Andrew Hill
Department of Anthropology,
Yale University, P.O. Box
208277, New Haven,
CT 06520, U.S.A.
E-mail: [email protected]
Meave Leakey
Department of Palaeontology,
National Museums of Kenya,
P.O. Box 40658, Nairobi,
Kenya.
E-mail: [email protected]
John D. Kingston
Department of Anthropology,
Emory University,
1557 Pierce Drive, Atlanta,
GA 30322, U.S.A.
E-mail: [email protected]
New cercopithecoids and a hominoid from
12·5 Ma in the Tugen Hills succession,
Kenya
The early evolutionary history of the cercopithecoids is poorly understood, primarily due to a lack of fossil material from between 15 and
about 9 Ma. Cercopithecoid primate specimens from a fossil site in
the Ngorora Formation of the Tugen Hills, Kenya, belong to the
genus Victoriapithecus, possibly a new species. These fossils are
associated with a hominoid specimen that resembles Proconsul, and
another tooth of a catarrhine, also probably hominoid. The locality is
BPRP#38, in the Kabasero type section of the Ngorora Formation,
and well dated at 12·5 Ma. If the hominoid specimen is confirmed as
Proconsul, it would be one of the most recent recorded. The relatively
diverse mammal fauna from the site in some ways resembles that of
Fort Ternan. The site is underlain, and not far removed in time, from
one of the best fossil macro-floras in Africa, which indicates lowland
rainforest conditions in this portion of the Rift Valley at 12·6 Ma.
2002 Academic Press
Steve Ward
Department of Anatomy,
Northeastern Ohio Universities
College of Medicine,
Rootstown, OH 44272,
U.S.A.
E-mail: [email protected]
Received 15 December 2000
Revision received
12 June 2001 and accepted
14 June 2001
Keywords: Hominoidea,
Cercopithecoidea, Miocene,
Ngorora, Tugen Hills,
Kenya.
Journal of Human Evolution (2002) 42, 75–93
doi:10.1006/jhev.2001.0518
Available online at http://www.idealibrary.com on
Introduction
The early history of the Cercopithecoidea in
Africa is sparse (Gundling & Hill, 2000). A
handful of primitive Old World monkeys is
known from a number of early Miocene sites
in East Africa ranging in age from approximately 19–17 Ma. These include an M2
from Napak, Uganda (Pilbeam & Walker,
1968), an isolated M3 from Ombo, Kenya
0047–2484/02/010075+19$35.00/0
(Le Gros Clark & Leakey, 1951), a mandible fragment and an isolated lower molar
from Loperot, Kenya (Szalay & Delson,
1979) and 16 specimens including mandibular and maxillary fragments and isolated
teeth from Buluk, northern Kenya (Leakey,
1985). In north Africa, early cercopithecoids
are known from two early Miocene localities. The specimens include three damaged
mandibles from Wadi Moghara, Egypt
2002 Academic Press
76
.  ET AL.
(Simons, 1969), and a mandible fragment
from Gebel Zelten, Libya (Delson, 1979).
From the supposed Middle Miocene at
Ongoliba, Congo, an M3 of a monkey has
been reported (Hooijer, 1963). In contrast
to these sparse and isolated occurrences, a
large collection of monkey cranial and postcranial fragments belonging to the genus
Victoriapithecus has been recovered from the
15 Ma, Middle Miocene site of Maboko
(von Koenigswald, 1969; Benefit, 1987,
1993; Benefit & McCrossin, 1989, 1993).
Another recently discovered occurrence
of Victoriapithecus material is from the
Kipsaramon site complex in the Tugen
Hills. At site BPRP#89, for example, dated
at 15·5 Ma (Hill et al., 1991; Behrensmeyer
et al., 2002) there is a partial left mandible
with M2 and M3, as well as isolated teeth
(e.g., KNM-TH 31013, a left P4; and
KNM-TH 31014, a right P4).
This early cercopithecoid material has
been attributed to two genera, Prohylobates
and Victoriapithecus, which share several
primitive dental traits and which differ
largely in their absolute size and molar proportions (Leakey, 1985; Benefit, 1987,
1993). Prohylobates is known from few
occurrences in the early Miocene of east and
north Africa (e.g. from Buluk, Wadi
Moghara, Gebel Zelten) whereas Victoriapithecus is well known from the exceptional
Maboko collection. Detailed studies by
Benefit (1987, 1993, 1994, 1999, 2000;
Benefit & McCrossin 1989, 1993, 1997) of
the numerous specimens from Maboko have
resulted in a good understanding of these
early monkeys which provides a sound basis
for comparison of new discoveries of Middle
Miocene cercopithecoids.
Earlier studies identified two species of
the genus Victoriapithecus in the Maboko
collection, V. macinnesi and V. leakeyi (von
Koenigswald, 1969; Delson, 1973; Simons
& Delson, 1978; Szalay & Delson, 1979).
These species were regarded as forming a
separate subfamily, the Victoriapithecinae,
within the Cercopithecidae. Benefit’s reanalysis of this material and a later collection
made by Pickford, along with her detailed
comparisons with a large number of modern
cercopithecoids, indicate that the Maboko
monkeys represent a single species, V.
macinnesi (Benefit, 1987). Harrison (1987)
reached a similar conclusion. The extended
time interval from which the collection is
derived resulted in a slightly high level of
variation in the specimens. Benefit identified
a number of primitive dental traits
unique to these early monkeys, and at least
three derived dental traits (and possibly
many more) common to the modern subfamilies Colobinae and Cercopithecinae,
but exclusive of the Victoriapithecinae. She
concluded that the modern subfamilies are
more closely related to one another than
either is to the Victoriapithecinae. She
therefore proposed that the Victoriapithecinae be raised to family rank (Benefit,
1987, 1993, 1994, 1999; see also Harrison,
1987).
