Re: Why did small dinos become extinct?

[Philip Chalmers <philipchalmers@blueyonder.co.uk>]

Most accounts of the K-T extinction state that no purely terrestrial 
animal larger than a cat survived (crocs and champsosaurs are / were 
semi-aquatic). Cat-/chicken-sized non-flying predatory dinos are known 
(most notably Compsognathus). Why did small non-flying predatory dinos 
not survive?

David Marjanovic suggests the whole terrestrial ecosystem was devastated 
too baldly to sustain viable populations of predatory dinos. But this is 
too simple:
* Mammals survived. Why could small small non-flying predatory dinos not 
survive in similar ecological niches?
* The greatest devastation of plants was in N America, less in other 
parts of the N hemisphere, and even less in the S hemisphere. One would 
expect small non-flying predatory dinos to survive in at least some of 
the less devastated areas.

He also bases his response solely on the impact hypothesis. I've seen 
suggestions that the N and S hemispheres had separate wind systems, as 
they do now, so most of the fallout from Chixculub ( well N of the 
tropics) would have affected only the N hemisphere, except for the CO2 
emissions. In others words, I don't think Chixculub is a sufficient 
explanation for the K-T extinction.

If another factor (e.g. Deccan Traps) was responsible for most of the 
extinction in the S hemisphere, one would expect a different pattern of 
extinction. This would only make the extinction of small non-flying 
predatory dinos a more complex problem.

David Marjanovic wrote:
> > I'm rather disappointed at the lack of response to my original 
> > question - is there a decent explanation for the extinction of small 
> > non-flying predatory dinosaurs (including those which are regarded by 
> > some as secondarily flightless birds)? The  "standard theory" of the 
> > K-T extinction is that a catastrophe killed off vegetation, the 
> > herbivores starved and so the carnivores starved. But one would 
> > expect that small non-flying predatory dinosaurs could have survived 
> > by preying on lizards, invertebrates, mammals, etc. which survived 
> > the K-T extinction.
>
> This requires that large numbers of individuals of mammals etc. 
> survived, enough to sustain viable populations of predators -- and 
> that was apparently not the case (as expected from the impact 
> hypothesis). Indeed, several clades of mammals and lizards died out 
> altogether.


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