Publications by authors named "Anna K Behrensmeyer"

29 Publications

  • Page 1 of 1

Increased ecological resource variability during a critical transition in hominin evolution.

Sci Adv 2020 Oct 21;6(43). Epub 2020 Oct 21.

Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA.

Although climate change is considered to have been a large-scale driver of African human evolution, landscape-scale shifts in ecological resources that may have shaped novel hominin adaptations are rarely investigated. We use well-dated, high-resolution, drill-core datasets to understand ecological dynamics associated with a major adaptive transition in the archeological record ~24 km from the coring site. Outcrops preserve evidence of the replacement of Acheulean by Middle Stone Age (MSA) technological, cognitive, and social innovations between 500 and 300 thousand years (ka) ago, contemporaneous with large-scale taxonomic and adaptive turnover in mammal herbivores. Beginning ~400 ka ago, tectonic, hydrological, and ecological changes combined to disrupt a relatively stable resource base, prompting fluctuations of increasing magnitude in freshwater availability, grassland communities, and woody plant cover. Interaction of these factors offers a resource-oriented hypothesis for the evolutionary success of MSA adaptations, which likely contributed to the ecological flexibility typical of foragers.
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http://dx.doi.org/10.1126/sciadv.abc8975DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7577727PMC
October 2020

Investigating Biotic Interactions in Deep Time.

Trends Ecol Evol 2021 01 13;36(1):61-75. Epub 2020 Oct 13.

School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.

Recent renewed interest in using fossil data to understand how biotic interactions have shaped the evolution of life is challenging the widely held assumption that long-term climate changes are the primary drivers of biodiversity change. New approaches go beyond traditional richness and co-occurrence studies to explicitly model biotic interactions using data on fossil and modern biodiversity. Important developments in three primary areas of research include analysis of (i) macroevolutionary rates, (ii) the impacts of and recovery from extinction events, and (iii) how humans (Homo sapiens) affected interactions among non-human species. We present multiple lines of evidence for an important and measurable role of biotic interactions in shaping the evolution of communities and lineages on long timescales.
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http://dx.doi.org/10.1016/j.tree.2020.09.001DOI Listing
January 2021

Middle Pliocene hominin distribution patterns in Eastern Africa.

J Hum Evol 2020 10 28;147:102856. Epub 2020 Aug 28.

Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, MRC 121, Washington, DC, 20013, USA.

Abundance distributions of large mammals are underused in exploring how ecological pressures vary across contemporaneous sites in the fossil record. To investigate variation in relative abundance across contemporaneous Pliocene mammal communities, we examine the time interval between ∼3.6 and 3.22 Ma at four sites in the Afar and Turkana basins: Hadar and the lower Omo Valley in Ethiopia and East Turkana and West Turkana in Kenya. Taphonomic and collection biases are examined using skeletal parts, body size, and taxonomic data from database collections. Taphonomic biases due to geologic conditions and fossil collection affected all sites, but those in the Turkana Basin appeared particularly affected by collecting bias. As a result, hominin relative abundance is calculated separately using a taphonomic control taxon, which shares similar collection biases and size. Comparisons of mammalian taxonomic groups revealed that the Omo region was dominated by suids and cercopithecids. The other sites are dominated by open habitat and mixed habitat associated bovids. Hominins had higher abundance wherein the dominant mammal taxa indicate a mix of woodland and grassland environments (Hadar) and were rarer at sites where the majority of taxa are associated with woodland vegetation (the Omo Valley). West Turkana is characterized by mixed habitats and the highest relative abundance of hominins relative to control taxa, but sampling issues due to the collection and reporting of papionins likely drive this result. East Turkana has few hominins relative to the control taxon and has dominant habitats indicative of floodplain grasslands but has a small sample size compared with the other sites. These analyses suggest that Kenyanthropus platyops and Australopithecus afarensis inhabited similar types of habitats across different rift basins. Most convincingly, this study contributes to a growing body of evidence suggesting that early hominins diverged from their great ape counterparts by abandoning woodland-dominated habitats.
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http://dx.doi.org/10.1016/j.jhevol.2020.102856DOI Listing
October 2020

Introduction: Hominin paleobiology in the early Pleistocene Okote Member, Koobi Fora Formation, Kenya.

