. And, let’s face it, there aren’t that many books devoted to pterosaurs to begin with, so another one on the market can only be a good thing.

Herein, please find my assorted thoughts on this most excellent book. First of all, though, some disclosure: as readers and followers will likely already know, I’m personal friends with Mark and have co-authored several studies with him. You might therefore conclude that the following review is not impartial; nevertheless, let’s see what happens. For the purposes of convention, I’m going to refer to Mark as ‘Witton’ throughout this review.

I already gave a summarised version of my general thoughts on the volume back in June 2013. Here’s the most important part of what I said: “[Pterosaurs is] written as an encyclopaedic tour through pterosaur diversity. This really is the ultimate guide to pterosaurs, providing us with a richer view of pterosaur diversity and behaviour than allowed in the two previous great volumes on the group (Wellnhofer 1991, Unwin 2005) and containing a substantial amount of review and analysis of pterosaur ecology and functional morphology”. I was surprised (but pleased) to see these words quoted on a flyer that Princeton University Press provided in the delegate package for the 2013 Society of Vertebrate Paleontology meeting. I should also say that the book is properly titled Pterosaurs: Natural History, Evolution, Anatomy. However, this title doesn't appear anywhere on the cover (or spine).

To business… Pterosaurs is a big book, featuring 26 chapters spread over more then 280 pages. Early chapters review the history of our ideas about pterosaurs, the evolutionary relationships and origin of the group, and what we know of their anatomy (bony and soft).

Pterosaur ancestry and those hypothetical proto-pterosaurs

Many issues covered here remain controversial: the consensus opinion supported by the majority of recent phylogenetic studies is that pterosaurs are crown-archosaurs, close to dinosaurs (remember, Ornithodira exists no matter where pterosaurs fall within Diapsida) (Sereno 1991, Benton 1999, Brusatte et al. 2010, Nesbitt 2011). This is the idea that Witton favours, which is fair enough since there are unpublished studies* showing that the crown-archosaur hypothesis is supported even when oddball taxa considered close to pterosaurs by some (Peters 2000) are included in the analysis too. Nevertheless, the crown-archosaur idea does look odd given that we lack taxa that appear in any way transitional between pterosaurs and other ornithodirans**… not that I’m saying that this necessarily means anything.

* I’m thinking of analyses run by Mickey Mortimer and Andrea Cau.

** Faxinalipterus minima – published in 2010 as a possible sister-taxon to the rest of Pterosauria – is not a pterosaur, nor obviously close to pterosaurs at all (Soares et al. 2013).

Witton follows the honourable tradition of inventing hypothetical proto-pterosaurs that bridge the gap between Scleromochlus-like ornithodirans and known, early pterosaurs. I’m not entirely sold on his use of the term HyPtA (meaning Hypothetical Pterosaur Ancestor) for these creatures – not exactly sexy – but his invention of the creatures themselves isn’t all that bad: invoking an anatomy and lifestyle for an ancestral organism involves the formulation of a set of hypotheses that will be supported or knocked down by future finds. And there are other proto-pterosaurs out there in the literature, just as there are proto-birds and proto-bats.

Flying, walking, climbing… and running and swimming?

Chapter 6 – ‘Flying reptiles’ – summarises current thinking on pterosaur aerodynamics and launch behaviour, one of Witton’s most interesting contentions being that pterosaurs have consistently been made too lightweight by previous authors. This has some impact on wing loading and hence flight style: as is familiar to pterosaur workers, Witton’s revised mass estimates and wing loadings make pterosaurs more comparable to the birds that they otherwise resemble in planform (Witton 2008, 2013, Witton & Naish 2008) – a satisfying picture that has been bolstered by conclusions from some other workers (but, of course, not all of them; this is pterosaur science we’re talking about).

