Publications by authors named "Myra F Laird"

19 Publications

  • Page 1 of 1

Human burials at the Kisese II rockshelter, Tanzania.

Am J Phys Anthropol 2021 Feb 21. Epub 2021 Feb 21.

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

Objectives: The Late Pleistocene and early Holocene in eastern Africa are associated with complex evolutionary and demographic processes that contributed to the population variability observed in the region today. However, there are relatively few human skeletal remains from this time period. Here we describe six individuals from the Kisese II rockshelter in Tanzania that were excavated in 1956, present a radiocarbon date for one of the individuals, and compare craniodental morphological diversity among eastern African populations.

Materials And Methods: This study used standard biometric analyses to assess the age, sex, and stature of the Kisese II individuals. Eastern African craniodental morphological variation was assessed using measures of dental size and a subset of Howells' cranial measurements for the Kisese II individuals as well as early Holocene, early pastoralist, Pastoral Neolithic, and modern African individuals.

Results: Our results suggest a minimum of six individuals from the Kisese II collections with two adults and four juveniles. While the dating for most of the burials is uncertain, one individual is directly radiocarbon dated to ~7.1 ka indicating that at least one burial is early Holocene in age. Craniodental metric comparisons indicate that the Kisese II individuals extend the amount of human morphological diversity among Holocene eastern Africans.

Conclusions: Our findings contribute to a growing body of evidence that Late Pleistocene and early Holocene eastern Africans exhibited relatively high amounts of morphological diversity. However, the Kisese II individuals suggest morphological similarity at localized sites potentially supporting increased regionalization during the early Holocene.
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http://dx.doi.org/10.1002/ajpa.24253DOI Listing
February 2021

Ingestive behaviors in bearded capuchins (Sapajus libidinosus).

Sci Rep 2020 11 30;10(1):20850. Epub 2020 Nov 30.

Department of Biomedical Sciences, University of Missouri Kansas City School of Medicine, 2411 Holmes Street, Kansas City, MO, 64108, USA.

The biomechanical and adaptive significance of variation in craniodental and mandibular morphology in fossil hominins is not always clear, at least in part because of a poor understanding of how different feeding behaviors impact feeding system design (form-function relationships). While laboratory studies suggest that ingestive behaviors produce variable loading, stress, and strain regimes in the cranium and mandible, understanding the relative importance of these behaviors for feeding system design requires data on their use in wild populations. Here we assess the frequencies and durations of manual, ingestive, and masticatory behaviors from more than 1400 observations of feeding behaviors video-recorded in a wild population of bearded capuchins (Sapajus libidinosus) at Fazenda Boa Vista in Piauí, Brazil. Our results suggest that ingestive behaviors in wild Sapajus libidinosus were used for a range of food material properties and typically performed using the anterior dentition. Coupled with previous laboratory work indicating that ingestive behaviors are associated with higher mandibular strain magnitudes than mastication, these results suggest that ingestive behaviors may play an important role in craniodental and mandibular design in capuchins and may be reflected in robust adaptations in fossil hominins.
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http://dx.doi.org/10.1038/s41598-020-77797-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7705727PMC
November 2020

Validation of a method for quantifying urinary C-peptide in platyrrhine monkeys.

Gen Comp Endocrinol 2021 Jan 10;300:113644. Epub 2020 Oct 10.

Department of Anthropology, Washington University in St. Louis, USA. Electronic address:

