CHEMERON
LOCATION
Open-air site (EAGRU JM85) in the Kapthurin river
valley of the Tugen Hills region, just to the southeast
of Lake Baringo, Rift Valley of central Kenya. Nearby
sites have produced much younger (and older) ho-
minid fossils that are not described here.referred by Hill et al. (1992) to Homo sp. indet., as the
earliest “securely known” member of that genus. In a
review of features of the horninid temporal bone,
Sherwood, Ward and Hill (2002) have recently red-
firmed this assignment for BC 1; but other interpreta-
tions remain possible.DISCOVERY MORPHOLOGY
J. Kimengich, October 1965. Fragmentary R temporal bone missing most of squa-
mous and mastoid regions.
MATERIAL Externally, inferior portion of squamosal is
KNM-BC 1, partial right temporal bone. marked by parallel rugosities running in a superopos-
terior direction. What remains of laterally markedly
flared posterior root of zygomatic arch takes origin
from above midline of rather large, subcircular, poste-
riorly tilted external auditory meatus. Small postgle-
noid plate pro-jects inferiorly from posterior root and
abuts auditory meatus. Huge articular fossa is almost
entirely preserved, missing only lateralmost part; it is
extremely wide mediolaterally, long a/p, and quite
deep. Anteriorly fossa is bounded by a well-developed
articular eminence. Vaginal process runs along center
of ectotympanic tube and fades laterally toward mea-
tus. Mastoid region, although broken, was evidently
quite flat, as indicated by preserved bone surfaces be-
low lateral extremity of what was evidently a distinct,
bulky nuchal ridge that did not reach meatus. No
supra-meatal crest. Breakage of superficial bone of
mastoid region reveals large numbers of small air cells.
Deep, distinct, almost horizontally oriented parietal
notch lies at rear of parietomastoid suture; notchDATING AND STRATIGRAPHIC CONTEXT
Surface find deriving from the Pliocene Upper
Chemeron Fm (Martyn, 1967). The JM8S locality has
been dated at 2.4 Ma by 4Ar/39Ar on anorthoclase from
a pumiceous tuff taken from 2.5 m below the hominid
horizon (Hill et al., 1992). This age has since been con-
firmed by additional dating studies (Deino and Hill,
2002) that have clarified the stratigraphic relationships
of important exposures of the Chemeron Formation in
the Kapthurin and Tabarin areas of the Tugen Hills.ARCHAEOLOGICAL CONTEXT
None.PREVIOUS DESCRIPTIONS AND ANALYSES
First described as a hominid of indeterminate affinity
(P. Tobias, in Martyn, 1967), this specimen was51