Its speakers, the hypothetical Proto-Iranians, are assumed to have lived in the 2nd millennium BC and are usually connected with the Andronovo archaeological horizon (see Indo-Iranians).
The Proto-Indo-European laryngeal consonants are likely to have been retained quite late in the Indo-Iranian languages in at least some positions.
[12] This change is found widely across the Iranian languages, indeed Indo-Iranian as a whole: it appears also in Vedic Sanskrit.
The Proto-Indo-Iranian aspirated stops *pʰ, *tʰ and *kʰ were spirantized into *f, *θ and *x in most Iranian languages.
The consonant cluster *ts (as in Proto-Indo-Iranian *matsya- "fish") has merged to *c, since both were identical in Iranian.
This change is typical for Old Persian and its descendants, as opposed to Avestan and most languages first attested in the Middle or New Iranian periods.