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Re: Why did small dinos become extinct?



"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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