On the Nature of Being a Pterosaur


Pterosaurs are one of those groups that attracts pure and unadulterated fascination, though not the kind that in children is bent to sabre-toothed tigers and roaring, rampaging dinosaurs. No, pterosaurs evoke a sense more of the subdued wonder, and intrigue, rather than outright and obvious awe; a sense that there is something both familiar yet alien about these beasties.

The following is my review of Mark Witton’s new book, Pterosaurs: Natural History, Evolution, Anatomy, from Princeton University Press. The reason I’m reviewing it (and I don’t review much at all) is because I received the book from Goodreads, who provided the book gratis.

Pterosaurs range in size from the very small (sits in the palm of your hand, a few kilograms in weight and less than a few feet in wingspan) to the very large (you can sit in the palm of their hand, several hundred kilograms in weight, and the wingspan of a multiseater powered aircraft). Now, compared to dinosaurs, pterosaurs can get down to their minimum size and perhaps smaller, but never as larger as them; that’s part of why dinosaurs enjoy such a happy time in the eyes of the public, children, and scientists alike: They contain the largest land animals that ever lived. But pterosaurs hold a few records themselves. There is also more, much more, about them we don’t know, but are finding out as workers — some of the most specialized among vertebrtate paleontologists,  some calling themselves “pterosauroologists” — delve into the mystery of these creatures. I’ve become involved in pterosaurs lately mostly due to my interests in the soft-tissue anatomy of the heads of extinct and modern vertebrates, focusing on the jaws and eating apparatus of jawed animals (hence the title of this blog). My first true pterosaur book was Peter Wellnhofer’s Illustrated Encyclopedia of Pterosaurs (1991, Salamander Books), an follow-up to David Norman’s Illustrated Encyclopedia of Dinosaurs (1988, Salamander Books), including rich illustrations by noted and famed paleo-life artist John Sibbick. There have been several books previous to focus on pterosaurs, but none were as specialized, or detailed, especially with photographs of the material, as Wellnhofer’s book. But alas, it became outdated. David Unwin’s 2003 Pterosaurs from Deep Time (Pi Press) followed, and shows more modern treatments and less … reptiley … looking pterosaurs. For in the time between these books, research exploded as the number of specialists dealing with these pterosaurs more than doubled. Soft-tissue preservation in pterosaurs received much more detailed investigation than previous, and the relationships among pterosaurs were being investigated. It seems time, though, that since Unwin’s book, new research and new taxa should be incorporated into a new “encyclopedia,” and so it is that Mark Witton’s Pterosaurs: Natural History, Evolution, Anatomy (2013, Princeton University Press) — a follow-up of sorts to Greg Paul’s The Princeton Field Guide to Dinosaurs (2010, Princeton University Press) — arrives.

This book hits at a good time. Pterosaur publicity is soaring, and new breakthroughs and studies from diverse fields are being integrated to provide clearer perspectives on the biology and natural history of these strange, flying animals. This book does a good job of summarizing several of the diverse arguments that fly — pardon me — around, though I will note that the author does lean toward a bias to the more scientifically supported research involving the aspects of pterosaur flight and take-off, and what they did whilst in the air. For example, there is something of a “rivalry” between competing theories of how pterosaurs got into the air, from an historical perspective on running takeoffs (or, classically how pterosaurs could not ever get off the ground) and requiring large expanded head “sails” to navigate versus a newer model in which a hindlimb-powered, quadrupedal launch could allow a pterosaur to move from a perfect standstill into an impelled flight posture in mere seconds. Witton clearly favors the latter, which, along with aeronautical specialists Jim Cunningham and Mike Habib they have published extensively since the early 2000s. The competing model is supported only by Sankar Chatterjee and Jack Templin, but as various of Habib’s and Witton’s works indicate, this is often at the expense actual data on how otherwise terrestrial animals get into the air. Witton spends far more time explicating the view he espouses and not as much on the competing view. A biased perspective is admissible, though, because this is a book being written from mostly a single person’s perspective, and as such we expect a filtered view, so we should also keep that in mind.

The book is laid out in three main sections: The first two deal first with an introduction to pterosaurs with a large anatomical and biological primer, and second with a group-by-group breakdown on major research and Witton’s perspective on that group, some of which has featured new taxa named or had researched performed by Witton; the second section is the largest, easily covering over half the book, as should be expected, as you should hardly expect to pick up a book on pterosaurs and not talk about individual groups. The third section is the briefest, detailing perspectives on phylogeny, diversity, and the decline and eventual extinction of pterosaurs. The book is also a hefty tome, being of thick, glossy pages despite being less than 300 of them, and with a beautiful, earthy dustcover (I have the hardcover version).

Witton’s writing is at times cliched, which helps promote an approachability but in a book that is meant and written generally for a knowledgeable audience it seems somewhat detracting. Further, the text, while of a nice size, is nonetheless dense with references. This will not be a book for the casual, uninformed reader, but for those who have some familiarity with the form of long-form reviews and scientific literature. This is perhaps expected, as one should not write a book about a small, specific group and write like one can only talk about them in the general — there are many unique taxa which require calling out, debates and conflicts among researchers deserving of attention. Witton walks a fine line between presenting a technical review and providing an introductory text for students unfamiliar with the group in question or students unfamiliar with scientific discourse at all.

