I’m still not sure whether I blog about Mesozoic archosaurs – specifically dinosaurs and pterosaurs – too often, or too infrequently. As I always say, the problem as I see it is that dinosaurs and pterosaurs have so much presence in the blogosphere that writing about them always feels like jumping on a bandwagon. On the other hand, Tet Zoo attracts many readers from outside the palaeontologically-themed segment of the blogosphere, many of whom presumably don’t get exposed to dinosaur and pterosaur news in the same way that I do. I hope you appreciate my dilemma. Enough preamble, why are we here? Because many neat new things have appeared in the recent literature, that’s why. We’ll start with the pterosaurs.

Curiously, two recent papers both describe similar discoveries: namely, mass accumulations of pterosaurs belonging to individuals of different sexes and growth stages. The first involves Hamipterus tianshanensis, a new, Lower Cretaceous pterosaur from the Tugulu Group of Xinjiang, China (Wang et al. 2014a). It’s a long-skulled, toothed pterodactyloid of the sort termed a pteranodontoid by some authors and an ornithocheiroid by others.

Approximately 40 specimens (perhaps many more) have been found together, and five eggs (which match other pterosaur eggs in terms of size, appearance and eggshell microstructure) are also present in the assemblage (Wang et al. 2014a). Ontogenetic changes are revealed in the sample, the larger animals having a wider upper jaw tip than the smaller ones (an observation which means that variation in upper jaw breadth shouldn’t be emphasised as an important character in phylogenetic or taxonomic terms) (Wang et al. 2014a). There are obviously good grounds here for thinking that a nesting site was present in the area, and that this assemblage indicates gregarious behaviour in this species.

Hamipterus is – like so many other pterosaurs – crested. The crest consists of a semicircular lappet located close to the snout tip, and a low, fibrous ridge that runs along the snout’s upper margin and was almost certainly enlarged in life by a soft tissue extension. Some individuals have a tall, rugose semicircular section that leans forwards, and others have a smaller, lower one. Here we come to the most controversial contention of this study: Wang et al. (2014a) suggest that this variation represents sexual dimorphism, with the bigger-crested animals being the males. The suggestion has even been made that the association hints at pair-bonding and male involvement in nesting (Martill 2014).

The idea that sexual dimorphism might be present is, of course, plausible. It is, as the authors note, in keeping with the hypothesis that cranial crests in pterosaurs evolved under sexual selection pressure (Knell et al. 2013), but it also looks like the sort of variation you’d expect to see in a population anyway, and – as yet – the possibility of sexual dimorphism hasn’t been properly tested (as usual, I will note here the fact that sexual dimorphism is not a requirement for sexual selection to be at play: see Hone et al. 2012). Recall that, in the definitely dimorphic Jurassic pterosaur Darwinopterus, anatomical features of the pelvis and a direct association between a crestless individual and an egg helped show that crestless animals are female and crested ones are male (Lü et al. 2011). There’s no data like this as goes Hamipterus... yet. It’s early days: we have to assume that Wang et al. (2014a) is an initial report, with more detailed analysis set to come.

Tapejarids in an oasis: Caiuajara

The second new pterosaur assemblage is from the Upper Cretaceous Caiuá Group of southern Brazil where about 47 specimens of another new pterosaur have been discovered, again in a jumbled mass-death deposit. This time, the animal is a tapejarid (a group of a short-faced, toothless, crested pterodactyloids), and it’s been named Caiuajara dobruskii (Manzig et al. 2014). Caiuajara (argh – how are you supposed to pronounce that?) has a tall, subtriangular crest projecting upwards from its snout as well as a rod-like crest that projects backwards and upwards from its occiput.

Numerous juveniles are present in the assemblage. In fact, the majority of the animals are juveniles and only two skulls belong to adults. This might suggest that the animals died in some sort of ‘nursery’ area or, at least, an area where juveniles were hanging out a lot, and the authors favour the idea that the area represents an oasis (otherwise surrounded by desert) where the remains of deceased juveniles accumulated over the years (Manzig et al. 2014). Again, we see changes in the shape of the mandible occurring during growth, with adults having a far more ‘extreme’ shape than younger animals. Juveniles also have ‘prototype’-style cranial crests compared to the giant crests of the substantially bigger subadult and adult individuals (Manzig et al. 2014).

