"I personally think impacts probably have played a major part in mass extinctions so I don't have any major quible with your comments. We just don't have conclusive evidence that is the case and we do have some good reasons to doubt it."

What good reasons? Some "reasons" come to mind: Super volcanos, cosmic events excluding impactors (e.g. changes in sun output, nearby supernovas, and changes local gas density of space), and events like over production of oxygen. I don't see these reasons as particularly "good". And some these reasons *COULD* have a relationship to impactors, e.g super volcano could be a result of a impactor- orginally formed and later trigger wide spread volcanic eruptions.

"My issue was that mass extinctions are not the major source of extinction as Peiser and some paleontological illiterates here seem to think."

Yes, but this is a nit not a point. Peiser was referring to mass extinction events, and Peiser was in a discussion, not writing on scientific peer reviewed paper.

"Climate change certainly impacted many if not most of the pachyderm extinctions you mentioned not to mention pressure from a new form of predator. The surviving pachyderms may benefit from a shortage of cliffs in their area."

What changing the climate?
Certainly it's not a result of human activity.