Publications by authors named "Bernard A Wood"

22 Publications

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through the looking glass.

Proc Natl Acad Sci U S A 2020 09 2;117(38):23202-23204. Epub 2020 Sep 2.

Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC 20052.

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http://dx.doi.org/10.1073/pnas.2016445117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7519337PMC
September 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 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

Pattern and process in hominin brain size evolution are scale-dependent.

Proc Biol Sci 2018 02;285(1873)

Center for the Advanced Study of Human Paleobiology, Department of Anthropology, The George Washington University, 800 22nd Street, NW, Washington, DC 20052, USA.

A large brain is a defining feature of modern humans, yet there is no consensus regarding the patterns, rates and processes involved in hominin brain size evolution. We use a reliable proxy for brain size in fossils, endocranial volume (ECV), to better understand how brain size evolved at both clade- and lineage-level scales. For the hominin clade overall, the dominant signal is consistent with a gradual increase in brain size. This gradual trend appears to have been generated primarily by processes operating within hypothesized lineages-64% or 88% depending on whether one uses a more or less speciose taxonomy, respectively. These processes were supplemented by the appearance in the fossil record of larger-brained species and the subsequent disappearance of smaller-brained and taxa. When the estimated rate of within-lineage ECV increase is compared to an exponential model that operationalizes generation-scale evolutionary processes, it suggests that the observed data were the result of episodes of directional selection interspersed with periods of stasis and/or drift; all of this occurs on too fine a timescale to be resolved by the current human fossil record, thus producing apparent gradual trends within lineages. Our findings provide a quantitative basis for developing and testing scale-explicit hypotheses about the factors that led brain size to increase during hominin evolution.
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http://dx.doi.org/10.1098/rspb.2017.2738DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5832710PMC
February 2018

Brain enlargement and dental reduction were not linked in hominin evolution.

Proc Natl Acad Sci U S A 2017 01 3;114(3):468-473. Epub 2017 Jan 3.

Center for the Advanced Study of Human Paleobiology, Department of Anthropology, The George Washington University, Washington, DC 20052.

The large brain and small postcanine teeth of modern humans are among our most distinctive features, and trends in their evolution are well studied within the hominin clade. Classic accounts hypothesize that larger brains and smaller teeth coevolved because behavioral changes associated with increased brain size allowed a subsequent dental reduction. However, recent studies have found mismatches between trends in brain enlargement and posterior tooth size reduction in some hominin species. We use a multiple-variance Brownian motion approach in association with evolutionary simulations to measure the tempo and mode of the evolution of endocranial and dental size and shape within the hominin clade. We show that hominin postcanine teeth have evolved at a relatively consistent neutral rate, whereas brain size evolved at comparatively more heterogeneous rates that cannot be explained by a neutral model, with rapid pulses in the branches leading to later Homo species. Brain reorganization shows evidence of elevated rates only much later in hominin evolution, suggesting that fast-evolving traits such as the acquisition of a globular shape may be the result of direct or indirect selection for functional or structural traits typical of modern humans.
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http://dx.doi.org/10.1073/pnas.1608798114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5255602PMC
January 2017

Functional Divergence of the Nuclear Receptor NR2C1 as a Modulator of Pluripotentiality During Hominid Evolution.

Genetics 2016 06 13;203(2):905-22. Epub 2016 Apr 13.

Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4R2 Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4R2

Genes encoding nuclear receptors (NRs) are attractive as candidates for investigating the evolution of gene regulation because they (1) have a direct effect on gene expression and (2) modulate many cellular processes that underlie development. We employed a three-phase investigation linking NR molecular evolution among primates with direct experimental assessment of NR function. Phase 1 was an analysis of NR domain evolution and the results were used to guide the design of phase 2, a codon-model-based survey for alterations of natural selection within the hominids. By using a series of reliability and robustness analyses we selected a single gene, NR2C1, as the best candidate for experimental assessment. We carried out assays to determine whether changes between the ancestral and extant NR2C1s could have impacted stem cell pluripotency (phase 3). We evaluated human, chimpanzee, and ancestral NR2C1 for transcriptional modulation of Oct4 and Nanog (key regulators of pluripotency and cell lineage commitment), promoter activity for Pepck (a proxy for differentiation in numerous cell types), and average size of embryological stem cell colonies (a proxy for the self-renewal capacity of pluripotent cells). Results supported the signal for alteration of natural selection identified in phase 2. We suggest that adaptive evolution of gene regulation has impacted several aspects of pluripotentiality within primates. Our study illustrates that the combination of targeted evolutionary surveys and experimental analysis is an effective strategy for investigating the evolution of gene regulation with respect to developmental phenotypes.
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http://dx.doi.org/10.1534/genetics.115.183889DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4896202PMC
June 2016

Viewpoints: diet and dietary adaptations in early hominins: the hard food perspective.

