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dinosaur extinction

I have a question for list members. Earlier today I attended a talk by 
Prof. David Penny (Massey University) as part of a Bioinformatics 
seminar programme at the University of Auckland. As some of you may 
know, David has been a major contributor in the area of molecular 
evolution. In particular, some of David's work has focused on the 
estimation of divergence dates amongst bird and mammal taxa.

Today David said that dinosaurs were driven to extinction by the rise 
of mammals and birds between 120 and 65 mya (yes - I know birds are 
dinosaurs too!). He didn't dispute the existence of the bolide impact 
at the KT boundary, but said all that did was knock off the remaining 
few dinosaurs. What I had not heard before was his claim that this 
competition was size-related. David felt that birds and mammals 
replaced dinosaurs from the bottom up. Thus the last dinosaurs were all 
large animals. Does anyone know if this is supported by the fossil 
record? I know that there has been a lot of debate about dinosaur 
diversity leading up to the KT boundary, but I haven't been aware of a 
size dimension to these diversity data.



Kendall Clements