Constructing hypotheses on behaviour in the fossil record

Those keeping up with papers on palaeoethology may well have noticed that a number of papers have gone online in the Journal of Zoology of late with a common theme. Darren Naish has a paper on the behaviour of fossil birds, Andy Farke has one on combat in ornithischians, and Pete Falkingham has a paper on interpretation of trackways. This is not a coincidence, but part of a special issue of the journal out today on behaviour in the fossil record and all of these contributions will eventually be published together with a number of others in a collection I have assembled as a guest editor. The volume has ended up rather dinosaur-biased which is unfortunate as a number of other papers were promised from other fields (including on whales and the Burgess shale) which never appeared and giving the set a more dino-centric appearance than I had planned or hoped for.

Adding to this is in fact my own paper in the volume. This was something I had been working on for a while before being asked to compile the special issue (indeed the fact that I was working on it, and it was intended got the journal may have precipitated the invitation) and in the context was the perfect home for the paper. As with similar cases I had nothing to do with my own manuscript and it was submitted separated and edited and refereed independently by the journal, and only after acceptance could it be added to the list. Most of the papers are reviews of one form or another, and in my case the paper written with my friend Chris Faulkes looks primarily at issues of hypothesis creation on behaviours for fossil taxa.

Our main contention is that in the past palaeontologists have been a bit over zealous in the production of hypotheses and the way in which they have been generated has made them difficult to assess or even simply discuss and in at least a few cases hould probably not have been suggested at all. We don’t think it inappropriate to generate hypotheses that cannot be immediately tested, or those that are difficult generally to assess, but a hypothesis must have at least some support behind it to make it valid in the first place, and poor uses of terms, lack of specificity, or even use of fundamentally flawed concepts have meant that there are problematic ideas in the scientific literature.

Mutual sexual selection is perhaps a good example here. I’ve now penned a number of papers with various authors about the issues surrounding this idea and how it may fit into archosaur evolution. The point is not whether or not we are right about this, but more the fact that this was something hinted at by Darwin, written about by Huxley and extensively studied by numerous ethologists for decades, and yet many palaeontological papers discussed sexual selection purely in terms of dimorphism, or the fact that sexually selected features should feature on only one gender, or indeed that sexual selection should be mutually exclusive of other functions. None of these things are true, so hypotheses that rely on one of these as are starting point are going to be fundamentally flawed, or at least problematic.

Thus the paper sets out to identify some key areas where we feel mistakes have tended to be made (myself drawing on examples from dinosaurs and pterosaurs, Chris from his area of expertise the mammals) and to also then try to find a set of guidelines that might help the better generation of hypotheses allowing for reduced confusion and better testing. Naturally we think this is going to benefit researchers, but given the rampant hypothesising that often accompanies any online discussions of the behaviours and ecology of extinct animals online and in other informal venues, it might just help clean up some of the more egregious suggestions that can be put forwards based on the most tenuous of links. Some of it may sound excessively simple and even obvious, but that doesn’t mean it hasn’t been an issue in the past. I actually had a chat with an ecologist the other day who bemoaned a similar set of problems in her field, and I think the issue is more one of advancement and general improvement that systematic errors or poor science.

Naturally we did try hard not to pick on individual papers (or people) but we did also want to point to some specific examples of the kinds of problems we were discussing and so a few things get the finger pointed at them, but they have mostly had specific rebuttals in the literature already, or were very much generic issues. Hopefully then, we’ve not bent any noses out of joint. I was certainly grateful to Andy Farke for reading an earlier version to check for overall tone and to see if it was working the way we wanted. Anyway, here are a few of the things we looked at.

Terms need to be more specific. Talking about ‘parental care’ say in general terms isn’t very helpful when this can encompass pre- or post-natal care, or both, and differing degrees of commitment from parents over very different timescales. So a statement like ‘X showed parental care and Y didn’t’ may not mean much if the parental care shown was minimal, or two papers might say this where one is referring to all parental care, and the other only post-natal, making them hard to compare.

Overlooking counterexamples or complexity. Descriptions of species or clades as ‘social’ has been creeping into the literature on dinosaurs and yet even if you do somehow have super evidence for sociality in a species, applying that to other taxa, or even other member of the same species is not necessarily a great idea. While we do have highly social species that basically can’t function when not in a group (like some molerats) even famously social animals like lions often spend part or much of their time apart, and some like cheetahs can be incredibly plastic, switching from social to solitary multiple times in their lives, and yet it would be a big mistake to suggest tigers are fundamentally social because their nearest relatives the lions are.

Extreme examples or oddities are useful to provide context or even limits on ideas. Some species have incredibly specific requirements or only live in certain environments, while others are much more adaptable. You don’t really find sand cats outside of deserts or dry environments, and while lions show up in quite a few places, you can get puma in everything from high mountains to praries, deserts and rainforests, yet there’s not especially obvious about their osteological anatomy that they could occupy so many more environments.

Make sure the analogy or reasoning behind it is actually correct. Not too long ago it was suggested that azhdarchids had long necks to reach into carcasses of large dinosaurs. However, given that the heads of the biggest azhdarchids (estimated at getting on for 2 m) are longer already than the longest sauropod ribs we know of (2 m) then any kind of neck is redundant in this context, let alone a long one, and vultures do fine with absolutely short necks and heads while feeding on carcasses of animals many times their size. The analogy that the hypothesis is being based on is fundamentally false and if that is the sole support for it as a concept, then it’s really not much of a hypothesis.

The short version of much of this could well be summarised as “look more at the behaviour of extant organisms”. I know Darren bangs this drum a lot on TetZoo and I’ve said it in plenty of talks and to lots of people if less so online. It is confounding when people say that such-and-such behaviour isn’t seen in reptiles when it plainly is, or that only animals with feature Y can do this behaviour when it’s known in numerous species, that are just less specialised towards it (or even show no obvious adaptations – like tree-climbing crocs). True this may not be common or normal, but to assume that it’s impossible, or that there is a perfectly consistent correlation is incorrect.

Part of the difficulty is a lack of good data on many of these things. Ethologists can simply observe behaviours and therefore don’t necessarily go looking for osteological or other correlates that we might be able to detect in the fossil record. That does make things harder, but we need to try and avoid getting trapped by ‘we don’t know if this correlates therefore this hypothesis is valid since we don’t know’. I am actually not against (in principle) hypotheses that are difficult if not currently impossible to test, but as with the azhdarchid neck example, there is a difference between something that can’t be tested, and something which is not even supported at the most basic of level. A hypothesis has to have some support, and some specificity about that will go a long way to making things much more clear and amenable to testing and allow a great fit of existing and future data.

What is most remarkable is how far things have come so quickly. So many modern analyses are using things like FEA and functional morphological analyses, are looking for correlates of behaviour (or aspects of ecology that link to behaviour), and more and better comparisons to extant forms and their anatomy are being used. Such important work or our understanding of the biology of extinct animals should not be let down by poor hypotheses and we do hope that, while things are improving already, this will help better communication and understanding of ideas.

 

D. W. E. Hone and C. G. Faulkes 2014 A proposed framework for establishing and evaluating hypotheses about the behaviour of extinct organisms (292: 260–267)