Urinary C-peptide (UCP) is a biomarker for insulin that can be used as a non-invasive physiological measure of energy balance. Previous research has validated the use of UCP to quantify energy balance in catarrhines; however, there have been no such studies in platyrrhines. Validation is necessary in this lineage of primates as divergent evolution has resulted in varied organization of insulin genes. Here, we evaluate a method for quantifying UCP in platyrrhines to measure energetic expenditure, a key component of calculating energy balance. Urine samples were opportunistically collected from laboratory-housed tufted capuchins (Sapajus apella) during exercise activities. To examine the efficacy of using UCP as a means for assessing energetic condition, we analyzed urine samples collected before and after exercise. Urinary C-peptide concentrations were measured using a commercial C-peptide radioimmunoassay. We found that on average, UCP concentrations were 0.34 ng/mL lower after exercise than they were prior to exercise (range =0.04 to 0.71 ng/mL). The rateofenergy expenditureper unit time was greater when capuchins were exercising at faster speeds. Concordantly, UCP concentrations decreased more following exercise at those faster speeds. Parallelism of serial dilutions of samples was calculated to assess the precision of UCP concentrations produced using these methods. Measured UCP concentrations decreased at expected intervals in accordance with each dilution factor. Our results provide biological validation of the use of a commercial assay for quantifying UCP as a measure of energy expenditure in this platyrrhine species.
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http://dx.doi.org/10.1016/j.ygcen.2020.113644DOI Listing
January 2021

Muscle architecture dynamics modulate performance of the superficial anterior temporalis muscle during chewing in capuchins.

Sci Rep 2020 04 14;10(1):6410. Epub 2020 Apr 14.

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

Jaw-muscle architecture is a key determinant of jaw movements and bite force. While static length-force and force-velocity relationships are well documented in mammals, architecture dynamics of the chewing muscles and their impact on muscle performance are largely unknown. We provide novel data on how fiber architecture of the superficial anterior temporalis (SAT) varies dynamically during naturalistic feeding in tufted capuchins (Sapajus apella). We collected data on architecture dynamics (changes in muscle shape or the architectural gear ratio) during the gape cycle while subjects fed on foods of different mechanical properties. Architecture of the SAT varied with phases of the gape cycle, but gape distance accounted for the majority of dynamic changes in architecture. In addition, lower gear ratios (low muscle velocity relative to fascicle velocity) were observed when animals chewed on more mechanically resistant foods. At lower gear ratios, fibers rotated less during shortening resulting in smaller pinnation angles, a configuration that favors increased force production. Our results suggest that architectural dynamics may influence jaw-muscle performance by enabling the production of higher bite forces during the occlusal phase of the gape cycle and while processing mechanically challenging foods.
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http://dx.doi.org/10.1038/s41598-020-63376-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7156371PMC
April 2020

Jaw kinematics and mandibular morphology in humans.

J Hum Evol 2020 02 13;139:102639. Epub 2019 Dec 13.

Centre for Anatomical & Human Sciences, Department of Archaeology and Hull York Medical School, University of York, York, UK.

Understanding the influence of feeding behavior on mandibular morphology is necessary for interpreting dietary change in fossil hominins. However, mandibular morphology is also likely to have an effect on feeding behavior, including jaw kinematics. Here we examine the relationships between mandibular morphology and jaw kinematics in humans using landmark-based morphometrics to quantify jaw movement. Three-dimensional movements of reflective markers coupled to the mandible and cranium were used to capture jaw movements while subjects chewed cubes of raw and cooked sweet potato. Geometric morphometric methods were adapted to quantify and analyze gape cycle motion paths. Gape cycles varied significantly across chewing sequences and between raw and cooked sweet potato. Variation in gape cycle size and shape is related to the width (intergonial distance) and length of the mandible. These results underline the fact that jaw kinematic variation within and between taxa is related to and may be influenced by mandibular morphology. Future studies examining kinematic variation should assess the influence of morphological differences on movement.
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http://dx.doi.org/10.1016/j.jhevol.2019.102639DOI Listing
February 2020

Homo naledi cranial remains from the Lesedi chamber of the rising star cave system, South Africa.

J Hum Evol 2019 07 28;132:1-14. Epub 2019 Apr 28.

Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg 2050, South Africa. Electronic address:

Excavations in the Lesedi Chamber (U.W. 102) of the Rising Star cave system from 2013 to 2015 resulted in the recovery of 131 fossils representing at least three individuals attributed to Homo naledi. Hominin fossils were recovered from three collection areas within the Lesedi Chamber. A partial skull with near complete dentition (LES1) and an associated partial skeleton were recovered from Area 102a, while craniodental remains from two other individuals were recovered from Areas 102b and 102c. Here we present detailed anatomical descriptions and metrical comparisons of the Lesedi Chamber H. naledi craniodental remains that preserve diagnostic morphology. The LES1 skull is a presumed male that is slightly larger in size, and shows greater development of ectocranial structures compared to other H. naledi specimens from the Dinaledi Chamber of the Rising Star cave system. Otherwise the Lesedi fossils are notably similar to the Dinaledi fossils in shape and morphology. The Lesedi fossils also preserve the delicate nasal and lacrimal bones that are otherwise unrecorded in the Dinaledi sample. Limited morphological differences between the Dinaledi and Lesedi Chamber hominin samples provides support for the hypothesis that these two assemblages share a close phyletic relationship.
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http://dx.doi.org/10.1016/j.jhevol.2019.03.019DOI Listing
July 2019

Taking a big bite: Working together to better understand the evolution of feeding in primates.

Am J Primatol 2019 05 8;81(5):e22981. Epub 2019 May 8.

Department of Anthropology, Rutgers University, New Jersey, New Brunswick.

The study of adaptation requires the integration of an array of different types of data. A single individual can find such integration daunting, if not impossible. In an effort to clarify the role of diet in the evolution of the primate craniofacial and dental apparatus, we assembled a team of researchers that have various types and degrees of expertise. This interaction has provided a range of insights for all contributors, and this has helped to refine questions, clarify the possibilities and limitations that laboratory and field settings offer, and further explore the ways in which laboratory and field data can be suitably integrated. A complete and accurate picture of dietary adaptation cannot be gained in isolation. Collaboration provides the bridge to a more holistic view of primate biology and evolution.
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http://dx.doi.org/10.1002/ajp.22981DOI Listing
May 2019

Joint angular excursions during cyclical behaviors differ between tetrapod feeding and locomotor systems.

J Exp Biol 2019 04 30;222(Pt 9). Epub 2019 Apr 30.

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

Tetrapod musculoskeletal diversity is usually studied separately in feeding and locomotor systems. However, comparisons between these systems promise important insight into how natural selection deploys the same basic musculoskeletal toolkit - connective tissues, bones, nerves and skeletal muscle - to meet the differing performance criteria of feeding and locomotion. In this study, we compare average joint angular excursions during cyclic behaviors - chewing, walking and running - in a phylogenetic context to explore differences in the optimality criteria of these two systems. Across 111 tetrapod species, average limb-joint angular excursions during cyclic locomotion are greater and more evolutionarily labile than those of the jaw joint during cyclic chewing. We argue that these findings reflect fundamental functional dichotomies between tetrapod locomotor and feeding systems. Tetrapod chewing systems are optimized for precise application of force over a narrower, more controlled and predictable range of displacements, the principal aim being to fracture the substrate, the size and mechanical properties of which are controlled at ingestion and further reduced and homogenized, respectively, by the chewing process. In contrast, tetrapod limbed locomotor systems are optimized for fast and energetically efficient application of force over a wider and less predictable range of displacements, the principal aim being to move the organism at varying speeds relative to a substrate whose geometry and mechanical properties need not become more homogeneous as locomotion proceeds. Hence, the evolution of tetrapod locomotor systems has been accompanied by an increasing diversity of limb-joint excursions, as tetrapods have expanded across a range of locomotor substrates and environments.
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http://dx.doi.org/10.1242/jeb.200451DOI Listing
April 2019

Inter-stride variability triggers gait transitions in mammals and birds.

Proc Biol Sci 2018 Dec;285(1893):20181766

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

Speed-related gait transitions occur in many animals, but it remains unclear what factors trigger gait changes. While the most widely accepted function of gait transitions is that they reduce locomotor costs, there is no obvious metabolic trigger signalling animals when to switch gaits. An alternative approach suggests that gait transitions serve to reduce locomotor instability. While there is evidence supporting this in humans, similar research has not been conducted in other species. This study explores energetics and stride variability during the walk-run transition in mammals and birds. Across nine species, energy savings do not predict the occurrence of a gait transition. Instead, our findings suggest that animals trigger gait transitions to maintain high locomotor rhythmicity and reduce unstable states. Metabolic efficiency is an important benefit of gait transitions, but the reduction in dynamic instability may be the proximate trigger determining when those transitions occur.
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http://dx.doi.org/10.1098/rspb.2018.1766DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6304052PMC
December 2018

A new fossil cercopithecid tibia from Laetoli and its implications for positional behavior and paleoecology.

