TMM 42489-2: the hypersonic überbass slide-loading pterosaur you have to leave on the shelf at Currys

We’ve got a little stereo in our kitchen that keeps us entertained when we’re cooking. It’s getting on a bit, though: it doesn’t always read CDs, songs begin skipping at the most inopportune moments and the speakers occasionally fail, requiring Fonzie-esque thumbs to reignite. While the latter undeniably draws respect from your male friends and makes the ladies swoon, having Mick Jagger develop the most irritating and incurable stutter when you’re busy straining pasta or removing hot dishes from the oven is starting to get a little irritating. Hence, last weekend, I went shopping for a replacement. While the internet is undeniably the place to buy things cheaply, there’s still something to be said for looking at your intended purchases in person and taking the demonstration models for a test drive. Problem is, the same time that you’re swayed by the bass levels, swish CD-loading motion and flashing lights of your desired rig is the same time that you notice that it’s two or three times what you can afford and, realistically, your shop floor experience with that stereo is the closest you’ll ever get to bringing hypersonic überbass slide-loading musiconica to your culinary experiences.

There are some pterosaur fossil specimens that seem similarly out of reach. They’re the ones that you see briefly when visiting museums, get sent a photograph of or see mentioned, briefly, in the literature. Should you make enquiries into their status, you’re very often told that someone else is researching them and, in true gentlemanly fashion, they’re to be left alone to pursue their studies to their conclusion. Other times, they’re just left alone because no-one is interested in them for the time being: this can be said of the ‘Painten Pelican’, a bizarre ctenochasmatoid on display in the Solnhofen Museum of Germany that appears to have something to do with Cycnorhamphus. It’s a seriously kick-ass, beautifully-preserved specimen of a gorgeous animal and I’d give my left arm to work on it, but until someone looks at it, it’s doing little else than sitting behind a glass panel. On occasion, interesting specimens are put up for sale online: recently, this shady process threw up a new Santana Formation pterosaur that, though Dave Martill pointed out to me that parts of this were fabricated, is almost certainly a new azhdarchoid taxon. One of the famous ‘KJ’ nyctosaurs (you know: the antler-crested ones described by Bennett [2003]) appeared on Ebay not too many weeks ago, too: both specimens, to my knowledge, have now disappeared off the radar completely. In all cases, these specimens are things that you can only pretend to play with at best: you can look at the pictures, infer what you can with very limited data and imagine what you could do with it should you be able to bring it home.


This brings us neatly to TMM 42489-2, or, as some of you may know it, the huge anterior skull and mandible fragment that Wellnhofer (1991) referred to Quetzalcoatlus on page 144 of his encyclopaedia (see image, above, drawn from the same photograph. Scale bar represents 100 mm). As we’ll see, it’s a dead exciting specimen but very little information about this specimen has been made public. It stems from the lower part of the Javelina Formation, the same Texan, latest Cretaceous sedimentological stomping ground as Quetzalcoatlus (Kellner 2004). It clearly belonged to a very large animal: although incomplete, the specimen is a good 800 mm long and around 350 mm tall: it’s entirely reasonable to think the entire skull was at least a metre in length when complete. Unlike many pterosaurs, it doesn’t bear a rostral headcrest but does bear a particularly expansive nasoantorbital fenestra. The rostrum itself is quite stubby and the upper jaw was quite deep, a condition that contrasts with the shallow lower jaw and the especially slender mandibular rami. Apparently, some cervical vertebrae (TMM 42489-1) were associated with this specimen, but little has been said of these other than that they were relatively shorter than those of Quetzalcoatlus (Kellner and Langston 1996). John Sibbick’s oft-copied reconstruction of Quetzalcoatlus in Wellnhofer (1991) took the morphology of TMM 42489-2 into account and gave his Quetz. a snub-nose. Thing is, the referral of TMM 4289-2 to Quetzalcoatlus is plain wrong: the skull material of Q. sp. was described by Kellner and Langston (1996) and while sharing the same generally crestless, pointy-tipped morphology, Q. sp. has a rostrum that is incredibly long – something like seven times longer than tall (see reconstruction of Q. sp, below, from Witton and Naish 2008. Scale bar represents 100 mm). Snub-nosed TMM 42489-2 is clearly not Quetzalcoatlus then, but we shouldn’t leave it there. Even the tiny experience we have with the specimen from Wellnhofer’s photograph shows that it must be something new for the Javelina Formation at least, but what is it?


