Anthropological Science Vol. 125(2), 45–51, 2017

The latest occurrence of the nyanzapithecines from the early Late Nakali Formation in Kenya, East Africa

Yutaka Kunimatsu1*, Yoshihiro Sawada2, Tetsuya Sakai3, Mototaka Saneyoshi4, Hideo Nakaya5, Ayumi Yamamoto6, Masato Nakatsukasa7 1Faculty of Business Administration, Ryukoku University, Kyoto 612-8577, Japan 2Professor Emeritus, Shimane University, Matsue 690-8504, Japan 3Department of Geoscience, Faculty of Science and Engineering, Shimane University, Matsue 690-8504, Japan 4Faculty of Biosphere-Geosphere Science, Okayama University of Science, Okayama 700-0005, Japan 5Department of Earth and Environmental Science, Faculty of Science, Kagoshima University, Kagoshima 890-0065, Japan 6Takeda General Hospital, Yamashina, Kyoto 601-1495, Japan 7Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

Received 30 October 2016; accepted 25 January 2017

Abstract The African fossil record is very poor between the mid-Middle and mid-Late Mio- cene. Nakali (~10–9.8 Ma) is one of the rare African localities that have yielded primate fossils from this period, including a new genus of great , Nakalipithecus nakayamai, and another large-bodied homi- noid species. The Nakali primate fauna also includes small-bodied ‘’ and Old World monkeys (most- ly colobines). In this article, we describe a new specimen of a small-bodied ‘ape’ discovered from Naka- li, which is assigned to nyanzapithecines. Nyanzapithecines are characterized by their derived dental morphology, and the previously known nyanzapithecines range in chronological age between the Late Oligocene and early Middle Miocene (~25–13.7 Ma). The new nyanzapithecine specimen from Nakali is therefore the latest occurrence of this group in the African fossil record, extending its chronological range by almost 4 million years younger.

Key words: Late Miocene, catarrhines, nyanzapithecines, East Africa,

a new species of Turkanapithecus (T. rusingensis), though Introduction the present hypodigm is comprised of several fragmentary The nyanzapithecines are a highly specialized group specimens from various localities (Rusinga/Mfwangano, of small to medium-sized non-cercopithecoid catarrhines Songhor, Napak, and Kipsaraman). Apart from East Africa, in the African Oligo-Miocene. At present, there are six Harrison (2010a) suggests that the fragmentary large upper genera (Nyanzapithecus, Mabokopithecus, Rangwapithecus, from Ryskop, South Africa (~18 Ma) (Senut et al., Turkanapithecus, Xenopithecus, Rukwapithecus) with nine 1997) may belong to the nyanzapithecines. If this is the case, species recognized in the nyanzapithecines (Harrison, the nyanzapithecines had obtained a wide distribution from 2010a; Pickford et al., 2010; Stevens et al., 2013) (Figure 1 east to southern Africa by ~18 Ma. The Ryskop material is, and Figure 2). however, represented by one half of an upper molar crown Rukwapithecus fleaglei was recently discovered from only. Nsungwe 2B, a Late Oligocene locality in Tanzania More derived taxa such as Nyanzapithecus and (~25 Ma) (Stevens et al., 2013). Rangwapithecus gordoni Mabokopithecus are mainly known from western Kenya and Xenopithecus koruensis are known from the Early Mio- with N. vancouveringorum mainly from the Early Miocene cene of western Kenya (Songhor and Koru, respectively) of Rusinga/Mfwangano (~18 Ma) and N. pickford and (Hopwood, 1933; Andrews, 1974, 1978; Cote, 2004; Hill et Mabokopithecus clarki from the early Middle Miocene of al., 2013), while Turkanapithecus kalakolensis was reported Maboko (~15 Ma) (Koenigswald, 1969; Harrison, 1986, from the Early Miocene of Kalodirr in northern Kenya 2002, 2010a). N. cf. pickfordi was also reported from the (Leakey and Leakey, 1986). Pickford et al. (2010) described early Middle Miocene Muruyur Formation (~14.5 Ma) in the Tugen Hills (Kelley et al., 2002; Pickford and Kunimatsu, 2005). On the other hand, N. harrisoni was described from * Correspondence to: Yutaka Kunimatsu, Faculty of Business Ad- material discovered from the early Middle Miocene of ministration, Ryukoku University, Kyoto 612-8577, Japan. Nachola (= Baragoi) (~15 Ma), on the eastern flank of the E-mail: [email protected] Rift Valley in northern Kenya (Kunimatsu, 1992, 1997; Published online 29 April 2017 Sawada et al., 2006). New specimens from Maboko might in J-STAGE (www.jstage.jst.go.jp) DOI: 10.1537/ase.170126 necessitate the taxonomic revision of Nyanzapithecus and

© 2017 The Anthropological Society of Nippon 45 46 Y. KUNIMATSU ET AL. Anthropological Science

Figure 1. Location of Nakali and other African Oligocene/Miocene localities mentioned in the text.