Am J Phys Anthropol 2013 Jul;151(3):339-55

Department of Anthropology, University at Albany, Albany, NY 12222, USA.

Recent biomechanical analyses examining the feeding adaptations of early hominins have yielded results consistent with the hypothesis that hard foods exerted a selection pressure that influenced the evolution of australopith morphology. However, this hypothesis appears inconsistent with recent reconstructions of early hominin diet based on dental microwear and stable isotopes. Thus, it is likely that either the diets of some australopiths included a high proportion of foods these taxa were poorly adapted to consume (i.e., foods that they would not have processed efficiently), or that aspects of what we thought we knew about the functional morphology of teeth must be wrong. Evaluation of these possibilities requires a recognition that analyses based on microwear, isotopes, finite element modeling, and enamel chips and cracks each test different types of hypotheses and allow different types of inferences. Microwear and isotopic analyses are best suited to reconstructing broad dietary patterns, but are limited in their ability to falsify specific hypotheses about morphological adaptation. Conversely, finite element analysis is a tool for evaluating the mechanical basis of form-function relationships, but says little about the frequency with which specific behaviors were performed or the particular types of food that were consumed. Enamel chip and crack analyses are means of both reconstructing diet and examining biomechanics. We suggest that current evidence is consistent with the hypothesis that certain derived australopith traits are adaptations for consuming hard foods, but that australopiths had generalized diets that could include high proportions of foods that were both compliant and tough.
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http://dx.doi.org/10.1002/ajpa.22285DOI Listing
July 2013

Stable isotope-based diet reconstructions of Turkana Basin hominins.

Proc Natl Acad Sci U S A 2013 Jun 3;110(26):10501-6. Epub 2013 Jun 3.

Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.

Hominin fossil evidence in the Turkana Basin in Kenya from ca. 4.1 to 1.4 Ma samples two archaic early hominin genera and records some of the early evolutionary history of Paranthropus and Homo. Stable carbon isotopes in fossil tooth enamel are used to estimate the fraction of diet derived from C3 or C4 resources in these hominin taxa. The earliest hominin species in the Turkana Basin, Australopithecus anamensis, derived nearly all of its diet from C3 resources. Subsequently, by ca. 3.3 Ma, the later Kenyanthropus platyops had a very wide dietary range--from virtually a purely C3 resource-based diet to one dominated by C4 resources. By ca. 2 Ma, hominins in the Turkana Basin had split into two distinct groups: specimens attributable to the genus Homo provide evidence for a diet with a ca. 65/35 ratio of C3- to C4-based resources, whereas P. boisei had a higher fraction of C4-based diet (ca. 25/75 ratio). Homo sp. increased the fraction of C4-based resources in the diet through ca. 1.5 Ma, whereas P. boisei maintained its high dependency on C4-derived resources.
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http://dx.doi.org/10.1073/pnas.1222568110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3696807PMC
June 2013

Brief communication: Molar development and crown areas in early Australopithecus.

Am J Phys Anthropol 2012 Aug 24;148(4):632-40. Epub 2012 May 24.

Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, CA 90033, USA.

