Identifying metameric variation in extant hominoid and fossil hominid mandibular molars

Hlusko, Leslea J.

doi:10.1002/ajpa.10051

Cited by 19 publications

(29 citation statements)

References 59 publications

(59 reference statements)

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“…We focused our analysis on the M 1 because, even within an individual, molars vary in both their morphological and metrical features (Bailey, 2002; Hlusko, 2002), such that combining molar types in a single analysis would not be warranted. The M 1 was chosen for this study because it is considered to be the least variable of the upper molars (Dahlberg, 1945).…”

Section: Introductionmentioning

confidence: 99%

Evolution of M¹ crown size and cusp proportions in the genus Homo

2009

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Previous research into tooth crown dimensions and cusp proportions has proved to be a useful way to identify taxonomic differences in Pliocene and Pleistocene fossil hominins. The present study has identified changes in both M 1 crown size and cusp proportions within the genus Homo , with M 1 overall crown size reduction apparently occurring in two main stages. The first stage (a reduction of ca. 17%) is associated with the emergence of Homo ergaster and Homo erectus sensu stricto . The second stage (a reduction of ca. 10%) occurs in Homo sapiens , but the reduced modern human M 1 tooth crown size was only attained in Upper Paleolithic times. The absolute sizes of the individual cusps are highly positively correlated with overall crown size and dental reduction produces a reduction in the absolute size of each of the cusps. Most of the individual cusps scale isometrically with crown size, but the paracone shows a negative allometric relationship, indicating that the reduction in paracone size is less than in the other M 1 cusps. Thus, the phylogenetically oldest cusp in the upper molars also seems to be the most stable cusp (at least in the M 1 ). The most striking change in M 1 cusp proportions is a change in the relative size of the areas of the paracone and metacone. The combination of a small relative paracone and a large relative metacone generally characterizes specimens attributed to early Homo , and the presence of this character state in Australopithecus and Paranthropus suggests it may represent the primitive condition for the later part of the hominin clade. In contrast, nearly all later Homo taxa, with the exception of Homo antecessor , show the opposite condition (i.e. a relatively large paracone and a relatively small metacone). This change in the relationship between the relative sizes of the paracone and metacone is related to an isometric reduction of the absolute size of the metacone. This metacone reduction occurs in the context of relative stability in the paracone as crown size decreases. Among later Homo taxa, both Homo heidelbergensis and Homo neanderthalensis show a further reduction of the metacone and an enlargement of the hypocone. Fossil and contemporary H. sapiens samples show a trend toward increasing the relative size of the protocone and decreasing the relative size of the hypocone. In Europe, modern human M 1 cusp proportions are essentially reached during the Upper Paleolithic. Although some variation was documented among the fossil taxa, we suggest that the relative size of the M 1 paracone and metacone areas may be useful for differentiating the earliest members of our genus from subsequent Homo species.

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Section: Introductionmentioning

confidence: 99%

Evolution of M¹ crown size and cusp proportions in the genus Homo

2009

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“…Considerable work has been carried out on the effects of modularity on human evolution, with special emphasis on craniofacial and mandibular morphology (e.g., Bookstein et al 2003; Lieberman et al 2004; Bastir et al 2005; Polanski and Franciscus 2006). As far as dental morphology is concerned, Hlusko and colleagues have used both geometric morphometric and classic morphometric methods to evaluate patterns of integration in hominoid and hominin dentition (Hlusko 2002; Hlusko et al 2004; Hlusko and Mahaney 2009). These studies have combined morphometric and quantitative genetic data to determine how much of phenotypic correlations between phenotypes result from the genetic correlation between them, in a notable attempt to understand the genetic basis of phenotypic variation (Hlusko 2004).…”

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“…The lack of canines and premolars in mice—the most commonly used experimental model—has focused studies of dental development on the differentiation between incisors and molars; nonetheless, mouse‐based models have been extended to explain how canines and premolars could be produced by overlapping domains of gene expression giving rise to incisors and molars (McCollum and Sharpe 2001). Studies of metameric variation in shape in hominins and hominoids are scarce and based mainly on mandibular molar morphology (Hlusko 2002; Singleton et al 2011). Nevertheless, Braga and et al (2010) have evaluated metameric variation at the enamel–dentine junction in the whole postcanine dentition of a small sample that includes the Australopithecus africanus fossil Sts52.…”

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confidence: 99%

“…As far as dental morphology is concerned, Hlusko and colleagues have used both geometric morphometric and classic morphometric methods to evaluate patterns of integration in hominoid and hominin dentition (Hlusko 2002;Hlusko et al 2004;Hlusko and Mahaney 2009). These studies have combined morphometric and quantitative genetic data to determine how much of phenotypic correlations between phenotypes result from the genetic correlation between them, in a notable attempt to understand the genetic basis of phenotypic variation (Hlusko 2004). These recent articles have provided a new methodological perspective on classic works, some of which attempted to correlate patterns of variation of different molars in terms of reduction of cusps (e.g., Keene 1965) and size (e.g., Garn et al 1963).…”

