>>715291863
I think even without the K-Pg extinction several mammal lineages would have still evolved to some degree, mostly due to them benefiting far better off of the inevitable spread of angiosperms and their symbiotic insects
first being the rodents, now while the Cretaceous already had rodent-like mammals, true rodents would have been able to exploit the angiosperms exceedingly well, and also would have formed a major issue for dinosaur eggs, I could genuinely see dedicated egg-eating rodents, combined with perennial angiosperms and grasslands replacing all other undergrowth be a slow but inevitable decline for the sauropods, perennial trees would have forced them into massive migrations, but they were also exceedingly poorly equipped to handle grasses
the combined pressure of this with their eggs being raided might have seen the largest land animals be brought down by some of the smallest
another group of mammals I could easily see evolve would be the bats, they managed to gain their niche despite competing against the one dinosaur that did not go extinct, in the birds, and birds themselves were already well on their way to displacing pterosaurs completely from smaller niches
As such the existence of non-avian dinosaurs wouldn't have impeded them much
And finally, the primates, which would have been one of the prime mammal beneficiaries of the spread of angiosperms and particularly, fruits
there already is a severe lack of arboreal non-avian dinosaurs in the cretaceous so it's yet another example of a group that would not have had too much competition
Carnivorians obviously would not have existed in their apex predator forms, but given just how many mustelid-shaped mammals we keep finding, it's reasonable to assume that mustelids or something similar to them would have evolved especially if rodents spread far themselves