Amazing stuff. As seems typical for pterosaurs, the skeletal proportions of the juveniles indicate that they were precocial ‘flaplings’, fully capable of flight, and thus presumably living independently from their parents (Unwin 2005). Given the palaeoenvironmental setting – an oasis surrounded by desert – I’ve been wondering what we might be able to glean about tapejarid lifestyle and ecology from Caiuajara. Based on cranial and wing anatomy, and the palaeoenvironmental context in which they’re found, I’ve generally favoured the idea that tapejarids were woodland-dwelling omnivores, vaguely similar to hornbills but less specialised for frugivory (cf. Witton 2013). The presence of Caiuajara in a region dominated by desert and ‘interdunal wetland’ (Manzig et al. 2014) might contradict this, but might not. Stay tuned for further work.

Thalassodromids in Transylvania? Not so fast...

Tapejarids are part of my favourite pterosaur group, Azhdarchoidea. In addition to the comparatively short-faced tapejarids and the very long-snouted, often gigantic azhdarchids, this group also includes the ‘intermediate-snouted’ thalassodromids, a group that’s included within Tapajeridae by several authors and found to group together with them in some phylogenetic studies. I’m sceptical of those results (largely because far too few characters have been used: a still-ubiquitous problem of the pterosaur phylogenetic literature) and still think (as per Martill & Naish 2006) that thalassodromids are closer to azhdarchids than to tapejarids. I could be wrong, of course; I often am.

Anyway, thalassodromids – whatever they are – are exclusively South American. Well, actually, a partial snout and lower jaw from Texas (the famous TMM 42489-2 specimen) has been identified as a thalassodromid (Kellner 2004, Martill & Naish 2006): this is, however, now regarded as a mistake and the specimen is more likely an azhdarchid. Oh, here’s another reminder of how similar thalassodromids and azhdarchids can be. Anyway, in view of this distribution, the announcement of a thalassodromid from the very latest Cretaceous of Romania was surprising, to say the least. The specimen concerned is a plate-like chunk of bone, identified as a partial cranial crest and deemed worthy of recognition as the species Thalassodromeus sebesensis (Grellet-Tinner & Codrea 2014).

I won’t bore you with the full, tedious Tale of the Transylvanian Thalassodromeus, other than tell you that the specimen is not a bit of thalassodromid at all, nor is it even a pterosaur [Mark Witton has covered the story here and here]. As noted by some people during the review process (that’s right: long before the paper was even published), the specimen is part of the plastron of the turtle Kallokibotion. Two different teams of authors felt strongly enough about this to write letters to the journal concerned; the end result is a multi-authored monster in which most people who work on pterosaurs voiced their concerns (Dyke et al. 2014). Exit Th. sebesensis and its associated palaeobiological and biogeographical speculations, pursued by a mob of angry pterosaurologists (Dyke et al. 2014).

Azhdarchid biology, behaviour, lifestyle... again

The pterosaurs that I’ve mentioned so far are all very nice, but they don’t belong to the most awesome and fascinating of pterosaur groups, Azhdarchidae: the generally long-snouted, long-necked, often enormous toothless Cretaceous pterosaurs that Mark Witton and I have interpreted as ‘terrestrial stalkers’ (Witton & Naish 2008, 2013). This work, combined with that on the flight behaviour and functional morphology of these amazing animals, has – I think – made azhdarchids ‘superstars’ of the sort that attract increasing amounts of research attention.

We’ll start with the substantial review of the group recently published by Averianov (2014). Two general conclusions emerge from this study: one being that various specimens should be synonymised into a small number of taxa, the other being that azhdarchids were likely not – as per Witton & Naish (2008, 2013; also Witton 2013) – animals of terrestrial, continental environments, but, rather, of nearshore marine environments as well as lakes, riversides and so on (Averianov 2014). I’m not going to respond to these assertions in detail, since that’s something that’ll have to happen in the technical literature.

But I will say that I don’t agree with Averianov’s general approach as goes taxonomic diversity within pterosaur groups. When more than one species within a group is reported from a given geological unit, his default assumption is that the species should be synonymised. So, in writing about the thalassodromids of the Brazilian Romualdo Formation, Averianov (2014) “accept[s] the synonymy of Tupuxuara longicristatus, Tupuxuara leonardi, and Thalassodromeus sethi proposed by Martill and Naish (2006)”, despite the fact that there’s now such convincing evidence refuting it that even Martill and Naish have long given up on it. He also implies that the Maastrichtian azhdarchids from Romania – little Eurazhdarcho and giant Hatzegopteryx – might be growth stages of the same animal, and goes through all of the diagnostic characters proposed for Eurazhdarcho and dismisses them (Averianov 2014). Having checked the features concerned, I think that virtually all of this is erroneous; the specifics will be addressed in papers currently in development.