Section 1 – Introduction and Biology

Pterosaurs are a hefty group, despite the brevity in numbers of workers whom dedicate their work to these creatures. They involve some of the most divergent anatomy amongst terrestrial vertebrates, one of only three groups to have achieved (it seems) fully powered flight and global distribution (excepting Antarctica, though birds have managed to colonize that continent). Witton walks the reader through a discussion on the history of pterosaur collection and discovery, focusing on the two sources for much of the 1800s records: southern England, and Germany. The history of Owen and Cuvier, at the time the primary investigators of what it meant to have pterosaurs in the fossil record, is skimmed, though Owen’s name isn’t mentioned at this point. So, too, is early and mid-1900s history skimmed, jumping us into a late-1900s–present discussion on the explosion of discoveries, especially those from places around the world we’d not previous found these fossils, including the incredible deposits of northeastern China and central Asia. Witton turns to investigative techniques of many of these fossils, which has largely consisted of physical preparation and sometimes destructive sectioning of fossils, though the level of “destruction” has varied to thin sectioning of ends to fully removing sections of bones. With the development of better tools, including the use of radiative imaging techniques, such as X-ray and computed tomography (CT), fossils can tell us much more with far less, and this also includes the use of ultraviolet lighting to reveal the otherwise hidden features of soft-tissues. It remains to be seen whether factors such as synchotronic, chemical analysis of these fossils will be done; though it should be noted that histological analysis through sectioning of limb bones remains one of the best ways to determine the relative ages of fossils where determinate growth phases can be determined, and pterosaurs are one such group where this technique works.

Witton takes a brief look at the history of competitive origins for pterosaurs, from initial identification of them as some form of weird mammal-bird (Johann Georg Wagler), full-blown mammals (Samuel Thomas von Sömmerring), bird-like lizards (Harry Govier Seeley), or merely sedentary “reptiles” (Georges Cuvier), the last perspective later refined after having “won” the debates with new phylogenetic research that found them to be either basal sauropsidans as either lepidosaur-relatives, or as archosauromorphans with so-called “protorosaurs,” or more popularly and best-supported as a group intermediate between crocodilians and dinosaurs (including birds). There has been extensive debate on this mostly in the last decade, though most research does agree that placing them close to or within the croc-dino split is best supported amongst all options. Witton takes time dealing with potential pterosaur relatives such as Euparkeria, Sharovipteryx, and Scleromochlus, as well as the “protorosaurs.” Witton them goes onto to discuss the plausible evolution of pterosaurs from a standard, reptilian Bauplan with extremely long legs, calling these “HyPtA”s, for (hypothetical pterosaur ancestors), and thus providing the first real step-by-step discussion of what me might be looking for as we transition from a Scleromochlus-like long-legged, short-armed croc-like animal into a long-armed, relatively short-legged, pterosaur-like precursor.

HyPtA, or maybe preferably hypta, is a term that may bear more experimental research and discussion, and makes firm predictions on biology and ecology in early pterosaur evolution. One should probably consider using these as the basis for discussion their evolution and predictions for the fossil record. It is also the first concept Witton firmly introduces that sets this book apart from a purely review type of book. Witton’s book is becoming more a research progenitor than merely a review.

Pterosaurs vary into two main morphotypes, the “rhamphorhynchoid” and the “pterodactyloid” types, classically separated by the length of the tail (long in the first, short in the second), the length of the neck (short in the first, long in the second), the number of bones and length of the fifth toe (two and long in the first, one and very, very short in the second). It might be best to note that pterosaurs don’t easily stick to this dichotomy, and have varied into the “anurognath” morphotype, with their short tails, short necks, long firth toe, but extremely long wings and wide, short and rounded heads; the intermediate “Darwinopterus” morphotype, which transitions between the “rhamphorhynchoid” and “pterodactyloid” types with a lengthening of the neck but retention of the long tail; but “pterodactyloids” also vary, with the “azhdarchid” and “ctenochasmatid” types being the most extreme, a neck longer than the head, extremely long hindlimbs, sometimes a very short wing, and a relatively long torso. These morphotypes have always meant that when discussing the general anatomy of pterosaurs, they have to be discussed as two morphotypes, side-by-side, and that’s what Witton does, as have Wellnhofer and Unwin before him. Witton has the benefit of working with even newer data than previously presented, including the nature of all the soft-tissue (muscles, internal organs including the pneumatic diverticulae that arise from the lungs, and the strange structure of the wing membranes and cranial crests).

When it comes to the internal organs, there is little to no data on the arrangement or size of various structures; though with research, it may become relatively academic to determine a min and max range for the size of the heart, and by diet how much must be taken up by a digestive system and gut, which is also aided by the presence of regurgitalites or coprolites (Witton’s vernacular is “guano”), or even gastrolites (fossilized vomit, feces, or stomach contents, the latter indicated as a rounded mass within the body cavity, rather than a elonagted, tube-like mass, termed a cololite). Witton speculates that a proventriculus, or a “crop,” was present in pterosaurs, but we do know that a muscular, and complex stomach was present and that some pterosaurs swallowed stones for some reasons (as in birds, crocs and dinosaurs); the reasons for gastrolith consumption may vary, as some birds and crocs use them for ballast, whilst they are typically used to help pulverize food and thus aid in digestion.