J Hum Evol 2020 08 25;145:102811. Epub 2020 May 25.

National Museums of Kenya, Nairobi, Kenya; Department of History and Archaeology, University of Nairobi, Kenya.

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http://dx.doi.org/10.1016/j.jhevol.2020.102811DOI Listing
August 2020

Animal bioturbation preserved in Pleistocene magadiite at Lake Magadi, Kenya Rift Valley, and its implications for the depositional environment of bedded magadiite.

Sci Rep 2020 04 22;10(1):6794. Epub 2020 Apr 22.

Department of Earth and Environmental Sciences, Mount Royal University, Calgary, AB, T5E 6K6, Canada.

Magadiite, a rare hydrous sodium-silicate mineral [NaSiO(OH)·4(HO)], was discovered about 50 years ago in sediments around Lake Magadi, a hypersaline alkaline lake fed by hot springs in the semi-arid southern Kenya Rift Valley. Today this harsh lacustrine environment excludes most organisms except microbial extremophiles, a few invertebrates (mostly insects), highly adapted fish (Alcolapia sp.), and birds including flamingos. Burrows discovered in outcrops of the High Magadi Beds (~25-9 ka) that predate the modern saline (trona) pan show that beetles and other invertebrates inhabit this extreme environment when conditions become more favourable. Burrows (cm-scale) preserved in magadiite in the High Magadi Beds are filled with mud, silt and sand from overlying sediments. Their stratigraphic context reveals upward-shallowing cycles from mud to interlaminated mud-magadiite to magadiite in dm-scale units. The burrows were formed when the lake floor became fresher and oxygenated, after a period when magadiite precipitated in shallow saline waters. The burrows, probably produced by beetles, show that trace fossils can provide evidence for short-term (possibly years to decades) changes in the contemporary environment that might not otherwise be recognised or preserved physically or chemically in the sediment record.
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http://dx.doi.org/10.1038/s41598-020-63505-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7176717PMC
April 2020

Reorganization of surviving mammal communities after the end-Pleistocene megafaunal extinction.

Science 2019 09;365(6459):1305-1308

Department of Biological Sciences, Macquarie University, New South Wales 2109, Australia.

Large mammals are at high risk of extinction globally. To understand the consequences of their demise for community assembly, we tracked community structure through the end-Pleistocene megafaunal extinction in North America. We decomposed the effects of biotic and abiotic factors by analyzing co-occurrence within the mutual ranges of species pairs. Although shifting climate drove an increase in niche overlap, co-occurrence decreased, signaling shifts in biotic interactions. Furthermore, the effect of abiotic factors on co-occurrence remained constant over time while the effect of biotic factors decreased. Biotic factors apparently played a key role in continental-scale community assembly before the extinctions. Specifically, large mammals likely promoted co-occurrence in the Pleistocene, and their loss contributed to the modern assembly pattern in which co-occurrence frequently falls below random expectations.
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http://dx.doi.org/10.1126/science.aaw1605DOI Listing
September 2019

Comparative isotopic evidence from East Turkana supports a dietary shift within the genus Homo.

Nat Ecol Evol 2019 07 17;3(7):1048-1056. Epub 2019 Jun 17.

Gorongosa National Park, Sofala, Mozambique.

