Re: Why did small dinos become extinct?

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

"They weren't. It's just that the small dinos in these niches were birds. "
The top of the para to which this comment responds contains "small 
_non-flying_ dinos". I'm interested in why small non-flying predatory 
dinos did not survive by preying on invertebrates, mammals, lizards, etc.

"Because almost all the granivores and insectivores died. If a predator 
feeds on ten prey species, and nine of those disappear while the tenth 
undergoes a population bottleneck, the predator starves to death."
The P-Tr extinction was much worse than the K-T, including the damage to 
plants ans insects, but cynodonts and archosaurs survived. Also some 
fairly large predators survived (crocs and champsosaurs, although they 
were at least semi-aquatic). I'd have expected small _non-flying_ 
predatory dinos to survive more easily than crocs and champsosaurs 
because small _non-flying_ predatory dinos could live on small prey. Is 
there any discussion of this puzzle in the literature?

David Marjanovic said in an earlier post, "Incidentally, no flightless 
theropod the size of Compsognathus or smaller is currently known from 
the Maastrichtian, AFAIK," and that's the impression I've got from what 
I've read. So part of the puzzle is why there were no chicken-sized 
_non-flying_ predatory dinos in the latest Cretaceous. My _guess_ is 
that they were squeezed out by some combination of birds, mammals and 
the young of larger predatory dinos (doome dbecuase they grew too large 
for this niche in a few years). Is there any discussion of this possible 
explanation in the literature?

Andreas Johansson wrote:

On Dec 12, 2007 4:56 PM, Philip Chalmers
> <philipchalmers@blueyonder.co.uk> wrote:
>   
> > Despite the thoroughness of David Marjanovic's response I think there
> > are still some gaps:
> >
> > "Because they (small non-flying dinos), or most of them at least, did
> > not have similar ecological niches. The surviving mammals and lizards
> > mentioned above were for the most part granivores and insectivores; of
> > the only dinosaurs in these niches, some survived -- all of them
> > happened to be neornithean birds (and lithornithids, if those don't
> > belong to Neornithes)."
> > Why were small dinos excluded from these niches?
> >     
>
> They weren't. It's just that the small dinos in these niches were birds.
>
>   
> > Why could small dinos not survive by preying on the granivores and
> > insectivores, as cats do now?
> >     
>
> Because almost all the granivores and insectivores died. If a predator
> feeds on ten prey species, and nine of those disappear while the tenth
> undergoes a population bottleneck, the predator starves to death.
>
>   
> > "No flightless theropod the size of *Compsognathus* or smaller is
> > currently known from the Maastrichtian, AFAIK." That's also my
> > impression, but the question is why not, given that there were earlier
> > very small flightless theropods?
> >     
>
> I don't know, but I suspect that the presence of very small
> nonflightless theropods had something to do with it.
>
>   


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