March 18, 2013 | 29
We’ve named another new pterosaur! Once again, the open-access online journal PLOS ONE hosts a paper that I and colleagues (Martin Simpson and Gareth Dyke, both of the University of Southampton) have published on a new taxon (Naish et al. 2013). This is the third paper I’ve published in PLOS ONE so far this year, and – ha ha – it’s only March. It’s also the second published contribution this year from our research group that focuses on Azhdarchoidea. This is the toothless, Cretaceous pterodactyloid clade that includes the sometimes small, short-snouted tapejarids, the larger, sail-crested thalassodromids, and the sometimes gigantic, long-snouted azhdarchids. The other paper was on the Romanian azhdarchid Eurazhdarcho langendorfensis (Vremir et al. 2013), covered here on Tet Zoo just a few weeks ago.
The new pterosaur is named Vectidraco daisymorrisae and it’s yet another new species from the Cretaceous rocks of the Isle of Wight in southern England. The name Vectidraco is not especially clever but means ‘dragon from the Isle of Wight’.
The species name honours Daisy Morris, the Isle of Wight girl who discovered the only known specimen. Overall, then, the name can be imagined as meaning ‘Daisy Morris’s Isle of Wight dragon’. Daisy – an avid natural historian and collector of bones, taxiderm specimens, fossils and such – was just 4 years old when she made the find back in November 2008.
I’m always dismayed by the length of time it takes to get technical papers written up, completed, and published. The review process can be interminable (let me make it clear that, on this occasion, it most certainly was not), but just finding the time to complete a technical project itself is an ordeal, especially when you lack funding and time and are over-loaded with other commitments. Anyway, we got there in the end. Daisy and her family did what I and most of my colleagues would regard as “the right thing”. They wanted to see the specimen written up properly and stored in an appropriate collection, so they donated it to The Natural History Museum, London (where it’s now accessioned as NHMUK PV R36621).
Vectidraco: when and where?
Vectidraco is not, unfortunately, based on anything like a complete skeleton. It’s a small but well preserved pelvis, just 40 mm long, that includes several of the associated vertebrae but no part of the prepubic bones. Nearly all of the sutures in the specimen are fully closed (one neurocentral suture and one intercentral suture are not), so we think that the specimen is a near-adult: close to, or at, skeletally mature size for this taxon (Naish et al. 2013).
If you’re wondering, I do not think that pterodactyloid pterosaurs grew continuously: instead, it seems that they reached a given adult size and stopped growing. While on that subject, note that indeterminate growth is certainly not as widespread in reptiles as people used to think. We now know that determinate growth is present in turtles, squamates and crocodylians, and it seems to have been widespread in dinosaurs.
As discussed below, we also think that Vectidraco is an azhdarchoid, and probably a non-neoazhdarchian azhdarchoid (see the cladogram below for help) similar to the tapejarids. Our reconstructions here work on the not unreasonable assumption that Vectidraco was either tapejarid-like, or what you might expect for an azhdarchoid that was potentially ancestral to both tapejarids and neoazhdarchians. Based on the proportions of tapejarids (some of which are known from excellent remains), Vectidraco most likely had a wingspan of about 75 cm and a total length (snout to tail-tip) of 35 cm or so (Naish et al. 2013). As such, it’s the smallest azhdarchoid yet reported (excluding Nemicolopterus, which I’m pretty sure is a juvenile Sinopterus).
Cretaceous Isle of Wight fossils tend to be from the famous Wealden Supergroup – the Isle of Wight crocodyliforms, dinosaurs and plesiosaurs that I’ve worked on previously (Hutt et al. 2001, Naish et al. 2004, Benson et al. 2009, 2013, Naish 2011, Salisbury & Naish 2011) are all from this unit – but Vectidraco is from a younger and less well known unit called the Atherfield Clay Formation. Martin is a world authority on the Atherfield Clay and was able to identify the matrix on the specimen as that of a specific section – it’s called the Chale Clay Member – of the Atherfield Clay Formation (Naish et al. 2013). An excellent ammonite record allows the divisions of the Atherfield Clay to be dated quite precisely, and the Chale Clay Member is Early Aptian and thus about 124 million years old (Lehmann et al. 2009).
