The paper I read specifically agreed with you. It said small, omnivorous, burrowing mammals were ideally adapted to the sudden world wide fire damage.
Also interesting - there is a dramatic increase in snake fossils and snake diversity after 66 mya.
I will guess that most of the amphibians came through in good shape, too.
Birds of prey didn't show up for another 20 million years, but I think they might have survived well in that new world, except possibly their eggs would have been vulnerable since most of the trees burned down.
Of course, everyone knows who will be the final two opponents in the Last Battle On Earth...
New York City Sewer Rats - versus - South Florida Palmetto Bugs
I think the cockroaches will eat the survivors...