Publications by authors named "Zeresenay Alemseged"

36 Publications

Isotopic evidence for the timing of the dietary shift toward C foods in eastern African .

Proc Natl Acad Sci U S A 2020 09 24;117(36):21978-21984. Epub 2020 Aug 24.

Department of Anthropology, University of Colorado Boulder, Boulder, CO 80302.

New approaches to the study of early hominin diets have refreshed interest in how and when our diets diverged from those of other African apes. A trend toward significant consumption of C foods in hominins after this divergence has emerged as a landmark event in human evolution, with direct evidence provided by stable carbon isotope studies. In this study, we report on detailed carbon isotopic evidence from the hominin fossil record of the Shungura and Usno Formations, Lower Omo Valley, Ethiopia, which elucidates the patterns of C dietary utilization in the robust hominin The results show that the most important shift toward C foods occurred at ∼2.37 Ma, within the temporal range of the earliest known member of the genus, , and that this shift was not unique to but occurred in all hominins from this fossil sequence. This uptake of C foods by hominins occurred during a period marked by an overall trend toward increased C grazing by cooccurring mammalian taxa from the same sequence. However, the timing and geographic patterns of hominin diets in this region differ from those observed elsewhere in the same basin, where environmental controls on the underlying availability of various food sources were likely quite different. These results highlight the complexities of dietary responses by hominins to changes in the availability of food resources.
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http://dx.doi.org/10.1073/pnas.2006221117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7486737PMC
September 2020

Dietary trends in herbivores from the Shungura Formation, southwestern Ethiopia.

Proc Natl Acad Sci U S A 2020 09 24;117(36):21921-21927. Epub 2020 Aug 24.

Division of Earth Sciences, National Science Foundation, Alexandria, VA 22314.

Diet provides critical information about the ecology and environment of herbivores. Hence, understanding the dietary strategies of fossil herbivores and the associated temporal changes is one aspect of inferring paleoenvironmental conditions. Here, we present carbon isotope data from more than 1,050 fossil teeth that record the dietary patterns of nine herbivore families in the late Pliocene and early Pleistocene (3.6 to 1.05 Ma) from the Shungura Formation, a hominin-bearing site in southwestern Ethiopia. An increasing trend toward C herbivory has been observed with attendant reductions in the proportions of browsers and mixed feeders through time. A high proportion of mixed feeders has been observed prior to 2.9 Ma followed by a decrease in the proportion of mixed feeders and an increase in grazers between 2.7 and 1.9 Ma, and a further increase in the proportion of grazers after 1.9 Ma. The collective herbivore fauna shows two major change points in carbon isotope values at ∼2.7 and ∼2.0 Ma. While hominin fossils from the sequence older than 2.7 Ma are attributed to , the shift at ∼2.7 Ma indicating the expansion of C grasses on the landscape was concurrent with the first appearance of The link between the increased C herbivory and more open landscapes suggests that lived in more wooded landscapes compared to later hominins such as and , and has implications for key morphological and behavioral adaptations in our lineage.
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http://dx.doi.org/10.1073/pnas.2006982117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7486712PMC
September 2020

Fossils from Mille-Logya, Afar, Ethiopia, elucidate the link between Pliocene environmental changes and Homo origins.

Nat Commun 2020 05 19;11(1):2480. Epub 2020 May 19.

Climate Change Institute, University of Maine, Orono, ME, 04469-5790, USA.

Several hypotheses posit a link between the origin of Homo and climatic and environmental shifts between 3 and 2.5 Ma. Here we report on new results that shed light on the interplay between tectonics, basin migration and faunal change on the one hand and the fate of Australopithecus afarensis and the evolution of Homo on the other. Fieldwork at the new Mille-Logya site in the Afar, Ethiopia, dated to between 2.914 and 2.443 Ma, provides geological evidence for the northeast migration of the Hadar Basin, extending the record of this lacustrine basin to Mille-Logya. We have identified three new fossiliferous units, suggesting in situ faunal change within this interval. While the fauna in the older unit is comparable to that at Hadar and Dikika, the younger units contain species that indicate more open conditions along with remains of Homo. This suggests that Homo either emerged from Australopithecus during this interval or dispersed into the region as part of a fauna adapted to more open habitats.
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http://dx.doi.org/10.1038/s41467-020-16060-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7237685PMC
May 2020

endocasts suggest ape-like brain organization and prolonged brain growth.

Sci Adv 2020 04 1;6(14):eaaz4729. Epub 2020 Apr 1.

Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA.

