My Sonic Headcanons!
I originally posted this as a comment, but I wanted to repost this so others can see it better, so enjoy!
(Spoilers for Frontiers, by the way)
Sonic's world is named Planet Gaia, after light and dark Gaia.
When the chaos emeralds were brought to Sonic's world, their energy from the chaos emeralds would mutate the landscape. Giving Planet Gaia it's natural corkscrews, loops, floating platforms, and anthropomorphic animals.
-The anthropomorphic animals would be offically called islanders, because they primarily lived on islands. (South Island, Westside Island and Angel Island for example.)
The master emerald had a similar effect, but solely on the echidnas on what would become angel island many years later.
During the classic era (1, CD, 2, 3&K, etc..) relations between the humans and the islanders would be pretty...iffy. Mostly because of the islanders' pre-installed fear of humanity and their tech via Dr. Robotnick, and humans' doubts of islanders thanks to their claws, fangs etc. This is why we only see Sonic, Tails, Knuckles, Amy, Big, Rouge and Shadow as the only islanders in the adventure games.
However, due to Sonic defeating Eggman time and time again in the classic games, saving Station Square from Perfect Chaos in Adventure 1, and saving the entire planet from certain destruction in adventure 2 and onward, humans and islanders started to get along pretty well!
Islanders tend to live with nature, not over it like humans. So you're more likely to find an islander village rather than a whole city.
All islanders are omnivores, but they'll lean to being more carnivorous or herbivorous. Tails as a fox would lean more towards meat than Cream who would lean more towards fruits and vegetables.
Since you can't eat an islander without getting sent to prison, humans and islanders alike tend to get their meat from the unevolved animals. Like the flickies and such.
The chaos emeralds can give any islander a super form, it'll just look different depending on species. Hedgehogs will get the typical 'Super Saiyan' look, for example. Evidenced by Sonic, Shadow, and Silver.
By the time Sonic forces happened, many islanders have migrated into human territory. Some even building cities for themselves! This explains all the cities we see.
'Islander' is a umbrella term, like calling people 'Black'.
Mammalian islanders tend to be the majority of islanders, with reptilian and insectiod islanders being more of a minority.
If you're seeing this, thanks for reading to the end, and hearing me ramble!