Recent studies suggest that the hypodigms representing the two earliest Australopithecus (Au. anamensis and Au. afarensis) form an ancestor-descendant lineage. Understanding the details of this possible transition is important comparative evidence for assessing the likelihood of other examples of ancestor-descendant lineages within the hominin clade. To this end we have analyzed crown and cusp base areas of high resolution replicas of the mandibular molars of Au. anamensis (Allia Bay and Kanapoi sites) and those of Au. afarensis (Hadar, Laetoli, and Maka). We found no statistically significant differences in crown areas between these hypodigms although the mean of M(1) crowns was smaller in Au. anamensis, being the smallest of any Australopithecus species sampled to date. Intraspecies comparison of the areas of mesial cusps for each molar type using Wilcoxon signed rank test showed no differences for Au. anamensis. Significant differences were found between the protoconid and metaconid of Au. afarensis M(2)s and M(3)s. Furthermore, the area formed by the posterior cusps as a whole relative to the anterior cusps showed significant differences in Au. afarensis M(1)s and in Au. anamensis M(2)s but no differences were noted for M(3)s of either taxon. Developmental information derived from microstructural details in enamel shows that M(1) crown formation in Au. anamensis is similar to Pan and shorter than in H. sapiens. Taken together, these data suggests that the overall trend in the Au. anamensis-Au. afarensis transition may have involved a moderate increase in M(1) crown areas with relative expansion of distal cusps.
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http://dx.doi.org/10.1002/ajpa.22089DOI Listing
August 2012

Microwear, mechanics and the feeding adaptations of Australopithecus africanus.

J Hum Evol 2012 Jan 29;62(1):165-8. Epub 2011 Nov 29.

Recent studies of dental microwear and craniofacial mechanics have yielded contradictory interpretations regarding the feeding ecology and adaptations of Australopithecus africanus. As part of this debate, the methods used in the mechanical studies have been criticized. In particular, it has been claimed that finite element analysis has been poorly applied to this research question. This paper responds to some of these mechanical criticisms, highlights limitations of dental microwear analysis, and identifies avenues of future research.
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http://dx.doi.org/10.1016/j.jhevol.2011.10.006DOI Listing
January 2012

How many landmarks? Assessing the classification accuracy of Pan lower molars using a geometric morphometric analysis of the occlusal basin as seen at the enamel-dentine junction.

Front Oral Biol 2009 21;13:23-29. Epub 2009 Sep 21.

Previous research has demonstrated that species and subspecies of extant chimpanzees and bonobos can be distinguished on the basis of the shape of enamel-dentine junction of lower molar crowns. Thus, there is potential for fossil taxa, particularly fossil hominins, to be distinguished at similar taxonomic levels using lower molar crown morphology. New imaging techniques allow for the collection of large amounts of shape data, but it is not clear whether taxonomic distinctiveness increases with the inclusion of more and more finely detailed aspects of crown shape. We examine whether increasing the amount of shape data collected will lead to an increase in the accuracy with which enamel-dentine junction (EDJ) shape classifies Pan lower first and second molars at the species and subspecies level. Micro-computed tomography was employed to non-destructively image the EDJ and geometric morphometric analytical methods were used to compare EDJ shape among samples of Pan paniscus, Pan troglodytestroglodytes, and Pan troglodytes verus. The results of discriminant analyses using three landmark sets (number of landmarks=8, 112, and 534 landmarks and semi-landmarks, respectively) indicate a high degree of classification accuracy for each landmark set, with small increases in accuracy as the numbers of landmarks are increased. The morphological differences in EDJ shape among the taxa are subtle, but consistent, and relate to the relative height and position of the dentine horns. Thus, EDJ shape can contribute to taxonomic analyses and the more information that can be included the better.
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http://dx.doi.org/10.1159/000242385DOI Listing
March 2010

Discrimination of extant Pan species and subspecies using the enamel-dentine junction morphology of lower molars.

Am J Phys Anthropol 2009 Oct;140(2):234-43

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

Previous research has demonstrated that species and subspecies of extant chimpanzees and bonobos can be distinguished on the basis of the shape of their molar crowns. Thus, there is potential for fossil taxa, particularly fossil hominins, to be distinguished at similar taxonomic levels using molar crown morphology. Unfortunately, due to occlusal attrition, the original crown morphology is often absent in fossil teeth, and this has limited the amount of shape information used to discriminate hominin molars. The enamel-dentine junction (EDJ) of molar teeth preserves considerable shape information, particularly in regard to the original shape of the crown, and remains present through the early stages of attrition. In this study, we investigate whether the shape of the EDJ of lower first and second molars can distinguish species and subspecies of extant Pan. Micro-computed tomography was employed to non-destructively image the EDJ, and geometric morphometric analytical methods were used to compare EDJ shape among samples of Pan paniscus (N = 17), Pan troglodytes troglodytes (N = 13), and Pan troglodytes verus (N = 18). Discriminant analysis indicates that EDJ morphology distinguishes among extant Pan species and subspecies with a high degree of reliability. The morphological differences in EDJ shape among the taxa are subtle and relate to the relative height and position of the dentine horns, the height of the dentine crown, and the shape of the crown base, but their existence supports the inclusion of EDJ shape (particularly those aspects of shape in the vertical dimension) in the systematic analysis of fossil hominin lower molars.
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http://dx.doi.org/10.1002/ajpa.21057DOI Listing
October 2009