As for the argument that azhdarchid fossils come from wetland and coastal settings... well, throughout our work on azhdarchids, Mark and I have been challenged by people who point to the fact that azhdarchid remains come from aquatic settings (those deposited on floodplains, in estuaries, or in riverbank sediments). Alas, they have conveniently forgotten the fact that most fossils come from sediments deposited by water, because (taphonomy 101) it’s water that results in the transportation and burial of the remains of once-living things. If we look at Averianov’s (2014) data, we see that almost half (46%) come from sediments deposited in the places typical for terrestrial, continental animals. Of the ‘marine’ occurrences he lists, it’s telling that many of the azhdarchid fossils come from sediments that also yield abundant dinosaurs, mammals, lizards and even frogs, salamanders and angiosperm leaves (Averianov 2014). The obvious conclusion is that the (generally fragmentary) fossils concerned had been transported away from the places where the animals actually lived.

So, there’s no support here for a view of marine or quasi-marine or wetland-frequenting azhdarchids – support for a terrestrial, continental view of the group (Witton & Naish 2008, 2013, Witton 2013) remains strong.

Tiny pterosaurs in the Late Cretaceous! And medullary bone, again

In other azhdarchid-related news, a couple of really interesting new papers have appeared on Bakonydraco galaczi, a weird animal from the Santonian Csehbánya Formation of Ikarkút in the Bakony Mountains of western Hungary. Bakonydraco combines azhdarchid-like characters with tapejarid-like ones and is hence regarded by some authors as a tapejarid, and by others as an azhdarchid. I was surprised on visiting the Hungarian Natural History Museum in Budapest some years ago to learn that a comparatively huge number (over 50) of partial Bakonydraco lower jaws have been discovered, many consisting only of the symphyseal region, some just a couple of centimetres in length.

Prondvai et al. (2014) subjected all of these to morphometric and histological analysis, and – unexpectedly – found that the three tiniest specimens are adult, not juveniles of B. galaczi! There are, therefore, two pterosaurs in the assemblage, one of which is tiny, yet to be named, and represented only by jaw tips. In the smallest of these miniature adults, the jaw tip is just 32 mm long, suggesting (back-of-the-envelope stuff here) a skull less than 150 mm long in total, and hence a wingspan of maybe 1 m or less (those more mathematically gifted might like to double-check some of this).

So – tiny pterosaurs in the Late Cretaceous at last? Do feel free to run with this for all it’s worth, since it has the potential to change our views about Late Cretaceous pterosaur diversity and evolution. This discovery also seemingly means that little Vectidraco from the Lower Cretaceous of England – estimated to have a wingspan of perhaps 75 cm or so (Naish et al. 2013) – might not be the smallest azhdarchoid reported thus far, after all.

Moving on... in another paper on the Bakonydraco specimens, Prondvai & Stein (2014) report the discovery of medullary bone in several of the specimens. People interested in the biology of fossil archosaurs will be well aware of medullary bone and what it is. It’s the special tissue that female dinosaurs - and, perhaps, pterosaurs - lay down on the inner walls of their bones and use when they need to create eggshell. What might be medullary bone has previously been reported from a femur of the bristle-toothed South American pterosaur Pterodaustro (Chinsamy et al. 2009).

But, waitaminute. The ‘medullary bone’ that Prondvai & Stein (2014) report was found inside those same Bakonydraco lower jaws discussed above, not in the shafts of the limb bones (the only places where it’s supposed to occur). It’s also found in quite a few of the specimens and doesn’t seem to be pathological in origin. What does it mean? We don’t know, but Prondvai & Stein (2014) suggest that it’s almost certainly nothing to do with reproduction, and might have evolved independently from the medullary bone present in dinosaurs. Alternatively, maybe dinosaurian medullary bone and pterosaurian ‘medullary-oid’ bone had a common origin but its function and role changed in the two lineages. Intriguing stuff.

An article has also appeared in which the bird-like respiratory system of pterosaurs has been linked to their evolution of giant size (Ruxton 2014). This sounds exactly like the sort of argument presented before in other studies (Claessens et al. 2007); in a sense it is, the novelty being that Ruxton proposes that the bird-like respiratory system would have decoupled the flight stroke from the action of breathing, and allowed for smaller lungs and hence bigger flight muscles. I must confess that I don’t see anything novel here, since people familiar with the way the avian respiratory system works are already familiar with its implications as goes body size evolution and flight style (maybe, however, they haven’t expressed it clearly in print before: "what people know" is often not the same as "that which has been expressed in print"). If you’re wondering why birds – who also, ha ha, possess an avian respiratory system – haven’t achieved the same size as the biggest pterosaurs, it's presumably to do with the different mechanical parameters operating on feathered wings vs membranous wings.