Human brains are three times larger, are organized differently, and mature for a longer period of time than those of our closest living relatives, the chimpanzees. Together, these characteristics are important for human cognition and social behavior, but their evolutionary origins remain unclear. To study brain growth and organization in the hominin species more than 3 million years ago, we scanned eight fossil crania using conventional and synchrotron computed tomography. We inferred key features of brain organization from endocranial imprints and explored the pattern of brain growth by combining new endocranial volume estimates with narrow age at death estimates for two infants. Contrary to previous claims, sulcal imprints reveal an ape-like brain organization and no features derived toward humans. A comparison of infant to adult endocranial volumes indicates protracted brain growth in , likely critical for the evolution of a long period of childhood learning in hominins.
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http://dx.doi.org/10.1126/sciadv.aaz4729DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7112758PMC
April 2020

Maxillary molar enamel thickness of Plio-Pleistocene hominins.

J Hum Evol 2020 05 19;142:102731. Epub 2020 Mar 19.

Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, 04103, Germany; School of Anthropology and Conservation, University of Kent, Canterbury, CT2 7NR, United Kingdom; Evolutionary Studies Institute, University of Witwatersrand, Johannesburg, South Africa. Electronic address:

Enamel thickness remains an important morphological character in hominin systematics and is regularly incorporated into dietary reconstructions in hominin species. We expand upon a previous study of enamel thickness in mandibular molars by examining a large maxillary molar sample of Plio-Pleistocene hominins (n = 62) and a comparative sample of extant nonhuman apes (n = 48) and modern humans (n = 29). 2D mesial planes of section were generated through microtomography, and standard dental tissue variables were measured to calculate average enamel thickness (AET) and relative enamel thickness (RET). AET was also examined across the lingual, occlusal, and buccal regions of the crown. This study confirms previous findings of increasing enamel thickness throughout the Plio-Pleistocene, being thinnest in Australopithecus anamensis and peaking in Australopithecus boisei, with early Homo specimens, exhibiting intermediate enamel thickness. Agreeing with previous findings, 2D plane of section enamel thickness is found to be a poor taxonomic discriminator, with no statistically significant differences observed between fossil hominins. For fossil hominins, modern humans, and Pongo, the occlusal region of enamel was the thickest, and the lingual enamel thickness was greater than buccal. Pan and Gorilla present the opposite pattern with enamel being thinnest occlusally. Comparison at each molar position between the maxilla and mandible revealed very few significant differences in fossil hominins but some evidence of significantly thicker maxillary enamel (AET) in modern humans and thinner maxillary enamel in Pan (RET).
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http://dx.doi.org/10.1016/j.jhevol.2019.102731DOI Listing
May 2020

Statistical estimates of hominin origination and extinction dates: A case study examining the Australopithecus anamensis-afarensis lineage.

J Hum Evol 2020 01 20;138:102688. Epub 2019 Nov 20.

Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL 60637, USA.

Reliable estimates of when hominin taxa originated and went extinct are central to addressing many paleoanthropological questions, including those relating to macroevolutionary patterns. The timing of hominin temporal ranges can be used to test chronological predictions generated from phylogenetic hypotheses. For example, hypotheses of phyletic ancestor-descendant relationships, based on morphological data, predict no temporal range overlap between the two taxa. However, a fossil taxon's observed temporal range is almost certainly underestimated due to the incompleteness of both the fossil record itself and its sampling, and this decreases the likelihood of observing temporal overlap. Here, we focus on a well-known and widely accepted early hominin lineage, Australopithecus anamensis-afarensis, and place 95% confidence intervals (CIs) on its origination and extinction dates. We do so to assess whether its temporal range is consistent with it being a phyletic descendant of Ardipithecus ramidus and/or a direct ancestor to the earliest claimed representative of Homo (i.e., Ledi-Geraru). We find that the last appearance of Ar. ramidus falls within the origination CI of Au. anamensis-afarensis, whereas the claimed first appearance of Homo postdates the extinction CI. These results are consistent with Homo evolving from Au. anamensis-afarensis, but temporal overlap between Ar. ramidus and Au. anamensis-afarensis cannot be rejected at this time. Though additional samples are needed, future research should extend our initial analyses to incorporate the uncertainties surrounding the range endpoints of Ar. ramidus and earliest Homo. Overall, our findings demonstrate the need for quantifying the uncertainty surrounding the appearances and disappearances of hominin taxa in order to better understand the timing of evolutionary events in our clade's history.
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http://dx.doi.org/10.1016/j.jhevol.2019.102688DOI Listing
January 2020

Comparative morphology and ontogeny of the thoracolumbar transition in great apes, humans, and fossil hominins.

J Hum Evol 2019 09 15;134:102632. Epub 2019 Jul 15.

Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, 60637, USA.