The large collection of Maboko monkeys,
although providing exceptional evidence for
the primitive characteristics of the Victoriapithecidae, leaves many questions unanswered concerning the mode and timing
of the origin of modern monkeys. What was
the origin of the Cercopithecidae, and the
modern cercopithecid subfamilies? The earliest cercopithecid reported from Africa is a
colobine from Ngeringerowa, a site complex
within the Ngorora Formation of the Tugen
Hills succession (Benefit & Pickford,
1986), which has now been dated by the
Baringo Paleontological Research Project
to between 9·5 Ma and 8·8 Ma (Deino,
personal communication). There is also an
isolated colobine tooth from the site of
Nakali (Aguirre & Leakey, 1974; Benefit &
Pickford, 1986). An isolated cercopithecoid
right P4 (KNM-BN 1251) from the
Ngorora site discussed here (BPRP#38,
=2/1) was also described in Benefit &
Pickford (1986). Later, Benefit (1999)
  
mistakenly equates this Ngorora site with
Nakali. However, Nakali is not in the Tugen
Hills, but on the eastern side of the Rift, and
is several million years younger than
BPRP#38.
The single right P4 from BPRP#38 has
been the only evidence of African cercopithecoids yet reported from the crucial six
million year interval between the last occurrence of the Victoriapithecidae, around
15 Ma, at Maboko and Kipsaramon, and
the first occurrence of the Colobinae at
Ngeringerowa at 9·5–8·8 Ma. The further
specimens described here from 12·5 Ma
deposits in the Tugen Hills succession
represent an interval in time which could
provide answers to important questions
concerning the origin and radiation of the
two modern cercopithecid subfamilies.
The record of African Miocene hominoids
is also poorly known after 14 Ma until the
appearance of hominids in the Pliocene.
Again, the Ngorora Formation in the Tugen
Hills provides the next evidence in time.
A molar tooth of uncertain attribution
(KNM-BN 1378) is known from site
BPRP#60 in the Bartabwa section of the
Formation, which is not yet precisely dated,
but is probably about 12 Ma (Bishop &
Chapman, 1970; Hill & Ward, 1988; Hill,
1994, 1999). A premolar similar to Proconsul
(KNM-BN 10489) comes from site
BPRP#65 (Hill et al., 1985; Hill & Ward,
1988; Hill, 1994, 1999), and is dated at
about 12·4 Ma (Deino et al., 1990). It is
associated with a canine (KNM-BN 10556)
in very poor condition, that could also be
hominoid, but if it is, it is unlikely to be from
the same species as the premolar (Hill &
Ward, 1988). Apart from these few specimens there is little from later in time than
the Fort Ternan site, dated at 14 Ma, which
has produced a variety of hominoids, but no
monkeys, until the Pliocene [additional
hominoid specimens in this interval include
Otavipithecus (Conroy et al., 1992), Samburupithecus from the Samburu Hills (Ishida &
77
Pickford, 1997), and the Lukeino molar,
also from the Tugen Hills (see Hill, 1999)].
The present paper does not rectify this
deficiency significantly, but adds one,
and possibly two, hominoid teeth to the
inventory.
Geology and dating
The Ngorora Formation was first investigated and mapped by Chapman, working
with the East African Geological Research
Unit (EAGRU), and first described by
Bishop & Chapman (1970). Further notes
on the fauna appeared in Bishop et al.
(1971) and the unit was discussed in more
detail in Chapman (1971). Aguirre excavated vertebrate fossil localities in the
Ngorora Formation for one season (Aguirre
& Leakey, 1974), and Pickford undertook
more detailed investigations (Bishop &
Pickford, 1975; Pickford, 1975a, 1978).
Initial age determinations are summarized in
Chapman & Brook (1978). The work of the
Baringo Paleontological Research Project
(BPRP) on the formation is reported in Hill
et al. (1985, 1986; Hill, 1995, 1999) and
more specific information concerning radiometric dating and paleomagnetic stratigraphy appear in Tauxe et al. (1985) and Deino
et al. (1990).
The unit is defined as lying between the
Tiim Phonolites beneath, and the Ewalel
Phonolites above, and in the type section at
Kabasero there are about 370–400 m of
sediments. Volcaniclastic deposits of the
Ngorora Formation are extensive geographically, occurring in disjunct fault bounded
basins, located mainly in the north of the
Tugen Hills range, but significant outcrops,
such as at Ngeringerowa, occur nearly
40 km further south.
The formation is also extensive in time,
representing over 4 Ma, a remarkably
long period for continental sediments in
Africa. Deino et al. (1990) report on the
78
.  ET AL.
lithostratigraphy, the paleomagnetic stratigraphy and a series of single crystal laser
fusion 40Ar/39Ar age determinations. That
paper revises and adds to the work published
in Tauxe et al. (1985) and Hill et al. (1985)
by applying single crystal laser fusion techniques to samples analyzed in these earlier
studies, as well as to additional material.
Dates for tuffs cited here are weighted mean
ages of inferred primary populations of
single crystal feldspar populations (Deino
et al., 1990). Age determinations on the
Tiim phonolite flow underlying the base of
the type section give a date of 13·15 Ma, and
sedimentation began shortly after this. Concordant dates on a series of tuffs through the
section document more or less continuous
sedimentation in the type section to younger
than 10·5 Ma. Elsewhere in the Formation,
to the south, we have dates as young as
8·8 Ma (Deino personal communication),
and dates on the capping Ewalel Phonolite
are 7·6 Ma and 7·2 Ma (Deino et al., 1990).
The series of radiometric determinations
from the Formation provide great control on
the ages of fossil occurrences through this
relatively long time span. The relation of
the radiometric information and the paleomagnetic stratigraphy, correlated to the
geomagnetic reversal time scale (GRTS),
has implications for deep sea spreading
rates, and the nature and quality of the data
suggest revisions to GRTS for this portion of
time (Deino et al., 1990).