Various anatomical details led us to identify Vectidraco as a member of the pterodactyloid clade Azhdarchoidea (an identification supported by the cladistic analyses we performed: read on). Regular Tet Zoo readers may know that, due to several lines of evidence, I regard azhdarchoids as pterosaurs of inland, terrestrial environments like floodplains, forests and tropical woodlands (Witton & Naish 2008, Vremir et al. 2013).
However, the Chale Clay Member is a marine unit, deposited under shallow shelf conditions. Does this tell us anything reliable about the palaeobiology of Vectidraco? Was it – for example – a marine azhdarchoid? That’s certainly not impossible, even if the majority of other azhdarchoid lineages were denizens of inland environments. As is well known, however, the remains of terrestrial animals frequently end up in marine sediments, so discoveries like this often don’t mean much, if anything.
Location-wise, Vectidraco was discovered in a landslip at Atherfield on the island’s south-west coast. This is really close to the classic ‘Tie Pits’ locality, well known as the source of the goniopholidid Anteophthalmosuchus hooleyi (originally described as a new specimen of Goniopholis, but renamed by Steve Salisbury and myself during 2011) and the iguanodontian Mantellisaurus atherfieldensis (originally described as a new species of Iguanodon). These fossils, however, are from the older Vectis Formation of the Wealden Supergroup.
From the global perspective, the presence of Vectidraco in the Atherfield Clay Formation is interesting, since it’s only the second pterosaur to ever be reported from this unit. The other one is a jaw fragment, listed in a table by Unwin et al. (2000) and identified by them as belonging to Ornithocheirus. Actually, a few ornithocheirid teeth have been found in the Atherfield Clay Formation more recently: I think our paper (Naish et al. 2013) is the first time they’ve been mentioned in print. For now, the Atherfield Clay pterosaur fauna therefore includes both large ornithocheirids and the small azhdarchoid Vectidraco.
Vectidraco: detailed anatomy, weirdness, pneumaticity
The detailed anatomy of Vectidraco forms part of the focus of our paper (Naish et al. 2013) and anyone seriously interested in the details should, of course, go there. Distinctive features include the long, rod-like preactabular process (a prong that points forwards from the front, upper part of the ilium), the giant, superficially T-shaped postacetabular processes (a structure that projects backwards and upwards from the rear upper part of the ilium), the depth of the pelvis ventral to the acetabulum, and the opening present between the pubis and ischium.
That last feature (the opening between the pubis and ischium) is peculiar since it looks a lot like the structure (termed the thyroid fenestra) normally absent in pterosaurs. Its presence in Vectidraco (and some other pterosaurs) must be assumed to be a reversal, though the fact that some pterosaurs posses it when juvenile and close it during adulthood also suggests the possibility that we’re seeing an expression of paedomorphosis. And that’s something that I’ll have to come back to at another time, since there are suggestions from elsewhere in pterosaur evolution and anatomy that paedomorphosis played a role in the evolution of pterodactyloids.
The weird, T-shaped post-acetabular process on the ilium is especially interesting. Quite why some pterodactyloids had these processes remains unknown, though Hyder et al. (2012) made the worthy suggestion that they anchored enlarged hindlimb retractor muscles and perhaps correlated with a strong degree of terrestriality (cf. Witton & Naish 2008). Unlike reptiles with long, muscular tails, pterodactyloids started their history with proportionally short, flimsy ones, so perhaps the post-acetabular process represents a novel solution to the need for enlarged hindlimb muscles (Hyder et al. 2012).
