Cercopithecoides cf. williamsi Mollett, 1947

Gommery, Dominique, Kgasi, Lazarus, Vilakazi, Nonhlanhla, Sénégas, Frank, Pickford, Martin, Kuhn, Brian, Schnyder, Johann & Pois, Véronique, 2023, First in situ middle Pliocene cercopithecoid fossils from the Palaeokarst System of Bolt’s Farm (South Africa), Geodiversitas 45 (5), pp. 163-195 : 182-183

Cercopithecoides cf. williamsi Mollett, 1947

MATERIAL EXAMINED. — Cranium. BPB 7, frontal bone ( Fig. 21 ).

DESCRIPTION

Cranium BPB 7 ( Fig. 21 )

General description and preservation. This specimen is the anterior part of the calvaria (maximum length: 54.9 mm; breadth: 83.5 mm) ( Fig.21 A-C)comprised of two isolated pieces ( Fig.21D ). It is less distorted than BPB 1. The left anterior part (corresponding to the upper part of the left orbit) is the most affected by distortion. Many cracks are present mainly in the posterior part. In anterior view, the upper part of the orbits, the glabella and the interorbital pillar are preserved. The latter is well preserved and broad (15.9 mm), typical of colobine monkeys, especially Cercopithecoides ( Freedman 1957, 1965, Szalay & Delson 1979; Frost & Delson 2002; Jablonski et al. 2008b; Jablonski & Frost 2010).This genus is common in South African Plio-Pleistocene sites. In superior view ( Fig. 21A ), there is an important ophryonic groove as is usual in Cercopithecoides . There are a few bits of bone missing from the frontal but one of them, the biggest, presents an oval outline and probably corresponds to a predation mark.

Calvaria. In superior view ( Fig. 21A ), the ophryonic groove is deep and broad antero-posteriorly. Posterior to the ophryonic groove, the frontal has a rounded aspect. The temporal lines are well developed anteriorly with a strongly salient aspect as in BF 42A.Despite the damage,the postorbital constriction seems weak.

Orbital region. The superior orbital margins and parts of the lateral orbital margins are preserved and thick (thickness of the superior: 7.9 mm at left and 7.4 mm at right) ( Fig. 21C ). The supraorbital torus is well developed and thick. The preserved part suggests that the orbits were large. The lower aspect of the interorbital pillar suggests that the nasal and maxilla sutures are not fused; this frontal bone probably belongs to a sub-adult. The interorbital pillar is large.The glabellar region is moderately inflated anteriorly but this part is abraded.

Remarks. The morphology and the size of the specimen are comparable to the homologous frontal areas of different specimens of the very large colobine Cercopithecoides williamsi such as BF 42A (Pit 23, BFCS) or AD 1326-6/M 236 (type specimen), M 2999/MP 113 and M 3055 (from Makapansgat Limeworks).In the absence of a complete muzzle and dentition ( Frost & Delson 2002; Jablonski & Frost 2010), we provisionally assign the fossil BPB 7 to C. cf. williamsi . It differs from the older species, C. kerioensis Leakey et al., 2003 ( Leakey et al. 2003; Jablonski & Frost 2010) (c. 5-4.2 Ma: Kenya), by its greater dimensions and thicker supraorbital torus despite the fact that this last feature seems variable in Cercopithecoides ( Anderson et al. 2013; Frost et al. 2014). Some colobine remains from Woranso-Mille ( Ethiopia) dated between 3.8 and 3.6 Ma were attributed to Cercopithecoides cf. meaveae Frost & Delson, 2002 ( Frost et al. 2014). This species was known previously only at Leadu and Hadar ( Ethiopia) between 3.4 to 3.28 Ma ( Frost & Delson 2002; Jablonski & Frost 2010). The remains from WoransoMille are larger than the youngest remains from Leadu and Hadar but are still smaller than those of C. willamsi . Another large colobine, similar in size to the genus Paracolobus Leakey, 1969 , is presumed to occur at Makapansgat ( Jablonski & Frost 2010) but it is represented by isolated teeth. Paracolobus differs from Cercopithecoides by a marked postorbital constriction, not present on BPB 7.

Figures

FIG. 21. — Anterior part of calvaria of Cercopithecoides cf. williamsi Mollett, 1947, specimen BPB 7: A, superior view; B, inferior view; C, frontal view; D, two isolated fragments of the calvaria. Scale bar: 10 mm.