The particular site discussed here
(BPRP#38; EAGRU 2/1; see Figure 1) was
discovered by Chapman in 1968 during the
course of his geological mapping and is the
first fossil locality recorded from the Formation. It is located in the Kabasero type
section of the Formation at UTM 36
8116718 N 0099510 (N 054 E 3551).
Subsequent collections from the site were
made by Aguirre, by Pickford, and by our
own expedition. Fossils at BPRP#38 are
associated with pumice and lithic pebble
conglomerate lenses interbedded with a
series of epiclastic, feldspathic sandstones
and primary airfall tuffs. Sediments in this
portion of the Kabasero succession are composed exclusively of pyroclastic material fluvially reworked by alluvial fan processes and
exhibit channeling and cross bedding features. Preservation of glass shards and abundant subangular pumice fragments in these
accumulations indicate limited transport
and weathering. Substantial local lateral
variations in thickness, continuity and facies
characterize the reworked beds. Intercalated
with these sediments are subaerial and
water-laid tuffs with minimal evidence of
reworking, which form distinctive marker
horizons at Kabasero, providing a means of
correlating between isolated or structurally
and stratigraphically complex exposures.
These tuffs include one with fossil plants
at site BPRP#55, an accretionary lapilli
tuff, and a crystal lithic tuff (RD53; Figure
2) which bracket the BPRP#38 fossil locality and provide a secure stratigraphic context for the site within the Ngorora
sequence.
Euhedral feldspar crystals were collected
by Robert Drake from a poorly sorted,
coarse-grained epiclastic sandstone directly
overlying the accretionary lapilli tuff (RD54), a well cemented tuffaceous sandstone
about 7 m stratigraphically above the lapilli
tuff with in situ fossils, comprising the
BPRP#38 site horizon (RD-51), and the
crystal lithic tuff (RD-53). The original
40
K/40Ar radiometric analyses on sanidine
phenocrysts from these three tuff horizons
provided dates of 12·37 Ma, 12·7 Ma and
11·57 Ma respectively (Hill et al., 1985;
Tauxe et al., 1985). More recent singlecrystal, laser fusion, 40Ar/39Ar analyses on
the same samples have given corresponding
dates of 12·560·01 Ma, 12·490·02 Ma
and 12·260·02 Ma (see Figure 2) which
are preferred here (Deino et al., 1990). The
overall homogeneous nature, extremely poor
sorting, and generally massive character of
the sediments between the accretionary
  
79
Figure 1. Map of the Tugen Hills, showing the location of site BPRP#38.
lapilli tuff and the RD-53 tuff suggests rapid
emplacement. The average sedimentation
rate is 11·2 cm/ka for the interval between
RD-54 and RD-51, and 9·9 cm/ka between
RD-51 and RD-53.
RD-51 was sampled from the same stratigraphic horizon as the BPRP#38 fossils,
which therefore can be dated at about
12·49 Ma.
Paleontology
There is a diverse fauna from the Ngorora
Formation, ranging through the entire time
span of the unit, from 13 Ma to less than
9 Ma. Although BPRP#38 is spatially
restricted (<12 m2), and most finds are
isolated teeth, it has produced a great
taxonomic diversity (Table 1), several of the
.  ET AL.
80
12.26 + 0.07 Ma (RD-53)
40 m
30
20
Site BPRP #38 - Fossil horizons
12.49 + 0.06 Ma (RD-51)
12.56 + 0.04 Ma (RD-54)
Accretionary lapilli tuff
10
Site BPRP #55 - Fossil plant horizon
0
Tuff
clay
silt
f ss
m ss
cs ss
cg
Conglomerate
Intercalated volcaniclastic siltstone
and sandstones with minor
conglomerate lenses
Figure 2. Geological section through site BPRP#38 near the type section of the Ngorora Formation,
indicating dates and relation of the fossil level to the plant tuff. (RD samples were collected by Robert
Drake in 1982).
specimens being significant enough to merit
particular taxonomic description in a range
of publications (Pickford, 1975b, 1986;
Gentry, 1978; Hamilton, 1978; Patterson,
1978; Thomas, 1981a,b; Benefit &
Pickford, 1986; Pickford & Fisher, 1987;
Winkler, 1990, 1994, 2002). Most previously published faunal lists from the
Tugen Hills have been assembled at the
level of geological formation. This list is
confined to one narrow time horizon and
provides a good idea of an East African
fauna tightly constrained to 12·5 Ma; a time
period otherwise unknown in sub-Saharan
Africa.
It is interesting to compare the BPRP#38
fauna with that from Fort Ternan
(Shipman, 1986; Harrison, 1992), a site
  
81
Table 1 Faunal list for site BPRP#38 in the Kabasero section of the Ngorora Formation
PISCES
REPTILIA
Crocodilia
gen. et sp. indet.
MAMMALIA
Primates
Victoriapithecidae
Victoriapithecus sp. indet. (23136–23143, BN 1251) (1)
Hominoidea family indet.
gen. et sp. indet. (BN 1461) (2)
possibly gen. et sp. indet. #2 (23144) (2)
Carnivora
?Ptolmaiidae
cf. Kelba guadeemae (BN 10036)
?Mustelidae
?Mellivorinae
gen. et sp. indet. (BN 2101)
Hyaenidae
gen. et sp. indet. (possibly a new species) (BN 10040)
Felidae
gen. et sp. indet. (BN 1441?)
Tubulidentata
Orycteropodidae
‘‘Orycteropus’’ chemeldoi (3)
Hyracoidea
Pliohyracidae
Parapliohyrax ngororaensis (BN 232, BN 1243) (4)
Proboscidea
Family indet.
gen. et sp. indet. (BN 1438)
Perissodactyla
Rhinocerotidae
gen. et. sp. indet. (BN 554, BN 135, BN 145)
Continued overleaf.
about 1·5 Ma older. At Fort Ternan no
crocodiles have been found. At BPRP#38
there are no macroscelidids, or other insectivores. At Fort Ternan there are no monkeys. A primate similar to Proconsul is
present at both sites, but there is only one
additional possible catarrhine present at
BPRP#38 (see below), whereas, according
to Harrison (1992) Fort Ternan has, in
addition to Proconsul, Kenyapithecus wickeri,
Simiolus, something like Kalepithecus, and a
species of oreopithecid. Among carnivores,
possibly three creodont taxa occur at Fort
Ternan; none has been recorded from
BPRP#38. A hyaenid is present at both
localities, although the one at BPRP#38
may be a new species (J. Barry personal
communication). A genet is known from
Fort Ternan; a felid, a possible arctocyonid
(Kelba), and a possible mustelid come from
BPRP#38. The aardvark ‘‘Orycteropus’’
chemeldoi is common to both sites. No hyrax
is known from Fort Ternan, whereas Parapliohyrax ngororaensis occurs at BPRP#38.
