Anthropol. Sci. 105(2), 117-141, 1997

New Species of Nyanzapithecus from Nachola, Northern Kenya

YUTAKA KUNIMATSU Research Institute, Kyoto University, Kanrin, Inuyama-shi, Aichi-ken, 484 Japan

Received April 11, 1997

Abstract Nyanzapithecus is a of East African apes, which has been suggested to be an ancestral stock of oreopithecids. A new species of this genus, Nyanzapithecus harrisoni, is described in this article. The description is based on the material discovered from Nachola, a middle Miocene locality (ca. 15 m.y.a.) in northern Kenya. N. harrisoni is slightly smaller than the previously known N. pickfordi and N. vancouveringorum, but shares with them such unique dental characters as elongated molar crowns, quite inflated cusps, and restricted occlusal basins and foveae. The presence of the new Nyanzapithecus species in Nachola has expanded the distribution and diversity of this genus, and suggests that oreopithecids may have been a relatively common element in the middle Miocene primate fauna of .

Key Words: hominoids, oreopithecids, Nyanzapithecus, East Africa, Miocene

INTRODUCTION The field research by the Japan-Kenya Joint Project has discovered hundreds of fossil from Nachola, a middle Miocene fossil locality in northern Kenya. The primate sample mainly consists of middle-sized hominoid assigned to (Ishida et al., 1984), but it also contains about twenty specimens of a small Miocene hominoid (Kunimatsu, 1992a). Although the small hominoid sample from Nachola only contains isolated teeth and a mandibular fragment, the dental morphology indicates that it belongs to Nyanzapithecus (Kunimatsu, 1992a). The Nachola sample, however, can be distinguished in size and some morphological features from the previous species of Nyanzapithecus known from western Kenya, and deserves to be separated from them as a new species. The present study aims to describe the morphology of the new species in details, with comparisons to the other two species of Nyanzapithecus. Nyanzapithecus is a unique Miocene ape discovered from East Africa. The genus was proposed by Harrison (1986a), when he described the sample of a small catarrhine primate from the middle Miocene deposits in , western Kenya. Harrison named the Maboko sample as N. pickfordi, and he also transferred to the new genus a smaller species of Rangwapithecus, which had been known previously as Rangwapithecus vancouveringorum from the early Miocene localities in western Kenya. (Andrews, 1974, 1978). 118 Y. KUNIMATSU

The presence of Nyanzapithecus in the early to middle Miocene of Kenya is quite interesting, because the dental morphology suggests that Nyanzapithecus is likely to be an ancestral stock of Oreopithecus, a unique and enigmatic fossil primate discovered from the late Miocene of Italy (Harrison, 1986a). Fragmentary evidence suggests that some other kinds of oreopithecids may have existed in the East African Miocene (Koenigswald, 1969; Harrison, 1986a, 1992). The recognition of a new species of Nyanzapithecus in the Nachola sample further extends the geographical distribution and the diversity of African oreopithecids. The origin of oreopithecids, therefore, may be traced back to the early/middle Miocene East Africa. It is important to study the African oreopithecids in understanding the origin of the modern hominoids, because the postcranial evidence of Oreopithecus suggests that it is in close relationship with the modern hominoids (Harrison, 1986b; Sarmiento, 1987). Unfortunately, the postcranium of Nyanzapithecus is only poorly known (McCrossin, 1992), and the oreopithecid status of Nyanzapithecus is a tentative hypothesis at present.

Geological background Nachola is located on the eastern side of the Suguta Valley (=a part of the Eastern Rift Valley), ca. 350 km north of Nairobi. In Nachola, the Miocene series unconform- ably overlays the basement. This series consists of volcanic and sedimen- tary rocks, and is divided into the Aka Aiteputh and Nachola Formations. The fossil primates were discovered from the Aka Aiteputh Formation along with abundant petrified wood (Sawada et al., in press). The fossil bearing sediments are sandwiched by volcanic rocks, and the age of the primate fossils was estimated by K-Ar method as 13 to 15 m.y.a. (Itaya and Sawada, in press). An analysis of the - ian fauna suggests that the age might be slightly older (Pickford and Kuga, in press).

Material All specimens of Nyanzapithecus in the present study were discovered from the site BG-X in Nachola during the field seasons of 1984 and 1986. Among the fossil sites in Nachola, the site BG-X is the most productive with plenty of primate fossils. From the site BG-X and some other sites in Nachola, a number of fossils of a middle-sized hominoid, which are tentatively assigned to Kenyapithecus sp., have been found (Ishida et al., 1984). However, Nyanzapithecus is a relatively rare element in the primate fauna of Nachola.

SYSTEMATICS

Order: Primates Linnaeus, 1758 Suborder: Anthropoidea Mivart, 1864 Infraorder: Geoffroy, 1812 Superfamily: Hominoidea Gray, 1825 New Species of Nyanzapithecus from Nachola, Northern Kenya 119

Family: Oreopithecidae Schwalbe, 1915 Genus: Nyanzapithecus Harrison, 1986a Species: Nyanzapithecus harrisoni sp. nov.

