Comparative dental development and microstructure of ... - UCL

164 A. D. BEYNON ET AL.
Beard et al., 1986; Begun et al., 1993;
Fleagle, 1983; Harrison, 1987, 1993; Lewis,
1971; Napier & Davis, 1959; Rose, 1997;
Ward et al., 1991, 1993). Overall, these
postcranial characters suggest Proconsul was
an arboreal quadruped with a varied positional
repertoire that indulged in relatively
slow climbing but which showed few signs of
forelimb suspensory behaviour (Walker,
1997). Evidence from the skull and dentition
includes characters that link Proconsul
with later hominoids. The estimated degree
of encephalization of P. heseloni, although
based on one specimen (KNM-RU 7290),
suggests that Proconsul had a bigger brain
than modern cercopithecoids of a comparable
body mass (Walker et al., 1983). Other
craniodental features such as the presence of
a frontal air sinus (Walker & Teaford,
1989), a wide frontal bone at bregma, the
development of a maxillary jugum, a low
crowned P 3 and reduced cusp heteromorphy
of the upper premolars are also each considered
by some to be hominoid synapomorphies
(Andrews, 1985). For a recent
review see Walker (1997).
Four species of Proconsul are now
described (Walker et al., 1993; Teaford
et al., 1993; Andrews, 1996). Proconsul
africanus and Proconsul major are known
from the type sites of Koru and Songhor in
western Kenya and P. major also from
Meswa Bridge in Kenya and Napak in
Uganda. P. heseloni and P. nyanzae are the
two species that are represented at Rusinga
and Mfangano Islands in Kenya (Walker
et al., 1993). Ruff et al. (1989) used crosssectional
measurements of the femoral
diaphysis and articular dimensions to estimate
the body weight of Proconsul specimens
from Rusinga and Mfangano. Rafferty et al.
(1995) subsequently made estimates from
ankle joint surface areas. Both estimates are
around 9–12 kg for the smaller P. heseloni
specimens (about the same as a siamang, or
twice that of smaller Hylobates species).
Body weight estimates for P. nyanzae are
closer to those of female chimpanzees of
the smallest subspecies averaging 35·6 kg
(Rafferty et al., 1995).
Reviewing the paleoecology and the
hominoid paleoenvironments, Andrews
(1996) presented evidence that Songhor and
Koru (dated at 19–20 Ma) have fossil faunas
which suggest environments closest to
tropical African, non-seasonal, wet, evergreen
forest faunas today, whereas the
slightly younger (17·5–17·9 Ma) Rusinga
and Mfangano Island sites were most similar
to dry seasonal forests and also had more
open conditions. This evidence may turn
out to be important in considering information
about whether the diets of these
different species of Proconsul were similar
and in interpreting the effects of seasonality
on developing tooth tissues among different
species of Proconsul (Macho et al., 1996).
The paleosols also provide useful environmental
information. Retallack et al. (1995)
have associated Proconsul from Rusinga
Island with soils interpreted as having supported
riparian woodland early in the ecological
succession of streamsides. These
workers found no evidence of soils that
would indicate extensive dry grasslands or
wet rain forest. Substantial paleobotanical
remains are found on Rusinga and
Mfangano. The type of P. heseloni was
deposited by a predator in a large hollow
tree (Walker & Teaford, 1988). Fossilized
fruits have been found in the same paleosol
as the partial skeletons, some teeth of which
form the biggest sample for this study, at the
Kaswanga Primate Site (Walker et al., 1985)
and again these paleobotanical finds point to
potential differences in seasonality and diet
in Proconsul from Rusinga Island.
On the basis of histological sections of
nine molar teeth attributed to P. africanus,
P. major and P. nyanzae, Gantt (1983,
1986), has previously reported that linear
measurements of enamel indicate thick
enamel, relative to body size estimates.
Gantt estimated enamel thickness in these