Sawecolobus lukeinoensis, Gommery & Senut & Pickford & Nishimura & Kipkech, 2022

Gommery, Dominique, Senut, Brigitte, Pickford, Martin, Nishimura, Takeshi D. & Kipkech, Joseph, 2022, The Late Miocene colobine monkeys from Aragai (Lukeino Formation, Tugen Hills, Kenya), Geodiversitas 44 (16), pp. 471-504 : 476-494

Sawecolobus lukeinoensis n. gen, n. sp.

( Figs 3-10 ; Tables 1-4 )

urn:lsid:zoobank.org:act:76AA98F9-3C9A-4826-957B-E2D5292323B9

TYPE SPECIMENS. — Holotype: BAR 758’00 – Partial skull with the complete face and the palate including the complete post-canine dentition on both sides except for the left P3/ . — Paratypes: BAR 756’00 , maxilla with I1/ and P3/-M3/ ; BAR 757’00 , partial skull with M2/-M3/ also with left P4/, right P3/-P4/ but damaged ; BAR 759’00 , left maxilla with P3/-M3/ ; BAR 760’00 , left mandibular fragment with m/2-m/3 and broken m1/ ; BAR 761’00 , back of calvarium ; BAR 762A’00 , the left maxilla with P4/-M3/, + BAR 762B’00 / OCO 1049’11 , right maxilla with P3/ and M1/-M3/ ; BAR 786’00 / BAR 1368’00 , left maxilla with M2/-M3/ ; BAR 1586’00 , an edentulous mandibular symphysis ; OCO 608’10 , mandible with right p/3-m/3 and left i/2-m/3 and OCO 100’01 , a fragment of edentulous mandible ; 21 isolated teeth ( BAR 784’00 , BAR 785’00 , BAR 1214’00 , BAR 1369’00 , BAR 1584’00 , BAR 1585’00 , BAR 470’01 , BAR 1595’01 , BAR 1597’01 , BAR 250’03 , BAR 1190’03 , BAR 1381’03 , BAR 1382’03 , BAR 349’04 , BAR 351’04 , BAR910’04 , OCO 104’10 , OCO 105’10 , OCO 335’10 , OCO 101’11 and OCO 305’11 ) ; and four post-cranial bones ( BAR 757’00 , an axis vertebra, BAR 914’04 , a proximal extremity of a right metatarsal V, OCO 336’10 , a distal extremity of a left humerus, and OCO 102’11 , a distal extremity of a right humerus).

DIAGNOSIS. — As for the genus.

TYPE LOCALITY. — Aragai in the Tugen Hills (Baringo County, Kenya).

GEOLOGICAL AGE. — From the basal part of the Lukeino Formation, the Kapgoywa Member dated to the Late Miocene (c. 6-5.7 Ma). ( Pickford & Senut 2001; Sawada et al. 2002).

ETYMOLOGY. — Named after the geological level, as well the geographical location, the Lukeino Formation (Tugen Hills, Baringo County, Kenya).

DESCRIPTION

BAR758 ’00 (Holotype) ( Fig. 4A 1-A 6 ; Table 1 )

General description and preservation. BAR 758’00 is a complete anterior part of a skull which suffered minor distortion during fossilization (maximum length: 60.3 mm; breadth: 61.5 mm; height: 46.5 mm). Of the calvarium only the frontal region is preserved which shows several cracks. The face is well-preserved including the orbits, the inter-orbital pillar, the nasal bones, the maxillae and the zygomatic bones (the right one being better preserved than the left one). The premaxilla is damaged and lacks all the anterior part. The same applies to the anterior/inferior part of the nasal aperture. The face is broad despite some distortion (maximal zygofrontal width: 59.8 mm (cf. Appendix 1: measurement MZM) and low (height between the prosthion and the upper part of the glabella: 38.7 mm).

The anterior part of the palate is missing and both canines and the incisors are absent (length from the anterior part to the distal part of the M3/s: 38.6 mm (see Appendix 1 for comparison with extant African colobine, PDL measurement). The right P3/ and P4/ are intact. The right M1/ is badly damaged; only the buccal side is preserved. The right M2/ is well preserved but lacks the metacone. The right M3/ is present but lacks the paracone and is partially hidden by matrix. The left P3/ is badly damaged and preserves only some lingual fragments. The left P4/ is well preserved. The left M1/ is intact but appears to have sunk into the alveolar process. The left M2/ is well preserved but lacks the mesiobuccal corner. The left M3/ is intact.

Orbital and frontal region. The inter-orbital pillar is broad (minimum: 7.5 mm) as is usual in colobine monkeys (cf. Appendix 1: measurement IW), but short (this is accentuated by the preservation, the pillar is displaced slightly under the nasal). It is broader superiorly (9.6 mm near the glabella). Most of the matrix inside the orbits was removed during mechanical preparation but not completely and it is impossible to describe the morphology of the bone inside the cavity. To preserve the fragile bone and avoid destroying some fragments, the matrix was partially extracted near the inferior margin of the orbit. It is especially true for the right orbit, near the nasal aperture, which leads to it having a deformed appearance. The mesio-lateral margins of the orbits present some cracks and moderate distortion. Despite the imperfect preservation, the orbits are rectangular, broad and low (right orbit: 13.5 mm high, 25.4 mm wide; left orbit: 15.5 mm high, 23.5 mm wide (cf. Appendix 1: measurement OH and OW). No incisura supraorbitalis can be seen.

The superior orbital margins are slightly thickened (right: 3.8 mm; left: about 3.5 mm). The glabellar region is moderately inflated anteriorly but prominent and slightly convex towards the supraorbital torus. The supraorbital torus is moderately developed. The ophryonic groove (or transverse supraglabellar groove [ Mollett van der Spuy 1947; Freedman 1957]) is deep and broad antero-posteriorly.This groove is laterally deeper and broader resulting in the presence of a fossa on both sides. The latero-superior corner of the orbits above the fronto-zygomatic suture present a specific aspect. This area corresponds to the junction of the temporal line with the orbit as in Cercopithecoides (including C. kerioensis ), Libypithecus , Mesopithecus , and Rhinocolobus but unlike Paracolobus . This area is triangular in Sawecolobus lukeinoensis n. gen., n. sp. and is oriented laterofronto-superiorly. The surface is antero-posteriorly flat and infero-superiorly slightly convex. The salient aspect of this area is reinforced by the presence of the broad fossa for the ophryonic groove. Cercopithecoides , Mesopithecus , Libypithecus and Rhinocolobus , are characterised by the proximity of the temporal lines and the frontal orientation of the orbits which appear as though stuck together. No other fossil colobines present the coalescent aspect seen in BAR 758’00.In some specimens of Paracolobus , a coalescent area occurs, but it is more infero-superiorly elongated than in BAR 758’00. The triangular aspect of the latero-superior corner of the orbits of BAR 758’00 is reminiscent of the same area in some Parapapio skulls such as BF 43.

The frontal is better preserved anteriorly than posteriorly. Behind the ophryonic groove, the skull vault is salient and strongly convex medially. The temporal lines are anteriorly salient. The postorbital constriction is weak. In morphology this region is similar to Cercopithecoides .

The right zygomatic is better preserved than the left one, but both are damaged, and the zygomatic arches are absent. It is long and almost frontally positioned with a nearly vertical and slightly convex surface. The infraorbital part of the zygomatic bone, especially the area of the zygomatico-maxillary suture is moderately low. The frontal process of the zygomatic bone is narrow as in Cercopithecoides and Mesopithecus , unlike Paracolobus and Rhinocolobus .

