Around 4000 years ago, a dog left its pawprints in this Sumerian brick :
Sumerian Clay Brick with a Dog's paw prints (2112-2000 BC), from ziggurat at Ur; Mesopotamia (modern-day Iraq).
According to scholars, around 2100 BC, a dog walked across this brick as it lay drying in teh sun when it was being made. Brick is stamped with an cuneiform inscription which tells that "Ur-Nammu, king of Ur, has built his temple for Nanna, his Lord. Also built city wall of Ur for him."
British Museum