Losses and convergence

A while back I covered convergence in evolution but I was dealing really with how anatomy can be modified in two or more lineages such that things can closely resemble each other, even when they are not necessarily closely related. However, while of course things can and do convergent evolve, there is a much more simple way that organism can end up looking similar without having to go through all that complex messing about with anatomical changes, you can just get rid of things.

Of course the genetic changes required to, for example, stop generating teeth or lose whole limbs can occur slowly as things are expressed less and less or get smaller and smaller until they vanish, or they can occur swiftly. Even single generations can suddenly be bereft of whole limbs (though of course it will take much longer for this character to spread through a population, even if it is strongly selected for). Still, these dramatic looking changes do come about (think of snakes, various lineages of limb-less lizards and amphibians for example) and of course the similarities (at least superficially, losing a leg is quite dramatic) can be striking.

These kinds of convergences can be harder to detect since by their very nature, they reduce the amount of information available. After all, if a lineage loses a limb then that’s a lot of information that is no longer present to compare to other animals. Until you find an earlier, limbed, relative, spotting what similarities it may have had with other groups (and what it is not similar to) can be tricky. Whales are an obvious example, with the ‘double roller’ joint of the astragalus in the ankle being a key feature in the discussion of whale origins (since it appears in artiodactyls and nothing else) but inevitably is absent in the living taxa what with them not really having hind legs and all, and only the appearance of various fossil forms has helped sort this out.

Scientific collaboration – genesis of the wrists

Those who know me well enough (or have been bored enough to read my publications list) will know that I am a frequent, if not nearly constant, collaborator. (Those who have also published a few papers themselves will know that there are lies, damned lies, and authorship lists). Nevertheless, I do collaborate a lot and the two main reasons I would give for this are increased expertise and increased originality in the work.

The former is rather obvious – colleagues with specialist knowledge (especially if from well outside your normal fields of interest) can provide lots of information and knowledge that you won’t have to hand, and might take a very long time to acquire. This is both a time saver and a paper-improver so it’s easy to see why people will want to club together on a project. Less obvious, but potentially more important, is that outsiders genuinely do often see things from a very different perspective that can take your work in new directions. It sounds like a cliche but I also find that it’s true.

A good recent example is the paper on dinosaurian wrist articulation that I wrote with Corwin Sullivan and colleagues. Corwin had been thinking about wrist joints in birds and dinosaurs and what he might describe how the joint had evolved. Having spotted that birds had a strongly abducted wrists and basal theropods a straight one, the change had to occur somewhere in maniraptorans. On the other side, I’d been thinking about the position and extent of various feather groups in theropods, but had not though of any good way that I could investigate the implications of the changing lengths of these feathers.

Ultimately the two came together as Corwin realised that there should be ostological features in the wrist that could be used to determine the flexibility of the wrist, but while of course this would be interesting in its own right, he thought there was likely more could be done and asked me what I thought of the idea. It immediately occurred to me that this was the kind of thing I’d been lacking – a possible correlate for the long arm feathers that I had been looking for and one that had the potential to explain, or at least examine, their evolution. The paper as it stands now really did largely come from the relatively short conversation that afternoon. We now had a couple of relatively concrete ideas about what we wanted to examine and how and what we might be able to tell from the results.

In the time since then, we have of course talked over the project quite a bit, but we have also discussed this ‘genesis’. Both of us are quite confident that there was little or no chance of us having produced the paper we did without the other. I’m not enough of an anatomist to have been able to sit down and work through the wrist anatomy of the theropods to work out how I might determine their flexibility (and it probably would not have even occurred to me to look there in the first place). Equally though, Corwin was working on how and when the wrist transition had occurred, but was stuck as to what might have caused this or what the selective advantage might have been.

Serendipitous perhaps, but it does demonstrate the value of working with colleagues with specialist knowledge, and with different ideas and takes on subjects than you have yourself. Of course this happens constantly simply when people read others’ research and make a connection to their own work or thoughts, but that does not detract from the gains that can be made by sharing ideas and working together.