I’m also really intrigued by the fact that there are deep, distinct fossae (concavities) on both the medial and lateral sides of the structure. Bony fossae in archosaurs are often pneumatic so… could these be pneumatic fossae? We already know that the pelvis was pneumatic in at least some pterodactyloid pterosaurs (Claessens et al. 2009), but our suggestion that the post-acetabular processes might be pneumatic is novel (so far as I know).
Similar fossae are seen in other pterosaurs, including in Tapejara and the Oker dsungaripterid (an animal that definitely needs a distinct taxonomic moniker but, strangely, wasn’t given one by its describer). In Tapejara the large, oval-shaped, medial fossa is subdivided by vertical partitions (Eck et al. 2011): this reminds me very much of the sort of thing you sometimes see in the pneumatic fossae of saurischian dinosaurs. Even better, Vectidraco‘s honeycomb-like arrangement of bony walls on the anterior part of the medial side clinches it, I think: the various fossae and internal cavities here were indeed pneumatic (Naish et al. 2013). At least some azhdarchoids, then, had pneumatized bone in this part of this pelvis. This is new information and it’s something that surely has some bearing on the palaeobiology of these animals.
The pterosaur pelvis and the pterosaur tree
Everyone who’s ever written about pterosaur skeletal anatomy has drawn attention to the fact that pterosaur pelves differ substantially in form. This isn’t exactly surprising given the variation present across the group (despite occasional inferences from some pterosaur specialists that pterosaurs are all pretty much the same as soon as you get beyond the skull). In fact there’s a noble tradition in the pterosaur literature whereby pterosaur researchers have published diagrams that feature the pelves of different taxa alongside one another (see Naish et al. (2013) for the full list).
Most recently, this diversity in pelvic form was discussed by Elaine Hyder and colleagues: like our team, they were interested in establishing the phylogenetic affinities of an isolated pterodactyloid pelvis (an azhdarchoid specimen from the Brazilian Crato Formation) and set about surveying pelvic diversity across the whole of Pterosauria (Hyder et al. 2012). That study could be seen as a forerunner to the Vectidraco one – it certainly proved useful as a source of data – but I have to emphasise that it didn’t appear until some time after our work on Vectidraco was well underway.
We wanted to know if the variation seen across the pterosaur pelvis was in any way concordant with our general understanding of pterosaur phylogeny. Hyder et al. (2012) were interested in this too, but only went as far as matching pelvic morphologies to different cladograms. We did the next logical thing and compiled and ran a cladistic analysis of characters from the pelvis alone (after compiling those pelvic characters, we also added them to an existing data set and ran that as well) (Naish et al. 2013).
The results are fairly encouraging, but not thrillingly so. Basically, a pelvis-only phylogenetic analysis generates a trees that has some similarities with the total-evidence tree produced by different research groups, but resolution is very poor and (in the strict consensus tree, anyway) many taxa that really should group together failed to do so (Naish et al. 2013). It would seem, however, that azhdarchoids are especially ‘obvious’ in pelvic anatomy, since one of the few clusters obviously present in the tree consists of azhdarchoid taxa (Vectidraco included). Takehome: there is some phylogenetic signal in the pelvis, but it’s weak and you need data from elsewhere in the skeleton to get a half-decent tree. Things could be improved, perhaps, if we included more specimens.
A ‘total-evidence’ tree – based on the dataset used by on Wang et al. (2012) – has far better resolution. Vectidraco was again recovered as an azhdarchoid, though Azhdarchoidea pretty much consisted of a polytomy in this instance. My gut feeling is that Vectidraco is not a member of Neoazhdarchia (the azhdarchoid clade that includes thalassodromids and azhdarchids), so ideally it should group close to, or with, tapejarids.