Using the same photograph to form their opinions, several authors have had a stab at identifying TMM 42489-2. Everyone is happy that it represents an azhdarchoid: the combination of a large nasoantorbital fenestra and toothless jaws is not yet known from any other pterosaur group. Lű et al. (2006) noted similarities in the mandibular morphology and that of the azhdarchid Bakonydraco (Ősi et al. 2005), suggesting it would be represent a different type of Javelina azhdarchid. Slightly more exciting suggestsions were made by Kellner (2004), who suggested it was a late-surviving Tupuxuara-like tapejarid*. Martill and Naish (2006) agreed (in sorts), referring to it as the ‘Javelina Formation Tupuxuara’. These suggestions are potentially quite significant: latest Cretaceous pterosaur assemblages are almost entirely dominated by azhdarchids and, if TMM 42489-2 is a non-azhdarchid azhdarchoid, it means the end-Cretaceous pterosaur show was just a little richer than previously thought. It’s also noteworthy that, in recent years, another group of straight-jawed azhdarchoids, the chaoyangopterids, has been discovered (e.g. Lű et al. 2008) and may provide another potential taxonomic stable for the specimen: again, the existence of this group in the Late Cretaceous would be significant. Clearly, then, TMM 42489-2 could be of considerable importance for those trying to understand pterosaur evolutionary history, so what is it?

*The content of Tapejaridae is controversial with two broad schemes doing the rounds. Tapejaridae sensu Kellner (e.g. Kellner 2003, 2004; Kellner and Campos 2007) includes the short-faced, bent-jawed tapejarids (Tapejarinae) and bony sail crested forms Tupuxuara and Thalassodromeus (Thalassodrominae), whereas Tapejaridae sensu Unwin (e.g. Unwin 2003; Lű et al. 2008) is restricted to the short-faced, bent jawed forms. Tupuxuara and Thalassodromeus (forming Thalassodromidae – see Witton 2009) are grouped with other straight-jawed azhdarhchoids, chaoyangopterids and azhdarchids in Neoazhdarchia. This latter scheme is my preferred arrangement, but we don’t really have time to go into why here. That's not to say that we won't at a later date, though.

I looked into the affinities of TMM 42489-2 a little for my PhD when overhauling thalassodromid taxonomy (Witton 2008) but, unfortunately, found you can't really say much with absolute certainty: one image and brief descriptions of this specimen don’t really give much to work with. The mandible, in my view, is quite similar to most neoazhdarchian mandibles but not really identical to any. They’re all slender with shallow mandibular symphyses and, yes, while it does resemble that of Bakonydraco more than anything else, the Bakonydraco mandible doesn’t really look like the mandibles of other azhdarchids (e.g. Kellner and Langston 1996). Hence, this is only of limited use in figuring out exactly what TMM 42489-2 is. Likewise, the observation that the associated cervicals are shorter than those of Quetzalcoatlus doesn’t help much: Friday afternoon maths lessons were shorter than some azhdarchid vertebrae and, crucially, the longest and characteristically ‘azhdarchid’ vertebrae are only seen in the middle of the neck: proximal and distal vertebrae are comparatively stunted and complex (Pereda Suberbiola et al. 2003; Witton and Naish 2008). In this respect, they resemble the somewhat elongated cervical vertebrae of chaoyangopterids and, at the moment, I’m a little perplexed as to how to distinguish between the two: I wouldn’t be surprised if some azhdarchid occurrences represented solely by isolated cervicals are overturned once a way to distinguish the two groups are known. For the time being, though, it looks like the cervicals associated with TMM 42489-2 can provide little help on identifying the rostrum itself – and especially since there’s so little information available on them.

Comparison between posterodorsal and posteroventral extensions of azhdarchoid premaxillae. A, Tupuxuara; B, Thalassodromeus; C, Zhejiangopterus; D, Quetzalcoatlus; E, Shenzhoupterus; F, Jidapterus; G, Chaoyangopterus; H, TMM 43489-2. Vectors of measurments of premaxillary extensions are shown with black lines and values of posterodorsal extension height compared to ventral are given next to each rostrum. From Witton (2008).