Muzzle and palate. The snout is well preserved, except for the anterior part of the premaxilla which is damaged. It is short. The root of the zygoma is located above the M1/-M2/ contact on both sides of the specimen despite minor distortion and are thus anteriorly positioned, similar to the position in Rhinocolobus turkanensis ( Frost & Delson 2002) and Kuseracolobus aramisi where it is variable (above M1/ or M1/-M2/) ( Frost 2001a, b) or at M1/ in Kuseracolobus hafu ( Hlusko 2006) . It is at M2/ for Paracolobus enkorikae and Paracolobus chemeroni which have more prognathic faces ( Hlusko 2007), Libypithecus , but also for Cercopithecoides kimeui which differs from Cercopithecoides williamsi in which it is more anteriorly positioned ( Frost & Delson 2002).

The nasal aperture is slightly inclined. It is narrow (9.1 mm wide), tall (about 17.1 mm high), showing an elongated oval outline (more or less as in BF 42A, Cercopithecoides williamsi ). The left inferior border of the nasal aperture is damaged, but the right one is better preserved: the base of the aperture is V-shaped with sharp edges. The nasal processes are poorly preserved on both sides of the nasal aperture but they are easily distinguished from the maxilla by a clear suture. Due to the preservation, it is difficult to observe the edges of the nasal bone; it is present with some cracks. It forms a vertical, transversely convex rectangle. The superior suture on the inter-orbital pillar is not visible.

The nasal aperture is low on the face in comparison with extant African colobines and some Asiatic colobines but is close to the position observed in Cercopithecoides and Mesopithecus . In BAR 758’00, the superior margin of the nasal aperture is located below the line joining the inferior margins of the orbits. In extant African colobines, the superior margin of the nasal aperture is located above this line.

The preserved portion of the right premaxilla suggests that it is conical, different from the squared-off shape seen in Kuseracolobus and Cercopithecoides . The same morphology is observed in BAR 756’00 and BAR 757’00. The right portion of the premaxilla is more laterally positioned than anteriorly as in BF 42A. It is more convex than flattened like BF 42A. No maxillary ridge and maxillary fossa are visible, the lateral surface of the muzzle being more or less convex.

The palate appears to be deep, especially posteriorly.Despite the distortion of the anterior part, the palate looks concave and suggests that this part is deep too. The dental arcade is preserved only in the post-canine area, although there is some alteration due to post-mortem distortion. Both postcanine tooth rows are curved; the palate is broadest close to the contact between M1/-M2/ (external width between M1/-M2/: 32.7 mm; see Appendix 1: measurement EPW). Most of the palate is covered with matrix but the bone is apparent near the right M2/ and the left M3/. On the left side, a smooth cavity occurs below the contact between M2/ and M3/ which corresponds to the groove of the posterior palatine foramen (about 4.6 mm long). The posterior edge of the palatine with the choanae is preserved in the left side (although it is difficult to distinguish from the matrix). It is oriented more strongly anteriorly than medially. This suggests that the staphylion (or posterior nasal spine) would have been anteriorly positioned, probably close to the line between the mesial parts of the M3/s.

Paranasal sinus. The maxillary region is severely damaged and distorted, preventing detailed examination of the maxillary sinus in the specimen ( Fig. 5A, B ). However, the frontal and sphenoid regions are well preserved and show that there is no sinus ( Fig. 5A, B ).

Dentition. The canines and incisors are not preserved in this specimen, but the sections of the roots are visible on the right side. The size of the roots suggest that the canine was small, indicating that this specimen belonged to a female. The gap between the canine and I2/ is small, but there is no diastema between these two teeth (unlike BF 42A and the well-preserved specimens from Makapansgat, both of which are attributed to Cercopithecoides williamsi ). The I2/ root is oval in section. It is probably the same for the I1/ but it is difficult to confirm. The other teeth are slightly worn and correspond to wear stages A3 (fully adult). The P3/ is the smaller of the two premolars ( Table 1 ) and the protocone is worn but present. The protocone is well developed in the P4/ as is usually the case in colobines ( Swindler 2002). The paracone and protocone are located mesially and aligned bucco-lingually in P3/ and P4/. The mesial fovea is much reduced in both premolars and the trigon basin is spacious, especially on P4/.

The crowns of the molars have a mesio-distally long and moderately deep trigon basin as is typical in colobine upper molars ( Delson 1975). The crowns are low. In the left M1/ the two lophs are almost equal in size. In the M2/s the mesial loph is broader than the distal one ( Table 1 ). The same occurs in the M3/s (as in BAR 756’00). The molars are bucco-lingually broad ( Table 1 ) compared to those of extant African colobines ( Appendix 2) and relative to the face ( Appendix 1: measurement MZW) ( Verheyen 1962; Swindler 2002). The M3/ has a mesial fovea that is longer mesio-distally than in the M1/ and M2/. The left M3/s have no distal fovea/talon basin but a central cusplet distally, in the left one some matrix covers this area.

Sex and age. The canine is small (as indicated by the section of the root) and there is no swelling of the maxilla in this area, suggesting that it is probably a female. The jugal teeth are worn but the M3/s weakly, which corresponds probably to A3 wear stages, indicating that the specimen belongs to a middle-aged adult.

BAR 756’00 ( Fig. 6B 1-B 3 ; Table 1 )

General description and preservation. This specimen represents an almost complete palate partially covered by matrix (maximum length: 50.5 mm, breadth: 32.7 mm and height: 23.9 mm). The dental rows bearing the postcanine teeth, the base of the two canines and part of the left I2/ are preserved. At the surface of the right maxilla, a fragment of a tooth root is present included in the matrix. The palate suffered from an antero-posterior distortion. The left side has slipped (the tooth row C/-M3/ is located posteriorly to the rest of the palate). The right side is laterally compressed. The root of the left zygomatic process of the maxilla is preserved and is located above the contact between M1/ and M2/, and is thus, very anteriorly positioned. The muzzle was short.

Dentition. The I2/s are not preserved. The I1/s are fragmentary, the left one being better preserved. The apex of the crown of the left I1/ is broken and the tooth is partially embedded in matrix. The crown is triangular and seems large compared to the postcanine teeth. The crowns of the canines are broken showing heart-shaped sections. The large size of the preserved part of the canines indicate that the fossil was a male individual. A short diastema (clearly marked on the right side) is present between the I2/ and C/.

The P3/s are the smaller of the premolars and possess a small protocone. The occlusal outline of the P3/s is subtriangular. The right P3/ has lost some enamel bucco-mesially. The protocone is more developed on P4/ as is usually the case in colobines ( Swindler 2002). As for BAR 758’00, the paracone and protocone are located mesially and aligned bucco-lingually in both premolars except in the right P4/ which has moved during fossilization. The mesial fovea is tiny and the distal one is spacious. The P4/s are wider bucco-lingually than the P3/s as in BAR 758’00.

The molars are well preserved except for longitudinal cracking on the left M1/ and M2/. The left M3/ has lost some enamel from the paracone. The molars are broader than long ( Table 1 ). The M2/ is the largest molar. The mesial and distal lophs of the M1/s are almost equal in size.The distal loph is narrower than the mesial one in the M2/s, and more so in the M3/s. The teeth are almost unworn, just the apex of the paracone and the hypocone on the M1/ which correspond to wear stage A1, which suggests that the individual was a young adult when it died. The mesial fovea is shorter mesio-distally and broader bucco-lingually in the M1/s and M2/s than the distal fovea.In the M3/s, the distal fovea is present and more buccal than central. Buccally, there are distal and mesial clefts in the M1/s and M2/s, only a mesial cleft on M3/s. They present the same morphological features concerning the trigon basin as in BAR 758’00.

BAR 757’00 ( Fig. 6A 1-A 6 ; Table 1 )

General description and preservation. BAR 757’00 preserves three quarters of a fragmentary skull (the posterior part is missing) associated with an axis vertebra (described in this part and not in the section on postcranial bones) (maximum length: 87.6 mm, breadth: 64.2 mm and height: 50.1 mm). It suffered distortion and cracking during fossilization, but the calvarium is better preserved than in BAR 758’00, especially the left side comprising the frontal, the parietal and the temporal. The left part of the basicranium is preserved. The face preserves the orbits, the inter-orbital pillar, the maxillae and the zygomatic bones but they show strong distortion due to lateral compression during fossilisation. The face is broad (maximal zygofrontal width: 64.2 mm (cf. Appendix 1: measurement MZM) and low (height between the preserved anterior part of the palate and the upper part of the glabella: 42.2 mm).