Variation among extant hominoid taxa in the anatomy of the thoracolumbar vertebral transition is well-established and constitutes an important framework for making inferences about posture and locomotion in fossil hominins. However, little is known about the developmental bases of these differences, posing a challenge when interpreting the morphology of juvenile hominins. In this study, we investigated ontogenetic variation in the thoracolumbar transition of juvenile and adult great apes, humans, and fossils attributed to Australopithecus and early Pleistocene Homo erectus. For each vertebra involved in the transition, we quantified functionally relevant aspects of zygapophyseal form: facet curvature in the transverse plane, facet orientation relative to midline, and the shift in these variables across the thoracolumbar transition, from the antepenultimate rib-bearing thoracic to the first lumbar vertebra (L1). Among extant hominids, adult individuals of Pan and Homo exhibit a greater shift in facet morphology across the thoracolumbar transition in comparison to Gorilla and Pongo. This pattern is driven by interspecific differences in the L1 facets, with those of chimpanzees and humans being more curved and more sagittally oriented. Chimpanzees and humans also experience more change in facet morphology during development relative to gorillas and orangutans. Humans differ from chimpanzees in achieving their adultlike configuration much earlier in development. The fossil specimens indicate that early hominins had adult morphologies that were similar to those of extant Homo and Pan, and that they achieved their adult morphologies early in development, like extant humans. Although it is unclear why adult chimpanzees and hominins share an adult morphology, we speculate that the early acquisition of adultlike L1 zygapophyseal morphology in hominins is an evolutionary novelty related to conferring stability to a relatively long lumbar spine as young individuals are learning to walk bipedally.
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http://dx.doi.org/10.1016/j.jhevol.2019.06.003DOI Listing
September 2019

Temporal evidence shows is unlikely to be the ancestor of .

Sci Adv 2019 05 8;5(5):eaav9038. Epub 2019 May 8.

Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL 60637, USA.

Understanding the emergence of the genus is a pressing problem in the study of human origins. has recently been proposed as the ancestral species of , although it postdates earliest by 800,000 years. Here, we use probability models to demonstrate that observing an ancestor's fossil horizon that is at least 800,000 years younger than the descendant's fossil horizon is unlikely (about 0.09% on average). We corroborate these results by searching the literature and finding that within pairs of purported hominin ancestor-descendant species, in only one case did the first-discovered fossil in the ancestor postdate that from the descendant, and the age difference between these fossils was much less than the difference observed between and earliest . Together, these results suggest it is highly unlikely that is ancestral to , and the most viable candidate ancestral species remains .
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http://dx.doi.org/10.1126/sciadv.aav9038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6506247PMC
May 2019

A missing piece of the Papio puzzle: Gorongosa baboon phenostructure and intrageneric relationships.

J Hum Evol 2019 05 5;130:1-20. Epub 2019 Mar 5.

ICArEHB - Interdisciplinary Center for Archaeology and Evolution of Human Behaviour, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; Primate Models for Behavioural Evolution Lab, Institute of Cognitive and Evolutionary Anthropology, School of Anthropology and Museum Ethnography, University of Oxford, UK; Gorongosa National Park, Sofala, Mozambique; Centre for Functional Ecology, Coimbra University, Portugal.

Most authors recognize six baboon species: hamadryas (Papio hamadryas), Guinea (Papio papio), olive (Papio anubis), yellow (Papio cynocephalus), chacma (Papio ursinus), and Kinda (Papio kindae). However, there is still debate regarding the taxonomic status, phylogenetic relationships, and the amount of gene flow occurring between species. Here, we present ongoing research on baboon morphological diversity in Gorongosa National Park (GNP), located in central Mozambique, south of the Zambezi River, at the southern end of the East African Rift System. The park exhibits outstanding ecological diversity and hosts more than 200 baboon troops. Gorongosa National Park baboons have previously been classified as chacma baboons (P. ursinus). In accordance with this, two mtDNA samples from the park have been placed in the same mtDNA clade as the northern chacma baboons. However, GNP baboons exhibit morphological features common in yellow baboons (e.g., yellow fur color), suggesting that parapatric gene flow between chacma and yellow baboons might have occurred in the past or could be ongoing. We investigated the phenostructure of the Gorongosa baboons using two approaches: 1) description of external phenotypic features, such as coloration and body size, and 2) 3D geometric morphometric analysis of 43 craniofacial landmarks on 11 specimens from Gorongosa compared to a pan-African sample of 352 baboons. The results show that Gorongosa baboons exhibit a mosaic of features shared with southern P. cynocephalus and P. ursinus griseipes. The GNP baboon phenotype fits within a geographic clinal pattern of replacing allotaxa. We put forward the hypothesis of either past and/or ongoing hybridization between the gray-footed chacma and southern yellow baboons in Gorongosa or an isolation-by-distance scenario in which the GNP baboons are geographically and morphologically intermediate. These two scenarios are not mutually exclusive. We highlight the potential of baboons as a useful model to understand speciation and hybridization in early human evolution.
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http://dx.doi.org/10.1016/j.jhevol.2019.01.007DOI Listing
May 2019

Connecting palaeoscientists in eastern Africa and the wider world.

