Systematics of early and middle Miocene Old World monkeys.

New information about the early cercopithecoids Prohylobates tandyi (Wadi Moghra, Egypt) and Prohylobates sp. indet. (Buluk and Nabwal, Kenya) is presented. Comparisons are made among all major collections of Early and Middle Miocene catarrhine monkeys, and a systematic revision of the early Old World monkeys is provided. Previous work involving the systematics of early Old World monkeys (Victoriapithecidae; Cercopithecoidea) has been hampered by a number of factors, including the poor preservation of Prohylobates material from North Africa and lack of comparable anatomical parts across collections. However, it is now shown that basal cercopithecoid species from both northern and eastern Africa can be distinguished from one another on the basis of degree of lower molar bilophodonty, relative lower molar size, occlusal details, symphyseal construction, and mandibular shape. Results of particular interest include: 1) the first identification of features that unambiguously define Prohylobates relative to Victoriapithecus; 2) confirmation that P. tandyi is incompletely bilophodont; and 3) recognition of additional victoriapithecid species.

Phylogenetic, paleodemographic, and taphonomic implications of Victoriapithecus deciduous teeth from Maboko, Kenya.

More than 240 milk teeth of Victoriapithecus macinnesi, representing all elements of the deciduous dentition, are described. Their morphology is intermediate between that of hominoids and cercopithecids. Unlike colobine and cercopithecine milk teeth, Victoriapithecus dp3s, dp4s, and at least 7 (14%) dp4s lack transverse distal loph(id)s and are not bilophodont. Victoriapithecus also differs from cercopithecids in having less elongated deciduous premolars, a dp3 metacone set mesial to a very small hypocone, a dp4 crista obliqua, and a dp4 hypoconulid. The deciduous canines and incisors of Victoriapithecus are like those of other cercopithecids in having an uneven distribution of enamel around a compressed (rather than cylindrical) root, but differ from cercopithecids and resemble hominoids in being more elongated. Since Colobinae and Cercopithecinae share features of the deciduous dentition that are derived relative to Victoriapithecus and hominoids, extant Old World monkeys are interpreted as representing the sister-taxon of the middle Miocene cercopithecoids. Due to a dramatic increase in the number of deciduous teeth found at Maboko Island, juvenile individuals represent a much larger proportion of recently excavated Victoriapithecus collections than is true of pre-1987 assemblages which mainly derive from sediment first excavated during the 1930s and 1940s. Age distribution differences between pre- and post-1987 samples indicate that paleontological collection procedures were more important than taphonomic biases in determining the paleodemographic profile of the Maboko fossils. Since the Victoriapithecus assemblage from Maboko is strikingly similar to that of fossil Theropithecus oswaldi from Olorgesailie in terms of the large number of specimens and high representation of juvenile and infant individuals, the latter can no longer be viewed as unique among cercopithecoid fossil assemblages. Rather than being related to a specific cause of death, such as selective hunting of T. oswaldi by Homo (Shipman et al. [1981] Curr. Anthropol. 22:257-268), the large number of cercopithecoids at both sites is attributed to the fact that both assemblages represent excavated samples and that the preferred habitats of the extinct monkeys were probably at or near the site of deposition. The greater number of young adult male than female canines in the apparently attritional Maboko Bed 5 assemblage, indicate that the social organization of V. macinnesi may have been similar to that of modern macaques, with males migrating out of their natal group and suffering higher death rates than females at puberty.

Ancestral facial morphology of Old World higher primates.

Fossil remains of the cercopithecoid Victoria-pithecus recently recovered from middle Miocene deposits of Maboko Island (Kenya) provide evidence of the cranial anatomy of Old World monkeys prior to the evolutionary divergence of the extant subfamilies Colobinae and Cercopithecinae. Victoria-pithecus shares a suite of craniofacial features with the Oligocene catarrhine Aegyptopithecus and early Miocene hominoid Afropithecus. All three genera manifest supraorbital costae, anteriorly convergent temporal lines, the absence of a postglabellar fossa, a moderate to long snout, great facial height below the orbits, a deep cheek region, and anteriorly tapering premaxilla. The shared presence of these features in a catarrhine generally ancestral to apes and Old World monkeys, an early ape, and an early Old World monkey indicates that they are primitive characteristics that typified the last common ancestor of Hominoidea and Cercopithecoidea. These results contradict prevailing cranial morphotype reconstructions for ancestral catarrhines as Colobus- or Hylobates-like, characterized by a globular anterior braincase and orthognathy. By resolving several equivocal craniofacial morphocline polarities, these discoveries lay the foundation for a revised interpretation of the ancestral cranial morphology of Catarrhini more consistent with neontological and existing paleontological evidence.

