While we are talking birds with odd beaks, skulls, ornaments and all that, it seemed most pertinent that I dig up this image of a cassowary from my collection. The crest at the top of the head is more properly called a casque and while studies show that it certain does have an ornamental / signaling function, it is used for a few other things as well including clearing foliage and detritus off the rainforest floor where the animals live.
To return then to yesterdays general theme, it is usually a bad idea to go looking for extra possible odd functions and features in fossil animals. If you have a good set of data that strongly supports a given function of a morphological feature – don’t try and then second guess yourself with a raft of extra odd (and untestable) features just because they crop up in one or two extant organisms.
Case in point being this one, I suppose it’s possible something like Monolophosaurus did use it’s crest in a similar way to a cassowary, but I wouldn’t want to argue that and nor is it common enough or tied to an obvious structural feature that you could realistically test it on the dinosaur.
However, when trying to work out the possible range of behaviours that an animal may have exhibited or when faced with something unusual, it can be well worth digging around (so to speak) in the literature on extant animals. There is such a raft of unusual things that living animals do and features they have that it would be impossible to consider them all when looking at a new fossil – to do so would be a waste of time and effort and a great many simply could not be assessed properly. They can provide a source of ideas and information that could easily be missed otherwise so as ever a balance must be struck, but stick to those that can reasonably be tested and avoid the extreme.
Share this Post
Dave Hone's Archosaur Musings 
Reminds me of a fairly amusing example I read in a paper on the cranial kinesis of _Carnotaurus_–as an afterthought in the conclusions section, they suggested that the animal may have used its hornlike projections to kill small prey.
Parsimony, teeth, etc. 😉
I think it is unfortunate that hypothesis about functional morphology are generally framed as mutually exclusive – feathers for thermoregulation vs. feathers for display or wings for gliding vs. WAIR vs. insect nets or whatever. Even when a relatively robust structure–function relationship can be drawn from the fossil record it does not necessarily follow that this rules out the role of alternate functions either in terms of the biology of organism or the evolutionary history of the structure. Judging from living taxa, strict parsimony does not seem to be to be all that useful of a guideline for interpreting the functional significance of structure, Egretta ardesiaca being a favorite example of mine. That said, there are a lot of loony speculations out there and plenty of others that seem plausible but are not obviously testable. One wonders about all of the cases in extinct taxa that we will never even think to imagine…
That’s about the size of it. Well said (better than I managed anyway).
Wittgenstein: “Whereof one cannot speak, thereof one must be silent.” It seems equally as wrong, though, to insist a structure was not applied for some use as to insist that it was, except where such use has been demonstrated to be physically impossible. Nature is much more imaginative, versatile, and experimental than we are.
Never mind extinct taxa; there are plenty of extant taxa sporting structures that are not understood. Start with the narwhal’s tusk. I haven’t read of any suggestion that it functioned as a phased-array auditory organ, despite its unique physical suitability for the role. One might almost conclude that few biologists are especially familiar with phased-array sensing.
Are our own incisors primarily for eating, or for display? Does it even make sense to ask the question?
I’m merely advocating to keep and open mind and that the diversity of morphology and the use to which they are put in extant taxa, can serve as models and ideas for palaeontologists to work from. True many features do serve multiple purposes and as I say, it’s impossible to list them all or test them all (in living or extinct taxa), but the more likely ones can be tested. If we had never seen feathers before we found Archaeopteryx I think we would have the wit to note that the extended ones on the arms might form useful wings and that the short fluffy ones on the body might serve for insulation and we could test those ideas with simple models in the lab, or with comparisons to other similar structured features. No, we could not instantly test (or even think) display functions, nest incubation, water absorption, flotation, or any of the other number of functions to which feathers *are* put, but that does not mean we should ignore possibilites *beyond* flight and insulation in this hypothetical example.
Later ideas, later ways of testing function, or new evidence about the structre of these new ‘feathers’ might lead us to new ideas, and stopping once one obvious one has been found and tested is a mistake, but so to is asserting all manner of possibilities without a good reason to support a new hypothesis. It’s about getting the balance right.
I saw cassowaries in the wild (one presumed male and one juvenile) in May as well as in the zoo in Port Douglas. Very cool, nearest thing to seeing a dinosaur…
Sorry, I can’t let you get away with that about the casque. Several purposes have been mooted for the Cassowary casque and they are:
1. Sexual display (perhaps, but not proven)
2. A fighting instrument (no evidence to support this)
3. Protecting the brain case by warding off branches as it charges through the undergrowth (probably at least partly correct because at least in two species the casque often becomes deformed over time)
4. As a resonance box in low frequency communication (my research still ongoing)
5. Used for knocking hanging branches to dislodge fruit – with a backward motion of the head (this would at least partially explain why the rear of the casque is often triangular, inclined to the front)
As far as I am aware no-one has ever suggested it might be used for removing “foliage and detritus off the rainforest floor”, but it would be interesting to hear your justification.