Diagnosis A species of Nyanzapithecus which differs from N. vancouveringorum in the following features: smaller size (the average size of upper M2 being ca . 83% of that in N. vancouveringorum); upper molar higher-crowned; molar cusps more inflated and higher; occlusal basins and foveae more restricted; occlusal outline of the upper molars tending to taper distally; lingual cingulum of upper molars more distinct and wider and slightly approaching toward the cervix lingually; upper M3 crown much shorter; lower molar relatively short (especially M3); lower P4 more elongated; mandible more gracile . N. harrisoni differs from N. pickfordi in the following features: smaller size (the average size of the upper M2 being ca. 75% of that in N. pickfordi); upper and lower molar crowns much less elongated; lingual cingulum of the upper molars with less developed mesial part and better-developed lingual part, slightly approaching toward the cervix lingually; hypocone linked to the protocone instead of the crista obliqua; less waisted upper molar crown; hypoconulid on lower M3 tending to be located more medially; lower P3 having a weak but continuous buccal cingulum .

Holotype KNM-BG15237: an isolated right upper M2 crown . The holotype and other specimens in the hypodigm are stored in the National Museums of Kenya (KNM) in Nairobi. The prefix BG indicates that the specimen comes from Nachola near Baragoi .

Type Locality BG-X, Nachola, near Baragoi, northern Kenya

Distribution Middle Miocene of Nachola (13-15 Ma)

Hypodigm Twenty three isolated teeth and one mandibular fragment from Nachola are assigned to Nyanzapithecus harrisoni (Table 1). Detailed descriptions of the specimens except for a lower P4 (KNM-BG17862) were given previously in Kunimatsu (1992a) . The dental material includes upper and lower molars and lower third and fourth .

Etymology After Terry Harrison, who contributed much to the study of the East African Miocene primates. 120 Y. KUNIMATSU

Table 1. Hypodigm of Nyanzapithecus harrisoni

DESCRIPTION

Mandible The mandibular fragment preserves part of the right corpus anterior to the P4/M1 boundary and the symphyseal region up to the level of the left canine. The crowns of the teeth are missing except for the right lower P3. The roots of the incisors, canines and right P4 remain in the alveoli. The distal half of the left canine root is exposed. A crack runs superoinferiorly in the mandibular body between the right canine and P3. The surface bone is missing from the buccal aspect at the level of the right canine. The labial surface of the symphysis is depressed by the postmortem deformation. The inferior border of the symphysis is slightly broken, but it appears that the inferior transverse torus is absent or very poorly developed. The superior transverse torus is developed about one third midway up from the inferior border, and extends posteriorly to the level of P3. The mandible is relatively gracile. New Species of Nyanzapithecus from Nachola, Northern Kenya 121

Upper Molars The upper Ml has a rounded occlusal outline. The preservation of the specimens is not good, as both specimens are weathered and/or lacking enamel. The crown is slightly longer than broad with the average length/breadth index of 106.0% (Table 1 and Fig. 1). The cusps are rounded cones of moderate height. The degree of cusp inflation seems weaker than in the upper M2, but this may possibly be a result of damage. The paracone, metacone and hypocone are similar in size, and the protocone is slightly larger. The distal cingulum adjacent to the hypocone is slightly swollen, contributing to the restriction of the talon basin. The occlusal crests are low, rounded, and poorly- developed. The mesial crest of the protocone runs mesiobuccally and ends at the slightly developed protoconule. The lingual cingulum is well-developed, and forms a broad and continuous C-shaped shelf surrounding the mesial and lingual aspects of the protocone. This shelf starts from the protoconule, and runs slightly up toward the cervix to end at the mesial aspect of the hypocone. The upper M2 is as long as broad or only slightly broarder than long (Table 2 and Fig. 2). The length/breadth index ranges between 97.1 and 100.0% with the average being 98.2%. The occlusal outline is more squared than in Ml, and the distal moiety is slightly narrower than the mesial moiety (Fig. 4). The enamel surface is smooth. The occlusal crests are low, rounded, and poorly-developed as in Ml. The cusps are inflated so that the trigon and talon basins are restricted. The mesial fovea is short and narrow, and is restricted by the voluminous paracone, well-developed protoconule and inflated crests. The hypocone is separated from the metacone by a distinct groove. There is no distal transverse crest between these two cusps. The distal cingulum is restricted by the expansion of the hypocone to a distinct but buccolingually short ledge on the distal aspect of the metacone. The metaconule is not developed. The hypocone is linked to the protocone by a low, rounded and short crest, though it is interrupted by a fine groove. The hypocone is separated clearly from the crista obliqua. The development of the lingual cingulum is variable. In two specimens (KNM-BG15232 and 15238), the cingulum is well-developed, both mesially and lingually, forming a wide shelf around the protocone. In KNM-BG15238, there is a weak and short cingulum on the lingual aspect of the hypocone. In two other specimens (KNM-BG15064 and 15237), the cingulum is reduced on the lingual aspect of the protocone, yet it is prominent mesially. Moreover, in one of these specimen (KNM-BG15237), a small tubercle is developed at the mesiolingual corner of the lingual cingulum. The buccal cingulum is almost absent. The upper M3 is represented by two isolated teeth (KNM-BG15344 and 17863). The crown is much narrower distally than mesially so that the occlusal outline strongly tapers distally (Fig. 5). In contrast to the M 1 and M2, the mesiodistal length of M3 is shorter than the buccolingual breadth. Hence, the average length/breadth index is only 87.4% (Table 1 and Fig. 3). The protocone is the largest cusp and is quite voluminous. The 122 Y. KUNIMATSU