Evolving flight while standing still

The other night Corwin noted one interesting aspect of the wrists paper in that we are hypothesising that the functional shift in the wrist occurred effectively to support a resting posture. Given that this wrist joint is an important component of the flight stroke, this effectively means that the ancestors of birds were evolving flight while standing still.

Humorous though this observation is, it masks another point which is that biomechanical studies and evolutionary studies of mechanics tend to focus (quite naturally) on motion. Animals that are not moving still have biomechanical issues to overcome however (like how birds rest on one foot, or horses can sleep standing upright) and while it’s easy to overlook them, this should not be forgotten.

“Is it safe?” The dentists’ nightmare – meet Zhenyuanopterus

So today I had to drop into CAGS to see Lu Jungchang, one of the leading researchers on pterosaurs in China and he handed me a reprint of his latest paper. Zhenyuanopterus is a truly remarkable boreopterid pterosaur with a 4 m wingspan and one hell of a set of teeth. To cap it off, the specimen is truly excellent – both complete and articulated and in wonderful condition.

Yet another UV Archaeopteryx – this time out: Daiting

Archaeopteryx continues to be a very interesting an important taxon and despite the wealth of research that has been poured onto it, there is always more to come. Part of this stems from the general inaccessibility of the specimens since not all are held in museums. As noted before, the specimens of Archaeopteryx are generally referred to by the names of the places in which they reside or by other familiar terms. Thus we have the original isolated feather, the London, Berlin, Munich, Haarlem, Maxberg, Eichstaett, Solnhofen and Thermopolis specimens. Of these the Maxberg specimen is now missing – probably not lost but likely in a private collection somewhere. Far less well known are the Buergermeister-Mueller specimen (the Solnhofen specimen is also in this museum) and the Daiting specimen.

It is the latter that we are most interested in here since it has been in private hands for many years and only came to light recently as a cast. The original has now been made available for study however and my friend and colleague Helmut Tischlinger (he of UV Archaeopteryx-es, pterosaurs and Microraptor) has done an initial description, topped, inevitably with some beautiful photographs. Helmut as ever has been good enough to allow me to show some of them here.

As you can see there is a pretty good skull present, parts of both arms and a furcula jammed into the eye socket. There are also traces of bone sticking out through the broken edge of the matrix implying that more material might be present, but buried. Also of special interest is that the specimen is from sediments quite a bit younger than those of the other Archaeopteryx specimens suggesting that they had a decent temporal distribution and were not quite the flash in the pan they might first appear to be.

Why Microraptor should never be drawn the same way again

One thing worth bringing up on the wrists front never quite made it into the paper (or even the supplementary material) in quite the way I would have liked. It gets a mention but not the emphasis required at least in terms of palaeoart but also in terms of the actual biology of the animal in hand (since there is only limited space and you can’t really go off on a tangent for a few hundred words even if you want to).

Microraptor, as we know, has very long arm feathers, far longer than anything else we looked at in fact. Those keeping up will also note that it has really rather strongly rooted feathers and thus, what you see in the holotype is what you get. Take another look at that and you can see that the big flight feathers on the hand are stick out at a fair angle from the hand, but still act as a kind of angled extension to the arm. They were also probably rooted firmly in place and could not move much, even if the animal wanted to move them. But what does this mean?

Well, if you take a look at most palaeoart of Microraptor and even academic reconstructions and drawings of the animal in published papers, people seem to have been cheating. Not in a dishonest sense I hasten to add, more that, whether they meant to or not, the image just does not match the anatomy of the specimen. I’ve even checked a few of these and the feathers are either not at the right angle to the hand (which would be fixed), or are much shorter than as are preserved. The feathers are so long, and indeed the arms are so long that, [important note looming] assuming the arms are held such that the palms face inwards (the ‘clapper’ position) the feathers will be stuck in the ground. They can’t not be, they are just too long and can’t be moved out of the way. Microraptor has a serious feather issue.

Even with a flexed wrist, Microraptor's feathers would be stuck in the ground. Even if the arm were held out straight and parallel to the ground, the problem would remain. Image from Sullivan et al., 2010.

