Exactly, sugar gliders and seals mean we don't need transitional fossils between 'land bats' and flying ones, or between 'land dolphins' and aquatic ones: we can already see that evolution can get a similar organism partway there, and if we find some smoking-gun fossils later, so much the better.

Flying squirrels evolved gliding independently from bats. Bats aren't rodents and they're not closely related.

Precisely, we are witnessing evolution in a similar direction in real time.

Hundreds of thousands of years in the future, their descendants might actually be flying not gliding.