Conference Presentations by Myra Laird
The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Cham... more The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to Homo naledi. 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 H. naledi. 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 H. naledi, and evidence of H. naledi from both recovery localities shows a consistent pattern of differentiation from other hominin species.
"Myra F. Laird1,3, Herman Pontzer2,3
1. Department of Anthropology, New York University, New Yor... more "Myra F. Laird1,3, Herman Pontzer2,3
1. Department of Anthropology, New York University, New York, NY; 2. Department of Anthropology, Hunter College, New York, NY; 3. New York Consortium of Evolutionary Primatology, New York, NY
Occlusal surface area varies among fossil hominins, and this variation is thought to reflect chewing performance; however, there is morphological equifinality when enlarging an occlusal surface; for example, both increasing slope (sharpness) and two-dimensional area of the post-canine teeth would increase the total occlusal surface. In order to explore this variation in modern humans, we quantified occlusal surface morphology and tested its relation to chewing efficiency. Occlusal surfaces were measured using the program ArcGIS from three-dimensionally scanned dental casts of each subject’s upper and lower right dental rows, third premolar to terminal molar. Slope, two and three-dimensional area, and volume were recorded for each subject and used to calculate morphological indices. Each subject participated in a series of almond chewing trials which were recorded using high speed motion capture and surface electromyography of the masseter muscle. From these trials, chewing efficiency was calculated from the change in particle size relative to mechanical work of the masseter. Chewing efficiency was significantly higher in individuals with smaller occlusal areas (both two-dimensional and three-dimensional areas) and volumes. However, chewing efficiency increased in individuals with greater occlusal slopes. For almonds and foods with similar mechanical properties, these results indicate that highly sloped but small dentitions are more efficient in modern humans. We discuss the implications of these results when estimating chewing efficiency in occlusally diverse hominins including Australopithecus and Paranthropus. "
"Myra F. Laird1,3, Herman Pontzer2,3
1. Center for the Study of Human Origins, Department of Ant... more "Myra F. Laird1,3, Herman Pontzer2,3
1. Center for the Study of Human Origins, Department of Anthropology, New York University, New York, NY; 2. Department of Anthropology, Hunter College, New York, NY; 3. New York Consortium of Evolutionary Anthropology, New York, NY
The functional relationships between mastication and craniodental morphology have primarily been studied by examining bite force in relation to chewing efficiency and dental morphology. However, relatively little is known about the relationship between dental morphology and chewing efficiency. This study examined how aspects of dental morphology affect efficiency during mastication by measuring this relationship in healthy human adults. The slope, volume, and relief of each subject’s right first and second upper and lower molars were calculated in ArcGIS using three-dimensionally scanned dental casts. Participants completed a series of trials in which five almonds were chewed for 10, 20, and 30 seconds and 10, 20, and 30 masticatory cycles; chewing efficiency was calculated for each trial using particle size. High speed motion capture and electromyography were used to estimate the mechanical work performed while chewing. As expected, particle size decreased as chewing work (cycles or mechanical work) increased. We discuss the relative contributions of dental morphology and mechanical work to chewing performance across subjects, as well as potential application to the hominin fossil record."
"MYRA F. LAIRD1, NATHAN E. HOLTON2,3, JILL E. SCOTT2, ROBERT G. FRANCISCUS2,3, STEVEN D. MARSHALL... more "MYRA F. LAIRD1, NATHAN E. HOLTON2,3, JILL E. SCOTT2, ROBERT G. FRANCISCUS2,3, STEVEN D. MARSHALL3, THOMAS E. SOUTHARD3.
1Department of Anthropology, New York University; 2Department of Anthropology, University of Iowa; 3Department of Orthodontics, University of Iowa.
Function of the mandibular curve of Spee (COS), a concave arc measured across the tooth occlusal surfaces from M3 to the canine, has been studied in extant humans primarily in clinical orthodontics. Although COS function is poorly understood, it may be tied to the maximization of bite force associated with mandibular molar tilt (Smith, 1986; Baragar and Osborn, 1987; Osborn, 1987). Since function of the COS is of clinical importance in extant humans, quantification of COS variation along a greater range of mandibular size, shape, and dental wear in fossil hominins may inform both contemporary orthodontic practice and dentognathic changes across Pleistocene Homo.