The feeding biomechanics and dietary ecology of Australopithecus africanus.

Proc Natl Acad Sci U S A 2009 Feb 2;106(7):2124-9. Epub 2009 Feb 2.

Department of Anthropology, University at Albany, 1400 Washington Avenue, Albany, NY 12222, USA.

The African Plio-Pleistocene hominins known as australopiths evolved a distinctive craniofacial morphology that traditionally has been viewed as a dietary adaptation for feeding on either small, hard objects or on large volumes of food. A historically influential interpretation of this morphology hypothesizes that loads applied to the premolars during feeding had a profound influence on the evolution of australopith craniofacial form. Here, we test this hypothesis using finite element analysis in conjunction with comparative, imaging, and experimental methods. We find that the facial skeleton of the Australopithecus type species, A. africanus, is well suited to withstand premolar loads. However, we suggest that the mastication of either small objects or large volumes of food is unlikely to fully explain the evolution of facial form in this species. Rather, key aspects of australopith craniofacial morphology are more likely to be related to the ingestion and initial preparation of large, mechanically protected food objects like large nuts and seeds. These foods may have broadened the diet of these hominins, possibly by being critical resources that australopiths relied on during periods when their preferred dietary items were in short supply. Our analysis reconciles apparent discrepancies between dietary reconstructions based on biomechanics, tooth morphology, and dental microwear.
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http://dx.doi.org/10.1073/pnas.0808730106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2650119PMC
February 2009

Hominid mandibular corpus shape variation and its utility for recognizing species diversity within fossil Homo.

J Anat 2008 Dec;213(6):670-85

Natural Sciences & Mathematics, The Richard Stockton College of New Jersey, Pomona, NJ 08240-0195, USA.

Mandibular corpora are well represented in the hominin fossil record, yet few studies have rigorously assessed the utility of mandibular corpus morphology for species recognition, particularly with respect to the linear dimensions that are most commonly available. In this study, we explored the extent to which commonly preserved mandibular corpus morphology can be used to: (i) discriminate among extant hominid taxa and (ii) support species designations among fossil specimens assigned to the genus Homo. In the first part of the study, discriminant analysis was used to test for significant differences in mandibular corpus shape at different taxonomic levels (genus, species and subspecies) among extant hominid taxa (i.e. Homo, Pan, Gorilla, Pongo). In the second part of the study, we examined shape variation among fossil mandibles assigned to Homo (including H. habilis sensu stricto, H. rudolfensis, early African H. erectus/H. ergaster, late African H. erectus, Asian H. erectus, H. heidelbergensis, H. neanderthalensis and H. sapiens). A novel randomization procedure designed for small samples (and using group 'distinctness values') was used to determine whether shape variation among the fossils is consistent with conventional taxonomy (or alternatively, whether a priori taxonomic groupings are completely random with respect to mandibular morphology). The randomization of 'distinctness values' was also used on the extant samples to assess the ability of the test to recognize known taxa. The discriminant analysis results demonstrated that, even for a relatively modest set of traditional mandibular corpus measurements, we can detect significant differences among extant hominids at the genus and species levels, and, in some cases, also at the subspecies level. Although the randomization of 'distinctness values' test is more conservative than discriminant analysis (based on comparisons with extant specimens), we were able to detect at least four distinct groups among the fossil specimens (i.e. H. sapiens, H. heidelbergensis, Asian H. erectus and a combined 'African Homo' group consisting of H. habilis sensu stricto, H. rudolfensis, early African H. erectus/H. ergaster and late African H. erectus). These four groups appear to be distinct at a level similar to, or greater than, that of modern hominid species. In addition, the mandibular corpora of H. neanderthalensis could be distinguished from those of 'African Homo', although not from those of H. sapiens, H. heidelbergensis, or the Asian H. erectus group. The results suggest that the features most commonly preserved on the hominin mandibular corpus have some taxonomic utility, although they are unlikely to be useful in generating a reliable alpha taxonomy for early African members of the genus Homo.
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http://dx.doi.org/10.1111/j.1469-7580.2008.00989.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2666136PMC
December 2008

