Brusatte et al. 2008

[john bois <jbois@verizon.net>]

...claims that dinosaurs may have been "lucky" in their successful passage 
through extinction "events", events which destroyed crurotarsans. The 
competing hypothesis is that dinosaurs were superior in some way and beat 
out their competitors because of some crucial adaptation (e.g., they were 
endothermic). In the paper, the latter model is questioned due to their 
finding that the two clades "lived side by side for 30 million years, and 
crurotarsans occupied more morphological space and were often more abundant 
and diverse than dinosaurs."

The paper brings alot of excellent data to bear...but the conclusion that 
the "dinosaurs were (likely) the beneficiaries...of some good luck" does not 
stand up.

Firstly, there is no discussion of the many possible critical adaptations 
that could have given dinosaurs a real edge--indeed, the idea of any 
dinosaurian "superiority" is couched in terms of a dusty old notion that has 
"long pervaded the literature". Further, it is suggested that research into 
competition hypotheses is not that profitable because  they are difficult to 
test and vague. This is true of course. But it is also true that factors 
that are difficult to test because they are lost in geological time, might 
have happened nevertheless. And there are some prime adaptations that 
potentially gave dinosaurs advantage that are not considered--increased 
parental investment, for example.

But more than this, I personally find the "lived side by side" argument 
unconvincing...and if it pleases the group I would like to drop an analogy 
on you all for your consideration:
I was listening to some big band jazz. I was struck by the limited role of 
the guitar. It was often restricted to the role of rhythm instrument. There 
was more diversity in the brass section. Occassionally, the guitarist would 
step forward and take a solo, but it was surely the brass players that were 
the stars of the day. So, what happened to allow the guitar to claim the 
dominant role in popular culture that it has occupied since the fifties? It 
was not because all the sax, trombone, and trumpet players were hit by a 
train; it was because a critical adaptation--amplification--changed the 
game. So, the fallacy behind the "lived side by side argument" is the 
assumption that organisms don't change, don't acquire game-changing 
adaptations; or, if they do, that their competitors can always 
counter-adapt.

Finally, here we go again with the luck of the extinction event. But unlike 
the end Cretaceous extinctions where there is at least a large body size 
differential between the winners and the losers, in the extinction events 
noted in the paper between dinosaurs and crurotarsans, there are no reasons 
proposed other than chance. Yes, chance plays a role in evolution, but it is 
increasingly being used to "explain" things as a kind of default, i.e., when 
we can't test a hypothesis the phenomena must be due to chance. This doesn't 
follow. And yet the notion is increasingly pervading the literature.