On the whole issue of pterosaur phylogenies, it’s difficult not to bring attention to a problem we have at the moment: the fact that published phylogenies of pterosaurs are disparate in several aspects, and (in my opinion) not nearly comprehensive enough in terms of how much character data they include. In fact, two of the best known, ‘go to’ phylogenetic studies of Pterosauria include, respectively, just 74 and 60 characters (Kellner 2003, Unwin 2003). Do these numbers really reflect the amount of information we should be incorporating in our analyses? Well, consider that those two analyses include, respectively, precisely ZERO characters from the pelvis. Several other studies have also failed to use a single pelvic character, while there are others that have used a massive 1, or even 3, characters.
Look again at the images of pterosaur pelves above. I don’t think you need to know anything in particular about pterosaurs, or about pelves, to realise that there are clearly quite a few characters here that are variable across the group and hence potentially codeable and worthy of inclusion in phylogenetic analyses. We identified 23 characters of the prepubis, pelvis and sacral vertebrae that came in discrete states and hence could be coded (Naish et al. 2013): I’m not sure that all of these will stand the test of time, but it’s a start. We’re working on expanding and improving all of this stuff as part of a larger study of pterodactyloids.
Western Europe vs China: so similar, yet why so different?
I said somewhat earlier that Vectidraco is from the early Aptian, and that it comes from a geological unit (the Atherfield Clay Formation) that also yields ornithocheirid fossils. Which other sorts of pterosaurs were present in early Aptian western Europe? Actually, not that many: only the long-jawed Prejanopterus curvirostra from La Rioja in Spain and Istiodactylus latidens from the Isle of Wight are from the western European record of this time (Naish et al. 2013).
However, Aptian pterosaurs are fairly well represented elsewhere, being known from the Yixian and Jiufotang formation of China and also from various other Chinese, Mongolian and Russian strata. What kinds of pterosaurs are represented by these fossils? Essentially, we see similar assemblages of lineages to what’s present in western Europe at the same time. That’s all very well and good, but a major difference between the western European fauna and that of China is that the latter region is home to a far, far greater number of species and specimens. Why?
Part of the reason comes from the fact that the Chinese assemblage is – in the opinion of at least some pterosaur workers, myself included – horrendously over-split, with several or many of the ‘species’ actually being individuals or growth variants of other species. However, other factors are at play here too, and an important one that I think deserves discussion concerns the different environmental and depositional settings of these different areas.
While “the Yixian and Jiufotang formation are dominated by fine-grained lacustrine deposits, interspersed by volcanic sediments that resulted in mass death assemblages and the rapid burial of small vertebrate carcasses” (Naish et al. 2013, p. 7), “western European deposits of coeval age (e.g. the sediments of the Wealden Supergroup) are typically dominated by floodplain and estuarine depositional settings where vertebrate remains were typically broken apart, scattered and scavenged before the more resistant parts were incorporated into the sediment record” (Naish et al. 2013, p. 7).
The end result is a Chinese record where small theropod, pterosaur, mammaliaform, squamate and lissamphibian skeletons are preserved in large numbers and in complete or near-complete fashion; meanwhile, western European members of the same groups are represented by odd bones belonging to just one or two individuals. Exhibit A: compare Vectidraco to the many Chinese specimens of Sinopterus and Huaxiapterus. Another example: compare the Ashdown maniraptoran (Naish & Sweetman 2011) with all those Chinese oviraptorosaurs and paravians!
In short, we’re seeing a strongly biased fossil record in Europe where small tetrapods are poorly preserved and, mostly, probably not preserved at all.
Vectidraco is certainly not an especially significant or game-changing fossil; it’s merely a small, nicely preserved specimen that allows the recognition of an interesting new taxon. But in terms of the new information it provides on detailed anatomy and pterosaur distribution in time and space, I think it’s a very worthy addition to our understanding of this group. Continuing work will build on various of the hypotheses and conclusions we present in our paper, and we hope that future discoveries in the Atherfield Clay will bring more of ‘Daisy’s dragon’ to light!
A popular book on the story of Daisy’s pterosaur – written by Martin Simpson and including copious original artwork by Mark Witton no less – has just been published but I don’t yet have information on it (will add a link as soon as it’s available).
