Sawecolobus, 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

Genus Sawecolobus n. gen.

urn:lsid:zoobank.org:act:5B71A489-0E76-4B7B-ABE0-2F868E0C244F

TYPE SPECIES. — Sawecolobus lukeinoensis n. sp., by present designation.

GENERIC DIAGNOSIS. — A small-to-medium sized extinct genus of colobine monkey with a short muzzle and a general morphology with a Cercopithecoides -like aspect. The calvarium is large, especially in the frontal region, and rounded. The sagittal crest is absent in females and is probably weak when present in males. The frontal is prominent and convex, being close to Cercopithecoides but more expressed than in Mesopithecus . The face is broad. The inter-orbital pillar is broad typical of colobines but here moderately developed. The orbits are big, broad, and low.The supraorbital tori are moderately thick.The glabellar region is slightly proeminent, less than in Cercopithecoides , but more than in Mesopithecus . The ophryonic groove is broad and moderately deep, but not as deep as in Cercopithecoides . The post-orbital constriction is very weak with short prominent temporal lines. The skull presents a specific triangular coalescent area oriented latero-fronto-superiorly at the latero-superior corner of the orbits above the fronto-zygomatic suture at the junction of the temporal lines and the orbits. The frontal process of the zygomatic bone is narrow. The infraorbital part of the zygomatic bone, especially the area of the zygomatico-maxillary suture, is moderately low. The roots of the zygoma are located below the contact between M1/-M2/. The maxillary sinuses (MS) are present as in Cercopithecoides but Sawecolobus n. gen. differs from Mesopithecus in which they are absent. The palate is short, the usual morphology in many short-faced colobines, and the hard palate ends at the level of M3/. It is characterized by a staphylion located very anteriorly. The shape of the premaxilla imparts an ogival aspect of the anterior part of the muzzle and not a squared-off rostrum as seen in Kurasocolobus and Cercopithecoides .

The mandibular symphysis is deep. The median mental foramen seems to be absent as is the case in most colobines except Procolobus , Cercopithecoides and Rhinocolobus . Unlike Cercopithecoides , in lateral view the contour is globally convex and inclined posteriorly with a lower break in the slope, and the anterior surface of the symphysis is convex transversally and not laterally compressed. The mandibular body is deep, gracile and vertical with a uniform height from m/1 to m/3. It does not present a strong lateral flare and the prominentia laterales are weak. The inferior border of the mandibular body is robust and tapers posteriorly near the gonial area, a morphology different from Kuseracolobus . There is no fossa on the lateral surface of the mandible and the lateral mental foramen is located below the p/4. The morphology of the base of the ascending ramus of the mandible suggests that it is almost vertical relative to the occlusal plane, less steep than in Mesopithecus , but not as inclined as it is in Cercopithecoides . It is situated near the rear of the m/3, more posteriorly than in Cercopithecoides and the extramolar sulcus is narrower medio-laterally.

In general, the dentition is typically colobine but presents some specificities. The canines reveal a strong dimorphism. On the mandible, the lower canine is labially curved as in Mesopithecus and Colobus but unlike Paracolobus enkorikae .

The presence of a protocone on P3/ is variable, and when present it is slightly developed. The M2/s are the largest molars. The p/3s are broader than the p/4s. The p/4s are very small in comparison with the other teeth. The protoconid and the metaconid in the p/4s are almost of the same height, the talonid is narrower than the anterior part of the tooth and bears a small entoconid. The breadth of the lower molars increases from m/1 to m/3, the distal width is broader that than the mesial width, except in the m/3s.

DIFFERENTIAL DIAGNOSIS. — The inter-orbital pillar is less broad than in typical Plio-Pleistocene Cercopithecoides (such as C. meaveae , C. kimeui , C. williamsi , C. haasgati and C. alemayehui ), but also in Paracolobus and Mesopithecus . It is more moderately developed, as in C. kerioensis and C. bruneti , and also in Libypithecus and Rhinocolobus . The nasal aperture is located low down on the face, its top being situated below the inferior orbital margins, as in African fossil colobine genera ( Cercopithecoides , Libypithecus , Paracolobus and Rhinocolobus ) and Mesopithecus but different from extant African colobines ( Procolobus , Piliocolobus and Colobus ) and the majority of Asiatic extant colobines ( Presbytis , Rhinopithecus , Semnopithecus and Trachypithecus ), except Nasalis which has the top of the nasal aperture situated above the inferior orbital margins.

The specific triangular coalescent area above the fronto-zygomatic suture, the temporal lines and the orbits is not as infero-superiorly elongated as in some specimens of Paracolobus , and is not distinct, unlike Cercopithecoides (including C. kerioensis ), Libypithecus , Mesopithecus and Rhinocolobus .

As in Cercopithecoides and Mesopithecus , in extant African colobines, and in extant Asian colobines ( Nasalis , Pygathrix , Rhinopithecus , Semnopithecus ), the frontal process of the zygomatic bone is narrow in S. lukeinoensis n. gen., n. sp. and not broad as in Dolichopithecus , Libypithecus , Paracolobus and Rhinocolobus . The infraorbital part of the zygomatic bone is moderately low as in Cercopithecoides , Mesopithecus and Nasalis but is higher than in Piliocolobus , Procolobus , some Colobus , Pygathrix , and Rhinopithecus , and lower than in Dolichopithecus , Libypithecus , Paracolobus and Rhinocolobus . In comparison with the different species of Cercopithecoides , the staphylion (or posterior nasal spine) is more anteriorly located, probably close to the line between the mesial parts of the M3/s.

ETYMOLOGY. — In recognition of the local people, the prefix ‘Sawe’ refers to the old age societal classes in the Tugen community (meaning wise). The other part of the name refers to its colobine status.