I agree with all of you
I am fully aware that my observations are only based on a single planet but I feel they are logical and until we find some more examples I can only say that I
personaly suspect that this is the way things are. Obviously I cannot know (though Lord would I ever like to
)
Also Chris, I agree that there are exceptions. As you say dinosaurs that stood on two legs could have developed the ability to manipulate tools, but I suspect there would not have been an evolutionary drive for that sort of lateral thinking. They were probably very effective predators as they were and for most of them that stood on two legs their arms, rather than developing as manipulators, seemed to be retreating to rather useless little limbs. I can't believe T Rex could realy do very much with those arms.
Rats and ideed many other predators are interesting in that they are clearly smart. Very necessary to be flexible enough to use the varying landscapes where their prey is. Things like; there's no good cover but there is a depression that could be used, where is the wind coming from etc. but I don't believe they will ever go beyond that without a pressing evolutionary need to free up their front limbs for manipulation.
Oddities like elephants could theoretically advance with their manipulative trunks but with only one manipulator you are limited by the inability to exerted opposing forces, twisting etc.
Another one is octopuses, again clearly smart and with multiple tentacles they can do twisting etc. However I think any purely water based speices faces a huge problem to evolve into a technological species as they don't get to discover fire, without which making even a hardened sharp spear is very difficult. Yes they might be able to use hot underwater vents in some way but I still think without mastery of fire any evolution of technology is very unlikely. I am always highly skeptical of books with ater based intelligent aliens.
I am still highly skeptical of any pure herbivore developing significant intelligence and going on to technology. I just don't see the same evolutionary drive. They simply don't need to do much thinking to find their food.
We can of course only speculate but my belief is that advanced intelligence will only come to mammalian
type species. Species that protect their young in nice safe wombs (or analogs of) whilst they develop much further than would be possible in, say, eggs and then go on to nuture and
teach their young (instinctive knowledge can never provide the flexible knowlege that teaching can.
I don't like to rule it out completely, I think if an herbivore did develop intelligence and tool use it would be fascinating to see as I suspect they would not develop aggressive warlike tendencies. Although herbivores might fight for the privilege to mate I don't think they very often fight for territory (though I may well be wrong there), so one herd fighting another just doesn't seem that likely.