Neogene paleobiogeography and East African paleoenvironments: contributions from the Tugen Hills rodents and lagomorphs.

A minimum of 28 genera of rodents and one genus of lagomorph were recovered from the Tugen Hills, Baringo District, Kenya, from localities dating from over 15.5 to about 4.4 Ma. The middle Miocene (sites dated between 15.8 and 15.3 Ma) rodent fauna recovered primarily from the Kipsaramon site complex, Muruyur Formation, includes a mixture of characteristically early Miocene taxa, and more derived forms. Composition of the African rodent fauna changes dramatically with the introduction of myocricetodontines, democricetodontines, and dendromurines, immigrants primarily from southern Asia. In the Tugen Hills, these taxa are first found in the Kabasero localities, Ngorora Formation, at sites dating from 12.5-12.33 Ma. A second major change in the African rodent fauna reflects the introduction of murines, immigrants from southern Asia. In the Tugen Hills murines are first encountered at Kapcheberek, Lukeino Formation, dated to 5.9-5.7 Ma. One rodent genus from the Lukeino Formation (Arvicanthis), and two from the Tabarin locality, Chemeron Formation (Heliosciurus, Paraxerus; 4.5-4.4 Ma), represent the earliest records of these extant African genera. A cricetomyine from the Ngorora Formation (12.5 Ma) is likely the earliest report of this exclusively African group. One of the earliest African records of porcupines (Hystricide) is from the Lukeino Formation. Lagomorphs are poorly represented, but include one of the earliest African occurrences of the family Leporidae from the Mpesida Beds (bracketed by dates of 7-6.2 Ma), and possibly a new genus of leporid from the Kapcheberek locality. Analysis of the Tugen Hills small mammals in association with other African records suggests several episodes of dispersal between Africa and Eurasia during the middle and late Miocene. Rodents from Kipsaramon are indicative of forests in conjunction with more open habitats. Those from the Kapcheberek locality are suggestive of a savanna habitat. The rodents from the Tabarin locality suggest a woodland environment.     

Creodonts and carnivores from the Middle Miocene Muruyur Formation at Kipsaraman and Cheparawa,Baringo District,Kenya

The Middle Miocene Muruyur Formation (ca 14.5 Ma), Tugen Hills, Kenya, has yielded a huge creodont and a variety of carnivores ranging in size from mongoose-sized viverrids and herpestids to lion-sized amphicyonids. The fauna partly fills what used to be a major gap in our knowledge of Neogene African carnivores, spanning the period between the better known Early Miocene assemblages of western Kenya and eastern Uganda, and the Late Miocene and Plio–Pleistocene faunas of East Africa. Present in the deposits are Megistotherium, two species of Hecubides, one species of Agnotherium, Herpestes, Vishnuictis, and one or two undetermined felids.     

Mio-Pliocene mammals from the Middle Awash, Ethiopia

The Middle Awash paleontological study area, located in the Afar Rift of Ethiopia, has yielded fossils spanning the last six million years. The geology and geochronology of the Mio-Pliocene sites of the study area have been refined and a reliable chronostratigraphy has been established by ⁴⁰Ar/³⁹Ar radiometric dating. The latest Miocene Adu-Asa Formation is divided into four members distinguished from each other by silicic and basaltic tuff marker horizons, most of which are dated basaltic tuffs. Radiometric dating has constrained the age of the Adu-Asa Formation to between 5.2-5.8 Ma. These dates are also supported by paleomagnetic results and biochronology. More than 2,000 fossil specimens were collected from the Adu-Asa Formation between 1992 and 2000. These fossils document 64 mammalian species belonging to 32 genera, 23 families, and 8 orders. This assemblage includes a number of new taxa. Included in the assemblage are First and Last Appearance Datums (FADs and LADs) of some groups, including the earliest record of the hominid genus Ardipithecus. Most of the taxa indicate a predominance of mesic and wooded habitat during the deposition of the Adu-Asa Formation. In these deposits, colobines, viverrids, mustelids, bovines, boselaphines, and tragelaphines are abundant, whereas alcelaphines are absent. Quantitative analyses of biogeographic relationships of the Middle Awash Late Miocene (MALM) mammalian fauna indicate stronger relationships with other African sites than with faunas from Eurasian sites. The MALM deposits have generated a critical dataset for analytic work on past environments, biogeographic relationships, and African vertebrate evolution. Moreover, the geographic position of the Middle Awash, coupled with its precise calibration and chronological span, make it a key section for interpreting latest Miocene faunal interchanges between Africa and Eurasia.     

