Duration of Dinosaur Reign

[Amado Narvaez <anarvaez@umd5.umd.edu>]

I have noticed what appears to me a wide disparity in the estimation of 
how long dinosaurs reigned on the earth, generally ranging from 140 
million years (in Sattler's _New Illustrated Dinosaur Dictionary_ 
published in 1990) and 180 million years (in Spinar and Currie's _The 
Great Dinosaurs_ published in 1994). Is the disparity due to evidence 
discovered in the last few years that extends the reign, or is the 60 
million year difference a case of "... 160 million years, give or take
20 million years..?"

Also, authors are fond of pointing out how long the dinosaurs reigned, 
comparing it to how brief the reign of humankind has been. Wouldn't it be 
more accurate to make a comparison based on individual species? 
Is there any evidence to indicate, for example, how many millions of 
years Deinonychus thrived before it became extinct?

----- Amado Narvaez
      anarvaez@umd5.umd.edu