Maboko Research Articles

Herbivore isotopic dietary ecology of the middle Miocene Maboko Formation, Kenya

Middle Miocene deposits at Maboko Island in the Nyanza Rift of Western Kenya (~15–14 Ma) have yielded a rich fossil mammalian record that documents a mid-Miocene faunal shift. Palaeoecological proxies for Maboko have previously been interpreted to indicate heterogeneous habitats, ranging from grassland to closed canopy forest and implicated in this turnover. Stable carbon and oxygen isotope data of fossil herbivore enamel from catarrhine-bearing deposits at Maboko were analyzed to reconstruct the nature of C3 vegetation (i.e., water-stressed or subcanopy), as well as determining if any C4 biomass, representative of more open woodland or grassland habitats, were consumed. Taxa sampled include representatives of ruminants, suoids, rhinocerotids, and proboscideans. δ13Cenamel and δ18Oenamel values of Maboko fossil herbivores indicate foraging strategies consistent with a C3 dominated ecosystem, exhibiting a range of δ13Cenamel signatures similar to those of extant browsing herbivores foraging in mosaics of open forest/woodland habitats. Within the Maboko sequence, isotopic evidence indicates varying environments based on variable dietary spectra associated with discrete fossiliferous units within the succession. Relative to other stratigraphic beds, isotopic signals of herbivore enamel from Bed 5b, for example, reflect more closed woodland/forest foraging. The overall ~4‰ range of δ13Cenamel values from Maboko (−14.1‰ to −10.2‰) is statistically similar to δ13Cenamel values from the slightly younger middle Miocene site of Fort Ternan and is consistent with faunal and paleosol evidence from Maboko suggesting ecological variability. However, the isotopic evidence from Maboko indicates that environmental variability is more constrained than previously reconstructed, instead ranging from more open canopy forest to open woodland habitats, albeit with some spatial and temporal heterogeneity. Closed canopy forest plants and C4 biomass were not detectable as dietary components for any herbivores sampled thus far; nor was there evidence of significantly water-stressed C3 vegetation (possibly C3 grasses) being consumed.

New dentognathic fossils of Noropithecus bulukensis (Primates, Victoriapithecidae) from the late Early Miocene of Buluk, Kenya

The late Early Miocene site of Buluk, Kenya, has yielded fossil remains of several catarrhine primates, including 16 dentognathic specimens of the stem cercopithecoid Noropithecus bulukensis. With the exception of the large sample of Victoriapithecus macinnesi from the middle Miocene of Maboko Island, Kenya, the majority of stem cercopithecoid taxa are represented by small sample sizes. We describe and analyze 91 new cercopithecoid fossils collected from Buluk between 2004 and 2018, including several previously undescribed tooth positions for N. bulukensis, and provide the first evaluation of dental metric and morphological variation in this sample. The results show that the expanded Buluk sample exhibits high levels of dental variation in the postcanine tooth row, similar to V. macinnesi at Maboko, but this variation is consistent with a single-species hypothesis. Subtle differences in the shape of the I1, breadth of the C1 and P3, relative breadth of M1, upper and lower molar distal shelf lengths, the degree of M2 basal flare, and a less-developed lower molar distal lophid differentiate the dentition of N. bulukensis from V. macinnesi. Although differences exist between the N. bulukensis and V. macinnesi dental samples, the high degree of variation within each sample complicates the identification of many individual specimens. New partial maxillae and mandibles allow reassessment of previously described diagnostic differences between N. bulukensis and V. macinnesi, negating upper molar arcade shape as a diagnostic feature and confirming the existence of differences in mandibular symphyseal morphology. Overall, new fossils from Buluk provide new evidence of the dentognathic anatomy of a medium-sized cercopithecoid that coexisted with a diverse group of noncercopithecoid catarrhines at the end of the early Miocene.