Neurology has only been investigated in a few pterosaurs, either through endocasts (natural and artificial) or through CT examination. These indicate a fairly avian-style brain in pterodactyloids, but a more croc-like, though still quite large, brain in “rhamphorhynchoids.” A large flocculus and semi-circular canal system and optic nerve indicates well-developed sense of balance and auditory and visual systems for perception, useful for aerial animals. They also suggest that pterosaurs held their heads naturally at different levels, basally level with the horizon, but in ornithocheiroids at least, inclined downward. Muscles are also fairly simple to work out, through the examination of muscle scars, and reference to the Extant Phylogenetic bracket; Witton follows the work of S. Christopher Bennett (2003) and Milton Hildebrand (1995) in modelling muscle shapes and positions. And here follows my first gripe with the book: Throughout, Witton’s art is clear and clean, but when it comes to diagrammatic use of color, there tends to be a fairly simplistic and somewhat confusing blend of colors, such as in describing brain structures with blobs of digit color and ample use of the pattern Fill tool in Photoshop. In some cases, colors of similar tone lie next to one another, and it is hard to differentiate them, or with the use of the fill patterns, what relative light or dark shapes are supposed to represent. This might seem relatively minor, but it impairs the visual capturing of data supposedly being represented. This is also true for the color-fill of shapes used to represent muscles.

Witton discusses the structure of the wing tissues in depth, and there is little here to build upon: further research is investigation, precisely, the morphology and arrangement of the tissues within the wing, from layers of thin muscles, vascularized tissues, and the position, arrangement, and morphology of actinofibrils, unique structures found only in the wings of pterosaurs. Witton also discusses the morphology of facial integument, the presence of lack thereof of cornified skin or cornified pads, the latter creating tissues such as beaks which overlie pads as a form of plate. Whilst the term “soft-tissue” is used for these, it should be noted that a cornified plate can be quite hard: it is the structure that generates human nail and other vertebrate claws, bird beaks, and rhinoceros horns; cornified skin can be hard, but is generally soft, and is the substance that is used for bird “cere,” but also the “bosses” or head bumps found in many artiodactyls, including rams and muskoxen. Numerous pterosaur fossils have been found with crests or claw or beak like structures around their bodies, many from the Crato Formation of South America, the Solnhofen Formation of Germany, and the Jiufotang Formation of China. These structures vary in their shapes, and for the beaks this means that some look like they have the outlines of layers of hard, cornified plates extending from the tips of the jaws, curling into odd shapes, or merely as an extension of the shape of the underlying bone. It is not clear whether these shapes reflect a specific type of tissue, but it has been commonly assumed, as evidence in Witton’s work, that these represent the beak tissues themselves.

Head crests are another thing. These vary dramatically, and seem to involve three different structures: the first is the underlying bone, which may extend as a small ridge with fluted sides or appear like a picket fence of some fashion, or as a smoother, thicker structure with tiny nutrient grooves extending across its surface; the second is a structure that has been termed “fibrous” — though this term has also been applied to the fluted basal bone crests in dsungaripterids, germanodactylids and wukongopterids — and which seems to form the base of the crest when there is no bone present, but is clearly distinct under UV light; and the third is a much, much larger structure which is always rounded at the far end, extending upwards and backwards. The detailed morphology of these structures has only been examined through the use of UV light; it seems that these structures would need better examination to reveal their secrets, such as their tissue composition, keratin presence, and layering effects revealing if the three types of tissues have a definite structure relating to any possible overlying crest. I’ve already noted Tobin Hieronymus‘s research on this blog before, and it was something of a shock to see that Witton hadn’t cited his work as possibly being relevant to the nature of beak structure; Hieronymus’ work has distinct application to investigation of homologies of various tissue types, including the presences of bosses, beaks, pads, looser connections of skin to the heads, jaws and claws of mammals, ceratopsians and birds (Hieronymus and Witmer, 2010; Hieronymus et al., 2009). I will admit that this research is pretty new, and finding that some analogies of structures are not apparent will reduce the explanatory power of those that are (neurovascular channels in bone, bone microstructure and surface ornamantation, pore orientation, number, and arrangement), but those features present are numerous and probably quite useful.

(I will note that it is quite unlikely, contra Chatterjee’s work, that the head crests formed as some sort of sail: The keratinous structures forming pterosaur crests were likely quite stiff, and for some probably composed of cornified plates rather than flimsier but rigid more-skin-like tissues (like, say, a “sail”).)

As noted above, Witton explores the issues surrounding the ability of pterosaurs to fly, moving from the historical legacy of bat-winged animals, to sedentary ground-based ones, to the running-takeoff of the early “modern” era of analysis, to the hypothesis put forward over a decade ago by Mike Habib (in part with the work of Jim Cunningham) that pterosaurs could launch through the use of a four-limbed, quadrupedal crouch–>leap–>unfurl–>flap. In mere 1.5 seconds, an animal like Anhanguera can achieve full flight from a still start.

Julia Molnar’s animation of the pterosaur quad-launch.

The diversity of pterosaur wingshape, side, and mass also influences take-off and flight styles, but as Witton writes, the wingshapes of pterosaur fall within morphometric morphospace of bats and birds, indicating that pterosaurs, despite their bizarre appearances, may have had ecological similarities with these other flapping vertebrates. But it is not simply enough to discuss pterosaurs as flying animals; Witton also explores other research that shows that despite being adept fliers and launchers, they were also fairly capable on the ground, some more than others, a strong comparison being made to many terrestrial birds (which can nonetheless fly) and research with Darren Naish that Witton has explored the terrestrial habits of Azhdarchidae, amongst similar pterosaurs. All trackeway evidence shows that when there are hindlimb traces, there are forelimb traces, but not always the inverse, and that locomotion for pterosaurs on the ground must have always been quadrupedal. This directly builds upon (and rejects) the work of earlier researchers such as Kevin Padian who explored the mechanics of bipedal pterosaurs on the assumption that the so-called pterosaur trackways weren’t definitive of pterosaurs, due to assumptions of a working bipedal locomotion model for animals such as Dimorphodon. These tracks have since become also securely pterosaurian in the eyes of trackway analyst. There are still hold-outs, and it is possible, albeit without explicit evidence, that some pterosaurs could move about bipedally. That is, on their hindlimbs, not their forelimbs, as this silly picture suggests…

If Sebulba were real, he'd have been a pterosaur.(I’d also rather think that if pterosaurs were going to go full hog terrestrial, or lose flight and needed to be bipeds, they’d use their arms and reduce their legs instead.)

