Article

Remnants of an ancient forest provide ecological context for Early Miocene fossil apes

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The lineage of apes and humans (Hominoidea) evolved and radiated across Afro-Arabia in the early Neogene during a time of global climatic changes and ongoing tectonic processes that formed the East African Rift. These changes probably created highly variable environments and introduced selective pressures influencing the diversification of early apes. However, interpreting the connection between environmental dynamics and adaptive evolution is hampered by difficulties in locating taxa within specific ecological contexts: time-averaged or reworked deposits may not faithfully represent individual palaeohabitats. Here we present multiproxy evidence from Early Miocene deposits on Rusinga Island, Kenya, which directly ties the early ape Proconsul to a widespread, dense, multistoried, closed-canopy tropical seasonal forest set in a warm and relatively wet, local climate. These results underscore the importance of forested environments in the evolution of early apes.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... No other plant macrofossil assemblages of comparable age have been reported from tropical Africa, although recent revisions to the geochronology of sediments at Rusinga Island, Kenya, estimate the fossiliferous deposits there range in age from 20 to 17 Ma (Peppe et al., 2011). Rusinga plant fossils consist of fruits and seeds with twigs and thorns (Chesters, 1957;Collinson, 1985;Collinson et al., 2009), in situ remains of tree stump casts and roots (Michel et al., 2014), and stratigraphically closely associated leaf impressions, all estimated to be approximately 18 Ma (Maxbauer et al., 2013;Michel et al., 2014). Reconstructions based upon these lines of evidence and the sediments themselves are interpreted as representing a variety of habitats, with an important role for deciduous broad-leaved woodland having a continuous canopy (Collinson et al., 2009), forested areas (Maxbauer et al., 2013;Michel et al., 2014), and riparian environments within a climate having pronounced dry seasons (Maxbauer et al., 2013). ...
... No other plant macrofossil assemblages of comparable age have been reported from tropical Africa, although recent revisions to the geochronology of sediments at Rusinga Island, Kenya, estimate the fossiliferous deposits there range in age from 20 to 17 Ma (Peppe et al., 2011). Rusinga plant fossils consist of fruits and seeds with twigs and thorns (Chesters, 1957;Collinson, 1985;Collinson et al., 2009), in situ remains of tree stump casts and roots (Michel et al., 2014), and stratigraphically closely associated leaf impressions, all estimated to be approximately 18 Ma (Maxbauer et al., 2013;Michel et al., 2014). Reconstructions based upon these lines of evidence and the sediments themselves are interpreted as representing a variety of habitats, with an important role for deciduous broad-leaved woodland having a continuous canopy (Collinson et al., 2009), forested areas (Maxbauer et al., 2013;Michel et al., 2014), and riparian environments within a climate having pronounced dry seasons (Maxbauer et al., 2013). ...
... Rusinga plant fossils consist of fruits and seeds with twigs and thorns (Chesters, 1957;Collinson, 1985;Collinson et al., 2009), in situ remains of tree stump casts and roots (Michel et al., 2014), and stratigraphically closely associated leaf impressions, all estimated to be approximately 18 Ma (Maxbauer et al., 2013;Michel et al., 2014). Reconstructions based upon these lines of evidence and the sediments themselves are interpreted as representing a variety of habitats, with an important role for deciduous broad-leaved woodland having a continuous canopy (Collinson et al., 2009), forested areas (Maxbauer et al., 2013;Michel et al., 2014), and riparian environments within a climate having pronounced dry seasons (Maxbauer et al., 2013). The fossils and their meaning at Rusinga differ significantly from what we have described for the Mush Valley paleoflora in this paper, but it is important to note that the Mush fossils may be close to three million years older and higher in elevation. ...
Article
Full-text available
Miocene paleoecology of East Africa has implications for human origins and understanding the vicariant legacy forests found today on either side of the East African Rift. Fossil leaves preserved in 21.73 million year old lacustrine sediments from the Mush Valley, Ethiopia, provide a unique opportunity to investigate forest composition and dominance-diversity patterns at an ecological scale. We classified and analyzed 2427 leaves in total from two to three quarries within each of six stratigraphic levels, spanning 7 m of section; we estimate each quarry census represents one to three centuries, and 50–60 kyrs separate the oldest and youngest levels. Pollen, phytolith, and compound-specific organic geochemical data were also collected in a detailed stratigraphic context to provide independent, integrated lines of evidence for landscape evolution and lacustrine paleoecology of the system that preserves the macrofossils. Forty-nine leaf morphotypes were documented, and Legume 1 dominated all samples. Nonmetric multidimensional scaling, Jaccard similarity analyses, and diversity and evenness indices demonstrate a degree of change comparable to community ecology dynamics, likely illustrating a dynamic stable state in forest vegetation surrounding the lake. Taxonomic assessments of leaves, phytoliths, and pollen are consistent with a closed canopy forest with limited palm diversity. A high abundance of des-A ring triterpenoid molecules (diagenetic products formed by microbial degradation under anoxic conditions) and very negative δ¹³C values (<−45‰) of several hopanoid compounds point to anoxic conditions at the lake bottom, consistent with exquisite fossil preservation. The proportion of mid-chain n-alkanes is low, signifying relatively few submerged plants, but increases up-section, which signals shallowing of the paleolake. The Mush Valley locality is unique in Africa with regard to its very early Miocene age and the abundance and quality of organic remains. This densely forested landscape in an upland volcanic region of the Ethiopian Plateau showed resilience amid volcanic eruptions and had botanical affinities with species found today in West, Central, and eastern Africa.
... The Kisingiri Volcano, which formed at the western extent of Kenya's Nyanza Rift, is associated with some of the richest fossil assemblages from the early Miocene in East Africa ( Fig. 1; Pickford, 1986;Drake et al., 1988;Peppe et al., 2009;Michel et al., 2014;Driese et al., 2016). The best-known Kisingiri locality, Rusinga Island, has been the focus of extensive paleontological and geological research, spanning more than eight decades and producing tens of thousands of fossil remains. ...
... The best-known Kisingiri locality, Rusinga Island, has been the focus of extensive paleontological and geological research, spanning more than eight decades and producing tens of thousands of fossil remains. With expeditions driven primarily by the discovery of early fossil apes (Leakey, 1943;MacInnes, 1943;Leakey, 1950, 1951;Andrews, 1974;Andrews and Simons, 1977;Teaford et al., 1988), the Miocene deposits on Rusinga have yielded more than 100 species of vertebrate animals (Pickford, 1986;Werdelin and Sanders, 2010), exquisitely preserved invertebrate fauna (Verdcourt, 1963;Wilson and Taylor, 1964;Paulian, 1976;Thackray, 1994), and abundant paleobotanical remains (Chesters, 1957;Collinson et al., 2009;Maxbauer et al., 2013;Michel et al., 2014). For this reason, Rusinga is a critical reference assemblage for studies of lower Miocene paleobiology and of East African floral and faunal succession. ...
... Deposits on Rusinga record a long section of Kisingiri's eruptive history, from the volcaniclastic Wayando Formation at the base of the stratigraphic sequence to the volcanic Lunene Lavas that cap it (Fig. 1C). Fossils have been found throughout the stratigraphic formations in the Rusinga Group, with the majority deriving from a variety of fluvial, alluvial, and volcaniclastic deposits in the Hiwegi Formation (e.g., Van Couvering, 1972;Pickford, 1986;Conrad et al., 2013;Jenkins, 2013;Maxbauer et al., 2013;Michel et al., 2014). Despite being the focus of some of the earliest K-Ar studies (Evernden et al., 1964;Bishop et al., 1969;Van Couvering and Miller, 1969), the age of deposits on Rusinga has been difficult to constrain due to the unique chemistry of volcanic materials and, in many cases, the significant postdepositional alteration of dateable minerals, such as biotite (see Drake et al., 1988). ...
Article
We describe new material of Rhinocerotidae recently collected in western Kenya. A skull from Karungu is one of the best-preserved Miocene skulls in Africa. It differs substantially from that of Rusingaceros leakeyi, the only other relatively well-known rhino from this region and age, in its degree of brachycephaly, possession of a deep nasal notch, and long nasal bones that probably carried a horn of moderate size. Miocene African rhinos are still too poorly known to resolve their phylogenetic relationships, but we tentatively assign this skull to a new species of Victoriaceros, a genus whose type species comes from the younger site of Maboko, although the Karungu skull has a much smaller nasal horn. A parsimony analysis resolves them as sister species within the Elasmotheriini, close to the other African genera Turkanatherium and Chilotheridium, but we consider this result debatable, as Victoriaceros differs considerably from them. Still, they might all be descended from European forms. A partial skull from Gumba is assigned to the Aceratheriini, making it one of the earliest representatives of this group and suggesting that the origin of this tribe could be African.http://zoobank.org/urn:lsid:zoobank.org:pub:2B1E8135-CCD4-43EB-826B-6DF7176DC74ESUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Geraads, D., T. Lehmann, D. J. Peppe, and K. P. McNulty. 2016. New Rhinocerotidae from the Kisingiri localities (lower Miocene of western Kenya). Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1103247.
... Peppe et al. (2011) recommend using CCA as an initial check to confirm that a fossil floras physiognomic space is captured by the calibration data. Peppe et al. (2011) and Peppe (unpublished data) have analyzed two floras that plotted outside the calibrated physiognomic space: Bonanza, an Eocene flora from North America, and Rusinga R3, a Miocene flora from Kenya (Michel et al. 2014; Fig. 13.3). Peppe et al. (2011) argued that the Bonanza flora was likely on outlier because the fossil flora was a mixture of two habitats resulting in a unique site mean physiognomic space. ...
... Leaf physiognomic methods for reconstructing paleoclimate have been applied hundreds, if not thousands of times to fossil floras from the Cretaceous through the Quaternary, and leaf trait methods for reconstructing paleoecology have begun to be applied to fossil plants throughout Earth's history. The following is a brief example of an application of these methods for reconstructing paleoclimate and paleoecology by Michel et al. (2014) that made it possible to reconstruct the climate and to determine the climatic, environmental, and ecological biome of the fossil site. The study of Michel et al. (2014) documented a diverse ssemblage of fossil vertebrates, leaves, and tree stump and root casts and used the fossil data to reconstruct the paleoclimate and paleoenvironment of the Michel et al. (2014), the paleoenvironment of the site was relatively poorly constrained. ...
... The following is a brief example of an application of these methods for reconstructing paleoclimate and paleoecology by Michel et al. (2014) that made it possible to reconstruct the climate and to determine the climatic, environmental, and ecological biome of the fossil site. The study of Michel et al. (2014) documented a diverse ssemblage of fossil vertebrates, leaves, and tree stump and root casts and used the fossil data to reconstruct the paleoclimate and paleoenvironment of the Michel et al. (2014), the paleoenvironment of the site was relatively poorly constrained. Michel et al. (2014) mapped a series of fossil tree stump casts of varying diameter preserved within the same stratigraphic layer across the R3 site. ...
Chapter
Full-text available
Plants are strongly influenced by their surrounding environment, which makes them reliable indicators of climate and ecology. The relationship between climate, ecology, plant traits and the geographic distribution of plants based on their climatic tolerances have been used to develop plant-based proxies for reconstructing paleoclimate and paleoecology. These proxies are some of the most accurate and precise methods for reconstructing the climate and ecology of ancient terrestrial ecosystems and have been applied from the Cretaceous to the Quaternary. Despite their utility, the relationships between plant traits and climate that underlie these methods are confounded by other factors such as leaf life-span and phylogenetic history. Work focused on better understanding these confounding factors, incorporating the influence of phylogeny and leaf economic spectrum traits into proxies, expanding modern leaf trait-climate and ecology calibration datasets to additional biogeographic areas and climate regimes, and developing automated computer algorithms for measuring leaf traits are important growing research areas that will help considerably improve plant-based paleoclimate and paleoecological proxies.
... Peppe et al. (2011) recommend using CCA as an initial check to confirm that a fossil floras physiognomic space is captured by the calibration data. Peppe et al. (2011) and Peppe (unpublished data) have analyzed two floras that plotted outside the calibrated physiognomic space: Bonanza, an Eocene flora from North America, and Rusinga R3, a Miocene flora from Kenya (Michel et al. 2014; Fig. 13.3). Peppe et al. (2011) argued that the Bonanza flora was likely on outlier because the fossil flora was a mixture of two habitats resulting in a unique site mean physiognomic space. ...
... Leaf physiognomic methods for reconstructing paleoclimate have been applied hundreds, if not thousands of times to fossil floras from the Cretaceous through the Quaternary, and leaf trait methods for reconstructing paleoecology have begun to be applied to fossil plants throughout Earth's history. The following is a brief example of an application of these methods for reconstructing paleoclimate and paleoecology by Michel et al. (2014) that made it possible to reconstruct the climate and to determine the climatic, environmental, and ecological biome of the fossil site. The study of Michel et al. (2014) documented a diverse ssemblage of fossil vertebrates, leaves, and tree stump and root casts and used the fossil data to reconstruct the paleoclimate and paleoenvironment of the Michel et al. (2014), the paleoenvironment of the site was relatively poorly constrained. ...
... The following is a brief example of an application of these methods for reconstructing paleoclimate and paleoecology by Michel et al. (2014) that made it possible to reconstruct the climate and to determine the climatic, environmental, and ecological biome of the fossil site. The study of Michel et al. (2014) documented a diverse ssemblage of fossil vertebrates, leaves, and tree stump and root casts and used the fossil data to reconstruct the paleoclimate and paleoenvironment of the Michel et al. (2014), the paleoenvironment of the site was relatively poorly constrained. Michel et al. (2014) mapped a series of fossil tree stump casts of varying diameter preserved within the same stratigraphic layer across the R3 site. ...
Preprint
Full-text available
Plants are strongly influenced by their surrounding environment, which makes them reliable indicators of climate and ecology. The relationship between climate, ecology, plant traits and the geographic distribution of plants based on their climatic tolerances have been used to develop plant-based proxies for reconstructing paleoclimate and paleoecology. These proxies are some of the most accurate and precise methods for reconstructing the climate and ecology of ancient terrestrial ecosystems and have been applied from the Cretaceous to the Quaternary. Despite their utility, the relationships between plant traits and climate that underlie these methods are confounded by other factors such as leaf life-span and phylogenetic history. Work focused on better understanding these confounding factors, incorporating the influence of phylogeny and leaf economic spectrum traits into proxies, expanding modern leaf trait-climate and ecology calibration datasets to additional biogeographic areas and climate regimes, and developing automated computer algorithms for measuring leaf traits are important growing research areas that will help considerably improve plant-based paleoclimate and paleoecological proxies.
