Kuseracolobus aramisi, FROST, 2001

FROST, STEPHEN R., 2001, New Early Pliocene Cercopithecidae (Mammalia: Primates) from Aramis, Middle Awash Valley, Ethiopia, American Museum Novitates 3350, pp. 1-36 : 15-23

Kuseracolobus aramisi , new species

SPECIFIC DIAGNOSIS: As for genus.

ETYMOLOGY: Named after the type site of Aramis.

HOLOTYPE: ARA­VP­1/87. A nearly complete male mandibular corpus with the entire postcanine dentition except the right m1, associated with left and right C, left c, and a left maxillary fragment with M1–3 found by A. Asfaw on December 18, 1992 (see fig. 9).

HYPODIGM: See appendix 2.

HORIZON: All specimens are derived from the Aramis Member of the Sagantole Formation, between the GATC and DABT, and are therefore dated to 4.4 Ma (Renne et al., 1999).

DESCRIPTION: The best cranial specimens, ARA­VP­6/1686 and KUS­VP­2/70 (see fig. 10), are both females. ARA­VP­6/1686 preserves both maxillae and premaxillae below the middle of the zygomatic process of the maxilla, but little of the palate. The entire dentition is preserved other than the right I2 and M2. KUS­VP­2/70 preserves a left premaxillomaxillary fragment with C­M1, most of the root of the zygoma, part of the lateral aspect of the face and piriform aperture, and most of the palatal process. A small fragment of the right maxilla with M1–2 and some of the palatal process is also preserved, along with the glabellar portion of the frontal and an isolated left I1. The holotype, ARA­VP­ 1/87, preserves a left maxillary fragment with M1–3 and the roots of P4, a small part of the palatine process, and the very base of the zygomatic process (see fig. 10). ARA­ VP­1/6 is a male left maxilla preserving P3­ M3 and the root of C (see fig. 10). It is highly Fig. 9 . Continued. damaged, however, revealing the roots of the teeth.

Kuseracolobus aramisi is larger in craniodental size than Colobus , Libypithecus , and Mesopithecus , but smaller than Cercopithecoides (other than a new species from Lothagam to be described by Leakey et al., in press), Paracolobus , Rhinocolobus , and Dolichopithecus . It is similar in size to Nasalis , the colobine from Leadu, the smaller colobine at Hadar, and larger subspecies of Semnopithecus . Colobines of similar dental size also occur in the Omo Shungura Formation in Members B, C, D, and G, from the Tulu Bor Member at Koobi Fora, and from the Upper Laetolil beds. It is also similar in dental size to Pl. alemui . The dental dimensions of K. aramisi are given in table 1.

Frontal. A small part of the glabellar area is preserved in KUS­VP­2/70 and ARA­VP­ 1/13. Both are similar in overall morphology to the Leadu colobine. The first specimen is a female and has an interorbital breadth of 12.1 mm; the second is of unknown sex and has an interorbital breadth of 10.8 mm, compared with 13.8 mm in the male Leadu specimen. Both Aramis specimens preserve nasals that are slightly pointed anterosuperiorly.

Maxilla. The most complete specimens are ARA­VP­6/1686 and KUS­VP­2/70, but the male ARA­VP­1/87 also preserves a left maxillary fragment. The root of the zygoma appears to be positioned above M1, or the M1/M2 contact in both male and female specimens. This placement of the zygoma is slightly more anterior than that found in C. williamsi from Koobi Fora and in most C. williamsi from South Africa. The piriform aperture is more vertically inclined and the rostrum shorter than in the male cercopithecines ARA­VP­6/437 and ARA­VP­6/933. The piriform aperture is quite narrow and tall, and the plane of its outline forms an angle slightly more than 60° with the alveolar margin in the subadult KUS­VP­2/70 and approximately 45° in ARA­VP­6/1686. The inferior portion of the piriform aperture is sharply V­shaped. In superior view, the premaxillae form a squared­off rostrum. The premaxillae would have been relatively short overall and generally similar in outline to those of the Leadu colobine and KNM­ER 4420.

