In earlier Common Slavic, vowel length was allophonic, an automatic concomitant to vowel quality, with short and all other vowels (including nasal vowels) long. By the end of the Common Slavic period, however, various sound changes (e.g. pre-tonic vowel shortening followed by Dybo's law) produced contrastive vowel length. This vowel length survives (to varying extents) in Czech, Slovak, Serbian, Croatian, Slovenian and Old Polish, but was lost entirely early in the history of Russian, with almost no remnants. (A possible remnant is a distinction between two "o"-like vowels, e.g. and , in some Russian dialects, that may partly reflect earlier length distinctions.)