There is an indeterminate proboscidean
from BPRP#38; Choerolophodon ngorora and
Prodeinotherium come from Fort Ternan.
Similarly, an unidentified rhinocerotid is
known from BPRP#38; Chilotheridium and
Paradiceros mukirii are recorded from Fort
Ternan.
As many more fossil specimens have been
recovered from Fort Ternan than from
BPRP#38, absences of taxa from Fort
82
.  ET AL.
Table 1 Continued
Artiodactyla
Anthracotheriidae
gen. et sp. indet. (BN 526)
Suidae
Lopholistriodon kidogosana (BN 862, BN 1162, BN 1254, BN 1259) (5)
Palaeomerycidae
Climacoceros gentryi (6)
Giraffidae
Paleotragus sp. (BN 172, BN 200)
Tragulidae
Dorcatherium sp. (BN 1159)
Bovidae
Boselaphini
Protragocerus sp. (BN 52, 54, 55, 58, 61–63, 65, 67–69) (7)
?Cephalophini
gen. et sp. indet. (BN 96) (8)
?Neotragini
Homoiodorcas tugenium (BN 92) (9)
?Caprinae
Pseudotragus? gentryi (BN 51, 350, 540, 1516, 1757) (10)
Probably other species
Rodentia (11)
Muridae
Cricetomyinae
gen. et sp. nov. (BN 10990)
For vertebrates, names are followed by the accession numbers of examples of specimens that we believe establish
that taxon at the site. All should be prefixed with KNM-TH except where otherwise indicated.
The following are the taxonomic references that describe specimens from this site:
(1) This paper [see also Benefit & Pickford (1986)].
(2) This paper.
(3) Pickford (1975b) [Patterson (1978) believed the generic status to be uncertain].
(4) Pickford & Fischer (1987) describe two isolated teeth from this site (BN 232, BN 1243).
Specimen KNM-BN 215 is listed by them as coming from site 2/11 (BPRP#39), also in the Kabasero section,
but younger. All the data regarding early Baringo collections that still remain in the archives of the Kenya National
Museum indicate that KNM-BN 215 comes from BPRP#38. If so it is interesting, as the specimen is a symphysis
with left and right mandibular bodies, broken off behind P3. It suggests that specimens more complete than
isolated teeth may be recoverable from BPRP#38 in the future.
(5) Pickford (1986).
(6) Hamilton (1978).
(7) Gentry (1978).
(8) Gentry (1978) [see also Thomas (1981a)].
(9) Thomas (1981a) [see also Gentry (1978)].
(10) Thomas (1981b).
(11) Winkler (1990, 1994, 2001).
Ternan are more significant than absences
from the Ngorora site. The absence of
victoriapithecids from Fort Ternan, for
example, is probably biologically rather than
statistically meaningful. On the other hand,
the presence of only one or two hominoid
species at BPRP#38 can be explained by the
relatively small sample size at the site, rather
than suggesting a genuine lower diversity.
Harrison (1992) documents a number of
changes between the faunas from Maboko
and Fort Ternan and suggests that this ‘‘. . .
could indicate that the slender estimated age
difference between the sites actually requires
revising, with Fort Ternan, perhaps, being
somewhat younger than 14 Ma’’. In this he
follows Pickford (1986), but Pickford’s
criterion is largely that the Fort Ternan
  
fauna is ‘‘more evolved’’—whatever that
means—than that of Nyakach, which he
dates at younger than 13·4 Ma, quoting fission track dates. Biostratigraphy is a respectable technique for providing relative dates
on geological horizons, but when it is
employed in the context of understanding
the nature and rate of faunal change itself,
then the circularity in argument can cause
problems. In addition, there is no real
reason at present to doubt radiometric estimates for the Fort Ternan fossiliferous
horizons of about 14 Ma. Moreover this
corresponds with interpretations of the overall geological history of the site and the
dating of overlying and underlying strata
(Shipman et al., 1980). Possibly a real
change may have affected the east African
fauna between 15 Ma and 14 Ma, and
tentatively it also appears, on the basis
of the information provided about site
BPRP#38 here, that the new state inaugurated by the change persisted until at least
12·5 Ma.
An interesting feature of BPRP#38 is its
proximity to one of the best Neogene fossil
macrofloras in Africa. Only 15 m below the
primate horizon is a tuffaceous unit that
preserves abundant fossils of branches and
leaves (BPRP#55). Jacobs & Kabuye are
studying this flora (Kabuye & Jacobs, 1986;
Jacobs & Kabuye, 1987, 1989; Jacobs &
Winkler, 1992). Originally published as
12·2 Ma in age (Jacobs & Kabuye, 1987),
our subsequent redating of the sequence
now permits a more accurate estimate. The
tuff dated at 12·56, RD54 (Deino et al.,
1990), occurs just above, suggesting, on the
basis of interpolation between dated horizons, an age for the plant horizon of
12·59 Ma.
The plant fossils occur in a 20-cm-thick
accretionary lapilli tuff in the form of whole
leaves which are extremely well preserved.
Jacobs & Winkler (1992) provide detailed
information on the taphonomy and mode of
origin of the deposit. The deposit is autoch-
83
thonous, with leaf fall occurring soon after
eruption, and deposition was close to the
parent plant. Consequently the deposit
represents the composition and diversity of
the original plant community very well. In
addition to whole leaf morphology, the
specimens allow the study of fine structure
by scanning electron microscopy. More than
55 species have been identified, which indicate a tropical moist or wet forest, in the
tropical lower montane or premontane
forest category (Jacobs & Kabuye, 1987) in
this portion of the Rift Valley during the late
Middle Miocene.