Nat Ecol Evol 2019 03;3(3):330-331

Department of Earth Sciences, National Museums of Kenya, Nairobi, Kenya.

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http://dx.doi.org/10.1038/s41559-019-0800-yDOI Listing
March 2019

Diversity analysis of Plio-Pleistocene large mammal communities in the Omo-Turkana Basin, eastern Africa.

J Hum Evol 2018 11 25;124:25-39. Epub 2018 Aug 25.

Department of Organismal Biology and Anatomy, The University of Chicago, 1027 E 57th St, Chicago, IL 60637, USA.

Knowing how the diversity of large mammal communities changes across space and time provides an important ecological framework for studying hominin evolution. However, diversity studies that apply methods currently used by neoecologists are rare in paleoanthropology and are also challenging due to diversity's unusual statistical properties. Here, we apply up-to-date analytical methods for understanding how species- and genus-level large mammalian diversity in the Omo-Turkana Basin changed through time and across space at multiple spatiotemporal scales (within each formation:10 km and 10 years; and within the basin as a whole: 10 km and 10 years). We found that, on average, Koobi Fora's large mammal community was more diverse than Nachukui's, which in turn was more diverse than Shungura's. Diversity was stable through time within each of these formations (alpha diversity), as was diversity in the basin as a whole (gamma diversity). Compositional dissimilarity between these three formations (beta diversity) was relatively low through time, with a 0.6 average proportion of shared species, suggesting dispersal acted to homogenize the region. Though alpha and gamma diversity were fairly stable through time, we do observe several notable peaks: during the KBS Member in Koobi Fora (30% increase), the Lokalalei Member in Nachukui (120% increase), and at 1.7 Ma in the entire basin (100% increase). We conclude by (1) demonstrating that habitat heterogeneity was an important factor influencing alpha diversity within each of the three formations, and (2) hypothesizing that diversity stability may have been driven by equilibrial dynamics in which overall diversity was constrained by resource availability, implying biotic interactions were an important factor in structuring the communities that included hominins as members. Our findings demonstrate the need to quantify how large mammal diversity changes across time and space in order to further our understanding of hominin ecology and evolution.
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http://dx.doi.org/10.1016/j.jhevol.2018.07.004DOI Listing
November 2018

A nearly complete foot from Dikika, Ethiopia and its implications for the ontogeny and function of .

Sci Adv 2018 07 4;4(7):eaar7723. Epub 2018 Jul 4.

Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA.

The functional and evolutionary implications of primitive retentions in early hominin feet have been under debate since the discovery of . Ontogeny can provide insight into adult phenotypes, but juvenile early hominin foot fossils are exceptionally rare. We analyze a nearly complete, 3.32-million-year-old juvenile foot of (DIK-1-1f). We show that juvenile individuals already had many of the bipedal features found in adult specimens. However, they also had medial cuneiform traits associated with increased hallucal mobility and a more gracile calcaneal tuber, which is unexpected on the basis of known adult morphologies. Selection for traits functionally associated with juvenile pedal grasping may provide a new perspective on their retention in the more terrestrial adult .
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http://dx.doi.org/10.1126/sciadv.aar7723DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6031372PMC
July 2018

Thoracic vertebral count and thoracolumbar transition in .

Proc Natl Acad Sci U S A 2017 06 22;114(23):6000-6004. Epub 2017 May 22.

Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637.

The evolution of the human pattern of axial segmentation has been the focus of considerable discussion in paleoanthropology. Although several complete lumbar vertebral columns are known for early hominins, to date, no complete cervical or thoracic series has been recovered. Several partial skeletons have revealed that the thoracolumbar transition in early hominins differed from that of most extant apes and humans. , and all had zygapophyseal facets that shift from thoracic-like to lumbar-like at the penultimate rib-bearing level, rather than the ultimate rib-bearing level, as in most humans and extant African apes. What has not been clear is whether had 12 thoracic vertebrae as in most humans, or 13 as in most African apes, and where the position of the thoracolumbar transitional element was. The discovery, preparation, and synchrotron scanning of the partial skeleton DIK-1-1, from Dikika, Ethiopia, provides the only known complete hominin cervical and thoracic vertebral column before 60,000 years ago. DIK-1-1 is the only known skeleton to preserve all seven cervical vertebrae and provides evidence for 12 thoracic vertebrae with a transition in facet morphology at the 11th thoracic level. The location of this transition, one segment cranial to the ultimate rib-bearing vertebra, also occurs in all other early hominins and is higher than in most humans or extant apes. At 3.3 million years ago, the DIK-1-1 skeleton is the earliest example of this distinctive and unusual pattern of axial segmentation.
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http://dx.doi.org/10.1073/pnas.1702229114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5468642PMC
June 2017

Dietary flexibility of Australopithecus afarensis in the face of paleoecological change during the middle Pliocene: Faunal evidence from Hadar, Ethiopia.