Protostylid expression at the enamel-dentine junction and enamel surface of mandibular molars of Paranthropus robustus and Australopithecus africanus.

J Hum Evol 2009 Jan 4;56(1):76-85. Epub 2008 Nov 4.

Hominid Paleobiology Doctoral Program, Department of Anthropology, 2110 G Street NW, The George Washington University, Washington, DC 20052, USA.

Distinctive expressions and incidences of discrete dental traits at the outer enamel surface (OES) contribute to the diagnoses of many early hominin taxa. Examination of the enamel-dentine junction (EDJ), imaged non-destructively using micro-computed tomography, has elucidated the morphological development of dental traits and improved interpretations of their variability within and among taxa. The OES expressions of one of these dental traits, the protostylid, have been found to differ among African Plio-Pleistocene fossil hominin taxa. In this study protostylid expression is examined at the OES and at the EDJ of Paranthropus robustus (n=23) and Australopithecus africanus (n=28) mandibular molars, with the goals of incorporating EDJ morphology into the definition of the protostylid and assessing the relative contribution of the EDJ and enamel cap to its expression in these taxa. The results provide evidence (a) of statistically significant taxon-specific patterns of protostylid morphology at the EDJ that are not evident at the OES; (b) that in P. robustus, thick enamel reduces the morphological correspondence between the form of the protostylid seen at the EDJ and the OES, and (c) that if EDJ images can be obtained, then the protostylid retains its taxonomic value even in worn teeth.
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http://dx.doi.org/10.1016/j.jhevol.2008.08.021DOI Listing
January 2009

Enamel-dentine junction (EDJ) morphology distinguishes the lower molars of Australopithecus africanus and Paranthropus robustus.

J Hum Evol 2008 Dec 27;55(6):979-88. Epub 2008 Sep 27.

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

Tooth crown morphology plays a central role in hominin systematics, but the removal of the original outer enamel surface by dental attrition often eliminates from consideration the type of detailed crown morphology that has been shown to discriminate among hominin taxa. This reduces the size of samples available for study. The enamel-dentine junction (EDJ) is the developmental precursor and primary contributor to the morphology of the unworn outer enamel surface, and its morphology is only affected after considerable attrition. In this paper, we explore whether the form of the EDJ can be used to distinguish between the mandibular molars of two southern African fossil hominins: Paranthropus (or Australopithecus) robustus and Australopithecus africanus. After micro-computed tomographic scanning the molar sample, we made high-resolution images of the EDJ and used geometric morphometrics to compare EDJ shape differences between species, in addition to documenting metameric variation along the molar row within each species. Landmarks were collected along the marginal ridge that runs between adjacent dentine horns and around the circumference of the cervix. Our results suggest that the morphology of the EDJ can distinguish lower molars of these southern African hominins, and it can discriminate first, second, and third molars within each taxon. These results confirm previous findings that the EDJ preserves taxonomically valuable shape information in worn teeth. Mean differences in EDJ shape, in particular dentine horn height, crown height, and cervix shape, are more marked between adjacent molars within each taxon than for the same molar between the two taxa.
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http://dx.doi.org/10.1016/j.jhevol.2008.08.013DOI Listing
December 2008

Inferences regarding the diet of extinct hominins: structural and functional trends in dental and mandibular morphology within the hominin clade.

J Anat 2008 Apr;212(4):486-500

Department of Anthropology, George Washington University, Washington, DC, USA.

