Thursday, November 16, 2006

Those sexy tupuxuarids

Thanks to my good friend (and former phd supervisor) Dave Martill, I am finally in possession of my own copy of David Unwin’s 2006 book The Pterosaurs from Deep Time. It’s a handsome, well-illustrated and well-written book literally packed full of data. Given that there are only a handful of books devoted to pterosaurs (the only ones worthy of note are Seeley’s 1901 Dragons of the Air*, Wellnhofer’s 1991 The Illustrated Encyclopedia of Pterosaurs and Buffetaut & Mazin’s multi-authored 2004 Evolution and Palaeobiology of Pterosaurs), the appearance of any new volume on the subject is noteworthy. However, Unwin’s book gets more than an honorary mention: it deserves some serious bigging-up, if you’ll pardon the expression, as it is, frankly, excellent. But what’s odd is that, thus far, I’ve only seen two reviews of it. The first (posted to an internet discussion group) was negative, but its author is notorious for holding a deeply idiosyncratic view of pterosaurs that cannot be, and isn’t, taken seriously. The second, produced by two close acquaintances of mine, is not really negative, but it’s not particularly positive either [adjacent image by Mark Witton, from his flickr site].

* This book is often said to be rare and expensive. Maybe that’s true, but I got mine for £3 in a second-hand book shop.

Given this lamentable situation let me continue with the bigging-up. The Pterosaurs from Deep Time is not, as some have said, a coffee-table book. Yeah, it features some big and highly attractive pictures (both excellent photos of specimens, and colour artwork), but in its thorough coverage of what we know about pterosaur diversity, evolution, biology and lifestyle, it is unparalleled and awesome. If only books like this existed on all the tetrapod groups. Seriously, I am hard pressed to think of any detail about pterosaurs that Unwin has not covered. Todd Marshall’s artwork, scattered throughout the book, is great, with accurate, dynamic animals poised in realistically cluttered, detailed environments. I’ve collaborated with Todd (I advised him when he produced artwork for Usbornes 2004 World Atlas of Dinosaurs), and I get the impression that he works hard to make fossil animals look like long-time denizens of their environments. Think about it: living animals generally aren’t pristine objects, looking as if they’ve just come out of the pages of a field guide; they are often physically untidy, or dirty. Their colours and surface textures may mimic or even incorporate the sediments and plants of their environment. They often look like they belong. This is the feeling I get from Todd’s animals.

My technical work, back when I could consider myself a palaeontologist (right now I consider myself simply unemployed), was on theropod dinosaurs. But as with so much in life I kept finding myself distracted and spending time on extraneous side projects, and every now and again I’ve dabbled on pterosaurs (e.g., Naish & Martill 2003). During 2004 and 2005, Dave Martill and I spent a lot of time on an unusual Cretaceous pterosaur from Brazil called Tupuxuara. Inspired mostly by the discovery of a new specimen, our research culminated in the 2006 publication of our paper ‘Cranial crest development in the azhdarchoid pterosaur Tupuxuara, with a review of the genus and tapejarid monophyly’. Snappy title, no? There’s lots to say about Tupuxuara: on its phylogenetic relationships and taxonomy, on its feeding behaviour, and on the changes that it underwent during growth. Let’s see how much of this I can get out of the way in what will eventually turn out to be several blog posts.

First described for a partial snout from the Brazilian Santana Formation, Tupuxuara longicristatus Kellner & Campos, 1988 is a toothless Cretaceous pterosaur with a rather long, subtriangular skull. A tall mid-line crest grew like a sail from the dorsal margin of the snout and cranium. It now seems that nearly all of the characters proposed initially to distinguish Tupuxuara from other pterodactyloid pterosaurs are problematic in not being unique to the genus, but in fact Tupuxuara is clearly diagnosable, being unique in having a sort of deep premaxillary crest in which the dorsal margin extends subparallel to the dorsal margin of the nasoantorbital fenestra (Martill & Naish 2006, p. 931). While Tupuxuara is known today from near-complete skeletons (frustratingly, these specimens still await proper description), the good thing about this diagnosis is that it applies even to the 1988 type material.

A second Tupuxuara species, T. leonardii Kellner & Campos, 1994, is also from the Santana Formation and, curiously, was also represented initially only by an incomplete section of snout. A few other tupuxuarid specimens have been reported. A specimen named Santanadactylus spixi Wellnhofer, 1985 is almost certainly a close relative of Tupuxuara (possibly even a member of the genus), despite the fact that it was named as a new species of an ornithocheirid genus (ornithocheirids are long-skulled toothed pterodactyloids closely related to Pteranodon and Nyctosaurus, and not particularly closely related to azhdarchoids). Various taxonomically indeterminate Crato Formation specimens also seem referable to the group. Then there is Thalassodromeus sethi Kellner & Campos, 2002, also from the Santana Formation of Brazil. Thalassodromeus is, supposedly, distinct from Tupuxuara, but this is debatable. More on this issue another time [adjacent Tupuxuara skull image from the pterosaurier site].