J Hum Evol 2016 10 30;99:93-106. Epub 2016 Aug 30.

Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287, USA.

One approach to understanding the context of changes in hominin paleodiets is to examine the paleodiets and paleohabitats of contemporaneous mammalian taxa. Recent carbon isotopic studies suggest that the middle Pliocene was marked by a major shift in hominin diets, characterized by a significant increase in C4 foods in Australopithecus-grade species, including Australopithecus afarensis. To contextualize previous isotopic studies of A. afarensis, we employed stable isotopes to examine paleodiets of the mammalian fauna contemporaneous with A. afarensis at Hadar, Ethiopia. We used these data to inform our understanding of paleoenvironmental change through the deposition of the Hadar Formation. While the majority of the taxa in the Hadar fauna were C4 grazers, most show little change in the intensity of C4 food consumption over the 0.5 million-year interval sampled. Two taxa (equids and bovins) do show increases in C4 consumption through the Hadar Formation and into the younger, overlying Busidima Formation. Changes in the distributions of C4-feeders, C3-feeders and mixed-C3/C4-feeders in the sampled intervals are consistent with evidence of dietary reconstructions based on ecomorphology, and with habitats reconstructed using community structure analyses. Meanwhile, A. afarensis is one of many mammalian taxa whose C4 consumption does not show directional change over the intervals sampled. In combination with a wide range of carbon and oxygen isotopic composition for A. afarensis as compared to the other large mammal taxa, these results suggest that the C3/C4 dietary flexibility of A. afarensis was relatively unusual among most of its mammalian cohort.
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http://dx.doi.org/10.1016/j.jhevol.2016.08.002DOI Listing
October 2016

Reply to Almécija: A new direction for reconstructing our last common ancestor with chimpanzees.

Proc Natl Acad Sci U S A 2016 Feb 9;113(8):E945. Epub 2016 Feb 9.

Department of Anthropology, California Academy of Sciences, San Francisco, CA 94118.

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http://dx.doi.org/10.1073/pnas.1525673113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4776488PMC
February 2016

Reply to Melillo: Woranso-Mille is consistent with an australopithecine shoulder intermediate between African apes and Homo.

Proc Natl Acad Sci U S A 2015 Dec 16;112(52):E7160. Epub 2015 Dec 16.

Department of Anthropology, California Academy of Sciences, San Francisco, CA 94118.

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http://dx.doi.org/10.1073/pnas.1521824112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4702962PMC
December 2015

Digital data collection in paleoanthropology.

Evol Anthropol 2015 Nov-Dec;24(6):238-49

Understanding patterns of human evolution across space and time requires synthesizing data collected by independent research teams, and this effort is part of a larger trend to develop cyber infrastructure and e-science initiatives. At present, paleoanthropology cannot easily answer basic questions about the total number of fossils and artifacts that have been discovered, or exactly how those items were collected. In this paper, we examine the methodological challenges to data integration, with the hope that mitigating the technical obstacles will further promote data sharing. At a minimum, data integration efforts must document what data exist and how the data were collected (discovery), after which we can begin standardizing data collection practices with the aim of achieving combined analyses (synthesis). This paper outlines a digital data collection system for paleoanthropology. We review the relevant data management principles for a general audience and supplement this with technical details drawn from over 15 years of paleontological and archeological field experience in Africa and Europe. The system outlined here emphasizes free open-source software (FOSS) solutions that work on multiple computer platforms; it builds on recent advances in open-source geospatial software and mobile computing.
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http://dx.doi.org/10.1002/evan.21466DOI Listing
September 2016

Stable isotopes serving as a checkpoint.

Proc Natl Acad Sci U S A 2015 Oct 23;112(40):12232-3. Epub 2015 Sep 23.

California Academy of Sciences, San Francisco, CA 94118

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http://dx.doi.org/10.1073/pnas.1516668112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4603446PMC
October 2015

Fossil hominin shoulders support an African ape-like last common ancestor of humans and chimpanzees.

Proc Natl Acad Sci U S A 2015 Sep 8;112(38):11829-34. Epub 2015 Sep 8.

Department of Anthropology, California Academy of Sciences, San Francisco, CA 94118.

