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RE: Why did small dinos become extinct?



Philip Chalmers 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?
>Why could small dinos not survive by preying on the granivores and 
>insectivores, as cats do now?
>
>"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?
>
>These two points are the central part of the question I originally 
>raised. The only explanation I can think of is that small flightless 
>theropods were squeezed out by the young of larger theropods and by 
>small predatory mammals (successors of Repenomamus). The young of larger 
>theropods were doomed because they grew to a size where they needed to 
>prey on large herbivores, which were exterminated by the catastrophe(s). 
>Are there better theories?
>
[snip
>... I was asking what feature(s) of dinos 
>or of latest Cretaceous ecosystems made it impossible for small 
>non-flying theropods to survive.

Might I humbly point to the success of squamates in the small terrestrial
predator niches?  Varanoids and snakes commonly reach larger body sizes than
Compsognathus et al., are well equipped for gobbling granivores and
insectivores but need much less energy than similar-sized mammals (or
probably dinosaurs), and they were more or less global in distribution by
the end of the Cretaceous after only starting to show up in the mid-Early K.
They show good lineage survival through the K/P boundary, which probably has
something to do with being able to fast for a year or more (especially in
relatively low temperatures). This is all pretty well known stuff, and does
it not seem sufficient to answer your question?

-----------------------------------------------

Dr John D. Scanlon, FCD
Palaeontologist, 
Riversleigh Fossil Centre, Outback at Isa
19 Marian Street / PO Box 1094
Mount Isa  QLD  4825
AUSTRALIA
Ph:   07 4749 1555
Fax: 07 4743 6296
Email: riversleigh@outbackatisa.com.au
http://tinyurl.com/f2rby