More innovative is Chapter 7 (‘Down from the skies’), devoted to terrestrial locomotion. Witton’s pterosaurs can bound, swim, climb, and most of them walk with narrow gaits (though these generalisations do not apply across the whole of Pterosauria, of course). The pterosaurs of the prior literature have been imagined as inelegant sprawlers, slow, clumsy and lame on the ground, unable even to resist light gusts of wind (recall how the terrestrial locomotion depicted for the Walking With Dinosaurs ornithocheirids was based on shuffling people, using brooms as crutches) (Wellnhofer 1988, Unwin 1988, 1997, 2005).

In fact, data from trackways, pelvic and limb morphology, limb bone thickness and bending strength (Fastnacht 2005), and inferred hindlimb and forelimb posture (Fujiwara & Hutchinson 2012) indicates very strongly that pterodactyloid pterosaurs at least were far more proficient on the ground than people have previously given them credit for. Witton weaves all these lines of evidence together in a compelling narrative and can be said to be leading a revolution on the terrestrial abilities of pterosaurs. I agree with him: it now seems that pterodactyloids were proficient and agile on the ground, though non-pterodactyloids likely were not.

Readers may also be surprised to see several Witton illustrations that show pterosaurs swimming and even diving. Some trackways seemingly show that some pterosaurs foraged in shallow water, their bodies afloat and their long forelimbs being used as punting tools. Given the aquatic habits of many pterosaur species, it’s hard to believe that they were incapable of at least some aquatic behaviour: despite claims made here and there about pterosaurs being too pneumatic to swim or dive, or with a wing form or body shape that would prevent swimming or diving, there are no obvious or compelling reasons disallowing such behaviour, and Witton proposes that taxa like Pteranodon might routinely have floated and dived.

Yes, there are frigatebirds (which can swim, if they really have to, but generally avoid doing so*), but hardly any pterosaurs are as specialised for a dedicated aerial existence as they are (nyctosaurids are the probable exception). Recently, Hone & Henderson (2013) used digitally simulated floating models to test the floating abilities of pterosaurs. It’s a brilliant and fun thing to do – did I ever mention that it’s been done before for giraffes? (Henderson & Naish 2010). Ha ha, I kid, I kid. Anyway, Hone & Henderson (2013) concluded that pterosaurs were pretty much incapable of floating or swimming. I'm sceptical of their conclusions, but it's good to see some actual science being applied to this interesting issue.

* They bathe by dunking themselves after swooping at the water from height and take off as soon as possible by frantic fluttering.

Chapter 8 – ‘The private lives of pterosaurs’ – reviews several areas that will be unfamiliar to the majority of non-specialists: what do we know about pterosaur prey items, pathologies, parasites, sex lives and growth strategies? The honest answer is “not much”, ha ha, but we do know enough to at least give us an insight into all of these areas. As is the case throughout the book, diagrams and life reconstructions depict the key evidence or show re-enactments of things that really must have happened.

Pterosaur diversity, group by group

The meat and proverbial potatoes of the book is formed by reviews of all pterosaurian groups. Each group (each ‘family’, if you like) gets its own chapter. Once upon a time, popular books would have given you the impression that pterosaur diversity consisted of Dimorphodon, Rhamphorhynchus, Pterodactylus and Pteranodon and not much else. But things have boomed in recent decades, such that the chapters here on wukongopterids, boreopterids, lonchodectids, chaoyangopterids, thalassodromids and others will be wholly novel to some readers.

On that note… as is well known, views on the phylogeny, systematics and nomenclature of pterosaurs vary quite considerably from one study to the next (though note that members of particular research communities do tend to converge on similar results… read into that what you want). Witton notes this and the arrangement he favours – in general, it’s the phylogenetic scheme recovered by Lü et al. (2010) – is of course not the one favoured by all pterosaur experts. But, come on, when you’re doing a book you have to come up with an arrangement of some sort.