J Hum Evol 2018 05 5;118:27-42. Epub 2018 Mar 5.

New York Consortium in Evolutionary Primatology, New York, NY, USA; Center for the Study of Human Origins, Department of Anthropology, New York University, NY 10003, USA.

Detailed analyses and comparisons of postcranial specimens of Plio-Pleistocene cercopithecids provide an opportunity to examine the recent evolutionary history and locomotor diversity in Old World monkeys. Studies examining the positional behavior and substrate preferences of fossil cercopithecids are also important for reconstructing the paleoenvironments of Plio-Pleistocene hominin sites. Here we describe a new fossil cercopithecid tibia (EP 1100/12) from the Australopithecus afarensis-bearing Upper Laetolil Beds (∼3.7 Ma) of Laetoli in northern Tanzania. The fossil tibia is attributed to cf. Rhinocolobus sp., which is the most common colobine at Laetoli. In addition to qualitative comparisons, the tibial shape of EP 1100/12 was compared to that of 190 extant cercopithecids using three-dimensional landmarks. Discriminant function analyses of the shape data were used to assess taxonomic affinity and shape variation relating to positional behavior. EP 1100/12 clustered with extant colobines, particularly the large-bodied genera Nasalis and Rhinopithecus. Comparisons reveal that EP 1100/12 belongs to a large-bodied monkey that engaged in arboreal pronograde quadrupedalism. These findings add further support to previous inferences that woodland and forest environments dominated the paleoenvironment of the Upper Laetolil Beds, which supported the diverse community of cercopithecids at Laetoli. The inferred paleoecology and the presence of large-bodied arboreally-adapted monkeys at Laetoli show that A. afarensis had access to a range of diverse habitats, including woodlands and forests. This supports the possibility that A. afarensis, with its potential range of positional capabilities, was able to utilize arboreal settings for food acquisition and refuge from predators.
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http://dx.doi.org/10.1016/j.jhevol.2018.02.005DOI Listing
May 2018

Middle and Later Stone Age chronology of Kisese II rockshelter (UNESCO World Heritage Kondoa Rock-Art Sites), Tanzania.

PLoS One 2018 28;13(2):e0192029. Epub 2018 Feb 28.

National Museum of Tanzania, Shaaban Robert Street, Dar es Salaam, Tanzania.

The archaeology of East Africa during the last ~65,000 years plays a central role in debates about the origins and dispersal of modern humans, Homo sapiens. Despite the historical importance of the region to these discussions, reliable chronologies for the nature, tempo, and timing of human behavioral changes seen among Middle Stone Age (MSA) and Later Stone Age (LSA) archaeological assemblages are sparse. The Kisese II rockshelter in the Kondoa region of Tanzania, originally excavated in 1956, preserves a ≥ 6-m-thick archaeological succession that spans the MSA/LSA transition, with lithic artifacts such as Levallois and bladelet cores and backed microliths, the recurrent use of red ochre, and >5,000 ostrich eggshell beads and bead fragments. Twenty-nine radiocarbon dates on ostrich eggshell carbonate make Kisese II one of the most robust chronological sequences for understanding archaeological change over the last ~47,000 years in East Africa. In particular, ostrich eggshell beads and backed microliths appear by 46-42 ka cal BP and occur throughout overlying Late Pleistocene and Holocene strata. Changes in lithic technology suggest an MSA/LSA transition that began 39-34.3 ka, with typical LSA technologies in place by the Last Glacial Maximum. The timing of these changes demonstrates the time-transgressive nature of behavioral innovations often linked to the origins of modern humans, even within a single region of Africa.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0192029PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5830042PMC
March 2018

Variation in human gape cycle kinematics and occlusal topography.