Primates
Primates from the site consist of eight teeth
belonging to a species of victoriapithecid
monkey, one incisor which we believe
belongs to a large hominoid, and one canine
tooth of less specific catarrhine attribution.
The incisor specimen (KNM-BN 1461)
was collected by Aguirre’s expedition in
1969, but is not mentioned in his publication (Aguirre & Leakey, 1974) and apparently was not identified. Benefit & Pickford
(1986) describe a single right P4 (KNM-BN
1251) from the site. In 1990 BPRP found
additional specimens on the surface at
BPRP#38 and we retrieved others on
subsequent dry sieving of the site later that
year.
Description of the material
Cercopithecoidea: Victoriapithecus sp. indet.
KNM-TH 23143, right P4 (Figure 3). This
complete isolated P4, with roots, is fairly
worn, so that detail on the occlusal surface is
lost. A lozenge shaped dentine area is
exposed on the paracone and a smaller bell
shaped area on the protocone. Although it is
not always possible to confidently differentiate isolated upper premolars, features listed
by Benefit (1993), including the absence of
a rootward extension of enamel onto the
mesiobuccal aspect of the root (Delson,
84
.  ET AL.
Figure 3. Upper teeth of Victoriapithecus. Above, from left to right, occlusal, mesial, lingual and distal
views of right M?2, KNM-TH 23137. Below left, occlusal and mesial views of right P4, KNM-TH 23143.
Below right, occlusal views of right M?1, KNM-TH 23138. The teeth have been coated with ammonium
chloride for greater clarity of the occlusal views.
1973), little disparity between the heights of
the protocone and paracone and lack of a
sharply angled mesiobuccal corner to the
occlusal surface, indicate that this tooth is
almost certainly a P4.
The tooth is indistinguishable from the P4
of V. macinnesi. Relative to extant monkeys
the Victoriapithecus P4s are relatively wider
buccolingually and have a relatively long
mesial shelf (Benefit, 1993). This P4 is relatively wide buccolingually (W/L=1·36, and
the mean for Victoriapithecus is 1·39). The
protocone is set just mesial to the paracone,
and there is no fissure separating the two
cusps. The height of the paracone of this
worn tooth is equal to the crown length
(4·58 mm) indicating that in the unworn
state the paracone height would have
exceeded the crown length, the condition
typical of V. macinnesi and Colobus. In Cercocebus, Cercopithecus and Papio, the crown
length is greater than the paracone height
(Benefit, 1993).
KNM-TH 23138, right M?1 (Figure 3). This
well-preserved upper molar crown, possibly
M1, lacks roots and is slightly worn. Small
circles of dentine are exposed on the buccal
cusps and larger bell shaped areas on the
lingual cusps (Benefit’s wear stage 5)
(Benefit, 1987). Characteristic of all V. macinnesi upper molars, and in contrast to many
other Old World monkeys, the tooth is
wider than it is long, the mesial and distal
widths are subequal and both are greater
than the length. The buccal and lingual
sides of the crown flare from the cusp tip to
the cervix and this is particularly pronounced lingually. A crista obliqua links the
protocone and metacone and there is no
transverse distal loph linking the metacone
and hypocone as is characteristic of the
  
Cercopithecidae. The metacone portion of
the crista obliqua forms a slight oblique
crest, partially restricting the trigon basin.
The protocone portion (postprotocrista)
intersects the metacone portion at a shallow
groove, but occlusal wear has obscured morphological details. The trigon basin is small
relative to the crown area and crown length,
partly due to the close proximity of the
buccal cusps to the lingual cusps, and partly
due to the crista obliqua restricting its size.
Both cusp proximity and the presence of a
crista obliqua are features of Victoriapithecus.
Among other features of this tooth is a small
cuspule at the base of a deep median lingual
cleft which terminates high above the cervix.
The mesial lingual groove is distinct and
V-shaped, and both the mesial and distal
buccal grooves, although short, are clearly
defined. There is a slight depression which
hints at the presence of a distal lingual
groove.
KNM-TH 23137, right M?2 (Figure 3). This
well-preserved right upper molar, possibly
M2, lacking most of the roots, is only slightly
worn with no dentine exposed (Benefit’s
wear stage 2). The tooth is much wider than
it is long and the mesial width is greater than
the distal. Characteristic of Victoriapithecus,
the unworn buccal and lingual cusp tips are
in close proximity and the buccal and lingual
sides of the crown flare even more markedly
than those of the M1, KNM-TH 23138,
described above. The flare is particularly
pronounced lingually and beneath the protocone there is a distinct bulge. The transverse distal loph is absent and the crista
obliqua is similar in position and development to that of the M1, although, because of
the lack of occlusal wear, it is more distinct.
The postprotocrista is clearly visible and
intersects the obliquely oriented metaconid
portion of the crista obliqua at a slight angle.
The triangular trigon basin is relatively small
and restricted by the crista obliqua. The
median lingual cleft is deep and like that of
85
the M1 terminates well above the cervix.
The mesial lingual groove is distinct and the
buccal lingual groove absent although there
is a hint of a depression in the position of the
distal lingual groove.
KNM-BN 1251, right P4 (Figure 4). This
little worn P4 crown has a small dentine
circle exposed on the protoconid. It is relatively long compared to its buccolingual
width and the enamel extends towards the
root on the mesiobuccal aspect of the protoconid, so that buccally the protoconid
appears high. The mesial shelf is distinctly
shorter than the distal shelf. The anterior
fovea is small compared to the posterior
fovea and a lophid links the protoconid and
metaconid. There is a small but distinct
cuspule just distal to the metaconid cusp
apex. The protoconid is the larger cusp and
is higher than the metaconid, but in contrast
to V. macinnesi, this is true both when the
occlusal relief is expressed as the distance
from the cusp tip to a point on the cervix
and as the height of the metaconid above the
lingual notch relative to that of the protoconid above the buccal notch). This is
characteristic of some colobines and in
contrast to cercopithecines and Victoriapithecus (Benefit, 1993). The tooth also
differs from that of V. macinnesi in its
dimensions. The V. macinnesi P4 is relatively
wider than those of most extant species,
being most similar to Cercocebus, and the
metaconid and protoconid are set far apart,
whereas the cusps of the BPRP#38 P4 are
more closely proximated and the tooth
significantly longer than wide.
