In ages past, planet Earth was dominated by the reptiles, but a
worldwide catastrophe wiped out a few species (the ancient
dinosaurs).
Humans now rule the planet, and we've been able to populate almost
all parts of the planet because of these reasons:
1) We use technology to help us adapt to new environments.
2) Our way of reproduction means that eggs would not be stolen by
predators, unlike the reptiles whose eggs were either stolen or
eaten by other creatures and usually only a minority of even none
of the eggs are able to hatch, making it difficult for a species to
continue to grow...
In the future, after the human race has been wiped out by
either:
1) A terrorist threat
2) Lost of environment due to natural/artificial disasters
3) Chemical/Nuclear warfare
4) Extraterrestrial Influence (Asteroid Impacts)
I believe that the next group of creatures that would reign over
the planet would be the Insectoids because:
1) Exoskeleton (Great adaptability to extreme environs)
2) Small Size (Able to hide in many places, better the chance of
survival)
3) Colonies (Like termites, ants, great team effort and work will
allow the insectoids to thrive in this new world)