Archive for May, 2011

Sauropod necks – what were they for?

Long time readers might well recall that for a few years I was a volunteer at London Zoo where I worked on what was the Cotton Terraces (now sadly rebranded as the “Africa Zone”) with various hoofstock and ungulates. It was, generally, an absolute joy and I learned a great deal about animal management and animals in general. Among my occasional charges were the giraffe and I have a long and abiding affection for them from my time there. This has in part manifested itself by my keeping up with giraffe research in the literature and when an opportunity arose to write about giraffes and dinosaurs, well, I could hardly resist.

So what do giraffes and dinosaurs have in common? Well not much to be honest, but perhaps inevitably the long necks of giraffe have been brought up a number of times in the past as analogues for the long necks of sauropods. It’s not unreasonable really as good analogues are important for inferring the functions and behaviours of extinct taxa and there are very few terrestrial long-necked herbivores out there, and even less that look even vaguely like sauropods. So the high reach of giraffes has been used to suggest sauropods reached high into the trees to feed.

Male giraffe sparring at Beijing zoo.

Set against this background has more recently been the controversy over sauropod neck postures and quite how much (or even if) they could raise their heads and necks. But it gets more complicated still (yay!). Back in the mid 1990s it was suggested that actually giraffe necks hadn’t evolved for feeding high in trees, but instead were sexually selected structures. Perhaps not surprisingly, the same hypothesis was then extended onto sauropods too! If they couldn’t raise their necks up, and the only obvious living example (in giraffes) was only an opportunistically high browser, then maybe sauropod necks were the result of sexual selection too? (Mike Taylor has a preview of these ideas here).

In a new paper out today myself and the SV-POW! boys (Messers [or rather, Doctors] Taylor, Wedel and Naish) take on this idea. The detail is of course in the paper but there are several interlinked threads to this paper that affect different lines of sauropod research and ecology. Perhaps most interestingly for me is the work on giraffes though, since actually the idea of sexual selection in these beautiful artiodactyls is far weaker than originally proposed and actually high browsing does seem to be the primary function of the neck.

Sauropod neck lengths. From Taylor et al. in press

Thus the original analogy can be restored and the analogy for sauropods having sexually selected necks rather falls by the wayside. Couple that with the existing work by my colleagues on the potential vertical reach of sauropods and another barrier falls by the wayside. Even if sauropods couldn’t reach high into trees though, that’s not necessarily a barrier to their long necks being adapted for feeding efficiency. Anyone who as seen a grazing goose will recognise their feeding pattern with the body of the bird only plodding along slowly but the long neck sweeping from side to side so that for every step forward (a big deal of effort for a 50 ton sauropod say) a fair area of new grass can be covered by the head. In short, a long neck can be efficient whether you are reaching up or not.

All together (and there is obviously more to this than I’m covering briefly here) we find no convincing evidence of sexual selection going on in sauropod necks and are satisfied that the long necks would have provided a significant horizontal and vertical reach and thus did afford a significant part of their feeding ecology. There’s no good evidence (at the moment, at least) that any sauropod necks were under sexual selection or indeed, that those of giraffes were. That doesn’t mean it wasn’t happening, but there is nothing to suggest it was.

This must, of course be hedged with a couple of most important and basic caveats to these kinds of papers. Critically is that of multifunctionality – that structures can have more than one function, so there could be some cryptic sexual selection ongoing alongside feeding advantages. Though as it happens in this case, it’s this very issue that helps us deal with some of the evidence for sexual selection. Secondly of course this paper is a review – we talk about general patterns and trends and evidence. We do not look at all sauropods in great detail and while we have great confidence in the findings of our paper we are talking about generalities – there is of course a reasonable chance that something was an exception.

Taylor, M.T., Hone, D.W.E., Wedel, M.J. & Naish, D. The long necks of sauropods did not evolve primarily through sexual selection. Journal of Zoology, in press.

A little link round-up

One of those occasional posts where I round up a few things that probably aren’t worth a post alone, but are worth putting out there.

I’ll being with self-interest and this large article in the Guardian on a variety of Chinese-dinosaur related topics. This covers the latest discoveries from Zhucheng, the work of Xu Xing, Chinese dinosaurs in general and Zhuchengtyrannus.

While we’re on the subject of journalism, here is a frankly terrifying catalogue of misinformation and, well, what can only be blatant falsehoods, perpetuated by a single journalist. Ah the joys of accurate science writing.