... Early Miocene deposits in the Nyanza rift valley of East Africa preserve a rich assemblage of mammalian remains, with nearly a century of research there focused on the evolutionary context of apes (e.g., Hopwood, 1933;Andrews, 1978;Walker et al., 1993;McNulty et al., 2007McNulty et al., , 2015. The early Miocene is recognized as a key interval in the development of anatomical and behavioral adaptations fundamental to interpreting the origin of the human lineage (Gebo et al., 1997;Michel et al., 2014;Begun, 2015;McNulty et al., 2015). These include aspects of the axial skeleton and extremities shared between early hominins and the primitive ape Ekembo (Lovejoy, 2009;Lovejoy et al., 2009a,b), frequent use of upright posture in Morotopithecus (Sanders and Bodenbender, 1994;Gebo et al., 1997;MacLatchy et al., 2000), advanced subnasal morphology in Rangwapithecus (Andrews, 1978;McNulty, 2003), and large body size and prolonged life history in Afropithecus, Ekembo, and Morotopithecus (Kelley, 1997(Kelley, , 2002. ...
... Ekembo (Clark and Leakey, 1951;McNulty et al., 2015). Pickford (1981) argued that the mammals represented in the Karungu fauna are generally similar to fauna of Hiwegi Formation on Rusinga Island (Figure 1), which contains abundant, well-preserved fossil catarrhine primates including Dendropithecus, Ekembo, Nyanzapithecus, and Limnopithecus, (Leakey, 1943;Clark and Leakey, 1951;Kelley, 1986Kelley, , 1993Pickford, 1986;Walker et al., 1993;Harrison, 2010;Michel et al., 2014;McNulty et al., 2015). Based on assessments of the faunas at Karungu and from the entire Hiwegi Formation on Rusinga Island, Nesbit Evans et al. (1981) interpreted them to represent similar paleoecological conditions. ...
... Estimations of MAT using NaK, PWI, and PPM 1.0 are all clearly too low given the equatorial setting of the locality and presence of taxa that currently inhabit thermic to hyperthermic climate zones (e.g., crocodilians and turtles). Instead we suggest that MAT was probably considerably warmer and similar to fossil leaf estimates from Rusinga Island of 23-35 • C (Michel et al., 2014). Paleosol studies frequently find the results from elemental proxies for MAT are below reasonable values, primarily because MAT is much less important in controlling soil weathering compared to other variables, such as MAP (e.g., Stinchcomb et al., 2016). ...
Article
Full-text available
Early Miocene outcrops near Karungu, Western Kenya, preserve a range of fluvio-lacustrine, lowland landscapes that contain abundant fossils of terrestrial and aquatic vertebrates. Primates are notably rare among these remains, although nearby early Miocene strata on Rusinga Island contain a rich assemblage of fossilized catarrhines and strepsirrhines. To explore possible environmental controls on the occurrence of early Miocene primates, we performed a deep-time Critical Zone (DTCZ) reconstruction focused on floodplain paleosols at the Ngira locality in Karungu. We specifically focused on a single stratigraphic unit (NG15), which preserves moderately developed paleosols that contain a microvertebrate fossil assemblage. Although similarities between deposits at Karungu and Rusinga Island are commonly assumed, physical sedimentary processes, vegetative cover, soil hydrology, and some aspects of climate state are notably different between the two areas. Estimates of paleoclimate parameters using paleosol B horizon elemental chemistry and morphologic properties are consistent with seasonal, dry subhumid conditions, occasional waterlogging, and herbaceous vegetation. The reconstructed small mammal community indicates periodic waterlogging and open-canopy conditions. Based on the presence of herbaceous root traces, abundant microcharcoal, and pedogenic carbonates with high stable carbon isotope ratios, we interpret NG15 to have formed under a warm, seasonally dry, open riparian woodland to wooded grassland, in which at least a subset of the vegetation was likely C 4 biomass. Our results, coupled with previous paleoenvironmental interpretations for deposits on Rusinga Island, demonstrate that there was considerable environmental heterogeneity ranging from open to closed habitats in the early Miocene. We hypothesize that the relative paucity of primates at Karungu was driven by their environmental preference for locally abundant closed canopy vegetation, which was likely absent at Karungu, at least during the NG15 interval if not also earlier and later intervals that have not yet been studied in as much detail.
... Kenya (Chesters, 1957;Michel et al., 2014;Oginga et al., 2017;Oginga, 2018), but also well-documented open environments and wooded grasslands (i.e. Hamilton, 1968;Jacobs et al., 1999;Kappelman et al., 2003;Lukens et al., 2017;Liutkus-Pierce et al., 2019). ...
... Andrews & Van Couvering, 1975;Evans et al., 1981;Collinson et al., 2009) owing to its tremendous preservation of plant and animal remains. More than 100 vertebrate species are now known from the Rusinga fossil beds, as are a wide variety of remains from other fossil animals and plants (MacInnes, 1943;Shackleton, 1951;Pickford, 1986;Walker et al., 1993;Walker, 2007;Michel et al., 2014) dating between about 20 to 17 Ma (Peppe et al., 2011(Peppe et al., , 2017b. The majority of previous research has focused on the highly fossiliferous Hiwegi Formation, and in particular on strata identified as the Fossil Bed Member, in which an estimated 80% of the Rusinga fossils are thought to have been discovered (e.g. ...
... Van Couvering, 1972;Pickford, 1986). However, recent work (see Michel et al., 2014;Peppe et al., 2017b) has shown that the 'Fossil Bed Member' is not contemporaneous from site to site, as originally postulated (e.g. Van Couvering, 1972;Andrews & Van Couvering, 1975;Evans et al., 1981;Drake et al., 1988;Collinson et al., 2009). ...
Article
Palaeontological deposits on Rusinga Island, Lake Victoria, Kenya, provide a rich record of floral and faunal evolution in the early Neogene of East Africa. Yet, despite a wealth of available fossil material, previous palaeoenvironmental reconstructions from Rusinga have resulted in widely divergent results, ranging from closed forest to open woodland environments. Presented here is a detailed study of the sedimentology and fauna of the early Miocene Hiwegi Formation at Waregi Hill on Rusinga Island, Kenya. New sedimentological analyses demonstrate that the Hiwegi Formation records an environmental transition from the bottom to the top of the formation. Lower in the Hiwegi Formation, satin‐spar calcite after gypsum in siltstone deposits are interpreted as evidence for open hypersaline lakes. Moving up‐section, carbonate deposits – interpreted previously as evidence of aridity – are actually diagenetic calcite cements, which preserve root systems of trees, suggesting a more closed environment; further up‐section, the uppermost palaeosol layer contains abundant root traces and tree‐stump casts, previously reported by as evidence of a closed‐canopy forest. These newly interpreted environmental differences are reflected by differences in faunal composition and abundance data from Hiwegi Formation fossil sites R1 and R3. Taken together, this work suggests that divergent palaeoenvironmental reconstructions in previous studies may have been informed by time‐averaging across multiple environments. Further, results demonstrate that during the early Miocene local or regional habitat heterogeneity already existed. Rusinga’s Hiwegi Formation varied both spatially and temporally, which challenges the interpretation that a broad forested environment stretched across the African continent during the early Neogene, transitioning later to predominately open landscapes that characterize the region today. This result has important implications for interpretations of the selective pressures faced by early Miocene fauna, including Rusinga Island’s well‐preserved fossil primates.
... Paleoenvironmental implications -Previous paleoenvironmental reconstructions from the Hiwegi Formation have inferred a habitat mosaic inhabited by early hominoids, such as Ekembo (see McNulty et al., 2015 ). Evidence for mosaic habitats comes from gastropod ( Verdcourt, 1963 ;Pickford, 1995 ) and mammal faunas (e.g., Andrews and Van Couvering, 1975 ), paleosols and paleobotany Maxbauer et al., 2013 ;Michel et al., 2014 ). Collinson et al. (2009) concluded that the overall paleoenvironmental signal, considering the evidence from plants, mammals, gastropods and paleosols, was one of "mixed habitats FIGURE 7 Digital transverse sections, produced by synchrotron-based X-ray tomographic microscopy, through fruits of modern African Cissus , using representative specimens to illustrate typical features of each seed morphotype listed in Table 1 dominated by woodlands, with waterside environments and small patches of forest big enough to support forest faunas" (p. ...
... Recent studies have revealed temporal paleoenvironmental changes through the Hiwegi Formation ( Michel et al., 2013( Michel et al., , 2014Garrett et al., 2015 ) and have suggested that interpretations of mosaic paleoenvironments may be based on time-averaged faunal and fl oral assemblages that confl ate separate, more homogeneous habitats. Th ese studies suggest that more open, drier woodland habitats low in the Hiwegi Formation (e.g., Grit Member) gave way to dense, closed canopy forest further up (e.g., Fossil Bed and Kibanga Members), with early hominoid fossils recovered from both paleoenvironments ( Garrett et al., 2015 ). ...
Preprint
Premise of the study: Fossilized seeds similar to Cissus (Vitaceae) have been recognized from the Miocene of Kenya, though some were previously assigned to the Menispermaceae. We undertook a comparative survey of extant African Cissus seeds to identify the fossils and consider their implications for the evolution and biogeography of Cissus and for African early Miocene paleoenvironments. Methods: Micro-computed tomography (µCT) and synchrotron-based X-ray tomographic microscopy (SRXTM) were used to study seed morphology and anatomy. Virtual taphonomy, using SRXTM data sets, produced digital fossils to elucidate seed taphonomy. Phylogenetic relationships within Cissus were reconstructed using existing and newly produced DNA sequences for African species. Paleobiology and paleoecology were inferred from African nearest living relatives. Key results: The fossils were assigned to four new Cissus species, related to four modern clades. The fossil plants were interpreted as climbers inhabiting a mosaic of riverine woodland and forest to more open habitats. Virtual taphonomy explained how complex mineral infill processes concealed key seed features, causing the previous taxonomic misidentification. Newly sampled African species, with seeds most similar to the fossils, belong to four clades within core Cissus, two of which are early diverging. Conclusions: Virtual taphonomy, combined with X-ray imaging, has enabled recognition of the first fossil Cissus and Vitaceae from Africa. Early-divergent members of the core Cissus clade were present in Africa by at least the early Miocene, with an African origin suggested for the Cissus sciaphila clade. The fossils provide supporting evidence for mosaic paleoenvironments inhabited by early Miocene hominoids.
... Paleoenvironmental implications -Previous paleoenvironmental reconstructions from the Hiwegi Formation have inferred a habitat mosaic inhabited by early hominoids, such as Ekembo (see McNulty et al., 2015 ). Evidence for mosaic habitats comes from gastropod ( Verdcourt, 1963 ;Pickford, 1995 ) and mammal faunas (e.g., Andrews and Van Couvering, 1975 ), paleosols and paleobotany Maxbauer et al., 2013 ;Michel et al., 2014 ). Collinson et al. (2009) concluded that the overall paleoenvironmental signal, considering the evidence from plants, mammals, gastropods and paleosols, was one of "mixed habitats FIGURE 7 Digital transverse sections, produced by synchrotron-based X-ray tomographic microscopy, through fruits of modern African Cissus , using representative specimens to illustrate typical features of each seed morphotype listed in Table 1 dominated by woodlands, with waterside environments and small patches of forest big enough to support forest faunas" (p. ...
... Recent studies have revealed temporal paleoenvironmental changes through the Hiwegi Formation ( Michel et al., 2013( Michel et al., , 2014Garrett et al., 2015 ) and have suggested that interpretations of mosaic paleoenvironments may be based on time-averaged faunal and fl oral assemblages that confl ate separate, more homogeneous habitats. Th ese studies suggest that more open, drier woodland habitats low in the Hiwegi Formation (e.g., Grit Member) gave way to dense, closed canopy forest further up (e.g., Fossil Bed and Kibanga Members), with early hominoid fossils recovered from both paleoenvironments ( Garrett et al., 2015 ). ...
Article
Full-text available
Premise of the study: Fossilized seeds similar to Cissus (Vitaceae) have been recognized from the Miocene of Kenya, though some were previously assigned to the Menispermaceae. We undertook a comparative survey of extant African Cissus seeds to identify the fossils and consider their implications for the evolution and biogeography of Cissus and for African early Miocene paleoenvironments. Methods: Micro-computed tomography (µCT) and synchrotron-based X-ray tomographic microscopy (SRXTM) were used to study seed morphology and anatomy. Virtual taphonomy, using SRXTM data sets, produced digital fossils to elucidate seed taphonomy. Phylogenetic relationships within Cissus were reconstructed using existing and newly produced DNA sequences for African species. Paleobiology and paleoecology were inferred from African nearest living relatives. Key results: The fossils were assigned to four new Cissus species, related to four modern clades. The fossil plants were interpreted as climbers inhabiting a mosaic of riverine woodland and forest to more open habitats. Virtual taphonomy explained how complex mineral infill processes concealed key seed features, causing the previous taxonomic misidentification. Newly sampled African species, with seeds most similar to the fossils, belong to four clades within core Cissus, two of which are early diverging. Conclusions: Virtual taphonomy, combined with X-ray imaging, has enabled recognition of the first fossil Cissus and Vitaceae from Africa. Early-divergent members of the core Cissus clade were present in Africa by at least the early Miocene, with an African origin suggested for the Cissus sciaphila clade. The fossils provide supporting evidence for mosaic paleoenvironments inhabited by early Miocene hominoids.
... Peppe et al. (2011) provide new information that suggests that the Hiwegi Formation is in fact older (≥18.0 Ma based on text and Fig. 2 of Michel et al. 2014) than previously thought, but still not as old as Songhor and Koru (ca. 19.6 Ma;Bishop et al. 1969;Hill et al. 2013) and Napak (ca. ...
... The similarities among the two sites may be a result of sampling size (Kulu = 26 genera; Hiwegi = 68 genera), but may also be the result of historically treating the many localities at Rusinga Island as a single time-averaged fauna . It seems unlikely that two faunal assemblages a million or more years apart (Peppe et al. , 2011 will be identical and perhaps there is a need for reanalysis of the Rusinga faunas, especially given the importance of these localities to understanding of the Early Miocene, as demonstrated by Michel et al. (2014). ...