It has been suggested that a shift in diet is one of the key adaptations that distinguishes the genus Homo from earlier hominins, but recent stable isotopic analyses of fossils attributed to Homo in the Turkana Basin show an increase in the consumption of C resources circa 1.65 million years ago, significantly after the earliest evidence for Homo in the eastern African fossil record. These data are consistent with ingesting more C plants, more animal tissues of C herbivores, or both, but it is also possible that this change reflects factors unrelated to changes in the palaeobiology of the genus Homo. Here we use new and published carbon and oxygen isotopic data (n = 999) taken from large-bodied fossil mammals, and pedogenic carbonates in fossil soils, from East Turkana in northern Kenya to investigate the context of this change in the isotope signal within Homo. By targeting taxa and temporal intervals unrepresented or undersampled in previous analyses, we were able to conduct the first comprehensive analysis of the ecological context of hominin diet at East Turkana during a period crucial for detecting any dietary and related behavioural differences between early Homo (H. habilis and/or H. rudolfensis) and Homo erectus. Our analyses suggest that the genus Homo underwent a dietary shift (as indicated by δC and δO values) that is (1) unrelated to changes in the East Turkana vegetation community and (2) unlike patterns found in other East Turkana large mammals, including Paranthropus and Theropithecus. These data suggest that within the Turkana Basin a dietary shift occurred well after we see the first evidence of early Homo in the region.
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http://dx.doi.org/10.1038/s41559-019-0916-0DOI Listing
July 2019

Diversity dynamics of Phanerozoic terrestrial tetrapods at the local-community scale.

Nat Ecol Evol 2019 04 18;3(4):590-597. Epub 2019 Feb 18.

School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK.

The fossil record provides one of the strongest tests of the hypothesis that diversity within local communities is constrained over geological timescales. Constraints to diversity are particularly controversial in modern terrestrial ecosystems, yet long-term patterns are poorly understood. Here we document patterns of local richness in Phanerozoic terrestrial tetrapods using a global data set comprising 145,332 taxon occurrences from 27,531 collections. We show that the local richness of non-flying terrestrial tetrapods has risen asymptotically since their initial colonization of land, increasing at most threefold over the last 300 million years. Statistical comparisons support phase-shift models, with most increases in local richness occurring: (1) during the colonization of land by vertebrates, concluding by the late Carboniferous; and (2) across the Cretaceous/Paleogene boundary. Individual groups, such as mammals, lepidosaurs and dinosaurs also experienced early increases followed by periods of stasis often lasting tens of millions of years. Mammal local richness abruptly tripled across the Cretaceous/Paleogene boundary, but did not increase over the next 66 million years. These patterns are consistent with the hypothesis that diversity is constrained at the local-community scale.
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http://dx.doi.org/10.1038/s41559-019-0811-8DOI Listing
April 2019

Grassland fire ecology has roots in the late Miocene.

Proc Natl Acad Sci U S A 2018 11 14;115(48):12130-12135. Epub 2018 Nov 14.

Department of Geosciences, The Pennsylvania State University, University Park, PA 16802.

That fire facilitated the late Miocene C grassland expansion is widely suspected but poorly documented. Fire potentially tied global climate to this profound biosphere transition by serving as a regional-to-local driver of vegetation change. In modern environments, seasonal extremes in moisture amplify the occurrence of fire, disturbing forest ecosystems to create niche space for flammable grasses, which in turn provide fuel for frequent fires. On the Indian subcontinent, C expansion was accompanied by increased seasonal extremes in rainfall (evidenced by δO), which set the stage for fuel accumulation and fire-linked clearance during wet-to-dry seasonal transitions. Here, we test the role of fire directly by examining the abundance and distribution patterns of fire-derived polycyclic aromatic hydrocarbons (PAHs) and terrestrial vegetation signatures in -alkane carbon isotopes from paleosol samples of the Siwalik Group (Pakistan). Two million years before the C grassland transition, fire-derived PAH concentrations increased as conifer vegetation declined, as indicated by a decrease in retene. This early increase in molecular fire signatures suggests a transition to more fire-prone vegetation such as a C grassland and/or dry deciduous woodland. Between 8.0 and 6.0 million years ago, fire, precipitation seasonality, and C-grass dominance increased simultaneously (within resolution) as marked by sharp increases in fire-derived PAHs, δO, and C enrichment in -alkanes diagnostic of C grasses. The strong association of evidence for fire occurrence, vegetation change, and landscape opening indicates that a dynamic fire-grassland feedback system was both a necessary precondition and a driver for grassland ecology during the first emergence of C grasslands.
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http://dx.doi.org/10.1073/pnas.1809758115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6275532PMC
November 2018

Pleistocene animal communities of a 1.5 million-year-old lake margin grassland and their relationship to Homo erectus paleoecology.

