Sunday, October 17, 2010

Dr. Witton dismisses more evidence for the existence of giant pterosaurs in the Lower Cretaceous


I really liked my English Literature teachers at school. They were extremely laid back, personable folks who treated us like adults, which is a big deal when you’re 16 years old. They encouraged individuality in our interpretations of books and, indeed, my experience with them had me seriously considering teaching English if this palaeontology lark went nowhere. They even bought us books at the end of our A’ Levels that they thought matched our personalities: I got Joseph Conrad’s Heart of Darkness - make of that what you will.

Unfortunately, they didn’t have the easiest ride when teaching me as I used to wind them up without end. Not, you understand, by drawing inflated phalluses on my exercise book, or by never handing assignments in, talking in class or constantly underachieving: no, I was routinely criticised for making them laugh with my essays. Apparently, nicknaming Hamlet ‘Hammy’ wasn’t standard practise and, so I hear, nine essays out of ten did not compare the cast of Volpone to characters from Only Fools and Horses. Likewise, passages in The Handmaid’s Tale weren’t often compared favourably to lyrics from Eurythmics numbers and, generally speaking, calling The Great Gatsby’s Tom Buchanan a douche wasn’t the done thing. Thing is, none of my teachers had any problems with what I was saying, but the way that I expressed myself was just not on. ‘Don’t write like this’, my teachers told me time and again, ‘your examiners won’t appreciate it’. This confused me as a 16 year old and still does now. Do exam markers have no sense of humour? I’ve yet to meet someone who marks GCSE’s and A’ Levels, but, from this, I imagine they must resemble the enjoyment-hating Blue Meanies from The Yellow Submarine, stamping out positivity with rocket-propelled gloves, clown-controlled explosives and apple-lobbing men in top hats. At least, I hope they do: it’s a much more interesting picture than a bunch of sour-faced miseries sitting in grey office cubicles, angrily scribbling over exam copy books in red pen.

Nowadays, the only scribing I do with intentional dryness is for scientific papers (and even this has been described as too florid by some referees). It produces a strange, sub-schizophrenic feeling when writing and reading it, almost like the ‘Witton’ character cited in other papers isn’t really me: he’s some faceless, professional authority on pterosaurs, someone working in a studious, clean office and certainly not writing papers crashed out on his sofa with repeats of Top Gear on the TV and holes in his socks. But no, these people are one and the same and, to prove it, this post features some suitably dry text I had rejected from a chapter I’m coauthoring on Wealden Supergroup pterosaurs with Dave Martill and Steve Sweetman. For those who don’t know, the Wealden Supergroup is a historically significant series of Lower Cretaceous deposits found across southern England and is one of Europe’s top sites for terrestrial vertebrates of this time. The text evaluates claims that some Wealden pterosaur material represents pterosaurs of gigantic proportions and, because it’s hardly significant enough to warrant its own paper and we discussed other claims for gigantic pterosaurs in the Lower Cretaceous several weeks back, it seems like ideal fodder for the Pterosaur.Net blog. Before it starts, though, it’s worth pointing out that if these and my previous musings on these topics are correct, giant (say, 7 m spans and above) are an exclusively Upper Cretaceous phenomenon. OK? Great. Without further ado, then, I hand you over to my concise, authoritative sounding alter ego, Dr. Witton. If anyone needs me, I’ll be in the lounge watching TV and playing with my feet.

Giant pterosaurs in the Wealden Supergroup?


Martill et al. (1996) and Howse et al. (2001) reported on several bone fragments from the Wessex Formation that allegedly revealed the presence of giant pterosaurs – possibly rivalling the 10 – 11 m wingspans of the largest known forms (Langston 1981) - amongst the Isle of Wight assemblage. The most pertinent of these fragments were a poorly preserved distal humerus (ICWMS 1995.631; 75 mm wide, A and B in the adjacent image [from Martill et al. 1996]) and a fragment of proximal first(?) wing phalanx (ICWMS 1995.629; 53 mm minimum width,C and D in the adjacent image) that, although fragmentary, are the largest articular ends of any pterosaur long bones yet reported from the Wealden.