Reconstructing the behavioral shifts that drove hominin evolution requires knowledge of the timing, magnitude, and direction of anatomical changes over the past ∼6-7 million years. These reconstructions depend on assumptions regarding the morphotype of the Homo-Pan last common ancestor (LCA). However, there is little consensus for the LCA, with proposed models ranging from African ape to orangutan or generalized Miocene ape-like. The ancestral state of the shoulder is of particular interest because it is functionally associated with important behavioral shifts in hominins, such as reduced arboreality, high-speed throwing, and tool use. However, previous morphometric analyses of both living and fossil taxa have yielded contradictory results. Here, we generated a 3D morphospace of ape and human scapular shape to plot evolutionary trajectories, predict ancestral morphologies, and directly test alternative evolutionary hypotheses using the hominin fossil evidence. We show that the most parsimonious model for the evolution of hominin shoulder shape starts with an African ape-like ancestral state. We propose that the shoulder evolved gradually along a single morphocline, achieving modern human-like configuration and function within the genus Homo. These data are consistent with a slow, progressive loss of arboreality and increased tool use throughout human evolution.
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http://dx.doi.org/10.1073/pnas.1511220112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586873PMC
September 2015

Paleodietary reconstruction using stable isotopes and abundance analysis of bovids from the Shungura Formation of South Omo, Ethiopia.

J Hum Evol 2015 Nov 2;88:127-136. Epub 2015 Sep 2.

Department of Geology, University of Dayton, 300 College Park, Dayton, OH 45469-2364, USA.

Preservation of the stable carbon isotopic composition of fossil tooth enamel enables us to estimate the relative proportion of C3 versus C4 vegetation in an animal's diet, which, combined with analysis of faunal abundance, may provide complementary methods of paleoenvironmental reconstruction. To this end, we analyzed stable carbon isotopic composition (δ(13)C values) of tooth enamel from four bovid tribes (Tragelaphini, Aepycerotini, Reduncini, and Alcelaphini) derived from six members of the Shungura Formation (Members B, C, D, F, G, and L; ages from ca. 2.90-1.05 Ma (millions of years ago) in the Lower Omo Valley of southwestern Ethiopia. The bovids show a wide range of δ(13)C values within taxa and stratigraphic members, as well as temporal changes in the feeding strategies of taxa analyzed throughout the middle to late Pliocene and early Pleistocene. Such variation suggests that the use of actualistic approaches for paleoenvironmental reconstruction may not always be warranted. Alcelaphini was the only taxon analyzed that retained a consistent dietary preference throughout the sequence, with entirely C4-dominated diets. Reduncini had a mixed C3/C4 to C4-dominated diet prior to 2.4 Ma, after which this taxon shifted to a largely C4-dominated diet. Aepycerotini generally showed a mixed C3/C4 diet, with a period of increased C4 diet from 2.5 to 2.3 Ma. Tragelaphini showed a range of mixed C3/C4 diets, with a median value that was briefly nearer the C4 end member from 2.9 to 2.4 Ma but was otherwise towards the C3 end member. These isotopic results, combined with relative abundance data for these bovids, imply that the environment of the Lower Omo Valley consisted of a mosaic of closed woodlands, with riverine forests and open grasslands. However, our data also signify that the overall environment gradually became more open, and that C4 grasses became more dominant. Finally, these results help document the range and extent of environments and potential diets that were available to the four hominin species encountered in the Shungura sequence.
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http://dx.doi.org/10.1016/j.jhevol.2015.07.009DOI Listing
November 2015

Taphonomy of fossils from the hominin-bearing deposits at Dikika, Ethiopia.

J Hum Evol 2015 Sep 13;86:112-35. Epub 2015 Aug 13.

Department of Anthropology, California Academy of Sciences, 55 Concourse Drive, San Francisco, CA 94118, USA. Electronic address:

Two fossil specimens from the DIK-55 locality in the Hadar Formation at Dikika, Ethiopia, are contemporaneous with the earliest documented stone tools, and they collectively bear twelve marks interpreted to be characteristic of stone tool butchery damage. An alternative interpretation of the marks has been that they were caused by trampling animals and do not provide evidence of stone tool use or large ungulate exploitation by Australopithecus-grade hominins. Thus, resolving which agents created marks on fossils in deposits from Dikika is an essential step in understanding the ecological and taphonomic contexts of the hominin-bearing deposits in this region and establishing their relevance for investigations of the earliest stone tool use. This paper presents results of microscopic scrutiny of all non-hominin fossils collected from the Hadar Formation at Dikika, including additional fossils from DIK-55, and describes in detail seven assemblages from sieved surface sediment samples. The study is the first taphonomic description of Pliocene fossil assemblages from open-air deposits in Africa that were collected without using only methods that emphasize the selective retention of taxonomically-informative specimens. The sieved assemblages show distinctive differences in faunal representation and taphonomic modifications that suggest they sample a range of depositional environments in the Pliocene Hadar Lake Basin, and have implications for how landscape-based taphonomy can be used to infer past microhabitats. The surface modification data show that no marks on any other fossils resemble in size or shape those on the two specimens from DIK-55 that were interpreted to bear stone tool inflicted damage. A large sample of marks from the sieved collections has characteristics that match modern trampling damage, but these marks are significantly smaller than those on the DIK-55 specimens and have different suites of characteristics. Most are not visible without magnification. The data show that the DIK-55 marks are outliers amongst bone surface damage in the Dikika area, and that trampling is not the most parsimonious interpretation of their origin.
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http://dx.doi.org/10.1016/j.jhevol.2015.06.013DOI Listing
September 2015

Bovid ecomorphology and hominin paleoenvironments of the Shungura Formation, lower Omo River Valley, Ethiopia.

