Which Baltic languages became extinct as their speakers were assimilated by neighboring populations?

Several Baltic languages have become extinct as their speakers were assimilated by neighboring populations over the centuries. These extinct languages include:1

• Old Prussian: Spoken in East Prussia, these speakers were assimilated by the Germans by the beginning of the 18th century.2
• Yotvingian (or Suduvian): These speakers were assimilated by Lithuanians in the north and Slavs in the south, becoming extinct around the 16th–17th century.2
• Curonian (Kurs), Selonian, and Semigallian: By the 16th century, these groups had lost their national identities and were assimilated by the Latvians and Lithuanians.2
• D-Balts: These groups, who lived in the upper reaches of the Dnieper River, were assimilated by Slavs between the 7th and 14th centuries.23

While Lithuanian and Latvian remain the only surviving members of the branch, the extinct languages left behind very little documentation, with the exception of Old Prussian, which provided some written records.21