This is a post about pachycephalosaurs. It’s not a post about feathered dinosaurs, huge dinosaurs, or any of the ones which you may be more familiar with from popular media. Pachycephalosaurs were the dome-headed little scrappers of the Cretaceous, around 85 to 66 million years ago. Their name means ‘thick-skulled lizard’ (pachy: thick, cephalon: skull, saurus: lizard), and they were a small group within the larger herbivorous group of dinosaurs called ornithischians.
It’s probably fair to say that these dinosaurs are one of the least popular groups; they didn’t have razor sharp teeth and sickle-switchblade claws, they didn’t grow to the size of houses, and they didn’t have rows of armoured shields and spikes along their backs. What they did have, however, is an unusual behaviour that signifies them as unique, and pretty amazing, beasties.
Fig.1 – A pachycephalosaur suffering an ‘ouchie’, or cranial lesion (PLoS)
Feathered dinosaurs might not still be the new boys in town in the fossil world, but there’s still a tonne of cool research being done on them. One of the main fields is trying to figure out if different species were capable of powered flight, like in most modern birds. The recent finding of Aurornis xui appears to have confined the ability to fly just to a single feathered lineage, the one leading to modern birds, but how do we figure out whether they could fly or not?
Reconstruction of Aurornis xui. Credit: Masato Hattori (source)
In a great many species, females exhibit preferences for larger males – including that world-dominating species Homo sapiens (though a recent PLoS ONE study reveals the effect is only modest in actual couples). Certainly in the marine environment, choices such as this correspond to greater fitness in a species, with larger individuals being more fertile than smaller ones. Fishing can disrupt mating systems by altering population size structure – that is, causing a shift to smaller individuals. This is a particular problem when populations are fragmented (due to patchy habitats), as there are already limits on partner choice. Lobsters populations are often fragmented and with this in mind, Drs Denice Robertson and Mark Butler have investigated the size preferences of the spotted spiny lobster (Panulirus guttatus).
Among the many issues with the fossil record is the case of gender identification. In modern organisms, it is usually pretty easy to tell which members of a particular species are the males and which are the females. This can either be through consistently perving on them to figure it out during copulation, or some aspect of their morphology, such as antlers, or you know, a penis or vagina. When it comes to fossil though, we often don’t find these typical gender-distinctive aspects of morphology preserved, as they are usually lost in one form or another to the ravages of time and the process of fossilisation.
I normally really don’t like writing about theropods, especially of the feathered variety, as it just seems like I’m jumping on the bandwagon that they were awesome and every aspect of them needs extensive media coverage. Ok, yeah, they can be pretty cool. But only, for me, in the context of the larger evolutionary patterns that they can reveal to us, such as the evolution of feathers and flight. Each new fossil doesn’t exactly transform our knowledge of this, but they do help us to refine our theories to a certain extent; whether or not that’s worthy of excessive media coverage and Nature publications, is not my judgement to make (no, it’s not).