On the Middle Miocene avifauna of Maboko Island, Kenya

The Middle Miocene sediments of Maboko Island (Lake Victoria) in western Kenya yielded numerous avian bones, which remained, however, little studied. The significance of this material is shown by the recent identification of an opisthocomiform bird. In the present study, further avian remains from Maboko Island are described. Most of the specimens belong to aquatic or semi-aquatic groups, of which some are closely related to taxa known from Early and Middle Miocene European avifaunas, that is, Nectornis cormorants (N. africanus nov. sp.) and Laricola-like Laromorphae. The fossil material also includes Ciconiidae (cf. Ciconia), Pelecanidae, Phoenicopteridae (Leakeyornis aethiopicus), Musophagidae, and a species of Ardeidae, which closely resembles the taxon Pikaihao from the Early Miocene of New Zealand. Some avian remains from Maboko Island belong to higher-level taxa unknown from the Middle Miocene of Europe. The occurrence of a giant Jacanidae (?Nupharanassa mabokoensis nov. sp.) is of particular interest, because these are globally absent in extant avifaunas and were previously only known from the Late Eocene/Early Oligocene of Egypt. Further unknown from contemporaneous European sites are small representatives of Jacanidae, Bucerotidae, and Alcedinidae, with the fossils of the latter two taxa being among the earliest published records of their respective groups. Several of the taxa that are common in contemporaneous European avifaunas have not been found in Maboko, and in spite of less pronounced climatic differences, Middle Miocene Afrotropical avifaunas already appear to have been distinct from contemporaneous European ones.

A hoatzin fossil from the middle Miocene of Kenya documents the past occurrence of modern-type Opisthocomiformes in Africa

ABSTRACT The fossil bird Namibiavis senutae from the early Miocene of Namibia was recently identified as an African stem-group representative of Opisthocomiformes (hoatzins). The species is known only from two wing and pectoral girdle bones, however, and the extent to which African Opisthocomiformes resembled their Neotropical relatives in skeletal morphology has remained elusive. I report a hoatzin tarsometatarsus from the middle Miocene of Maboko Island in Kenya, which, except for a peculiar autapomorphic fusion of the first metatarsal, closely matches the tarsometatarsus of the extant Opisthocomus hoazin. Although a well-founded classification on the species level is not possible, the new fossil documents the existence of essentially modern-type Opisthocomiformes in the Miocene of Africa. Being 2–2.5 Ma younger than N. senutae, the specimen further extends the temporal and spatial range of Miocene African Opisthocomiformes.

Enamel and dentine development and the life history profile of Victoriapithecus macinnesi from Maboko Island, Kenya

Two permanent lower second molar teeth (KNM-MB 19841 and KNM-MB 27844) attributed to Victoriapithecus macinnesi were prepared for histological analysis. A further five male and three female canine teeth were replicated with a silicone impression material and perikymata counts subsequently made on epoxy casts over the whole crown surface. Daily enamel cross striations averaged 6 microm apart in both cuspal and lateral enamel of the molars and the total crown formation times were approximately 1.24 years in the molars and, using the same periodicity determined from the molars, 1.84 and 1.36 years respectively in the male and female canines. Rates of dentine formation matched those known for extant macaques and were used to calculate root extension rates, which averaged 11.5 microm per day over the whole 8 mm root length of KNM-MB 19841. The period between M2 initiation and gingival emergence was estimated to be approximately 1.95 years in Victoriapithecus which is greater than estimates for Cebus albifrons and Chlorocebus aethiops, (which are similar in body mass to Victoriapithecus), but less than estimates made here for several macaque species. A speculative picture of dental development in Victoriapithecus emerges that is slower than that known for modern vervet monkeys and may have been more similar to that in some smaller modern macaque species.

Paleosols and paleoenvironments of the middle Miocene, Maboko Formation, Kenya.