J Hum Evol 2015 Nov 21;88:108-126. Epub 2015 Jul 21.

Research Centre for Evolutionary Anthropology and Palaeoecology, School of Natural Sciences and Psychology, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK. Electronic address:

The Shungura Formation in the lower Omo River Valley, southern Ethiopia, has yielded an important paleontological and archeological record from the Pliocene and Pleistocene of eastern Africa. Fossils are common throughout the sequence and provide evidence of paleoenvironments and environmental change through time. This study developed discriminant function ecomorphology models that linked astragalus morphology to broadly defined habitat categories (open, light cover, heavy cover, forest, and wetlands) using modern bovids of known ecology. These models used seven variables suitable for use on fragmentary fossils and had overall classification success rates of >82%. Four hundred and one fossils were analyzed from Shungura Formation members B through G (3.4-1.9 million years ago). Analysis by member documented the full range of ecomorph categories, demonstrating that a wide range of habitats existed along the axis of the paleo-Omo River. Heavy cover ecomorphs, reflecting habitats such as woodland and heavy bushland, were the most common in the fossil sample. The trend of increasing open cover habitats from Members C through F suggested by other paleoenvironmental proxies was documented by the increase in open habitat ecomorphs during this interval. However, finer grained analysis demonstrated considerable variability in ecomorph frequencies over time, suggesting that substantial short-term variability is masked when grouping samples by member. The hominin genera Australopithecus, Homo, and Paranthropus are associated with a range of ecomorphs, indicating that all three genera were living in temporally variable and heterogeneous landscapes. Australopithecus finds were predominantly associated with lower frequencies of open habitat ecomorphs, and high frequencies of heavy cover ecomorphs, perhaps indicating a more woodland focus for this genus.
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http://dx.doi.org/10.1016/j.jhevol.2015.06.006DOI Listing
November 2015

Enamel thickness trends in Plio-Pleistocene hominin mandibular molars.

J Hum Evol 2015 Aug 27;85:35-45. Epub 2015 May 27.

Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig 04103, Germany.

Enamel thickness continues to be an important morphological character in hominin systematics and is frequently invoked in dietary reconstructions of Plio-Pleistocene hominin taxa. However, to date, the majority of published data on molar enamel thickness of Pliocene and early Pleistocene hominins derive from naturally fractured random surfaces of a small number of specimens. In this study we systematically analyze enamel thickness in a large sample of Plio-Pleistocene fossil hominins (n = 99), extant hominoids (n = 57), and modern humans (n = 30). Based on analysis of 2D mesial planes of section derived from microtomography, we examine both average and relative enamel thickness, and the distribution of enamel across buccal, occlusal, and lingual components of mandibular molars. Our results confirm the trend of increasing enamel thickness during the Pliocene that culminates in the thick enamel of the robust Australopithecus species, and then decreases from early Homo to recent modern humans. All hominin taxa share a regional average enamel thickness pattern of thick occlusal enamel and greater buccal than lingual enamel thickness. Pan is unique in exhibiting the thinnest average enamel thickness in the occlusal basin. Statistical analysis indicates that among Pliocene hominins enamel thickness is a weak taxonomic discriminator. The data underlying these results are included in a table in the Supplementary Online Material.
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http://dx.doi.org/10.1016/j.jhevol.2015.03.012DOI Listing
August 2015

Diet of Australopithecus afarensis from the Pliocene Hadar Formation, Ethiopia.

Proc Natl Acad Sci U S A 2013 Jun 3;110(26):10495-500. Epub 2013 Jun 3.

Department of Geology, University of South Florida, Tampa, FL 33620, USA.

The enhanced dietary flexibility of early hominins to include consumption of C4/crassulacean acid metabolism (CAM) foods (i.e., foods derived from grasses, sedges, and succulents common in tropical savannas and deserts) likely represents a significant ecological and behavioral distinction from both extant great apes and the last common ancestor that we shared with great apes. Here, we use stable carbon isotopic data from 20 samples of Australopithecus afarensis from Hadar and Dikika, Ethiopia (>3.4-2.9 Ma) to show that this species consumed a diet with significant C4/CAM foods, differing from its putative ancestor Au. anamensis. Furthermore, there is no temporal trend in the amount of C4/CAM food consumption over the age of the samples analyzed, and the amount of C4/CAM food intake was highly variable, even within a single narrow stratigraphic interval. As such, Au. afarensis was a key participant in the C4/CAM dietary expansion by early australopiths of the middle Pliocene. The middle Pliocene expansion of the eastern African australopith diet to include savanna-based foods represents a shift to use of plant food resources that were already abundant in hominin environments for at least 1 million y and sets the stage for dietary differentiation and niche specialization by subsequent hominin taxa.
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http://dx.doi.org/10.1073/pnas.1222559110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3696813PMC
June 2013

Dietary and paleoenvironmental reconstruction using stable isotopes of herbivore tooth enamel from middle Pliocene Dikika, Ethiopia: implication for Australopithecus afarensis habitat and food resources.