Authors:
Myra F Laird

Am J Phys Anthropol 2017 11 19;164(3):574-585. Epub 2017 Aug 19.

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

Objectives: This study tested hypotheses relating intraspecific variation in occlusal morphology and intraspecific variation in jaw movements during feeding. Gape cycle kinematic variation was hypothesized to correlate with gape cycle number within a chewing sequence as well as with food toughness and stiffness. Gape cycle kinematic variation was also hypothesized to correlate with variation in occlusal area, slope, and volume.

Methods And Materials: Twenty-six adult human subjects chewed four foods with varying material properties while their jaw movements were recorded using three-dimensional coordinates of facial markers captured with a Vicon camera system. Post-canine occlusal morphology of each subject was quantified in ArcGIS using dental topographic analysis of dental casts.

Results: Gape cycle duration did not vary with gape cycle number, food toughness, or food stiffness. Gape cycle vertical and lateral displacement correlated negatively with gape cycle number, while foods with higher toughness and Young's modulus had greater jaw vertical and lateral displacement. Subjects with steeper occlusal slopes had longer gape cycle durations and greater amounts of vertical displacement during the slow closing phase of the gape cycle.

Discussion: The results suggest that gape cycle durations are relatively consistent despite changes in food properties and gape cycle number, while occlusal slope affects gape cycle duration and vertical displacement during inferred occlusal contact. However, gape cycle number and bolus properties explain greater amounts of kinematic variation than does occlusal morphology.
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http://dx.doi.org/10.1002/ajpa.23298DOI Listing
November 2017

New fossil remains of from the Lesedi Chamber, South Africa.

Elife 2017 05 9;6. Epub 2017 May 9.

Evolutionary Studies Institute, University of the Witwatersrand, Wits, South Africa.

The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to . Further exploration led to the discovery of hominin material, now comprising 131 hominin specimens, within a second chamber, the Lesedi Chamber. The Lesedi Chamber is far separated from the Dinaledi Chamber within the Rising Star cave system, and represents a second depositional context for hominin remains. In each of three collection areas within the Lesedi Chamber, diagnostic skeletal material allows a clear attribution to . Both adult and immature material is present. The hominin remains represent at least three individuals based upon duplication of elements, but more individuals are likely present based upon the spatial context. The most significant specimen is the near-complete cranium of a large individual, designated LES1, with an endocranial volume of approximately 610 ml and associated postcranial remains. The Lesedi Chamber skeletal sample extends our knowledge of the morphology and variation of , and evidence of from both recovery localities shows a consistent pattern of differentiation from other hominin species.
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http://dx.doi.org/10.7554/eLife.24232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5423776PMC
May 2017

The skull of Homo naledi.

J Hum Evol 2017 03 14;104:100-123. Epub 2016 Nov 14.

Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Department of Anthropology, Texas A&M University, College Station, TX 77843, USA. Electronic address:

The species Homo naledi was recently named from specimens recovered from the Dinaledi Chamber of the Rising Star cave system in South Africa. This large skeletal sample lacks associated faunal material and currently does not have a known chronological context. In this paper, we present comprehensive descriptions and metric comparisons of the recovered cranial and mandibular material. We describe 41 elements attributed to Dinaledi Hominin (DH1-DH5) individuals and paratype U.W. 101-377, and 32 additional cranial fragments. The H. naledi material was compared to Plio-Pleistocene fossil hominins using qualitative and quantitative analyses including over 100 linear measurements and ratios. We find that the Dinaledi cranial sample represents an anatomically homogeneous population that expands the range of morphological variation attributable to the genus Homo. Despite a relatively small cranial capacity that is within the range of australopiths and a few specimens of early Homo, H. naledi shares cranial characters with species across the genus Homo, including Homo habilis, Homo rudolfensis, Homo erectus, and Middle Pleistocene Homo. These include aspects of cranial form, facial morphology, and mandibular anatomy. However, the skull of H. naledi is readily distinguishable from existing species of Homo in both qualitative and quantitative assessments. Since H. naledi is currently undated, we discuss the evolutionary implications of its cranial morphology in a range of chronological frameworks. Finally, we designate a sixth Dinaledi Hominin (DH6) individual based on a juvenile mandible.
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http://dx.doi.org/10.1016/j.jhevol.2016.09.009DOI Listing
March 2017

Skull diversity in the Homo lineage and the relative position of Homo naledi.

