Squats always were abhumans I think... it was something like heavy gravity conditions as they settled near the galactic core.
Felinids - and most of those others - we never learned about beyond the name I believe, but given GWs naming sense there's a suspicion of a planet full of catgirls out there. Think there was an article about abhumans in White Dwarf that mentioned them a dozen plus years ago.
EDIT: And as for the original wondering. Check 6th Edition, page 404 (I'm serious!) which has a bit on Abhumans that looks to have been copy-pasted into 8th...
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.
Last edited by Shandathe; 09-04-17 at 09:27 PM.