The middle Miocene (15 Ma) Maboko Formation of Maboko Island and Majiwa Bluffs, southwestern Kenya, has yielded abundant fossils of the earliest known cercopithecoid monkey (Victoriapithecus macinnesi), and of a kenyapithecine hominoid (Kenyapithecus africanus), as well as rare proconsuline (Simiolus leakeyorum, cf. Limnopithecus evansi) and oreopithecine apes (Mabokopithecus clarki, M. pickfordi), and galagids (Komba winamensis). Specific habitat preferences can be interpreted from large collections of primate fossils in different kinds of paleosols (pedotypes). Fossiliferous drab-colored paleosols with iron-manganese nodules (Yom pedotype) are like modern soils of seasonally waterlogged depressions (dambo). Their crumb structure and abundant fine root-traces, as well as scattered large calcareous rhizoconcretions indicate former vegetation of seasonally wet, wooded grassland. Other fossiliferous paleosols are evidence of nyika bushland (Ratong), and early-successional riparian woodland (Dhero). No fossils were found in Mogo paleosols interpreted as saline scrub soils. Very shallow calcic horizons (in Yom, Ratong, and Mogo paleosols) and Na-montmorillonite (in Mogo) are evidence of dry paleoclimate (300-500 mm MAP=mean annual precipitation). This is the driest paleoclimate and most open vegetation yet inferred as a habitat for any Kenyan Miocene apes or monkeys. Victoriapithecus was abundant in dambo wooded grassland (Yom) and riparian woodland (Dhero), a distribution like that of modern vervet monkeys. Kenyapithecus ranged through all these paleosols, but was the most common primate in nyika bushland paleosols (Ratong), comparable to baboons and macaques today. Mabokopithecus was virtually restricted to riparian woodland paleosols (Dhero), and Simiolus had a similar, but marginally wider, distribution. Habitat preferences of Mabokopithecus and Simiolus were like those of modern colobus monkeys and mangabeys. A single specimen of Komba was found in dambo wooded grassland paleosol (Yom), a habitat more like that of the living Senegal bushbaby than of rainforest galagids. A shift to non-forest habitats may explain the terrestrial adaptations of Victoriapithecus, basal to the cercopithecid radiation, and of Kenyapithecus, basal to the hominoid radiation. Both taxa are distinct from earlier Miocene arboreal proconsulines, oreopithecines and galagids.

Ancestral loss of the maxillary sinus in Old World monkeys and independent acquisition in Macaca.

Cercopithecoid monkeys are unique among primates in that all species (except macaques) lack a maxillary sinus, an unusual condition among eutherian mammals. Although this uncommon distribution of cranial pneumatization was noted previously, the phylogenetic ramifications have not been investigated fully. Recently, character state optimization analysis of computed tomography (CT) data from extant Old World monkeys suggested that the loss of the sinus may have occurred at the origin of the group, unlike previous hypotheses positing only a reduction in size of the structure. To critically evaluate the "early loss" hypothesis, a recently recovered complete cranium of Victoriapithecus macinnesi from Maboko Island, Kenya, was examined by CT to determine the extent of its cranial pneumatization. This taxon is crucial for evaluating character state evolution in Old World monkeys, due to its phylogenetic position, preceding the cercopithecine/colobine split. CT analysis reveals only cancellous bone lateral of the nasal cavity, indicating that Victoriapithecus does not possess a maxillary sinus. Phylogenetic evaluation of the fossil with extant catarrhine taxa strongly supports the early loss of the sinus in cercopithecoids. The results suggest that the maxillary sinus found in the genus Macaca is not homologous with that of other eutherians, which may provide insights into the origin and function (if any) of the paranasal pneumatizations.

Victoriapithecus: The key to Old World monkey and catarrhine origins

The past ten years have witnessed major changes in reconstructions of the history of Old World monkeys, most of them driven by new material of the Miocene monkey Victoriapithecus from Maboko Island, Kenya. Before the mid-1980s, predictions about the morphological and ecological adaptations of the earliest cercopithecoids relied heavily on evidence from extant colobine and cercopithecine monkeys. It was argued that the earliest cercopithecoids were largely or at least partly folivorous, had short colobine-like faces, and were arboreal. The only studies suggesting that some of these arguments were not true were based on limited knowledge of the anatomy of Victoriapithecus. The presence of semi-terrestrial adaptations in middle Miocene monkeys hinted to some that early monkeys may not have been arboreal. Others attempted to cope with the discrepancy between neontological predictions and the fossil evidence by proposing that limb bones with stronger terrestrial adaptations within the Maboko sample were derived cercopithecine remains, while those with more arboreal features belonged in the subfamily Colobinae and should be regarded as primitive.

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.

