This video give a bit of tidbits to Sonic lore, such as implying the civilization that once inhabited Starfall Islands may had once known the echidnas in Sky Sanctuary. Whenever this was before or after the rising of Angel Island it's unknown.
Have I told you my "Starfall Island was formerly Nocturne Clan territory" theory yet?
Yep, already read youres here :
https://sonic.fandom.com/f/p/4400000000000168613It could be true after hearing the other two islands' name *SPOILER* :
Rhea (Gaia's titan daughter) and Uranus (the sky god, kinda fit with the Angel islands).but Brotherhood wasn't canon so may be the story won't go there or would be a little different.