The sundial belonged to the Srubna or Srubnaya culture, a Late Bronze Age society.

The sundial belonged to the Srubna or Srubnaya culture, a Late Bronze Age society. It is believed that the sundial was placed on top of the grave to mark the final resting place of a young man sacrificed or otherwise marked as a messenger to the gods or ancestors. Credit: Archaeoastronomical Research Center at Southern Federal University

The skeletons of the dead are normally found lying in a crouched position on their left side. The heads are often facing the East, whilst the legs and arms are bent, with the hands in front of the face. A ceramic pot was often placed near the head of the deceased, possibly for ritual purposes. Although the dead were usually buried in kurgans, numerous single buried skeletons have also been found within the vicinity of the houses for the living. It has been suggested that these skeletons belonged to the victims of foundation rituals.

https://www.ancient-origins.net/history/bronze-age-srubna-culture-and-their-unique-timber-graves-dead-002897