The permanent dentition and phylogenetic position of Victoriapithecus from Maboko Island, Kenya

Abstract More than 800 cercopithecoid permanent teeth collected since 1973 at Maboko Island are described. The 15 million-year-old fossils are attributed to a single paleospecies Victoriapithecus macinnesi. Criteria previously used to separate the 59 Victoriapithecus teeth known from Maboko before 1973 into two species, one with colobine and the other with cercopithecine affinities, are shown to be invalid. V. macinnesi differs from extant cercopithecoids in having M1-M3 cristae obliquae and M1/M2 hypoconulids that are differentially expressed across the molar row, being more common on mesial than distal teeth. The species is similar to extant Macaca in having a high degree of M3 size variation that may be related to sexual dimorphism. In contrast, I1-M2 size variation is similar to that observed for most extant cercopithecoid species. Phylogenetic comparison of Victoriapithecus and Prohylobates indicates that although the two genera are distinct, they share a unique combination of primitive catarrhine and derived cercopithecoid dental traits. Colobinae and Cercopithecinae share at least three and probably five traits that are derived relative to the Miocene cercopithecoids. It is concluded that the Miocene and more recent Old World monkeys represent mutual sister-groups with Prohylobates and Victoriapithecus belonging to the family Victoriapithecidae and Colobinae and Cercopithecinae to the family Cercopithecidae.

An oreopithecid proximal humerus from the middle miocene of Maboko Island, Kenya

A proximal humerus, recently recovered from the middle Miocene of Maboko Island, Kenya, provides the earliest evidence of postcranial structure and adaptation of Oreopithecidae. Provisionally attributed toNyanzapithecus pickfordi (Harrison, 1986), the specimen manifests a globose head, subequally large tuberosities, and a board, shallow bicipital groove. Although readily distinguished from the fundamentally cercopithecoid proximal humeral morphology ofVictoriapithecus (Senut, 1986), the Maboko Island oreopithecid, shows none of the derived features that are characteristic of the proximal humeri of extant hominoids. It is inferred from proximal humeral anatomy that the Maboko Island oreopithecid was an active arboreal scansor with moderate mobility at the shoulder but lacking adaptations for circumduction of the arm. In combination with craniodental evidence, proximal humeral morphology indicates that Oreopithecidae was a clade of hominoids which originated before the last common ancestor of extant apes and went extinct, without issue, in the later Miocene.

A reassessment of the taxonomic and phylogenetic affinities of the fossil catarrhines from fort Ternan, Kenya

This paper presents a reassessment of the taxonomic and phylogenetic affinities of the fossil catarrhine primates from the important middle Miocene site of Fort Ternan in Kenya. Although the sample of specimens is rather small, the material can be attributed to at least five different species, identified here asKenyapithecus wickeri, Proconsul sp., a large species of oreopithecid,Simiolus sp., and a small species of catarrhine of indeterminate status.Kenyapithecus wickeri probably represents a conservative sister-taxon of the extant large hominoids. It is more derived than“Sivapithecus” africanus from Maboko Island, from which it can be distinguished at the generic level. A small species of catarrhine from Fort Ternan can be attributed toSimiolus. It is probably a different species fromSimiolus enjiessi from the early Miocene of East Africa, but additional material is needed to confirm its taxonomic distinctiveness. The occurrence of at least five species of catarrhine primates at Fort Ternan confirms that species diversity levels were as high during the middle Miocene as they had been during the early Miocene. However, the overall taxonomic and ecological composition of the middle Miocene catarrhine community was quite different, evidently due to a significant change in the local ecological setting. Taxonomic differences between the catarrhine faunas at Fort Ternan and Maboko Island can probably be explained as a consequence of a chronological separation between the two sites, and, to a lesser degree, to paleoecological differences.

New species of bushbaby from the middle Miocene of Maboko Island, Kenya

A mandible recovered from ca. 15 million year old deposits of Maboko Island, Kenya, represents the first bushbaby known from the middle Miocene. The specimen is from a new species of Komba, a genus previously known from early Miocene occurrences in western Kenya and northeastern Uganda. Komba is revised, with emended diagnoses proposed for the genus, type-species, and referred species. Komba sp. nov. is distinguished by its larger size and differences of molar cusp acuity, buccal cingulum expression, and mental foramen configuration. Contrary to previous opinion, species of Komba probably diverged prior to the last common ancestor of extant Galaginae, and it is unlikely that they represent early stages of living bushbaby species lineages. Although contemporary Progalago is widely regarded as a galagine, aspects of upper molar, lower premolar, and mandibular corpus morphology indicate that it is more closely related to lorisines. Unlike the greater success currently enjoyed by bushbabies, lorisines were more diverse and almost as abundant as galagines in the early Miocene of eastern Africa.