Otherwise I agree entirely about the dangers of imputing the function of features in fossils based on extant species and anthropomorphic misconceptions.
I did say: “while studies show that it certain does have an ornamental / signaling function, it is used for a few other things as well including” – in other words, these were only *some* of the suggested functions.
As for the floor clearing, I believe it’s discussed here:
Mack, A. L., Jones, J., 2003. Low-frequency vocalizations by cassowaries (Casuarius spp.). The Auk 120, 1062-1068.
If several birds or other extant animals used a morphologically similar crest in a particular way, say the Helmeted Hornbill and the Greater Hornbill sharing defensive, display or foraging behaviors It would be at least plausible if not probable to extend that to extinct creatures.
I’ve never seen a cassowary in the wild but I’ve seen plenty of emus.
Agreed, if we KNOW what the morphologically similar item is used for in extant species it is reasonable to extend this behaviour to extinct species. Unfortunately in respect of the Cassowary casque we don’t know what it is used for and so far as I know there is no extinct comparable species to relate it to anyway. We do know the structure and composition of the Cassowary casque but field observations are too few to draw conclusions and captive birds have only shown captivity related behaviour which has not led to any new angles on the casque. If an extinct bird were shown to possess a similar casque we might be able to look for parallels. As it is, there is one other extant bird, Macrocephalon maleo, which has a casque and probably (again probably) uses it to protect the skull as it frequently takes flight by flying through thick ground rainforest vegetation.
The Emu is the sister species to the Cassowary and does not have a casque. Since the Emu is an open country ratite, we assume the Cassowary casque has something to do with its rainforest habitat.
I think it would be plausible, yes, but you’d need a strong correlate between an exact structure and an exact function (as you can do with tooth shape say, or leg lengths etc.) to provide a strong basis. Otherwise it just becomes an untestable hypothesis. You need to make sure that the feature you see and the action it is being used for are largely exclusive – i.e. do other hornbills (or other birds) with different shaped bills also perform this behaviour, or do they have the structure and not do this behaviour?
In short you are right, the kind of observation you suggest would lead to a hypothesis that it might also be present / used similarly in a fossil taxon, but as I note above, this is jsut the starting point and not an end point.
Dear David, I don’t have the relevant publication to hand, but I spent some time with Andy Mack in PNG and I am certain he never implied that the Cassowary casque was used for clearing detritus from the forest floor. This sounds like a misquote or misunderstanding of what was actually said. I have emailed him about this discussion.
The Cassowary’s casque and this diversion are a long way from Archosaurs, but do make the point that the morphology of extant species and its function needs to be fully understood before being used in any hypotheses concerning similarly endowed extinct species.
Regards, Richard
Richard,
I don’t have the paper to hand either (at least not at home, it might be lost in the office somewhere). I confess that that comment was taken from a colleague in a paper we are collaborating on so perhaps I’m misquoting him, or he’s misquoting the paper. I’ll certainly be interested to know what he says as cassowaries and their casques get a brief mention in our manuscript and extra information is always welcome. I’ll try and dig up a copy to in order to double check – thanks for bringing this up.
While I do try to be as accurate on here as possible, errors will creep in. In any case, while this may yet be an error, the point was to illustrate that an apparently simple feature with an apparent single function can be multi-functional and that these can be unexpected, cryptic and untestable. This is therfore pertinent to archosaurs (and not least since birds are extant archsaurs and thus form part of the EPB for dinosaurs and others) and palaeontology in general since of course we rely on extant organisms to provide us with models and examples of functional morphology to apply to fossil animals – it’d be a damn site harder to work out what different teeth and jaws did say, if all modern animals were edentlous suction feeders.
We actually have three of the beasts here (Papua).
What would you like to know?
We do see them do some strange things with their casque,
but they would never use it for sweeping detritus.
It actually appears to a counterbalance weight
to improve their balance and protect their skull.
The typical Cassowary can be an absurdly awkward creatures:
imagine a snake walking on stilts carrying a heavy bowling ball.
The weight of the casque gives head-strikes more power.
Having a hefty casque at the end of a long neck
gives their head movements a semblance of a gyroscopic
stabilization in quick strikes.
Let me know and I will ask them
{politely, of course ;^}
Forgot to mention –
I see a lot of references which say their favorite food is
vegetarian with some occasional meat,
but the truth is the Cassowary is fiercely carnivorous.
They go absolutely bonkers when you offer chicken or steak,
and they only eat berries and such when they are desperate.