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Morphological Integration in the Hominin Dentition: Evolutionary, Developmental, and Functional Factors

Gómez‐Robles

Polly

2012

Evolution

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As the most common and best preserved remains in the fossil record, teeth are central to our understanding of evolution. However, many evolutionary analyses based on dental traits overlook the constraints that limit dental evolution. These constraints are diverse, ranging from developmental interactions between the individual elements of a homologous series (the whole dentition) to functional constraints related to occlusion. This study evaluates morphological integration in the hominin dentition and its effect on dental evolution in an extensive sample of Plio-and Pleistocene hominin teeth using geometric morphometrics and phylogenetic comparative methods. Results reveal that premolars and molars display significant levels of covariation; that integration is stronger in the mandibular dentition than in the maxillary dentition; and that antagonist teeth, especially first molars, are strongly integrated. Results also show an association of morphological integration and evolution. Stasis is observed in elements with strong functional and/or developmental interactions, namely in first molars. Alternatively, directional evolution (and weaker integration) occurs in the elements with marginal roles in occlusion and mastication, probably in response to other direct or indirect selective pressures. This study points to the need to reevaluate hypotheses about hominin evolution based on dental characters, given the complex scenario in which teeth evolve.

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“…As the sister taxon to the hominin clade, Pan occupies a pivotal position in discussions of hominid molar diversity (e.g., Corruccini and McHenry,1979; McHenry and Corruccini,1980,1981; Uchida,1996; Scott and Lockwood,2004; Pilbrow,2006; Bailey,2008). On both morphological and phylogenetic grounds, Pan is a logical model for early hominin molar shape variation (Corruccini and McHenry,1979; Hlusko,2002). It is also the only widely accepted, extant hominid exemplar of both interspecific and intraspecific variation (Bailey,2008).…”

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Allometric and Metameric Shape Variation in Pan Mandibular Molars: A Digital Morphometric Analysis

Singleton

Rosenberger

Robinson

et al. 2010

The Anatomical Record

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The predominance of molar teeth in fossil hominin assemblages makes the patterning of molar shape variation a topic of bioanthropological interest. Extant models are the principal basis for understanding dental variation in the fossil record. As the sister taxon to the hominin clade, Pan is one such model and the only widely accepted extant hominid model for both interspecific and intraspecific variation. To explore the contributions of allometric scaling and meristic variation to molar variation in Pan, we applied geometric shape analysis to 3D landmarks collected from virtual replicas of chimpanzee and bonobo mandibular molars. Multivariate statistical analysis and 3D visualization of metameric and allometric shape vectors were used to characterize shape differences and test the hypothesis that species of Pan share patterns of metameric variation and molar shape allometry. Procrustes-based shape variables were found to effectively characterize crown shape, sorting molars into species and tooth-row positions with !95% accuracy. Chimpanzees and bonobos share a common pattern of M 1 -M 2 metameric variation, which is defined by differences in the relative position of the metaconid, size of the hypoconulid, curvature of the buccal wall, and proportions of the basins and foveae. Allometric scaling of molar shape is homogeneous for M 1 and M 2 within species, but bonobo and chimpanzee allometric vectors are significantly different. Nevertheless, the common allometric shape trend explains most molar-shape differences between P. paniscus and P. troglodytes. When allometric effects are factored out, chimpanzee and bonobo molars are not morphometrically distinguishable. Implications for hominid taxonomy and dietary reconstruction are discussed. Anat Rec, 294:322-334, 2011. V V C 2010 Wiley-Liss, Inc.

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Identifying metameric variation in extant hominoid and fossil hominid mandibular molars

Cited by 19 publications

References 59 publications

Evolution of M¹ crown size and cusp proportions in the genus Homo

Evolution of M¹ crown size and cusp proportions in the genus Homo

Morphological Integration in the Hominin Dentition: Evolutionary, Developmental, and Functional Factors

Allometric and Metameric Shape Variation in Pan Mandibular Molars: A Digital Morphometric Analysis

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Identifying metameric variation in extant hominoid and fossil hominid mandibular molars

Cited by 19 publications

References 59 publications

Evolution of M1 crown size and cusp proportions in the genus Homo

Evolution of M1 crown size and cusp proportions in the genus Homo

Morphological Integration in the Hominin Dentition: Evolutionary, Developmental, and Functional Factors

Allometric and Metameric Shape Variation in Pan Mandibular Molars: A Digital Morphometric Analysis

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Product

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Evolution of M¹ crown size and cusp proportions in the genus Homo

Evolution of M¹ crown size and cusp proportions in the genus Homo