J Hum Evol 2018 09 30;122:70-83. Epub 2018 Jun 30.

Division of Anthropology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA; Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany.

The ecological and selective forces that sparked the emergence of Homo's adaptive strategy remain poorly understood. New fossil and archaeological finds call into question previous interpretations of the grade shift that drove our ancestors' evolutionary split from the australopiths. Furthermore, issues of taphonomy and scale have limited reconstructions of the hominin habitats and faunal communities that define the environmental context of these behavioral changes. The multiple ∼1.5 Ma track surfaces from the Okote Member of the Koobi Fora Formation at East Turkana provide unique windows for examining hominin interactions with the paleoenvironment and associated faunas at high spatiotemporal resolution. These surfaces preserve the tracks of many animals, including cf. Homo erectus. Here, we examine the structure of the animal community that inhabited this landscape, considering effects of preservation bias by comparing the composition of the track assemblage to a skeletal assemblage from the same time and place. We find that the track and skeletal assemblages are similar in their representation of the vertebrate paleocommunity, with comparable levels of taxonomic richness and diversity. Evenness (equitability of the number of individuals per taxon) differs between the two assemblages due to the very different circumstances of body fossil versus track preservation. Both samples represent diverse groups of taxa including numerous water-dependent species, consistent with geological interpretations of the track site environments. Comparisons of these assemblages also show a pattern of non-random hominin association with a marginal lacustrine habitat relative to other vertebrates in the track assemblage. This evidence is consistent with behavior that included access to aquatic foods and possibly hunting by H. erectus in lake margins/edaphic grasslands. Such behaviors may signal the emergence of the adaptative strategies that define our genus.
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http://dx.doi.org/10.1016/j.jhevol.2018.04.014DOI Listing
September 2018

Chronology of the Acheulean to Middle Stone Age transition in eastern Africa.

Science 2018 04 15;360(6384):95-98. Epub 2018 Mar 15.

Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA.

The origin of the Middle Stone Age (MSA) marks the transition from a highly persistent mode of stone toolmaking, the Acheulean, to a period of increasing technological innovation and cultural indicators associated with the evolution of We used argon-40/argon-39 and uranium-series dating to calibrate the chronology of Acheulean and early MSA artifact-rich sedimentary deposits in the Olorgesailie basin, southern Kenya rift. We determined the age of late Acheulean tool assemblages from 615,000 to 499,000 years ago, after which a large technological and faunal transition occurred, with a definitive MSA lacking Acheulean elements beginning most likely by ~320,000 years ago, but at least by 305,000 years ago. These results establish the oldest repository of MSA artifacts in eastern Africa.
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http://dx.doi.org/10.1126/science.aao2216DOI Listing
April 2018

Long-distance stone transport and pigment use in the earliest Middle Stone Age.

Science 2018 04 15;360(6384):90-94. Epub 2018 Mar 15.

Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA.

Previous research suggests that the complex symbolic, technological, and socioeconomic behaviors that typify had roots in the middle Pleistocene <200,000 years ago, but data bearing on human behavioral origins are limited. We present a series of excavated Middle Stone Age sites from the Olorgesailie basin, southern Kenya, dating from ≥295,000 to ~320,000 years ago by argon-40/argon-39 and uranium-series methods. Hominins at these sites made prepared cores and points, exploited iron-rich rocks to obtain red pigment, and procured stone tool materials from ≥25- to 50-kilometer distances. Associated fauna suggests a broad resource strategy that included large and small prey. These practices imply notable changes in how individuals and groups related to the landscape and to one another and provide documentation relevant to human social and cognitive evolution.
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http://dx.doi.org/10.1126/science.aao2646DOI Listing
April 2018

Environmental dynamics during the onset of the Middle Stone Age in eastern Africa.

Science 2018 04 15;360(6384):86-90. Epub 2018 Mar 15.

Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada.