The premaxillae are broken and are represented only by some fragments near the pyramidal aperture and the posterior part of the palate is present. Only the left and right M2/ and M3/ are present but they are deeply worn. The M1/s are absent. The left P4/, the right P3/ and the right P4/ are severely damaged. A tooth fragment observed on the anterior part of the palate could represent the left P3/.

Calvarium. The bone is pervasively cracked, and a major crack extends backwards from the left side posterior to the ophryonic groove to the middle of the rear of the skull. This alters the shape of the calvarium which would have been more rounded and shorter. The frontal is very convex and tall anteriorly, the postorbital constriction is weak (width: 47.5 mm). As for BAR 758’00, BAR 757’00, it exhibits a deep and broad anteroposteriorly oriented ophryonic groove which ends in a fossa on both sides. The temporal lines are well developed anteriorly but abraded by erosion. The temporal lines extend backwards, are quickly blurred and do not converge on the top of the calvarium. The morphology of this region is similar to that of BAR 757’00 and Cercopithecoides , Rhinocolobus and Mesopithecus and unlike Paracolobus and Libypithecus . The parieto-temporal area is high and rounded.Even though the right side is broken, it seems that the maximum width of the calvarium is in a high position as in BF 42A, which confirms its rounded morphology.

Basicranium. Matrix covers most of the preserved portion of the basicranium. An anterior fragment, above the pterygo-maxillary fissure of the lateral pterygoid plate is present on both sides but the left one is better preserved and deep. Some matrix obscures the pterygo-maxillary fissure on the right side. The origin of the zygomatic process is preserved. On the left side, the poorly preserved fossa mandibularis seems to be reduced and shallow. The postglenoid process is salient and robust.Some matrix covers the external auditory meatus. A portion of the tympanic plate is visible as is the petrosal, which is well developed. The petrosal is elongated antero-posteriorly and slightly laterally oblique (as observed in some Piliocolobus badius ). In BF 42A, this bone is shorter antero-posteriorly and more elongated laterally.A large mastoid process is present but is slightly eroded.

Orbital region. The face of BAR 757’00 is more damaged than that of BAR 758’00 and the orbits are more affected. However, some features are visible: the inter-orbital pillar is broad (8.8 mm wide) as is usual in colobine monkeys (cf. Appendix 1: measurement IW) and short as in BAR 758’00. It is also broader superiorly than inferiorly. The orbits are filled with matrix, more than in the holotype. The upper parts of the orbits show some cracking, but the shape is not seriously affected. The infero-lateral corner of both sides is more affected by distortion and they are thus slightly displaced inside the orbit. Despite all these distortions, the orbits are broad and low showing a rectangular outline (more marked in the right orbit) (right orbit: 18.1 mm high and 26.2 mm wide; left orbit: 18.2 mm high and 22.7 mm wide (cf. Appendix 1: measurements OH and OW).

As for BAR 758’00, the superior orbital margins are slightly thickened (about 3.5 mm on the right side and 3.6 mm on the left one). The glabellar region is damaged but the convexity of the supero-median orbital margin and the aspect of the inter-orbital pillar suggests that it is moderately inflated and weakly incurved to the level of the supraorbital torus as in BAR 758’00. The supraorbital torus is slightly more developed than in BAR 758’00 (sexual dimorphism?) but it is different from that of Cercopithecoides in which it is strongly salient. The superficial bone is missing on the lateral margin of the left orbit. No incisura supraorbitalis is observable.

Below the orbits, two infra-orbital foramina are preserved on the left side and only one on the right side.

On the right side, at the latero-superior corner of the orbits above the fronto-zygomatic suture, the temporal lines and the orbits form at their junction a specific triangular coalescent area latero-fronto-superiorly broad, antero-posteriorly flat and slightly convex infero-superiorly as seen in BAR 758’00 but better expressed. On the left side, this area is more eroded and is not as well preserved but presents the same morphology.

The infraorbital part of the zygomatic bones presents many cracks and is distorted; they have suffered compression during fossilization. The infero-lateral part is missing on the left. The right one is long, frontally positioned, despite the distortion, and low. The infraorbital parts of the zygomatic bone are moderately low and the frontal processes of the zygomatic bone are narrow as in BAR 758’00.

Muzzle and palate. The snout is more distorted than that of BAR 758’00. Most of the premaxilla is missing. The maxilla is strongly distorted. The roots of the zygomatic bones are located above the contact between M1/-M2/, and are thus very anteriorly positioned. The muzzle is short. The nasal aperture is damaged, and the nasal is absent. The nasal processes, long and narrow, are well preserved on both sides of the aperture. The general morphology of the nasal aperture indicates that it was tall, narrow and oval as in BAR 758’00. However, probably due to the distortion during fossilisation, the aperture appears to be more inclined.

It is difficult to describe the anterior view of the muzzle because the premaxillae are not preserved. No maxillary ridge is observed. On the lateral aspect of the muzzle, a deep depression is present but it is not a maxillary fossa and is probably due to lateral compression during fossilisation.

The preserved portion of the anterior part of the palate is slightly distorted and the palate is deeper than in BAR 758’00. In comparison, the palate of BF 42A is shallower than in BAR 757’00 and BAR 758’00. The postcanine tooth row (only the M2/s and M3/s are preserved) is curved and the palate seems broadest near the contact of the M1/-M2/ (M1/s are not preserved) (external width between M1/-M2/: 34.1 mm (cf. Appendix 1: measurement EPW). The palate is partly obscured by matrix and is moderately deep. The hard palate ends at M3/. In the posterior part of the hard palate, on the right side, the groove of the posterior palatine foramen is visible below the distal end of the M2/ and the mesial two thirds of the M3/, but it is filled with matrix. This groove is short (5.8 mm long). In BF 42A, this groove extends more posteriorly behind the M3/. The hard palate ends distally beyond the M3/ in Paracolobus enkorikae and even farther back in Paracolobus chemeroni ( Hlusko 2007) . In Cercopithecoides bruneti , it extends posteriorly to M2/ ( Pallas et al. 2019). The posterior edge of the palatine with the choanae is well preserved in the right side (better preserved than in BAR 758’00). It is also oriented more strongly anteriorly than medially. It is not possible to observe the exact position of the staphylion, but the preserved morphology suggest strongly that it has an anterior position probably close to the line between the mesial ends of the M3/s. In BF 42A, the staphylion is situated slightly posteriorly to the M3/s, as in C. williamsi ( Szalay & Delson 1979: figs 197-198), and in the holotypes of C. meaveae ( Frost & Delson 2002: figs 20, 23) and of C. kimeui ( Leakey 1982: fig. 2). Despite sexual differences, the staphylion is posterior to well posterior to the M3/ in Colobus ( Verheyen 1962: pls 1-2; Pallas et al. 2019: fig. 3), posterior in Piliocolobus ( Verheyen 1962: pl. 6; Pallas et al. 2019: fig. 3) and at the level of the distal loph of the M3/ in Procolobus ( Verheyen 1962: pl. 7; Pallas et al. 2019: fig. 3)

Paranasal sinus. The left maxilla is well preserved, whereas the right one is severely damaged and distorted. The maxillary sinus (MS) is present at the level of M2/-M3/ on the left side ( Fig. 5C, D ). The right MS was also detected while it is distorted in the ventro-dorsal direction. The left MS region is separated from the nasal cavity by a thin bony wall that in part involves cancellous bone. The left MS excavates the alveolar region at the level of the M2/, whereas the right one has no trait for such an excavation ( Fig. 5C ). Unfortunately, the nasal conchae and ostium were destroyed or severely distorted. The frontal sinus is not formed in this specimen, and the frontal and sphenoid bones are occupied by cancellous bone.

