Its speakers, the hypothetical Proto-Indo-Iranians, are assumed to have lived in the late 3rd millennium BC, and are often connected with the Sintashta culture of the Eurasian Steppe and the early Andronovo archaeological horizon.
In many reconstructions, instances of *iH and *uH occur instead of *ī and *ū. Proto-Indo-Iranian is hypothesized to have contained two series of stops or affricates in the palatal to postalveolar region.
The following table shows the most common reflexes of the two series (Proto-Iranian is the hypothetical ancestor to the Iranian languages, including Avestan and Old Persian):[4][5] Proto-Indo-European is usually hypothesized to have had three to four laryngeal consonants, each of which could occur in either syllabic or non-syllabic positions.
Pronouns, nouns and adjectives are inflected into the eight cases of PIE: nominative, genitive, dative, accusative, vocative, ablative, locative and instrumental (with also a comitative/sociative meaning).
Despite Proto-Indo-Iranian preserving much of the original morphology of Proto-Indo-European, an important innovation in the noun is the creation of a genitive plural ending *-nām used with vowel stems.