J Hum Evol 2013 Jan 28;64(1):21-38. Epub 2012 Nov 28.

Department of Geology, University of South Florida, Tampa, FL 33620, USA.

Carbon and oxygen isotopes of mammalian tooth enamel were used to reconstruct paleoenvironments of Australopithecus afarensis from the middle Pliocene locality of Dikika, Ethiopia. Isotopic analyses were conducted on 210 mammalian herbivore teeth from 15 different taxa collected from the Basal Member (~3.8-3.42 Ma) and Sidi Hakoma Member (3.42-3.24 Ma) of the Hadar Formation. The isotopic analyses aim specifically at reconstructing shifts in the relative abundance of C(4) grasses in mammalian diets, and more generally at paleoclimate factors such as aridity and seasonality, as well as habitat structure. Carbon isotopic data suggest a wide range of foraging strategies, characterized by mixed C(3)/C(4) to C(4)-dominated diets in wooded grasslands to open woodlands. Weighted average C(4) dietary proportions range between 60% and 86% in the Basal Member and 49% and 74% in the Sidi Hakoma Member. Paleoclimatic conditions based on the reconstructed mean annual water deficit from the δ(18)O(enamel) values indicate a wetter climate as compared to either the early Pliocene or the Pleistocene nearby. The middle Pliocene habitat structure at Dikika could be as diverse as open grassland and wooded grassland, and woodland to forest in the Sidi Hakoma Member while wooded grassland, woodland to grassland are evident in the Basal Member. All habitats except closed woodland and forest are persistent through both members; however, the relative proportion of individual habitats changed through time. These changes could have put the fauna in competition for preferred habitats and food resources, which could have forced migration, adaptation to other resources and/or extinction. Thus, the existence of A. afarensis throughout the middle Pliocene indicates either this species might have adapted to a wide range of habitats, or its preferred habitat was not affected by the observed environmental changes.
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http://dx.doi.org/10.1016/j.jhevol.2012.05.015DOI Listing
January 2013

Australopithecus afarensis scapular ontogeny, function, and the role of climbing in human evolution.

Science 2012 Oct;338(6106):514-7

Department of Anatomy, Midwestern University, Downers Grove, IL 60515, USA.

Scapular morphology is predictive of locomotor adaptations among primates, but this skeletal element is scarce in the hominin fossil record. Notably, both scapulae of the juvenile Australopithecus afarensis skeleton from Dikika, Ethiopia, have been recovered. These scapulae display several traits characteristic of suspensory apes, as do the few known fragmentary adult australopith representatives. Many of these traits change significantly throughout modern human ontogeny, but remain stable in apes. Thus, the similarity of juvenile and adult fossil morphologies implies that A. afarensis development was apelike. Additionally, changes in other scapular traits throughout African ape development are associated with shifts in locomotor behavior. This affirms the functional relevance of those characteristics, and their presence in australopith fossils supports the hypothesis that their locomotor repertoire included a substantial amount of climbing.
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http://dx.doi.org/10.1126/science.1227123DOI Listing
October 2012

Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia.

Nature 2010 Aug;466(7308):857-60

Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, DeutscherPlatz 6, Leipzig 04103, Germany.

The oldest direct evidence of stone tool manufacture comes from Gona (Ethiopia) and dates to between 2.6 and 2.5 million years (Myr) ago. At the nearby Bouri site several cut-marked bones also show stone tool use approximately 2.5 Myr ago. Here we report stone-tool-inflicted marks on bones found during recent survey work in Dikika, Ethiopia, a research area close to Gona and Bouri. On the basis of low-power microscopic and environmental scanning electron microscope observations, these bones show unambiguous stone-tool cut marks for flesh removal and percussion marks for marrow access. The bones derive from the Sidi Hakoma Member of the Hadar Formation. Established (40)Ar-(39)Ar dates on the tuffs that bracket this member constrain the finds to between 3.42 and 3.24 Myr ago, and stratigraphic scaling between these units and other geological evidence indicate that they are older than 3.39 Myr ago. Our discovery extends by approximately 800,000 years the antiquity of stone tools and of stone-tool-assisted consumption of ungulates by hominins; furthermore, this behaviour can now be attributed to Australopithecus afarensis.
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http://dx.doi.org/10.1038/nature09248DOI Listing
August 2010