Prehistoric mass extinctions
The article about the part that the Deccan Traps may have played in the extinction of the dinosaurs reminded me of a thought I had some time ago concerning mass extinctions: pandemics.
The wikipedia article on mass extinctions mentions diseases in the 'Other hypotheses' section: "Many other hypotheses have been proposed, such as the spread of a new disease, or simple out-competition following an especially successful biological innovation. But all have been rejected, usually for one of the following reasons: they require events or processes for which there is no evidence; they assume mechanisms which are contrary to the available evidence; they are based on other theories which have been rejected or superseded."
However, I can't see how diseases can be excluded for the reasons given there.
For example, with regard to the lack of evidence, the number of complete fossilised animals found across all species is pretty small whereas we'd really need a large number of complete specimens from a single species to spot health differences due to disease in that species, and that's assuming that the disease leaves traces on the bits of the animal that do get fossilised. And then we must remember that many dinos are only known from partial fossil remains. In view of this I find it difficult to see how disease could be ruled out on the grounds of lack of evidence when the totality of the evidence we do have barely amounts to confirmation that the animal actually existed. Indeed, I think it's a pretty sure bet to say that we don't have fossil evidence of every creature that has existed, or even what percentage of all the creatures that have existed and become extinct that we are aware of.
I also can't see how a pandemic disease would necessarily be dependent upon other events or processes; diseases would have been evolving alongside everything else and wouldn't need special events or processes to result in a pandemic.
It seems to me that unless we postulate that there were no diseases in prehistory (which would mean that disease is a relatively new phenomenon) then diseases in dinosaurs must have been a certainty, and if diseases were a certainty then pandemics must have been a possibility.
What I do find interesting, and which might support a pandemic hypotheses for some mass extinctions, is the degree of selectivity when these mass extinctions occurred; they seem to have affected only a limited number of families/genera and whilst this may reflect the susceptibility of those particular families/genera to the environmental phenomena that is usually blamed for mass extinctions it may equally reflect their susceptibility to a particular disease.