It’s summer blockbuster season at the cinema. This year, we’ve already had another superhero flick, a new Terminator doing the rounds at the moment, giant transforming robots hot on his heels, and an angsty teenage wizard following behind that. Depending on your point of view, this is either the best time of the year to visit the silver screen or good reason to stay outside and work on your suntan. For me, it’s got to be the latter: sure, I loved the blockbusters of my day: Ghostbusters II, Independence Day and Jurassic Park stand out as memorable cinema trips from yesteryear, but, even though the same people are still making the movies, I’ve grown out of them. The Jurassic Park guys had a heavy hand in the new Indiana Jones movie, and it was crap. Likewise, the Independence Day boys have filled our screens with several unadulterated pieces of tripe, Godzilla, The Day After Tomorrow and 10,000 BC. I figured that it was them doing something wrong, that they’d lost some of their magic in the way that musicians can loose their spark over time. Unfortunately, I checked: their old movies are just as bad, it’s just that I’m no longer a puppydog that laps up any onscreen action as long as the movie as plenty of roary-roary creatures and some lasers.
Nowadays, being a whole week and a bit from 25, I’d rather watch a movie based on Chekov than Clancy, or be confused by Lynch than bored by Bruckheimer. The difference is the emphasis on scale: I don’t need big set pieces, action and devious plots to overthrow the world as we know it to be entertained: I just need two people in a complicated relationship, perhaps an edge of surrealism, and I’m very happy. I want to be emotionally challenged: I’ve seen enough celluloid explosions already, now I want to see real life. Give me longing and desire, or explore the brevity of happiness. Show brooding revenge and darkness, or people struggling with their own salvation. Instead of chases involving gruff men in black cars, I want people running away from their pasts. This is the stuff that makes for a rewarding film. American Beauty or, say, Mulholland Drive may be stories set within a narrow space and feature only a handful of players, but they offer a reward that just can’t be paralleled by any globe-trotting, high-octane thrill-seeking adventure with dozens of characters.
The same can be said for your world of pterosaur research*. There well over 100 pterosaur species now known and you can make a good name for yourself by studying the whole lot of them at once. Work on, I don’t know, an epic comparison of flight styles or some sweeping study of their systematics. Tell the world that everything they thought they knew about one aspect of pterosaur palaeobiology, mass estimation, say, is wrong, or reveal a finding from one critter that has implications for the whole clan. Alternatively, you could be really, really specific and work on just a few species at once. This is also kind of cool, because you become a total expert on that one little clique: you know everything of note that’s ever been said about them, and can spout streams of information to anyone foolish enough to ask. While this doesn’t really put you in excellent stead for conversation at parties, it does mean that you begin to feel a real affinity for your little corner of the Big Picture and you can tell the Big Boys doing the grand, epic work things that they just haven’t had time to notice.
*Yes, yes, I know: flimsiest link ever.
This brings us neatly to one little group of pterosaurs, Thalassodromidae. They’re the sexy-looking pterosaurs with stonking sail-like headcrests made entirely from bone and, for the moment, we only know of two genera: Tupuxuara and Thalassodromeus. They both come from the Cretaceous Santana Formation of Brazil and, to date, there’s no conclusive evidence that they existed anywhere else. There are some pterosaur arm bones from Europe and Texas that could be thalassodromid, but they could also be something else. Regular readers, if I’ve got any left after such a long posting hiatus (I have good reasons, honest) will recognise them as reasonable regulars of this corner of cyberspace: they appeared yonks ago in my first-ever press release image (the consequences of which are another reason for my lack of posting – fair number of folks after original artwork, these days) and then appearing several more times, most notably in the ‘down with skim-feeding’ press work of 2007. They were also a focal point of my PhD, as I not only discussed their feeding habits through research into skim-feeding, but also looked at virtually ever aspect of their taxonomy. Turns out, y’see, that the thalassodromid story is far more complicated than you might expect, full of enough twists, turns and heightened emotions to fill a period drama. Here's why.