Dentition. As in BAR 758’00, the incisors and the canines are missing but the section of the canine roots are visible, better on the left side. The size of the section suggests that the canine was small (Left C/: MD = 3.7 mm, BL = 4.5 mm) indicating that the specimen was a female.When present, the teeth are worn and correspond to wear stage A6 suggesting an old individual. The premolars are poorly preserved; the only possible observation is that the P3/s are smaller than the P4/s. The M1/s are absent. The M2/s and the M3/s are heavily worn. The mesial lophs of the molars are broader than the distal ones. Two roots are visible buccally and lingually, but they are separate buccally and coalescent lingually.

Axis. This vertebra is stuck at the back of the palate partially embedded in matrix. Only the anterior part is preserved showing the vertebral body associated with the odontoid process, the superior articular facets, and part of the neural arch on the left side. Its general shape is conical as is usually the case in cercopithecoids.

Sex and age. The proportions of the face are greater than in BAR 758’00. The size of the preserved section of the canine root suggests a small canine which indicates a female. The preserved teeth are deeply worn typical of an old adult (wear stage A6).

BAR 759’00 ( Fig. 4B 1-B 3 ; Table 1 )

General description and preservation. BAR 759’00 is a left hemi-maxilla embedded in matrix, of which only the P3/- M3/ are visible.

Dentition. All the teeth are well preserved. The P3/s are sub-triangular and have no protocone. The protocone is well developed on P4/ and the two cuspids are aligned buccolingually. This premolar is relatively wide bucco-lingually. The morphology is similar to that in BAR 758’00. The mesial and distal lophs of the M1/ are almost equal in width. The distal loph is narrower than the mesial one in the M2/s, and more so in the M3/s. The morphology of the molars is the same as in the previously described fossils. The distal fovea is small and buccally positioned in M3/. Only the distal buccal cleft is visible, matrix covers most of the buccal surface of the molars. Only the linguo-mesial cusp of the M1/ is worn (wear stage A1). This hemi-maxilla belongs probably to a young adult.

BAR 760’00 ( Fig. 4C 1-C 3 ; Table 1 )

General description and preservation. BAR 760’00 is a portion of a left mandible broken mesially at the middle of m/1. The m/2 and m/3 are present. The posterior part of the mandible is fragmentary and partly embedded in the matrix.

Mandibular corpus. It is well preserved; the discrete cracking does not affect the body. It is deep compared to the size of the molars (height between m/1 and m/2: 21.3 mm; width between m/1 and m/2: 7.9 mm (see Appendix 1: respective measurements MH and NW)). The lateral surface is almost flat and vertical. The buccal surface is convex below the m/2. The corpus mandibularis is broader in its middle part, but the inferior edge is robust and broad. Its depth is equal from m/1 to m/3 up to the gonial area and not increasing as in Kuseracolobus . A prominentia lateralis exists under the m/3 partly obscured by matrix but it is weak. The beginning of the mesial edge of the ascending ramus is present under the matrix and the extramolar sulcus is narrow medio-laterally, unlike Cercopithecoides williamsi , Cercopithecoides bruneti , Kuseracolobus aramisi , Kuseracolobus hafu , Mesopithecus pentelici , Paracolobus chemeroni and Rhinocolobus turkanensis in which it is large ( Szalay & Delson 1979; Leakey 1982; Frost 2001a, b; Pallas et al. 2019) and as well as in Paracolobus enkorikae where it is intermediate ( Hlusko 2007).

Dentition. Some matrix covers the buccal side of the molars. The protoconid of the m/2 is broken. The distal lophid is broader than the mesial one and the distal fovea is spacious. The m/3 is well preserved with the mesial lophid broader than the distal one. The buccal parts of the lophids of the m/2 and m/3 are moderately worn but the lingual ones are salient and unworn. The specimen represents a mediumaged adult individual (wear stage A3 or A4).

BAR 761’00 ( Fig. 7A 1-A 2 )

General description and preservation. This is a portion of the back of a skull (central and right side) (maximum length: 37.1 mm; width: 46.2 mm). In size, it is close to the skulls BAR 758’00 and BAR 757’00. The parietal is convex and has a smooth surface which indicates that there was no sagittal crest. The nuchal plane is flat and seems tall and short. There is no sign of a sagittal crest or of a nuchal crest. Part of the right mastoid process is present but is not well preserved. These observations indicate that this fragment was a part of a rounded and short calvarium.

BAR 762A’00 + BAR 762B’00/OCO 1049’11 ( Fig. 7B 1- B 3 ; C 1-C 3 ; Table 1 )

General description and preservation. This composite specimen is comprised of two hemi-maxillae: the right one (BAR 762B’00: a maxillary portion with the three molars found in 2000 (maximum length: 30.4 mm; breadth: 11.4 mm; height: 16.3 mm) + OCO 1049’11: a fragment with a piece of the root of the canine and the P3/ found in 2011) and the left one (BAR 762A’00: a portion of maxilla with P4/-M3/) (maximum length: 39.3 mm; breadth: 16.3 mm; height: 21.2 mm). A fragment of the root of the zygomatic is preserved on each side of the maxilla and is located very anteriorly above the contact between M1/-M2/. The muzzle was probably short. Some matrix covers the median part of the palate. Dentition. The right P3/, sub-triangular in occlusal view is preserved and shows a weak protocone. A tiny fragment of enamel is missing bucco-distally from the apex.The protocone is well developed in the P4/ and is slightly worn. As for the previous fossils, the two cuspids are mesially positioned and aligned bucco-lingually. The P4/s are relatively broad buccolingually. The molars are well preserved, the M2/s being the largest of the molars. On the buccal aspect, a tiny accessory cusp (mesostyle) is present in the M2/s in the middle of median cleft. The mesial and distal lophs of the M1/s are almost equal in breadth. The distal loph is narrower than the mesial one in the M2/s, and more so in the M3/s. The lophs are so well preserved that it is possible to see a central slit which separates the endocrista of the opposite cusplets. On the buccal side of the M1/s and M2/s the mesial and distal clefts are visible, and only the mesial one on the M3/s. The M3/s have a reduced distal fovea. The left M3/ has a cusplet between the distal cingulum and the postmetacrista. The right one shows the same cusplet but extremely small and another bigger one in the middle of the distal cingulum. The M3/s are unworn, the protocone of the M2/s is slightly worn. The M1/s are lingually more worn than the other molars; this corresponds to wear stage A2 and suggests that the individual was probably a young adult.

BAR 786’00/BAR 1368’00 ( Fig. 7D 1-D 3 ; Table 1 )

General description and preservation. This fossil consists of two fragments which fit together: BAR 1368’00, a left M2/ and BAR 786’00 a portion of the left hemi-maxilla with the M3/ (maximum length: 21.4 mm; breadth: 14.2 mm; height: 21.2 mm). A fragment of hard palate is preserved in BAR 786’00. The groove of the posterior palatine foramen is present opposite the M3/. The hard palate seems to end at the M3/ level.

Dentition. Only the left M2/ and M3/ are preserved and are quite worn. M2/ is the bigger of the teeth. The distal loph is narrower than the mesial one in the M2/, and more so in the M3/. The M2/ presents an eroded tiny accessory cusp (mesostyle) in the middle of median buccal cleft. The distal fovea in the M3/ is small and worn. On the buccal side, the mesial and distal cleft are visible on M1/ and M2/. The wear stage could correspond to A3, the specimen is a medium-aged adult individual.

OCO 100’01 ( Fig. 8A 1-A 3 )

This specimen is 20.2 mm long comprising a fragment of right mandible partly covered with matrix and associated with other small fragments of bone. The corpus mandibularis is as narrow as in BAR 760’00 and OCO 608’10. The preserved parts of the two surfaces are vertical. In occlusal view, sections of four tooth roots are seen, but are difficult to identify. Not much can be said about the fragment.

