KNM-ER-3733 discovered in 1975 at Koobi Fora, Kenya, by Bernard Ngeneo. Fossil is near-complete Homo ergaster cranium, also called African Homo erectus. Age determined as 1.63±0.15 million years by magnetostratigraphy. Brain size measures 850cc. Less robust than male fossils KNM-ER-3883 and KNM-WT-15000 from same site. Conjectured female based on reduced robustness. Adult specimen due to extensive tooth wear. Third molars erupted before death. Cranial sutures fully fused. One of oldest Homo ergaster skulls worldwide. Found next to Lake Turkana. KNM-ER refers to Kenya National Museum, East Rudolf. Securely dated compared to oldest Homo fossils from Europe and Asia. Paleo-magnetic results delimit age to 1.78–1.48 Ma.