Siouan languages
Siouan or Siouan–Catawban is a language family of North America that is located primarily in the Great Plains, Ohio and Mississippi valleys and southeastern North America with a few other languages in the east.
Mandan
The Mandan language or "Nų́ų́ʔetaa íroo" belongs to the Siouan language family. It was initially thought to be closely related to the languages of the Hidatsa and the Crow. However, since the Mandan language has been in contact with Hidatsa and Crow for many years, the exact relationship between Mandan and other Siouan languages (including Hidatsa and Crow) has been obscured. For this reason, linguists classify Mandan most often as a separate branch of the Siouan family.