This contribution investigates the evolution of diet in the Pan-Homo and hominin clades. It does this by focusing on 12 variables (nine dental and three mandibular) for which data are available about extant chimpanzees, modern humans and most extinct hominins. Previous analyses of this type have approached the interpretation of dental and gnathic function by focusing on the identification of the food consumed (i.e. fruits, leaves, etc.) rather than on the physical properties (i.e. hardness, toughness, etc.) of those foods, and they have not specifically addressed the role that the physical properties of foods play in determining dental adaptations. We take the available evidence for the 12 variables, and set out what the expression of each of those variables is in extant chimpanzees, the earliest hominins, archaic hominins, megadont archaic hominins, and an inclusive grouping made up of transitional hominins and pre-modern Homo. We then present hypotheses about what the states of these variables would be in the last common ancestor of the Pan-Homo clade and in the stem hominin. We review the physical properties of food and suggest how these physical properties can be used to investigate the functional morphology of the dentition. We show what aspects of anterior tooth morphology are critical for food preparation (e.g. peeling fruit) prior to its ingestion, which features of the postcanine dentition (e.g. overall and relative size of the crowns) are related to the reduction in the particle size of food, and how information about the macrostructure (e.g. enamel thickness) and microstructure (e.g. extent and location of enamel prism decussation) of the enamel cap might be used to make predictions about the types of foods consumed by extinct hominins. Specifically, we show how thick enamel can protect against the generation and propagation of cracks in the enamel that begin at the enamel-dentine junction and move towards the outer enamel surface.
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http://dx.doi.org/10.1111/j.1469-7580.2008.00877.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2409106PMC
April 2008

Dental trait expression at the enamel-dentine junction of lower molars in extant and fossil hominoids.

J Hum Evol 2008 Feb 28;54(2):173-86. Epub 2007 Nov 28.

Hominid Paleobiology Doctoral Program, Department of Anthropology, 2110 G Street NW, The George Washington University, Washington, DC 20052, USA.

Discrete dental traits are used as proxies for biological relatedness among modern human populations and for alpha taxonomy and phylogeny reconstruction within the hominin clade. We present a comparison of the expression of lower molar dental traits (cusp 6, cusp 7, trigonid crest pattern, and protostylid) at the enamel-dentine junction (EDJ) in a variety of extant and fossil hominoid taxa, in order to assess the contribution of the EDJ to the morphology of these traits at the outer enamel surface (OES). Molars (n=44) were imaged nondestructively using high-resolution microCT, and three-dimensional surface models of the EDJ and OES were created to compare trait expression at each surface. Our results indicate that these dental traits originate at the EDJ, and that the EDJ is primarily responsible for their degree of expression at the OES. Importantly, variable trait morphology at the EDJ (often not easily recognizable at the OES) indicates that different developmental processes can produce traits that appear similar at the enamel surface, suggesting caution in intra- and intertaxonomic comparisons. The results also highlight the importance of the EDJ for understanding the morphological development of discrete traits, and for establishing graded scales of variation to compare trait frequency among groups for the purpose of taxonomic and/or phylogenetic analysis. Finally, this study demonstrates that imaging the EDJ of both worn and unworn fossil hominin teeth provides a novel source of information about tooth development and variation in crown morphology.
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http://dx.doi.org/10.1016/j.jhevol.2007.09.012DOI Listing
February 2008

Masticatory biomechanics and its relevance to early hominid phylogeny: an examination of palatal thickness using finite-element analysis.

J Hum Evol 2007 May 20;52(5):585-99. Epub 2007 Feb 20.

Department of Anthropology, University at Albany, 1400 Washington Ave., Albany, NY 12222, USA.