Facial anatomy of Victoriapithecus and its relevance to the ancestral cranial morphology of Old World monkeys and apes.

Recently discovered craniofacial fossils of the middle Miocene cercopithecoid Victoriapithecus are described. The frontal, zygomatic, maxilla, and premaxilla anatomy differ from the previously proposed colobine-like ancestral cercopithecoid morphotype in several significant respects. This morphotype was based on the assumption that features held in common by subordinate hominoid and cercopithecoid morphotypes (Colobinae and Hylobatidae) are primitive for Old World monkeys. Cranial similarities between Victoriapithecus, which represents the sister-group of both colobine and cercopithecine monkeys, and the shorter-snouted Cercopithecinae (Macaca and Cercopithecus) indicate that the last common ancestor of Old World monkeys possessed the following features: a narrow interorbital septum, moderately long snout, moderately long and anteriorly tapering premaxilla, large procumbent upper central incisors set anterior to and with longer roots than lateral incisors, moderately tall face below the orbits, teardrop-shaped nasal aperture of low height and moderate width, and probably long and narrow nasal bones. The Victoriapithecus cranium is also characterized by features not present in modern cercopithecids. These include a deep malar region of the zygomatic and the presence of a frontal trigon due to the occurrence of temporal lines that merge with supraorbital costae close to the midline of each orbit and converge anterior to bregma. These features are interpreted as primitive retentions from the basal catarrhine condition as indicated by the occurrence of these features among primitive catarrhines (Aegyptopithecus) and Miocene hominoids (Afropithecus).

The lacrimal fossa of cercopithecoidea, with special reference to cladistic analysis of Old World monkey relationships.

Re-examination of lacrimal fossa patterns in extant cercopithecoids indicates that the last common ancestor of Cercopithecini and Papionini, and hence of Cercopithecinae, probably retained a maxillary contribution to the lacrimal fossa, as did the common ancestor of Colobinae. Consequently, the presence of a maxilla-lacrimal fossa cannot be used to assess the subfamily affinity of Old World monkeys. In addition to being correlated with general facial lengthening, the derived, exclusively lacrimal pattern of Erythrocebus, Mandrillus, Papio, Theropithecus and some (but not all) guenons, macaques and mangabeys may be associated with extreme narrowing of the interorbital septum. Moreover, the derived condition may have evolved in response to independent exploitation of open country habitats as it enhances protection of the lacrimal sac and serves to reduce eye infection in terrestrial species.

Earliest known Old World monkey skull.

Similarities of the skull are commonly used to support hypotheses of ancestor-descendant relationships between fossil and living ape genera, especially between the late Miocene apes Sivapithecus and Dryopithecus from Eurasia and the living orang-utan (Pongo) from Borneo and Sumatra. Yet determining whether craniofacial traits shared by extant and Miocene apes are primitive or derived is severely hampered by the rarity of well-preserved fossil crania, particularly of early members of their closest outgroup, the Old World monkeys (Cercopithecoidea). The discovery of a complete and undistorted skull of Victoriapithecus at middle Miocene deposits from Maboko Island, Kenya, provides evidence of intact cranial-vault and basicranial morphology, brain size and craniofacial hafting for a primate from between 32 and 7 million years ago. Victoriapithecus represents a branch of Old World monkey that is intermediate between extant cercopithecids (Colobinae and Cercopithecinae) and the common ancestor they shared with apes (Hominoidea). The skull preserves traits widely thought to be derived for extant and fossil members of a proposed Sivapithecus/Pongo clade, but which now appear to be primitive features of ancestral Old World higher primates in general.

Recently recovered Kenyapithecus mandible and its implications for great ape and human origins.

We report here a Kenyapithecus africanus juvenile mandible recovered from middle Miocene (ca. 14-16 million years) deposits of Maboko Island (Lake Victoria), Kenya. Symphyseal and dental attributes of the mandible distinguish K. africanus, a species widely regarded as the earliest known member of the great ape and human clade, from other Miocene large-bodied hominoids. The Maboko Island mandible exhibits a markedly proclined symphyseal axis, massive inferior transverse torus, mesiodistally narrow, high-crowned, and strongly procumbent lateral incisor, and molars with cingula restricted to the median buccal cleft. Although the presence of some of these conditions in Kenyapithecus was suggested earlier, the fragmentary and ill-preserved nature of previously known specimens led certain authorities to doubt their validity. Our assessment of mandibular and dental morphology indicates that K. africanus diverged after Proconsul and Griphopithecus but prior to the last common ancestor of Sivapithecus, extant great apes, and humans. The robustly constructed mandibular symphysis and anterior dentition suggest that incisal biting played as important a role as thick molar enamel in the dietary adaptations of K. africanus.