Figure 2. Chronological distribution of the nyanzapithecines and Oreopithecus.

Mabokopithecus (Benefit et al., 1998), but detailed descrip- (Kunimatsu et al., 2007, 2016; Nakatsukasa, 2009; tion of them has yet to be done. Nakatsukasa et al., 2010; Handa et al., 2015; Tsubamoto et A few isolated teeth from the mid-Middle Miocene of Fort al., 2015). Ternan and Kapsibor (~13.7 Ma) are considered to belong to During fieldwork in the early Late Miocene locality at a large species of the nyanzapithecines (Harrison, 1986, Nakali, an isolated left P3 (KNM-NA 55061: Figure 3) of a 1992, 2010a). They very likely represent a new species, but small non-cercopithecoid catarrhine was discovered through the presently available material is so fragmentary that they surface collection. Although this is a single, isolated tooth, are retained as nyanzapithecine indet. (Harrison, 2010a). its unique crown morphology strongly suggests that it be- This is the latest occurrence of the nyanzapithecines in the longs to the nyanzapithecines, which are previously known fossil record so far known. from Early to early Middle Miocene sites in Kenya and from Nakali was briefly investigated by previous expeditions in an Oligocene site in Tanzania (Harrison, 1986, 2002, 2010a; the 1960s and 1970s (Aguirre and Leakey, 1974; Benefit and Kunimatsu, 1992, 1997; Kelley et al., 2002; Pickford and Pickford, 1986; Hill, 1994; Gundling and Hill, 2000). The Kunimatsu, 2005; Stevens et al., 2013). The discovery of the Kenya–Japan Joint Expedition to Nakali started new field- Nakali specimen extends the younger limit of the chronolog- work in 2002 (Nakatsukasa, 2009). Since then, thousands of ical range of the nyanzapithecines by almost 4 million years fossils including vertebrates and plant leaves have been from ~13.7 Ma to 9.9–9.8 Ma (Kunimatsu et al., 2007). recovered through surface collection and excavation Vol. 125, 2017 THE LATEST OCCURRENCE OF THE NYANZAPITHECINES 47

Figure 3. (a) Left P3s of nyanzapithecine gen. et sp. indet. from Nakali (a1: KNM-NA 55061) and Nyanzapithecus vancouverngorum from Rusinga, Kenya (a2: KNM-RU 2058) (occlusal, stereo). (b, c) Mesial and distal views of the same specimens of nyanzapithecine gen. et sp. indet. (left) and N. vancouveringorum (right). Scale = 5 mm.

