What is the origin of the bound taw letter in the Arabic alphabet?

by edenapple
CptBuck

Not to discourage other answers, but you might get a better response in /r/linguistics. Not least because I've only ever seen that referred to as "ta marbuta" تاء مربوطة and had to goolge what a "bound taw letter" was. I also can't speak to other semitic languages well enough to say whether or not it exists in, say, Hebrew or Syriac.