Witton ends the first section with a glimpse into the life of a pterosaur, from their hatching to their growth, feeding behaviors, and eventual death. I have something of a hand in this part of the game, especially the feeding part, so will withhold comments on that section for some specific points. Nonetheless, Witton deals with fossils that describe the associations of other taxa, especially pterosaur bones that have been described with larger carnivore teeth in them (a spinosaur from South America, and a dromaeosaur from North America). Pterosaur are not just feeders, they were also food; it is something to bear in mind. But pterosaurs were also a major consumer in the food chains of their respective ecologies, especially in pterosaur-dominated assemblages like the Romualdo and Crato Formations of Brazil, in which pterosaurs make up the bulk of tetrapod fossils. Pterosaurs have been recovered from deposits ranging from far-shore, marine environments (Niobrara, in the Western Interior Seaway), near-shore, or lowland terrestrial but fluviatile deposits (the Jurassic deposits of the Alpine Italian, German and French regions; Cambridge Greensands), lacustrine but inland (Crato and Romualdo of Brazil, Tiaojishan, Yixian and Jiufotang of China, Dzharakuduk of Kazakhstan), or even further from the shore but in the lowlands or floodplains (Hell Creek and Two Medicine of Montana, USA). These regions have their own predator and prey species, from small terrestrial vertebrates, insects, fish, etc., that likely played a role in controlling or permitting pterosaur specialization and distribution. It has also been put forward that pterosaurs show distinct sexual dimorphism, with sexing apparently present in Pteranodon and Darwinopterus populations, though the sample sizes and preservation of specimens is extremely poor and it may be presumptive to make these claims without broader data ranges than a dozen or so for each taxon. Indeed, only one adult “male” Geosternbergia sternbergi (=Pteranodon sternbergi) is known, with the upright and trapezoidal crest, which leaves one curious about presumptions of taxic splitting and claims of sex and ontogeny in all respects.

Witton concludes this section with a brief overview of pterosaur phylogeny, presenting a phylogeny by which he will array the second section on taxa:

Phylogeny of Pterosaurs from Lü et al., 2010, showing the "50% majority rule" analysis. This output was the product of an aborted analysis, and a full run of this analysis produces a slightly different topology. Witton uses this and a further analysis that ran the same analysis (Unwin, 2010) as the basis for arrangement of taxa in the second section. Red lines refer to general morphotypes among pterosaurs, whilst blue dots refer to three peculiar taxa whose relationships are very contentious (technically, this is also true of Haopterus, but only recently). Grey lines reflect approximate "natural" relationships, which are not indicated by Witton.

Phylogeny of Pterosaurs from Lü et al., 2010, showing the “50% majority rule” analysis. This output was the product of an aborted analysis, and a full run of this analysis produces a slightly different topology. Witton uses this and a further analysis that ran the same analysis (Unwin, 2010) as the basis for arrangement of taxa in the second section. Red lines refer to general morphotypes among pterosaurs, whilst blue dots refer to three peculiar taxa whose relationships are very contentious (technically, this is also true of Haopterus, but only recently). Grey lines reflect approximate “natural” relationships, which are not indicated by Witton.

Witton has illustrated this entire volume on his lonesome, and demonstrate able skill with pen as will the digital brush used to general beautiful “paintings” for each taxonomic group: Basal pterosaurs, anurognathids, dimorphodontids, eudimorphodontids or “campylognathoidids,” “rhamphorhynchids,” the more recently-described “intermediate” Wukongopteridae containing Darwinopterus, “ornithocheirids,” Pteranodontia, including nyctosaurids and pteranodontids, ctenochasmatoids, “dsungaripteroids,” tapejarids, chaoyangopterids, “lonchodectids,” thalassodromids, and azhdarchids.

Before I continue, let me note something: There is something of a competitive split among pterosaur workers when it comes to phylogeny (at least), and this work extends to names for clades. Two competing phylogenetic schemes, beginning with two competing phylogenetic analyses were published in 2003 as part of the Flugsaurier symposium proceedings. The first, produced by Dave Unwin, rolled out an expansive new nomenclature for several otherwise recognized but unnamed clades; the second, from Alex Kellner, was less ambitious on nomenclature, though it supported a strange taxon, Asiaticognathidae, which doesn’t contain any taxon named “Asiaticognathus” (this was done, I am told, due to Kellner’s concern that without the Linnaean System, terms like -idae could be applied without rank-based identities, and thus without rank-based code rules). It’s a laudable ideal, and one I happen to share … but, baby steps.

2003 pterosaur phylogenies compared

Colored bars represent four major pterodactyloid taxa drawn out for comparison between the two phylogenies. Red: Ornithocheiroidea; Orange: Pteranodontia; Green: Dsungaripteroidea; Blue: Azhdarchoidea. Taxa have differing diagnoses and definitions, and thus differ in content as phylogenies shift. Red arrow points to “Lonchodectidae,” the clade that never was (see [n1] below for clarity). Names in boldface refer to clades named or (not left unnamed) in their respective phylogenies.