Article
Full-text available
The site of Loperot in West Turkana, Kenya, is usually assigned to the Early Miocene. Recent discoveries at Loperot, including catarrhine primates, led to a revision of its mammalian fauna. Our revision of the fauna at Loperot shows an unusual taxonomic composition of the catarrhine community as well as several other unique mammalian taxa. Loperot shares two non-cercopithecoid catarrhine taxa with Early Miocene sites near Lake Victoria, e.g., Songhor and the Hiwegi Formation of Rusinga Island, but Loperot shares a cercopithecoid, Noropithecus, with Buluk (Surgei Plateau, near Lake Chew Bahir). We use Simpson's Faunal Resemblance Index (Simpson's FRI), a cluster analysis, and two partial Mantel tests, to compare Loperot to 10 other localities in East Africa representing several time divisions within the Early and Middle Miocene. Simpson's FRI of mammalian communities indicates that Loperot is most similar in its taxonomic composition to the Hiwegi Formation of Rusinga Island, suggesting a similarity in age (≥18 Ma) that implies that Loperot is geographically distant from its contemporaries, i.e.
... While the genus exhibits many monkey-like characters, it also evinces a number of nascent ape-like features, to be discussed below. The early Miocene habitat has been reconstructed from analysis of a single paleosol from Rusinga preserving diverse and abundant fossils, including tree leaves (Michel et al. 2014). Multi-proxy reconstruction of the paleohabitat indicates a dense multistoried closed canopy tropical forest (Michel et al. 2014). ...
... The early Miocene habitat has been reconstructed from analysis of a single paleosol from Rusinga preserving diverse and abundant fossils, including tree leaves (Michel et al. 2014). Multi-proxy reconstruction of the paleohabitat indicates a dense multistoried closed canopy tropical forest (Michel et al. 2014). Three species of Proconsul, P. africanus (or heseloni), P. nyanzae and P. major (~20 Ma), are most often parsed from the numerous fossil individuals. ...
Article
Apes, members of the superfamily Hominoidea, possess a distinctive suite of anatomical and behavioral characters which appear to have evolved relatively late and relatively independently. The timing of paleontological events, extant cercopithecine and hominoid ecomorphology and other evidence suggests that many distinctive ape features evolved to facilitate harvesting ripe fruits among compliant terminal branches in tree edges. Precarious, unpredictably oriented, compliant supports in the canopy periphery require apes to maneuver using suspensory and non-sterotypical postures (i.e. postures with eccentric limb orientations or extreme joint excursions). Diet differences among extant species, extant species numbers and evidence of cercopithecoid diversification and expansion, in concert with a reciprocal decrease in hominoid species, suggest intense competition between monkeys and apes over the last 20Ma. It may be that larger body masses allow great apes to succeed in contest competitions for highly desired food items, while the ability of monkeys to digest antifeedant-rich unripe fruits allows them to win scramble competitions. Evolutionary trends in morphology and inferred ecology suggest that as monkeys evolved to harvest fruit ever earlier in the fruiting cycle they broadened their niche to encompass first more fibrous, tannin- and toxin-rich unripe fruits and later, for some lineages, mature leaves. Early depletion of unripe fruit in the central core of the tree canopy by monkeys leaves a hollow sphere of ripening fruits, displacing antifeedant-intolerant, later-arriving apes to small-diameter, compliant terminal branches. Hylobatids, orangutans, Pan species, gorillas and the New World atelines may have each evolved suspensory behavior independently in response to local competition from an expanding population of monkeys. Genetic evidence of rapid evolution among chimpanzees suggests that adaptations to suspensory behavior, vertical climbing, knuckle-walking, consumption of terrestrial piths and intercommunity violence had not yet evolved or were still being refined when panins (chimpanzees and bonobos) and hominins diverged.
... The fossil soil profiles that formed on the Rusinga sediments [Bestland, 1990] had calcareous horizons, which form under conditions of seasonal drying of the soil but with a high water table [Bestland and Retallack, 1993]. Fossil leaves indicate the presence of wet forest, with predicted higher rainfall during this time [Maxbauer et al., 2013;Michel et al., 2014], but the geological evidence of a high water table may suggest that the forest could be a ground water forest existing under local, edaph-Folia Primatol 6 Andrews DOI: 10.1159/000501557 ic conditions, rather than high rainfall. Analysis of carbon isotopes indicates that the vegetation consisted of trees and shrubs probably growing under conditions of water stress [Bestland, 1990]. ...
... At one site on Rusinga Island (R3) the dense remains of tree stumps and roots in a brown soil indicate the presence of forest. There is leaf litter that suggests evergreen forest, and this evidence is associated with proconsulids and probably with earlier finds of dendropithecids [Michel et al., 2014]. Other evidence on environments associated with proconsulids on Rusinga Island has come from land gastropods, indicating mixed savanna and bush with gallery forest [Verdcourt, 1963] and fossil mammals indicating mixed environments on Rusinga Island, Songhor and Koru [Andrews and Van Couvering, 1975;Andrews et al., 1979;Lehman et al., 2012]. ...
Article
For much of their history, fossil apes retained many monkey-like features in posture and body structure. They also occupied a range of habitats, of which tropical forest was only a part, and there is evidence of increasing terrestriality in the fossil record as it is known at present (2019). In the early Miocene (18–20 million years ago, Ma), fossil apes were pronograde arboreal slow climbers, associated mainly with forest environments and deciduous woodland and with some indications of terrestrial behaviour, particularly the larger species. Their hands had long and opposable thumbs, and the phalanges were curved. In the early middle Miocene (15–16 Ma), apes were still monkey-like in body plan and posture and were associated almost entirely with non-forest, deciduous woodland habitats, with increasing evidence of terrestrial adaptations. Hand proportions remained the same. Towards the end of the middle Miocene (12 Ma), some fossil ape species had broadened chests, long clavicles, medial torsion of the humerus and re-positioning of the scapula to the back. These adaptations may have been linked with more upright posture, as in the living apes, but unlike them, the hand phalanges were short, robust and less curved, and the thumb remained long. Associated environments were deciduous woodland rather than forest. This body plan was retained in part in some later Miocene apes (10 Ma), some of which also had more elongated limbs and hands (thumb length not known), and hind limbs modified for greater flexibility, analogous with the orang utan. Associated environments were subtropical deciduous woodlands and subtropical evergreen laurophyllous woodland in southern Europe. Other late Miocene European apes had adaptations for living on the ground, and some of these also shared characters of the skull with orang utans. They are associated with more open deciduous woodland habitats. This body plan and environment were retained in the early hominin, Ardipithecus ramidus , but with a more robust postcranial skeleton and incipient bipedalism. Based on shared character states in fossil apes, living apes and early hominins, 27 characters are identified as probable attributes of the last common ancestor (LCA) of apes and humans. The likely environment of the LCA was tropical deciduous woodland with some evidence of more open habitats, and this remained unchanged in the transition from apes to early hominins.
... Recent comparative studies in western North America (e.g., Gilbert et al. 2010, Wang et al. 2011, Swenson et al. 2012, Chisholm et al. 2013, Wang et al. 2013, Michel et al. 2014 show the value of large (25.6 ha) and medium-sized (1 ha) plots, but this scientific value is maximized when data are directly comparable. With collaborators, I established two 25.6 ha plots (the Yosemite Forest Dynamics Plot in Yosemite National Park, California, and the Wind River Forest Dynamics Plot in the Gifford Pinchot National Forest, Washington ) affiliated with both the Smithsonian network of forest observation plots and the USGS Sierra Nevada monitoring network. ...
Article
When forest ecosystems develop over millennia, trees live five centuries, and mortality unfolds over decades, direct repeated observation (hereafter, longitudinal data) may be the only way to understand the fate of forests. Longitudinal data sets contribute greatly to our understanding, complementing experimental, modeling, and chronosequence approaches. Changing climate is changing forests, perhaps most rapidly through altered mortality regimes, and the elusive nature of integrated mechanistic understanding requires refinements and extensions to historically productive protocols. Changing climate reduces the inferential power of chronosequence techniques and changes model parameterization, and only some of the different factors contributing to tree mortality are expected to respond to climate variability and change. Because annual tree mortality rates are 5% to 1% for trees >= 1 cm dbh in young and old forests (respectively), detecting changes in mortality rates requires tracking thousands of trees, particularly to examine rare sub-populations of concern (e.g., large-diameter trees). And because mortality factors can be spatially aggregated and density-dependent, the causes and rates of tree mortality depend on the relationships between forest spatial structure and the direct and indirect effects of climate. Permanent plots with a combination of larger size, higher spatial precision, and greater sampling frequency will be required to further elucidate spatially explicit aspects of western forest demography. The combination of the longitudinal protocols developed by the Smithsonian Center for Tropical Forest Science, originally for studying tropical forest species diversity, and those developed by the US Geological Survey for annual tree mortality assessment together uniquely allow robust investigation of climate-mediated change in temperate forests.
... A and C-horizons) as a test of the importance of careful sampling and palaeosol taxonomy (Table S1). Estimates of MAP (mm yr À1 ) use the CIA-K (Sheldon et al., 2002), CALMAG (Nordt & Driese, 2010a), Depth to Bk (DBK;Retallack, 2005) and goethite-hematite (G/H; Hyland et al., 2015) transfer functions, and are shown in Fig. 6 with solid symbols for B-horizon-only estimates, and open symbols for estimates based on both appropriate and inappropriate (A and C-horizon) samples as defined by the original authors; CALMAG was specifically developed for use with one soil order (Vertisols; Nordt & Driese, 2010a), but it has recently been proposed that it can be applied to other soil orders in some cases (Michel et al., 2014), an idea that can be tested here. Mean annual precipitation estimates based on CIA-K and CALMAG proxies provide statistically indistinguishable mean values for B-horizon samples, with a similarly limited range of estimates across the landscape (within transfer function error; Fig. 6). ...
Article
Full-text available
Terrestrial sediments are a significant archive of past conditions, and the critical zone in particular is important for understanding past and ongoing interactions between the atmosphere, biosphere and lithosphere. Understanding the details of a palaeolandscape or palaeocatena record can greatly improve palaeoenvironmental descriptions and palaeoclimate reconstructions during crucial time periods in the past. This article presents multi-proxy data including palaeosol descriptions, major element geochemistry, magnetic composition and stable isotope geochemistry from an early Eocene palaeosol transect, which show distinct trends in palaeosol features and geochemistry across the landscape, particularly in terms of the differences between A-horizon and B-horizon samples. Whereas A-horizon geochemical and physical features are highly variable and reflect other not strictly pedogenic controls, B-horizon composition is extremely consistent. Given that most palaeoclimatic or palaeoenvironmental proxies based on palaeosols use B-horizon features, these results highlight the robustness of those proxies. At the same time, the difference between A and B horizons and the variability within A-horizons of the same palaeosol in different geomorphic settings underscores the importance of palaeosol description, detailed sampling, and a multi-proxy approach to produce both precise and accurate reconstructions of past environments and climates using terrestrial sedimentary records. This article is protected by copyright. All rights reserved.
... Likewise, Pickford (1986) recognized only P. nyanzae from Rusinga and Mfangano, notably highlighting the distinct morphology of Kisingiri Proconsul when compared to Tinderet and Ugandan specimens. Despite these and other objections, the presence of P. nyanzae and P. heseloni at the Kisingiri localities has come to be universally accepted (Begun et al., 1994;Leakey et al., 1995;Rafferty et al., 1995;Ward et al., 1995;MacLatchy and Bossert, 1996;Harrison, 2002Harrison, , 2010Smith et al., 2003;Ishida et al., 2004;Nakatsukasa et al., 2007;Deane, 2009;Harrison and Andrews, 2009;Peppe et al., 2009;Pickford et al., 2009;Michel et al., 2014). ...
Conference Paper
Full-text available
The Gregory Rift Valley is known for many Plio-Pleistocene sites that have yielded abundant fossil hominins, most of which lie on the Rift Valley floor. Here we report a new Pliocene site, Kantis, on the shoulder of the Gregory Rift Valley, which extends the geographical range of Australopithecus afarensis to the highlands of Kenya. This species, known from sites in Ethiopia, Tanzania, and possibly Kenya, is believed to be adapted to a wide spectrum of habitats, from open grassland to woodland. The Kantis fauna is generally similar to that reported from other contemporaneous Au.afarensis sites on the Rift Valleyfloor. However, its composition and stable carbon isotopic data from dental enamel suggest a higher component ofC4 vegetationthan in thesesites. Although the Gregory Rift Valley has been the focus of paleontologists’ attention for many years, surveys of the Rift shoulder may provide new perspective on African Pliocene mammal and hominin evolution.
... Likewise, Pickford (1986) recognized only P. nyanzae from Rusinga and Mfangano, notably highlighting the distinct morphology of Kisingiri Proconsul when compared to Tinderet and Ugandan specimens. Despite these and other objections, the presence of P. nyanzae and P. heseloni at the Kisingiri localities has come to be universally accepted (Begun et al., 1994;Leakey et al., 1995;Rafferty et al., 1995;Ward et al., 1995;MacLatchy and Bossert, 1996;Harrison, 2002Harrison, , 2010Smith et al., 2003;Ishida et al., 2004;Nakatsukasa et al., 2007;Deane, 2009;Harrison and Andrews, 2009;Peppe et al., 2009;Pickford et al., 2009;Michel et al., 2014). ...
... Karungu is located along the shores of Lake Victoria in southwest Kenya (À0.844 S, 34.157 E), 50 km south of the well-known Miocene (e.g., Le Gros Clark and Leakey, 1950;Van Couvering, 1972;Leakey, 1974;Andrews, 1981;Pickford, 1986;Teaford et al., 1988;Walker and Teaford, 1988;Peppe et al., 2009;Michel et al., 2014) and Pleistocene (Pickford and Thomas, 1984;Tryon et al., 2010Tryon et al., , 2012Tryon et al., , 2014Faith et al., 2011, in press) localities on Rusinga and Mfangano Island ( Fig. 1) and 65 km southwest of the Miocene-to-Pleistocene deposits on the Homa Peninsula (e.g., Oswald, 1914;Andrews, 1916;Behrensmeyer et al., 1995;Ditchfield et al., 1999). Although much of the landscape around Karungu is now under cultivation, the historic vegetation included evergreen bushland and thicket in the immediate area, grading to woodlands and more humid Afromontane rainforests further inland (White, 1983;van Breugel et al., 2012). ...
