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dinosaurs vs. therapsids, etc.



Several comments have been made about why dinosaurs dominated mammals in 
the early Mesozoic.

Remember that therapsids are not mammals.  Conversely, if I have learned 
phylogenetic taxonomy (who, ME?), mammals are a derived sort of 
therapsid.  Anyway, for most of the Triassic, it was archosaurs vs. 
therapsids, not mammals.  

The first mammals were quite small, and were insectivores plus carnivores 
of very small things (like maybe lizards or each other), and differed in 
that regard from other therapsids except those closest to mammals (I 
realize there is one exception to the latter, although that therapsid 
lineage apparently came to an end before the end of the Triassic).  Did 
these shrew-like mammals really compete with dinosaurs?

Perhaps the reason mammals were not able to diversify to include large 
terrestrial herbivores and carnivores is the same reason that shrews or 
rodents have not been able to succeed against the Carnivora or 
artiodactyls.  In the case of the mammals, of course there is nothing in 
this situation relating to any basic superiority of a larger taxonomic 
group.  Maybe there wasn't in the case of dinosaurs vs. early mammals, 
either.  The dinosaurs that existed at that time were superior to the 
mammals that existed at that time for the niches won/occupied by 
dinosaurs.  I think that at the present time we lack the data to explain 
why, and I suspect we will be telling just so stories about this forever.

I must have some sort of personality defect that makes me arrive at such 
gloomy conclusions.  But somebody once said that he/she who believes 
nothing is closer to the truth than he/she who believes what is wrong.


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Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu