A new study, based on three dinosaur groups, has concluded that the Mexico asteroid strike should be viewed as the last nail in the coffin of these reptiles rather than the direct cause of their mass extinction (https://www.theguardian.com/science/2016/apr/18/dinosaurs-in-decline-long-before-asteroid-catastrophe-study-reveals). The authors conclude that the 'vigour' of these animals had already declined, as there appeared to be a marked decline in the creation of new species, in the period well before the strike. This is an interesting observation but it could be the case that the groups were well adapted to their available environments (no change over millennia doesn't always mean 'about to become extinct'). One could even argue that dinosaurs were diversifying, giving rise to the birds and the mammals, which were capable of exploiting new environments as well as surviving the aftermath of the asteroid hit.