In a preliminary study, we documented that COS concavity is significantly correlated with alveolar prognathism when comparing African-American and European-American samples. Here, we test the hypothesis that this relationship remains significant when extending the range of mandibular size and shape variation to include Pleistocene Homo mandibles. A maximum of 56 3-D coordinate landmarks were recorded along the occlusal surface of the dentition, facial skeleton, and mandible in 289 African-American and European-American individuals from the Cleveland Museum of Natural History and casts of n=7-22 fossil Homo specimens from several repositories. The data was analyzed using principal components analysis of Procrustes scaled shape variables and thin plate spline analysis. Results show that fossil hominins generally confirm, and extend, the correlation between a less concave COS and pronounced alveolar prognathism found in our extant humans. Moreover, these results are not inconsistent with previous research regarding dietary adaptation and function."
"MYRA F. LAIRD1, NATHAN E. HOLTON1,2, JILL E. SCOTT1, ROBERT G. FRANCISCUS1,2, STEVEN D. MARSHALL... more "MYRA F. LAIRD1, NATHAN E. HOLTON1,2, JILL E. SCOTT1, ROBERT G. FRANCISCUS1,2, STEVEN D. MARSHALL2, THOMAS E. SOUTHARD2.
1Department of Anthropology, University of Iowa; 2Department of Orthodontics, University of Iowa.
The curve of Spee (COS), a concave arc technically measured from the mandibular condyles across the tooth occlusal surfaces from M3 to the canine, is of importance during orthodontic treatment, and its presence is also occasionally mentioned in discussions of fossil hominins. Nonetheless, COS configuration is variable, and the precise developmental mechanisms that affect its variability are poorly understood. A recent analysis of longitudinal ontogenetic data derived from a Euro-American sample (Marshall et al., 2008) documented that the COS is affected by differential eruption of the permanent molars. However, craniomandibular form can influence both dental eruption and the maintenance of normal occlusion, and it is important to consider overall facial morphology when assessing COS variation.
Given that COS curvature is oriented anteroposteriorly, we tested the hypothesis that COS configuration covaries with lower facial proganathism, such that more orthognathous lower faces should exhibit greater occlusal curvature. We tested this hypothesis on a sample of Euro-Americans and African-Americans (total n=291, Cleveland Museum of Natural History) who collectively exhibit a large range of lower facial orthognathism to prognathism. Several 3-D coordinate landmarks that defined the occlusal surface of the dentition and broader aspects of the facial skeleton and mandible were assessed using principal components analysis of Procrustes scaled shape variables. Our results support the hypothesis that the COS is associated with the degree of subnasal alveolar projection, with the European derived sample exhibiting a more pronounced curve on average and the African derived sample characterized by a flatter occlusal surface. "
Papers by Myra Laird
Supplemental Figure 1: A hypothetical schematic illustrating the underlying trigger for gait tran... more Supplemental Figure 1: A hypothetical schematic illustrating the underlying trigger for gait transitions based on the (A) the energy minimization hypothesis and (B) the dynamic stability hypothesis. According to the energy minimization hypothesis, when the relationship between energy consumption per unit distance is plotted against locomotor speed, there is a set of intersecting curves characteristic of each specific gait type (e.g., walking, trotting, galloping). The peaks of these lines represent speeds with a high cost of transport, and the valleys are energetically optimal locomotor speeds. At self-selected speeds, animals tend to choose the most economical speeds within a given gait type and avoid speeds that are energetically costly. When animals are forced to accelerate, energy costs increase rapidly as animals adopt speeds near the peaks of a specific cost of transport curve. These energy costs continue to increase until it is no longer energetically efficient to maintain a ...
Speed-related gait transitions occur in many animals, but it remains unclear what factors trigger... more 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.
Palaeogeography, Palaeoclimatology, Palaeoecology
Journal of Human Evolution
Understanding the influence of feeding behavior on mandibular morphology is necessary for interpr... more 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.
American Journal of Primatology
The study of adaptation requires the integration of an array of different types of data. A single... more 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.