A review of pterosaur wing anatomy and flight behaviour has also recently been published by Middleton & English (2014), and the extent of skeletal pneumatisation in pterosaurs has been explored by my friends and colleagues Liz Martin and Colin Palmer (Martin & Palmer 2014). They basically find that pterosaur bones are even more pneumatic than reported before.

Remarkable Ikrandraco, and the hypothesis that just won’t die

Finally, we’ll finish with yet another recently named Cretaceous ornithocheiroid-type pterodactyloid: Ikrandraco avatar from the Chinese Jiufotang Formation. Ikrandraco – known from two specimens, found far apart – is certainly a neat looking beast, its most notable feature being a deep, semicircular crest on its lower jaw (there’s no crest on the snout, making the animal look wonderfully asymmetrical) (Wang et al. 2014b). It also has a great name: its mandibular crest reminded the authors of the lower jaw crest present in the Ikran creatures – the banshees – from the movie Avatar, hence the binomial (there’s a Tet Zoo Guide to the Creatures of Avatar, just sayin’).

What’s with the crest? Yes, you’ve guessed it... in keeping with the tradition of the pterosaur literature, the authors propose that Ikrandraco was a skim-feeder that somehow used its dentary crest to cut through the water (Wang et al. 2014b). To be fair, they do note that structures like the dentary crest might well have been multi-functional, that Ikrandraco lacks the unusual modifications present in Rynchops (the only habitual skim-feeder we know of), and that Ikrandraco was a sort of part-time, facultative skim-feeder, not a dedicated, full-time one. [Adjacent image by John Conway; available here.]

But, hoping that those familiar with the pterosaur literature will forgive me for what I’m about to say, I don’t think the skim-feeding hypothesis has much going for it.

For one thing, the crest is positioned a short distance away from the lower jaw’s tip, meaning that any prey item would be contacted by the jaw’s tip before the crest had made contact with the water containing the prey. Contrast this with the behaviour of Rynchops, where the blade-like lower jaw makes contact with prey items at the same time as it’s cutting through the water. Then there’s the fact that the mandibular crest of Ikrandraco possesses an unusual (and unique) hook-like structure at its posterior end, suggested by the authors to be the anchor of an enlarged mandibular pouch. Well, hold on: skim-feeding is tremendously difficult and inefficient, and it can only work when the animal is cleaving through the water as neatly as possible (Humphries et al. 2007). If Ikrandraco has a giant pouch of some sort right next to its crest, any imagined interaction between the crest and the water would presumably be messy, since the water displaced backwards by the skimming action is now going to be hitting the lower surface of the pouch.

To reiterate: what gives with these crests, then? We don’t really know why pterosaurs have these structures, and I’d certainly agree with the authors that a biomechanical role of some sort might be plausible, as might a role in sociosexual display. But skim-feeding is just so weird and problematic that I think people should be more reluctant to point to it as a possible explanation for the structures concerned. Apologies for going over all of this again (Tet Zoo regulars, or pterosaurophiles, will be pretty familiar with the skim-feeding hypothesis by now, and the problems always mentioned in connection with it).

Of course, the research discussed here hardly covers everything published on pterosaurs in 2014. Numerous other new species have been named, and numerous other interesting studies on palaeobiology, anatomy, functional morphology and lifestyle have been published too. But already this article is too long, and already there are so many other things to write about. Fear not, pterosaur fans; we will be visiting them again, soon enough.

There are now quite a few Tet Zoo articles on pterosaurs, so many that I'm now going to group them into subject areas...

Pterosaurs in general

Darwinopterus and other wukongopterids

Azhdarchoids

Pterosaurs in books and exhibitions

Refs - -

Averianov, A. 2014. Review of taxonomy, geographic distribution, and paleoenvironments of Azhdarchidae (Pterosauria). ZooKeys 432, 1-107.

Chinsamy, A., Codorniú, L. & Chiappe, L. M. 2009. Palaeobiological implications of the bone histology of Pterodaustro guinazui. Anatomical Record 292, 1462-1477.