The identity of these bones as giant pterosaurs is questionable, however. Both Martill et al. (1996) or Howse et al. (2001) report the allegedly giant remains as those of indeterminate pterosaurs, but the distal profile of ICWMS 1995.631 corresponds well with the distal humeri of ornithocheiroids (Hooley 1913; Wellnhofer 1985; Kellner and Tomida 2000) and is almost certainly a member of this clade. Accordingly, greater constraint can be placed on its size than previously realised. ICWMS 1995.631 is 17 per cent wider than the (63 mm) distal width of the Istiodactylus humerus reported by Hooley (1913; BMNH R706) but only 5 per cent wider than the same dimension (71 mm) reported for Anhanguera by Kellner and Tomida (2000; NSM-PV 19892). It is also substantially smaller than that of a large Pteranodon (102 mm; Bennett 2001; YPM 1175). The wingspans of these forms can be relatively well constrained at 5 m in the former cases and between 6 – 7 m for the latter. The transverse dimensions of these bones will not equate to proportional increases in humeral length either as pterosaur long bone articulations increase with positive allometry compared to length (for a good graphic example, compare the 5 and 10 -11 m span Quetzalcoatlus humeri figured by Wellnhofer [1991], p. 141). Thus, ICWMS 1995.631 would be negligably longer than the Istiodactylus and Anhanguera humeri mentioned above, suggesting it too was around 5 m in wingspan. It represents, therefore, a relatively large ornithocheirid but a ‘medium’ sized pterosaur overall.

The size of the individual represented by the possible first wing phalanx ICWMS 1995.629 is harder to determine as the specimen itself is hard to identify. Although the thinness of the bone wall indicates it is a pterodactyloid bone, the specimen lacks any features of note bar the expansion of one end and an oval cross section. Such attributes could apply to several pterosaur long bones: the distal half of the humerus, either end of the radius or ulna or the proximal wing metacarpal but, crucially, do not apply to the proximal phalanx of the wing finger. In at least some pterosaurs, these bones have cross sections that resemble rounded triangles, not ovals (Wellnhofer 1985). The identity of ICWMS 1995.629 as a giant pterosaur is dependent on its identification as a proximal wing phalanx as, if it represents another of the elements listed above, its proportions are unremarkable. With an identity as a proximal wing phalanx doubtful, its status as a pterosaurian giant is also unlikely.

Thus, there is no evidence that the Wealden Supergroup contained pterosaurs of particularly gigantic size. While the 5 m span Wealden forms are much larger than any modern flying animals, their wingspans are quite typical of Lower Cretaceous forms and much smaller than the true giants that would evolve later in the Cretaceous.

References

  • Bennett, S. C. 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Palaeontographica Abteilung A, 260, 1-153.
  • Hooley, R. W. 1913. On the skeleton of Ornithodesmus latidens; an Ornithosaur from the Wealden Shales of Atherfield (Isle of Wight). Quarterly Journal of the Geological Society, 96, 372-422.
  • Howse, S. C. B., Milner, A. R. and Martill, D. M. 2001. Pterosaurs. In: Martill, D. M. and Naish, D. (eds.), Dinosaurs of the Isle of Wight. Palaeontological Association, Field Guide to Fossils 10, pp. 324-335.
  • Kellner, A. W. A. and Tomida., Y. 2000. Description of a new species of Anhangueridae (Pterodactyloidea) with comments on the pterosaur fauna from the Santana Formation (Aptian -Albian), Northeastern Brazil. National Science Museum, Tokyo, Monographs, 17, 1-135.
  • Langston, W. Jr. 1981. Pterosaurs. Scientific American, 244, 92-102.
  • Martill, D. M., Frey, E., Green, M. and Green, M. E. 1996. Giant pterosaurs from the Lower Cretaceous of the Isle of Wight, UK. Neues Jahrbuch fur Geologie und Pal√§ontologie, Monatshefte, 1996, 672-683.
  • Wellnhofer, P. 1985. Neue pterosaurier aus der Santana-Formation (Apt) der Chapada do Araripe, Brasilien. Palaeontographica. Abteilung A, 187, 105-182.
  • Wellnhofer, P. 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander Books Ltd., London. 192 pp.

3 comments:

  1. Why on earth was this cogent critique rejected from the manuscript?

    ReplyDelete
  2. The MS in question is a PalAss field guide, and their treatment of vertebrates is somewhat confused (e.g. ultra-detailed, like Dinosaurs of the Isle of wight, or far more generalised, like Fossils of the Chalk). I figured we were going for a more detailed approach, but apparently not.

    ReplyDelete
  3. I don't know what you're on about about those bones being hard to identify. Just from the photo alone I can positively identify them all as coming from Chunkodactylus.

    Hey! Someone has to be the peanut gallery here.

    Mike from Ottawa

    ReplyDelete