The major taxa shown in colored bars represent the old taxa in which content differs between the two phylogenies; in the case of Dsungaripteroidea, this taxon contains all of the others in Kellner’s phylogeny, whilst in Unwin’s it is highly restricted and Ornithocheiroidea takes precedence. Kellner’s Tapejaroidea has the same maximum content as Unwin’s Lophocratia, though the definitions are different (Tapejaroidea: Dsungaripterus + Tapejara + Quetzalcoatlus, presumably their type species; Lophocratia: Pterodaustro guinazaui + Quetzalcoatlus northropi), which makes them effective synonyms when ornithocheiroids are the sister taxon to ctenochasmatoids, pteranodontoids, dsungaripterids, and azhdarchoids. Otherwise, when ctenochasmatoids are more basal, Lophocratia becomes a synonym of Pterodactyloidea. And that’s the problem. Witton explores the phylogeny but uses (exclusively) Unwin’s terminology; this might be wise given the broader range of nomenclature employed, but other phylogenetic analyses, including those of Brian Andres, employed in Andres & Ji (2008) have developed strong disagreements, with ctenochasmatoids as the most basal pterodactyloid lineage. Witton explains the difficulties with the several competing phylogenies, but employs one he is most likely familiar with and may personally agree with.

Section 2 – the Pterosauria

The second section of the book is split into large taxon groups, each prefaced with a unique illustration done in Witton’s richly colored digital style, and includes skeletal reconstructions for several taxa, sometimes more than one per chapter, which in turn accompany a life reconstruction in the same pose, the launch-phase of the quad launch, right after the hindlegs have left the ground. Some of these are very colorful (Darwinopterus modularis is shown with high-contrast banding for the crest and a vibrant blue tail, of the few times Witton uses blues) and others very drab (Dimorphodon macronyx in browns and a deep russet coat), or complex cryptic coloration (Anurognathus ammoni, but with a white belly). Research is up to date on most taxa, though as 2012 ended and 2013 snuck around the corner, Witton had to update his MS to include new taxa to at least include them and say something meaningfully. So this text is mostly up to date as of 2010-2011. Some of the reconstructions are peculiar, but not altogether out of place with the diversity shown; however, one deserves particular mention:

Nicknamed the “Painten Pelican,” a skul referred by Bennett (2013) to Cycnorhamphus suevicus (of which Gallodactylus suevicus is a junior synonym). Image from pterosaur-net.blogspot.com and a post by Mark Witton.

Cycnorhamphus suevicus is a basal ctenochasmatoid known from two partial skulls and skeletons from Solnhofen-equivalent formations in France. However, an apparently larger skull from Germany (referred to as the “Painten Pelican,” above) suggests an adult morphology for a species which Bennett notes is otherwise known from immature specimens. The skull’s bizarre jaw structure immediately calls to mind some degree of deformity, though Bennett (and Witton) argue that the jaw is “correct.” I am personally one to take such an argument with a grain of salt, for it is not always that appearances should be trusted. Soft-tissue appears to be present in the form of a rectangular strip above the skull, and a rounded flap beneath the tip of the upper jaw, shown as a particular rugose-looking irregularity in the slab. This being apparently authentic and not, perhaps, an irregularity resulting from uneven splitting of the slab, it was suggested to Bennett that the ventral flap was a displaced portion of the upper crest, though he discarded this idea and argued it was a median palatal structure. Witton reconstructs this animal with the ventral flap being one of a pair on either side of the jaw, and perfectly shaped to cover the gap when the jaws closed. I find myself perplexed at this reconstruction, though have no better argument to make sight-unseen.

Each chapter in this section includes a short review-style summary of the history of the group and a discussion on the included species: An introduction, a general discussion on anatomy, factors relating to their biology (flight, terrestrial behavior) or ecology (feeding, etc.) and a narrower subsection on subordinate taxa (Rhamphorhynchidae is split into Rhamphorhynchinae and Scapognathinae). A map indicates a current-world distributions for taxa, and this is one place where I think Witton could have expanded generously with a modern and ancient map per group, as many of these taxa are known from relatively short periods of time with little geological shifting (“campylognathoidids” from the Norian, Late Triassic), whilst others are known across broad ranges (dsungaripterids from across nearly the entire Early Cretaceous). The composition or assignment of taxa to these chapters can be tricky, and Witton often has to deal with “wild card” taxa which have been argued to go one place in one paper, in another by someone else, etc. These ambiguous assignments could be dealt with in a broader “miscellaneous” chapter, but the concise format for each chapter would make this clunky. A few highlights:

As noted further above, three particular taxa cause some issues when it comes to these phylogenies, the first being the so-called “Lonchodectidae.”[n1] Phylogenetic relationships for “lonchodectids” varies depending on its content: The Cambridge Greensands include a diverse range of taxa based on jaw fragments alone, but Unwin (2001) referred to several species of Lonchodectes postcranial material without direct reference to association, either because of similar size and same quarry location. However, when isolated from their postcrania, Lonchodectes spp. tend to array as either ornithocheiroids or, potentially, ctenochasmatoids (as was the case with Unwin, 2001), depending on the species used; when only postcrania are used, these tend to fall in as azhdarchoids, most similar to a complex of taxa including Tapejara wellnhoferi, Azhdarcho lancicollis, and Chaoyangopterus zhangi (Rodrigues & Kellner, 2013). This prompted Rodrigues & Kellner (2013) to run several analyses in corrected versions of Lü et al. (2010) and other analyses wherein they recovered Lonchodectes as a paraphyletic series of grades without much phylogenetic signal among the ornithocheiroid grade — which is prone to happen when one tosses in species despite high morphologic disparity.

