Yes, but not all diverged from each other from before the impact. It sounds like if you trace back humans, dogs, cats, cows, and many other mammals, they all have a common ancestor from after the impact. There is one species of rodent like thing you could snuff out after the impact that would wipe out most of the mammals in the world. This solenodon critter wouldn't be wiped out though. If you want to snuff out humans, cats, dogs, cows, and solenodons by erasing one single species, you'd need to go back to a time from before the impact and kill some ancient mammal critter that was alive when dinosaurs were the dominant animals.

Basically, solenodons are mammals, but they have been on their own genetic branch for a very long time.