We are reliant, therefore, on rostral morphology alone to identify TMM 42489-2. Thankfully, there may be just enough data here to do the job. It appears that neoazhdarchians can be roughly diagnosed by attributes of their rostra when viewed in lateral profile through looking at the morphology and size ratio of the upper and lower bars encompassing the nasoantorbital fenesta (see image, above), the shape of the dorsal rostral margin and the slenderness of the rostrum itself (Martill and Naish 2006; Witton 2008). Thalassodromids have straight or convex dorsal rostral margins, comparatively tall upper premaxillary bars that extend posterodorsally in sub-parallel fashion and short, deep rostra; chaoyangopterids have very slender but also sub-parallel upper premaxillary bars, concave dorsal margins and short rostra, while azhdarchids have upper premaxillary bars that are much deeper than the lower distally but rapidly taper proximally, straight dorsal margins and extremely long rostra. TMM 42489-2 doesn’t meet any of these exactly but does come close: aside from the long rostrum, it’s ticks all the boxes for an azhdarchid rostrum with its straight dorsal margin and tapering upper premaxillary bar. While the rostral biometrics do undoubtedly resemble those of thalassodromids more than azhdarchids, it’s notable that the azhdarchid Bakonydraco has an usually short, wide mandible: the skull of this form is unknown, but, assuming it has a similar width/length ratio to the lower jaw, it should also have a short rostrum unless its skull morphology differs dramatically from those of other azhdarchoids. Likewise, the poorly-known but wide-skulled azhdarchid Hatzegopteryx presumably had a short rostrum or, if proportioned like better known azhdarchid skulls, would’ve had a most unwieldy 5 m long jaw (Buffetaut et al. 2002, 2003).

Based on the little evidence we have, then, TMM 42489-2 can be tentatively interpreted as a new type of snub-nosed azhdarchid. If this is correct, TMM 42489-2 may not be quite as exciting as when it was considered a late-surviving thalassodromid as proposed by Kellner (2004) or Martill and Naish (2006), but it does provide some enrichment of the uppermost Cretaceous pterosaur scene by demonstrating significant morphological variation between azhdarchids. The differences in snout morphology will have some implications on feeding habits and dietary preferences, and these hints of ecological differentiation may explain how azhdarchids managed to be so abundant and successful. Plus, it’s made that little more exciting by being quite big - a 5 m wingspan seems quite reasonable for an azhdrchid with a 1 m long skull - and it almost certainly represents a new taxon, being readily distinguished from all other toothless pterosaurs through the shape of its rostrum. Can we do anything about all this, though? Can we heck: until the specimen is properly described and figured, it would be foolish to make it the focus of any study or attach a name to it. Until someone studies TMM 42489-2 properly then, it remains the pterosaur equivalent of an electronic store demonstration model: full of buzz, promise and excitement, but something that you can't really do anything with until you're ready to make the investment. Or someone else invests in it for you, which would be great.

References

• Bennett, S. C. 2003. New crested specimens of the Late Cretaceous pterosaur Nyctosaurus. Palaeontologische Zeitschrift, 77, 61-75.
• Buffetaut, E., Grigorescu, D. and Csiki, Z. 2002. A new giant pterosaur with a robust skull from the latest Cretaceous of Romania. Naturwissenschaften, 89, 180-184.
• Buffetaut, E., Grigorescu, D. and Csiki, Z. 2003. Giant azhdarchid pterosaurs from the terminal Cretaceous of Transylvania (western Romania). In: Buffetaut, E. and Mazin, J. M. (eds.) Evolution and Palaeobiology of Pterosaurs, Geological Society Special Publication, 217, 91-104.
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• Kellner, A. W. A. and Campos, D. A. 2007. Short note on the ingroup relationships of the Tapejaridae (Pterosauria, Pterodactyloidea). Boletim do Museu Nacional, Nova Séroe, Rio de Janeiro - Brasil. Geologia, 75, 1-14.
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• Pereda Suberbiola, X., Bardet, N., Jouve, S., Iarochéne, M., Bouya, B. and Amaghzaz, M. 2003. A new azhdarchid pterosaur from the Late Cretaceous phosphates of Morocco. In: Buffetaut, E. and Mazin, J. M. (eds.) Evolution and Palaeobiology of Pterosaurs, Geological Society Special Publication, 217, 79-90.
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• Witton, M. P. 2009. A new species of Tupuxuara (Thalassodromidae, Azhdarchoidea) from the Lower Cretaceous Santana Formation of Brazil, with a note on the nomenclature of Thalassodromidae. Cretaceous Research, 30, 1293-1300.
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