Pterosaurs: far from samey; nuance and variation everywhere you look

Anyway, each of these chapters introduces us to the group in question, reviews and discusses what we know of its anatomy, discusses the probable flight and grounded, terrestrial behaviour of the group’s members and, finally, provides an overview of palaeoecology. The last thing there – the discussion of palaeoecology – is one of the most novel aspects of the book. Tradition and convention would have it that pterosaurs flew over the surface of the sea and caught fish, or flew close to watery places and caught dragonflies and other flying insects. Admittedly, this ‘samey’ view of pterosaurs was challenged by the idea that dsungaripterids might have eaten shelled molluscs (Wellnhofer 1991) and that tapejarids were perhaps frugivorous (Wellnhofer & Kellner 1991). But, otherwise, the overwhelming impression has always been that pterosaurs caught fish or insects while flying on the wing.

In fact, details present across the pterosaur skeleton show, Witton (2013) argues, that all those different pterosaur groups were doing different things – sometimes subtly different things, sometimes strikingly different things. As an example, let’s briefly consider the long-snouted, long-winged ornithocheiroid-type pterosaurs (istiodactylids, boreopterids, ornithocheirids, nyctosaurids and pteranodontids), virtually all of which possess proportionally small, relatively weakly muscled hindlimbs. These pterosaurs all look more or less alike, and, yeah, the general view has been that they pretty much all do the same thing… they, you know, flew over the surface of the sea and grabbed fish.

But when all of their anatomical nuances, proportional differences and so on are examined, a case can be made that we are, in fact, seeing groups of species that, even within this one clade, perhaps did such diverse things as scavenge from vertebrate carcasses in terrestrial environments, grab fish from the sea surface, float or swim and ‘cage’ mouthfuls of small, planktonic prey, float and made short surface dives, and live a frigatebird-like life (Witton 2013).

In short, Witton’s view of pterosaurs is exciting and refreshing in its diversity, complexity and plausibility. Think of modern animal groups, whether they be gulls, seals or anoles: anatomical differences reflect different feeding and foraging strategies, nuances and niche-specific behaviours are everywhere, and no two species are ever really alike. This sort of thing was surely true of extinct animals – I’m sure it was, we all are. But this is about the first time that we’ve seen this many ideas on pterosaur behaviour and lifestyle.

I personally think that more ideas of this sort are needed – so long as, that is, that they are internally logical, look at data from all available lines of evidence, and appear grounded in a good understanding of biomechanics, ecology, and the anatomy, behaviour, diversity and functional morphology of living animals. As should be obvious from the fact that I co-author with him (Witton & Naish 2008, 2013), I think that Mark is very good at this sort of thing (certainly better than those palaeontologists who take just one or two features and concoct an unrealistic and unlikely behavioural hypothesis) and I generally find myself agreeing with his conclusions and hypotheses.

However, it’s important to note that, at the moment, many of the ideas that Witton discusses and explores are, indeed, just ideas: typically proposed here for the first time ever, they now require investigation using rigorous, quantitative techniques. But, hey, you have to start somewhere. Mark knows this and his hypotheses should serve as an inspiration for future studies.

If there’s anything that becomes a takehome with regard to this book, it’s that pterosaurs are more diverse in anatomy and proportions than has been made obvious before. Without naming names, the general impression created by some pterosaur workers is that pterosaurs are basically all alike, only with different skulls. As is made clear, not only through the text, but also thanks to those standardised reconstructions, pterosaurs actually exhibit notable and significant differences in the length and form of the neck, in wing length, in hindlimb size, and in… well, in everything, really.

Some underappreciated diversity

Let’s look at just a few examples of this underappreciated diversity. Among the weirdest of pterosaurs are the campylognathoidoids*. Check out some of the strangeness in these animals. Campylognathoides has absurdly robust humeri that make it look “like a little pterosaurian gorilla” (Witton 2013,p. 119) as well as ridiculously elongate wing-fingers. Meanwhile, Caviramus (taken by Witton to include Raeticodactylus and remarkable for its bony nasal horn) has incredibly long, slender humeri nearly 20 times longer than they are wide at mid-shaft. Clearly, these weird early pterosaurs were doing something unusual – as usual, the question is: what?