Claessens, L. P. A. M., O’Connor, P. M. & Unwin, D. M. 2009. Respiratory evolution facilitated the origin of pterosaur flight and aerial gigantism. PLoS ONE 4 (2): e4497. doi:10.1371/journal.pone.0004497

Dyke, G. J., Vremir, M., Brusatte, S., Bever, G., Buffetaut, E., Chapman, S., Csiki-Sava, Z., Kellner, A. W. A., Martin, E., Naish, D., Norell, M., Ősi, A., Pinheiro, F. L., Prondvai, E., Rabi, M., Rodrigues, T., Steel, L., Tong, H., Vila Nova, B. C. & Witton, M. 2014. Thalassodromeus sebesensis-a new name for an old turtle. Comment on “Thalassodromeus sebesensis, an out of place and out of time Gondwanan tapejarid pterosaur”, Grellet-Tinner and Codrea. Gondwana Research doi: 10.1016/j.gr.2014.08.004

Grellet-Tinner, G. & Codrea, V. A. 2014. Thalassodromeus sebesensis, an out of place and out of time Gondwanan tapejarid pterosaur. Gondwana Research doi: 10.1016/j.gr.2014.06.002

Headden, J. A. & Campos, H. B. N. 2014. An unusual edentulous pterosaur from the Early Cretaceous Romualdo Formation of Brazil. Historical Biology doi: 10.1080/08912963.2014.904302

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.

Humphries, S., Bonser, R. H. C., Witton, M. P. & Martill, D. M. 2007. Did pterosaurs feed by skimming? Physical modelling and anatomical evaluation of an unusual feeding method. PLoS Biology 5, No. 8, e204 doi:10.1371/journal.pbio.0050204

Kellner, A. W. A. 2004. New information on the Tapejaridae (Pterosauria, Pterodactyloidea) and discussion of the relationships of this clade. Ameghiniana 41, 521-534.

Knell, R., Naish, D., Tomkins, J. L. & Hone, D. W. E. 2012. Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution 28, 38-47.

Lü, J., Unwin, D. M., Deeming, D. C., Jin, X., Liu, Y. & Ji, Q. 2010. An egg-adult association, gender, and reproduction in pterosaurs. Science 331, 321-324.

Manzig, P. C., Kellner, A. W. A., Weinschütz, L. C., Fragoso, C. E., Vega, C. S., Guimaräes, G. B., Godoy, L. C., Liccardo, A., Ricetti, J. H. Z. & de Moura, C. C. 2014. Discovery of a rare pterosaur bone bed in a Cretaceous desert with insights on ontogeny and behavior of flying reptiles. PLOS ONE 9(8): e100005. doi:10.1371/journal.pone.0100005

Martill, D. M. 2014. Which came first, the pterosaur or the egg? Current Biology 24, R615-617.

- . & Naish, D. 2006. Cranial crest development in the azhdarchoid pterosaur Tupuxuara, with a review of the genus and tapejarid monophyly. Palaeontology 49, 925-941.

Martin, E. G. & Palmer, C. 2014. Air space proportion in pterosaur limb bones using computed tomography and its implications for previous estimates of pneumaticity. PLoS ONE 9(5): e97159. doi:10.1371/journal.pone.0097159

Middleton, K. M. & English, L. T. 2014. Challenges and advances in the study of pterosaur flight. Canadian Journal of Zoology 92, 1-15.

Naish, D., Simpson, M. I. & Dyke, G. J. 2013. A new small-bodied azhdarchoid pterosaur from the Lower Cretaceous of England and its implications for pterosaur anatomy, diversity and phylogeny. PLoS ONE 8(3): e58451. doi:10.1371/journal.pone.0058451

Prondvai, E., Bodor, E. R. & Ösi, A. 2014. Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity. Paleobiology 40, 288-321.

- . & Stein, K. H. W. 2014. Medullary bone-like tissue in the mandibular symphyses of a pterosaur suggests non-reproductive significance. Scientific Reports 4: 6253 doi: 10.1038/srep06253

Ruxton, G. 2014. Avian-style respiration allowed gigantism in pterosaurs. The Journal of Experimental Biology 217, 2627-2628.

Unwin, D. M. 2005. The Pterosaurs from Deep Time. New York, Pi Press.

Wang, X., Kellner, A. W. A., Jiang, S., Wang, Q., Ma, Y., Paidoula, Y., Cheng, X., Rodrigues, T., Meng, X., Zhang, J., Li, N. & Zhou, Z. 2014a. Sexually dimorphic tridimensionally preserved pterosaurs and their eggs from China. Current Biology doi:10.1016/j.cub.2014.04.054

Wang, X., Rodrigues, T., Jiang, S., Cheng, X. & Kellner, A. W. A. 2014b. An Early Cretaceous pterosaur with an unusual mandibular crest from China and a potential novel feeding strategy. Scientific Reports 4, article number: 6329; doi:10.1038/srep06329

Witton, W. P. 2013. Pterosaurs. Princeton University Press, Princeton & London.

- . & Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE 3: e2271.

- . & Naish, D. 2013. Azhdarchid pterosaurs: water-trawling pelican mimics or “terrestrial stalkers”? Acta Palaeontologica Polonica doi: http://dx.doi.org/10.4202/app.00005.2013