The maxillary dental arcade is best preserved in ARA­VP­6/1686, and although distorted bilaterally, it is reasonably intact on the left. KUS­VP­2/70 and ARA­VP­1/87 also preserve partial tooth rows. The dental arcade forms a gentle arc from M3 to C, being widest around the M1/M2 contact, with no tooth deviating from this line. There is a sharp angle at the canines, and the incisors form a relatively straight, flat arc between the canines. The palate is partially preserved in KUS­VP­2/70 and appears to have been fairly shallow and flat. It is slightly deeper in the male ARA­VP­1/87, which preserves a small part of the palatal process.

Mandible. The mandible is best preserved in the male specimen ARA­VP­1/87, which retains much of the corpus and most of the rami, although the margins and gonion are damaged and the condyles are lacking. Except for the right m1, the entire postcanine dentition is preserved. ARA­VP­1/5 (see fig. 11) is the symphysis of a male with the left c­m1 and right p3­m1. ARA­VP­1/290 (see fig. 11) is probably a subadult male symphysis with the left i1–2 and p4­m1 and the crowns of the canines and p3s erupting. ARA­VP­6/796 (see fig. 11) is the symphysis of a female with the left m1 through right p4. ARA­VP­1/1774 (see fig. 11) preserves the right corpus down the inferior margin un­ der the m1–3. ARA­VP­1/564 (see fig. 11) preserves part of the corpus below the molars, but none of the margin. Other specimens preserve more fragmentary portions.

The symphysis is quite steeply sloping, rather deep overall, and has a vertical profile. Both transverse tori are robust. The superior transverse torus extends posteriorly to the distal portion of p3, and is fairly steeply sloping. Anteriorly, the symphysis lacks a median mental foramen.

A shallow fossa is present on the lateral surface of the corpus. This is largely due to the presence of lateral bulging near the inferior margin, which is the widest part of the corpus. This can be most clearly seen in the female ARA­VP­6/796, but also in ARA­ VP­1/290. This morphology is unlike that of the Leadu colobine, AL231–1a (a specimen from Hadar most likely to be the same taxon as the Leadu colobine), and Cercopithecoides (particularly KNM­ER 4420), where the corpus is the widest at mid­height. The mental foramen seems to be single in all of the mandibles recovered, and its position varies from the below the m1/p4 contact in ARA­ VP­1/1774 to the p3/p4 contact in the juvenile ARA­VP­1/290. The corpus is fairly deep overall, especially compared with the Leadu colobine (see fig. 12), AL231–1a, or Cercopithecoides from both East and South Africa. It is shallower but thicker than mandibles of Paracolobus mutiwa and Rhinoco­ lobus. In ARA­VP­1/87 the right corpus deepens posteriorly from p3 to m3, although there is damage below the m1 through mesial m3. ARA­VP­1/1774 deepens from m1 to m3 and preserves a bulge below the m2. The gonial area is partially preserved in ARA­ VP­1/87 and is expanded, although not to the extent seen in Paracolobus mutiwa . This is quite distinct from the comparatively unexpanded gonial area seen in the Leadu colobine and Cercopithecoides .

Viewed superiorly, there is a wide extramolar sulcus, and the oblique line blends into the corpus at mesial m2 or distal m1, comparable to that in the Leadu colobine and AL231–1a. There is no strongly marked ridge at the anterior limit of the masseter scar. The mandibular dental arcade, although slightly distorted, is best preserved in ARA­ VP­1/87. It forms a parabolic arch, except that the area across the incisors is flattened.

Dentition. The dentition overall is typical for colobines. The upper incisors are smaller and far less flaring than in papionins. The mesial and distal margins of the I1 crown are roughly parallel and slant mesially, and the widest part of the crown is approximately at mid­height. Lingually, there is a cingulum around the base. The I2 is caniniform in crown shape and also has a lingual cingulum. The lower incisors possess lingual enamel and are small, peglike teeth compared with those of papionins. The i1 lingual surface is shoveled, and the crown is slightly flaring in anterior view. The i2 has a crown that is narrower overall, is more of a parallelogram in outline, and possesses a distal cuspule, or ‘‘lateral prong’’ (Delson, 1975). The canines are typical of cercopithecids, being comparatively large teeth and highly sexually dimorphic.

