150 years after people
The descendants of house cats now live in the vertical ecosystems that have formed in abandoned skyscrapers. Cats have become the apex predators of the skyscrapers, living on mice and birds. These cats have never touched the ground; they find all they need to survive in the gutted skyscrapers where they spend their entire lives. Because they spend all their time above ground some cats evolve into flying cats, being able to glide like flying squirrels.
10,000 years after people
The descendants of house cats still survive in the wild. Most house cats have remained small due to the presence of big cats such as cougars, but of the descendants of some house cats have evolved to be bigger in areas where there is no big cat population before, and are now the size of bobcats.