Trends in postcanine occlusal morphology within the hominin clade: The case of Paranthropus

Bailey, Shara E.; Wood, B. A.

doi:10.1007/978-1-4020-5845-5_3

Cited by 17 publications

(36 citation statements)

References 34 publications

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“…Specifically, the results are consistent with the suggestion that the early Homo taxa H. habilis and H. rudolfensis lack some of the features shared by more derived members of the genus Homo (Wood & Collard, 1999; Wood & Richmond, 2000; Bailey & Wood, 2007). The M 1 cusp proportions in these early Homo specimens are more similar to those of early hominin taxa such as Australopithecus and Paranthropus than they are to H. erectus s. s. The derived M 1 proportions seen in three early Homo individuals from East Africa, KNM‐ER 1813, OH 21 and OH 39, may be interpreted as a manifestation of the polymorphism we have seen in other groups of hominin taxa, or it could be evidence that the taxonomic allocation of these specimens warrants revision.…”

Section: Discussionsupporting

confidence: 86%

“…To clarify the polarity of cusp areas and relationships within the genus Homo , data on early hominin specimens representing the genera Australopithecus and Paranthropus were also considered. Although there are important dental differences between Australopithecus and Paranthropus , both show a similar trend toward trait intensification, including additional cusps on the maxillary molars (Bailey & Wood, 2007). Since our focus is on the genus Homo , we combined the Australopithecus and Paranthropus specimens within a single pooled early hominin sample to serve as an outgroup comparison for early Homo .…”

Section: Methodsmentioning

confidence: 99%

“…Numerous studies have focused on tooth crown shape and on the details of occlusal and subocclusal morphology (Corruccini & McHenry, 1980; Wood & Abbott, 1983; Wood et al. 1983, 1988; Wood & Uytterschaut, 1987; Wood & Engleman, 1988; Brown, 1994; Bailey, 2004; Bailey & Lynch, 2005; Guatelli‐Steinberg & Irish, 2005; Bailey & Wood, 2007; Gómez‐Robles et al. 2007, 2008; Souday, 2008).…”

Section: Introductionmentioning

confidence: 99%

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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: Discussionsupporting

confidence: 86%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2009

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“…When more than one cusps/cuspules were present at the ‘normal’ position of a given accessory cusp, these were considered (at least preliminarily) part of the same accessory cusp complex [e.g. LM ‘double’ C6 reported by Bailey & Wood () and Skinner et al. ()].…”

Section: Methodsmentioning

confidence: 99%

“…; Wood & Engleman, ; Suwa et al. ; Bailey, , ; Bailey & Wood, ; Martinón‐Torres et al. , , ; Bailey et al.…”

Section: Introductionunclassified

Homology, homoplasy and cusp variability at the enamel–dentine junction of hominoid molars

et al. 2017

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Evolutionary studies of mammalian teeth have generally concentrated on the adaptive and functional significance of dental features, whereas the role of development on phenotypic generation and as a source of variation has received comparatively little attention. The present study combines an evolutionary biological framework with state-of-the-art imaging techniques to examine the developmental basis of variation of accessory cusps. Scholars have long used the position and relatedness of cusps to other crown structures as a criterion for differentiating between developmentally homologous and homoplastic features, which can be evaluated with greater accuracy at the enamel-dentine junction (EDJ). Following this approach, we collected digital models of the EDJ and outer enamel surface of more than 1000 hominoid teeth to examine whether cusp 5 of the upper molars (UM C5) and cusps 6 and 7 of the lower molars (LM C6 and LM C7) were associated each with a common developmental origin across species. Results revealed that each of these cusps can develop in a variety of ways, in association with different dental tissues (i.e. oral epithelium, enamel matrix) and dental structures (i.e. from different cusps, crests and cingula). Both within and between species variability in cusp origin was highest in UM C5, followed by LM C7, and finally LM C6. The lack of any species-specific patterns suggests that accessory cusps in hominoids are developmentally homoplastic and that they may not be useful for identifying phylogenetic homology. An important and unanticipated finding of this study was the identification of a new taxonomically informative feature at the EDJ of the upper molars, namely the post-paracone tubercle (PPT). We found that the PPT was nearly ubiquitous in H. neanderthalensis and the small sample of Middle Pleistocene African and European humans (MPAE) examined, differing significantly from the low frequencies observed in all other hominoids, including Pleistocene and recent H. sapiens. We emphasize the utility of the EDJ for human evolutionary studies and demonstrate how features that look similar at the external surface may be the product of different developmental patterns. This study also highlights the importance of incorporating both developmental and morphological data into evolutionary studies in order to gain a better understanding of the evolutionary significance of dental and skeletal features.