The other two taxa are the two (only) named species of Germanodactylus, cristatus and rhamphastinus. While names separately, Germanodactylus species share a lot of features with one another, including relatively straight jaws, relatively short-crowned teeth, jaw tips that tape to points, a rounded margin for the occiput seen in side view, and other features that seem relatively plesiomorphic and rather Pterodactylus + ctenochasmatid like. Indeed, Germanodactylus is so often a problem that the two species are typically included side by side, as one (cristatus) tends to seem more basal than the other (rhamphastinus). Germanodactylus rhamphastinus is the more dsungaripterid-like, but this is generally due to the small length of both upper and lower jaws which lack teeth. It is likely wise to discuss them separately, though Witton sidles them into Dsungaripteroidea in his taxon chapters, though does discuss both the lumping of the species into Germanodactylus and the latter into Dsungaripteroidea, as opposed to Ctenochasmatoidea.

Some taxa presented are known from only juvenile remains, and this has caused some concern over taxonomic assignment of further material (see Cycnorhamphus, above). One such taxon, Nemicolopterus crypticus, is known from the Jiufotang of China in the same layers as species referred to as Sinopterus and Huaxiapterus (or, alternately, just Sinopterus), and is a tiny, edentulous taxon with a sharply-downturned rostrum — though also as above I suspect some level of distortion due to the varying widths of the jaw tip from the rear of the skull; a common feature in the Jiufotang for skeleton is that elements can be slightly twisted along their lengths. One other thing I would like to see, and it is something that could temper the discussion on whether certain features are authentic, is a discussion on the taphonomy involved in some specimens, that relative disarticulation can result in arguments about natural separation of elements. This is especially apparent when dealing with Tapejaridae chapter, as many, many skulls of Sinopterus/Tapejara are shown with the caudal process of the premaxilla, which extends along the skull and terminates with the occipital crest, being partiallyremoved from the rest of the skull roof. Artistic interpretations of the natural skull or life appearance common treat this separation as natural, though every skull so far described for Tupandactylus (imperator, navigans) show a firm attachment, with what appears to be the lacrimals or nasals sitting alongside or beneath the premaxillary caudal process; this is especially apparent in the holotype of Sinopterus dongi, where the rest of the skull appears intact, but portions of the palatal region or jugal are dorsally splayed, showing that the marginal, ephemeral contact of lacrimal/nasal to premaxilla may be taphonomic, and the entire premaxilly skewed away from the skull unnaturally. Again … some taphonomic discussion would be pleasing.

Section 3 – the End

The final chapter is a brief discussion on the decline and disappearance of pterosaurs, about whether there was a diversity decline preceding their extinction, and whether there is a historical effect to their recover (and thus lack of one for the “end times”). Sadly missing from this final discussion is the relationship of end Cretaceous giant pterosaurs as opposed to the increasing diversity of birds. It is possible, one can say, that birds increased in diversity as pterosaurs diminished during the late Early Cretaceous and throughout the Late Cretaceous, failing to compete with the larger forms, and this forming an ecological split: small avian taxa, large pterosaur taxa. Food must have been similar, and in some ways, ability to manage resources superior for birds, for this to be true. This may not have been the case, as it seems taxic diversity increases when dealing with lagerstätten, fossil facies comprising continual deposits of silt, sand and clays into anoxic lake, lagoon, or riverbeds. The dearth of these types of facies in the Late Cretaceous may be one reason why taxic recognition diminishes after the Early Cretaceous. Obviously, one bright forward future would be the discovery of lagerstätten in the Late Cretaceous, examination of large-bodied species, and investigation of why, if there are no pterosaurs, they aren’t there?

Closing Thoughts

Pterosaurs are an amazingly diverse group, and it is no wonder that they capture so securely the imagination of vertebrate specialists. But pterosaurs are also relatively rare, which means that fewer people can spend time with them. Unfortunately, this means that conflicts among researchers are more pronounced, so that when there are two groups, or three, there is a clear division amongst workers. This seems a sad state when it is so easily possible for the various divisions among paleontologists with an interest in pterosaurs can band together. Alas, this only seems to happen for symposia and conferences.

Recommended?

Yes, with kudos. Witton’s book is the most up-to-date review of Pterosauria, though there is some to be desired. If future editions are planned, I hope to see the taxa included receive a more thorough write-up, and for the phylogenetic data involved a bit more coverage, especially since much of pterosaur analyses are in phylogenetics. Historical maps, cleaner color graphics outside of Witton’s quirky digital style, and more coverage of the discourse involved would be wonderful. I am especially interested in more details if Witton desires for integument, but that does also depend largely on the research to be done.

[n1] I am unaware of any formal systematic work which coined the term “Lonchodectidae.” Two citations are often given, either Hooley (1914) or Unwin (2001). However, neither of these works contain formal terms to describe and name the taxon: Hooley (1914) revised the systematics of the Cambridge Greensands pterosaurs and coined the names Lonchodectes and Amblydectes for species that were, previously, merely lumped in with Ornithocheirus; Unwin (2001) used the term “Lonchodectidae,” but never qualified this, nor did he cite any previous source for the name, though this is true also of “Pteranodontidae” and “Ornithocheiridae,” and it is likely that Unwin felt the term was established. Following Unwin (2001) further papers have considered the name as having been established by one of these authors, and cited one of these sources for the name. Neither is correct, and “Lonchodectidae” has never been formally established.

