How did East Scandinavian dialects differ from West Scandinavian dialects during the Viking Age?

During the Viking Age (c. 750–1050), Scandinavian speakers generally viewed their language as a single entity, often referred to as "Danish" in contrast to "German." However, the differing political orientations of the various kingdoms led to the emergence of distinct dialectal areas: a more conservative West Scandinavian region (Norway and its colonies, particularly Iceland) and a more innovative East Scandinavian region (Denmark and Sweden).1

Key linguistic differences between these areas included:

• Monophthongization: A primary feature of East Scandinavian was the monophthongization of the Old Scandinavian diphthongs ei, au, and øy into ē and ø. For example, steinn ("stone") became stēn, lauss ("loose") became løs, and høyra ("hear") became høra. These diphthongs were generally preserved in West Scandinavian, as well as on the island of Gotland and in most North Swedish dialects.1
• Pronoun usage: The pronoun ek ("I") remained ek in West Scandinavian (and in Jutland). In contrast, it shifted to jak in East Scandinavian, which evolved into modern forms like the Danish jeg and Swedish jag.1