It has been proposed that morphological characters functionally related to mastication may be unreliable indicators of early hominid phylogeny. One hypothesis states that masticatory characters are highly prone to homoplasy. A second hypothesis states that such characters are likely to be morphologically integrated and thus violate the assumption of character independence implicit in all phylogenetic analyses. Evaluation of these hypotheses requires that masticatory features be accurately identified, but, to date, there have been relatively few attempts to test precisely which early hominid features are functionally related to chewing. This paper uses finite-element analysis to evaluate the functional relationships of a character--palatal thickness--that is one of several Paranthropus synapomorphies putatively related to mastication. A finite-element model of 145,680 elements was created from sixty-one 2-mm-thick CT scans of a Macaca fascicularis skull. The model was assigned the elastic properties of facial bone and loaded with muscle forces corresponding to the moment of centric occlusion during mastication. The model was constrained so as to produce a reaction force (corresponding to the bite force) at M(1). With a few exceptions, the strain patterns in the finite-element model compare well with those gathered from published and unpublished bone-strain experiments. The model was then modified to have a thick palate. The model was reloaded using an identical loading regime, and the strain patterns of the original and thick-palate models were compared. Although a thickened palate acts to reduce palatal strain, strains are elevated in other facial regions. This suggests that a thick palate would not have evolved in isolation as an adaptation to withstand masticatory stress. Rather, a thick palate may have evolved in concert with a suite of other facial features that share a stress-resistance function. This appears to be consistent with hypotheses positing that at least some facial features related to chewing evolved in an integrated fashion. More functional studies of other facial features are needed, as are formal studies of morphological integration.
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http://dx.doi.org/10.1016/j.jhevol.2006.11.019DOI Listing
May 2007

Interobserver error involved in independent attempts to measure cusp base areas of Pan M1s.

J Anat 2004 Oct;205(4):323-31

CASHP, Department of Anthropology, The George Washington University, Washington, DC, USA.

Cusp base areas measured from digitized images increase the amount of detailed quantitative information one can collect from post-canine crown morphology. Although this method is gaining wide usage for taxonomic analyses of extant and extinct hominoids, the techniques for digitizing images and taking measurements differ between researchers. The aim of this study was to investigate interobserver error in order to help assess the reliability of cusp base area measurement within extant and extinct hominoid taxa. Two of the authors measured individual cusp base areas and total cusp base area of 23 maxillary first molars (M(1)) of Pan. From these, relative cusp base areas were calculated. No statistically significant interobserver differences were found for either absolute or relative cusp base areas. On average the hypocone and paracone showed the least interobserver error (< 1%) whereas the protocone and metacone showed the most (2.6-4.5%). We suggest that the larger measurement error in the metacone/protocone is due primarily to either weakly defined fissure patterns and/or the presence of accessory occlusal features. Overall, levels of interobserver error are similar to those found for intraobserver error. The results of our study suggest that if certain prescribed standards are employed then cusp and crown base areas measured by different individuals can be pooled into a single database.
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http://dx.doi.org/10.1111/j.0021-8782.2004.00334.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1571349PMC
October 2004

Early hominin limb proportions.

J Hum Evol 2002 Oct;43(4):529-48

Department of Anthropology, George Washington University, 2110 G St, NW, Washington, DC 20052, USA.

Recent analyses and new fossil discoveries suggest that the evolution of hominin limb length proportions is complex, with evolutionary reversals and a decoupling of proportions within and between limbs. This study takes into account intraspecific variation to test whether or not the limb proportions of four early hominin associated skeletons (AL 288-1, OH 62, BOU-VP-12/1, and KNM-WT 15000) can be considered to be significantly different from one another. Exact randomization methods were used to compare the differences between pairs of fossil skeletons to the differences observed between all possible pairs of individuals within large samples of Gorilla gorilla, Pan troglodytes, Pongo pygmaeus, and Homo sapiens. Although the difference in humerofemoral proportions between OH 62 and AL 288-1 does not exceed variation in the extant samples, it is rare. When humerofemoral midshaft circumferences are compared, the difference between OH 62 and AL 288-1 is fairly common in extant species. This, in combination with error associated with the limb lengths estimates, suggests that it may be premature to consider H. (or Australopithecus) habilis as having more apelike limb proportions than those in A. afarensis. The humerofemoral index of BOU-VP-12/1 differs significantly from both OH 62 and AL 288-1, but not from KNM-WT 15000. Published length estimates, if correct, suggest that the relative forearm length of BOU-VP-12/1 is unique among hominins, exceeding those of the African apes and resembling the proportions in Pongo. Evidence that A. afarensis exhibited a less apelike upper:lower limb design than A. africanus (and possibly H. habilis) suggests that, if A. afarensis is broadly ancestral to A. africanus, the latter did not simply inherit primitive morphology associated with arboreality, but is derived in this regard. The fact that the limb proportions of OH 62 (and possibly KNM-ER 3735) are no more human like than those of AL 288-1 underscores the primitive body design of H. habilis.
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October 2002