* As per my comment above about disparate views on phylogeny, not all workers recognise this group as a clade. Witton describes the possible artificiality of his grouping together of the constituent taxa. Again, if you’re covering animals on a group-by-group basis, what you gonna do? A degree of paraphyly and non-monophyly has to be tolerated (yeah, paraphrasing McKenna and Bell there).

As you’ll know from the reconstructions you’ve seen of long-tailed pterosaurs like Rhamphorhynchus, some (or all?) long-tailed pterosaurs possess soft-tissue vanes at the tips of their tails. And, thanks to Rhamphorhynchus, everybody knows that this vane was diamond-shaped or subtriangular (its form seemingly changing during ontogeny (Bennett 1995)). Right? Well, Rhamphorhynchus isn’t the only pterosaur where the soft-tissue structures on the tail are actually preserved, and those structures known for other taxa are markedly different. Little Sordes from Kazakhstan has a long, lobed structures shaped like a long, narrow leaf – perhaps all of its close relatives did too – while Pterorhynchus has a series of paired serrations that run along the sides of the end half of its tail.

We need more books like this

The pace of pterosaur research means that, needless to say, many new things have appeared since Pterosaurs appeared. There are quite a few new, recently named taxa that would have warranted discussion or mention including the Tupuxuara-like azhdarchoid Caupedactylus, the small azhdarchoid Vectidraco, the Patagonian azhdarchid Aerotitan, and a raft of new Cambridge Greensand taxa. Witton’s scepticism about the alleged azhdarchoid identity of Aurorazhdarcho (he has it wrongly spelt Auroazhdarcho [sic]) has since been confirmed by Bennett’s (2013) paper on Pterodactylus and Ardeadactylus, and then there’s the whole awkward situation involving Lonchodraco and Lonchodraconidae. New studies on pterodactyloid limb posture have appeared (Fujiwara & Hutchinson 2012, Costa et al. 2013), and so on and on.

Overall, the style of the text is friendly and conversational, even witty and vernacular. There are definitely places where I feel that it needed to be a bit tighter, and I get the impression that better copy-editing was needed. On other negative points, one or two of the illustrations look a bit rushed (I don’t much like the theropod on p. 102) and I’m not sure that the curly lines used in a few of the diagrams (e.g., Figs 7.8 and 9.2) – they look like something out of a Tim Burton movie – fit with the rest of the book. However, these are exceptions in an otherwise glorious tour-de-force.

As if it’s not clear enough from what I’ve already said, Witton’s Pterosaurs is a remarkable visual feast, packed full of novel art as well as excellent photographs that he clearly worked hard to obtain. There are, in fact, illustrations of some sort on virtually every single page – you will never get bored of looking at this book. A major Wittonian innovation is the invention of a consistent pose for pterosaurian reconstructions (both skeletons and life restorations). Reminiscent of Greg Paul’s lateral-view dinosaurs, they make it easy to compare and contrast the many taxa Witton illustrates. And look out for the nods and witty homages: without giving the game away, there are references here to Batman Begins, the arthropod-filled gorges of Skull Island… and what, exactly, is that marking on the lonchodectid’s wing?

If you like or are even vaguely interested in pterosaurs, or, hell, are interested in tetrapod evolution, diversity or history in general, you really need to see this book. I dearly hope that it inspires others to produce similar, spectacularly well-illustrated volumes on other tetrapod groups. The world would be a better place for it.

Witton, M. P. 2013. Pterosaurs. Princeton University Press, Princeton and Oxford. Hardback, pp. 291, $35.00 / £24.95, ISBN 978-0-691-15061-1. Buy it here. A kindle version is available here. A sample of text is available here. Mark's blog (technically, the MarkWitton.com Blog) is here and his website is here.

For previous Tet Zoo articles on pterosaurs, see...

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