There are of course solutions to this problem and we illustrate and describe them. First of all, if you pronate the hands a little (i.e. rotate the hands inwards towards a ‘slapper’ position) then of course the feathers will now point at least partially to the side rather than down, and while this makes them stick out awkwardly, they won’t drag on the ground. Secondly, if you raise the arm right back so that the humerus is parallel to the spine, and then crook the elbow and / or the wrist a lot, you can get the feathers to point backwards or even up. The arm is in an odd looking position and might even get in the way of the legs (though of course birds, with an ever more abducted wrist, pull this off quite neatly) but again the feathers are at least clear of the ground.

Bringing the humerus back to be subparallel to the spine and then bending the elbow and the wrist finally brings the feathers free of the ground. Image from Sullivan et al., 2010.

Now Microraptor has some really big feather and clearly led a rather unusual life. Most, if not all of these things would be unnecessary for pretty much every other feathered dinosaur, but the general point is important. Feathers (whatever their purpose) were very important for the animals that had them, and as we can see from the fossils, they evolved to have lots of them and big one, and were kept in good condition. You don’t see dromaeosaurs or oviraptorosaurs with frayed feather tips and ragged edges, they looked after them and this includes not scragging them on vegetation or abrading them on the ground. Whatever else Microraptor was doing, it was looking after its feathers. This means it did not hold its arms in a way that would have led to profound damage to the feathers (or may just have even been physically impossible if those feather shafts were especially inflexible), and thus one of these, admittedly unusual, postures must have been adopted. You can’t manipulate the anatomy and you can’t contradict the evidence, so anyone thinking of drawing Microraptor in an old-style ‘Velociraptor’ pose with the hands held in front of the animal below the head needs to think again.

Biologically this is also interesting and potentially important. After all if the hands of Microraptor (or any similarly feathered dinosaur) tried to bring its hands to its mouth while holding something or to strike at prey in front of it, then it won’t be able to without dragging its feathers across the floor. This puts rather a limit on what the arms can actually do, especially when brought forwards. This isn’t necessarily and issue for the animal, such a penalty would clearly be a trade off against having those enormous flight feathers. But it does mean that if we are to successfully consider and test ideas about how the hands and arms of maniraptorans evolved and were used, we have to take such issues into account and not consider the bones in isolation – those feathers were important too.

(A few extra caveats / details. Yes, feather shafts are at least a bit flexible, and could probably be crushed against the ground without breaking them or doing too much damage, and yes lots of preening would help keep them in good shape. However, doing this every time the animal wanted to bring the arms forwards would in the long term risk damaging them, especially if done often, and preening also brings its own costs in terms of time and effort. On balance, it is far easier to just keep the feathers off the ground the bend shafts, ‘unzip’ barbs, and break tips that it is to go through that rigmarole and risk constantly. It’s also possible that the feathers were less firmly fixed / more motile than in modern birds, but they do have to take the forces of flight [presumably] and we do see things like quill knobs that argues for a very secure and fixed attachment).

I guess I should add, in the best traditions of SV-POW! and Tet Zoo, massive ‘Musings bonus points’ will be available to anyone who can find a ‘correct’ Microraptor online or produce one themselves.

Guest post: Birds in a flap thanks to dinosaur wrists

My latest paper is out today on the subject of theropod wrists. However, first credit must go to project leader Corwin Sullivan who has also penned this post for the Musings on our research. I’ll be adding a bit more tomorrow with my take on the paper, but for now, take it away Corwin….

Filler post, and the thoughts of palaeontologists again

Apologies for the lack of detailed posts in the last couple of days, but starting tomorrow expect a big flurry with some exciting new research and guest posts coming.

I was just idly wondering how much the phrase “some palaeontologists think” gets used (online at least) and as ever, Google is your friend. The number is a surprisingly small 480, but switch to the US spelling and it’s a quite massive 23 000 for “some paleontologists think”. The rather worse “some palaeontologists believe” racks up 11 000 for the UK spelling, and some 37 000 with ‘paleontologists.

Getting more general, “some scientists think” has a staggering 2 500 000 hits and “some scientists believe” 1 300 000.

Eeek.

Birds in 3D

Leon Claessens directed me today towards his online archive of bird morphology based on various 3D scans of living and fossil taxa. It’s a great scientific resource and well worth some time looking around even if you are not big on your bird anatomy. Enjoy.