Finally, a pterosaur snout and lower jaw from the late Maastrichtian Javelina Formation of Texas, illustrated in Wellnhofer’s Illustrated Encyclopedia of Pterosaurs and labelled therein as Quetzalcoatlus, also seems to be a tupuxuarid and possesses a snout morphology highly similar to that regarded as diagnostic for Tupuxuara. This is really interesting for a few reasons. It shows that tuxupuarids existed in North America as well as South America, and also shows that they survived until late in the Cretaceous. Virtually all Maastrichtian pterosaurs are azhdarchids and it is implied by some that this was the only pterosaur group to make it to this time. If the Javelina Formation specimen really is a tupuxuarid, it indicates that at least one other pterodactyloid clade survived this late.

What sort of pterosaur is Tupuxuara? Based mostly on characteristic features of the skull and hand, there is universal agreement among pterosaur experts that Tupuxuara is an azhdarchoid: that is, a close relatives of the azhdarchids – those large to enormous long-necked pterodactyloids that, I argue, most likely lived a stork-like lifestyle. But, among azhdarchoids, is Tupuxuara particularly close to azhdarchids, or is it actually more closely related to the bizarre, shorter-skulled Tapejara? Here we come to a fundamental disagreement among pterosaur experts.

Pointing to similarities in the shape of the orbit, snout tip and crest, and the anatomy of the coracoid, Alex Kellner (2003a, b, 2004) has argued that Tapejara and Tupuxuara should be united as the Tapejaridae. Conversely, noting derived characters in the hand and skull seen in Tupuxuara and azhdarchids but not in Tapejara, Unwin (2003) has proposed that Tupuxuara forms a clade with the azhdarchids (dubbed Neoazhdarchia), rather than one with Tapejara. Several recently described azhdarchoids complicate this area. Sinopterus and Huaxiapterus, both with two species each (all from the Lower Cretaceous of China), appear intermediate in some respects between Tapejara and azhdarchids, and the supposed Tapejara species T. navigans is also more like azhdarchids in some details than it is like the type species of Tapejara, T. wellnhoferi.

In a new evaluation of the characters employed in this debate, Dave and I concluded that the concept of Neoazhdarchia is better supported than the idea of a Tapejaridae that includes Tupuxuara (Martill & Naish 2006). Note, however, that our cladistic analysis is weak with a small data set. Furthermore, while we didn’t find Tupuxuara to group together with Tapejara, we did sometimes find Tapejara to group together with Sinopterus. While Kellner’s concept of Tapejaridae may be paraphyletic, it therefore seems that there is a clade that we should call Tapejaridae: it includes Tapejara wellnhoferi, Sinopterus and Huaxiapterus. A subsequent study came to the same conclusion (Lü et al. 2006).

What I found particularly interesting is that we didn’t find the several Tapejara species to group together, but this isn’t surprising given how distinct they are. The type species, T. wellnhoferi, is relatively short-skulled and with a modest bony crest and just a short bony projection at the skull’s rear margin. T. imperator and T. navigans, in contrast, are longer-skulled, with immense vertical crests, supported by thin subvertical spines at their leading edges. A really long bony spike projects backwards from the skull’s rear margin in T. imperator. A study due to be published soon revises the taxonomy of these supposed close relatives: more news on that when it appears [adjacent image shows T. imperator. Yet again borrowed from Mark Wittons flickr site. Sorry Mark].

And I’ll have to stop there. Given that the main point of Martill & Naish (2006) was to document ontogenetic changes that occurred in Tupuxuara – changes linked to the probable use of the cranial crest as a sexual signal – it’s ironic that I haven’t covered this story here, but I will in future. And, as I said, there’s also the debate about tupuxuarid feeding biology and so on. And don’t worry if you’re hoping to see more on phorusrhacids – I haven’t finished with them yet. Stuff on British dinosaurs coming soon. Oh yeah – pdfs of both Naish & Martill (2003) and Martill & Naish (2006) are available, feel free to ask and I can send them.

For previous posts on pterosaurs see Pterosaur wings and Why azhdarchids were giant storks. Posts on tupuxuarids have been promised for a while: see Attack of the blue foamy pterosaurs. For those interested, we are now at 33 ‘100 year European mammals. For the latest news on Tetrapod Zoology do go here.

Refs - -

Kellner, A. W. A. 2003a. 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.

- . 2003b. Comments on the phylogeny of the Pterodactyloidea. Rivista del Museo Civico di Scienze Naturali “Enrico Caffi” 22, 31-37.

