KNM-ER 3733

Koobi Fora Area 104
Specimen number:
KNM-ER 3733
3.96, 36.3
Date min:
1,630,000 Bp
Date max:
1,780,000 Bp
Homo, Homo ergaster
Time periods:
Calabrian, Pleistocene
Homo ergaster KNM-ER 3733 IMG 5637 BMNH

Homo ergaster KNM-ER 3733 IMG 5637 BMNH

KNM-ER 3733 is a relatively complete Homo ergaster cranium discovered in situ by Bernard Ngeneo in 1975 in Area 104 of the Koobi Fora formation in Kenya. The supraorbital tori being just exposed on the surface. The maxillary and facial skeleton was fragmented and exposed within a distance of about 50cm from the vault. Tooth crowns and an assortment of small fragments were recovered by sieving the area immediately below the skull. The cranium is large with only a slight postorbital constriction. The supraorbital tori are prominent, protruding anteriorly[1].


KNM-ER 3733 is commonly attributed to an adult female determined by less robust cranial morphology, however, since no certain sex determination can be made which is a common limitation in palaeoanthropology[2]. It has an endocranial capacity of 848 ml. The supraorbitals arc separately over each orbit and project forward as well as upward. There is thus a distinct posttoral sulcus in front of the quite steep frontal rise, which rapidly peaks before the profile descends more gradually rearward. Seen from behind, the braincase is rather tall compared to its breadth, and its side walls are curbing. The raised temporal lines start quite far medially[3].

The geological age of KNM-ER 3733 has been a subject of debate because of changing interpretations over the stratigraphy of KBS member. Feibel et al. [4] used the position of the top of the Olduvai Subchron to estimate an age of ~1.78 Ma. Brown et al. [5] used tephrochronology to reinterpret the position of the top of the Olduvai Subchron in the type section of the KBS member and posited that the estimated (interpolated) age is 1.63 Ma. McDougall et al.[6] suggested an age of 1.65 Ma for the fossil. Lastly, through magnetostratigraphy of samples from Area 104,  Lepre & Kent (2015)[7] determined its age to be ~1.63 Ma.

KNM-ER 3733 is also involved in another debate which is about classifying fossils as “African Homo erectus” vs a separate Homo ergaster. After its discovery, it was classified as Homo erectus by the Koobi Fora team [8][9], but some researchers classified it as Homo ergaster [10]. Homo ergaster is the designation of choice for the growing number of palaeoanthropologists who believe that the fossils previously allocated to “African Homo erectus” are sufficiently different from the Asian-type material of Homo erectus to warrant assignment to a distinct species[3].


Cited References

  1. 1.

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  7. 7.

  8. 8.

    Further hominids from the Plio-Pleistocene of Koobi Fora Kenya

    American Journal of Physical Anthropology , 67(2)

  9. 9.

    The hominids of East Turkana

    Scientific American, 239(2)

  10. 10.

This page was last edited on November 10, 2022 at 08:49:56 UTC