Next, there is this really very long essay on the current problems in science education, specifically the lack of jobs for postdocs and young researchers and the shift away from senior positions. Much of the later half is more applicable to the US than the UK or Europe, but many of the fundamental problems (not enough jobs, more money coming from industry etc.) are universal or very similar.

Finally, with the ongoing budget cuts and the general lack of funding in UK science (and combined with the problems above) means that museums are very vulnerable. Even huge, important and venerable institutions are losing jobs. So if you have the inclination, drop over here and sign up to help save them.

Wing decay

This is a photo from last summer’s fieldwork in Xinjiang in western China and it makes rather a nice point about taphonomy and preservation. Obviously the preservation of feathers is a rather important aspect of dinosaur palaeontology so an understanding of how they act in living (well, dead) birds is a great source of data for us. As noted in the past, feathers can and do both articulate and even attach to the bones of both birds and dinosaurs and this can be seen in a few fossils and very clearly in living taxa.

You can see this rather well here. Whatever bird these wings came from is long gone, as has the skin and muscles, but the feathers, while a bit tatty, are still there. Not only are they still there, but they’re also still articulated on the bones in a pretty natural position. So feathers are structures that are remarkably resistant to decay and resistant to moving from their natural positions. This of course tells us two things about fossils.

First this tells us that we can reasonably assume that fossils like Microraptor maintain their feathers in a natural position when fossilised. Even in such a heavily weathered and battered specimen like the one shown here the wing feathers at least suck it all up without any real trouble. So a near complete and articulated specimen with all manner of small feathers etc. in situ really is about as natural as you can reasonably expect.

Secondly, this also explains why you often get fossils with feathers and not much else in the way of soft tissues. Things like muscles and skin are exceptionally rare as specimens (as indeed are other things like pterosaur wings or amphibian gills) and even in the kinds of localities that preserve such things, feathers are still more common. Look at Archaeopteryx for example – several specimens have beautiful arrays of feathers but no other soft tissues at all – not even necessarily good claws or bits of cartilage which are pretty robust as non-bony things go. Well that’s not quite true as most of the feathers preserved in these are as impressions, though some original bits remain, though this is very much true of various Liaoning specimens for example.

Still this does show you what can be learned from just a few scraps of dead animal lying in the dirt. Obviously what I’m talking about here is based on papers published on the subject of bird decay, but this lone bit of bird is a good example of how this goes and what it can tell us about fossils 150 million years in the ground.

Finding the fliers – pterosaur discoveries

Having spent a couple of posts talking dinosaur discovery rates, it seemed worth musing for a few lines on the same phenomenon with regards to pterosaurs. As noted, new pterosaurs are being discovered at only about a quarter of the rate of new dinosaurs, though given that there are far fewer pterosaur than dinosaur researchers and the overall greater rarity of pterosaurs, this in fact probably represents an overall relatively higher rate of pterosaur discovery even if the absolute numbers are lower. That is already quite significant to my pterosaur-centric mind and belies the pterosaur revolution we seem to be undergoing.

On a slightly cloudier note, the ongoing controversy and problematic taxonomy of a number of groups or genera does mean that it’s likely that a number of these new taxa will be sunk back into obscurity. While obviously this is the fate of some taxa in all groups, to my eye the pterosaurs to tend to do a bit worse in this area that do say the dinosaurs. Still, when just a few years ago Dave Unwin surmised there were only around 110 valid pterosaur genera after nearly 200 years of research, the fact that we have been able to add around 20 more in the last three years alone is stunning. Next year might well provide a bumper harvest too with the next Flugsaurier volume due.

While they’re never going to get the same attention as dinosaurs, the last decade for pterosaur research really does point to a quiet revolution. We have more active researchers now than ever before (and by a fair margin) and we seem to be drawing in more attention from other workers (that is, there are quite a few dinosaur and archosaur guys who dabble with pterosaurs when in the past they wouldn’t have done so) and we’re getting together regularly too and producing whole volumes of papers. We’re seeing not just a huge increase in the numbers of new genera, but even entire new clades like the boreopterids and chaoyangopterids, unexpected late surviving toothed taxa, and of course Darwinopterus makes quite a difference. There are also major increases in our knowledge of older taxa – there are lots more anuroganthids and azhdarchids than a few years back, and other discoveries are adding massively to our knowledge. You’d struggle to find even a handful of really good specimens with soft tissues a decade ago but now we are positively blessed, and we now have 4 pterosaur eggs (and three of them with embryos) when before 2004 we had none.