Limnopithecus legetet (14) L. evansi (4) macinnesi (13) clarki (8) Kalepithecus songhorensis (2) Nyanzapithecus pickfordi (6) N. vancouveringorum (2) N.harrisoni (2)

Size of UpperM1(MDX BL)

Limnopithecus legetet (14) L. evansi (4) Dendropithecus macinnesi (13) Micropithecus clarki (8) Kalepithecussonghorensis (2) Nyanzapithecus pickfordi (6) N. vancouveringorum (2) N. harrisoni (2)

Length/Breadth Index of UpperM1

Fig. 1. Size and length/breadth index of upperMl. Size=mesiodistal length X buccolingual breadth; index=mesiodistal lengthX 100/buccolingual breadth. The mean, range and standard deviation are indicated by the vertical bar, shaded box and horizontal line, respectively.

Table 2. Nyanzapithecus harrisoni: Dental dimensions New Species of Nyanzapithecus from Nachola, Northern Kenya 123

Limnopithecus legetet (8) L. evansi (5) Dendropithecus macinnesi (15) Micropithecus clarki (7) Kalepithecus songhorensis (2) Nyanzapithecus pickfordi (2) N. vancouveringorum (3) N. harrisoni (4)

Size of Upper M2 (MD X BL)

Limnopithecus legetet (8) L. evansi (5) Dendropithecus macinnesi (15) Micropithecus clarki (7) Kalepithecus songhorensis (2) Nyanzapithecus pickfordi (2) N. vancouveringorum (3) N. harrisoni (4)

Length/Breadth Index of Upper M2

Fig. 2. Size and length/breadth index of upper M2. Size=mesiodistal length•~buccolingual breadth;

index=mesiodistal length•~100/buccolingual breadth. The mean, range and standard are

indicated by the vertical bar, shaded box and horizontal line, respectively. paracone is somewhat smaller than the protocone. The metacone is reduced, being restricted to a small tubercle. In one specimen (KNM-BG17863), the hypocone is small, but a well-developed tubercle appears buccal to the hypocone on the distal cingulum, restricting the talon basin. In another specimen (KNM-BG15344), the hypocone seems to be fused with this subsidiary tubercle, and forms a large, voluminous cusp which occupies most of the talon. In this case, the talon basin is restricted to a small, pit- like fovea. The lingual cingulum is distinct, and tends to be more developed mesially than lingually. A small tubercle is developed at the mesionlingual corner of the lingual cingulum. The buccal cingulum is weakly developed between the paracone and metacone. 124 Y. KUNIMATSU

Limnopithecus legetet (9) L. evansi (8) Dendropithecus macinnesi (8) Micropithecus clarki (1) Nyanzapithecus pickfordi (1) N. vancouveringorum (2) N. harrisoni (2)

Size of Upper M3 (MD X BL)

Limnopithecus legetet (9) L. evansi (8) Dendropithecus macinnesi (8) Micropithecus clarki (1) Nyanzapithecus pickfordi (1) N. vancouveringorum (2) N. harrisoni (2)

Length/Breadth Index of Upper M3

Fig. 3. Size and length/breadth index of upper M3. Size=mesiodistal length X buccolingual breadth;

index=mesiodistal length•~100/buccolingual breadth. The mean, range and standard

deviation are indicated by the vertical bar, shaded box and horizontal line, respectively.

Lower Premolars The lower P3 (Figs. 6, 7) is represented by two isolated teeth (KNM-BG15325 and 17844) and one right P3 preserved in a mandibular fragment (KNM-BG14709). It is unicuspid with two roots. The crown is low and moderately bilaterally compressed in KNM-BG 15325 and 14709, while in KNM-BG 17844 it is slightly higher and slightly more bilaterally compressed. The average length/breadth index is 157.3% (Table 1). The occlusal crests are low and rounded. The mesial crest of the main cusp is short, and it meets the well-developed and elevated lingual cingulum inferiorly. The lingual crest is slightly longer, and it ends at the cingulum. The distal crest is much more indistinct than the former two crests. The lingual cingulum extends distally and New Species of Nyanzapithecus from Nachola, Northern Kenya 125

Fig. 4. Stereograph of a right upper M2 (KNM-BG 15237) of N. harrisoni, taken by SEM. The mesial surface is toward the top. Scale=5mm.

Fig. 5. Stereograph of a right upper M3 (KNM-BG 15344) of N. harrisoni, taken by SEM. The mesial surface is toward the top. Scale=5mm. becomes continuous with the distal margin that surrounds the shallow distal fovea. The enamel of the mesiobuccal surface extends only slightly onto the mesial root. The mesiobuccal surface is surrounded basally by a weak but continuous buccal cingulum. The lower P4 (Figs. 8, 9) is represented by two isolated teeth. The crown is elon- gated mesiodistally and narrow buccolingually, so that the average length/breadth 126 Y. KUNIMATSU

Limnopithecus legetet (8) L. evansi (5) Dendropithecus macinnesi (9) Micropithecus clarki (3) Kalepithecus songhorensis (11) Nyanzapithecus pickfordi (1) N. harrisoni (3)

Size of Lower P3 (L X B)

Limnopithecus legetet (8) L. evansi (5) Dendropithecus macinnesi (9) Micropithecus clarki (3) Kalepithecus songhorensis (11) Nyanzapithecus pickfordi (1) N. harrisoni (3)

Length/Breadth Index of Lower P3

Fig. 6. Size and length/breadth index of lower P3. Size=mesiodistal length•~buccolingual breadth;

index=mesiodistal length•~100/buccolingual breadth. The mean , range and standard deviation are indicated by the vertical bar, shaded box and horizontal line, respectively. index is 152.6%. The occlusal outline is ovoid. The two main cusps are high and closely approximated to each other. The occlusal crests are low, rounded and poorly-defined. The mesial fovea shows marked elevation compared to the distal basin. The buccal cingulum is developed, but it is separated into mesial and distal parts.