Firstly, their name: Thalassodromidae. Not much can be controversial about a name, right? Well, there’s been some disagreement about whether the group should be christened this or another moniker, Tupuxuaridae. No one’s actually come to blows over this yet, but different teams of authors have firmly stuck to one name or the other. While you may imagine that there’s no real issue with using different names for the same group, it defies the weighty International Commision of Zoological Nomenclature, the institution that has governed the naming of animals since 1895. These chaps state that you cannot name the same animal, or the same group of animals, more than once. This is sensible enough, especially when you’re trying to write specifically and scientifically, and both Tupuxuaridae and Thalassodromidae are exactly the same thing, so there should only be one name. Thankfully, the ICZN provides guidelines to suss this sort of thing out, and, typically, the earliest name wins out. This would make Tupuxuaridae the winner, as this was first coined in 2006. However, it was only mentioned in passing as part of a discussion over pterosaur phylogeny and, in fact, it was almost certainly an error: the authors of the paper were paraphrasing another set of authors who mentioned tupuxuarids, not the formalised term Tupuxuaridae. Is this a big deal? In the eyes of the ICZN, yes: their code explicitly states that names need to be erected explicitly, and the casual naming of the group in the 2006 doesn’t cut this gravy. Or mustard. Whatever, the important thing is that Thalassodromidae, despite appearing a year later (2007) was erected explicitly, and therefore takes priority.
So, now we know what to call them, then, but what are they? There’s no disagreement that they belong to Azhdarchoidea, the same pterosaur group as the short-faced tapejarids, stork-amatic azhdarchids and slender-skulled chaoyangopterids, but which one of these groups are they most closely related to? This argument has been raging since at least 2003, with some authors saying their crest structure ropes them to Tapejaridae, while others argue that other aspects of their skulls and skeletons tie them to azhdarchids and chaoyangopterids in a group termed Neoazhdarchia. The jury is perhaps still out on this, but I think the weight of evidence places thalassodromids in Neoazhdarchia: all pterosaurs in this group have long, straight jaws with shallow mandibles, relatively long snouts in front of their nasoantorbital fenestra (that big hole positioned in front of the skull in pterodactyloid pterosaurs), eye sockets significantly positioned below the top of the same opening, straight or concave margins along the top of their snouts and a fused shoulder region (the notarium). Several features have also been used to lump thalassodromids with tapejarids, but the only remaining valid character of this pairing is that their headcrests start at the front of the skull. Compared to the number of characters that suggest the contrary, this is argument is pretty weak and, for my money, nowhere near as well supported as the Neoazhdarchia hypothesis.
OK, so we’ve got a name, and a good indication where they fit on the pterosaur tree, but how many thalassodromids are there? We've already mentioned the two genera of the group, Tupuxuara and Thalassodromeus, but how many species were there? Well, more than most have suggested, in my view. Circa 2002, we recognised two species of Tupuxuara and single speceis in it's sister genus, Thalassodromeus. Then, the controversy wand was waved again and it was suggested that all these taxa represented different ages of one Tupuxuara species. This has since been proven not be the case, and we’re back to at least three species again. At least? Yes, at least: there’s two Tupuxuara skulls with unusually reclined crania, particularly low orbits and angular, diamond-shaped nasoantorbital openings. These features aren’t known in any other Tupuxuara material, suggesting these skulls may represent a third Tupuxuara species. Problem is, one Tupuxuara species is only represented by rostral remains, and these elements are unknown in the two Tupuxuara skulls with peculiar crania. Hence, the two morphologies cannot be compared and we’re left wondering if we’ve got three or four thalassodromid morphs in the same locality. Sheesh.