At the risk of a little hyperbole, I really think we are in the midst of something special happening with pterosaurs and I genuinely think that in a few decades we will look back at the time between around 2000 and 2020 as the time when we really got to grips with these taxa and much of our knowledge settled into a familiar pattern. There will of course be more surprises and changes to our ideas, but this is very probably the beginning of a new age of pterosaur science and their renaissance (which dinosaurs had in the 80s and 90s) is begun.

Discovery rates

I talked yesterday about the rate of discovery for dinosaurs and the almost overwhelming mass on new taxa that are constantly appearing. While this is inherently important, what’s more interesting is what this can (or rather cannot) tell us about the total number of dinosaur species that might be out there. In short, 175-ish years since dinosaurs first started being found and recognised as such there has been no real sign of discoveries slowing down and in fact the rate looks to be picking up. With new and important localities in Australia, Argentina and Asia looking very profitable, this might accelerate still further. Even allowing for synonymy we are obviously getting quite a lot of new dinosaurs right now.

In the past people have attempted to predict the total number of dinosaur species that might be out there to be recovered (and obviously that;s not the same as how many there were – not all of them would have entered the fossil record or be identifiable). However, this rather relies on knowing how the discovery rate is changing and also it might change in the future. The rate of discovery of species of all kinds (both living and fossil) follow pretty similar patterns (as shown here rather well on Tet Zoo). They start slow, then shift into an exponential phase and eventually as researchers get near the limit of species to be found, this tails off and flattens out as it takes more and more work to find fewer and fewer species.

The thing is, as long as you are in the exponential phase of discovery, it’s impossible to tell when then tail off is going to be hit. It could be in a couple of years, or it could continue for decades. For the moment, all we can say is that it’s still going up, fast, and with no tail off in sight, we can expect these kinds of discoveries to keep coming. It’ll be some time yet before we can start to think about knowing just how many dinosaurs are out there to add to our taxonomic list.

Dinosaur discoveries

The other day I was shamelessly self-googling Zhuchengtyrannus to keep an eye on how it was spreading through the web. I’ve been surprised at the longevity the story has had and the fact that (admittedly increasingly short and obscure) reports and blog posts are appearing.  One thing that did crop up was the appearance of ZT on a Wikipedia list of new dinosaurs for 2011. While of course this includes various things that are still ‘in press’, it’s only just hit May and already we are at some 26 new genera, and 2010 apparently produced 61 with another 44 from 2009. We are then averaging around 1 a week or even more for new dinosaurs (and by the way, about 1 a month for pterosaurs too). That is really quite something to keep up with and I freely admit that I really struggle.

There are already well over a thousand valid dinosaur genera and about 150 for pterosaurs and I certainly can’t remember all of them, let alone add another half dozen per month. (And don’t forget that of course there are hundreds more invalid names too). Plus a name’s not that much use on it’s own, for it to be of much purpose in your daily work you should at least try to know who described it, where it’s from, how old it is, and which group it belongs to. I also feel like I’m falling further and further behind since I was never really on top of them as it was, and the rate of discovery is massive and seems to be growing.

This is in part perhaps, driving the trend towards specialisation in palaeontology. That compendium of dinosaur biology ‘The Dinosauria’ listed just 8 troodontid taxa back in 2004 (and most of them were known from incomplete remains), but there are now at least 15 of them known and at least a couple more on the way, many of which are known from multiple specimens, and with feathers etc. also preserved. To be an expert on them now takes a great deal more knowledge and study than it did even 5 years ago – someone doing a PhD on them could find the field has tripled in the time it takes them to write a thesis!

That is not something that is conducive to effective cross-referencing of literature. I find it quite common that between my submission of a paper and it’s return from review or time to publication a new taxon has appeared or a directly relevant new paper is published. Integrating this into your work is not always as easy at you might think and sadly I have found some referees to be quite niggly about this (one individual admonished me for not including a paper that hadn’t been published until after I had submitted my manuscript – it seems precognition is now also a requisite for academia). It does make life hard when the rate of research actively exceeds the publication turnaround time and if we keep to, or even accelerate past, one taxon a week, that will only get worse.