Stratigraphy, age and environments of the late Miocene Mpesida Beds, Tugen Hills, Kenya.

Interpretations of faunal assemblages from the late Miocene Mpesida Beds in the Tugen Hills of the Central Kenyan Rift Valley have figured prominently in discussions of faunal turnover and establishment of the modern East African communities. These faunal changes have important implications for the divergence of the human lineage from the African apes ca. 8-5 Ma. While fossil material recovered from the Mpesida Beds has traditionally been analyzed collectively, accumulating evidence indicates that Mpesida facies span the 7-6 Ma interval and are scattered more than 25 km along the eastern flanks of the Tugen Hills. Stratigraphic distinctions between Mpesida facies and younger sediments in the sequence, such as the Lukeino Formation, are not yet fully resolved, further complicating temporal assessments and stratigraphic context of Mpesida facies. These issues are discussed with specific reference to exposures of Mpesida facies at Rurmoch, where large fossil tree fragments were swept up in an ancient ash flow. Preserved anatomical features of the fossil wood as well as estimated tree heights suggest a wet, lowland rainforest in this portion of the rift valley. Stable isotopic analyses of fossil enamel and paleosol components indicate the presence of more open habitats locally. Overlying air-fall tuffs and epiclastic debris, possibly associated with the ash flow, have yielded an assemblage of vertebrate fossils including two teeth belonging to one of the earliest colombines of typical body size known from Africa, after the rather small Microcolobus. Single-crystal, laser-fusion,(40)Ar/(39)Ar dates from a capping trachyte flow as well as tuffs just below the lava contact indicate an age of greater than 6.37 Ma for the fossil material.     

The Hand of Cercopithecoides williamsi (Mammalia,Primates): Earliest Evidence for Thumb Reduction among Colobine Monkeys

Thumb reduction is among the most important features distinguishing the African and Asian colobines from each other and from other Old World monkeys. In this study we demonstrate that the partial skeleton KNM-ER 4420 from Koobi Fora, Kenya, dated to 1.9 Ma and assigned to the Plio-Pleistocene colobine species Cercopithecoides williamsi, shows marked reduction of its first metacarpal relative to the medial metacarpals. Thus, KNM-ER 4420 is the first documented occurrence of cercopithecid pollical reduction in the fossil record. In the size of its first metacarpal relative to the medial metacarpals, C. williamsi is similar to extant African colobines, but different from cercopithecines, extant Asian colobines and the Late Miocene colobines Microcolobus and Mesopithecus. This feature clearly links the genus Cercopithecoides with the extant African colobine clade and makes it the first definitive African colobine in the fossil record. The postcranial adaptations to terrestriality in Cercopithecoides are most likely secondary, while ancestral colobinans (and colobines) were arboreal. Finally, the absence of any evidence for pollical reduction in Mesopithecus implies either independent thumb reduction in African and Asian colobines or multiple colobine dispersal events out of Africa. Based on the available evidence, we consider the first scenario more likely.     

The age of Orrorin tugenensis,an early hominid from the Tugen Hills,Kenya

Throughout the history of the East African Rift valley, tectonic depressions and volcanic dams formed within the graben in which Middle Miocene to Recent volcanic rocks and lacustrine to fluvial sediments accumulated. During the Late Miocene, voluminous trachytes erupted in the vicinity of Kabarnet and almost filled the valley to its brim. Continued tectonic activity formed new basins floored by the Kabarnet Trachyte, one of which was located in the region immediately east of the present day Tugen Hills. The Lukeino sediments that accumulated in this basin crop out over an area of 44 km × 13 km. In 2000, Orrorin tugenensis, which is important for understanding the earliest stages of human evolution, was found in the Lukeino Formation 〚12〛, 〚13〛. It is concluded that the Lukeino formation accumulated between 6.0 and 5.7 Ma.     