Bennett, S. C. 2013. The morphology and taxonomy of the pterosaur Cycnorhamphus. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 267 (1): 23-41.
Chatterjee, S. & Templin, R. J. 2004. Posture, locomotion, and paleoecology of pterosaurs. Geological Society of America, Special Paper 376.
Habib, M. B. 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana B28: 161-168.
Hieronymus, T. L. & Witmer, L. M. 2010. Homology and evolution of avian compound rhamphothecae. The Auk 127: 590–604. [PDF]
Hieronymus, T. L., Witmer, L. M., Tanke, D. H. & Currie, P. J. 2009. The facial integument of centrosaurine ceratopsids: Morphological and histological correlates of novel skin structures. The Anatomical Record 292: 1370-1396. [PDF]
Hooley R. W. 1914. On the ornithosaurian genus Ornithocheirus, with a review of the specimens from the Cambridge Greensand in the Sedgwick Museum, Cambridge. Annals and Magazine of Natural History 78: 529-557.
Kellner, A. W. A. 2003. Pterosaur phylogeny and comments on the evolutionary history of the group. pp.105-137 in Buffetaut, E. & Mazin, J. M. (eds.) Evolution and Palaeobiology of Pterosaurs. Geological Society Special Publications.
Lü J.-c., Unwin, D. M., Jin X., Liu Y., Ji Q. 2010. Evidence for modular evolution in a long–tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society B 277: 383–389.
Rodrigues, T. & Kellner, A. W. A. 2013. Taxonomic review of the Ornithocheirus complex (Pterosauria) from the Cretaceous of England. ZooKeys 308: 1-112.
Unwin, D. M. 2001. An overview of the pterosaur assemblage from the Cambridge Greensand (Cretaceous) of Eastern England. Mitteilungen aus dem Museum für Naturkunde in Berlin, Geowissenschaftliche Reihe 4: 189–221.
Unwin, D. M. 2003. On the phylogeny and evolutionary history of pterosaurs. pp. 139-190 in Buffetaut, E. & Mazin, J. M. (eds.) Evolution and Palaeobiology of Pterosaurs. Geological Society Special Publications 217.
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 ONE 5: e13982.

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11 Responses to On the Nature of Being a Pterosaur

  1. Mark Witton says:

    Hi Jaime,

    Thanks for the thorough review: glad to see I came out OK! I think a lot of the points you raise – greater discussion of integument, taphonomy and so forth – can’t be substantiated in a book like this because such studies are still wanting. I’ve obviously gone out on a few limbs here and there, but have tried to stay away from making detailed claims about topics that I, or anyone else for that matter, has any grounding in. There is also the fact that this is meant to be a relatively breezy overview of the entire group that is accessible to anyone with an interest in palaeontology. Ultra-detailed discussion of aspects like taxonomy would probably turn a lot of readers away. In any case, such literature already exists, and readers are told the relevant papers to check out if they want to immerse themselves in more detailed taxonomy. On some of your other points…

    “It has also been put forward that pterosaurs show distinct sexual dimorphism, with sexing apparently present in Pteranodon and Darwinopterus populations, though the sample sizes and preservation of specimens is extremely poor and it may be presumptive to make these claims without broader data ranges than a dozen or so for each taxon”

    That really depends on the taxonomy you follow. In the taxonomy used in the book (I discuss Kellner’s 2009 paper and why I don’t follow it), all pteranodontid remains from the Niobrara Chalk and associated deposits represent Pteranodon. That gives a sample size of well over 1000 specimens (something like 1400 at last count, I think) and, while only a handful preserve headcrests, the distribution of big crests in the ‘large’ morphs and reduced crests in the ‘small’ morphs is 100% consistent. Darwinopterus isn’t known from as many specimens by far, but the sample size is increasing: there’s certainly well over a dozen already.

    “This being apparently authentic and not, perhaps, an irregularity resulting from uneven splitting of the slab, it was suggested to Bennett that the ventral flap was a displaced portion of the upper crest, though he discarded this idea and argued it was a median palatal structure.”

    I think it’s pretty clear that this is a real palatal structure and not an artefact or a chunk of displaced crest. The texture is very different. Moreover, I’m pretty confident that the jaw morphology is not pathological in nature: there’s not an irregular fibre of bone or swelling anywhere along its length. Regarding the reconstruction, Bennett’s work on this animal had not been published when that chapter was written and illustrated, so all I had to work off was my own photos and observations, hence the slight difference in interpretation.

    “I think Witton could have expanded generously with a modern and ancient map per group, as many of these taxa are known from relatively short periods of time with little geological shifting”

    Problem is, virtually all pterosaur groups (even those you mention in your text) range over many tens of millions of years. There are a couple, sure, that are a little more restricted, but it would be nigh on impossible to chose an appropriate map for most lineages (this problem is graphically demonstrated on page 261). I suppose I could have generated multiple maps for each group, but that would eat up a lot of space and time for relatively little payoff.

    “Sadly missing from this final discussion is the relationship of end Cretaceous giant pterosaurs as opposed to the increasing diversity of birds.”

    If I read this correctly, I think I did address these points. The idea of birds vs. pterosaurs is covered on in fig. 26.3 (plot of pterosaur diversity and avian diversity over time) and in the text on page 263. Page 262 discusses the reasons why the absence of small Maastrichtian pterosaur species may have played a part in pterosaur extinction. Does these address your points, or have I missed something?