J Hum Evol 2017 03 9;104:124-135. Epub 2016 Nov 9.

Department of Archaeology, University of Cape Town, Rondebosch 7701, South Africa; Human Evolution Research Institute, University of Cape Town, Rondebosch 7701, South Africa. Electronic address:

The discovery of Homo naledi has expanded the range of phenotypic variation in Homo, leading to new questions surrounding the mosaic nature of morphological evolution. Though currently undated, its unique morphological pattern and possible phylogenetic relationships to other hominin taxa suggest a complex evolutionary scenario. Here, we perform geometric morphometric analyses on H. naledi cranial and mandibular remains to investigate its morphological relationship with species of Homo and Australopithecus. We use Generalized Procrustes analysis to place H. naledi within the pattern of known hominin skull diversity, distributions of Procrustes distances among individuals to compare H. naledi and Homo erectus, and neighbor joining trees to investigate the potential phenetic relationships between groups. Our goal is to address a set of hypotheses relating to the uniqueness of H. naledi, its affinity with H. erectus, and the age of the fossils based on skull morphology. Our results indicate that, cranially, H. naledi aligns with members of the genus Homo, with closest affiliations to H. erectus. The mandibular results are less clear; H. naledi closely associates with a number of taxa, including some australopiths. However, results also show that although H. naledi shares similarities with H. erectus, some distances from this taxon - especially small-brained members of this taxon - are extreme. The neighbor joining trees place H. naledi firmly within Homo. The trees based on cranial morphology again indicate a close relationship between H. naledi and H. erectus, whereas the mandibular tree places H. naledi closer to basal Homo, suggesting a deeper antiquity. Altogether, these results emphasize the unique combination of features (H. erectus-like cranium, less derived mandible) defining H. naledi. Our results also highlight the variability within Homo, calling for a greater focus on the cause of this variability, and emphasizing the importance of using the total morphological package for species diagnoses.
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http://dx.doi.org/10.1016/j.jhevol.2016.09.014DOI Listing
March 2017

The evolutionary relationships and age of Homo naledi: An assessment using dated Bayesian phylogenetic methods.

J Hum Evol 2016 08 12;97:17-26. Epub 2016 Jun 12.

Human Evolutionary Studies Program, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada; Department of Archaeology, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada; Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Department of Archaeology, University of Aberdeen, St Mary's Building, Elphinstone Road, Aberdeen, AB24 3UF, UK. Electronic address:

Homo naledi is a recently discovered species of fossil hominin from South Africa. A considerable amount is already known about H. naledi but some important questions remain unanswered. Here we report a study that addressed two of them: "Where does H. naledi fit in the hominin evolutionary tree?" and "How old is it?" We used a large supermatrix of craniodental characters for both early and late hominin species and Bayesian phylogenetic techniques to carry out three analyses. First, we performed a dated Bayesian analysis to generate estimates of the evolutionary relationships of fossil hominins including H. naledi. Then we employed Bayes factor tests to compare the strength of support for hypotheses about the relationships of H. naledi suggested by the best-estimate trees. Lastly, we carried out a resampling analysis to assess the accuracy of the age estimate for H. naledi yielded by the dated Bayesian analysis. The analyses strongly supported the hypothesis that H. naledi forms a clade with the other Homo species and Australopithecus sediba. The analyses were more ambiguous regarding the position of H. naledi within the (Homo, Au. sediba) clade. A number of hypotheses were rejected, but several others were not. Based on the available craniodental data, Homo antecessor, Asian Homo erectus, Homo habilis, Homo floresiensis, Homo sapiens, and Au. sediba could all be the sister taxon of H. naledi. According to the dated Bayesian analysis, the most likely age for H. naledi is 912 ka. This age estimate was supported by the resampling analysis. Our findings have a number of implications. Most notably, they support the assignment of the new specimens to Homo, cast doubt on the claim that H. naledi is simply a variant of H. erectus, and suggest H. naledi is younger than has been previously proposed.
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http://dx.doi.org/10.1016/j.jhevol.2016.04.008DOI Listing
August 2016

Spatial determinants of the mandibular curve of Spee in modern and archaic Homo.

