Which group of American Indians were the first to bury there dead?

The Adena culture, which existed in what is now the eastern United States around 1000 BCE to 200 CE, is one of the earliest known groups of American Indians to practice burial of their dead. They created elaborate burial mounds, often incorporating grave goods and artifacts, which reflected their beliefs and social structures. This practice of burial and mound construction set a precedent for later cultures in the region, such as the Hopewell and Mississippian cultures.