Article
The opening and closing of the equatorial East African forest belt during the Quaternary is thought to have influenced the biogeographic histories of early modern humans and fauna, although precise details are scarce due to a lack of archaeological and paleontological records associated with paleoenvironmental data. With this in mind, we provide a description and paleoenvironmental reconstruction of the Late Pleistocene Middle Stone Age (MSA) artifact- and fossil-bearing sediments from Karungu, located along the shores of Lake Victoria in western Kenya. Artifacts recovered from surveys and controlled excavations are typologically MSA and include points, blades, and Levallois flakes and cores, as well as obsidian flakes similar in geochemical composition to documented sources near Lake Naivasha (250 km east). A combination of sedimentological, paleontological, and stable isotopic evidence indicates a semi-arid environment characterized by seasonal precipitation and the dominance of C4 grasslands, likely associated with a substantial reduction in Lake Victoria. The well-preserved fossil assemblage indicates that these conditions are associated with the convergence of historically allopatric ungulates from north and south of the equator, in agreement with predictions from genetic observations. Analysis of the East African MSA record reveals previously unrecognized north-south variation in assemblage composition that is consistent with episodes of population fragmentation during phases of limited dispersal potential. The grassland-associated MSA assemblages from Karungu and nearby Rusinga Island are characterized by a combination of artifact types that is more typical of northern sites. This may reflect the dispersal of behavioral repertoires-and perhaps human populations-during a paleoenvironmental phase dominated by grasslands. Copyright © 2015 Elsevier Ltd. All rights reserved.
... In this section, we focus paleosol applications at Olduvai Gorge to demonstrate the process and utility of paleosol research ( Fig. 9.5). Other similar studies have recently been completed at significant fossil sites in western Kenya at Rusinga Island (Michel et al. 2014) and Karungu (Beverly et al. 2015a;Lukens et al. 2017b). ...
Chapter
Full-text available
Soils form as a product of physical, chemical, and biological activity at the outermost veneer of Earth’s surface. Once buried and incorporated into the sedimentary record, these soils, now paleosols, preserve archives of ancient climates, ecosystems, and sedimentary systems. Paleopedology, the study of paleosols, includes qualitative interpretation of physical characteristics and quantitative analysis of geochemical and mineralogical assays. In this chapter, the paleosol macroscopic, micromorphological, mineralogical, and geochemical indicators of paleoecology are discussed with emphasis on basic analytical and interpretative techniques. These data can reveal a breadth of site-specific interpretations of vegetation, sedimentary processes, climatic variables, and durations of landscape stability. The well-known soil-forming factors are presented as a theoretical framework for understanding landscape-scale soil evolution through time. Vertical and lateral patterns of stacked paleosols that appear in the rock record are discussed in order to address practical approaches to identifying and describing paleosols in the field. This chapter emphasizes a robust multi-proxy approach to paleopedology that combines soil stratigraphy, morphology, mineralogy, biology, and chemistry to provide an in-depth understanding of paleoecology.
... Kidwell and Bosence (1991). Studies that document close temporal and spatial association of multiple Early Miocene catarrhine species within a single stratum (e.g., Michel et al., 2014) are quite rare. ...
... These horizons were selected based on previous work describing and sampling paleosols from the Cathedral Bluffs Member in the GRB ( Fig. 1; Hyland , and based on the characteristics of soils sampled for the paleosol paleoclimate model dataset (Stinchcomb et al., 2016), in order to generate the most robust input data for the PPM 1.0 spline model. While the PPM 1.0 model produces multiple possible estimates of paleo-MAT, the estimate shown to be most reliable via concurrent comparisons with other paleotemperature methods (paleobotanical and paleosol proxies) is the "high MAT" value we present here (Michel et al., 2014;Stinchcomb et al., 2016;Driese et al., 2016). We further justify our use of the "high" estimate because the PPM 1.0 training dataset heavily samples soils from temperate regions (specifically the conterminous USA), which tend to have lower MAT (≤ 10 • C) and therefore could place excess weight on low values in the model predictive space. ...
Article
Full-text available
Paleogene greenhouse climate equability has long been a paradox in paleoclimate research. However, recent developments in proxy and modeling methods have suggested that strong seasonality may be a feature of at least some greenhouse Earth periods. Here we present the first multi-proxy record of seasonal temperatures during the Paleogene from paleofloras, paleosol geochemistry, and carbonate clumped isotope thermometry in the Green River Basin (Wyoming, USA). These combined temperature records allow for the reconstruction of past seasonality in the continental interior, which shows that temperatures were warmer in all seasons during the peak Early Eocene Climatic Optimum and that the mean annual range of temperatures was high, similar to the modern value (∼ 26 • C). Proxy data and down-scaled Eocene regional climate model results suggest amplified seasonality during greenhouse events. Increased seasonality reconstructed for the early Eocene is similar in scope to the higher seasonal range predicted by downscaled climate model ensembles for future high-CO2 emissions scenarios. Overall, these data and model comparisons have substantial implications for understanding greenhouse climates in general , and may be important for predicting future seasonal climate regimes and their impacts in continental regions.
... Roth-Nebelsick et al. (2017) discussed the responses of functional leaf traits, especially the leaf mass per area (M A ) in the leaf economics spectrum (LES), to the Paleogene climate change of Europe, which elucidated interrelationships of leaf traits with the environment. However, few data of paleo-M A are known from low latitudes, where the most biological diversity in both modern-and paleo-worlds appears high (Michel et al., 2014). ...
... Tropical East Africa contained rainforest with palms and forest grasses in the highlands and a mix of deciduous broad-leaved woodland and forest in the lowlands (Collinson et al., 2009;Currano et al., 2019;Maxbauer et al., 2013;Michel et al., 2014). In southern Africa, the Cape region and eastern shores hosted humid, subtropical forests in the early Miocene, while it is thought that a "proto-savanna" had already developed in southern Namibia (Neumann & Bamford, 2015). ...
Article
Full-text available
The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned toward modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval—the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as a particularly appropriate analog for future climate scenarios, and for assessing the predictive accuracy of numerical climate models—the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re-interpretation of proxies, which might mitigate the model-data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here, we review the state-of-the-art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modeling studies.
... These horizons were selected based on previous work describing and sampling paleosols from the Cathedral Bluffs Member in the GRB ( Fig. 1; Hyland , and based on the characteristics of soils sampled for the paleosol paleoclimate model dataset (Stinchcomb et al., 2016), in order to generate the most robust input data for the PPM 1.0 spline model. While the PPM 1.0 model produces multiple possible estimates of paleo-MAT, the estimate shown to be most reliable via concurrent comparisons with other paleotemperature methods (paleobotanical and paleosol proxies) is the "high MAT" value we present here (Michel et al., 2014;Stinchcomb et al., 2016;Driese et al., 2016). We further justify our use of the "high" estimate because the PPM 1.0 training dataset heavily samples soils from temperate regions (specifically the conterminous USA), which tend to have lower MAT (≤ 10 • C) and therefore could place excess weight on low values in the model predictive space. ...
Article
Full-text available
https://deepblue.lib.umich.edu/bitstream/2027.42/148644/1/Hyland_et_al_2018_CotP-Eocene_Climate_Equability.pdf
... The evolutionary split between humans (Homo spp.) and chimpanzees (Pan spp.) is generally agreed to have occurred in the equatorial rainforest of East Africa approximately 5-8 million years ago (Ma) [1][2][3][4]. According to one hypothesis (the "Hylobatian Model" [5]), the last common ancestor (LCA) of humans and chimpanzees was a small-to mediumsized gibbon-like ape [5][6][7][8] that lived exclusively in the upper reaches of closed forest canopies, where it fed primarily on fresh fruit [9]. ...
Article
Full-text available
Human straight-legged bipedalism represents one of the earliest events in the evolutionary split between humans (Homo spp.) and chimpanzees (Pan spp.), although its selective basis is a mystery. A carrying-related hypothesis has recently been proposed in which hair loss within the hominin lineage resulted in the inability of babies to cling to their mothers, requiring mothers to walk upright to carry their babies. However, a question remains for this model: what drove the hair loss that resulted in upright walking? Observers since Darwin have suggested that hair loss in humans may represent an evolutionary strategy for defence against ticks. The aim of this review is to propose and evaluate a novel tick-based evolutionary hypothesis wherein forest fragmentation in hominin paleoenvironments created conditions that were favourable for tick proliferation, selecting for hair loss in hominins and grooming behaviour in chimpanzees as divergent anti-tick strategies. It is argued that these divergent anti-tick strategies resulted in different methods for carrying babies, driving the locomotor divergence of humans and chimpanzees.
... Structural heterogeneity has been a long-recognized feature of old-growth forests (i.e., Lutz et al. 2013;Michel et al. 2014;Furniss et al. 2017;Engone-Obiang et al. 2019), and that heterogeneity creates complex vertical habitat for a variety of arboreal taxa (i.e., Blomdahl et al. 2019). It is likely that the extreme heterogeneity in deadwood also creates a variety of terrestrial habitat niches. ...
Article
Full-text available
Background Baseline levels of tree mortality can, over time, contribute to high snag densities and high levels of deadwood (down woody debris) if fire is infrequent and decomposition is slow. Deadwood can be important for tree recruitment, and it plays a major role in terrestrial carbon cycling, but deadwood is rarely examined in a spatially explicit context. Methods Between 2011 and 2019, we annually tracked all trees and snags ≥1 cm in diameter and mapped all pieces of deadwood ≥10 cm diameter and ≥1 m in length in 25.6 ha of Tsuga heterophylla / Pseudotsuga menziesii forest. We analyzed the amount, biomass, and spatial distribution of deadwood, and we assessed how various causes of mortality that contributed uniquely to deadwood creation. Results Compared to aboveground woody live biomass of 481 Mg ha ⁻¹ (from trees ≥10 cm diameter), snag biomass was 74 Mg ha ⁻¹ and deadwood biomass was 109 Mg ha ⁻¹ (from boles ≥10 cm diameter). Biomass from large-diameter trees (≥60 cm) accounted for 85%, 88%, and 58%, of trees, snags, and deadwood, respectively. Total aboveground woody live and dead biomass was 668 Mg ha ⁻¹ . The annual production of downed wood (≥10 cm diameter) from tree boles averaged 4 Mg ha ⁻¹ yr ⁻¹ . Woody debris was spatially heterogeneous, varying more than two orders of magnitude from 4 to 587 Mg ha ⁻¹ at the scale of 20 m × 20 m quadrats. Almost all causes of deadwood creation varied in importance between large-diameter trees and small-diameter trees. Biomass of standing stems and deadwood had weak inverse distributions, reflecting the long period of time required for trees to reach large diameters following antecedent tree mortalities and the centennial scale time required for deadwood decomposition. Conclusion Old-growth forests contain large stores of biomass in living trees, as well as in snag and deadwood biomass pools that are stable long after tree death. Ignoring biomass (or carbon) in deadwood pools can lead to substantial underestimations of sequestration and stability.
... Several species have been described, with body mass reconstructions ranging from 17 to 50 kg (approximately 37-110 lbs.). A paleoenvironmental study reconstructed the habitat of Proconsul to be a dense, closed-canopy tropical forest (Michel et al. 2014). One of the most interesting questions about this taxon is whether or not it possessed a tail, a lack of which is an important characteristic for distinguishing living apes from Old World monkeys. ...
Chapter
Full-text available
Learning Objectives • Understand the major trends in primate evolution from the origin of primates to the origin of our own species • Learn about primate adaptations and how they characterize major primate groups • Discuss the kinds of evidence that anthropologists use to find out how extinct primates are related to each other and to living primates • Recognize how the changing geography and climate of Earth have influenced where and when primates have thrived or gone extinct The first fifty million years of primate evolution was a series of adaptive radiations leading to the diversification of the earliest lemurs, monkeys, and apes. The primate story begins in the canopy and understory of conifer-dominated forests, with our small, furtive ancestors subsisting at night, beneath the notice of day-active dinosaurs. From the archaic plesiadapiforms (archaic primates) to the earliest groups of true primates (euprimates), the origin of our own order is characterized by the struggle for new food sources and microhabitats in the arboreal setting. Climate change forced major extinctions as the northern continents became increasingly dry, cold, and seasonal and as tropical rainforests gave way to deciduous forests, woodlands, and eventually grasslands. Lemurs, lorises, and tarsiers-once diverse groups containing many species-became rare, except for lemurs in Madagascar where there were no anthropoid competitors and perhaps few predators. Meanwhile, anthropoids (monkeys and apes) emerged in the Old World, then dispersed across parts of the northern hemisphere, Africa, and ultimately South America. Meanwhile, the movement of continents, shifting sea levels, and changing patterns of rainfall and vegetation contributed to the developing landscape of primate biogeography, morphology, and behavior. Today's primates provide modest reminders of the past diversity and remarkable adaptations of their extinct relatives. This chapter explores the major trends in primate evolution from the origin of the Order Primates to the beginnings of our own lineage, providing a window into these stories from our ancient past.
... Tropical East Africa contained rainforest with palms and forest grasses in the highlands and a mix of deciduous broad-leaved woodland and forest in the lowlands (Collinson et al., 2009;Currano et al., 2019;Maxbauer et al., 2013;Michel et al., 2014). In southern Africa, the Cape region and eastern shores hosted humid, subtropical forests in the early Miocene, while it is thought that a "proto-savanna" had already developed in southern Namibia (Neumann & Bamford, 2015). ...