The V. macinnesi P4 differs from modern
cercopithecids in its oblique orientation to
the tooth row, a feature considered to be
primitive. Although it is difficult to assess
the orientation of an isolated tooth, several
features of KNM-BN 1251 suggest that its
orientation was also skewed. When the tooth
is held so that the lingual side would be
parallel to that of the molars, the anterior
86
.  ET AL.
Figure 4. Lower canine of Catarrhini gen. et sp. indet. (above left) and lower cheek teeth of
Victoriapithecus. Above left, mesial, distal and occlusal views of right male lower canine, KNM-TH 23144.
Above right, occlusal and buccal views of left M?1, KNM-TH 23142. Centre left, occlusal and buccal
views of right P4, KNM-BN 1251. Centre right, occlusal and buccal views of right M?2, KNM-TH 23141.
Below left, occlusal, buccal and mesial views of right M3, KNM-TH 23136. Below right, occlusal and
buccal views of right M3, KNM-TH 23139. The teeth have been coated with ammonium chloride for
greater clarity of the occlusal views.
fovea is lingual to the midline of the crown
and the protoconid is mesial to the metaconid. In addition, the distal contact facet is
on the mesial buccal border of the tooth
rather than on the midline. These typical
victoriapithecid features suggest that the
natural orientation of the tooth was oblique
to the molar row.
KNM-TH 23142, left M?1 (Figure 4). This is
another well-preserved lower molar crown
which retains only a small portion of the
distal root. There is slight wear, so that small
dentine patches are exposed on the two
buccal cusps (Benefit’s wear stage 3). The
tooth has a rather square outline: the mesial
and distal widths are almost identical and
only slightly less than the mesiodistal length.
The molar is bilophodont and has a very
small but distinct hypoconulid. Although
the small size of this cusp argues against
it being a true hypoconulid, its position
is identical to that of V. macinnesi
hypoconulids and it is almost certainly
homologous. The height of the metaconid
is greater than that of the entoconid, a
  
character also shared with V. macinnesi.
There is a shallow but distinct median lingual notch and deep median buccal notch.
The mesial buccal groove is similar in size to
the distal buccal groove, although the latter
incises the crown more deeply. Both mesial
and distal lingual grooves are absent.
KNM-TH 23141, right M?2 (Figure 4). This
well-preserved lower molar crown, possibly
M2, is slightly more worn than the M?1
described above. Small dentine pits can be
seen on all the cusps except the metaconid
which shows slight signs of wear (Benefit’s
wear stage 4). There is no sign of a
hypoconulid. There is marked flare on the
buccal face from cusp tip to cervix with
distinct bulging below the median buccal
cleft, whereas the lingual face is rather steep
sided. The mesial and distal shelves are
short and the mesial shorter than the distal.
The mesial and distal buccal grooves are
distinct and short, and on both, the mesial
and distal lingual grooves are absent.
KNM-TH 23136 and 23139, right M3 (Figure
4). These two M3 crowns are similar in
morphology and at a similar stage of wear
with distinct dentine circles exposed on the
two buccal cusps (Benefit’s wear stage 4).
KNM-TH 23136 has the roots intact.
KNM-TH 23139 lacks the anterior root and
the crown is broken mesially and lingually
and the metaconid lost.
The hypoconulid is well-developed and
positioned slightly buccally. That of
KNM-TH 23139 contributes to a rather
pointed distal margin in contrast to
KNM-TH 23136 which is rounded. A small
tuberculum sextum, represented by a raised
area of enamel, can be observed between the
metaconid and hypoconid on each tooth.
The mesial width of KNM-TH 23136 is
greater than the distal width. There is a
distinct mesial buccal groove on both teeth
and there is no trace of a mesial lingual
87
groove on KNM-TH 23136 (this area is
missing on KNM-TH 23139).
Hominoidea: gen. et sp. indet.
KNM-BN 1461, right I1. This specimen is a
crown of an I1. Wear on the incisal edge has
removed the mammelons. Slight chipping of
the mesial and distal surfaces of the crown
has eradicated interproximal contact facets.
Overall the crown is relatively tall and narrow. In size it is comparable to the mandibular central incisors of Proconsul hesloni.
The labial surface is essentially featureless
except for an inter-mammelon groove that
descends from the incisal edge to a point
about half way to the labial cervix. The
lingual surface is almost devoid of surface
detail. There is a poorly expressed lingual
pillar. Neither a basal tubercle nor any sign
of a lingual cingulum is evident. Comparisons of KNM-BN 1461 with modern and
fossil cercopithecoids and hominoids support attribution of the Ngorora incisor to
Hominoidea, gen. et sp. indet. In particular,
the height of the crown relative to its basal
diameter, in addition to its robusticity,
relative to that of cercopithecoids and
archaic or ‘‘stem’’ hominoids clearly justify
this assignment. Other characters supporting assignment to hominoidea include a
vertical, rather than curved labial crown
surface, and absence of lingual cingulum
elements.
Catarrhini: gen. et sp. indet.
KNM-TH 23144, lower right C (Figure 4).
The root of this lower male canine is
broken off just beneath the cervix and is
largely missing. The crown, which lacks a
small part of the tip, is otherwise well
preserved and has only slight wear on the
mesial surface close to the tip. Like V.
macinnesi the crown is low relative to the
width. This is in contrast to those of most
other cercopithecoids, which have relatively
higher crowned lower male canines. In size
.  ET AL.
88
the canine is absolutely larger than any
Victoriapithecus specimen recorded from
Maboko (Table 2).