Lower Molars The lower M1 (KNM-BG15231) has an oval occlusal outline. The crown is relatively long (Table 1 and Fig. 10), and slightly narrower mesially than distally . The cusps are inflated and the occlusal crests are low, rounded and poorly-developed. The mesial New Species of Nyanzapithecus from Nachola, Northern Kenya 127

Fig. 7. A: Stereograph of a left lower P3 (KNM-BG 15325) of N. harrisoni, taken by SEM. The mesial surface is toward the top. Scale=5mm. B: Buccal view of the same specimen, but the scale is not the same with A. fovea is narrow and quite restricted. On this specimen, a small swelling which is fused to the mesial aspect of the metaconid contributes much to the restriction of the mesial fovea. The talonid basin is relatively short and is restricted by the voluminous cusps , but it is deeply excavated. The lingual notch is pronounced. The distal fovea is a shallow 128 Y. KUNIMATSU

Limnopithecus legetet (4) L. evansi (2) Dendropithecus macinnesi (12) Micropithecus clarki (4) Kalepithecus songhorensis (10) Nyanzapithecus pickfordi (4) N. vancouveringorum (1) N. harrisoni (2)

Size of Lower P4 (MD X BL)

Limnopithecus legetet (4) L. evansi (2) Dendropithecus macinnesi (12) Micropithecus clarki (4) Kalepithecus songhorensis (10) Nyanzapithecus pickfordi (4) N. vancouveringorum (1) N. harrisoni (2)

Length/Breadth Index of Lower P4

Fig. 8. Size and length/breadth index of lower P4. Size=mesiodistal length•~buccolingual breadth;

index=mesiodistal length•~100/buccolingual breadth. The mean, range and standard

deviation are indicated by the vertical bar, shaded box and horizontal line, respectively. pit which is linked to the talonid basin by a groove. The buccal cingulum is reduced to such an extent that it is limited to a weak trace on the wmesialaspect of the protoconid and to distinct pits between the buccal cusps. The lower M2 is similar in morphology to the lower M1. However, the M2 is slightly larger than the M1, and the mesial and distal moieties are similar in breadth. The crown is elongated. The average length/breadth index is 125.9%. This is a fairly high value relative to those of the early Miocene apes, but it still lies near the upper end of the range of Dendropithecus macinnesi (Table 1 and Fig. 11). The other two species of Nyanzapithecus show much higher values (=longer crown). The protoconid, hypoconid, metaconid and entoconid are similar in size, and the hypoconulid is slightly smaller New Species of Nyanzapithecus from Nachola, Northern Kenya 129

Fig. 9. A: Stereograph of a left lower P4 (KNM-BG15318) of N. harrisoni, taken by SEM. The mesial surface is toward the top. B: Superobuccal view of the same specimen. Scale=5mm for A & B. than the other four cusps. A tuberculum sextum tends to be developed on M2, occupying the small distal fovea (Fig. 13). At least, three less worn M2s (KNM-BG15228, 15235, 15240) have a well-developed tuberculum sextum. The enamel appears to be relatively thick. The wear facets are first developed on the buccal cusps, but soon the lingual cusps also come to be worn, so that the dentine exposure appears on both the buccal and lingual cusps in worn specimens. From the pattern of dentine exposure, N. harrisoni seems to have high dentine/enamel relief. The lower M3 is also characterized by voluminous cusps and restricted occlusal foveae and basins, but it is different from the M1 and M2 in some details , such as the occlusal outline and the development of the buccal cingulum (Fig. 14). The crown of the M3 tapers distally, so that the occlusal outline is triangular. In contrast to N. pickfordi 130 Y. KUNIMATSU

Limnopithecus legetet (11) L. evansi (10) Dendropithecus macinnesi (16) Micropithecus clarki (7) Kalepithecus songhorensis (3) Nyanzapithecus pickfordi (1) N. vancouveringorum (1) N. harrisoni (1)

Size of Lower M1 (MD X BL)

Limnopithecus legetet (11) L. evansi (10) Dendropithecus macinnesi (16) Micropithecus clarki (7) Kalepithecus songhorensis (3) Nyanzapithecus pickfordi (1) N. vancouveringorum (1) N. harrisoni (1)

Length/Breadth Index of Lower M1

Fig. 10. Size and length/breadth index of lower M1. Size=mesiodistal length•~buccolingual

breadth; index=mesiodistal length•~100/buccolingual breadth. The mean, range and

standard deviation are indicated by the vertical bar, shaded box and horizontal line,

respectively.