New observations on the Late Miocene–Early Pliocene Lutrinae (Mustelidae: Carnivora,Mammalia) from the Middle Awash,Afar Rift,Ethiopia

New observations on the Late Miocene and Earliest Pliocene mustelids from the Middle Awash of Ethiopia are presented. The Middle Awash study area samples the last six million years of African vertebrate evolutionary history. Its Latest Miocene (Asa Koma Member of the Adu-Asa Formation, 5.54–5.77 Ma) and Earliest Pliocene (Kuseralee and Gawto Members of the Sagantole Formation, 5.2 and 4.85 Ma, respectively) deposits sample a number of large and small carnivore taxa among which mustelids are numerically abundant. Among the known Late Miocene and Early Pliocene mustelid genera, the Middle Awash Late Miocene documents the earliest Mellivora in eastern Africa and its likely first appearance in Africa, a new species of Plesiogulo, and a species of Vishnuonyx. The latter possibly represents the last appearance of this genus in Africa. Torolutra ougandensis is known from both the Late Miocene and Early Pliocene deposits of the Middle Awash. The genus Sivaonyx is represented by at least two species: S. ekecaman and S. aff. S. soriae. Most of the lutrine genera documented in the Middle Awash Late Miocene/Early Pliocene are also documented in contemporaneous sites of eastern Africa. The new observations presented here show that mustelids were more diverse in the Middle Awash Late Miocene and Early Pliocene than previously documented.     

New sabre-toothed cats in the Late Miocene of Toros Menalla (Chad)

The Toros Menalla Late Miocene Formation (7 Ma), Djurab desert, Chad, has yielded a large number of vertebrate remains, and among them around twenty taxa of carnivores. Recent collections allow us to describe two sabre-toothed felids assigned to the genera Lokotunjailurus and cf. Megantereon. The former does exist in the Nawata Formation, Lothagam, northern Kenya with a slightly derived species and the TM specimens are considered as belonging to a new species. The latter cannot be identified to the species level, but it could be one of the earliest specimens of Megantereon known in the world and it would reinforce the hypothesis of an Old World origin for this taxon. Both allow us to put forward some biogeographical conclusions.     

Dental Eruption Sequences in Fossil Colobines and the Evolution of Primate Life Histories

Unlike other catarrhines, colobines show early molar eruption relative to that of the anterior dentition. The pattern is variable, with Asian genera (Presbytina) showing a greater variability than the African genera (Colobina). The polarity of early relative molar eruption, as well as the degree to which it is related to phylogeny, are unclear. Schultz (1935) suggested that the trend reflects phylogeny and is primitive for catarrhines. More recently, however, researchers have proposed that life history and dietary hypotheses account for early relative molar eruption. If the colobine eruption pattern is primitive for catarrhines, it implies that cercopithecines and hominoids converged on delayed relative molar eruption. Alternatively, if the colobine condition is derived, factors such as diet and mortality patterns probably shaped colobine eruption patterns. Here we update our knowledge on eruption sequences of living colobines, and explore the evolutionary history of the colobine dental eruption pattern by examining fossil colobine taxa from Eurasia (Mesopithecus) and Africa (Kuseracolobus aramisi and Colobus sp.) and the basal cercopithecoid Victoriapithecus macinnesi. We scored specimens per Harvati (2000). The Late Miocene-Early Pliocene Mesopithecus erupts the second molar early relative to the incisors, while the Early Pliocene Kuseracolobus aramisi does not. These results demonstrate that the common colobine tendency for early molar eruption relative to the anterior dentition had appeared by the Late Miocene, and that some of the diversity observed among living colobines was already established in the Late Miocene/Early Pliocene. We discuss the implications of these results for phylogenetic, life history, and dietary hypotheses of dental development.     