Article
Full-text available
The Miocene epoch (23.03-5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned toward modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval-the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO 2 , and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO 2 (∼400-600 ppm), the MCO has been suggested as a particularly appropriate analog for future climate scenarios, and for assessing the predictive accuracy of numerical climate models-the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re-interpretation of proxies, which might mitigate the model-data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here, we review the state-of-the-art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modeling studies. Plain Language Summary During the Miocene time period (∼23-5 million years ago), Planet Earth looked similar to today, with some important differences: the climate was generally warmer and highly variable, while atmospheric CO 2 was not much higher. Continental-sized ice sheets were only present on Antarctica, but not in the northern hemisphere. The continents drifted to near their modern-day positions, and plants and animals evolved into the many (near) modern species. Scientists study the Miocene because present-day and projected future CO 2 levels are in the same range as those reconstructed for the Miocene. Therefore, if we can understand climate changes and their biotic responses from the Miocene past, we are able to better predict current and future global changes. By comparing Miocene climate reconstructions from fossil and chemical data to climate simulations produced by computer models, scientists are able to test their understanding of the Earth system under higher CO 2 and warmer conditions than those of today. This helps in constraining future warming scenarios for the coming STEINTHORSDOTTIR ET AL. Key Points: • Miocene floras, faunas, and paleogeography were similar to today and provide plausible analogs for future climatic warming • The Miocene saw great dynamism in biotic and climate systems, but the reasons for these shifts are still not well understood • The pCO 2-temperature-ice relationships during major Miocene climate oscillations and transitions warrant further research
... The conspicuous absence of cercopithecoids from early Miocene sites in Western Kenya with otherwise diverse catarrhine communities is well documented (Benefit, 2000;Cote, 2008;Benefit and McCrossin, 2010). Some authors have suggested that early Old World monkeys had a preference for more open environments than the majority of apes and stem catarrhines (Benefit and McCrossin, 2010), resulting in their absence from sites like the Hiwegi Formation on Rusinga Island, where heterogeneous environments included woodland and forested biomes (Collinson et al., 2009;Maxbauer et al., 2013;Michel et al., 2014). The depositional environment of Buluk indicates a river system with an extensive floodplain (Watkins, 1989), and the presence of fossilized tree trunks up to 1 m in diameter suggests the presence of some woody cover (Watkins, 1989;Leakey et al., 2011). ...
Article
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.
... They were pronograde tree-climbers. They have been found associated with both tropical rain forest and tropical woodland environments [1][2][3][4][5] and appear to have been mainly fruit eaters [4] and arboreal within these habitats [5]. ...
Article
Full-text available
The relationship of evolution with diet and environment can provide insights into modern disease. Fossil evidence shows apes and early human ancestors were fruit‐eaters living in environments with strongly seasonal climates. Rapid cooling at the end of the middle Miocene (15‐12Ma: millions of years ago) increased seasonality in Africa and Europe, and ape survival may be linked with a mutation in uric acid metabolism. Climate stabilized in the later Miocene and Pliocene (12‐5Ma), and fossil apes and early hominins were both adapted for life on ground and in trees. Around 2.5Ma, early species of Homo introduced more animal products into their diet, and this coincided with developing bipedalism, stone tool technology and increase in brain size. Early species of Homo such as Homo habilis still lived in woodland habitats, and the major habitat shift in human evolution occurred at 1.8Ma with the origin of Homo erectus. Homo erectus had increased body size, greater hunting skills and a diet rich in meat, control of fire and understanding about cooking food, and moved from woodland to savanna. Group size may also have increased at the same time, facilitating the transmission of knowledge from one generation to the next. The earliest fossils of Homo sapiens appeared about 300kyr, but they had separated from Neanderthals by 480kyr or earlier. Their diet shifted towards grain‐based foods about 100kyr ago, and settled agriculture developed about 10kyr ago. This pattern remains for many populations to this day and provides important insights into current burden of lifestyle diseases.
Article
Full-text available
Premise: Reconstructing plant canopy light environment and architecture from the fossil record includes proxies derived from cell wall undulation, cell size, and carbon isotopes. All approaches assume that plant taxa will respond predictably to changes in light environments. However, most species-level studies looking at cell wall undulation only consider "sun" or "shade" leaves, therefore we lack a fully quantitative taxon-specific method. Methods: We quantify the response of cell wall undulation, cell size, and carbon isotopes of Platanus occidentalis using two different experimental setups: (1) two growth chambers at low and high light and (2) a series of outdoor growth experiments using green and black shade cloth at different densities. We then developed and applied a proxy for daily light integral (DLI) to fossil Platanites leaves from two early Paleocene floras from the San Juan Basin in New Mexico. Results: All traits responded to light environment. Cell wall undulation was the most useful trait for reconstructing DLI in the geological record. Median reconstructed DLI from early Paleocene leaves was ~44 mol m-2 d-1, with values ranging from 28 - 54 mol m-2 d-1. Conclusions: Cell wall undulation of P. occidentalis is a robust, quantifiable measurement of light environment that can be used to reconstruct paleo-light environment from fossil leaves. The distribution of high DLI values from fossil leaves may provide information on canopy architecture; indicating that either (1) most of the canopy mass is within the upper portion of the crown or (2) leaves exposed to more sunlight are preferentially preserved. This article is protected by copyright. All rights reserved.
Conference Paper
Background/Question/Methods Forest stands undergo long-term changes in composition, structure, and function as a consequence of: internal processes related to demography and competitive interactions; disturbances at a variety of scales, frequencies and causes, and changes in basic environmental conditions, such as climate. The long time periods involved make the quantitative study of many aspects of forest development difficult. As a consequence, there is much reliance on short-term observations, studies of chronosequences, and modeling in the development and testing ecological theory. There also seems to be an unfortunate tendency for model outputs to be accepted as real, rather than viewed as working hypotheses. Results/Conclusions Ultimately real-world data are necessary to critically test ecological theory related to forest tree demography and long-term changes in the structure and function of ecosystems. Long-term observations of large forest plots are the primary source for these data. Such plots not only allow us to critically test theory but also stimulate the development of new theoretical constructs. They can also provide early warming systems for important but subtle changes in demography that are occurring as a result of climate change. A global system of permanent sample plots in natural forest ecosystems is needed that will provide representative data on demographic processes, with particular emphasis on rates, causes, and patterns of mortality, and on key structural and functional attributes of these ecosystems. A forest plot network might well be linked to the National Ecological Observatory (NEON) program in the United States. Challenges and important attributes of such a plot network will be discussed, using examples drawn from our experiences in the forests of the Pacific Northwest.
Article
The lower Miocene of Rusinga Island (Lake Victoria, Kenya) is best known for its vertebrate fossil assemblage but the multiple stratigraphic intervals with well-preserved fossil leaves have received much less attention. The Hiwegi Formation has three fossil leaf-rich intervals, which span the entire formation from oldest to youngest: Kiahera Hill, R5, and R3. Here, we describe new fossil collections from Kiahera Hill and R3 and compared these floras to previous work from R5, as well as modern African floras. The oldest flora at Kiahera Hill was most similar to modern tropical rainforests or tropical seasonal forests and reconstructed as a warm and wet, closed forest. This was followed by a relatively dry and open environment at R5, which was reconstructed as a woodland to open tropical seasonal forest. The youngest flora at R3 was most similar to modern tropical seasonal forests and was reconstructed as a warm and wet spatially heterogenous forest. Floral composition of all three floras differed, but the Kiahera Hill and R3 floras were more similar to each other than either flora was to the R5 flora. The Kiahera Hill flora had few monocots or herbaceous taxa, was dominated by large leaves, and had higher species richness and greater evenness than the R3 flora. Our work, coupled with previous studies, suggests that the R3 landscape consisted of both closed forest areas and open areas with seasonal ponding. The absence of morphotypes from the R5 flora that were present in the Kiahera Hill and R3 floras provides evidence for local extirpation during the R5 time interval. Thus, this work indicates that the Hiwegi Formation on Rusinga Island samples multiple environments ranging from more closed tropical forests to more open woodlands in the Early Miocene and provides important context for the evolution and habitat preference of early apes.
Article
A 50 m thick stratigraphic section at Ngira, near Karungu on the shore of Lake Victoria in western Kenya, documents the early Miocene paleoenvironments of the area. The basal Ngira paleosol is a 7.6 m thick, oxisolic Vertisol that formed during a prolonged period of pedogenesis; it began as a smectite-dominated Vertisol that was later overprinted through polypedogenesis to become a kaolinitic paleosol highly depleted of all base cations, with abundant Fe concentrations and depletions, and complexly variegated color mottle patterns that reflect extensive ferruginization. Paleoenvironmental reconstructions using bulk geochemistry indicate warm and wet conditions during development of the Ngira paleosol that probably supported a tropical seasonal forest on a stable upland surface for 10s to 100s of thousands of years. Following this long-lived stable landscape, rapid subsidence, perhaps associated with slip on a high-angle fault associated with the onset or progression of the Nyanza Rift and/or the development and eruptive history of the nearby Kisingiri volcano, buried the paleosol and formed a nascent lake basin that experienced multiple transgressions and regressions. During one interval of regression, fluvial sandstones and conglomerates were deposited along with fluvio-lacustrine sandstones and claystones that include weakly developed paleosols. These weakly-developed paleosols indicate a relatively dry paleoenvironment with seasonal precipitation, and probably a shrubland/bushland or riparian forest habitat. Important terrestrial and aquatic vertebrate fossils are primarily preserved within fluvial and fluvio-lacustrine deposits, indicating that the terrestrial Karungu fauna lived in a relatively dry and open habitat. This study demonstrates polypedogenesis and inferences regarding onset of abrupt tectonic activity in the early Miocene in equatorial eastern Africa, and emphasizes the contrasts between landscape stability of the Ngira paleosol and the poorly developed soils in the fluvio-lacustrine facies.
Article
The ecological preferences of ruminant artiodactyls are commonly used to reconstruct the paleoenvironment of Neogene fossil localities throughout Africa. However, comparatively little research has focused on the ecology of ruminant artiodactyls from the Miocene of Africa. Here, we contribute new molar mesowear and hypsodonty data for the ruminant artiodactyls from the early and middle Miocene of Kenya and Uganda. Macroscopic dental characteristics of 608 tragulids, stem pecorans, giraffoids, and bovids dated to between 20 and 13.7 Ma were analyzed. Our hypsodonty results reveal that, whereas tragulids remain brachydont throughout the early and middle Miocene, pecoran ruminants experience an increase in hypsodonty due to the appearance of high-crowned bovids and climacoceratids that migrate into eastern Africa in the middle Miocene. Results from dental mesowear analysis suggest that all tragulids and pecorans were likely browsers, with only one taxon showing mesowear values that overlap with both browsers and mixed feeders in both the upper and lower molars (Canthumeryx sirtensis). None of the taxa analyzed had mesowear scores indicative of a grazing diet. Surprisingly, middle Miocene bovids and climacoceratids, despite possessing gross tooth morphologies adapted to abrasive diets, were largely utilizing a browsing diet. Although the early and middle Miocene habitats of eastern Africa were likely very heterogenous, none of the ruminant artiodactyls present in these habitats is interpreted as having incorporated grasses into their diet in significant quantities.
Article
Full-text available
Paleosols (fossil soils) are abundant in the sedimentary record and reflect, at least in part, regional paleoclimate. Paleopedology thus offers a great potential for elucidating high resolution, deep-time paleoclimate records. However, many fossil soils did not equilibrate with climate prior to burial and instead dominantly express physical and chemical features reflective of other soil forming factors. Current models that use elemental oxides for climate reconstruction bypass the issue of soil-climate equilibration by restricting datasets to narrow ranges of soil properties, soil-forming environments and mean annual precipitation (MAP) and mean annual temperature (MAT). Here we evaluate a data-driven paleosol-paleoclimate model (PPM 1.0) that uses subsoil geochemistry to test the ability of soils from wide-ranging environments to predict MAP and MAT as a joint response with few initial assumptions. The PPM 1.0 was developed using a combined partial least squares regression (PLSR) and a nonlinear spline on 685 mineral soil B horizons currently forming under MAP ranging from 130 to 6900 mm and MAT ranging from 0 to 27 °C. The PLSR results on 11 major and minor oxides show that four linear combinations of these oxides (Regressors 1-4), akin to classic oxide ratios, have potential for predicting climate. Regressor 1 correlates with increasing MAP and MAT through Fe oxidation, desilication, base loss and residual enrichment. Regressor 2 correlates with MAT through temperature-dependent dissolution of Na-and K-bearing minerals. Regressor 3 correlates with increasing MAP through decalcification and retention of Si. Regres-sor 4 correlates with increasing MAP through Mg retention in mafic-rich parent material. The nonlinear spline model fit on Regressors 1 to 4 results in a Root Mean Squared Error (RMSE MAP) of 228 mm and RMSE MAT of 2.46 °C. PPM 1.0 model simulations result in Root Mean Squared Predictive Error (RMSPE MAP) of 512 mm and RMSPE MAT of 3.98 °C. The RMSE values are lower than some preexisting MAT models and show that subsoil weathering processes operating under a wide range of soil forming factors possess climate prediction potential, which agrees with the state-factor model of soil formation. The nonlinear, multivariate model space of PPM 1.0 more accurately reflects the complex and nonlinear nature of many weathering processes as climate varies. This approach is still limited as it was built using data primarily from the conterminous USA and does not account for effects of diagenesis. Yet, because it is calibrated over a broader range of climatic variable space than previous work, it should have the widest array of potential applications. Furthermore, because it is not dependent on properties that may be poorly preserved in buried paleosols, the PPM 1.0 model is preferable for reconstructing deep time climate transitions. In fact, previous studies may have grossly underestimated paleo-MAP for some paleosols.
Article
Full-text available
The evolution of C4 grassland ecosystems in eastern Africa has been intensely studied because of the potential influence of vegetation on mammalian evolution, including that of our own lineage, hominins. Although a handful of sparse vegetation records exists from middle and early Miocene terrestrial fossil sites, there is no comprehensive record of vegetation through the Neogene. Here we present a vegetation record spanning the Neogene and Quaternary Periods that documents the appearance and subsequent expansion of C4 grasslands in eastern Africa. Carbon isotope ratios from terrestrial plant wax biomarkers deposited in marine sediments indicate constant C3 vegetation from ∼24 Ma to 10 Ma, when C4 grasses first appeared. From this time forward, C4 vegetation increases monotonically to present, with a coherent signal between marine core sites located in the Somali Basin and the Red Sea. The response of mammalian herbivores to the appearance of C4 grasses at 10 Ma is immediate, as evidenced from existing records of mammalian diets from isotopic analyses of tooth enamel. The expansion of C4 vegetation in eastern Africa is broadly mirrored by increasing proportions of C4-based foods in hominin diets, beginning at 3.8 Ma in Australopithecus and, slightly later, Kenyanthropus. This continues into the late Pleistocene in Paranthropus, whereas Homo maintains a flexible diet. The biomarker vegetation record suggests the increase in open, C4 grassland ecosystems over the last 10 Ma may have operated as a selection pressure for traits and behaviors in Homo such as bipedalism, flexible diets, and complex social structure.