Guest Post: Introducing Aussiedraco

Today we have a sort of double guest post with both Taissa Rodrigues and Fabiana Costa writing together on a recently named Australian pterosaur. Be prepared for some serious ornithocheirid taxonomy:

Not so long ago, Tamara Fletcher posted her ‘Lessons from a First Paper‘ on the Musings. It’s quite interesting how papers with subjects relevant to your own manuscript are published just when you think you are finally finished! It was fantastic to get the chance to read her very detailed paper and include the information before submission.

We have been wondering about Australian pterosaurs for a while. It has been thirty years since their first description and still all known material is very fragmented. Unless you have a very diagnostic piece of bone, fragmentary material creates taxonomic uncertainty. This was the case of the Australian material: almost all of it was in a sort of “ornithocheirid limbo”, where no one seemed to know exactly what it was.

Let’s take, for instance, the first mandible ever described from Australia. It has been referred as: Ornithocheirus, Anhanguera Lonchodectes and then again Ornithocheirus. Oddly enough, a couple of these referrals was based on a certain taxonomic review, but did not agree on the same name. So, what is this material?

Pterosaur skull piece. From Kellner et al., 2011.

In order to answer this question, we had to take a look at this specimen in different levels. First, we know that it is related to both Ornithocheirus and Anhanguera because it has teeth, an elongated mandibular symphysis, and a mandibular groove. So we can place it in the clade Pteranodontoidea, more closely related to its genera. The exact phylogenetic position is still undefined; as already stressed, the specimen is very fragmentary, and futhermore current pterosaur analyses include very few mandibular characters.

Second, is it Ornithocheirus, Anhanguera, or Lonchodectes? This is the part where we thank our funding agencies for all the travelling we had to do! Let’s take the type species Ornithocheirus simus. It is known by a very robust and massive upper jaw, quite unlike the lanceolated mandible of the Australian specimen. It seemed quite unlikely that such disparate specimens would represent the same genus, so we ruled it out. There are several species in Anhanguera and the taxonomy is controversial, so let’s consider just the type species, Anhanguera blittersdorffi… oops, no mandible in the type specimen, but there is a superbly preserved referred material whose mandible has a distal expansion and a nice mandibular crest. So, another genus ruled out. We had the chance to see all the species referred in Lonchodectes and, once again, the differences rose. As David Unwin has already pointed out in his review of the Cambridge Greensand pterosaurs, lonchodectids have a characteristic parapet-like palate, which is also absent in the Australian material. All these morphological characters, together with the different ages and distinct deposits, suggest that the Australian material could represent a new genus.

Our final question was: could it be a new species, or merely undiagnosable? There are plenty of lanceolated mandibles in the Cambridge Greensand, but none of them had the characters that this Australian piece has. Besides some differences in the distance and size of the dental alveoli, it is unique in that it has a convex dorsal margin and a straight ventral margin, the opposite of what we see in other pteranodontoid mandibles. Working with this material was a quite good exercise of comparison.

All things taken into consideration: unique characters, combination of characters, do not fit into a known genus, and the Australian material is typically fragmentary; we thought it deserved to be considered a new genus and species. We wanted to honour the person who not only described it thirty years ago, but also made a difference to Australian paleontology and named it Aussiedraco molnari.

Kellner, Alexander W.A.; Taissa Rodrigues and Fabiana R. Costa (2011). “Short note on a pteranodontoid pterosaur (Pterodactyloidea) from western Queensland, Australia”. Anais da Academia Brasileira de Ciências 83 (1): 301–308.

Really? I mean, *really*? A bird?

I’ve got a proper (guest) post coming soon, but I simply had to share this.

Courtesy of Marc Jones.

An arrangement of archosaurs

As I’m sure many readers are aware that Sterling Nesbitt has just published a monumental chunk of his PhD thesis as a major monograph on archosaur phylogenetics. While obviously new phylogenetic analyses are constantly being published, these tend to rehash and recycle existing work heavily (and that’s not necessarily a bad thing) and tend to be limited in scope. Very big, detailed, comprehensive analyses are incredibly rare since they require a huge amount of time to be applied to the problem. You have to have a really good understanding of anatomy, the historical aspects of taxonomy and phylogeny of the groups at hand, go over all the existing datasets, see tons of material, and then analyse and reanalyse and write it all up. To do all of that for a group as vast and complex as the archosaurs is a truly major achievement and he’s done it in incredible depth.

Few of the results are perhaps really even remotely surprising, but that’s by the by. That gives us great confidence in our other, smaller, studies and tells us we were on the right track. More importantly, Sterling has thrashed out (as far as I can tell, it’s 300 pages long! and I’ve not read a fraction of it in detail yet) some of the more poorly defined characters and redefiend them and their states and then as a result of his work, redefined every major node on the archosaur tree.