There is not a lingual cingulum, though a small pit is dis- Material tinctly incised on the lingual aspect of the crown near the The nyanzapithecine specimen described in this article base of the postprotocrista and there are a few short, vertical (KNM-NA 55061) was collected on the surface at Site grooves on the mesial aspect of the protocone. The preparac- NA38, where an upper molar of Nakalipithecus nakayamai rista is low and rounded, running mesially from the apex to had been discovered previously (Kunimatsu et al., 2007). end at a tiny style. The postparacrista is better developed The sediments exposed at Site NA38 belong to the Upper than the preparacrista, and runs distally to end at a tiny style. Member of the Nakali Formation (Kunimatsu et al., 2007). There is a short mesiolingual ridge, which comes out from Site NA38 is located several hundred meters south of Site the paracone apex to meet the preprotocrista. Distal to the NA39, where the majority of the N. nakayamai specimens junction between these two ridges lies a distinct longitudinal were excavated (Kunimatsu et al., 2007; Nakatsukasa, groove, which separates the bases of the protocone and par- 2009). The magnetostratigraphic reversed polarity zone in acone. The protocone has two ridges, pre- and postprotocris- the Upper Member is correlated to Chron C5n.1n (9.88– ta. The preprotocrista runs mesiobuccally, and becomes in- 9.74 Ma) on the basis of the 40Ar–39Ar ages. Because of the flated after the junction with the mesiolingual ridge from the rapid sediment accumulation, the age of the fossils is esti- paracone. The preprotocrista further runs mesiobuccally and mated to be 9.9–9.8 Ma (Kunimatsu et al., 2007; Sakai et al., meets the mesial marginal ridge at a point very close to the 2013). base of the preparacrista. Consequently, the mesial cingulum Systematics and fovea are quite strongly restricted to be a small pit. The Order Linnaeus, 1758 postprotocrista is as well developed as the postparacrista, Suborder Anthropoidea Mivart, 1864 and runs distally and slightly buccally to meet the well- Infraorder Catarrhini Geoffroy, 1812 defined distal marginal ridge. The lingual cingulum isre- Superfamily incertae sedis stricted to a prominent but very short ledge at the distal end Nyanzapithecine gen. et sp. indet. of the lingual aspect. In buccal view, the buccal cingulum is absent except for the short ledges at the mesial and distal ends of the buccal face. Description 3 KNM-NA 55061 is a left upper P with the roots missing. Discussion The crown is slightly worn, showing small lakes of dentine exposed on the apices of the two main cusps. The occlusal The newly discovered Nakaki specimen (KNM-NA outline of the crown is ovoid with the buccal moiety being 55061) is similar to previously known nyanzapithecines, only slightly longer than the lingual moiety, suggesting that especially the genus Nyanzapithecus, in having a relatively this tooth is a P3 rather than P4. The lingual flare is elongated crown, high and inflated cusps positioned closely moderately developed, while the buccal face is nearly verti- to each other, a well-developed protocone that is only slight- cal. The cusps are high and inflated. The protocone is very ly smaller and lower than the paracone, a prominent distal well developed, being only slightly lower than the paracone. cingulum which is elevated high from the cervix. On the 48 Y. KUNIMATSU ET AL. Anthropological Science