Article
Full-text available
Paleosols (fossil soils) are abundant in the sedimentary record and reflect, at least in part, regional paleoclimate. Paleopedology thus offers a great potential for elucidating high resolution, deep-Time paleoclimate records. However, many fossil soils did not equilibrate with climate prior to burial and instead dominantly express physical and chemical features reflective of other soil forming factors. Current models that use elemental oxides for climate reconstruction bypass the issue of soil-climate equilibration by restricting datasets to narrow ranges of soil properties, soil-forming environments and mean annual precipitation (MAP) and mean annual temperature (MAT). Here we evaluate a data-driven paleosol-paleoclimate model (PPM1.0) that uses subsoil geochemistry to test the ability of soils from wide-ranging environments to predict MAP and MAT as a joint response with few initial assumptions. The PPM1.0 was developed using a combined partial least squares regression (PLSR) and a nonlinear spline on 685 mineral soil B horizons currently forming under MAP ranging from 130 to 6900 mm and MAT ranging from 0 to 27 °C. The PLSR results on 11 major and minor oxides show that four linear combinations of these oxides (Regressors 1-4), akin to classic oxide ratios, have potential for predicting climate. Regressor 1 correlates with increasing MAP and MAT through Fe oxidation, desilication, base loss and residual enrichment. Regressor 2 correlates with MAT through temperature-dependent dissolution of Na-and K-bearing minerals. Regressor 3 correlates with increasing MAP through decalcification and retention of Si. Regressor 4 correlates with increasing MAP through Mg retention in mafic-rich parent material. The nonlinear spline model fit on Regressors 1 to 4 results in a Root Mean Squared Error (RMSEMAP) of 228 mm and RMSEMAT of 2.46 °C. PPM1.0 model simulations result in Root Mean Squared Predictive Error (RMSPEMAP) of 512mmand RMSPEMAT of 3.98 °C. The RMSE values are lower than some preexisting MAT models and show that subsoil weathering processes operating under a wide range of soil forming factors possess climate prediction potential, which agrees with the state-factor model of soil formation. The nonlinear, multivariate model space of PPM1.0 more accurately reflects the complex and nonlinear nature of many weathering processes as climate varies. This approach is still limited as it was built using data primarily from the conterminous USA and does not account for effects of diagenesis. Yet, because it is calibrated over a broader range of climatic variable space than previous work, it should have the widest array of potential applications. Furthermore, because it is not dependent on properties that may be poorly preserved in buried paleosols, the PPM1.0 model is preferable for reconstructing deep time climate transitions. In fact, previous studies may have grossly underestimated paleo-MAP for some paleosols.
Poster
Full-text available
The poster that I made for my school’s ”Celebration of Student Research Day”. Really similar to my SE-GSA poster, but this one is a lot more focused towards geochemistry, rather than stratigraphy.
Chapter
Ancient environmental and sea-level changes are very likely to have played key roles in primate speciation, extinction, adaptation, and dispersal. Most modern primates are ecologically dependent on trees and inhabit tropical environments, and the same was true for many extinct primates. In the warm Paleocene and Eocene when the tropical broadleaf forest biome extended to high latitudes, primates inhabited North America and northern Eurasia. Ranges then contracted into lower latitudes in the Eocene and Oligocene when global cooling caused a commensurate reduction in suitable tree cover, only to expand again in the Miocene, when most primates across Africa, Eurasia, and South America exploited diverse forest and woodland environments, which may have been very different to those observed in similar regions today. By the end of the Miocene through to the Pleistocene, grassland expansion allowed more terrestrial and open habitat primates to radiate, although most retained some ecological dependence on trees. Sea-level changes occurring since the origin of primates, causing events such as the closure of the eastern Tethys Sea, appearance of the Isthmus of Panama, and shifts in Southeast Asian archipelagos, influenced primate dispersal and diversification. Changes to ocean circulation caused by sea-level change may have impacted global climate, which in turn would have altered primate environments.
Article
The modern vegetation of East Africa is a complex mosaic of rainforest patches; small islands of tropic-alpine vegetation; extensive savannas, ranging from almost pure grassland to wooded savannas; thickets; and montane grassland and forest. Here I trace the evolution of these vegetation types through the Cenozoic. Paleogene East Africa was most likely geomorphologically subdued and, as the few Eocene fossil sites suggest, a woodland in a seasonal climate. Woodland rather than rainforest may well have been the regional vegetation. Mountain building started with the Oligocene trap lava flows in Ethiopia, on which rainforest developed, with little evidence of grass and none of montane forests. The uplift of the East African Plateau took place during the middle Miocene. Fossil sites indicate the presence of rainforest, montane forest and thicket, and wooded grassland, often in close juxtaposition, from 17 to 10 Ma. By 10 Ma, marine deposits indicate extensive grassland in the region and isotope analysis indicates that this was a C3 grassland. In the later Miocene rifting, first of the western Albertine Rift and then of the eastern Gregory Rift, added to the complexity of the environment. The building of the high strato-volcanos during the later Mio-Pliocene added environments suitable for tropic-alpine vegetation. During this time, the C3 grassland was replaced by C4 savannas, although overall the extent of grassland was reduced from the mid-Miocene high to the current low level. Lake-level fluctuations during the Quaternary indicate substantial variation in rainfall, presumably as a result of movements in the intertropical convergence zone and the Congo air boundary, but the impact of these fluctuations on the vegetation is still speculative. I argue that, overall, there was an increase in the complexity of East African vegetation complexity during the Neogene, largely as a result of orogeny. The impact of Quaternary climatic fluctuation is still poorly understood.
Article
Full-text available
Paleogene greenhouse climate equability has long been a paradox in paleoclimate research. However, recent developments in proxy and modeling methods have suggested that strong seasonality may be a feature of at least some greenhouse periods. Here we present the first multi-proxy record of seasonal temperatures during the Paleogene from paleofloras, paleosol geochemistry, and carbonate clumped isotope thermometry in the Green River Basin (Wyoming, USA). These combined temperature records allow for the reconstruction of past seasonality in the continental interior, which shows that temperatures were warmer in all seasons during the peak early Eocene climatic optimum and that the mean annual range of temperature was high, similar to the modern value (~ 26 °C). Proxy data and downscaled Eocene regional climate model results suggest amplified seasonality during greenhouse events. Increased seasonality reconstructed for the early Eocene is similar in scope to the higher seasonal range predicted by downscaled climate model ensembles for future high-CO2 emissions scenarios. Overall, these data and model comparisons have substantial implications for understanding greenhouse climates in general, and may be important for predicting future seasonal climate regimes and their impacts in continental regions.
Chapter
Fluvial systems are highly sensitive to changes in climatic conditions. Hence, fluvial sedimentary records provide important hints on palaeoclimatic ambit. Some commonly practiced potential climatic resources in connection to fluvial realm, such as paleosols, floodplain sediments, climate-sensitive lithologies (coal, evaporite, eolianite), and palaeoecological components (fossil plants and trace fossils) have been put forward for discussion; along with their methods of application, both qualitative and quantitative, off-target in a brief way. Four Phanerozoic sedimentary intervals from India have been chosen to exemplify how to decode palaeoclimatic signals from fluviatile deposits: Early Cretaceous (1) Bhuj Formation, Kutch Basin in western India and (2) Basal Siliciclastic Formation, Cauvery Basin in southern India, (3) Mio–Pliocene Siwalik Group, Darjeeling, Sub-Himalaya in north-eastern India, and (4) Late Permian Raniganj Formation with Early Triassic Panchet Formation in Raniganj Basin, eastern India. Palaeoclimatic investigation on riverine palaeosols of Bhuj Formation (Kutch Basin) estimates mean annual precipitation (MAP) and mean annual temperature (MAT) yielding values of 417-1381 mm/year and average 12°C, respectively, with moderate to high soil maturity. Comparable results obtained from Basal Siliclastic Formation (Cauvery Basin) showing 844-1060 mm/year (MAP) and average 12.5°C (MAT) with moderate degree of weathering. Floodplain sediments of both the formations bear flora besides coal stringers, petrified wood fragments, rhizoconcretions, rootlets, and trace fossils within estuarine mudflat of the Bhuj Formation. An overall apparently warm temperate humid palaeoclimate is implied in the case of both. The present study also strives to concentrate over the monsoonal intensification and transformation from C3 to C4 vegetation along the entire 2000 km-long exposure belt of the Mio–Pliocene of Siwalik basin. The geochemical characteristics from foreland molasse deposits taken into cognizance to check the spatial trends in climate change has largely been meted out through the Darjeeling Sub-Himalaya, West Bengal. The spatial variation in precipitation rate and temperature along with ¹³C enrichment from west to east attests the modern trend and also elicit the present Himalayan Mountain Belt configuration. Predominantly fluvial Raniganj Formation (with abundance of coal) and Panchet Formation (devoid of coal) encompassing the Permo-Triassic transition in Raniganj Basin, West Bengal, indicate significant variations in palaeoclimate reflected in their lithology and bio assemblages.
Article
A major goal in post‐synthesis evolutionary biology has been to better understand how complex interactions between traits drive movement along and facilitate the formation of distinct evolutionary pathways. I present analyses of a character matrix sampled across the haplorrhine skeleton that revealed several modules of characters displaying distinct patterns in macroevolutionary disparity. Comparison of these patterns to those in neurological development showed that early ape evolution was characterized by an intense regime of evolutionary and developmental flexibility. Shifting and reduced constraint in apes was met with episodic bursts in phenotypic innovation that built a wide array of functional diversity over a foundation of shared developmental and anatomical structure. Shifts in modularity drove dramatic evolutionary changes across the ape body plan in two distinct ways: 1) an episode of relaxed integration early in hominoid evolution coincided with bursts in evolutionary rate across multiple character suites; 2) the formation of two new trait modules along the branch leading to chimps and humans preceded rapid and dramatic evolutionary shifts in the carpus and pelvis. Changes to the structure of evolutionary mosaicism may correspond to enhanced evolvability that has a ‘preadaptive’ effect by catalyzing later episodes of dramatic morphological remodeling. This article is protected by copyright. All rights reserved
Article
Full-text available
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 alternating 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.
Article
Full-text available
The relationship between species richness and ecosystem function, as measured by productivity or biomass, is of long-standing theoretical and practical interest in ecology. This is especially true for forests, which represent a majority of global biomass, productivity and biodiversity. Here, we conduct an analysis of relationships between tree species richness, biomass and productivity in 25 forest plots of area 8–50 ha from across the world. The data were collected using standardized protocols, obviating the need to correct for methodological differences that plague many studies on this topic. We found that at very small spatial grains (0.04 ha) species richness was generally positively related to productivity and biomass within plots, with a doubling of species richness corresponding to an average 48% increase in productivity and 53% increase in biomass. At larger spatial grains (0.25 ha, 1 ha), results were mixed, with negative relationships becoming more common. The results were qualitatively similar but much weaker when we controlled for stem density: at the 0.04 ha spatial grain, a doubling of species richness corresponded to a 5% increase in productivity and 7% increase in biomass. Productivity and biomass were themselves almost always positively related at all spatial grains. Synthesis. This is the first cross-site study of the effect of tree species richness on forest biomass and productivity that systematically varies spatial grain within a controlled methodology. The scale-dependent results are consistent with theoretical models in which sampling effects and niche complementarity dominate at small scales, while environmental gradients drive patterns at large scales. Our study shows that the relationship of tree species richness with biomass and productivity changes qualitatively when moving from scales typical of forest surveys (0.04 ha) to slightly larger scales (0.25 and 1 ha). This needs to be recognized in forest conservation policy and management.
Article
Full-text available
Estimates of past precipitation are of broad interest for many areas of inquiry, including reconstructions of past environments and topography, climate modeling, and ocean circulation studies. The shapes and sizes of living leaves are highly sensitive to moisture conditions, and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators. Most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations. However, when tested on extant forests, this method has consistently overestimated precipitation. We present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set. The significant relationship that results, in addition to having value for paleoclimatic reconstruction, refines understanding of the long-observed positive relationship between leaf area and precipitation. Seven precipitation estimates for the Eocene of the Western United States are revised as lower than previously published but remain far wetter than the same areas today. Abundant moisture may have been an important factor in maintaining warm, frost-free conditions in the Eocene because of the major role of water vapor in retaining and transporting atmospheric heat.
Article
Full-text available
Precise estimates of past temperatures are critical for understanding the evolution of organisms and the physical biosphere, and data from continental areas are an indispensable com- plement to the marine record of stable isotopes. Climate is considered to be a primary selective force on leaf morphology, and two widely used methods exist for estimating past mean annual temperatures from assemblages of fossil leaves. The first approach, Leaf Margin Analysis, is uni- variate, based on the positive correlation in modern forests between mean annual temperature and the proportion of species in a flora with untoothed leaf margins. The second approach, known as the Climate-Leaf Analysis Multivariate Program, is based on a modern data set that is multivariate. I argue here that the simpler, univariate approach will give paleotemperature estimates at least as precise as the multivariate method because (1) the temperature signal in the multivariate data set is dominated by the leaf-margin character; (2) the additional characters add minimal statistical precision and in practical use do not appear to improve the quality of the estimate; (3) the predictor samples in the univariate data set contain at least twice as many species as those in the multivariate data set; and (4) the presence of numerous sites in the multivariate data set that are both dry and extremely cold depresses temperature estimates for moist and nonfrigid paleofloras by about 2 8C, unless the dry and cold sites are excluded from the predictor set. New data from Western Hemisphere forests are used to test the univariate and multivariate meth- ods and to compare observed vs. predicted error distributions for temperature estimates as a func- tion of species richness. Leaf Margin Analysis provides excellent estimates of mean annual tem- perature for nine floral samples. Estimated temperatures given by 16 floral subsamples are very close both to actual temperatures and to the estimates from the samples. Temperature estimates based on the multivariate data set for four of the subsamples were generally less accurate than the estimates from Leaf Margin Analysis. Leaf-margin data from 45 transect collections demonstrate that sampling of low-diversity floras at extremely local scales can result in biased leaf-margin per- centages because species abundance patterns are uneven. For climate analysis, both modern and fossil floras should be sampled over an area sufficient to minimize this bias and to maximize re- covered species richness within a given climate.
