Earth, 1000 years ago.
There was many small tribes, all of them consisted of different animals. But the three primary were Hedgehog, Fox and Echidna. Then, a hedgehog named Niki had an idea. His idea was to combine all the small tribes into one big one, he explained it would combine all their ideas and help the economy. Everyone agreed and society boomed. The echidnas eventually decided to split up from civilization, and moved to Angel Island, but they would still allow anyone to visit.
Earth, 13 years ago.
Then, one night, nearly all the echidnas and Chao vanished. Only Knuckles the Echidna remained, and made it his sworn duty to protect the Master Emerald from anything that could harm it. This also prevented Knuckles from allowing anyone from visiting. Though he did sometimes visit and take interviews.
Knuckles the Echidna - I've never seen a hedgehog or fox in my life.
Earth, 8 years ago.
One the night of March 4th, a blue hedgehog was born. His original name was Maurice, but after it was discovered he had super speed. He was given the nickname Sonic, Sonic the Hedgehog. He was originally teased for having super speed, but after beating Dr. Eggman, he was praised for his ability.
References:
Sonic's birthday - This is a reference to Manic saying "on the second even day of the third month when the moon is full, BAM it shows up just like clockwork" in the episode Mobodoon, this suggests Sonic's birthday was on March 4th.
Sonic's name - Sonic's actual name in the Archie Comics.
Knuckles saying he hasn't seen a hedgehog or fox - This is a reference to Echidnas being in Australia while Hedgehogs or Foxes aren't.