Development of the African Middle Stone Age (MSA) before 300,000 years ago raises the question of how environmental change influenced the evolution of behaviors characteristic of early We used temporally well-constrained sedimentological and paleoenvironmental data to investigate environmental dynamics before and after the appearance of the early MSA in the Olorgesailie basin, Kenya. In contrast to the Acheulean archeological record in the same basin, MSA sites are associated with a markedly different faunal community, more pronounced erosion-deposition cycles, tectonic activity, and enhanced wet-dry variability. Aspects of Acheulean technology in this region imply that, as early as 615,000 years ago, greater stone material selectivity and wider resource procurement coincided with an increased pace of land-lake fluctuation, potentially anticipating the adaptability of MSA hominins.
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http://dx.doi.org/10.1126/science.aao2200DOI Listing
April 2018

Hominin track assemblages from Okote Member deposits near Ileret, Kenya, and their implications for understanding fossil hominin paleobiology at 1.5 Ma.

J Hum Evol 2017 11 13;112:93-104. Epub 2017 Sep 13.

Division of Anthropology, American Museum of Natural History, New York, NY 10024, USA; Humboldt Foundation Fellow at Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig D-04103, Germany.

Tracks can provide unique, direct records of behaviors of fossil organisms moving across their landscapes millions of years ago. While track discoveries have been rare in the human fossil record, over the last decade our team has uncovered multiple sediment surfaces within the Okote Member of the Koobi Fora Formation near Ileret, Kenya that contain large assemblages of ∼1.5 Ma fossil hominin tracks. Here, we provide detailed information on the context and nature of each of these discoveries, and we outline the specific data that are preserved on the Ileret hominin track surfaces. We analyze previously unpublished data to refine and expand upon earlier hypotheses regarding implications for hominin anatomy and social behavior. While each of the track surfaces discovered at Ileret preserves a different amount of data that must be handled in particular ways, general patterns are evident. Overall, the analyses presented here support earlier interpretations of the ∼1.5 Ma Ileret track assemblages, providing further evidence of large, human-like body sizes and possibly evidence of a group composition that could support the emergence of certain human-like patterns of social behavior. These data, used in concert with other forms of paleontological and archaeological evidence that are deposited on different temporal scales, offer unique windows through which we can broaden our understanding of the paleobiology of hominins living in East Africa at ∼1.5 Ma.
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http://dx.doi.org/10.1016/j.jhevol.2017.08.013DOI Listing
November 2017

Herbivore teeth predict climatic limits in Kenyan ecosystems.

Proc Natl Acad Sci U S A 2016 Nov 24;113(45):12751-12756. Epub 2016 Oct 24.

Department of Geosciences and Geography, University of Helsinki, FI-00014 Helsinki, Finland.

A major focus in evolutionary biology is to understand how the evolution of organisms relates to changes in their physical environment. In the terrestrial realm, the interrelationships among climate, vegetation, and herbivores lie at the heart of this question. Here we introduce and test a scoring scheme for functional traits present on the worn surfaces of large mammalian herbivore teeth to capture their relationship to environmental conditions. We modeled local precipitation, temperature, primary productivity, and vegetation index as functions of dental traits of large mammal species in 13 national parks in Kenya over the past 60 y. We found that these dental traits can accurately estimate local climate and environment, even at small spatial scales within areas of relatively uniform climate (within two ecoregions), and that they predict limiting conditions better than average conditions. These findings demonstrate that the evolution of key functional properties of organisms may be more reflective of demands during recurring adverse episodes than under average conditions or during isolated severe events.
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http://dx.doi.org/10.1073/pnas.1609409113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5111722PMC
November 2016

Pleistocene footprints show intensive use of lake margin habitats by Homo erectus groups.

Sci Rep 2016 05 20;6:26374. Epub 2016 May 20.

Division of Anthropology, American Museum of Natural History, New York, New York 10024, USA.