The Journal of Experimental Biology
Tetrapod musculoskeletal diversity is usually studied separately in feeding and locomotor systems... more 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 predi...
by Elizabeth Sawchuk, Kathryn de Luna, John Arthur, Alex Bertacchi, Jessica Inés Cerezo-Román, Potiphar Kaliba, Maggie Katongo, Myra Laird, Jason E Lewis, Audax Mabulla, George Mudenda, Christine Ogola, and Pamela R Willoughby Nature, 2022
Multiple lines of genetic and archaeological evidence suggest that there were major demographic c... more Multiple lines of genetic and archaeological evidence suggest that there were major demographic changes in the terminal Late Pleistocene epoch and early Holocene epoch of sub-Saharan Africa1,2,3,4. Inferences about this period are challenging to make because demographic shifts in the past 5,000 years have obscured the structures of more ancient populations3,5. Here we present genome-wide ancient DNA data for six individuals from eastern and south-central Africa spanning the past approximately 18,000 years (doubling the time depth of sub-Saharan African ancient DNA), increase the data quality for 15 previously published ancient individuals and analyse these alongside data from 13 other published ancient individuals. The ancestry of the individuals in our study area can be modelled as a geographically structured mixture of three highly divergent source populations, probably reflecting Pleistocene interactions around 80–20 thousand years ago, including deeply diverged eastern and southern African lineages, plus a previously unappreciated ubiquitous distribution of ancestry that occurs in highest proportion today in central African rainforest hunter-gatherers. Once established, this structure remained highly stable, with limited long-range gene flow. These results provide a new line of genetic evidence in support of hypotheses that have emerged from archaeological analyses but remain contested, suggesting increasing regionalization at the end of the Pleistocene epoch.
American Journal of Physical Anthropology, 2021
Objectives: The Late Pleistocene and early Holocene in eastern Africa are associated with complex... more 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 radiocar-bon 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 pas-toralist, 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 Pleis-tocene and early Holocene eastern Africans exhibited relatively high amounts of morphological diversity. However, the Kisese II individuals suggest morphological
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Conference Presentations by Myra Laird
1. Department of Anthropology, New York University, New York, NY; 2. Department of Anthropology, Hunter College, New York, NY; 3. New York Consortium of Evolutionary Primatology, New York, NY
Occlusal surface area varies among fossil hominins, and this variation is thought to reflect chewing performance; however, there is morphological equifinality when enlarging an occlusal surface; for example, both increasing slope (sharpness) and two-dimensional area of the post-canine teeth would increase the total occlusal surface. In order to explore this variation in modern humans, we quantified occlusal surface morphology and tested its relation to chewing efficiency. Occlusal surfaces were measured using the program ArcGIS from three-dimensionally scanned dental casts of each subject’s upper and lower right dental rows, third premolar to terminal molar. Slope, two and three-dimensional area, and volume were recorded for each subject and used to calculate morphological indices. Each subject participated in a series of almond chewing trials which were recorded using high speed motion capture and surface electromyography of the masseter muscle. From these trials, chewing efficiency was calculated from the change in particle size relative to mechanical work of the masseter. Chewing efficiency was significantly higher in individuals with smaller occlusal areas (both two-dimensional and three-dimensional areas) and volumes. However, chewing efficiency increased in individuals with greater occlusal slopes. For almonds and foods with similar mechanical properties, these results indicate that highly sloped but small dentitions are more efficient in modern humans. We discuss the implications of these results when estimating chewing efficiency in occlusally diverse hominins including Australopithecus and Paranthropus. "
1. Center for the Study of Human Origins, Department of Anthropology, New York University, New York, NY; 2. Department of Anthropology, Hunter College, New York, NY; 3. New York Consortium of Evolutionary Anthropology, New York, NY
The functional relationships between mastication and craniodental morphology have primarily been studied by examining bite force in relation to chewing efficiency and dental morphology. However, relatively little is known about the relationship between dental morphology and chewing efficiency. This study examined how aspects of dental morphology affect efficiency during mastication by measuring this relationship in healthy human adults. The slope, volume, and relief of each subject’s right first and second upper and lower molars were calculated in ArcGIS using three-dimensionally scanned dental casts. Participants completed a series of trials in which five almonds were chewed for 10, 20, and 30 seconds and 10, 20, and 30 masticatory cycles; chewing efficiency was calculated for each trial using particle size. High speed motion capture and electromyography were used to estimate the mechanical work performed while chewing. As expected, particle size decreased as chewing work (cycles or mechanical work) increased. We discuss the relative contributions of dental morphology and mechanical work to chewing performance across subjects, as well as potential application to the hominin fossil record."