and N. vancouveringorum, the lower M3 in N. harrisoni does not show any particular elongation of the crown (Table 2 and Fig. 12). The buccal cingulum is slightly better- developed relative to that of the M1 and M2, and is often decorated with bead-like tubercles. The protoconid and metaconid are well-developed. The hypoconid and hypoconulid are slightly smaller, and the entoconid is usually the smallest cups, which is much reduced and low relative to the metaconid. The mesial fovea is quite narrow and restricted, and it is barely separated from the talonid basin, since the development of the mesial transverse crest is poor. The hypoconulid is slightly medially placed, and it is separated from the entoconid by a distinct groove so that the distal fovea is not New Species of Nyanzapithecus from Nachola, Northern Kenya 131

Limnopithecus legetet (15) L. evansi (16) Dendropithecus macinnesi (15) Micropithecus clarki (6) Kalepithecus songhorensis (4) Nyanzapithecus pickfordi (2) N. vancouveringorum (1) N. harrisoni (5)

Size of Lower M2 (MD X BL)

Limnopithecus legetet (15) L. evansi (16) Dendropithecus macinnesi (15) Micropithecus clarki (6) Kalepithecus songhorensis (4) Nyanzapithecus pickfordi (2) N. vancouveringorum (1) N. harrisoni (5)

Length/Breadth Index of Lower M2

Fig. 11. Size and length/breadth index of lower M2. Size=mesiodistal length•~buccolingual

breadth; index=mesiodistal length•~100/buccolingual breadth. The mean, range and

standard deviation are indicated by the vertical bar, shaded box and horizontal line, clearly defined. In two specimens (KNM-BG15233, 15341), a tuberculum sextum is observed.

DISCUSSION Abundant fossils of Miocene apes have been reported from East Africa since the 1930s (Hopwood, 1933a, 1933b). Many of the fossil localities are concentrated in the vicinity of in western Kenya, where various genera of Miocene apes have been discovered from early to middle Miocene sediments. Eastern Uganda has also yielded some early Miocene fossils of Micropithecus and Proconsul from Napak and a large hominoid from Moroto. In 1980s, three new genera (Afropithecus, Turkanapithecus 132 Y. KUNIMATSU

Limnopithecus legetet (13) L. evansi (6) Dendropithecus macinnesi (10) Micropithecus clarki (5) Kalepithecus songhorensis (1) Nyanzapithecus pickfordi (3) N. vancouveringorum (1) N. harrisoni (5)

Size of Lower M3 (MD X BL)

Limnopithecus legetet (13) L. evansi (6) Dendropithecus macinnesi (10) Micropithecus clarki (5) Kalepithecus songhorensis (1) Nyanzapithecus pickfordi (3) N. vancouveringorum (1) N. harrisoni (5)

Length/Breadth Index of Lower M3

Fig. 12. Size and length/breadth index of lower M3. Size=mesiodistal length•~buccolingual

breadth; index=mesiodistal length•~100/buccolingual breadth. The mean, range and

standard deviation are indicated by the vertical bar, shaded box and horizontal line,

respectively. and Simiolus), dated to 16-18 Ma, were reported from Kalodirr on the western side of Lake Turkana, northern Kenya (Le Gros Clark and Leakey, 1951; Pilbeam, 1969; Andrews, 1978; Harrison, 1982, 1986a; Leakey and Leakey, 1986a, 1986b, 1987). The material of the small catarrhine primate from Nachola differs from most of the East African Miocene apes such as Proconsul, Dendropithecus, Limnopithecus, Kalepithecus and Micropithecus in having elongated molar crowns, quite inflated cusps, only poorly developed occlusal crests, quite restricted occlusal basins and foveae, and lower P4 crown being very long and narrow. These features indicate that the Nachola sample is clearly attributable to Nyanzapithecus. Some Miocene apes from Kenya, such New Species of Nyanzapithecus from Nachola, Northern Kenya 133

Fig. 13. Stereograph of a left lower M2 (KNM-BG15235) of N . harrisoni, taken by SEM. The mesial surface is toward the top. Scale=5mm .

Fig. 14. Stereograph of a left lower M3 (KNM-BG15227) of N. harrisoni , taken by SEM. The mesial surface is toward the top. Scale=5mm. as Simiolus enjiessi, Micropithecus leakeyorum and Turkanapithecus kalakolensis , have relatively long molars, but they are clearly distinguished from Nyanzapithecus by cusp morphology and other related characters (Harrison, 1989; Leakey and Leakey, 134 Y. KUNIMATSU

1986b, 1987).

The sample from Nachola shows some minor differences from the known two species of Nyanzapithecus. It is also geographically different from the other two Nyanzapithecus species, both of which are known only from western Kenya. The finding of N. harrisoni extended the distribution of Nyanzapithecus to northern Kenya. Along with the other

Nachola sample of a larger hominoid that is tentatively attributed to Kenyapithecus, the presence of Nyanzapithecus in Nachola is interesting since a similar combination occurs in Maboko (K. africanus and N. pickfordi) (Pickford, 1985, 1986; Harrison, 1986a;

McCrossin, 1994). An apparent difference is the strong dominance of cercopithecoids

() in Maboko (Harrison, 1986a; Benefit, 1987). Although some cercopithecoid fossils have been collected from Nachola (under study), cercopithecoids seem to be rare in the Nacholar primate fauna. This may indicate some temporal and/ or ecological differences between the two localities, yet further researches on the paleoecology in Nachola is necessary. Meanwhile, N. vancouveringorum, which is older than the other two species, occurs in the Rusinga/Mfwangano area together with a different primate fauna that includes Proconsul nyanzae, P. heseloni and Dendropithecus macinnesi, but no cercopithecoids (Andrews, 1978; Harrison, 1988; Walker et al.,