The canine differs from that of V. macinnesi and other cercopithecoids in several
significant features, which suggest it is certainly not Victoriapithecus and it is unlikely to
be a cercopithecoid. There is a distinct cingulum that extends lingually from the base
of the mesial ridge around a prominent heel
onto the distal aspect of the crown. Cercopithecoids generally lack a cingulum and
when present it is short and restricted to the
base of the mesial ridge. V. macinnesi lacks a
prominent heel. The mesial ridge and the
parallel running mesial sulcus are long,
straight, distinct and evenly developed. The
mesial ridge and sulcus of cercopithecoids
are most prominent towards the base. At
the base of the mesial ridge, the enamel
margin is only slightly raised, whereas in
cercopithecoids it is markedly raised to produce a tight V with the apex at the base of
the ridge. There are two additional sulci,
both absent on Victoriapithecus lower
canines, on the buccal aspect, either side of
the buccal margin. Both are deeper towards
the base of the crown and peter out towards
the tip.
The canine differs from known cercopithecoid and hominoid lower canines. It
probably has more features in common with
hominoids, but in the absence of associated
posterior teeth it is impossible to refer it with
any certainty to one or the other.
Discussion
Comparison of the eight cercopithecoid
teeth with V. macinnesi reveals strong similarities between the upper cheek teeth and
lower molars, which are indistinguishable
from comparable teeth from Maboko and
show the same diagnostic primitive characters. Benefit (1987) found that in V.
macinnesi, the development, orientation and
presence of the crista obliqua was variable
and differentially expressed along the molar
row, being most frequent on M1 and least
frequent on M3. Both the M1 and M2 from
BPRP#38 retain a crista obliqua. True distal
lophs or hypolophs are rare among V.
macinnesi upper molars, and when they
occur they are frequently in combination
with the crista obliqua or other crests
(Benefit, 1993). Both of the BPRP#38
upper molars lack distal lophs. V. macinnesi
unworn molars have lingual and buccal
cusps more closely approximated than those
of most Cercopithecidae. The close proximity of the cusps of the lightly worn M2,
KNM-TH 23137, is consistent with those of
V. macinnesi. This results in marked flaring
of the buccal and lingual sides of the crown
from tip to cervix, and a bulge is often
apparent on the buccal side of the crown
below the base of the median lingual cleft, a
feature common to both V. macinnesi and
the BPRP#38 molars. The lower molars
also show similarities in the presence of the
hypoconulid on the M1 and in the relative
dimensions of this tooth which is only
slightly longer than wide. The retention of a
hypoconulid on M1 and M2 is variable in V.
macinnesi, and the M1 is more square than
that of modern extant cercopithecids
(Benefit, 1987). The lower third molars, like
those of V. macinnesi, show a high disparity
between the mesial and distal widths. The
difference between the M3 mesial and distal
widths of the Maboko monkeys is more
extreme than that observed for the majority
of extant species with the exception of
Cercocebus albigena (Benefit, 1987). These
characters of the molars indicate affinities
with the Victoriapithecidae.
In contrast, the isolated P4 is distinguishable from V. macinnesi. Although it shares
primitive traits typical of the Victoriapithecidae it is distinguished by other features.
The primitive traits relate to its skewed
orientation relative to the long axis of the
molar row, such that the mesial portion of
the tooth is buccal to the distal portion. This
L
L
C
W
W
OL
P4
4·65
4·25–4·8
0·2734
5·88
9
4·58
L
P4
6·47
L
7
AW
M1
6·9
DW
6·9
L
8·4
AW
M2
7·87
DW
W
5·43
AW
5·3
4·5–6·3
0·3642
7
29
5·56
DW
7·16
AW
7·14
DW
8·98
8·9
L
5·56
AW
M3
AW
4·7
DW
DW
7·38
6·72
6·4
8·87
6·33
5·34
6·2–8·85 5·7–8·65 5·3–7·75 6·8–10·85 5·15–7·65 4·1–6·6
0·5187 0·5854 0·5332
0·9383
0·5568
0·5176
7
8·71
8·33
10·57
8·8
9·7
86
85
89
75
72
70
7·62
L
M2
L
M3
The Victoriapithecus measurements are from Benefit (1993). Abbreviations are as follows: L: maximum mesiodistal length, W: maximum buccolingual width,
AW: maximum mesial buccolingual width, DW: maximum distal buccolingual width, OL: maximum length of the P4 between mesial and distal margins of the
occlusal surface.
6·12
5·26
5·55–6·9 4·25–5·6
0·2957
0·2795
4·83
4·7
40
39
6·37
L
M1
6·5
6·17
6·59
6·3
7.28
8·06
7·41
6·0–7·0 5·45–6·75 5·9–7·05 5·25–6·85 6·55–8·5 6·7–9·5 6·2–8·65
0·29775
0·2711
0·2767
0·269
0·4666 0·5832 0·5
4·57
4·34
4·2
4·3
6·4
7·23
6·76
9
38
34
37
57
55
57
6·24
W
KNM-TH 23144
7·54
4·97
KNM-BN 1251
5·52
4·22
KNM-TH 23142
KNM-TH 23141
KNM-TH 23136
KNM-TH 23139
Victoriapithecus
Mean
6·62
4·89
5·58
4·72
Range
5·7–7·35 4·0–5·85 3·65–6·8 3·75–6·5
S.D.
0·372
0·3608 0·738
0·5284
CV
5·62
7·4
13·2
11·2
n
47
47
41
49
Lower teeth
KNM-TH 23143
KNM-TH 23138
KNM-TH 23137
Victoriapithecus
Mean
Range
S.D.
CV
n
Upper teeth
C
Table 2 Measurements of cercopithecoid teeth, and of Catarrhini gen. et sp. indet. (KNM-TH 23144)
  
89
90
.  ET AL.
is expressed in a number of features
described above which the BPRP#38 P4
shares with the P4 of V. macinnesi. The
BPRP#38 P4 differs from that of V. macinnesi in other significant ways including
the reduced width relative to the mesiodistal length (occlusal length/width=1·3),
and the higher protoconid relative to the
metaconid.