Comparative assessment of the ischial morphology of Victoriapithecus macinnesi

AbstractAn almost complete primate ischium was recovered from middle Miocene (ca. 15 ma) deposits of Maboko Island (Kenya) in 1987. The specimen shows numerous similarities to the ischial morphology of extant cercopithecids and is attributed to Victoriapithecus macinnesi (Von Koenigswald, 1969), the early Old World monkey best known from Maboko Island. The Victoriapithecus ischium provides the first evidence of early Old World monkey pelvic girdle anatomy. The ischium is characterized by an obliquely oriented and broadly flaring tuberosity, a relatively small acetabulum with little ventrally directed curvature of its caudal portion, a long ischial body and a flange‐like ischial spine positioned caudal to the rim of the acetabulum. In these features, Victoriapithecus most closely resembles the vervet monkey, Cercopithecus aethiops. The fossil specimen indicates that Victoriapithecus possessed ischial callosities, a mobile tail and adaptations for (possibly cursorial) quadrupedalism with an adducted posture of the thigh.The occurrence of ischial callosities in Victoriapithecus extends the documented antiquity of this feature in catarrhines by more than 12 million years and shows that the distinctive “sitting‐sleeping” adaptations of Old World monkeys (Washburn, 1957) originated prior to the divergence of Colobinae and Cercopithecinae. Differences of developmental sequence and tissue composition indicate that the ischial pads of cercopithecids, hylobatids, and pongids may have arisen independently, through parallel evolution. Contrary to Strasser and Delson (1987), discontinuity of ischial callosities was probably the primitive condition for male cercopithecids.

Age of the primate-bearing deposits on Maboko Island, Kenya

Renewed field work on the Miocene deposits of Maboko Island Benefit & McCrossin 1989 has produced a weath of new fossil material with important implications for vertebrate evolution in the early Neogene of East Africa. The deposits are of particular importance due to the abundance of primate fossils recovered from them. This report presents new geologic data concerning the stratigraphy and age of the fossiliferous deposits on Maboko. Maboko Island lies in the Winam Gulf of Lake Victoria (Figure 1). The geologic setting and history of research on the island have been reviewed by Andrews et al. 1981. Fossiliferous deposits were first reported from the island in 1930s and a Miocene age attributed to them on faunal grounds. Some controversy arose over the dating of the Maboko deposits, sparked by suggestion of an unconformity in the sequence and the presence of faunal elements of clearly Pleistocene age within the Miocene assemblage. The fluvial character of the Maboko deposits does include erosional surfaces, but there is no indication that they are of significant duration. Pleistocene fossils are found scattered about the island as a surface lag deposited during a late Pleistocene highstand of Lake Victoria. Subsequent studies on Maboko Island recovered additional fossil material, and suggested an age of 15–16 ma for the fauna, based on faunal considerations and isotopic dating of presumed correlative units exposed on the mainland (Andrews et al., 1981). This report presents the first numerical calibration of the age of the Miocene sequence on Maboko Island.

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.

A new species of Micropithecus from the middle Miocene of Kenya

Recently recovered material of a small catarrhine primate from the middle Miocene locality of Maboko Island in Kenya (dated at 15–16 m.y.) can be referred to a new species of Micropithecus, M. leakeyorum. The dental differences between M. leakeyorum and the type species, M. clarki, suggest that M. leakeyorum was less specialised for frugivory than M. clarki, and probably included in its diet a greater proportion of young leaves or fruits of coarser consistency. This inference is concordant with a general shift in the diet of the catarrhine community from generalised frugivory during the early Miocene to an increased emphasis on folivory during the middle Miocene. This restructuring of the trophic and taxonomic composition of the primate paleocommunity is associated with an apparent increase in the occurrence of woodland habitats in East Africa, probably due to local tectonic events and possible also to global climatic changes. The recognition of a new species of Micropithecus from Maboko Island, along with other recent studies of the Miocene catarrhines from East Africa, demonstrates that middle Miocene apes were more diverse than had been previously thought. This finding has important implications for understanding the dynamics and evolution of the catarrhine community in East Africa during the early part of the Miocene.

