My recent paper on sexual selection touches on quite a few areas of dinosaur and pterosaur ecology and possible behaviours. Most notably (or rather, of most likely interest to people who like dinosaurs) is what we have to say about the possibilities for degrees of sociality in theropods. The idea that some theropods (and yeah, inevitably, especially dromaeosaurs and tyrannosaurs) may have lived in groups seems to be the subject of more debate, disagreement and hyperbole on the web than any other subject (and I bet there’s more coming in the comments), and yet there is remarkable little actually written about this in the literature. There is now a little bit more though.
Space limited what we could say but there are two points that we did get in and are worth elaborating on just a little here. First off, for those theropods rocking crests, these are more likely to be taxa regularly engaging in social interactions. That’s not to say they were necessarily living in groups, they might still have been solitary. However, they might well have encountered each other often in territory disputes, or even engaged in activities like lekking. Basically a big and honest signal can be a good advert of your fitness (or overall health) and thus you can avoid serious combat with another theropod that covered in claws and teeth that you’ know you’d lose to. Thins like the evidence for craniofacial biting already shows this kind of thing may have been going on, but this is taking it from another, if related, angle.
Secondly there was a paper not too long ago by Roach & Brinkman on the evidence for sociality in Deinonychus. In general they made some very good points and noted that much of the evidence purported to support this idea was questionable at best. However, they also argued that there were no cooperatively hunting extant archosaurs and thus this could be ruled out from an extant phylogenetic bracket point of view. Now one needs to be careful about quite how ‘sociality’ or ‘groups’ or ‘cooperation’ are defined, but as we note in the paper there are a variety of birds which hunt together, even cooperatively, and in the case of some hornbills – on the ground. By any measure that would seem to be a great analogy for small theropods and show that it’s not unknown in birds. There’s even evidence for degrees of cooperation in caimen and yes, going further out from archosaurs, komodo dragons. Coupled with the inherent strong plasticity of behaviour, I don’t think there’s any good reason to rule this out.
Now there’s noting there that definitively rules it in either, but I do think it likely that at least some species of theropods were at least highly tolerant of each other as individuals, and might well have formed socially structured, functioning groups. We have all but the flimsiest of evidence for that right now, but that’s no surprise really given how hard it is to get evidence of this kind of thing. However, there’s certainly no reason to say it was impossible and analysing the available evidence and searching for more is pretty far from a fruitless task.