Am J Phys Anthropol 2016 10 27;161(2):226-36. Epub 2016 Jun 27.

Department of Orthodontics, The University of Iowa, Iowa City, Iowa, 52242.

Objectives: The curve of Spee (COS) is a mesio-distally curved alignment of the canine through distal molar cusp tips in certain mammals including modern humans and some fossil hominins. In humans, the alignment varies from concave to flat, and previous studies have suggested that this difference reflects craniofacial morphology, including the degree of alveolar prognathism. However, the relationship between prognathism and concavity of the COS has not been tested in craniofacially variant populations. We tested the hypothesis that greater alveolar prognathism covaries with a flatter COS in African-American and European-American populations. We further examined this relationship in fossil Homo including Homo neanderthalensis and early anatomically modern Homo sapiens, which are expected to extend the amount of variation in the COS from the extant sample.

Methods And Materials: These hypotheses were tested using three-dimensional geometric morphometrics. Landmarks were recorded from the skulls of 166 African-Americans, 123 European-Americans, and 10 fossil hominin mandible casts. Landmarks were subjected to generalized Procrustes analysis, principal components analysis, and two-block partial least squares analysis.

Results: We documented covariation between the COS and alveolar prognathism such that relatively prognathic individuals have a flatter COS. Mandibular data from the fossil hominin taxa generally confirm and extend this correlation across a greater range of facial size and morphology in Homo.

Discussion: Our results suggest that the magnitude of the COS is related to a suite of features associated with alveolar prognathism in modern humans and across anthropoids. We also discuss the implications for spatial interactions between the dental arches.
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http://dx.doi.org/10.1002/ajpa.23020DOI Listing
October 2016

Chewing efficiency and occlusal functional morphology in modern humans.

J Hum Evol 2016 Apr 6;93:1-11. Epub 2016 Feb 6.

New York Consortium of Evolutionary Primatology, New York, NY, USA; Department of Anthropology, Hunter College, New York, NY, USA.

The reduction of occlusal dimensions in early Homo is often proposed to be a functional adaptation to diet. With their smaller occlusal surfaces, species of early Homo are suggested to have reduced food-processing abilities, particularly for foods with high material properties (e.g., increased toughness). Here, we employ chewing efficiency as a measure of masticatory performance to test the relationships between masticatory function and food properties. We predicted that humans are more efficient when processing foods of lower toughness and Young's modulus values, and that subjects with larger occlusal surfaces will be less efficient when processing foods with higher toughness and Young's modulus, as the greater area spreads out the overall bite force applied to food particles. Chewing efficiency was measured in 26 adults using high-speed motion capture and surface electromyography. The dentition of each subject was cast and the occlusal surface was quantified using dental topographic analysis. Toughness and displacement-limited index were negatively correlated with chewing efficiency, but Young's modulus was not. Increased occlusal two-dimensional area and surface area were positively correlated with chewing efficiency for all foods. Thus, larger occlusal surface areas were more efficient when processing foods of greater toughness. These results suggest that the reduction in occlusal area in early Homo was associated with a reduction in chewing efficiency, particularly for foods with greater toughness. Further, the larger occlusal surfaces of earlier hominins such as Australopithecus would have likely increased chewing efficiency and increased the probability of fracture when processing tough foods.
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http://dx.doi.org/10.1016/j.jhevol.2015.11.005DOI Listing
April 2016

Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa.

Elife 2015 Sep 10;4. Epub 2015 Sep 10.

Evolutionary Studies Institute and Centre of Excellence in PalaeoSciences, University of the Witwatersrand, Johannesburg, South Africa.

Homo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa.
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http://dx.doi.org/10.7554/eLife.09560DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4559886PMC
September 2015