Article
Full-text available
Leaf mass per area (MA) is a central ecological trait that is intercorrelated with leaf life span, photosynthetic rate, nutrient concentration, and palatability to herbivores. These coordinated variables form a globally convergent leaf economics spectrum, which represents a general continuum running from rapid resource acquisition to maximized resource retention. Leaf economics are little studied in ancient ecosystems because they cannot be directly measured from leaf fossils. Here we use a large extant data set (65 sites; 667 species-site pairs) to develop a new, easily measured scaling relationship between petiole width and leaf mass, normalized for leaf area; this enables MA estimation for fossil leaves from petiole width and leaf area, two variables that are commonly measurable in leaf compression floras. The calibration data are restricted to woody angiosperms exclusive of monocots, but a preliminary data set (25 species) suggests that broad-leaved gymnosperms exhibit a similar scaling. Application to two well-studied, classic Eocene floras demonstrates that MA can be quantified in fossil assemblages. First, our results are consistent with predictions from paleobotanical and pa- leoclimatic studies of these floras. We found exclusively low-MA species from Republic (Washington, U.S.A., 49 Ma), a humid, warm-temperate flora with a strong deciduous component among the an- giosperms, and a wide MA range in a seasonally dry, warm-temperate flora from the Green River Formation at Bonanza (Utah, U.S.A, 47 Ma), presumed to comprise a mix of short and long leaf life spans. Second, reconstructed MA in the fossil species is negatively correlated with levels of insect herbivory, whether measured as the proportion of leaves with insect damage, the proportion of leaf area removed by herbivores, or the diversity of insect-damage morphotypes. These correlations are consistent with herbivory observations in extant floras and they reflect fundamental trade-offs in plant-herbivore associations. Our results indicate that several key aspects of plant and plant-animal ecology can now be quantified in the fossil record and demonstrate that herbivory has helped shape the evolution of leaf structure for millions of years.
Article
Full-text available
Three main features of paleosols are useful for distinguishing them from enclosing rocks: root traces, soil horizons, and soil structures. Fossil root traces are best preserved in formerly waterlogged paleosols. In oxidized paleosols their organic matter may not be preserved, but root traces can be recognized by their irregular, tubular shape, and by their downward tapering and branching. Often root traces are crushed like a concertina, because of compaction of the surrounding paleosol during burial. The top of a paleosol may be recognized where root traces and other trace fossils are truncated by an erosional surface. Root and other trace fossils are not useful for recognizing paleosols of middle Ordovician and older age, since large land organisms of such antiquity are currently unknown. Soil horizons usually have more gradational boundaries than seen in sedimentary layering. Commonly these gradational changes are parallel to the truncated upper surface of the paleosol. Some kinds of paleosol horizons are so lithologically distinct that they have been given special names; for example, cornstone (Bk) and ganister (E); the letter symbols are equivalent horizon symbols of soil science. Compared to sedimentary layering, metamorphic foliation, and igneous crystalline textures, soil structure appears massive, hackly, and jointed. The basic units of soil structure (peds) are defined by a variety of modified (for example, iron-stained or clayey) surfaces (cutans). Peds may be granular, blocky, prismatic, columnar, or platy in shape. Concretions, nodules, nodular layers, and crystals are also part of the original soil structure of some paleosols. Complications to be considered during field recognition of paleosols include erosion of parts of the profile, overlap of horizons of different paleosols, development of paleosols on materials eroded from preexisting paleosols, and the development of paleosols under successive and different regimes of weathering.
Article
Full-text available
We describe 28 fossil plant morphotypes from the Aspen Shale flora (Cretaceous: middle to late Albian) in southwestern Wyoming. This impression flora includes 6 ferns, 1 sphenopsid, 2 conifers, 17 dicotyledonous angiosperm (dicot) leaves and 2 dicot reproductive structures. The Aspen Shale megaflora is most similar to that of Subzone IIB of the Potomac Group of the eastern United States. Analysis of the Aspen Shale sedimentology and botanical composition shows occupation of open, paludal sites by a succession of progressively more complex plant communities. Like other middle Cretaceous floras, these data suggest that early angiosperms were weedy, herbaceous to shrubby, early successional competitors to ferns on open substrates. The description and illustration of the Aspen Shale morphotypes is presented as an example of how an entire flora can be described and analyzed before full taxonomic determinations have been made.
Chapter
Full-text available
Hominoids, or taxa identified as hominoids, are known from much of Africa, Asia, and Europe since the Late Oligocene. The earliest taxa, from Africa, resemble extant hominoids but share with them mainly primitive characters. Middle and Late Miocene taxa are clearly hominoids, and by the end of the Middle Miocene most can be attributed to either the pongine (Pongo) or hominine (African ape and human) clade. Interestingly, there is no fossil record of the hylobatid clade (gibbons and siamangs). Miocene hominoids experienced a series of dispersals between Africa, Europe, and Asia that mirror those experienced by many other contemporaneous land mammals. These intercontinental movements were made possible by the appearance of land bridges, changes in regional and global climatic conditions, and evolutionary innovations. Most of the attributes that define the hominids evolved in the expansive subtropical zone that was much of Eurasia. Hominines and pongines diverge from each other in Eurasia, and the final Miocene dispersal brings the hominine clade to Africa and the pongine clade to Southeast Asia. Having moved south with the retreating subtropics, hominines and pongines finally diverge in situ into their individual extant lineages.
Article
Full-text available
Large-diameter trees dominate the structure, dynamics and function of many temperate and tropical forests. Although both scaling theory and competition theory make predictions about the relative composition and spatial patterns of large-diameter trees compared to smaller diameter trees, these predictions are rarely tested. We established a 25.6 ha permanent plot within which we tagged and mapped all trees ≥1 cm dbh, all snags ≥10 cm dbh, and all shrub patches ≥2 m(2). We sampled downed woody debris, litter, and duff with line intercept transects. Aboveground live biomass of the 23 woody species was 507.9 Mg/ha, of which 503.8 Mg/ha was trees (SD = 114.3 Mg/ha) and 4.1 Mg/ha was shrubs. Aboveground live and dead biomass was 652.0 Mg/ha. Large-diameter trees comprised 1.4% of individuals but 49.4% of biomass, with biomass dominated by Abies concolor and Pinus lambertiana (93.0% of tree biomass). The large-diameter component dominated the biomass of snags (59.5%) and contributed significantly to that of woody debris (36.6%). Traditional scaling theory was not a good model for either the relationship between tree radii and tree abundance or tree biomass. Spatial patterning of large-diameter trees of the three most abundant species differed from that of small-diameter conspecifics. For A. concolor and P. lambertiana, as well as all trees pooled, large-diameter and small-diameter trees were spatially segregated through inter-tree distances
Article
Full-text available
A paratropical floodplain forest in southern Mexico was investigated to determine the effect of heterogeneity within the standing vegetation on the taxonomic composition of the accumulating plant litter. Twelve study sites over 20 km of the Río San Pedro were sampled. Four subenvironments of the floodplain were defined on topography, geomorphology, and distance from the channel. Litter samples collected from the channel or in low-lying areas close to the channel (forebanks) generally show low species richness and are homogenous throughout the study area. Litter samples taken from levees and overbank facies (back-levees) are more heterogeneous, species-rich, and tend to reflect the local flora with greater accuracy than do channel samples. This analysis of modern samples analogous to paleobotanical collections from rocks of fluvial origin indicates that paleofloras sampled for reconstructing regional paleoecology and making inferences regarding paleoclimate will be improved by multiple sampling from a range of different subenvironments.
Article
Full-text available
Plant communities of the geologic past can be reconstructed with high fidelity only if they were preserved in place in an instant in time. Here we report such a flora from an early Permian (ca. 298 Ma) ash-fall tuff in Inner Mongolia, a time interval and area where such information is filling a large gap of knowledge. About 1,000 m(2) of forest growing on peat could be reconstructed based on the actual location of individual plants. Tree ferns formed a lower canopy and either Cordaites, a coniferophyte, or Sigillaria, a lycopsid, were present as taller trees. Noeggerathiales, an enigmatic and extinct spore-bearing plant group of small trees, is represented by three species that have been found as nearly complete specimens and are presented in reconstructions in their plant community. Landscape heterogenity is apparent, including one site where Noeggerathiales are dominant. This peat-forming flora is also taxonomically distinct from those growing on clastic soils in the same area and during the same time interval. This Permian flora demonstrates both similarities and differences to floras of the same age in Europe and North America and confirms the distinct character of the Cathaysian floral realm. Therefore, this flora will serve as a baseline for the study of other fossil floras in East Asia and the early Permian globally that will be needed for a better understanding of paleoclimate evolution through time.
Article
Full-text available
The affinities of the Hippopotamidae are at the core of the phylogeny of Cetartiodactyla (even-toed mammals: cetaceans, ruminants, camels, suoids, and hippos). Molecular phylogenies support Cetacea as sister group of the Hippopotamidae, implying a long ghost lineage between the earliest cetaceans (approximately 53 Ma) and the earliest hippopotamids (approximately 16 Ma). Morphological studies have proposed two different sister taxa for hippopotamids: suoids (notably palaeochoerids) or anthracotheriids. Evaluating these phylogenetic hypotheses requires substantiating the poorly known early history of the Hippopotamidae. Here, we undertake an original morphological phylogenetic analysis including several "suiform" families and previously unexamined early Miocene taxa to test previous conflicting hypotheses. According to our results, Morotochoerus ugandensis and Kulutherium rusingensis, until now regarded as the sole African palaeochoerid and the sole African bunodont anthracotheriid, respectively, are unambiguously included within the Hippopotamidae. They are the earliest known hippopotamids and set the family fossil record back to the early Miocene (approximately 21 Ma). The analysis reveals that hippopotamids displayed an unsuspected taxonomic and body size diversity and remained restricted to Africa during most of their history, until the latest Miocene. Our results also confirm the deep nesting of Hippopotamidae within the paraphyletic Anthracotheriidae; this finding allows us to reconstruct the sequence of dental innovations that links advanced selenodont anthracotheriids to hippopotamids, previously a source of major disagreements on hippopotamid origins. The analysis demonstrates a close relationship between Eocene choeropotamids and anthracotheriids, a relationship that potentially fills the evolutionary gap between earliest hippopotamids and cetaceans implied by molecular analyses.
Article
Full-text available
Genomic comparisons have established the chimpanzee and bonobo as our closest living relatives. However, the intricacies of gene regulation and expression caution against the use of these extant apes in deducing the anatomical structure of the last common ancestor that we shared with them. Evidence for this structure must therefore be sought from the fossil record. Until now, that record has provided few relevant data because available fossils were too recent or too incomplete. Evidence from Ardipithecus ramidus now suggests that the last common ancestor lacked the hand, foot, pelvic, vertebral, and limb structures and proportions specialized for suspension, vertical climbing, and knuckle-walking among extant African apes. If this hypothesis is correct, each extant African ape genus must have independently acquired these specializations from more generalized ancestors who still practiced careful arboreal climbing and bridging. African apes and hominids acquired advanced orthogrady in parallel. Hominoid spinal invagination is an embryogenetic mechanism that reoriented the shoulder girdle more laterally. It was unaccompanied by substantial lumbar spine abbreviation, an adaptation restricted to vertical climbing and/or suspension. The specialized locomotor anatomies and behaviors of chimpanzees and gorillas therefore constitute poor models for the origin and evolution of human bipedality.
Article
Full-text available
New early Miocene forelimb fossils have been recovered from the Songhor and Lower Kapurtay localities in southwestern Kenya. We describe four specimens that are similar in size and functional capabilities. Their specific allocation is problematic but these forelimb specimens must belong to either Rangwapithecus gordoni or Proconsul africanus. If these new postcranial specimens should belong to R. gordoni, on the basis of size and common dental specimens found at Songhor, they represent a new elbow complex. The morphology of these fossils is anatomically and functionally similar to that of Proconsul. The proconsuloid elbow complex allows extensive forelimb rotations and is capable of performing arboreal quadrupedalism and climbing activities. No suspensory adaptations are apparent. The proconsuloid elbow complex remains a good ancestral condition for hominoid primates.
Article
Precise estimates of past temperatures are critical for understanding the evolution of organisms and the physical biosphere, and data from continental areas are an indispensable complement to the marine record of stable isotopes. Climate is considered to be a primary selective force on leaf morphology, and two widely used methods exist for estimating past mean annual temperatures from assemblages of fossil leaves. The first approach, Leaf Margin Analysis, is univariate, based on the positive correlation in modern forests between mean annual temperature and the proportion of species in a flora with untoothed leaf margins. The second approach, known as the Climate-Leaf Analysis Multivariate Program, is based on a modern data set that is multivariate. I argue here that the simpler, univariate approach will give paleotemperature estimates at least as precise as the multivariate method because (1) the temperature signal in the multivariate data set is dominated by the leaf-margin character; (2) the additional characters add minimal statistical precision and in practical use do not appear to improve the quality of the estimate; (3) the predictor samples in the univariate data set contain at least twice as many species as those in the multivariate data set; and (4) the presence of numerous sites in the multivariate data set that are both dry and extremely cold depresses temperature estimates for moist and nonfrigid paleofloras by about 2°C, unless the dry and cold sites are excluded from the predictor set. New data from Western Hemisphere forests are used to test the univariate and multivariate methods and to compare observed vs. predicted error distributions for temperature estimates as a function of species richness. Leaf Margin Analysis provides excellent estimates of mean annual temperature for nine floral samples. Estimated temperatures given by 16 floral subsamples are very close both to actual temperatures and to the estimates from the samples. Temperature estimates based on the multivariate data set for four of the subsamples were generally less accurate than the estimates from Leaf Margin Analysis. Leaf-margin data from 45 transect collections demonstrate that sampling of low-diversity floras at extremely local scales can result in biased leaf-margin percentages because species abundance patterns are uneven. For climate analysis, both modern and fossil floras should be sampled over an area sufficient to minimize this bias and to maximize recovered species richness within a given climate.
Book
Soil micromorphology deals with the microscopic study of undisturbed soil and regolith samples, making use especially of thin sections and petrographic techniques. It exists as a discipline for almost 70 years. Micromorphology is used by pedologists, quaternary geologists, sedimentologists, and since two decennia intensively by archaeologists. This book provides the state of art in the field of genetic interpretation of micromorphological features, which is not restricted to the classic genetic soil horizons, but also covers processes of soil material formation and weathering, and the results of human activities and regoliths in a wider sense. State of art in the field of genetic interpretation of micromorphological features Over 2,600 different references Written by 46 leading experts in the field.