Reconstructing hominin paleoecology is critical for understanding our ancestors' diets, social organizations and interactions with other animals. Most paleoecological models lack fine-scale resolution due to fossil hominin scarcity and the time-averaged accumulation of faunal assemblages. Here we present data from 481 fossil tracks from northwestern Kenya, including 97 hominin footprints attributed to Homo erectus. These tracks are found in multiple sedimentary layers spanning approximately 20 thousand years. Taphonomic experiments show that each of these trackways represents minutes to no more than a few days in the lives of the individuals moving across these paleolandscapes. The geology and associated vertebrate fauna place these tracks in a deltaic setting, near a lakeshore bordered by open grasslands. Hominin footprints are disproportionately abundant in this lake margin environment, relative to hominin skeletal fossil frequency in the same deposits. Accounting for preservation bias, this abundance of hominin footprints indicates repeated use of lakeshore habitats by Homo erectus. Clusters of very large prints moving in the same direction further suggest these hominins traversed this lakeshore in multi-male groups. Such reliance on near water environments, and possibly aquatic-linked foods, may have influenced hominin foraging behavior and migratory routes across and out of Africa.
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http://dx.doi.org/10.1038/srep26374DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4873780PMC
May 2016

Holocene shifts in the assembly of plant and animal communities implicate human impacts.

Nature 2016 Jan 16;529(7584):80-3. Epub 2015 Dec 16.

Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.

Understanding how ecological communities are organized and how they change through time is critical to predicting the effects of climate change. Recent work documenting the co-occurrence structure of modern communities found that most significant species pairs co-occur less frequently than would be expected by chance. However, little is known about how co-occurrence structure changes through time. Here we evaluate changes in plant and animal community organization over geological time by quantifying the co-occurrence structure of 359,896 unique taxon pairs in 80 assemblages spanning the past 300 million years. Co-occurrences of most taxon pairs were statistically random, but a significant fraction were spatially aggregated or segregated. Aggregated pairs dominated from the Carboniferous period (307 million years ago) to the early Holocene epoch (11,700 years before present), when there was a pronounced shift to more segregated pairs, a trend that continues in modern assemblages. The shift began during the Holocene and coincided with increasing human population size and the spread of agriculture in North America. Before the shift, an average of 64% of significant pairs were aggregated; after the shift, the average dropped to 37%. The organization of modern and late Holocene plant and animal assemblages differs fundamentally from that of assemblages over the past 300 million years that predate the large-scale impacts of humans. Our results suggest that the rules governing the assembly of communities have recently been changed by human activity.
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http://dx.doi.org/10.1038/nature16447DOI Listing
January 2016

Four million years of African herbivory.

Proc Natl Acad Sci U S A 2015 Sep 31;112(37):11428-9. Epub 2015 Aug 31.

Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013

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http://dx.doi.org/10.1073/pnas.1514580112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4577182PMC
September 2015

A century of change in Kenya's mammal communities: increased richness and decreased uniqueness in six protected areas.

PLoS One 2014 9;9(4):e93092. Epub 2014 Apr 9.

Evolution of Terrestrial Ecosystems Program. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution Washington, District of Columbia, United States of America.

The potential for large-scale biodiversity losses as a result of climate change and human impact presents major challenges for ecology and conservation science. Governments around the world have established national parks and wildlife reserves to help protect biodiversity, but there are few studies on the long-term consequences of this strategy. We use Kenya as a case study to investigate species richness and other attributes of mammal communities in 6 protected areas over the past century. Museum records from African expeditions that comprehensively sampled mammals from these same areas in the early 1900's provide a baseline for evaluating changes in species richness and community structure over time. We compare species lists assembled from archived specimens (1896-1950) to those of corresponding modern protected areas (1950-2013). Species richness in Kenya was stable or increased at 5 out of 6 sites from historical to modern times. Beta-diversity, in contrast, decreased across all sites. Potential biases such as variable historical vs. modern collection effort and detection of small-bodied, rare, and low-visibility species do not account for the observed results. We attribute the pattern of decreased beta diversity primarily to increased site occupancy by common species across all body size classes. Despite a decrease in land area available to wildlife, our data do not show the extinctions predicted by species-area relationships. Moreover, the results indicate that species-area curves based solely on protected areas could underestimate diversity because they do not account for mammal species whose ranges extend beyond protected area boundaries. We conclude that the 6 protected areas have been effective in preserving species richness in spite of continuing conversion of wild grasslands to cropland, but the overall decrease in beta diversity indicates a decline in the uniqueness of mammal communities that historically characterized Kenya's varied landscape.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0093092PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3981716PMC
January 2015

Bone assemblages track animal community structure over 40 years in an African savanna ecosystem.