Table 1. Measurements of upper in nyanzapithecines poorly represented by a left M1 (KNM-FT 36), a right P4 (MD: mesiodistal length, BL: buccolingual breadth in mm) 2 (KNM-FT 37), a right M3 (KNM-FT 38), a left M (KNM- Taxon & Accession MD/BL Tooth MD BL MD × BL KR 9755), and possibly a left upper canine (KNM-FT 41) No. % (Harrison, 1986, 1992, 2010a). Compared to Nyanzapithecus, Nakali nyanzapithecine the Fort Ternan/Kapsibor nyanzapithecine is much larger, in KNM-NA55061 P3 5.2 5.8 30.2 89.7 contrast to the Nakali nyanzapithecine, which is smaller than Nyanzapithecus vancoveringorum other nyanzapithecines (Table 1). Although the Nakali P3 KNM-RU 1894 P3 5.8 7.5 43.5 77.3 (KNM-NA 55061) is similar to the Fort Ternan P4 (KNM-FT KNM-RU 1778 P3 5.5 6.6 36.3 83.3 37) in having the protocone and paracone high and inflated, KNM-RU 1778 P4 5.5 6.6 36.3 83.3 and positioned close to each other, there are considerable KNM-RU 2058 P4 4.9 6.2 30.4 79.0 differences even if we take into account the fact that their Nyanzapithecus pickfordi tooth types are slightly different (P3 and P4). The Nakali P3 KNM-MB 11804 P3 5.5 6.6 36.3 83.3 has more prominent occlusal ridges, while they are only KNM-MB 9447* P4 4.8 6.3 30.2 76.2 poorly developed in the Fort Ternan P4. In the latter, the me- KNM-MB 9754 P4 5.4 6.2 33.5 87.1 sial cingulum is a well-developed shelf-like structure, con- KNM-MB 11671 P4 5.4 6.2 33.5 87.1 tinuous all along the mesial margin of the crown, in strong Turkanapithecus kalakolensis contrast to the extremely restricted condition in the former. 3 KNM-WT 16950 P3 6.2 8.1 49.9 77.0 The distal transverse crest is not developed in the Nakali P KNM-WK 16957 P3 6.0 7.7 46.2 77.9 so that the longitudinal groove between the main cusps runs KNM-WT 16950 P4 5.2 7.8 40.6 66.7 distally up to the distal cingulum. On the other hand, a very Rangwapithecus gordoni low and thick transverse crest confines the central fovea KNM-SO 700 P3 6.2 9.0 55.8 68.9 distally and clearly separates it from the distal fovea and 4 KNM-SO 401 P4 5.7 7.2 41.0 79.2 cingulum in the Fort Ternan P . Concerning the upper pre- KNM-SO 488 P4 5.8 7.9 45.8 73.4 molar size and morphology, the Nakali nyanzapithecine is KNM-SO 700 P4 5.8 8.3 48.1 69.9 more similar to Nyanzapithecus than to the Fort Ternan/ KNM-SO 1081 P4 5.3 7.0 37.1 75.7 Kapsibor nyanzapithecine. Fort Ternan nyanzapithecine In the collection at the National Museums of Kenya, there KNM-FT 37 P4 7.4 9.1 67.3 81.3 is an isolated upper of a small non-cercopithecoid * Probably KNM-MB 9446 in Harrison (1986). catarrhine recovered from the Ngorora Formation, Tugen Hills (Pickford, 1978; Andrews, 1980; Harrison, 1982), which is slightly older (~12.5 Ma) than Nakali, but is younger other hand, the Nakali specimen differs from the upper P3 of than the majority of the African Miocene localities that have Nyanzapithecus and other nyanzapithecines in the course of yielded small non-cercopithecoid catarrhines. As the speci- the preprotocrista (Figure 3). In the Nakali specimen, the men (KNM-BN 993) is a right upper P4 crown (Harrison, preprotocrista is much more buccally directed to meet the 1982), the tooth type is not completely identical with the mesial marginal ridge at a point very close to the base of the Nakali P3 described in this article. However, comparing the preparacrista. Consequently, the mesial fovea and cingulum size and general morphology with the latter, the crown of are extremely restricted buccolingually to be a distinct pit at KNM-BN 993 is smaller (MD: 3.6 mm, BL: 5.5 mm, the buccal end of the mesial margin. The Nakali specimen MD × BL: 19.8 mm2) and relatively much broader (MD/BL: further differs from the other nyanzapithecines in its smaller 65.5%) with much more extensive lingual basal flare size and having a relatively more elongated crown (Table 1). (Table 1). In addition, the main cusps are not inflated and In addition, it is different from N. vancouveringorum and R. more heteromorphic. In sum, the Ngorora P4 (KNM-BN gordoni in lacking a well-developed, continuous lingual 993) neither matches the Nakali P3 (KNM-NA 55061) nor cingulum (Harrison, 1986). belongs to the nyanzapithecines. Rossie and Hill (2005) re- These morphological differences suggest that the Nakali ported several new catarrhine specimens from the Ngorora specimen very likely belongs to a new species of the nyan- Formation, representing at least two species, one of which zapithecines, more closely related to Nyanzapithecus than to can be recognized to be “a new species of small-bodied Rangwapithecus or Turkanapithecus. As far as the premolar ape bearing some resemblance to Simiolus enjiessi and morphology is concerned, it may be a more specialized Kalepithecus songhorensis.” Although detailed description member of the lineage, considering the more elongated of these new fossils has yet to be done, it appears unlikely crown and the unique ridge pattern. However, as there is that they belong to the nyanzapithecines if they resemble S. only a single upper premolar at present, we refrain from enjiessi and K. songhorensis from the Early Miocene of East creating a new taxon and prefer to leave it as nyanzapithe- Africa (Harrison, 1986, 1988, 2002, 2010a; Leakey and cine gen. et sp. indet. Leakey, 1987). Among the previously known samples, the few isolated The phylogenetic relationship between the African nyan- teeth from Fort Ternan and Kapsibor are the latest occur- zapithecines and European Oreopithecus has been debated rence of the nyanzapithecines. The age of Fort Ternan is (Benefit and McCrossin, 1997, 2001; Harrison and Rook, dated to 13.7 ± 0.3 Ma (Pickford et al., 2006), and Kapsibor 1997; Harrison, 2002, 2010a). Based on the remarkable sim- is at the same stratigraphic level as Fort Ternan (Pickford, ilarities in peculiar dental morphology between these two 1986). The Fort Ternan and Kapsibor materials are only groups, Harrison (1986) initially suggested that the nyan- Vol. 125, 2017 THE LATEST OCCURRENCE OF THE NYANZAPITHECINES 49 zapithecines were ancestral to Oreopithecus known from the Ward and Brown, 1986; Brown and Ward, 1988; Pilbeam et Late Miocene of Italy, assigning them in the Oreopithecidae. al., 1990; Madar et al., 2002). With only an isolated P3 spec- Later, he changed the interpretation, suggesting that imen on hand, evaluation of the phylogenetic relationship Oreopithecus was a specialized dryopithecine and was not between Oreopithecus and nyanzapithecines is beyond the closely related to the African nyanzapithecines (Harrison scope of the present study. However, it is interesting that this and Rook, 1997). Oreopithecus shares many suspensory ad- discovery of the nyanzapithecine specimen from Nakali aptations with the extant hominoids and European dryopith- narrows the gap between the temporal distributions of ecines (Harrison and Rook, 1997), which are not observed in Oreopithecus in the Late Miocene of Europe and the nyan- the African nyanzapithecines (Harrison, 1982, 2002; Leakey zapithecines in the Early to Middle Miocene of Africa (Fig- and Leakey, 1986; Leakey et al., 1988; McCrossin, 1992; ure 2). Rose, 1993, 1994). If the postcranial similarities are true The presently available nyanzapithecine material from synapomorphies among Oreopithecus, extant hominoids, Nakali is quite limited, but it extends the chronological dis- and European dryopithecines, the peculiar dental morpholo- tribution of the nyanzapithecines by almost 4 million years gy observed in Oreopithecus and nyanzapithecines is a re- from the early Middle to the early Late Miocene (Harrison, sult of parallel evolution (Harrison and Rook, 1997). On the 1986, 2010a; Kunimatsu, 1992, 1997). To date, no nyan- other hand, if the peculiar dental morphology reflects the zapithecine or other non-cercopithecoid small catarrhines close phylogenetic relationship between Oreopithecus and have been discovered from Africa after the age of Nakali. nyanzapithecines, it may suggest parallelism in postcrania From the Nakali Formation, a considerable number of cerco- during the hominoid evolution. The situation is similar to the pithecoid fossils have been recovered. Many of them are a problem, in which the craniodental evidence small (~4 kg) colobine Microcolobus (Kunimatsu et al., strongly suggests a close phylogenetic relationship between 2007; Nakatsukasa et al., 2010). This is not a dedicated foli- Sivapithecus and extant , while the postcranial vorous primate, unlike living colobines (Benefit, 2000), and specimens provide contradictory evidence (Pilbeam, 1982; could have been a potential competitor for sympatric, small, non-cercopithecoid catarrhines. Climatic change and fluctu- ation in the Late Miocene caused a transition from C3 to C4 environment in Africa during 10–7 Ma (Cerling et al., 1997; Uno et al., 2011). This environmental change shrunk and fragmented forested habitats for primates, leading to extinc- tion of local populations. At the same time, it might have escalated competition between small non-cercopithecoid catarrhines and similar-sized cercopithecoids (Simons, 1970; Andrews, 1981). However, it is still premature to con- clude that the cercopithecoids eventually replaced the non-cercopithecoid catarrhines via direct competition (Harrison, 2010b; Nakatsukasa and Kunimatsu, 2012). Re- vealing the aspects of their extinction would shed light on the decline of the diversity of African hominoids and the origins of living African apes and humans.