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

Lü, J., Jin, X., Unwin, D. M., Zhao, L., Azuma, Y. & Ji, Q. 2006. A new species of Huaxiapterus (Pterosauria: Pterodactyloidea) from the Lower Cretaceous of western Liaoning, China with comments on the systematics of tapejarid pterosaurs. Acta Geologica Sinica 80, 315-326.

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

Naish, D. & Martill, D. M. 2003. Pterosaurs – a successful invasion of prehistoric skies. Biologist 50 (5), 213-216.

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.

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8 Comments:

Blogger Steve Bodio said...

ALL pterosaurs are sexy. More please!

Good links folks...

3:57 AM  
Anonymous Dave Hone, Munich said...

Darren,

There are a few reviews out there in book land! I've written two reviews for Unwin's book - one for the PalAss newsletter with Gareth Dyke and now one for the Times Higher Education Supplement.

There has also been a very odd one on PalArch by Veldmeijer (he seems to think its primary literature aimed at researchers), plus a couple by Martill and Peters on Amazo that are worth reading....

9:11 AM  
Blogger Darren Naish said...

Thanks Dave: I'd seen the Amazon 'reviews' (they're not really reviews are they - more like off-the-cuff comments) but had missed the others.

How exactly does one get to do book reviews for the Times Higher?

12:41 PM  
Anonymous Dave Hone, Munich said...

Darren,

Well Peters' review on Amazon is at least 'interesting'!

I got to do the THES by e-mailing them and asking. It was luck really, Unwin was disappointed that there had been no 'academic' reviews so asked me to hawk around. I e-mailed THES and it turned out that they had been waiting for someone to do it. They also wanted Mark Norell's "Unearthing the Dragon" done (from the same publishers) and as I was off to China that sealed the deal.

Those reviews are in this weeks issue (dated 15th) if anyone cares. So thre you go - ask and ye might just receive....

Dave

1:13 PM  
Anonymous Mark Lees said...

I concur that 'The Pterosaurs from Deep Time'is an excellent book, both informative and a thoroughly enjoyable read.

It is some months since I read it so I dont recall the details, but there were some points I disagreed with, but nonetheless enjoyed reading Unwin's coverage of the topics.

I am particularly intrigued by the evidence of indeterminate growth in pterosaurs and the fact that they actually grew significantly after 'fledging' (or whatever the correct word is to describe the equivalent for pterosaurs!).

In general birds (except flightless ones) achieve adult size rapidly. Even forms that take several years to attain sexual maturity (such as raptors and larger gulls) tend to be close to adult size when they fledge. The reason appears fairly straightforward, changing dimensions of the flight apparatus (not just the wings, but all the associated 'stuff') poses a real danger of compromising flying efficiency.

So why did it seem to work for pterosaurs? Did it constrain the options of design available to them? It appears to me that pterosaurs did not expoit as wide a range of ways of flying as do birds - perhaps their indeterminate growth pattern and therefore on going changes in flight dimensions rendered some forms of flight unavailable to them. This is entirely speculative, I like to see someone who understands flight mechanics explore this area.

Completely different matter: the elephant scenes on Planet Earth last week may have been noteworthy, but chimpanzees hunting and eating other chimpanzees this week was something new to me.

1:25 PM  
Blogger Darren Naish said...

Response to Mark's last comment: when Jane Goodall reported the cannibalism practised by Passion, one of the Gombe National Park chimps (Goodall 1977), it was first thought to be some kind of psychotic behaviour. While it makes sense to kill the juveniles of competing chimp groups - and chimps frequently 'wage war' on neighbouring communities (presumably in an effort to defend resources) - the cannibalism that occurs within groups is far more difficult to interpret. Some have argued that it is a 'sensible' extension of infanticide (Nishida et al. 1979), but this is problematical for several reasons. I'll stop there.

On the Planet Earth sequence, I initially thought they were going to show a torture scene. That's right: when a chimp troop captures an individual from a troop they are at 'war' with, they do what we would regard as torture.

Refs - -

Goodall, J. 1977. Infant-killing and cannibalism in free-living chimpanzees. Folia Primatologica 28, 259–282.

Nishida, T., Uehara, S. & Nyundo, R. 1979. Predatory behavior among wild chimpanzees of the mahale mountains. Primates 20, 1-20.

6:07 PM  
Anonymous Dave Hone said...

Back to pterosaurs for Mark. They certainly show less variation in wing dimensions and proportions than do birds. Its actually abbout the same degree as in bats (though of course with a very different shape & structure).

Given the flying ability of adult pterosaurs of all sizes, it wold make sense that juveniles are more or less scaled-down adults and therefore would be capable of flight. Of course there is also some circumstantial evidence and good reasoning to suggest that even pterosaur hatchlings could fly.

7:09 PM  
Blogger skeeler said...

On the strength of your recommendation, I ordered The Pterosaurs from Deep Time. It seems very informative but still accessible to a non-paleontologist such as myself. I'm enjoying it quite a bit.

8:38 PM  

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