Science 2009 May;324(5930):1061-4

African Conservation Center, Box 62844, Nairobi, Kenya.

Reconstructing ancient communities depends on how accurately fossil assemblages retain information about living populations. We report a high level of fidelity between modern bone assemblages and living populations based on a 40-year study of the Amboseli ecosystem in southern Kenya. Relative abundance of 15 herbivorous species recorded in the bone assemblage accurately tracks the living populations through major changes in community composition and habitat over intervals as short as 5 years. The aggregated bone sample provides an accurate record of community structure time-averaged over four decades. These results lay the groundwork for integrating paleobiological and contemporary ecological studies across evolutionary and ecological time scales. Bone surveys also provide a useful method of assessing population changes and community structure for modern vertebrates.
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http://dx.doi.org/10.1126/science.1171155DOI Listing
May 2009

Early hominin foot morphology based on 1.5-million-year-old footprints from Ileret, Kenya.

Science 2009 Feb;323(5918):1197-201

School of Conservation Sciences, Bournemouth University, Poole, BH12 5BB, UK.

Hominin footprints offer evidence about gait and foot shape, but their scarcity, combined with an inadequate hominin fossil record, hampers research on the evolution of the human gait. Here, we report hominin footprints in two sedimentary layers dated at 1.51 to 1.53 million years ago (Ma) at Ileret, Kenya, providing the oldest evidence of an essentially modern human-like foot anatomy, with a relatively adducted hallux, medial longitudinal arch, and medial weight transfer before push-off. The size of the Ileret footprints is consistent with stature and body mass estimates for Homo ergaster/erectus, and these prints are also morphologically distinct from the 3.75-million-year-old footprints at Laetoli, Tanzania. The Ileret prints show that by 1.5 Ma, hominins had evolved an essentially modern human foot function and style of bipedal locomotion.
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http://dx.doi.org/10.1126/science.1168132DOI Listing
February 2009

Ecological changes in Miocene mammalian record show impact of prolonged climatic forcing.

Proc Natl Acad Sci U S A 2008 Aug 18;105(34):12145-9. Epub 2008 Aug 18.

Museum of Paleontology and Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA.

Geohistorical records reveal the long-term impacts of climate change on ecosystem structure. A 5-myr record of mammalian faunas from floodplain ecosystems of South Asia shows substantial change in species richness and ecological structure in relation to vegetation change as documented by stable isotopes of C and O from paleosols. Between 8.5 and 6.0 Ma, C(4) savannah replaced C(3) forest and woodland. Isotopic historical trends for 27 mammalian herbivore species, in combination with ecomorphological data from teeth, show three patterns of response. Most forest frugivores and browsers maintained their dietary habits and disappeared. Other herbivores altered their dietary habits to include increasing amounts of C(4) plants and persisted for >1 myr during the vegetation transition. The few lineages that persisted through the vegetation transition show isotopic enrichment of delta(13)C values over time. These results are evidence for long-term climatic forcing of vegetation structure and mammalian ecological diversity at the subcontinental scale.
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http://dx.doi.org/10.1073/pnas.0805592105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2527879PMC
August 2008

Atmosphere. Climate change and human evolution.

Science 2006 Jan;311(5760):476-8

Department of Paleobiology, Smithsonian Institution, Washington, DC 20560, USA.

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http://dx.doi.org/10.1126/science.1116051DOI Listing
January 2006

Small mid-Pleistocene hominin associated with East African Acheulean technology.

Science 2004 Jul;305(5680):75-8

Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0112, USA.