BAR 1586’00 ( Fig. 8B 1-B 3 )

General description and preservation. This fragment (15.7 mm height; 12.5 mm width) is a part of a mandibular symphysis, well preserved in its occlusal and labial parts (despite a median vertical crack). The medial mental foramen is not visible. The beginning of the planum alveolare is preserved. It is almost vertically inclined and concave. The symphysis is vertical and gracile, differing from the broad symphysis seen in Cercopithecoides .

Only the roots of the left i/1, i/2, /c and of the right i/1 and i/2 are preserved. The mesial part of the right canine alveolus is preserved. The roots of the incisors have a compressed ovoid outline. The incisors would have been small and close together as suggested by the morphology of the roots, typical of colobine monkeys. The roots of i/1 are slightly bigger than those of i/2. There is no diastema between the incisors and the canines as in Cercopithecoides , Kuseracolobus , Mesopithecus and unlike Libypithecus and Paracolobus .

Sex and age. The left canine root and the socket of the right one are small. The left canine root has a compressed and ovoid outline. These features and the relatively small size suggest that this specimen probably represents a female individual.

OCO 608’10 ( Fig. 8C 1-C 3 ; Table 1 )

General description and preservation. The mandible OCO 608’10 is composed of nine isolated fragments of the same fossil embedded in a hard matrix (maximum length: 56.6 mm; breadth: 45.4 mm; height: 34.7 mm). An extensive mechanical preparation was done to extract the specimen from the matrix but it could not be completed because of the fragility of the fossil. The right side, the most complete, comprises the corpus mandibularis, the base of the ascending ramus and all the post-canine teeth. Most of the inferior border of the left mandibular corpus is absent but the post-canine teeth are better preserved and prepared than on the opposite side. On the symphysis, vertical cracks and a slight lateral distortion between the left i/2 and /c are visible. Some matrix remains inside the mandible and covers the posterior surface of the symphysis.

Symphysis. The symphysis is damaged inferiorly; it is deep but also seems long (only 20.2 mm preserved (seeAppendix 1: measurement SL) compared to the total the length of the dental arch of 42 mm (see Appendix 1: measurement NW). Despite the damage, the inferior edge of symphysis seems to extend at least as far posteriorly as the p/4. Laterally, the contour of the anterior surface is inclined globally posteriorly but presents a break in the slope, the upper third is less inclined than the lower part. However, the contour appears to be convex. In Cercopithecoides williamsi , this anterior surface appears slightly inclined and straighter despite a lower third that is more inclined posteriorly (below the medial mental foramen). Furthermore, the inferior edge of the symphysis extends less posteriorly, to the p/3 (especially in BF 42B). In Cercopithecoides bruneti , the external part doesn’t present a break in slope with a straight and inclined contour ( Pallas et al. 2019) and neither does C. kerioensis ( Leakey et al. 2003) . In Paracolobus enkorikae , the symphysis presents a rounded slope with a slight break for the lower half ( Hlusko 2007). In Rhinocolobus , the symphysis extends posteriorly at a shallow angle but a break in the slope exists below the alveoli ( Frost & Delson 2002). In anterior view, the symphysis of OCO 608’10 is narrow, convex transversely and not laterally compressed in the middle of each side, unlike Cercopithecoides williamsi . No medial mental foramen is visible as is the case in most colobines except in Procolobus , Cercopithecoides and Rhinocolobus .

Mandibular corpus. The left mandibular corpus is broken. The right one is deep and vertical as is the case in BAR 1586’00. The buccal surface is slightly convex and the lateral fossa is absent. The inferior edge is broken on the right side, but it does not present a strong lateral flare as in Cercopithecoides (in C. kerioensis , the lateral flare is more important than in C. williamsi ( Leakey et al. 2003) . A lateral mental foramen is present under the p/4. The area of the prominentia laterales is too eroded to confirm or not its presence.A narrow extramolar sulcus is present between the m/3 and the ramus.

Dentition. The right and left post-canine teeth are well preserved. Only the right m/1 presents a transverse crack on its mesial lophid. The right teeth being slightly more covered by matrix than those of the left side, the latter are used for the descriptions.

The incisors are broken or embedded in matrix but the enamel is visible on the left i/2. The right canine is broken. The big left canine has lost the supero-distal portion of the crown. It is labially curved and tilted as in Mesopithecus and Colobus but unlike Paracolobus enkorikae ( Hlusko 2007) . The premolars are heteromorphic as in all Cercopithecidae ( Swindler 2002) . The p/3s are longer and broader than the p/4s; they are sectorial and monocuspidate (developed protoconid). There is a developed mesio-buccal flange as is usual in Cercopithecoidea , but they were not yet honed by the upper canine ( Zingeser 1969). The preprotocristid is very salient and the mesial cingulum forms a swelling which continues lingually. The trigonid is small and shallow. The postprotocristid is less salient and shorter than the preprotocristid. The lingual surface is complex with two vertical crests. The disto-lingual part of the teeth is covered by matrix. The p/4s are more tricuspid than bicuspid ( Hornbeck & Swindler 1967). The metaconid is opposite the protoconid ( Swindler & Orlosky 1974) and the two cusps are almost of equal height but the protoconid is more massive than the metaconid. A small but salient entoconid is present disto-lingually. They have a mesio-buccal flange, less than for the p/3s, typical of colobine in which flare is more prominent than in cercopithecines ( Swindler 2002). It is well preserved and not yet worn by contact with the P3/ ( Zingeser 1969). The preprotocristid is very salient and together with the mesial cingulum, it forms a tall, curved mesio-buccal wall to the trigonid basin which is small and shallow. The postprotocristid is less salient than the preprotocristid. The endoprotocristid is longer than the endometacristid and the two cristids are separated by a discrete slit. The distal cingulum is short and bucco-distally positioned. The talonid basin is narrow and larger than the trigonid basin. A short endoentocristid is present (some matrix covers this in the right p/4). The distal part of the p/4 is low and narrower than the rest of the premolar, it looks like a long distal heel (like a platform). This is not so marked in Colobus , Piliocolobus , Cercopithecoides williamsi , Kuseracolobus , Libypithecus and Paracolobus but a bit more in Procolobus . The p/4s do not have a lingual notch separating the talonid basin from the metaconid unlike Kuseracolobus sp. from Kanapoi ( Frost et al. 2020b) and Libypithecus which do.

The molars increase in size from m/1 to m/3 as is usual in colobines ( Table 1 ; Appendix 2). The m/1s are small compared to the m/2s and m/3s. The width strongly increases from m/1 to m/3 (the same but to a lesser degree occurs in Cercopithecoides , Kuseracolobus and extant African colobines but not in Paracolobus .). The distal lophid of the m/1s is broader than the mesial one; the same applies to the m/2s. In m/3s, the mesial lophid is the broadest. The hypoconulid is present in the m/3s as is usual in colobines, but it is buccally positioned, prominent and very salient.

Sex and age. The post-canine teeth are unworn which suggests that the specimen represents a young adult individual. The canine is big, and the p/3 is tall mesially, a morphology typical of male individuals.

ISOLATED TEETH

The collection includes 21 isolated teeth which are briefly presented in Table 2 . They are attributed to Sawecolobus lukeinoensis n. gen., n. sp. on the basis of their morphology and dimensions.

Incisors

Apart from the damaged left I1/ of BAR 756’00, the collection from Aragai is represented by only two isolated incisors, BAR 910’04 and BAR 1214’00. These teeth are small as is usual in colobines.