Acknowledgments We thank the NACOSTI of Kenya for research permis- sion, the staff of the National Museums of Kenya for their assistance, B. Onyango, T. Mukhuyu, W. Mangao, P. Nzube, D. Mutinda, N. Kanyenze, K. Munguti, S. Oginga, E. Afwande, S. Yatur, M, Nzube, J. Mbithi, B. Okot, J. Kamula, and V. Kennedy for their support during fieldwork, and H. Ishida for logistic support. We are grateful to A. Mariba, D. Arupe, and other Baringo County officers, and the people of Akwichatis and Nasorot. We also appreciate the assistance from the JSPS Nairobi Research Station during our research in Kenya. We thank the Primate Research Institute, Kyoto University, for the permission to access to the primate skele- tal and cast collections through the Cooperative Research Program. We thank Terry Harrison and an anonymous re- viewer for their useful comments. This expedition and com- 3 Figure 4. Line drawings of left P s of nyanzapithecine sp. indet parative studies were funded by grants from the JSPS and from Nakali (KNM-NA 55061; right column) and Nyanzapithecus vancouveringorum from Rusinga, Kenya (KNM-RU 2058; left col- MEXT (KAKENHI #18255006, #22255006, #25257408, umn). Upper row: occlusal view. Lower row: mesial view. #24570254, #16H02757). Scale = 5 mm. The inset shows upper premolar traits. 50 Y. KUNIMATSU ET AL. Anthropological Science

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