1Department of Anthropology, New York University; 2Department of Anthropology, University of Iowa; 3Department of Orthodontics, University of Iowa.
Function of the mandibular curve of Spee (COS), a concave arc measured across the tooth occlusal surfaces from M3 to the canine, has been studied in extant humans primarily in clinical orthodontics. Although COS function is poorly understood, it may be tied to the maximization of bite force associated with mandibular molar tilt (Smith, 1986; Baragar and Osborn, 1987; Osborn, 1987). Since function of the COS is of clinical importance in extant humans, quantification of COS variation along a greater range of mandibular size, shape, and dental wear in fossil hominins may inform both contemporary orthodontic practice and dentognathic changes across Pleistocene Homo.
In a preliminary study, we documented that COS concavity is significantly correlated with alveolar prognathism when comparing African-American and European-American samples. Here, we test the hypothesis that this relationship remains significant when extending the range of mandibular size and shape variation to include Pleistocene Homo mandibles. A maximum of 56 3-D coordinate landmarks were recorded along the occlusal surface of the dentition, facial skeleton, and mandible in 289 African-American and European-American individuals from the Cleveland Museum of Natural History and casts of n=7-22 fossil Homo specimens from several repositories. The data was analyzed using principal components analysis of Procrustes scaled shape variables and thin plate spline analysis. Results show that fossil hominins generally confirm, and extend, the correlation between a less concave COS and pronounced alveolar prognathism found in our extant humans. Moreover, these results are not inconsistent with previous research regarding dietary adaptation and function."
1Department of Anthropology, University of Iowa; 2Department of Orthodontics, University of Iowa.
The curve of Spee (COS), a concave arc technically measured from the mandibular condyles across the tooth occlusal surfaces from M3 to the canine, is of importance during orthodontic treatment, and its presence is also occasionally mentioned in discussions of fossil hominins. Nonetheless, COS configuration is variable, and the precise developmental mechanisms that affect its variability are poorly understood. A recent analysis of longitudinal ontogenetic data derived from a Euro-American sample (Marshall et al., 2008) documented that the COS is affected by differential eruption of the permanent molars. However, craniomandibular form can influence both dental eruption and the maintenance of normal occlusion, and it is important to consider overall facial morphology when assessing COS variation.
Given that COS curvature is oriented anteroposteriorly, we tested the hypothesis that COS configuration covaries with lower facial proganathism, such that more orthognathous lower faces should exhibit greater occlusal curvature. We tested this hypothesis on a sample of Euro-Americans and African-Americans (total n=291, Cleveland Museum of Natural History) who collectively exhibit a large range of lower facial orthognathism to prognathism. Several 3-D coordinate landmarks that defined the occlusal surface of the dentition and broader aspects of the facial skeleton and mandible were assessed using principal components analysis of Procrustes scaled shape variables. Our results support the hypothesis that the COS is associated with the degree of subnasal alveolar projection, with the European derived sample exhibiting a more pronounced curve on average and the African derived sample characterized by a flatter occlusal surface. "
Papers by Myra Laird
1. Department of Anthropology, New York University, New York, NY; 2. Department of Anthropology, Hunter College, New York, NY; 3. New York Consortium of Evolutionary Primatology, New York, NY
Occlusal surface area varies among fossil hominins, and this variation is thought to reflect chewing performance; however, there is morphological equifinality when enlarging an occlusal surface; for example, both increasing slope (sharpness) and two-dimensional area of the post-canine teeth would increase the total occlusal surface. In order to explore this variation in modern humans, we quantified occlusal surface morphology and tested its relation to chewing efficiency. Occlusal surfaces were measured using the program ArcGIS from three-dimensionally scanned dental casts of each subject’s upper and lower right dental rows, third premolar to terminal molar. Slope, two and three-dimensional area, and volume were recorded for each subject and used to calculate morphological indices. Each subject participated in a series of almond chewing trials which were recorded using high speed motion capture and surface electromyography of the masseter muscle. From these trials, chewing efficiency was calculated from the change in particle size relative to mechanical work of the masseter. Chewing efficiency was significantly higher in individuals with smaller occlusal areas (both two-dimensional and three-dimensional areas) and volumes. However, chewing efficiency increased in individuals with greater occlusal slopes. For almonds and foods with similar mechanical properties, these results indicate that highly sloped but small dentitions are more efficient in modern humans. We discuss the implications of these results when estimating chewing efficiency in occlusally diverse hominins including Australopithecus and Paranthropus. "