BAR 1214’00 ( Fig. 9B 1-B 5 ), a right I1/, presents many colobine features ( Swindler 2002) such as a deep central groove on the lingual surface and a strong lingual cingulum, and the mesial and distal marginal ridges are present but, in this specimen, salient with a stronger mesial marginal ridge. Mesially, there is a clear interstitial contact facet caused by contact with the left I1/. The worn occlusal surface corresponds to wear stage A2 and could belong to a young adult.

BAR 910’04 ( Fig. 9A 1-A 5 ), a right I2/, is caniniform and reduced, a morphology seen in colobines. The labial cingulum is strong. Buccally, several hypoplastic lines are visible, but a strong line occurs at mid-crown. The occlusal surface is slightly worn distally and could represent wear stage A2 or the beginning of A3, suggesting that the specimen also belongs to a young adult.

Lower canines

Of the seven lower canines known from Aragai, two belong to males (BAR 785’00 and BAR 1584’00) and four to females (BAR 1369’00, BAR 1381’03, BAR 1382’03, BAR 351’04 and OCO 104’10). The morphology and size of these canines indicate the presence of strong sexual dimorphism in Sawecolobus lukeinoensis n. gen., n. sp. For a better understanding of the morphology of the tooth category, the description of each sex will start with the best-preserved specimen. For interpreting the canine honing mechanism, Zingeser (1969) was consulted.

Male. BAR 1584’00 ( Fig. 9L 1-L 4 ) is a complete and well preserved left lower canine. The crown is tapered and sharp and slightly inclined buccally. On the disto-lingual part of the crown, the extensive honing facet with the upper canine suggests wear stage A4 (adult). Distally, a strong doubled distal tubercle forms a distal heel and occurs at the base of the crown at the top of a shallow disto-lingual groove (sulcus) which extends along the root. The distal heel was considered by Lucas & Teaford (1994) to be common in colobines and it becomes more noticeable with wear. Mesially, a relatively deep mesial groove is worn apically by a honing facet for the I2/. The “V”-shaped mesial cervix rises weakly apically and is bordered by a weak cingulum. A broad shallow groove rises along the mesial face of the root but is less marked than in BAR 785’00.

In BAR 785’00 ( Fig. 9F 1-F 4 ) only the root and the lower part of the lower canine crown are preserved. A small honing facet is present on the disto-lingual part of the crown on which basis this canine is inferred to belong probably to a young adult. The honing facet is located just above a strong disto-lingual tubercle at the base of the crown which corresponds to the distal heel, under which a shallow sulcus extends along the root disto-lingually. The “V”-shaped mesial cervix is developed and rises apically, bordered by a cingulum. A broad and shallow groove runs along mesial surface of the root.

Female. The right lower canine BAR 1381’03 ( Fig. 9H 1-H 4 ), is the best-preserved female lower canine. It lacks only the apical part of the root which is slightly compressed mesiodistally, probably during fossilization. The apex of the crown is slightly worn. There is no honing facet indicating wear stage A1. The canine belongs to a young adult. Hypoplastic lines are well marked on the labial and distal faces, but the most prominent one occurs at the base of the crown, just above the cervix and may have resulted from stresses related to weaning. The crown is straight. In distal view, there is a salient cingulum which forms a discrete disto-lingual tubercle. Two narrow and shallow grooves run down the root distolingually but could be due to fossilization. In mesial view, a small and salient crest runs from the apex of the crown to a well-marked distal cingulum. The “V”-shaped mesial cervix extends weakly apically, as well as the cingulum. A narrow shallow groove runs down the root. In mesial and distal views, the lingual part of the crown is low and forms a pronounced overhang or a platform (distal heel of Lucas & Teaford (1994)). In labial view, the crown is moderately high and narrow. The surface is strongly convex. The mesial face of the root presents two shallow grooves, the one closer to the lingual edge of the root is more pronounced and is probably the only natural one (cf. BAR 1369’00 and BAR 1382’03).

BAR 1369’00 ( Fig. 9G 1-G 4 ) is an entire right lower canine with a worn apex. A honing facet is visible at the junction between crown and root in distal and lingual views. The wear stage can be A4 or A5. The “V”-shaped mesial cervix is developed apically, as well as the cingulum. A narrow and flat groove runs along the mesial surface of the root. In distal view, the surface of the root is convex labio-lingually. The root is elongated contrasting with a low crown.

BAR 1382’03 ( Fig. 9I 1-I 4 ) is a small left lower canine preserving the crown with a worn apex and part of the root compressed mesio-distally but less so than in BAR 1381’03 and OCO 104’10. A developed honing facet has damaged the distal part of the crown (area of the distal overhang or platform) and part of the root. The wear stage is A4 or A5. BAR 1382’03 resembles BAR 1381’03 in the morphology of the “V”-shaped mesial cervix, small and salient mesial crest on the crown and the associated cingulum, and a mesial groove on the root. In lingual and distal views, the distal overhang or platform is almost completely gashed by the honing facet. The distal surface of the root is convex labio-distally.

BAR 351’04 ( Fig. 9J 1-J 4 ) is a damaged left lower canine crown. The apex of the crown is broken off. The discrete distolingual tubercle is almost smooth. The “V”-shaped mesial cervix, the lower part of the mesial crest on the crown and neighbouring strong cingulum have the same characteristics as the other female canines described above. In mesial and distal views, the lingual overhang or platform is clearly defined.

OCO 104’10 ( Fig. 9K 1-K 3 ) is a well-preserved left lower canine. This tooth is morphologically identical to the right canine BAR 1381’03 with the same worn aspect of the apex and hypoplastic lines, especially the biggest one at the base of the crown above the cervix. OCO 104’10 and BAR 1381’03 could belong to the same individual. The root is compressed mesio-distally but less so than BAR 1381’03, the root also seems to be affected by fossilisation. The distal and mesial surfaces present two shallow grooves, both of which are pronounced.

Upper canines

The upper canines are represented by three partial canines (BAR 784’00, BAR 1595’01 and OCO 105’10) and a fragment of root (BAR 1585’00), all of them belong to male individuals. The upper canines are morphologically similar to those of large extant African colobines and are of the same size or slightly larger than the biggest male of Colobus guereza ( Appendix 3).

BAR 784’00 ( Fig. 9C 1-C 4 ) is a left upper canine which preserves the crown with a broken apex and part of the root. The mesial groove is deep, curved rootwards and runs along the root. The buccal slit is well marked. The disto-lingual part of the cervix of the crown was compressed during fossilization. The canine is bucco-lingually flattened and resembles a dagger.

The upper and lower apices of the left upper canine BAR 1595’01 ( Fig. 9D 1-D 4 ) are broken off, but the crown did not suffer compression during fossilization. The mesial groove is deeper than in BAR 784’00. The lingual surface of the distal crest presents a honing facet for the p/3 (wear stage A4 which suggests an adult individual).

BAR 1585’00 is the upper part of an upper canine root with part of honing facet on its distal side.

OCO 105’10 ( Fig. 9E 1-E 4 ) is a right upper canine represented by a crown missing the apex and part of the root. The mesial sulcus is well preserved on the root and is as deep as in BAR 784’00. There is a huge honing facet on the distal side of the tooth and a moderate honing facet cut off by the mesial groove on the apex. The wear stage could be A5.

Premolars

Aragai yielded two isolated premolars.

OCO 101’11 ( Fig. 10B 1-B 4 ) is a well-preserved right p/3 with a lightly worn protoconid (wear stage A2; young adult). There is no honing facet despite a relatively welldeveloped mesio-buccal flange which is however less extended than in OCO 608’10 suggesting that it could be a female as in Colobus and Piliocolobus . It also presents some hypoplastic lines. An acerate lingual ridge descends from the protoconid towards the small metaconid. The metaconid is distally positioned and not opposite the protoconid. The shallow mesial fovea (or trigonid basin) is smaller than the distal fovea which is deep. The mesial cingulum is slightly developed. Strong pre- and postprotocristids are salient and descend from the protoconid mesially and distally respectively. Distally a contact facet with the p/4 is weak. The postprotocristid is separated from the distal cingulum by a cusplet. A short postmetacristid has a cusplet in its median part and is separated by a small slit from the distal cingulum. There is another cusplet lingually in the distal cingulum. There are two straight coalescent roots, the mesial of which is the stronger and the apices are curved gently distally.