The upper premolars are typical bicuspid teeth. The protocone of the P3 is usually present and often large, but is sometimes reduced. The P3 is generally more triangular in occlusal outline, and the P4 often has a bit more of a talon. The p3 is sexually dimorphic as for most cercopithecids, particularly in the development of the mesiobuccal flange. It is also typical of colobines in that the paraconid is generally more pronounced than in cercopithecines. The male mesiobuccal flange is shorter than those of male cercopithecines (although longer than female cercopithecines), is more inferiorly directed, and the talonid extends more lingually. The p4 is a more molariform tooth, but may develop a mesiobuccal flange in males. There is also a greater amount of cusp relief (i.e., the difference between the height of the cusps and the lowest points of the crown between them) than is the case in cercopithecines.

The molar crowns are only slightly flaring with tall, widely spaced cusps that are con­ nected by sharp cross­lophs. On the upper molars, the paraloph is broader than the hypoloph, but less so than in cercopithecines. The buccal notch has a ‘‘crease’’ reaching toward the cervix from the buccal notch. A distal fifth cuspule is variably present on the M3. The upper molars are all roughly similar in overall size and generally arranged in a straight line. The lower molars have very deep lingual notches with high cusps. The distal cingulum of m1–2 forms a distal cuspule 6–8% of the time, depending on scoring. On the m3, the hypoconulid is well developed, and there is typically (62–92%, depending on scoring) a tuberculum sextum as well. This contributes to the presence of a well­developed distal lingual notch between the hypoconulid and the entoconid. There is also a well­developed distal buccal cleft. The metalophid is usually wider than the protolophid on m1–2 but generally not on m3 (although it is occasionally). These lophid proportions for K. aramisi are typical of Asian colobines (which may be the primitive state for the subfamily; see Szalay and Delson, 1979) but different from extant African colobines.

Of the deciduous dentition, the di2 is possibly known in ARA­VP­1/2092. It looks like a miniature of the permanent i2, with a relatively narrow crown and a distal prong. This is distinct from normal papionin morphology, where the lower dIs are rather broad. Of the deciduous premolars, upper and lower dP4s are known. The dP4 is much like the M1, but far more flaring, with more approximated cusps. The mesial and distal foveae are relatively longer than in the molars. The dp4 is similar to the m1, but is narrower relative to its length, with a metalophid that is wider in comparison to the protolophid than in m1. The lophids are not quite as well developed as those of the molars, but are better developed than those of the deciduous premolars of cercopithecines.

BODY WEIGHT AND SEXUAL DIMORPHISM

Based on the available dental material that is assignable to sex, body weight has been estimated here for the Aramis cercopithecids utilizing the methods and prediction equations of Delson et al. (2000). In their study,

TABLE 2 Distribution of Characters in Various Cercopithecid Generaa

subfamily­specific equations for each sex were derived based on a large cercopithecid sample with associated or literature­compiled body weights. These equations were used here on the Aramis dental material that is assignable to sex and subfamily. The results are based on the means of several estimates based on equations for dental measurements found to be most accurate at predicting body weights of known samples (for a thorough discussion, see Delson et al., 2000). Males and females of Pliopapio alemui are estimated to have had a mean body weight of 12 kg (range 10–15 kg) and 8.5 kg (7–10 kg), respectively. These estimates yield a ratio of male­to­female body mass of 1.4:1. This value is similar to that seen in such extant species as Lophocebus albigena , Macaca sylvanus , M. nemestrina leonina , and Cercopithecus aethiops pygerythrus . M. sylvanus is similar in body weight to Pl. alemui , whereas the others are smaller.

Body weight estimates have been made for Kuseracolobus aramisi in the same manner. Males and females of this population are estimated to have had mean body weights of approximately 18 kg (range 14–22 kg) and 12 kg (10–14 kg), respectively. This yields a ratio of 1.5:1 for male­to­female body weight. This level of dimorphism is similar to that of most subspecies of Semnopithecus entellus , Pygathrix (Rhinopithecus) roxellana , and Procolobus badius oustaleti . Of these taxa, only S. entellus approaches K. aramisi in weight (Delson et al., 2000).

Figures

Fig. 9. Holotype of Kuseracolobus aramisi ARA­VP­1/87. Occlusal view. Opposite page: lateral views, left side above, right (reversed) below.