Geology and geochronology of the middle Miocene Kipsaramon site complex, Muruyur Beds, Tugen Hills, Kenya.

The Muruyur Beds are a substantial sedimentary deposit within a middle Miocene sequence of mafic volcanic flows associated with early stages of rifting in the central Kenyan Rift Valley. They are best represented in the Muruyur region, near Bartabwa, north of Kipsaramon, where dates range from 16.0 to 13.4 Ma. At Kipsaramon, located about 10 km south of Muruyur along the crest of the Tugen Hills, the upper Muruyur Beds are absent and the lower part can be divided into three members. Important fossil sites within Member 1 are dated between 15.8 and 15.6 Ma, and within Member 3 between 15.6 and 15.4 Ma. BPRP#89, in Member 1, is a bonebed at least 2500 m(2)in areal extent and up to 30 cm thick, which constitutes one of the richest concentrations of in situ fossil vertebrate bones in eastern Africa. BPRP#91, at approximately the same level at BPRP#89, is the source of a hominoid talus and other mammal and bird fossils. In Member 3, BPRP#122 has produced specimens of at least five individuals of the hominoid Equatorius, including a partial skeleton. The Muyuyur Beds were deposited near the western margin of a lake that was formed during the early stages of faulting and volcanism in the African Rift system. The bonebed in Member 1 appears to represent the influx of fluvially transported vertebrate and plant remains into a shallow portion of the lake. Elements of the fauna as well as stable isotopes that indicate both forest and more open environments occurred in proximity to the lake during the time of deposition of Member 1.     

Brachypotherium (Perissodactyla,Rhinocerotidae) from the late Miocene of Samburu Hills,Kenya

Several isolated cheek teeth and mandibular specimens of Rhinocerotidae (Mammalia, Perissodactyla) from the upper Miocene Namurungule Formation in Samburu Hills, Kenya, are redescribed. Previously, these specimens had been identified as Chilotheridium pattersoni, Chilotheridium sp., Paradiceros mukirii, and Paradiceros sp. They are reidentified here as documenting the genus Brachypotherium based on their bucco-lingually broad molariform upper premolars with short crochet and flattened buccal walls on both upper and lower molars, the latter having a shallow external groove. Comparisons with other Brachypotherium species suggest that the present specimens belong to Brachypotherium sp. cf. B. minor. The presence of Brachypotherium in the Samburu Hills, at ca. 9.5 Ma, is concordant with the paleoenvironment (presence of lacustrine and river environments) known for this locality during the early late Miocene.     

A new large Pliocene colobine species (Mammalia: Primates) from Asa Issie, Ethiopia

The Colobinae (Mammalia: Primates) are relatively unknown from the African middle to late Miocene. When they appear in the Pliocene they are unambiguous and already fairly diverse taxonomically, geographically, and ecologically. Discoveries from Pliocene sediments in eastern and southern Africa document a radiation of large-bodied colobines very different from those known today. Paleontological research in Ethiopia has recently led to the discovery and identification of another large-bodied colobine species from the early Pliocene site of Asa Issie, discovered in 2000. This new colobine is larger than but morphologically very similar to its sister taxon Kuseracolobus aramisi, an older taxon also described from the Middle Awash. This new species has significant implications for our understanding of the Pliocene colobine adaptive radiation.     

Fossil Cercopithecidae from the Hadar Formation and surrounding areas of the Afar Depression,Ethiopia

