138 AFRICA
petrosal is featureless (no doming in region of arcuate
eminence, no superior petrosal sinus). Internally, sur-
face of maxilla bears indications of a large maxillary
sinus extending upward to region of nasomaxillary
suture.
ER 992 Morph
KNM-ER 820. Juvenile mandible with corpus and
part of L ramus. Is and Mls have erupted; Ldc and
both dmls and dm2s present. M2s in crypt.
Tight curve across front of jaw externally and es-
pecially internally. Tooth rows moderately divergent.
Bone of corpus relatively thick b/l across symphyseal
region. Symphyseal region arcs back gently in profile.
Genial pit broad and shallow. Single mental foramen
lies under each dm2. Mandibular foramen open and
very long. Remnants exist of fairly large internal pillar
that must have descended from coronoid process to
meet lingual alveolar crest.
Resembles ER 992 in Ml morphology. 12s some-
what larger than 11s; distal margins more flared. Decid-
uous teeth quite worn. dc was apparently simple,
triangular, with longer distal than medial edge. dmls
had two very splayed roots; were very exodaenodont
over anterior root. dml paracristid curved sharply
lingually and terminated leaving small notch-like open-
ing in lingual side of trigonid basin. dm2s had well-
developed, slightly buccally placed hypoconulids; appear
to have had m/d short but b/l wide trigonid basins. Ap-
parently dm2 hypoconulid extended lingually just be-
yond midline of crown. Mls essentially unworn, show-
ing extensive thick, deep wrinkling, very well-developed
trigonid basin, and large centrally placed hypoconulid
with distinct notch between it and hypoconid. M1
hypoconid extended lingually beyond midline of crown.
KNM-ER 992 (type specimen of Homo ergaster).
Mandible in two halves missing incisors, most of right
ramus, and left condylar area. Symphysis damaged.
Teeth quite heavily worn.
Corpus moderately deep and fairly narrow from
side to side. Symphyseal region smoothly arced exter-
nally and slightly receding; devoid of any features.
Shape of dental arcade hard to determine, but dental
rows long and jaw would have been fairly narrow at
front. Internally on corpus almost no morphology: no
mylohyoid line, submandibular fossa long and shallow;
digastric fossae small and shallow. Internally on angle
are some moderate rugosities low down; externally,
the angle is somewhat concave but not rugose, with no
significant inflection either way. Left coronoid process is
broad and long; internally, a very strong pillar runs down
from near tip of coronoid, starting vertically and then
rapidly arcing forward to join lingual margin of alveolar
crest. Most distal part (at least) of M3 would have been
hidden behind the anterior margin of the ramus. Mental
foramina single on both sides; they lie under P2s.
Occlusal surfaces of all teeth, including canines,
are worn quite flat (lingual sides do not remain higher
than buccal sides), but enamel is hardly penetrated.
What remains of the C has a slight lingual tubercle;
met on either side by margocristids. P1 has a rather
centrally placed protoconid, connected by a ridge to
the lingual swelling opposite it. Anterior and posterior
foveae both quite large; anterior fovea is longer m/d
and posterior fovea wider b/l. P2 is a more rounded
tooth. Protoconid located slightly more anteriorly
than the relatively small metaconid; a short crest con-
nects the two cusps. P2 posterior fovea was much
larger in all dimensions than the small anterior fovea.
All three Ms bear centrally placed hypoconulids and
narrow but distinct trigonid basins. Enamel distinctly
wrinkled on M3 and would have been somewhat
wrinkled on M2. Buccal sides of Ms become more
rounded in sequence M1-3. Only on M1 does
hypoconid extend lingually across midline of tooth.
M2 hypoconulid noticeably projects distally. The
molars are relatively elongate m/d and narrow b/l.
M3 is larger than M3, which is larger than Ml.
KNM-ER 1507. Partial L juvenile corpus with
dml, dm2, M1, and M2 beginning to erupt. Larger
than ER 820, but teeth similar in morphology. dm2
less worn than on ER 820, and shows some wrinkling
of the enamel; M1 very deeply wrinkled.
KNM-ER 1590. Many small cranial vault pieces,
reassembled into larger pieces, notably parietals
including coronal and sagittal sutures. Also several
isolated teeth, not all from same individual. Only one
tooth from this collection, ER 1590B (presented
below), appears consistent with this morph. Most of
the rest of ER 1590 is described in “Others” category.
ER 1590F described under “Non-hominid.”
ER 1590B. LI’; very weathered. Root was very
long, stout. Crown very tall, wide m/d, and laterally
flaring. Lingual surface just slightly rippled; lingual
tubercle starts high on crown.KNM-ER 3734. L mandibular corpus with C-M2,
very badly worn.