Why did all dinosaurs, rather than just some of them, go extinct during the K-T extinction event? Birds are an exception, but being able to fly, they are also a very special kind of creature, and specalization doesn't usually help with resilience.
My understanding is that dinosaurs filled a very broad and diverse set of ecological niches. In view of this diversity, it is counterintuitive to me that all members of such a diverse set of species would disappear, rather than just a fraction of them.
Did they have (or lack) a common set of features that distinguished them from mammals and birds and made them particularly susceptible to whatever caused the extinction? Did their niches cease to exists temporarily? (It couldn't be the case for all of their niches, could it?) Did mammals already have superior potential which could finally be realized because something upset the global ecological balance?
To sum up, my question is why a large and diverse group disappeared completely rather than partially. There must be some ecological principles that could illuminate it.
Please excuse this naive question from an ignorant but interested layman.