1993). Kenyapithecus is also known from Fort Ternan (Andrews and Walker, 1976;

Pickford, 1985, 1986; Harrison, 1992). No sample of Nyanzapithecus is represented, though three isolated teeth from Fort Ternan were attributed to oreopithecids by

Harrison (1992). They are much larger than Nyanzapithecus and are badly weathered or moderately/heavily worn. While Fort Ternan is a middle Miocene locality, slightly younger (ca. 14 Ma) than Maboko, no cercopithecoids have been discovered. Instead, Simiolus is a common taxon in Fort Ternan (Harrison, 1992). Simiolus may have played in the primate fauna of Fort Ternan a more or less similar role with that of

Victoriapithecus in Maboko, since it has sharp, well-developed occlusal crests and therefore is considered to have been much folivorous.

Comparison to N. pickfordi

The hypodigm of N. pickfordi consists of nearly ninety isolated teeth and a premaxilla known from the middle Miocene of Maboko Island in Lake Victoria, western Kenya

(Harrison, 1986a). When compared to N. pickfordi, the Nachola material is somewhat smaller in dental size except for the lower M3 and lower P3. The average crown area

(length•~breadth) of the Nachola sample is similar in the lower M3 to or slightly larger

(ca. 10%) in the lower P3 than that of N. pickfordi.

The first and second upper molar crowns are considerably elongated mesiodistally in Nachola relative to those of the early Miocene apes, but the degree of elongation is much less pronounced than in N. pickfordi. The mean length/breadth indices of the

other Miocene apes are approximately 80-90% for both upper M1 and M2. In the

Nachola sample, the average length/breadth indices are 106.0% for the upper M1 and New Species of Nyanzapithecus from Nachola, Northern Kenya 135

98.2% for M2, while these values are 112.1% for M1 and 113.4% for M2 in N. pickfordi. The upper M3 of the Nachola sample consists of only two specimens at present. Both of them differ from M1 and M2 in their crown proportion. They are similar in proportion to those of the early Miocene small apes, while N. pickfordi has more elongated upper M3s. The average length/breadth indices are 87.4% for the Nachola sample, and 103.8% for N. pickfordi. The lingual cingulum in N. harrisoni is distinct and variable in its expression. In some specimens, it is as well developed lingually as mesially, but in other specimens, it is reduced lingually. In N. pickfordi, the mesial part of the cingulum is more strongly developed and wider than the lingual part. In N. harrisoni, the lingual cingulum approaches the cervix as it passes to the lingual aspect, while it is sub-horizontal in N. pickfordi. The latter is unique in having the hypocone linked to the crista obliqua by a short crest (Harrison, 1986a), while the hypocone of N. harrisoni is linked to the protocone as in other non-cercopithecoid catarrihines. The upper molar crown is more strongly waisted midway along the crown length in N. pickfordi than in Nachola. The lower molars show a similar tendency to the upper molars. The crown is less elongated than in N. pickfordi. Consequently, the talonid basin is relatively short and broad in contrast to the long and narrow talonid basin in N. pickfordi. Especially, the M3 crown proportion is similar to those of the other Miocene apes, and does not show such extreme elongation as seen in the M3 crowns of N. pickfordi. This feature is consistent with the short upper M3 crowns mentioned above. The hypoconulid of M3 tends to be located more medially in N. harrisoni. The lower P3 has a very weak, but continuous cingulum developed basally along the buccal aspect of the crown. Hurzeler (1958) described that in the lower P3 of Oreopithecus bambolii, "a continuous cingulum surrounds the external cusp" (p17). Based on his figure 11 (p16), the buccal cingulum appears to be more distinct in Oreopithecus. It is not observed on the single lower P3 specimen (KNM-MB9469) attributed to N. pickfordi at present (Harrison, 1986a).

