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Re: Why did small dinos become extinct?



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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