Hadar is well known as one of the most productive early hominin sites in the world. Between 1972 and 1994 a large sample of fossil cercopithecid specimens was collected from Hadar and the nearby sites of Geraru, Ahmado, and Leadu. At least five, and possibly six, species are present in the sample, including two chronological subspecies of Theropithecus oswaldi. T. o. cf. darti is known from the Middle Pliocene deposits in the Hadar area, along with Parapapio cf. jonesi, cf. Rhinocolobus turkanaensis, and a new species of Cercopithecoides, C. meaveae. There are also isolated molars from the Middle Pliocene of a large colobine which most likely represent cf. R. turkanaensis, but may also represent another large colobine known from the nearby site of Maka in the Middle Awash. T. o. oswaldi is represented from younger deposits of Late Pliocene and Early Pleistocene age, along with the large colobine Cercopithecoides kimeui. Throughout the sequence Theropithecus oswaldi is by far the most abundant cercopithecid, with the other taxa being comparatively rare. The Parapapio material from Hadar is important as the only securely identifiable material of the genus in the East African Pliocene. Furthermore, the Hadar material includes the only associated postcranial remains for the genus. If the tentative identification of Rhinocolobus is correct, then the Hadar sample is the only known occurrence outside of the Turkana Basin. Cercopithecoides meaveae is a new species, currently only known from the Hadar region, most importantly by the associated partial skeleton from Leadu. It appears to show adaptations for terrestrial locomotion. Finally, Cercopithecoides kimeui, a very large colobine previously known from Olduvai Gorge, Koobi Fora, and Rawi is recorded from the uppermost part of the Formation.     

Neogene reef coral assemblages of the Bocas del Toro region, Panama: the rise of Acropora palmata

Temporal patterns are evaluated in Neogene reef coral assemblages from the Bocas del Toro Basin of Panama in order to understand how reef ecosystems respond to long-term environmental change. Analyses are based on a total of 1,702 zooxanthellate coral specimens collected from six coral-bearing units ranging in age from the earliest Late Miocene to the Early Pleistocene: (1) Valiente Formation (12–11 Ma), (2) Fish Hole Member of the Old Bank Formation (5.8–5.6 Ma), (3) La Gruta Member of the Isla Colon Formation (2.2–1.4 Ma), (4) Ground Creek Member of the Isla Colon Formation (2.2–1.4 Ma), (5) Mimitimbi Member of the Urracá Formation (1.2–0.8 Ma), and (6) Hill Point Member of the Urracá Formation (1.2–0.8 Ma). Over 100 coral species occur in the six units, with faunal assemblages ranging from less than 10% extant taxa (Valiente Formation) to over 85% extant taxa (Ground Creek Member). The collections provide new temporal constraints on the emergence of modern Caribbean reefs, with the La Gruta Member containing the earliest occurrence of large monospecific stands of the dominant Caribbean reef coral Acropora palmata, and the Urracá Formation containing the last fossil occurrences of 15 regionally extinct taxa. Canonical correspondence analysis of 41 Late Miocene to Recent reef coral assemblages from the Caribbean region suggests changes in community structure coincident with effective oceanic closure of the Central American Seaway (~3.5 Ma). These changes, including increased Acropora dominance, may have contributed to a protracted period of elevated extinction debt prior to the major peak in regional coral extinctions (~2–1 Ma).     

Mitochondrial data support an odd-nosed colobine clade

To obtain a more complete understanding of the evolutionary history of the leaf-eating monkeys we have examined the mitochondrial genome sequence of two African and six Asian colobines. Although taxonomists have proposed grouping the "odd-nosed" colobines (proboscis monkey, douc langur, and the snub-nosed monkey) together, phylogenetic support for such a clade has not been tested using molecular data. Phylogenetic analyses using parsimony, maximum likelihood, and Bayesian methods support a monophyletic clade of odd-nosed colobines consisting of Nasalis, Pygathrix, and Rhinopithecus, with tentative support for Nasalis occupying a basal position within this clade. The African and Asian colobine lineages are inferred to have diverged by 10.8 million years ago (mya or Ma). Within the Asian colobines the odd-nosed clade began to diversify by 6.7 Ma. These results augment our understanding of colobine evolution, particularly the nature and timing of the colobine expansion into Asia. This phylogenetic information will aid those developing conservation strategies for these highly endangered, diverse, and unique primates.     

