The JW answer to this is that there must have been some purpose for them that we don't yet understand.
But dinos were pretty violent, basic animals who killed without mercy. I know not all of them but alot of them did. The ones that were vegetarian ate huge masses of vegatation, how is that productive to the earth?
If god created man in his image then what base image did he use for the dinos? And why start off with the dinos at all? Why not just create man?
And... why also not stick a little scripture in the bible, somewhere around the point just before god rests ont he 7th day saying something like " oh yeah and i tried filing the world with monsters who had no moral code and not the brain power to be able to worship me. I let them get on with it for a few million years then killed them all off... just couldn't get them to sacrifice a lamb on the sabbath you know?!"
theres alot in the bible about not stumbling others... well did god not think how stumbled mankind would be when they of course came accross the fossils of these beasts?