1. Center for the Study of Human Origins, Department of Anthropology, New York University, New York, NY; 2. Department of Anthropology, Hunter College, New York, NY; 3. New York Consortium of Evolutionary Anthropology, New York, NY
The functional relationships between mastication and craniodental morphology have primarily been studied by examining bite force in relation to chewing efficiency and dental morphology. However, relatively little is known about the relationship between dental morphology and chewing efficiency. This study examined how aspects of dental morphology affect efficiency during mastication by measuring this relationship in healthy human adults. The slope, volume, and relief of each subject’s right first and second upper and lower molars were calculated in ArcGIS using three-dimensionally scanned dental casts. Participants completed a series of trials in which five almonds were chewed for 10, 20, and 30 seconds and 10, 20, and 30 masticatory cycles; chewing efficiency was calculated for each trial using particle size. High speed motion capture and electromyography were used to estimate the mechanical work performed while chewing. As expected, particle size decreased as chewing work (cycles or mechanical work) increased. We discuss the relative contributions of dental morphology and mechanical work to chewing performance across subjects, as well as potential application to the hominin fossil record."
1Department of Anthropology, New York University; 2Department of Anthropology, University of Iowa; 3Department of Orthodontics, University of Iowa.
Function of the mandibular curve of Spee (COS), a concave arc measured across the tooth occlusal surfaces from M3 to the canine, has been studied in extant humans primarily in clinical orthodontics. Although COS function is poorly understood, it may be tied to the maximization of bite force associated with mandibular molar tilt (Smith, 1986; Baragar and Osborn, 1987; Osborn, 1987). Since function of the COS is of clinical importance in extant humans, quantification of COS variation along a greater range of mandibular size, shape, and dental wear in fossil hominins may inform both contemporary orthodontic practice and dentognathic changes across Pleistocene Homo.
In a preliminary study, we documented that COS concavity is significantly correlated with alveolar prognathism when comparing African-American and European-American samples. Here, we test the hypothesis that this relationship remains significant when extending the range of mandibular size and shape variation to include Pleistocene Homo mandibles. A maximum of 56 3-D coordinate landmarks were recorded along the occlusal surface of the dentition, facial skeleton, and mandible in 289 African-American and European-American individuals from the Cleveland Museum of Natural History and casts of n=7-22 fossil Homo specimens from several repositories. The data was analyzed using principal components analysis of Procrustes scaled shape variables and thin plate spline analysis. Results show that fossil hominins generally confirm, and extend, the correlation between a less concave COS and pronounced alveolar prognathism found in our extant humans. Moreover, these results are not inconsistent with previous research regarding dietary adaptation and function."
1Department of Anthropology, University of Iowa; 2Department of Orthodontics, University of Iowa.
The curve of Spee (COS), a concave arc technically measured from the mandibular condyles across the tooth occlusal surfaces from M3 to the canine, is of importance during orthodontic treatment, and its presence is also occasionally mentioned in discussions of fossil hominins. Nonetheless, COS configuration is variable, and the precise developmental mechanisms that affect its variability are poorly understood. A recent analysis of longitudinal ontogenetic data derived from a Euro-American sample (Marshall et al., 2008) documented that the COS is affected by differential eruption of the permanent molars. However, craniomandibular form can influence both dental eruption and the maintenance of normal occlusion, and it is important to consider overall facial morphology when assessing COS variation.
Given that COS curvature is oriented anteroposteriorly, we tested the hypothesis that COS configuration covaries with lower facial proganathism, such that more orthognathous lower faces should exhibit greater occlusal curvature. We tested this hypothesis on a sample of Euro-Americans and African-Americans (total n=291, Cleveland Museum of Natural History) who collectively exhibit a large range of lower facial orthognathism to prognathism. Several 3-D coordinate landmarks that defined the occlusal surface of the dentition and broader aspects of the facial skeleton and mandible were assessed using principal components analysis of Procrustes scaled shape variables. Our results support the hypothesis that the COS is associated with the degree of subnasal alveolar projection, with the European derived sample exhibiting a more pronounced curve on average and the African derived sample characterized by a flatter occlusal surface. "