It seemed there was no role left for the asteroid impact or impacts at all.
The dinosaurs were doomed anyway:
except there was still evidence of an environmental catastrophe at the KT boundary.
The awkward unavoidable fact that remains to support the impact theory was the fern spike.
The predominance of fern spores in the KT boundary layers suggests that all vegetation was destroyed for a time.
Those who are convinced that Chicxulub killed off the dinosaurs argue that the fern spike, caused by the impact,
is still the key to understanding the mass extinction.
It's reasonable to think that all the standing vegetation all over the earth was destroyed,
so we don't understand exactly how yet,
but certainly its evidence of a dramatic catastrophe in the terrestrial eco system from the impact.
Because the vegetation was not destroyed by wild fires,
the most likely cause seems to be global darkness brought on by the impact dust
and that would have been catastrophic for the dinosaurs.