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“Lucy” redux: A review of research on Australopithecus afarensis

Kimbel

Delezene

2009

American J Phys Anthropol

208

143

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In the 1970s, mid-Pliocene hominin fossils were found at the sites of Hadar in Ethiopia and Laetoli in Tanzania. These samples constituted the first substantial evidence for hominins older than 3.0 Ma and were notable for some remarkable discoveries, such as the ''Lucy'' partial skeleton and the abundant remains from the A.L. 333 locality at Hadar and the hominin footprint trail at Laetoli. The Hadar and Laetoli fossils were ultimately assigned to the novel hominin species Australopithecus afarensis, which at the time was the most plesiomorphic and geologically ancient hominin taxon. The discovery and naming of A. afarensis coincided with important developments in theory and methodology in paleoanthropology; in addition, important fossil and genetic discoveries were changing expectations about hominin divergence dates from extant African apes. This coincidence of events ensured that A. afarensis figured prominently in the last 30 years of paleoanthropological research. Here, the 301 year history of discovery, analysis, and interpretation of A. afarensis and its contexts are summarized and synthesized. Research on A. afarensis continues and subject areas in which further investigation is needed to resolve ongoing debates regarding the paleobiol- Just over three decades ago, the east African early hominin species Australopithecus afarensis was recognized as the oldest, most apelike human ancestor. Although specimens now attributed to the species had resided in fossil collections since the 1930s, the bulk of the sample was amassed during field work in the 1970s at two sites, Hadar, Ethiopia, and Laetoli, Tanzania. Today, the species' hypodigm numbers more than 400 specimens collected from a half-dozen sites, most of which are still actively being worked (Table 1). Refinements in radioisotopic dating have established the species' first and last known appearances at 3.7 and 3.0 Ma, respectively. At the time of their discovery, these specimens constituted the first informative sample of hominin fossils older than 3.0 Ma.Studies on subjects ranging from the rise of striding bipedal locomotion to the origin of the uniquely human pattern of growth and development to the evolution of hominin dietary adaptations have drawn heavily on data from the remains of A. afarensis. Taxonomic and phylogenetic research, which experienced a major renaissance in paleoanthropology beginning around the time when A. afarensis was discovered, has benefited from the extensive baseline data on fossil hominin skeletal and dental variation residing in the Hadar site-sample. Some of the research topics that focus on A. afarensis-the extent to which terrestrial bipedality was the committed form of locomotion, the degree of sexual dimorphism in body size and implications for social behavior, and the ''shape'' of the phylogenetic tree prior to the emergence of the Homo and robust australopith lineages, to name just three prominent examples-are still actively debated today, which merely drives home the message that finding solutions to scien...

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Trends in postcanine occlusal morphology within the hominin clade: The case of Paranthropus

Cited by 17 publications

References 34 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

Homology, homoplasy and cusp variability at the enamel–dentine junction of hominoid molars

“Lucy” redux: A review of research on Australopithecus afarensis

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Trends in postcanine occlusal morphology within the hominin clade: The case of Paranthropus

Cited by 17 publications

References 34 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

Homology, homoplasy and cusp variability at the enamel–dentine junction of hominoid molars

“Lucy” redux: A review of research on Australopithecus afarensis

Contact Info

Product

Resources

About

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

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