FLK I (Frida Leakey Korongo) site lies on the bank of the main gorge, just above the confluence of two rivers. It was discovered in 1931 and was the first site at which stone tools were found in situ in Bed 1. On the morning of July 17, 1959, while out on a walk at FLK I, Mary Leakey noticed a portion of a skull poking out of the ground [6]. This discovery is labeled OH 5, which became the holotype for Zinjanthropus (renamed Paranthropus boisei) [3].

FLK 22

The FLK site Level 22 also called FLK Zinj and FLK 22 (1.84 Ma) in Bed I, Olduvai Gorge (Tanzania), has played a pivotal role in the reconstruction of early Pleistocene hominin behavior for the past three decades [7]. OH 5, a cranium and the holotype of Paranthropus boisei, commonly known as Zinjanthropus, a genus name assigned to it earlier by Louis Leakey [3] was recovered from this level. The hominin remains recovered during the excavations also included three more individuals of Homo habilis and Paranthropus boisei (OH6, OH35, OH44) [8][9][10][5]. 

The OH 5 cranium is from an adolescent, probably male, with an estimated age at death of 15 - 17 years [11][10]. OH 6 comprises a mandibular third premolar, right maxillary first molar, right maxillary second incisor, and six calvaria fragments from a 5-6 year old Homo habilis child [10]. OH 35 is a tibia and fibula of an adult Homo habilis [9][8][12] or possibly Paranthropus boisei [10]. The fourth hominin, OH 44, a surface find made in 1970 and thought to have eroded from FLK Zinj [13][10], is a right maxillary first molar of a Homo habilis child aged 4-5 years [10][14]. The age of the Zinjanthropus level is bracketed by two volcanic tufts, both dated to approximately 1.84 Ma [15][4][16][17]. 

FLK Zinj contains roughly 60,000 faunal specimens (3,500 of which are identifiable to at least skeletal part) representing a minimum of 48 large mammal carcasses (most of them bovid) as well as over 2,500 Oldowan stone artifacts [4][18][19][20]. Bone weathering on the fossils from FLK Zinj indicates that the assemblage likely accumulated over a time range of 5-10 years [21][22].

FLK Zinj site contains some of the best-preserved evidence for meat-eating by hominins and has been extensively used to reconstruct early hominin behavior [22]. The Leakeys interpreted FLK Zinj as an “occupation” or “living floor” [3][23][4] on which hominins made stone tools to butcher a large size range of ecologically diverse mammals (e.g., Bunn [24], Potts and Shipman [25], Kroll and Isaac [26], Blumenschine and Pobiner [27]). Other interpretations have been offered (e.g., Potts [28]; Binford [29], Njau and Blumenschine [30]), but FLK Zinj epitomizes to many researchers an ancient progenitor of a modern hunter-gatherer home base to which a full group’s subsistence and social activities were tethered over consecutive days and nights [31].