Do direct descendents of "sub" (As a preposition) only exist in Ibero-Romance(Spanish,Asturian,and Portuguese)?Most other Romance languages seem to use the derivative "subtus" to express "under".
I found, indeed, this word mentioned in: Meyer-Lübke - Romanisches etymologisches WörterbuchRomanian has su.
As well as in Catalan sota derives from subtus (see @Penyafort's post above), Spanish sota also derives from subtus and it's used as a prefix on some words like, for example, sotavento, sotabanco or sotacoro. On the other hand, sota as a preposition existed but it isn't used anymore. So (derived from sub) still exists as a preposition but its use is becoming rare (if it's not already rare) so it may end becoming out of use in a not too distant future.Most other Romance languages seem to use the derivative "subtus" to express "under".
In Spanish:In Sardinian there are at least three different ways to express "under" or "below"
- sutta or a sutta (from "subta") - under
- josso (from "deorsum"; compare also with Romanian "jos") - down, below, downstairs
- in basciu (compare with Portuguese "abaixo") - down, below