For previous Tet Zoo articles on azhdarchoids and other pterosaurs, see…
And for articles on various of the other Cretaceous animals mentioned here, see…
Refs – -
Benson, R. B. J., Brusatte, S. L., Hutt, S. & Naish, D. 2009. A new large basal tetanuran (Dinosauria: Theropoda) from the Wessex Formation (Barremian) of the Isle of Wight, England. Journal of Vertebrate Paleontology 29, 612-615. [free pdf]
Benson, R. B. J., Ketchum, H. F., Naish, D. & Turner, L. E. 2012. A new leptocleidid (Sauropterygia, Plesiosauria) from the Vectis Formation (Early Barremian-early Aptian; Early Cretaceous) of the Isle of Wight and the evolution of Leptocleididae, a controversial clade. Journal of Systematic Palaeontology DOI: 10.1080/14772019.2011.634444 [free pdf]
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
Eck, K., Elgin, R. A., Frey, E. 2011. On the osteology of Tapejara wellnhoferi Kellner 1989 and the first occurrence of a multiple specimen assemblage from the Santana Formation, Araripe Basin, NE-Brazil. Swiss Journal of Palaeontology 130, 277-296.
Hutt, S., Naish, D., Martill, D. M., Barker, M. J. & Newbery, P. 2001. A preliminary account of a new tyrannosauroid theropod from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research 22, 227-242. [free pdf]
Kellner, A. W. A. 2003. Pterosaur phylogeny and comments on the evolutionary history of the group. In Buffetaut, E. & Mazin, J.-M. (eds) Evolution and Palaeobiology of Pterosaurs. Geological Society Special Publication 217. The Geological Society of London, pp. 105-137.
Lehmann, J., Heldt, M., Bachmann, M. & Hedi Negra, M. E. 2009. Aptian (Lower Cretaceous) biostratigraphy and cephalopods from north central Tunisia. Cretaceous Research 30, 895-910.
Naish, D. 2011. Theropod dinosaurs. In Batten, D. J. (ed.) English Wealden Fossils. The Palaeontological Association (London), pp. 526-559.
- ., Martill, D. M., Cooper, D. & Stevens, K. A. 2004. Europe’s largest dinosaur? A giant brachiosaurid cervical vertebra from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research 25, 787-795. [free pdf]
- ., 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
- . & Sweetman, S. C. 2011. A tiny maniraptoran dinosaur in the Lower Cretaceous Hastings Group: evidence from a new vertebrate-bearing locality in south-east England. Cretaceous Research 32, 464-471. [free pdf]
Salisbury, S. W. & Naish, D. 2011. Crocodilians. In Batten, D. J. (ed.) English Wealden Fossils. The Palaeontological Association (London), pp. 305-369.
Unwin, D. M. 2003. On the phylogeny and evolutionary history of pterosaurs. In Buffetaut, E. & Mazin, J.-M. (eds) Evolution and Palaeobiology of Pterosaurs. Geological Society Special Publication 217. The Geological Society of London, pp. 139-190.
- ., Lü, J. & Bakhurina, N. N. 2000. On the systematic and stratigraphic significance of pterosaurs from the Lower Cretaceous Yixian Formation (Jehol Group) of Liaoning, China. Mitteilungen aus dem Museum für Naturkunde in Berlin, Geowissenschaftliche Reihe 3, 181-206.
Vremir, M., Kellner, A. W. A., Naish. D. & Dyke, G. J. 2013. A new azhdarchid pterosaur from the Late Cretaceous of the Transylvanian Basin, Romania: implications for azhdarchid diversity and distribution. PLoS ONE 8(1): e54268. doi:10.1371/journal.pone.0054268
Wang, X., Kellner, A. W. A., Shunxing, J. & Xin, C. 2012. New toothed flying reptile from Asia: close similarities between early Cretaceous pterosaur faunas from China and Brazil. Naturwissenschaften 99, 249–257.