Article
CRM (Crew Resource Management) has been widely applied in the field of aviation. Both early and recent CRM literature emphasizes that aviation personnel must be trained. During ground training courses, aviation personnel, especially flight crew members, are trained in cockpit management via verbal concepts. The final goal of CRM training course, such as IATA, the 6th generation of TEM (Threat & Error Management), is continuingly developing new knowledge and philosophy to reduce the number of aircraft incidents and accidents caused by human errors. This paper develops a CRM interactive querying model to enhance a helicopter pilot's SA (Situation Awareness) effectively. To validate this concept, after helicopter missions have been completed, the SART (Situation Awareness Rating Technique) subjective assessment method is used to evaluate the improvement of pilot's SA. Results show that interactive querying of pilots with CRM concepts can directly enhance pilots' levels of SA, and can indirectly enhance CRM.
Article
A fossilized nest found in a 17 Ma paleosol on Rusinga Island is similar in many respects to those constructed by bees. The nest consists of subellipsoidal cells arranged in paired, parallel rows, which are themselves arranged in clusters. Typical cells average approximately 6 mm by 3.5 mm, and have curved dorsal surfaces and nearly flat ventral surfaces. The nest is here referred to a new ichnospecies: Celliforma habari. The cell shape and nest architecture are most like those of modern bees of the subfamily Halictinae (Apoidea: Halictidae), and probably were constructed by bees with a societal structure that was at least communal and quite possibly more highly social. The nest suggests a subhumid to humid climate and angiosperm-dominated vegetation for Rusinga Island during Early Miocene time.
Article
A means of estimating tree diameter at breast height from stump measurements has many applications. In this paper, metric equations are derived for estimating diameters at breast height from measured stump heights for all commercial tree species in British Columbia by age class and biogeoclimatic zones. The model found best was the same one as used by Alemdag and Honer (1977) for eleven tree species from eastern and central Canada. This prediction system can be incorporated into any local volume equation to derive a tree volume prediction model based on stump diameter and stump height.
Article
Paleontological evidence demonstrates that early catarrhines (i.e., the clade comprising Old World monkeys, apes and humans) first occurred in Afro-Arabia during the Early Oligocene and were restricted to this zoogeographic region until the Early Miocene. The estimated divergence date for catarrhines and platyrrhines, based on molecular evidence, indicates that catarrhines may have had an even earlier phylogenetic history that extends back to about 40-44 Ma into the Middle Eocene. During this long period of isolation in Afro-Arabia, several major clades of catarrhines, including the Propliopithecoidea, Pliopithecoidea, Saadanioidea, Dendropithecoidea, Cercopithecoidea, and Hominoidea, originated. The Cercopithecoidea and the Hominoidea comprise all extant catarrhines, and are referred to as crown catarrhines. The Propliopithecoidea, Pliopithecoidea, Saadanioidea, and Dendropithecoidea are extinct lineages of catarrhines that diverged prior to the last common ancestor of hominoids and cercopithecoids, and are referred to as stem catarrhines.
This largely descriptive classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes: organic matter content, horizonation, redox conditions, in situ mineral alteration, illuviation of insoluble minerals/compounds, and accumulation of soluble minerals. The most prominent of these features/processes provides the key to classifying a paleosol into one of nine orders. Four of the order names are borrowed from soil Taxonomy (Histosol, Spodosol, Oxisol, Vertisol), whereas the other five order names are presented here for the first time (Calcisol, Gypsisol, Gleysol, Argillisol, Protosol). The orders may be preceded by one or more subordinate modifiers that describe other important features, should enhance communication and aid in the standardization of terminology. -from Authors
Article
The species Proconsul africanus from the early Miocene of East Africa has long been recognized from Koru (the type locality), Songhor, Rusinga Island and Mfangano Island. Comparison of the type series from Koru with specimens from Rusinga and Mfangano indicates that this material does not belong to a single species. The material from Koru and from Songhor belongs to a single species that takes the name P. africanus and which is not represented at Rusinga or Mfangano. The Rusinga and Mfangano material exhibits levels of metric variation in the teeth and postcranial skeleton that are incompatible with its recognition as one species. The larger species at Rusinga and Mfangano takes the name Proconsul nyanzae. The smaller species does not have a name available for it and is described here as a new species, Proconsul heseloni.
Article
This paper presents a review of the evolutionary relationships of the early catarrhine primates. The first stage of the analysis involves the reconstruction of the inferred ancestral morphotypes of the major groups of extant anthropoids. The introduction of the fossil taxa into the phylogenetic scheme represents the second and final stage of the analysis. The results of this cladistic analysis suggests that: (1) the parapithecids are a specialized group of basal anthropoids, (2) Oligopithecus savagei may represent the earliest recognizable catarrhine, (3) Propliopithecus (= Aegvptopithecus) and Pliopithecus apparently represent the successive sister taxa to the modern catarrhines, (4) Dendropithecus and Proconsul are best regarded as basal catarrhines of modern aspect, and (5) Victoriapithecus is a primitive cercopithecoid monkey which represents the siter taxon of the extant Old World monkeys.
Article
Fossil floras are an important source of quantitative terrestrial paleoclimate data. Many paleoclimate estimates are based on relationships observed in modern vegetation between leaf morphology and climate, such as the increase in the percentage of entire-margined species with increasing temperature and the increase in leaf size with increasing precipitation. An important question is whether these observed relationships are universal or regional; for example, recent stud- ies suggest that significant differences exist between floras from three domains: the Northern Hemi- sphere, New Zealand/Australia, and subalpine zones. Also, debate exists over which statistical models of modern data sets, univariate or multivariate, provide the most accurate estimates of pa- leoclimate. In this study, 12 foliage samples from living Bolivian forests are compared with data sets from different regions. Models based on data sets from North America and Japan, namely the Climate-Leaf Analysis Multivariate Program (CLAMP) data set of J. A. Wolfe, and from east Asia produce reasonably accurate estimates of temperature and precipitation, suggesting that the cli- mate-leaf morphology relationships for Bolivian vegetation do not differ significantly from those for Northern Hemisphere vegetation. The mean leaf size for a given mean annual precipitation is smaller than for a data set from the Western Hemisphere and Africa, but this difference is most likely due to different sampling methods. As for estimating climate from fossil floras, these results, along with the analysis of four other regional data sets, imply that the most accurate climate es- timates will be produced by the predictor data set with the most similar climate-leaf morphology relationships. Unfortunately, our present lack of understanding of why climate-morphology rela- tionships vary between the North America/Japan, New Zealand/Australia, and subalpine domains makes it difficult to identify data sets similar to paleofloras. Until we learn more, it is probably best to compare fossil floras to predictor data sets from the same domain. The performance of the var- ious statistical methods depends on the nature of the predictor data set. Multiple regression anal- ysis tends to produce the most accurate estimates for small data sets with a narrow range of en- vironmental variation that have similar relationships to the flora, and linear regression or canonical correspondence analysis for the larger and more varied CLAMP data set. If a similar predictor data set is not available, then nearest-neighbor analysis can still produce accurate paleoclimate esti- mates.
Article
New total-fusion K/Ar ages indicate that all of the fossiliferous formations that make up the lower part of the Early Miocene Kisingiri sequence in W Kenya at Rusinga Island, Mfwangano Island, and Karungu were deposited during an interval of <0.5Ma at approx 17.8Ma ago. This contrasts markedly with K/Ar ages previously published from these detrital-tuffaceous formations, which suggested that they were deposited over an interval of as much as 7Ma between 23-16Ma, overlapping the age-ranges of all other E African Early Miocene sites including Koru, Songhor, Napak, Bukwa, Loperot, Muruarot and Buluk. In addition, the analytical problems revealed by the new Kisingiri results cast doubt on biotite ages which provide dating for the most important sites. Thus, the strong differences between the Kisingiri fauna and those of Koru, Sonhor and Napak, long held to be due to ecology because of the apparent overlap in ages, may actually be due to a difference in time. If this view of the geochronology is correct, it may now be possible to identify adaptive trends and evolutionary succession in the E African Early Miocene faunas. -Authors
Article
The palaeoecology of the Miocene sites of Western Kenya is reviewed. Because fossil floras are usually not preserved the evidence on palaeoecology is mostly obtained from the fossil faunas. These are analysed by five methods: analysis of indicator species, habitat spectra, taxonomic habitat indices, ecological diversity analyses, and socio-ecology. The results indicate that the Songhor fauna was probably derived from forest habitat close to the place of deposition. In the Koru area the faunas from the Legetet Formation and the Chamtwara Member of the Kapurtay Agglomerates were similarly derived from forest habitats, but the Koru Formation fauna indicates more open conditions. The Rusinga and Karungu faunas have not been analysed in detail, and as they are associated with flood plain sedimentary environments it is probable that they are biased and not representative of any on living community, although there is some evidence also for forest conditions. This is supported by evidence from the fossil flora of Rusinga. Two Middle Miocene faunas from Maboko and Fort Ternan both indicate the presence of woodland or woodland savanna habitats, suggesting a major ecological shift from the faunal habitat of the Early Miocene.
Article
Early Miocene (18 Ma) volcaniclastic deposits of the Hiwegi Formation on Rusinga Island include at least six distinct kinds of paleosols, representing different parts of former ecosystems. Four localities (R1 site of L. S. B. Leakey, nearby site of Pickford, R106 of M. Leakey, and Kaswanga site of Walker) for articulated or cranial material of two species of Proconsul are all in the same kind of paleosol. These are here called Chuodho paleosols, and represent woodlands early in ecological succession of streamsides. Proconsul heseloni is best known from the lower Hiwegi and Kiahera Formations, and was replaced in the same habitat by P. nyanzae in the geologically younger middle Hiwegi Formation. In contrast, articulated skeletons of Dendropithecus macinnesi were found in another kind of paleosol (here called Tek), representing dry upland forest including hackberries (Celtis rusingensis). Other paleosols represent other kinds of early successional vegetation, woodland and dambo grassy woodland. Paleoclimate was dry (300-650 mm mean annual precipitation) and mildly seasonal. The paleosols formed along braided streams on outwash and airfall ash of a carbonatite-nephelinite volcano. The Hiwegi Formation accumulated during the building of this volcano about 18 million years ago.
Article
Geochemical differences in bulk rock geochemistry, mass balance weathering calculations and carbon isotope ratios of palaeosol organic matter between early Miocene palaeosols from the Kisingiri volcano are the result of both changes in the depositional regime and a shift in climatic conditions. Wayondo Formation palaeo-Alfisols located on Rusinga Island (Gumba Beds) and at nearby Karungu, which were deposited prior to the commencement of the main phase of volcanic activity (17.8 Ma), possess well developed clay horizons, moderate base cation contents and strong degrees of weathering. These palaeosols, when compared to their unweathered granitic parent exhibit collapse and loss of 80–90% of base cations and silica suggesting that their formation was during a period of landscape stability, when climatic conditions were humid to sub-humid. In comparison the overlying Kiahera Formation palaeosols, which were deposited during hydromaginatic activity at Kisingiri, exhibit a wide range of dilation and addition, together with individual elemental losses of up to 50%. Together, these weathering trends suggest that there was a climatic shift from wetter conditions to drier, semi-arid conditions, during the initial stages of the volcanoe's growth. This is supported by δ13C values of soil organic matter from A-horizons of the Wayondo Formation palaeosols (Rusinga Island −25.9‰ and Karungu −25.0‰) and the volcanically derived Hiwegi Formation (−23.2‰) and Kiahera Formation (−24.2‰) palaeosols. While all δ13C values are indicative of vegetation using the C3 synthetic pathway, δ13C values of the palaeosols that formed during the eruption (Hiwegi and Kiahera) show more 13C-enriched values compared with the pre-volcanic palaeosols (Wayondo). The reason for the relatively 13C-enriched values is suggested to be due to reduced fractionation due to seasonal or year-round water stress in an environment that had changed from humid (Wayondo) to sub-humid/semi-arid with the onset of volcanic activity. The greater abundance of calcareous material within these syn-eruptively formed fossil soils, compared with the pre-volcanic ones, also supports a change towards greater aridity. δ13C values of organic matter from the Kulu Lake Beds (in the Hiwegi Formation) have average δ13C value of −25.4‰. However, it is not possible to determine whether these values reflect the δ13C values of the terrestrial vegetation of the watershed or whether they are dominated by lacustrine-produced organic matter. Our data indicate that the well-developed Gumba and Karungu fossil soils of the Wayondo Formation represent part of a sustained stable alluvial system and had formed under humid conditions. With the onset of volcanic activity and the creation of a rapidly aggrading pyroclastic system, on which the Kiahera, Kulu and Hiwegi Formations of the Rusinga Group formed, changes occurred in the weathering regime and in the δ13C values of organic matter, suggesting a change towards greater aridity in the pre-versus syn-volcanically formed palaeosols.
Article
Apes and Old World monkeys are prominent components of modern African and Asian ecosystems, yet the earliest phases of their evolutionary history have remained largely undocumented. The absence of crown catarrhine fossils older than ∼20 million years (Myr) has stood in stark contrast to molecular divergence estimates of ∼25-30 Myr for the split between Cercopithecoidea (Old World monkeys) and Hominoidea (apes), implying long ghost lineages for both clades. Here we describe the oldest known fossil 'ape', represented by a partial mandible preserving dental features that place it with 'nyanzapithecine' stem hominoids. Additionally, we report the oldest stem member of the Old World monkey clade, represented by a lower third molar. Both specimens were recovered from a precisely dated 25.2-Myr-old stratum in the Rukwa Rift, a segment of the western branch of the East African Rift in Tanzania. These finds extend the fossil record of apes and Old World monkeys well into the Oligocene epoch of Africa, suggesting a possible link between diversification of crown catarrhines and changes in the African landscape brought about by previously unrecognized tectonic activity in the East African rift system.
Article
This paper recounts the history and significance of Morotopithecus bishopi, an early Miocene East African ape. Morotopithecus differs in intriguing ways from its contemporary Proconsul. While craniodental differences are slight, the known elements of its postcranium suggest that Morotopithecus was capable of modern ape–like positional behaviors, including vertical postures, deliberate climbing, and arm hanging. In contrast, Proconsul and other early and middle Miocene hominoids have been reconstructed as above–branch quadrupeds. Paleoanthropologists are currently divided over whether and which of the anatomical features associated with upright posture and suspension in the modern apes are due to inheritance or independent evolution. This debate has important implications for interpreting the phylogenetic positions of both Morotopithecus and Proconsul, as well as for reconstructing the pattern and timing of the emergence of modern ape adaptations.