Prohylobates is not well represented in
the fossil record so that characters that
are diagnostic of Prohylobates are not
well defined. More complete Prohylobates
remains are needed to fully understand
the morphological characteristics of the
genus.
The precise taxonomic identification of
isolated teeth is often problematic since
many diagnostic characters relate to the relative size and proportions of the teeth. It is
often impossible to identify the serial position of isolated molars with any confidence.
The isolated teeth described above clearly
demonstrate the presence at BPRP#38 of
(1) a victoriapithecid with upper and lower
molar teeth which are indistinguishable
from those of V. macinnesi, and (2) a
victoriapithecid which can probably be distinguished from V. macinnesi on the morphology of the P4. The question remains
as to whether the BPRP#38 collection
represents one or more species. While more
complete material with associated anterior
and posterior teeth is required to resolve this
question, it is possible to consider the specimens as representing a single new species
of Victoriapithecus, distinguished from V.
macinnesi on the morphology of the P4. But
at present the material is considered too
incomplete to be confident of this and to
permit the naming and diagnosis of a new
species. This collection of eight teeth could
represent as few as three individuals. The
two right lower M3s are very lightly worn
whereas the upper M?2 is unworn so must
represent a third individual. The wear on the
remaining teeth does not preclude any of
them being associated with one or other
of these three individuals.
As for the noncercopithecoid teeth,
KNM-BN 1461 is morphologically almost
identical to the mandibular incisors of
KNM-RU 7290, Proconsul heseloni (Walker
et al., 1993). However, it is also very similar
in the features described here to KNM-MB
11830, attributed to Equatorius africanus
(Pickford, 1985; Ward et al., 1999). Based
on the description of a newly erupted,
unworn E. africanus I2 (McCrossin &
Benefit, 1993), the Ngorora incisor morphology would seem compatible with the
lateral incisors of Equatorius. In the final
analysis, beyond assigning KNM-BN 1461
to Hominoidea, specifically to a large
hominoid taxon, little more can be done to
identify the affinities of the specimen.
The mandibular canine KNM-TH 23144
is also possibly attributable to a hominoid
primate. As this canine is clearly not Proconsul, and as mandibular canines are poorly
diagnostic generally, there is a possibility
that a large hominoid taxon hitherto
unknown was present in the Tugen Hills
area about 12·5 Ma. A similar situation
exists at site BPRP#65, in the Bartabwa area
of the Ngorora Formation, and dated at
12·42 Ma (Hill et al., 1985; Deino et al.,
1990), where a large hominoid P4
(KNM-BN 10489) was recovered at the
same locality as KNM-BN 10556, a poorly
preserved canine (Hill & Ward, 1988).
As noted by Alpagut et al. (1990), fossil
hominoid P4s are notoriously variable, and
difficult to orient when isolated. Hill &
Ward (1988) were inclined to assign the
BPRP#65 P4 provisionally to Proconsul,
while recognizing the tenuous nature of the
attribution. If the enigmatic canine from the
Bartabwa locality is a hominoid, however, it
is clearly not attributable to Proconsul (Hill &
Ward, 1988). Whether or not Proconsul
exists at these Ngorora sites, there is certainly another large hominoid present,
which is so far little known.
  
Summary
The collection of eight isolated cercopithecoid
teeth from the Ngorora Formation, Tugen
Hills, shows that victoriapithecids were still
present 12·5 Ma ago, two and a half million
years later in time than their previously established last appearance. However, they retained
primitive characters typical of their 15 Ma
predecessors at Maboko. These characters
include: relatively wide upper molars with
closely approximated buccal and lingual
cusps, marked buccal and lingual flare, variable occurrence of a crista obliqua and absence of distal lophs; skewed orientation of the
P4 relative to the long axis of the molar row;
M1s that are relatively square; variable retention of M1 and M2 hypoconulids; and M3s that
are distally constricted. Although there are
some morphological similarities with colobines in the P4, other characters in common
with the victoriapithecids are shared with the
cercopithecids (Benefit, 1987, 1993). Overall,
the affinities are clearly with Victoriapithecus.
There is no evidence in this collection of
isolated teeth to suggest that at 12·5 Ma the
colobine or cercopithecine subfamilies had
evolved. However, this does not constitute evidence that they had not. Colobines are known
from about 9·5 Ma at Ngeringerowa, in
the Tugen Hills (Benefit & Pickford, 1986;
Gundling & Hill, 2000), and it is by no means
necessary that they evolved from the Victoriapithecidae, nor that, even if they did, victoriapithecids should not exist after they had
diverged. This cercopithecoid at BPRP#38
occurs in association with at least one large
hominoid species and a diverse mammalian
fauna reminiscent in some ways of that from
Fort Ternan. The horizon is not far removed
in time from a varied fossil macroflora,
indicating a tropical moist or wet forest.
Acknowledgements
This research is part of the work of the
Baringo Paleontological Research Project
91
(BPRP), based at Yale University, and carried out in collaboration with the National
Museums of Kenya. We thank the Government of the Republic of Kenya for
permission to carry out research in Kenya
(Permit OP/13/001/C 1391/ issued to AH),
and permission to excavate from the
Minister for Home Affairs and National
Heritage. BPRP has been supported by
grants to AH from NSF (most recently
SBR-9208903), the Louise H. and David S.
Ingalls Foundation, the Louise Brown
Foundation, Clayton Stephenson, and Yale
University. John Kingston received funding
from NSF (# BNS 9014433), from the
Bill Bishop Memorial Fund, Boise Fund,
GSA, Sigma Xi and the L.S.B. Leakey
Foundation. Thanks for field help are
due to Boniface Kimeu, Kiptalam Cheboi
and Sally McBrearty. We had useful
discussions with Al Deino concerning the
geochronology. John Barry generously provided unpublished notes on some of the
Carnivora, and gave us helpful comments
on the manuscript. Alan Walker very kindly
took the photographs that form Figures 3
and 4.
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