Kenyanthropus and Australopithecus afarensis represent
two putative ancestral hominids from the period of 4 to 3 million years
ago.While their brains were small and the skulls were more apelike, they
walked upright. Some features, such as the hips of Australopithecus afarensis,
were essentially human in their structure.
DATES: 3.9 to 3.0 million years ago
SITES: Hadar, Ethiopia; Middle Awash, Ethiopia; Omo, Kenya; Koobi Fora,
Kenya; Laetoli, Tanzania; Chad (Morell, 1995; Johanson, 1982)
--The 1995 Chad discovery is interesting because it is 5400 km west of
the Rift Valley sites (Brunet, 1995).
SPECIMENS: many individuals, cranial, dental, and post-cranial remains
including Lucy and First Family
The cranial capacity was 375-500 cc which is larger than the chimp average.
The brain weight/body size ratio is outside of the chimp range. A. afarensis
had an apelike face with sloping, low forehead, a bony ridge over its
eyes, a flat nose, and no chin. Most of its skull is apelike. The face
did not protrude to the same extend that the face of a chimp does. The
pelvis and leg of A. afarensis were very similar to those of humans. The
legs were a little shorter than in humans. The pelvis allowed bipedal
walking but there is no evidence of an enlarged birth canal that would
have permitted enlarged fetal crania (Johanson, 1979; Susman, 1984; Hill,
1985; Leakey, 1972; Lovejoy, 1972; Lovejoy, 1993).
The hands and feet of A. afarensis were similar to those of humans although
the long forearms, the curved finger and toe bones, and the angle of the
shoulder socket may indicate it spent some time spent in trees. The narrow
metacarpal heads (ends of the bones that make up the hand) may have prevented
tool use (Skelton, 1986; Johanson, 1979; Gibbons, 1997b; Susman, 1994).
The height range was 33 to 57. The females were
smaller than males and Lucy (see next illustration) is the smallest specimen
known. Australopithecus afarensis was bipedal given evidence from the
pelvis, knee, and the position of the foramen magnum (where the spinal
cord enters the skull). The images below indicate that australopithecines
possess a more anterior foramen magnum, indicative of a bipedal stance.
Footprint trackways known as the Laetoli footprints (2 sets: one of 5
prints, one of 12 prints) are consistent with the A. afarensis stature,
date (3.6 to 3.8 mya), and surrounding fossils. The gait of the individuals
that made these footprints is more shambling than in modern humans but
it was certainly bipedal and unlike the quadrupedal baboon-like prints
found nearby (White, 1980; Day, 1980; Leakey, 1979; Wolpoff).
The canines and jaw shape of A. afarensis were intermediate between
apes and humans with large sexually dimorphic canines, a diastema (space)
between teeth sometimes present, molarized premolars, large molars, and
thick enamel on molars. The teeth represent a generalists denticia
(as in humans) and lack the tooth specializations seen in some later australopithecines
(Skelton, 1986; Johanson, 1979; Wolpoff, 1978). There is evidence of some
carnivory by early australopithecines (de Heinzelin, 1999).
The habitat of A. afarensis seems to have been woodland and more open
than that of A. ramidus. The appearance of this new habitat was caused
by the changes in Miocene climate with its greater cooling, aridity, and
increased seasonality (Johanson, 1982). The degree of sexual dimorphism
in Australopithecus afarensis was similar to that observed in modern human
DATE: 3.5 million years ago
SITE: Lake Turkana, Kenya
SPECIMENS: 1 complete cranium; isolated skull portions (temporal, maxillary)
Kenyanthropus was similar to Australopithecus afarensis in many respects
including size of the braincase, the temporal fossa for lower jaw, other
temporal bone characteristics, and the size of its canines. It lacked
the venous sinus system observed in several Australopithecus species.
It is more similar to Homo than A. afarensis with regards to its flatter
face which doesnt protrude as far and in some dental characteristics.
The cranium is within the size range of gracile australopithecines. (Wong,
2001; Leakey, 2001) . Some have suggested classifying Kenyanthropus as
the earliest member of Homo, ancestral to Homo habilis (Cela-Conde, 2003).