Comparison to N. vancouveringorum Only a few specimens are attributable to N. vancouveringorum, and their preservation is not good. The type specimen (KNM-RU2058) is a left maxillary fragment with P4- M3. The heavily worn and weathered condition of the teeth makes it difficult to compare the Nachola material to N. vancouveringorum. However, the molars of KNM-RU2058 appear to be low-crowned, with low and moderately inflated cusps. The M1 is smaller than M2, and is worn nearly flat with the dentine pits on the protocone and hypocone having become continuous with each other to make a large area of dentine exposure on the lingual half of the occlusal surface. The lingual cingulum of the molars appears to be narrow and continuous from the mesial to the lingual aspects of the protocone. There may be a weak extension of the cingulum on the lingual aspect of the hypocone, 136 Y. KUNIMATSU but it is not certain because of the wear and weathering. The M3 is expanded, and it is slightly larger than the M2. This feature is unique among the East African Miocene apes; the M3 is usually similar to or smaller than the M2 in size. Among them, Rangwapithecus gordoni has the expanded upper M3 that is larger than the M2. In fact, until Harrison (1986a) reassigned N. vancouveringorum to Nyanzapithecus, it had been considered to be congeneric with R. gordoni (Andrews, 1974, 1978). KNM-MW52 is a small maxillary fragment with two upper molars from Mfwangano, but it is larger than KNM-RU2058. As the original specimen is lost, observation could be made only on a plaster cast preserved in the National Museums of Kenya. Andrews (1978) attributed this specimen to R. gordoni, probably based on its relatively large size, but the molar morphology and geographical distribution suggest that it may rather belong to N. vancouveringorum (Kunimatsu, 1992b). The two molars have been considered to be M1-M2 (Andrews, 1978; Kunimatsu, 1992b), but the occlusal outline and relative size and position of the metacone suggest that they may probably be M2-M3. Although the posterior molar is about 20% larger than the anterior one, such an expanded M3 relative to the M2 occurs on the type maxilla of R. gordoni (KNM-S0700). If the assignment of KNM-MW52 to N. vancouveringorum is correct, N. harrisoni is clearly smaller in dental size than N. vancouveringorum. Even in case that KNM-MW52 is not included in the hypodigm, the known specimens of N. vancouveringorum is consistently larger than the equivalent teeth in N. harrisoni. N. vancouveringorum and N. harrisoni are similar in proportion of the upper M1 and M2 that are as long as broad or only slightly longer than broad. Although the comparison is made difficult by the paucity and bad preservation of the specimens assigned to N. vancouveringorum, the Nachola sample differs in the following features: upper molars are higher-crowned; cusps are more inflated and higher; occlusal basins and foveae are more restricted; lingual cingulum is more distinct, approaching the cervix lingually; upper M3 crown is short; lower molar crowns are shorter and broader with more restricted talonid basin and foveae; lower M3 does not show any particular elongation relative to those of early Miocene apes; hypoconulid of the lower M3 is located more medially; lower P4 crown is more elongated. Compared to the single mandibular specimen (KNM-RU1855) assigned to N. vancouveringorum, the Nachola mandibular fragment (KNM-BG 14709) is much smaller. For example, the symphyseal height of the latter is only 73.7% of the former. The mandible of N. harrisoni is much more gracile than that of N. vancouveringorum. The mandibular robusticity index (thickness/height) is 30.6% at the symphysis and 37.1% at P4 for the Nachola sample, while they are respectively 49.2% and 57.0% in N. vancouveringorum.

Phyletic relationship Based on the above described differences, it is concluded that the Nachola sample represents a third species of Nyanzapithecus. The age of N. pickfordi is estimated as New Species of Nyanzapithecus from. Nachola, Northern Kenya 137

15 m.y.a., and N. vancouveringorum is known from an older age (ca. 18 m.y.a.). Nachola is dated to 13-15 m.y.a. by K-Ar method (Itaya and Sawada, in press). The faunal analysis (Pickford and Kuga, in press) being taken into account, the age of Nachola seems to be around 15 m.y.a., which is similar to that of N. pickfordi. However, N. pickfordi is considered to be more derived than Nachola in such features as the quite strongly elongated upper and lower molar crowns, the extensive development of the mesial part of the lingual cingulum with reduction of the lingual part, more reduced distal cusps relative to the mesial ones, and hypocone connected to the crista obliqua instead of the protocone. Although N. vancouveringorum appears to have some derived features (e.g. more elongated lower molar crown & narrower and deeper talonid basin), it also seems to have more primitive features such as the lower-crowned upper molars, the upper molar cusps being less inflated, less restricted occlusal basins and foveae, narrower lingual cingulum, and less elongated lower P4 crown. Both of the two upper M3s of N. harrisoni show reduction of the distal moiety of the crown, and they are much broader than long (the average length/breadth index=87.2%), while on the type specimen of N. vancouveringorum, the M3 is slightly longer than broad (the index=103.9%), and is slightly larger in crown area than the M2. The elongated upper M3 crown that is slightly larger than the anterior molars is also seen in an early Miocene species, Rangwapithecus gordoni, which may have had some relationship to Nyanzapithecus (Andrews, 1974, 1978; Harrison, 1986a). Since the lower M3s in the Nachola sample also correspond to their upper counterparts in having relatively short crown whose proportion is similar to those of the other East African Miocene apes, it appears likely that having relatively short third molars is not just an individual variation, but is a feature that distinguish N. harrisoni from the other Nyanzapithecus species. Harrison (1986a) suggested that Nyanzapithecus is set together with Oreopithecus in Oreopithecidae which forms a separate family in the superfamily Hominoidea. This interpretation is based on the similarities of the dental morphology between the two taxa. Another possibility is that the similarities are a result of convergence. In this case, the unique dental features observed in Nyanzapithecus and Oreopithecus are independ- ently evolved to be adapted to some similar diet, and they do not indicate any close phyletic relationship between the two taxa. The hominoid status of Oreopithecus is supposed on the basis of its postcranial morphology which suggests an arboreal suspensory locomotion for this primate (Harrison, 198613,Sarmiento, 1987). The postcrania of Nyanzapithecus is quite poorly understood at present. McCrossin (1992) described a proximal humeral fragment from Maboko, which he assigned to N. pickfordi. This specimen has a generalized morphology and does not show similarity to modem hominoids in particular. Because there is not enough data for the proximal humeral morphology of Oreopithecus, it is difficult either to deny or to affirm the relationship between Oreopithecus and 138 Y. KUNIMATSU