The history and chronology of siwalik cercopithecids

Cercopithecid monkeys make a comparatively late appearance in the Miocene Siwalik formations of the Indian Subcontinent. The oldest well-dated specimen is a 6.3 MY old colobine, ?Presbytis sivalensis, and it is doubtful that any cercopithecids were present in the Siwalik faunas prior to 7.0 MY, a date that is considerably later than estimates for their appearance elsewhere in Eurasia. Cercopithecines appear later than colobines. Although their temporal ranges are uncertain, cercopithecines evidently were not present before 3.2 MY and possibly not until 2.5 MY. They are represented by three species,?Macaca palaeindica, Procynocephalus subhimalayanus, andTheropithecus delsoni. In the Siwaliks the appearances of colobines and cercopithecines coincide with or follow shortly after major faunal changes that also bring other northern Eurasian and African taxa into the region.     

Tragoportax cf. rugosifrons (Schlosser, 1904) from the late Miocene of Cessaniti (Southern Italy)

This paper describes remains attributable to Tragoportax cf. rugosifrons (Schlosser, 1904) found in the late Miocene site of Cessaniti (Vibo Valentia, Calabria) and the surrounding area. The studied specimens come from the Clypeaster sandstones, included in a marine/fluvial succession dated between 8 and 7.2 Ma. At Cessaniti, Tragoportax is associated with Stegotetrabelodon syrticus Petrocchi, 1941; Samotherium cf. boissieri Forsyth-Major, 1888; Bohlinia cf. attica Matthew, 1929; and an undetermined Rhinocerotid still under study. The genus Tragoportax was common in Eurasia and Africa during the late Miocene. The occurrence of Tragoportax cf. rugosifrons at Cessaniti confirms the peculiarity of the assemblage, with its association of species of North African and Pikermian (Greco-Iranian bioprovince) affinities.     

Dental remains of Equatorius africanus from Kipsaramon, Tugen Hills, Baringo District, Kenya.

Forty-one isolated large hominoid teeth, as well as most of the mandibular and three maxillary teeth associated with a partial skeleton, were recovered from middle Miocene Muruyur sediments near Kipsaramon in the Tugen Hills, Baringo District, Kenya. The isolated teeth were collected as surface finds and the skeleton was excavated in situ at locality BPRP#122 dated between 15.58 Ma and 15.36 Ma. The majority of the teeth recovered at BPRP#122 are referable to a minimum of five individuals of the hominoid Equatorius africanus. Three of the teeth, however, are provisionally assigned to Nyanzapithecus sp. The new hominoids from Kipsaramon add to an increasing inventory of specimens that suggest greater large hominoid taxonomic diversity from the middle Miocene of Kenya than was previously recognized. It is suggested that there are two large-bodied hominoid species present at Mabako, only one of which is assignable to Equatorius.     

Partial skeleton of Theropithecus brumpti (Primates, Cercopithecidae) from the Chemeron Formation of the Tugen Hills, Kenya

Here we describe a complete skull and partial skeleton of a large cercopithecoid monkey (KNM-TH 46700) discovered in the Chemeron Formation of the Tugen Hills at BPRP Site #152 (2.63 Ma). Associated with the skeleton was a mandible of an infant cercopithecoid (KNM-TH 48364), also described here. KNM-TH 46700 represents an aged adult female of Theropithecus brumpti, a successful Pliocene papionin taxon better known from the Omo Shungura Formation in Ethiopia and sites east and west of Lake Turkana, Kenya. While the morphology of male T. brumpti is well-documented, including a partial skeleton with both cranial and postcranial material, the female T. brumpti morphotype is not well-known. This skeleton represents some of the first associated evidence of cranial and postcranial female T. brumpti remains. In addition to the complete skull, postcranial material includes elements of the axial skeleton and lower limb. While aspects of the skeleton conform to those of specimens previously assigned to T. brumpti, other features on the femur and tibia appear to differ from those previously described for this species. It is unclear whether these differences represent general variation within the T. brumpti population, variation between the sexes in T. brumpti, or the incorrect assignment of previous isolated hindlimb specimens. In total, the observable morphological features of the hindlimb suggest that KNM-TH 46700 was a terrestrial quadruped similar to modern savannah baboons (Papio). From the available evidence, it is difficult to assess whether or not KNM-TH 46700 frequently engaged in the specialized squatting and shuffling behavior observed in extant geladas (Theropithecus gelada).