    • On sexual dimorphism. Just to let you know, it’s not that I think there was NO dimorphism, but only that sample size should be higher. I understand that, setting aside Kellner’s recognition of numerous taxa (some already named, like Geosternbergia for sternbergi) for this discussion, the number of fully adult, well-preserved, cranial and postcranial remains is ridiculously low. Most remains are partial, fragmented, or shattered, and this includes the work Bennett uses for argues for sexual dimorphism. Even so, Bennett recognizes sternbergi, and that’s good enough. I also understand and agree with the ontogeny, but the problem is most ontogenetic argumens are based on either skull shape OR pelvic shape, and I’m not so certain that partially flattened, distorted pelves are very strong in the surety department. Otherwise, I do actually agree with you — as much as my staments matter.

      On the “Painten Pelican.” My first, and indeed most people’s first, inclination to to say “That looks like a pathology or taphonomic artefact.” Note that I state that both you and Bennett argue the structure is authentic. I merely wanted to voice the other side of it. I’m sure you’ve seen the ctenochasmatid skeleton that Tischlinger is working on, shown here at Dave’s site. The rostrum tip is twisted about its long axis, but the rest of the skull remains intact. I can think that if authentic, a natural pathology can result in bone fibers or sutures to grow “normally” but around a deformed shape. DDT, at least, causes similar deformities in the beaks of birds; I think Darren has gone on the subject more than a few times at TetZoo. It’s not that I think either you or Bennett are Wrong, and I didn’t want to belabor my counterpoint too much in the review itself, but that such a bizarre shape would seem to require a bizarre answer. The simplest answer may be the correct one, and that’s that the jaw is normally straight. Who knows. This could be a salmon among pterosaurs, growing out its snout during mating season!

      I can kind of agree with you on the issue of time and space, but I figured it would have been possible to do that at, say, half the size of the other, for context. Several chapters already end with substantial white space, suggesting at least that many maps can be fit in without expanding the page count. Although, I’d note that picking intervals around 30-50my will not result in that substantial of a difference of geography: they’d only need to approximate, but could take into account paleogeography, one of the features not expounded upon much in the book, at least not extensively enough to matter.

      On pterosaur diversity. Ok, I may have been the one to miss that. The figure has the data, but I was skimming the text for the explication.

      • Michael O'Sullivan says:

        I don’t want to jump in or anything, but on the comment that “the number of fully adult, well-preserved, cranial and postcranial remains is ridiculously low”. The Niobara _Pteranodon_ assemblage does not have a single animal below I think 70% of the adult size. This is well beyond a large juvenile and is fully within the sub-adult range. Added to that, much of the material is from full grown adults. The issue with the Niobara formation is not the lack of adults but the lack of juveniles. We really have no idea what a young _Pteranodon_ is like. Plus, at 70% adult size, these are arguably sexually active animals, and almost certainly at an age where sexual dimorphism is either pronounced or becoming pronounced.

        Sorry for jumping in there, just a comment in passing.

        • I’ll admit my ignorance on this point, though I’m curious to know the skeletal/cranial completeness of the majority of these specimens. Do you think there is substantial data to support dimorphism despite Kellner’s expanded taxonomy?

          • Michael O'Sullivan says:

            Honestly yes. I think as well as we can understand these topics in the fossil record, Bennett makes a compelling case. Within the Niobara formation we have multiple diagnosable pelves and head crests. His argument about these being sexually dimorphic is supported by the more recent description of the female _Darwinopterus_ which possessed broader “child-bearing hips” and a lack of a crest. _Darwinopterus_, a very distantly related animal is showing the same pattern Bennett is arguing exists in _Pteranodon_. You’ve got the making of a supportable phylogentic bracket there. We’re also seeing these differences in animals which are otherwise identical, except for size. Size is of course a risky character in any diagnosis of fossil taxa but in this case, since small size is associated with a small adult crest and broad hips, it is a reasonable caveat to the argument that these smaller animals are female.

            As for in the light Kellner’s 2010 rediagnosis, I have to say I agree with Mark Witton and Chris Bennett on the diversity of Niobara. As figured, _P. sternbergi_ and _P. longiceps_ are clearly more similar than they are different. For me to accept a generic difference I would need more convincing characters than those presented in the paper. Also, his erection of Dawndraco is highly dubious to me as the morphology of the crest as figured is nearly identical to the posterior morphology we see in the crest in _P. sternbergi_. Now, while pterodactyloids are currently outside my field of research, I would suggest that Dawndraco is a sub-mature male _P. sternbergi_ and what we’re seeing is an ontogenetic signal rather than a taxonomic one. Which I would personally find more interesting.

          • I’m willing to keep sternbergi within Pteranodon, barring any likelihood that sternbergi ends up closer to some other taxon than to longiceps that itself isn’t also just as close. That is, if sternbergi and longiceps maintain their relative positions with one another, there is no effective difference; Occam’s Razor suggests we keep things the same until we need to change them to be more effective at communication. But I take truck with the argument that there is any validity to “generic” over “specific” assignment: I don’t think there is a convincing argument behind determination over whether a taxon is merely a species, or a species + genus, and no level of uniqueness will do. There are scores of fossil taxa diagnosed on a single or pair of characters, not really unique to them but unique in combination at least, and this will increase as we fill in all the missing sections between species we can.

            I do have a little problem with the use of ischiadic contact being qualified as whether a pelvis is “open” or “closed” substantively enough. There MUST be a way to determine this, especially in crushed fossils like every single specimen of a wukongopterid, without having to resort to “well, those two litter bones there; they ain’t touching, you see.”

  2. Christopher Collinson says:

    Just a minor nitpick:
    “a skull referred by Bennett (2012) to Cycnorhamphus canjuersensis (of which Gallodactylus suevicus is a junior synonym)”

    Its Cycnorhamphus suevicus and Gallodactylus canjuersensis, with Cycnorhamphus suevicus having priority.

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