Nyanzapithecus on the basis of the present postcranial evidence (McCrossin, 1992). Further postcranial evidence from Nachola and/or Maboko is necessary and will be quite important to determine the phyletic positions and relationships of Nyanzapithecus and Oreopithecus. If the other postcranial bones of Nyanzapithecus prove to be as generalized as the proximal humerus, its dental similarities with Oreopithecus may have been obtained through convergence, and Nyanzapithecus may have no close phyletic relationship with Oreopithecus. In case that the dental morphology is synapomorphic between Nyanzapithecus and Oreopithecus, the modern hominoid-like suspensory adaptations in Oreopithecus may have independently evolved. Benefit and McCrossin (1997), based on craniodental specimens collected from Maboko in 1996, suggest that the latter interpretation may be more correct. Considering the similarities in the dental morphology and the paucity of the postcranial evidence, I prefer in the present study to follow the interpretation of Harrison (1986a) that Nyanzapithecus is assigned to Oreopithecidae, though recent discoveries of European Miocene hominoids may necessitate us to reconsider the phyletic positions of Oreopithecus and Nyanzapithecus (Harrison, personal communication).

Diet Nyanzapithecus has elongated molar and crowns as in Oreopithecus, and in one species, N. pickfordi, the degree of elongation exceeds that of Oreopithecus (Harrison, 1986a). However, there are some differences in dental morphology between these taxa. In Oreopithecus, the molar cusps are higher with the occlusal crests being much more developed and sharper than in Nyanzapithecus. The molars of Nyanzapithecus are characterized by the lower cusps and quite poor development of the occlusal crests. Although living folivorous primates, such as Gorilla and colobines, have long and narrow molar crowns, they also show higher cusps and sharper occlusal crests compared to their more frugivorous relatives, such as Pan and cercopithecines, respectively. The occlusal morphology of Nyanzapithecus molars does not seem to be so suitable for cutting fibers of leaves and herbs. Rather, considering the relatively thick enamel, inflated cusps and poorly developed crests, it appears to have specialized in crushing and grinding of hard objects. It is interesting that the molar morphology of oreopithecids is superficially similar to that of suids in elongated and moderately high crown, mesially developed lingual cingulum, rounded conical cusps, configuration of cusps, occlusal basins and foveae. Some similar functional requirements may be reflected in their morphologies. In general, suids are omnivorous, and their dietary repertoire includes vegetable material (e.g. fungi, leaves, roots, bulbs, tubers, fruits), invertebrates (e.g. snails, insects, earthworms) and vertebrate (e.g. reptiles, young , eggs, small rodents, carrion) (Nowak, 1991; MacDonald and Barrett, 1993; Haltenorth and Diller 1980). The moderately low and robust upper incisors (Harrison, 1986a) also suggest that processing hard foods by the anterior teeth was required by Nyanzapithecus. New Species of Nyanzapithecus from Nachola, Northern Kenya 139

Probably, Nyanzapithecus was adapted to a hard diet with omnivorous tendency, in correspondence to the climatic changes during the middle Miocene. Oreopithecus is considered to be more specialized to folivory (Ungar and Kay, 1995). This dietary difference is not surprising, as the two taxa are widely separated both temporally (ca. 6 million years) and geographically (East Africa and Southern Europe).

CONCLUSIONS The sample of a small catarrhine primate from Nachola, northern Kenya, represents a third species of Nyanzapithecus, two species of which have been described previously from the western Kenyan localities (Rusinga, Mfwangano and Maboko). Although there seems to be little temporal gap between Nachola and Maboko, N. harrisoni from the former retains more primitive features compared to N. pickfordi from the latter. The relationship between N. harrisoni and N. vancouveringorum is not clear because of the paucity of the N. vancouveringorum sample, but the differences in size and morphology indicate that the two samples are distinguishable at the species level. The temporal and geographical distribution of Nyanzapithecus suggests that the origin of oreopithecids may be placed in the early Miocene of East Africa (Harrison, 1986a). The dental features indicate that the unique dental morphology of oreopithecids first evolved as an adaptation for some hard diet with an omnivorous tendency, and it was later modified to adapt for a more folivorous diet in Oreopithecus. The finding of a new Nyanzapithecus species in Nachola increases the diversity of this genus, and suggests that oreopithecids may have been a relatively common element, though not dominant, of the primate fauna in the middle Miocene of East Africa. Yet, we know every little about oreopithecid evolution. There is little evidence about postcraial morphology of Nyanzapithecus critical for understanding the relationship to the postcranial evolution of the modern hominoids. The large temporal and geographical gap between Nyanzapithecus in East Africa and Oreopithecus bambolii in Italy has to be filled. Further intensive researches are needed in East Africa, and perhaps in the northern part of the African continent.

ACKNOWLEDGEMENTS I thank the government of Kenya, and the trustees of the National Museums of Kenya for the permission to conduct research in Kenya. I am grateful to Drs. Meave Leakey, William Anyonge, Mrs. Emma Mbua and other staff members of NMK for their support, and to Dr. Hidemi Ishida for allowing me to join in the Japan-Kenya Joint Project. I thank Dr. Terry Harrison for reading my manuscript. I am also grateful to the people in Nachola and the Baragoi Catholic Church for their assistance during the field researches. This study is a part of the Japan-Kenya Joint Project that has been financially supported by the Grant-in-Aid for Overseas Scientific Survey from Mombushou (the Japanese Ministry of Education, Science and Culture). The author 140 Y. KUNIMATSU received a fund from the Ishida Foundation for the research in the National Museums of Kenya.

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