Re: Why did small dinos become extinct?

[Dann Pigdon <dannj@alphalink.com.au>]

john hunt writes: 

> If you accept the global de-vegetation theory it is possible to postulate a
> fast extinction of all large animals (bigger than a cat), everything that
> was not an insectivore, as there must have been a bug spike to go with the
> fern spike. 
>
> Not sure how the crocs made it through though.

No doubt there was an initial glut of carcasses for crocs and small 
theropods to scavenge from. Once they were gone (either eaten or rotted 
away), the lower metabolism of crocs may have given them an advantage, since 
they could have gone longer between meals than a high-performance theropod. 

Being able to swim (crocs) or fly (volant theropods) may have also been an 
advantage, as either mode of travel would have allowed animals to cross long 
distances in search of scarce food. Purely terrestrial animals (non-volant 
theropods) may not have been able to travel the necessary distances between 
food resources efficiently enough. If you use more energy finding food than 
the food itself provides, then you eventually starve. 

Then there are questions of genetic bottlenecks. Some modern rodents can 
found an entire population based on a single pregnant female, with few 
inbreeding problems. Other species suffer far more from inbreeding, and 
require a much larger gene pool to remain viable. I suspect those species 
susceptible to inbreeding tend to fare poorly during mass extinction events, 
while those that can bounce back quickly despite genetic bottlenecks tend to 
thrive. In the case of theropods, perhaps only some of the volant varieties 
were able to cross large enough distances between isolated pockets of 
survival to maintain a necessary level of genetic diversity. 

___________________________________________________________________ 

Dann Pigdon
GIS / Archaeologist              geo cities.com/dannsdinosaurs
Melbourne, Australia             heretichides.soffiles.com
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