So, thalassodromids are clearly a taxonomic minefield, with disagreements over just about every aspect of their systematics. Do details of their palaeoecology fare any better? Well, not really. My Portsmouth chums published a paper a few years back about growth in thalassodromid headcrests, noting from an immature specimen that the top-portion of the crest appears to grow along the skull as the animal aged, suggesting only fully-developed adults would sport the full flamboyance of a thalassodromid headcrest. This isn’t the fist time such a finding has been made, of course: we know that at least some other pterosaurs underwent similar growth patterns, and thalassodromids seem pretty typical in this regard. Even this finding is tinged with a caveat, though: the specimen that showed this growth strategy, identified as Tupuxuara by my buddies, is very probably a piece of Thalassodromeus. D’oh.
And then, of course, there’s the skim-feeding stuff. Thalassodromeus, y’see, was meant to be the Pterosaur Skim-Feeder Extraordinaire, and it’s descriptors were so confident of it’s proposed feeding habits that they named it, accordingly, ‘sea-runner’. It’s no secret that I think this is hokum, but I’m not going to write out why again: it will suffice to say that biomechanical modelling and comparative anatomy have clearly demonstrated the total lack of substance behind the proposed skim-feeding habits of Thalassodromeus and all other pterosaurs, for that matter (and yet, bizarrely, it still crops up from time-to-time in the technical literature).Unfortunately, there has been no further investigation into exactly what thalassodromids did do for a living, but some loose conclusions can be drawn from their skeletal bauplan. Like other azhdarchoids, their wings are relatively short and, bearing a relatively low aspect ratio, would’ve been handy for flight in terrestrial settings (what with the high lift such wings produce, not to mention the fact that their stunted ends will clip less vegetation). Their hindlimbs are pretty typically developed for non-ornithocheiroid pterodactyloids, meaning they were probably quite comfortable when milling about terrestrially. The neck of Tupuxuara is pretty short but otherwise strong and flexible: it bears no indications of dip-feeding, but it presumably didn’t place as many lifestyle-restrictions on its owner as the necks of azhdarchids probably did. Thalassodromid skulls show some variation: the Tupuxuara skull is quite slender and delicately-built with flat occlusal surfaces at the jaw tip, whereas the skull of Thalassodromeus is pretty durned chunky and has laterally tapered, superficially scissor-like jaw tips. Presumably, this reflects niche partitioning between these contemporary genera, with Thalassodromeus perhaps capable of taking relatively big prey compared to the delicately-built Tupuxuara. In fact, I’ll bet that the bladed jaws of Thalassodromeus were quite a limiting factor on prey size: while they would increase bite pressure along the occlusal margins, bladed jaws might make handling small foodstuffs awkward – imagine substituting chopsticks for two knife edges and you’ll see where I’m coming from. There’s nothing noted in their skeletons to suggest a preference for any type of prey however, so we may provisionally conclude that thalassodromids were generalists that ate anything from fish through to small dinosaurs. However, seeing as excellently, excellently preserved, complete thalassodromid skeletons are still sitting on museum shelves awaiting description, we may eventually be able to pin down their habits more specifically when more details of their anatomy are known.
And that, dear friends, may be all we can sum-up about thalassodromids for the time being. Like a Gore Verbinski movie, it's been a tale of frustration and convolution and there’s clearly some way to go before all the loose ends are wrapped up. However, the point here, I suppose, is that so much drama has been got out of so few species from one point on the map, and that sorting out these relatively minor controversies can be just as rewarding as figuring out some enormous, pan-palaeontological issue.
And, speaking of very focused views, there’s a profile up top of the aforementioned Tupuxuara with a strange skull, complete with a frog dangling from its mouth. It’s not the most exciting contribution to my portfolio and, what with the lighting and all, you can only just see the low orbit and reclined crania. Oh well: at least it’s something new and, hey, I’ve never seen a pterosaur depicted in lateroventral view before. And that’s important. Like recycling.
And on that note, I’m starting to yawn with alarming regularity and should shove off to bed. Before I go, though: apologies to all those who've tried to contact me with no success in the last few months: I'm not deliberately being rude or lazy, just a bit swamped. Accordingly, this leaves me a bit knackered most of the time, just like now. Hence, with the Sandman a callin', toodleoo for now.