No, an asteroid struck the Yucatan effecting global weather to the point that nothing bigger than a chicken was able to thrive.
What was left of the dinosaurs evolved into the birds of today.
What you're seeing is simply variations on a theme with regard to attracting suitable mates, fending off competition, avoiding predation and increasing the likelihood of finding a decent meal.
Full size dinosaurs would've been a real issue.
So I threw a rock.
Go mammals!