OCO 305’11 ( Fig. 10A 1-A 4 ) is a well-preserved crown of P3/. The apex of the paracone is slightly worn (wear stage A1 of a very young adult). The protocone forms more of a salient smooth curved crest rather than a typical cusp but it nevertheless exists. The preparacrista is more salient than the postparacrista. The low endoparacrista joins the developed salient endoprotocrista. The mesial fovea (trigon basin) is small and shallow and the distal basin (talon basin) is large and deep. The distal cingulum is salient and long.

Molars

Five isolated molars were discovered at Aragai, three lowers (BAR 1190’03, BAR 394’04 and OCO 335’10) and two uppers (BAR 470’01 and BAR 1597’01).

BAR 1190’03 ( Fig. 10E 1-E 5 ) is a left m/2 The specimen is complete comprising the crown, the roots and some mandibular bone. The morphology of the occlusal surface corresponds to wear stage A4 indicating that this tooth belongs to an adult.

BAR 349’04 ( Fig. 10G 1-G 5 ) is a right m/2. The crown is well preserved except for the disto-buccal part which is missing. Only the cervical part of the roots is preserved. The crown is slightly worn suggesting wear stage A2 which corresponds to a young adult. Its large size indicates that it could belong to a male individual.

OCO 335’10 ( Fig. 10H 1-H 5 ) is a right m/2. The crown and the two roots are well preserved, and is smaller than BAR 1190’03. The crown is slightly worn and suggests wear stage A2. The two specimens show similarities: square occlusal outline, the talonid equal to the trigonid, wellmarked lophids, a reduced mesial fovea and a wider distal one which is bordered by a strong cingulum. The lingual cusps are much higher than the buccal ones, a feature characteristic of colobines. The metaconid is well developed, higher than the entoconid. The protoconid and hypoconid are almost equal in height. The buccal cuspids are horizontal. The hypoconulid is absent at least in BAR 1190’03 and OCO 335’10.

BAR 250’03 ( Fig. 10F 1-F 5 ) is the distal fragment of a right m/3, the three cuspids (entoconid, hypoconid and hypoconulid) are slightly eroded and not deeply worn suggesting wear stage A1 or A2. The molar belongs to a young adult. Lingually to the hypoconulid, two discrete cuspids are present but neither could be recognized as the tuberculum sextum ( Saheki 1966; Swindler & Orlosky 1974). The hypoconid is as high as the hypoconulid but the hypoconulid is bigger.

BAR 470’01 ( Fig. 10C 1-C 5 ) and BAR 1597’01 ( Fig. 10D 1- D 2 ) are two left M2/s. BAR 470’01 preserves the crown and the cervical parts of the lingual and the distal roots. The contour of the crown is moderately trapezoidal (the buccal surface is mesio-distally longer than the lingual one, the protocone is more salient lingually than the hypocone and they are isolated by a deep groove) as are M2/s of BAR 756’00, BAR 758’00, BAR 762A’00 and BAR 762B’00, and as well as those of Colobus and Piliocolobus , different from M1/ in which the contour is more square. The morphology of the occlusal surface corresponds to wear stage A3, typical of adults. Only the lingual side of BAR 1597’01 is preserved and the cusps are slightly worn as in wear stage A2 (young adult) and present a well-marked hypoplastic line close to the cervix. BAR 470’01 has contact facets mesially and distally for the M1/ and M3/ respectively. The trigon basin is deep and short. There is a small and clear mesostyle in the median buccal cleft between the paracone and the metacone. The mesial and distal cingula are well developed in BAR 1597’01 but worn in BAR 470’01. In both teeth, the fovea are clearly visible, but poorly developed.

POSTCRANIAL BONES

Aragai yielded four cercopithecoid post-cranial bones: BAR 757’00, an axis vertebra (which is described above), BAR 914’04, a proximal right metatarsal V and two distal humeri (OCO 102’11, a right distal humerus, OCO 336’10, a left distal humerus). They were found in the same restricted area as the craniodental material.

BAR 914’04 ( Fig. 11A 1-A 5 ) comprises two fragments which fit together (maximum length: 22.2 mm; maximum width: 7.7 mm, proximal height (measurement n° 3 in Gommery et al. 2009: 5.6 mm). The proximal end is slightly eroded, but the shaft is well preserved. The morphology of the superior and medial views of the proximal extremity are similar to those of the extant African colobines in the morphology of the articular facet for the cuboid which does not occupy all the surface in proximal view but is located more laterally (height: 7.1 mm, width: 3.6 mm). This differs from Parapapio from Waypoint 160 at Bolt’s Farm, WP 19 ( Gommery et al. 2009), from Laetoli, LAET 76-3870 ( Harrison 2011) and from Hadar, A.L.363-1f/1 ( Frost & Delson 2002), in which the articular facet occupies all the surface or is supero-medial. In median view, the articular facet for the metatarsal IV is important (height: 6.3 mm, width: 3.1 mm). In plantar view, as usual, there are two facets for the sesamoid bones. Laterally, there is a moderately developed bony bulge as is the case in extant African colobines. The distal part of the shaft appears robust relative to the proximal part of the metatarsal and is flattened medio-laterally in comparison to those of extant African colobines. The aspect of the shaft is very similar to WP 19 from Bolt’s Farm but differs from that of Paracolobus chemeroni from the Tugen Hills, KNM BC 3 AA ( Birchette 1982). The size of BAR 914’04 is intermediate between Piliocolobus and Procolobus , so it can be attributed with confidence to Sawecolobus lukeinoensis n. gen., n. sp.

OCO 102’11 ( Fig. 11B 1-B 3 ) is a well-preserved right distal humeral articulation with a broken lateral epicondyle (maximum length: 13.1 mm; maximum width: 21.2 mm, maximum height: 11.8 mm). OCO 102’11 is smaller than the specimens of the Piliocolobus sample. In distal view, the trochlear surface is narrow relative to the total articular width. The rounded capitulum humeri is distally salient and separated from the trochlea humeri by a low and smooth crest. The zona conoidea appears short and low. The disto-lateral edge of the capitulum is damaged but the lateral edge of the radial fossa is preserved and marks the end of the capitulum which appears cylindrical as in African colobines. The preserved distal part of the medial epicondyle indicates that it is strong, short and projects strongly posteriorly. The angle of the medial epicondyle is approximately 50° and falls within the range of variation of African colobines as well as that of many other Cercopithecoidea ( Frost & Delson 2002). In anterior view, the trochlea is short proximodistally and wide. The preserved part of the radial fossa is deeper and larger than the coronoid fossa, as is typical in colobines ( Olivier & Caix 1959; Szalay & Delson 1979; Frost & Delson 2002). The zona conoidea is narrow and moderately-to-slightly shallow, differing from those of Colobus and Piliocolobus . The surface of the lateral edge of the trochlea, which separates it from the zona conoidea, forms a smooth ridge elongated antero-posteriorly and is not as prominent as in Cercopithecus lhoesti ( Gebo & Sargis 1994) . It is somewhat similar to those of Colobus , Piliocolobus and Lophocebus , and more pronounced than that of Chlorocebus ( Senut 1989; this study). It is more pronounced than in Cercopithecoides and in Rhinopithecus from Hadar ( Frost & Delson 2002) or cf. Paracolobus from Nkondo (NK 322’88) ( Senut 1994) and Kuseracolobus aramisi (DID-VP-1/78) ( Frost et al. 2009). The medial trochlear flange projects disto-medially. It is straighter than in Colobus and Piliocobus where it projects more medially and less distally, but is less straight than in Lophocebus and especially in Cercocebus ( Senut 1989; this study). It is less straight than in Cercopithecoides and unlike that of Rhinopithecus from Hadar ( Frost & Delson 2002) or cf. Paracolobus from Nkondo (NK 322’88) ( Senut 1994) and Kuseracolobus aramisi (DID-VP-1/78) ( Frost et al. 2009) in which it is straight. In posterior view, the articular surface is oblique latero-proximally to disto-medially as evidenced by the inclination of the medial trochlear rim, as in Cercopithecus mitis ( Gebo & Sargis 1994) but also in Colobus , Piliocolobus , Lophocebus and Cercocebus .