Hominin fossils from the African mid-Pleistocene are rare despite abundant Acheulean tools in Africa and apparently African-derived hominins in Eurasia between 1.0 and 0.5 million years ago (Ma). Here we describe an African fossil cranium constrained by 40Ar/39Ar analyses, magnetostratigraphy, and sedimentary features to 0.97 to 0.90 Ma, and stratigraphically associated with Acheulean handaxes. Although the cranium represents possibly the smallest adult or near-adult known between 1.7 and 0.5 Ma, it retains features observed in larger Homo erectus individuals, yet shows a distinct suite of traits indicative of wide population variation in the hominins of this period.
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http://dx.doi.org/10.1126/science.1097661DOI Listing
July 2004

Faunal change, environmental variability and late Pliocene hominin evolution.

J Hum Evol 2002 Apr;42(4):475-97

Evolution of Terrestrial Ecosystems Program, Department of Paleobiology, MRC 121, Smithsonian Institution, Washington, DC 20560-0121, USA.

Global change during the late Pliocene was manifested in declining temperatures, increased amplitude of climate cycles, and shifts in the periodicity of orbital climate forcing. Linking these changes to the evolution of African continental faunas and to hominin evolution requires well-documented fossil evidence that can be examined through substantial periods of time. The Omo sequence of southern Ethiopia provides such a database, and we use it to analyze change in the abundances of mammal taxa at different levels of temporal and taxonomic resolution between 4 and 2 Ma. This study provides new evidence for shifts through time in the ecological dominance of suids, cercopithecids, and bovids, and for a trend from more forested to more open woodland habitats. Superimposed on these long-term trends are two episodes of faunal change, one involving a marked shift in the abundances of different taxa at about 2.8+/-0.1 Ma, and the second the transition at 2.5 Ma from a 200-ka interval of faunal stability to marked variability over intervals of about 100 ka. The first appearance of Homo, the earliest artefacts, and the extinction of non-robust Australopithecus in the Omo sequence coincide in time with the beginning of this period of high variability. We conclude that climate change caused significant shifts in vegetation in the Omo paleo-ecosystem and is a plausible explanation for the gradual ecological change from forest to open woodland between 3.4 and 2.0 Ma, the faunal shift at 2.8 +/-0.1 Ma, and the change in the tempo of faunal variability of 2.5 Ma. Climate forcing in the late Pliocene is more clearly indicated by population shifts within the Omo mammal community than by marked turnover at the species level.
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http://dx.doi.org/10.1006/jhev.2001.0535DOI Listing
April 2002

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

J Hum Evol 2002 Jan-Feb;42(1-2):11-38

Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0121, USA.

The Muruyur Beds are a substantial sedimentary deposit within a middle Miocene sequence of mafic volcanic flows associated with early stages of rifting in the central Kenyan Rift Valley. They are best represented in the Muruyur region, near Bartabwa, north of Kipsaramon, where dates range from 16.0 to 13.4 Ma. At Kipsaramon, located about 10 km south of Muruyur along the crest of the Tugen Hills, the upper Muruyur Beds are absent and the lower part can be divided into three members. Important fossil sites within Member 1 are dated between 15.8 and 15.6 Ma, and within Member 3 between 15.6 and 15.4 Ma. BPRP#89, in Member 1, is a bonebed at least 2500 m(2)in areal extent and up to 30 cm thick, which constitutes one of the richest concentrations of in situ fossil vertebrate bones in eastern Africa. BPRP#91, at approximately the same level at BPRP#89, is the source of a hominoid talus and other mammal and bird fossils. In Member 3, BPRP#122 has produced specimens of at least five individuals of the hominoid Equatorius, including a partial skeleton. The Muyuyur Beds were deposited near the western margin of a lake that was formed during the early stages of faulting and volcanism in the African Rift system. The bonebed in Member 1 appears to represent the influx of fluvially transported vertebrate and plant remains into a shallow portion of the lake. Elements of the fauna as well as stable isotopes that indicate both forest and more open environments occurred in proximity to the lake during the time of deposition of Member 1.
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http://dx.doi.org/10.1006/jhev.2001.0519DOI Listing
March 2002