New primate fossils from the Middle Miocene of Maboko Island, Kenya

Understanding the biogeography and evolution of Miocene catarrhines relies on accurate specimen provenience. It has long been speculated that some catarrhine specimens among the early collections from Miocene sites in Kenya have incorrect provenience data. The provenience of one of these, the holotype of Equatorius africanus (NHM M16649), was previously revised based on x-ray fluorescence spectroscopy. Here we use nondestructive portable x-ray fluorescence spectroscopy to test the provenience of additional catarrhine specimens that, based on morphology and/or incomplete provenience information, were identified as possibly having been collected at a different site from that recorded at museum accession. We test the hypotheses that two specimens purportedly from the Early Miocene site of Rusinga (KNM-RU 1681 and KNM-RU 1999) are instead from Maboko, three specimens purportedly from the Middle Miocene site of Fort Ternan (KNM-FT 8, KNM-FT 41, and KNM-FT 3318) are instead from Songhor, and one specimen accessioned as being from Songhor (KNM-SO 5352) is from that site. Elemental data reveal that two of the specimens (KNM-FT 3318 and KNM-RU 1681) are likely to have been collected at sites other than their museum-accessioned provenience, while two others (KNM-RU 1999, and KNM-FT 41) were confirmed to have correct provenience. Results for both KNM-FT 8 and KNM-SO 5352, while somewhat equivocal, are best interpreted as supporting their accessioned provenience. Our results have implications for the distribution of certain catarrhine species during the Miocene in Kenya. Confirmation of the provenience of the specimens also facilitates taxonomic attribution, and resulted in additions to the morphological characterizations of some species. The protocol presented here has potential for wider application to assessing questions of provenience for fossils from other locations and periods.

New postcranial remains of Victoriapithecus from the middle Miocene of Kenya

Recent collections at the middle Miocene site of Maboko Island in Kenya have yielded a relatively large sample of isolated postcranial bones that can be assigned with some degree of confidence to the early cercopithecid. Victoriapithecus. This paper provides a detailed description of the postcranial morphology of Victoriapithecus, and offers some general conclusions concerning its inferred locomotor behavior and phylogenetic status. The range of metrical and morphological variation exhibited by the material does not exceed that seen in modern species of Old World monkeys. This findings is consistent with recent re-interpretations of the cranio-dental material that indicate that only a single species of Victoriapithecus may be represented at Maboko Island. Victoriapithecus appears to be a relatively small (with an estimated average body weight of 3·5–4·0 kg), agile and active quadrupedal monkey, adapted to moving effectively in both arboreal and terrestrial settings. In its overall morphology, and probably also in its inferred locomotor behavior. Victoriapithecus is most closely similar to modern-day semi-terrestrial Old World monkeys.

New fossil anthropoids from the middle Miocene of East Africa and their bearing on the origin of the oreopithecidae.

Recent paleontological collections at the middle Miocene locality of Maboko Island in Kenya, dated at 15-16 million years, have yielded numerous new specimens belonging to at least five species of fossil anthropoids. The most common species of ape at the site, a medium-sized primate with a very distinctive dental morphology, clearly represents a previously undescribed taxon. When compared with other Miocene anthropoids from East Africa, it has its closest affinities with the poorly known species Rangwapithecus vancouveringi from the early Miocene locality of Rusinga Island. The species from Maboko Island is described here as belonging to a new genus of fossil anthropoid, to which "Rangwapithecus" vancouveringi is also referred. The new genus has a highly distinctive suite of derived characters of its molars and premolars, which it shares with Oreopithecus bambolii from the late Miocene of Europe. These synapomorphies indicate a close phyletic relationship between the East African species and Oreopithecus and form the basis for the inclusion of these taxa in a single family, the Oreopithecidae Schwalbe, 1915. In many respects, however, the East African forms are more conservative than Oreopithecus, and in a general sense they can be regarded as an intermediate grade between Oreopithecus and the more generalized early Miocene catarrhines, the proconsuloids. There is, therefore, good fossil evidence to indicate that the origins of the Oreopithecidae can be traced back to the early Miocene of Africa.