OCO 336’10 ( Fig. 11C 1-C 3 ) is a left distal humerus. It is smaller (maximum length: 14 mm; maximum width: 18.3 mm; maximum height: 10.8 mm) and is more gracile than OCO 102’11 (some anatomical features are less pronounced). In distal view, as for OCO 102’11, the trochlear surface is narrow relative to the total articular width. The capitulum is cylindrical. The well-preserved medial epicondyle confirms the observation made on the right humerus. The angle of the median epicondyle is approximately 52°. In anterior view, the trochlea is short proximo-distally and narrow. The radial fossa is deep and large. The coronoid fossa is reduced. The zona conoidea is also narrow and shallow. The smooth and low ridge which separates the capitulum humeri from the trochlea humeri is less pronounced than in OCO 102’11. The surface of the ridge corresponding to the lateral edge of the trochlea is slightly eroded but is very similar to that of OCO 102’11. In posterior view, only the distal part of the fossa olecrani is preserved and is deep and narrow as in the vervet monkey ( Chlorocebus aethiops ) and some Cercopithecus ( C. (Cephus) ascanius , C. lhoesti , C. neglectus ). There is no groove between the trochlea and the medial epicondyle. The medial trochlear rim projects distally, but less than in OCO 102’11.

Figures

FIG. 3. — The mandible OCO 608’10 in hard phosphatic matrix before mechanical preparation. Scale bar: 1 cm.

FIG. 4. — Sawecolobus lukeinoensis n. gen., n. sp.: A, holotype BAR 758’00, skull: A1, facial view; A2, posterior view; A3, superior view; A4, left lateral view; A5, palatal view; A6, right lateral view; B, BAR 759’00, left hemi-maxilla: B1, buccal view; B2, occlusal view; B3, lingual view;C, BAR 760’00, left hemi-mandible: C1, buccal view; C2, occlusal view; C3, lingual view. Scale bars: 1 cm.

FIG. 5. — CT scans of Sawecolobus lukeinoensis n. gen., n. sp., crania: A, B, frontal and mid-sagittal scans of BAR 758’00; C, D, frontal scans of BAR 757’00, respectively; C2, D2, are expanded images of C1 and D1, respectively. The bony region has rather low CT values and is coloured in dark grey on the CT scans. The frontal and sphenoid bones are fully occupied by cancellous bone in both specimens (*). The maxillary sinus (MS) is separated by the thin bony wall (dotted line, BW) that, in part, includes cancellous bone (dotted circle) on the left side in BAR 757’00, but its trace is detected on the right. The left M3/ alveolus is excavated by the maxillary sinus in BAR 757’00 (**). Scale bars: 1 cm.

FIG. 6. — Sawecolobus lukeinoensis n. gen., n. sp.: A, skull BAR 757’00: A1, palatal view; A2, facial view; A3, superior view; A4, posterior view; A5, left lateral view; A6, right lateral view; B, Maxilla BAR 756’00: B1, left lateral view; B2, palatal view; B3, right lateral view. Scale bars: 1 cm.

FIG. 7. — Sawecolobus lukeinoensis n. gen.,n. sp.: A, skull fragment BAR 761’00:A1, nucho-lateral view;A2, internal view;B, right maxilla fragment BAR 762B’00 (maxilla fragment with M1/ to M3/) + OCO 1049’11 (P3/) associated with BAR 762A’00: B1, lingual view; B2, occlusal view; B3, buccal view; C, left maxilla fragment BAR 762A’00 (maxilla fragment with P4/ to M3/) associated with BAR 762B’00: C1, lingual view; C2, occlusal view; C3, buccal view; D, left maxilla fragment BAR 786’00 (partial maxilla with M3/) + BAR 1368’00 (left M2/): D1, buccal view; D2, occlusal view; D3, lingual view. Scale bars: 1 cm.

FIG. 8. — Sawecolobus lukeinoensis n. gen., n. sp.: A, right mandibular fragment OCO 100’11: A1, buccal view; A2, occlusal view; A3, lingual view; B, mandibular symphysis BAR 1586’00: B1, labial view; B2, occlusal view; B3, lingual view; C, mandible OCO 608’10: C1, occlusal view; C2, right lateral view; C3, left lateral view. Scale bars: 1 cm.

FIG. 9. — Sawecolobus lukeinoensis n. gen., n. sp.: A, B, incisors: A, right I2/ BAR 910’04: A1, lingual view; A2, labial view; A3, mesial view; A4, distal view; A5, occlusal view; B, right I1/ BAR 1214’00: B1, occlusal view; B2, lingual view; B3, labial view; B4, mesial view; B5, distal view; C-L, canines: C, left upper canine BAR 784’00: C1, mesial view; C2, distal view; C3, lingual view; C4, buccal view; D, left upper canine BAR 1595’01: D1, distal view; D2, mesial view; D3, lingual view; D4, buccal view; E, right upper canine OCO 105’10: E1, distal view; E2, mesial view; E3, buccal view; E4, lingual view; F, left lower canine BAR 785’00: F1, lingual view; F2, labial view; F3, mesial view; F4, distal view; G, right lower canine BAR 1369’00: G1, lingual view; G2, labial view; G3, mesial view; G4, distal view; H, right lower canine BAR 1381’03: H1, lingual view; H2, labial view; H3, mesial view; H4, distal view; I, left lower canine BAR 1382’03: I1, lin-

FIG. 10. — Sawecolobus lukeinoensis n. gen., n. sp., post-canine teeth: A, left P/3 OCO 305’11: A1, buccal view; A2, lingual view; A3, mesial view; A4, occlusal view; B, right p/3 OCO 101’11: B1, mesial view; B2, distal view; B3, lingual view; B4, buccal view; C, left M2/ BAR 470’00: C1, lingual view; C2, distal view; C3, buccal view; C4, mesial view; C5, occlusal view; D, left: M2/ BAR 1597’01: D1, occlusal view; D2, buccal view of interior of tooth; E, left m/2 BAR 1190’03: E1, buccal view; E2, mesial view; E3, lingual view; E4, distal view; E5, occlusal view; F, half right m/3 BAR 250’03: F1, lingual view; F2, distal view; F3, mesiobuccal view; F4, mesial view; F5, occlusal view; G, right m/2 BAR 349’04: G1, lingual view; G2, distal view; G3, buccal view; G4, mesial view; G5, occlusal view; H, right m/2 OCO 335’10: H1, buccal view; H2, mesial view; H3, lingual view; H4, distal view; H5, occlusal view. Scale bars: 5 mm except for H, 1 cm.

FIG. 1. — View of the site of Aragai, in the foreground,with the characteristic orange-red sediment of the Lukeino Formation,in the background are the Tugen Hills.

FIG. 2. — View of the site of Aragai,in the foreground,the small area (with orange-red sediment and around the big Balanites tree) which yielded the colobine material.

FIG. 11. — Sawecolobus lukeinoensis n. gen., n. sp., postcranial bones: A, proximal right metatarsal V, BAR 914’04: A1, plantar view; A2, lateral view; A3, superior view; A4, medial view; A5, distal view; B, right distal humerus OCO102’11: B1, anterior view; B2, posterior view; B3, distal view; C, left distal humerus OCO 336’10: C1, anterior view; C2, posterior view; C3, distal view. Scale bars: 1 cm.