I had always intended to avoid this topic on the Musings as it is a complex issue full of lots of details and subtleties about anatomy, functional morphology, phylogenetics, and evolutionary distances and temporal separations. I’ve nothing against tricky topics per se, but ones like this combine a whole raft of issues (some of which I am only partly familiar with) and often require a mind-numbing amount of detail to illustrate the problems (or more accurately controversies) correctly, and you can guarantee that many people will not be able to follow it well, and thus you leave the audience more confused than before you started. Alternatively you simply skim over the depths in such a way that you do not even really address the issues (or even list them all) and risk giving the audience an answer pretty much on your say so, and not presenting them with the evidence for your (or the scientific community’s) position on the subject.
The latter approach is actually the tack I’ll be taking here, and I hope that people will simply accept my summary of the issue at hand (as indeed they have in the past when the primary difference was perhaps the fact that I simply didn’t advertise that I was going to massively gloss over the issues). If you *do* want to go into the issues they have been dealt with in some considerable detail on various blogs and websites, in books, and even in plenty of freely available PDFs of research papers online, (many of which are reviews and perfectly accessible to non experts) and of course you can always leave questions on Dinobase or AAB.
So what is the topic exactly? What is a BAD or a BAND for that matter, and why has it apparently sparked so much controversy (apparently) and why is it so complex? These are all questions at least some of you might be asking rhetorically right about now, so in an inevitable bit of cheekiness, you’ll have to click on the ‘continue reading’ button to get the answer.
In short the two are acronyms for the opposing positions on bird origins. Either Birds Are Dinosaurs, or Birds Are NOT Dinosaurs depending on your position.
I rather suspect that for many people it is a surprise to learn that there are any specialists who do not think that birds are derived theropods (i.e. birds descended from theropod dinosaurs). In fact you have probably not even heard of any other competing hypothesis as to the origin of birds outside of the basic derived theropod one. This is because there are effectively only a handful of people who do not accept this theory of bird origins, but as with all such tiny minorities they are very vocal. As a result, there are in fact a ton of papers presenting a BAND perspective despite the overwhelming evidence for birds being theropod descendants. The alternate position, as voiced, is that birds evolved from a far more basal archosaur than derived theropods (perhaps something close to the crocodilian lineage) and simply remain absent in the fossil record until popping up with Archaeopteryx and other later birds. This is also typically accompanied with one of two additional positions to allow for the issue of feathered dinosaurs: either some feathered dinosaurs (like the dromaeosaurs) are in fact secondarily flightless birds that just happen to have evolved to look exactly like theropod dinosaurs in all manner of extreme convergences, or alternatively that there are no feathered dinosaurs, and what others describe as feathers in the fossil record is simply rotting tissue that happens to look like feathers.
I hate to be disrespectful to any professional colleague on here since (personally speaking) I do not think such public places are the correct forum for such discussions (and I don’t think most people are that bothered about our spats as long as the work gets done and the issues resolved), and I will as a result try to keep things as un-incendiary as possible but the short version is that the BAND position is wrong. Very wrong in fact, and indeed demonstrably so, and frankly it’s about time it was dropped.
Since by now youas a reader are aware of cladistics and phylogenetic reconstructions, and how parsimony is applied to such positions we can examine the reasons for such a positive dismissal of the problem. The short version is that when we try to reconstruct phylogenetic relationships and infer evolutionary history we have to consider all of the evidence available, and than apply the most parsimonious explanation to the results. In short, we don’t artificially leave anything out and we accept the most parsimonious explanation of the available data as to how things are related to each other. We go with the weight of evidence – what set of systematic relationships are best supported by the anatomical and evolutionary features? In some cases (like pterosaurs) those ties are very weak and it means that even if you do get an answer there is the possibility it will change with a little more evidence supporting the other side.
In the case of bird origins however, that evidence is absolutely overwhelming, and it is pretty much inconceivable that it will ever change. One would have to find dozens, if not hundreds of features and a ton of new fossils that not only overcome the weight of evidence favouring BAD, but then push it in the other direction to support BAND. Given that each new fossil and analysis over the last 20 or 30 years has found greater and greater support for BAD, not less, that hardly looks likely.
Why then does this situation continue? It’s hard to say to be quite honest, and in fact rather unusually there has been a bit of discussion about this in the literature. It basically seems some people are just too wedded to their ideas and simply refuse to give into the weight of evidence they are facing. While this is of course human nature to a large degree (no one likes to be wrong, especially not publicly, and especially not in such a big way and when being shouted down by huge numbers of your peers), it has reached almost extreme proportions.
However, the ultimate point of this post and the indefensibility of the BAND position goes back to the evidence and parsimony. What the BAND position amounts to, is special pleading. To be sure the evidence for BAD is not perfect (palaeontology never is: there are gaps, ghost lineages, reversions, and convergences) but it is incredibly strong. Basically the BAND group have a few challenges to the BAD position such as the idea that dromaeosaurs are simply convergent and did not descend from other theropods, that feathered dinosaurs are no such thing, that the changes in the fingers (more on this another time) between birds and dinosaurs is impossible and a few others. However, what they want is for these to be the *only* points being considered and for us to effectively throw out the supporting evidence for a BAD position (the numerous anatomical characters of feathers, wrist shape, ankles and feet, the pelvis and skull and more – not only for the BAD position, but also of course that which ties all of the theropods together, since they want dromaeosaurs to be birds). They want us to ignore the majority of the evidence and simply accept a very small minority in exchange.
Some of the points that have been raised by the BAND group are valid ones, and at least some of their papers have in fact driven further research as people look for more evidence to rebut their claims and strengthen the BAD ties (such as work on feather preservation and evolution). There is no harm in questioning data or interpretations of data – indeed it is a fundamentally healthy state for science to be in where there is a climate that allows such research and criticism. The problem lies in the vociferous defence of a terminal position that wastes the time of all concerned, and gives a false impression to those not acquainted with the field as to the state of the debate. In this case it is especially problematic, as leading BAND proponents write extensively for books aimed at ornithologists working on living birds who themselves are not necessarily experts in palaeontology. Thus much of their information these workers have been fed has in the past come from a vocal minority, pushing a minority view that has very little support either in the fossil record or the scientific community.
So hopefully I have got to the core issue here (evaluation of evidence) without getting bogged down in the complexities of the issue. At least some of the specifics I will deal with at some point in the future, but really I just wanted to get across the point about evidence. One has to consider everything (for and against)