This is the real boon for me, making explicit statements about character evolution across the tree and allowing us to say more about what changed when and how and in conjunction with what else. The amount of characters too (over 400) also means that some important nodes now have a lot more support than they used to.

Archosaur phylogeny. From Nesbitt, 2011.

And the rest of it. From Nesbitt, 2011.

Obviously I’m especially interested in pterosaur origins, not least through having looked at some of the characters that tie them to the archosaurs with Sterling just this year. Some of these are disucssed and assessed here, but overall what we see is a much stronger support for an ornithodiran (that is pterosaurs + the dinosaursomorphs) position of pterosaurs than ever before.

Sterling recovers some 12 characters directly the supporting ornithodia, (with perhaps 13 more depending on issues of transformation that I won’t go into here). That is, in the context of something this big, really quite a lot. In fact it’s as many characters as he finds to support the dinosaurs (also 12) and many more than supports the dinosauromorphs (just 5). In short, what has always been a very poorly supported node is, in this analysis, an incredibly well supported node.

There are of course a few little caveats to this in that this is non a dedicated analysis of the pterosaurs and their relationships, and despite the huge size of this work, there are some more detailed and specialised characters that can be added in and there will doubtless be quibbles about exact codings and taxa. I can see a few things I would explore if I was to go and do this. That’s not to denigrate his work one iota (after all this isn’t what he’s trying to do!), I’m merely saying that IF you were to use this as the basis of pterosaur origins, I think there’s more that should be done. However, this is very robust indeed as nodes go, and I think at the very least it adds a lot of support to this hypothesis where previously it had been rather less clear cut.

The only thing I can really say to conclude is congratulations to Sterling and thank you. This is a piece of work which will aid almost every archosaur worker for, quite probably, decades. That is a real achievement.

Scutes and osteoderms

The two terms of the title are often used somewhat interchangeably (and I’ve been guilty of that myself in the past) but in fact they have rather different meanings, despite their close relationship. Here is a series of fossilised crocodile osteoderms that I picked up a few years back. The term osteoderm literally means bones in the skin and that’s exactly what these are, piece of bony armour that sit in the skin.

Scutes on the other hand are the keratinous sheathes that cover the osteoderms. You can see some of these here in this croc with those bigger chunky scale-like pieces running along the back. That of course means all those fossil ‘scutes’ from things like crocs and ankylosaurs and titanosaurs should really be called osteoderms. In fact while of course claws and similar things do preserve from time to time, and there are bits of horn sheathes etc. out there, I’m not aware of any scutes being known from the Mesozoic (though not working on any of the more obvious groups, I could easily have missed them).

Mamenchisaurus ungual

Having mentioned the other day the sheer size of some sauropod claws, it seemed long overdue that I drag out this photo from about five years ago. It’s an ungual of that great long-necked beast Mamenchisaurus. Unfortunately I don’t have with me any of the shots that would put this close-up in context so I’m not sure if it’s a manual or pes one, though memory tells me it’s in the hand. Regardless the two key issues are relate to it’s dimensions.

First of all, it’s big. Really quite big. OK, so this is a very large animal (this individual was around 15 m as I recall) but even so, that claw is getting on for some 20 cm in length. That’s pretty huge, even in context. Secondly, it’s also big compared to the phalanx it articulates with. Given how sauropod hands and feet are built, you can’t imagine that this ever really had to swing around on that joint but instead poked out of a fleshy foot. Yet it’s nearly twice the height of it’s articulating phalanx so it’s hard to imagine that the claw is just big as some kind of evolutionary hangover, but was actively being selected or maintained at this big size, despite its discrepancy with the rest of the foot. In short, yeah, that’s pretty huge.

Dinosaur data storage

Not as you might think a new archive of dinosaur data, but this, a dinosaur that stores data:

One of my students was awesome enough to give me this as a gift for supervising her undergraduate thesis work (which included my little trip to Germany in December). It’s rather obviously a tiny tyrannosaur with a USB drive fitted, but awesomely, it’s been painted to match a certain overexposed tyrannosaur. This is truly wonderful and I am most grateful – the only problem is I’m frightened to use it!

For anyone not totally sick of this dinosaur, you can check out my appearance on live Irish TV for a week or so back (follow this link and go back to the 27th of April).

@Dave_Hone on Twitter

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