Molar biomechanical function in South African hominins
            Australopithecus africanus
            and
            Paranthropus robustus

Diet is a driving force in human evolution. Two species of Plio-Pleistocene hominins, Paranthropus robustus and Australopithecus africanus , have derived craniomandibular and dental morphologies which are often interpreted as P. robustus having a more biomechanically challenging diet. While dietary reconstructions based on dental microwear generally support this, they show extensive dietary overlap between species, and craniomandibular and dental biomechanical analyses can yield contradictory results. Using methods from anthropology and engineering (i.e. anthroengineering), we quantified the molar biomechanical performance of these hominins to investigate possible dietary differences between them. Thirty-one lower second molars were 3D printed and used to fracture gelatine blocks, and Bayesian generalized linear models were used to investigate the relationship between species and tooth wear, size and shape, and biomechanical performance. Our results demonstrate that P. robustus required more force and energy to fracture blocks but had a higher force transmission rate. Considering previous dietary reconstructions, we propose three evolutionary scenarios concerning the dietary ecologies of these hominins. These evolutionary scenarios cannot be reached by investigating morphological differences in isolation, but require combining several lines of evidence. This highlights the need for a holistic approach to reconstructing hominin dietary ecology.

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Dental microwear texture analysis on extant and extinct sharks: Ante- or post-mortem tooth wear?

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/j.palaeo.2020.110147 ◽

2021 ◽

Vol 562 ◽

pp. 110147

Author(s):

Katrin Weber ◽

Daniela E. Winkler ◽

Thomas M. Kaiser ◽

Živilė Žigaitė ◽

Thomas Tütken

Keyword(s):

Texture Analysis ◽

Tooth Wear ◽

Post Mortem ◽

Dental Microwear ◽

Dental Microwear Texture Analysis

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Untangling the environmental from the dietary: dust does not matter

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2016.1032 ◽

2016 ◽

Vol 283 (1838) ◽

pp. 20161032 ◽

Cited By ~ 59

Author(s):

Gildas Merceron ◽

Anusha Ramdarshan ◽

Cécile Blondel ◽

Jean-Renaud Boisserie ◽

Noël Brunetiere ◽

...

Keyword(s):

Critical Role ◽

Tooth Wear ◽

Textural Analysis ◽

Significant Determinant ◽

Intrinsic Properties ◽

Dental Microwear ◽

Natural Conditions ◽

Evolutionary Mechanisms ◽

Food Items ◽

Selection Of

Both dust and silica phytoliths have been shown to contribute to reducing tooth volume during chewing. However, the way and the extent to which they individually contribute to tooth wear in natural conditions is unknown. There is still debate as to whether dental microwear represents a dietary or an environmental signal, with far-reaching implications on evolutionary mechanisms that promote dental phenotypes, such as molar hypsodonty in ruminants, molar lengthening in suids or enamel thickening in human ancestors. By combining controlled-food trials simulating natural conditions and dental microwear textural analysis on sheep, we show that the presence of dust on food items does not overwhelm the dietary signal. Our dataset explores variations in dental microwear textures between ewes fed on dust-free and dust-laden grass or browse fodders. Browsing diets with a dust supplement simulating Harmattan windswept environments contain more silica than dust-free grazing diets. Yet browsers given a dust supplement differ from dust-free grazers. Regardless of the presence or the absence of dust, sheep with different diets yield significantly different dental microwear textures. Dust appears a less significant determinant of dental microwear signatures than the intrinsic properties of ingested foods, implying that diet plays a critical role in driving the natural selection of dental innovations.

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Inference of Diets of Early Hominins from Primate Molar Form and Microwear

Journal of Dental Research ◽

10.1177/0022034518822981 ◽

2019 ◽

Vol 98 (4) ◽

pp. 398-405 ◽

Cited By ~ 3

Author(s):

P.S. Ungar

Keyword(s):

Food Preferences ◽

Tooth Wear ◽

Early Pleistocene ◽

Dental Microwear ◽

Dietary Specialization ◽

The Past ◽

Early Homo ◽

Occlusal Surfaces ◽

Adaptive Nature ◽

Fossil Hominin

Paleontologists use fossil teeth to reconstruct the diets of early hominins and other extinct species. Some evidence is adaptive: nature selects for tooth size, shape, and structure best suited to specific food types. Other evidence includes traces left by actual foods eaten, such as microscopic tooth wear. This critical review considers how molars work, how they are used, and how occlusal topography and dental microwear can be used to infer diet and food preferences in the past, particularly for hominins of the Pliocene and early Pleistocene. Understanding that cheek teeth function as guides for chewing and tools for fracturing allows us to characterize aspects of occlusal form that reflect mechanical properties of foods to which a species is adapted. Living primates that often eat leaves, for example, have longer crests and more sloping occlusal surfaces than those that prefer hard foods. Studies of feeding ecology have shown, however, that tooth shape does not always correspond to preferred food items. It often follows mechanically challenging foods whether eaten often or rarely. Other lines of evidence that reflect actual tooth use are required to work out food preferences. Microwear textures, for example, reflect foods eaten by individuals in the past such that hard seeds and bone tend to leave complex, pitted surface textures, whereas tough leaves and meat more often leave anisotropic ones covered in long, parallel scratches. The study of fossil hominin molars shows how these various attributes are combined to infer diet and food preference in the past. A trend in occlusal morphology suggests decreased dietary specialization from Australopithecus to early Homo, and increasing dispersion in microwear complexity values is consistent with this. On the other hand, occlusal morphology may suggest dietary specialization in Paranthropus, although different species of this genus have different microwear texture patterns despite similar craniodental adaptations.

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Evidence for habitual climbing in a Pleistocene hominin in South Africa

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1914481117 ◽

2020 ◽

Vol 117 (15) ◽

pp. 8416-8423 ◽

Cited By ~ 1

Author(s):

Leoni Georgiou ◽

Christopher J. Dunmore ◽

Ameline Bardo ◽

Laura T. Buck ◽

Jean-Jacques Hublin ◽

...

Keyword(s):

South Africa ◽

South African ◽

Modern Human ◽

Behavioral Differences ◽

Terrestrial Environment ◽

Present Evidence ◽

Australopithecus Africanus ◽

Locomotor Pattern ◽

Morphological Adaptations ◽

Morphological Differences

Bipedalism is a defining trait of the hominin lineage, associated with a transition from a more arboreal to a more terrestrial environment. While there is debate about when modern human-like bipedalism first appeared in hominins, all known South African hominins show morphological adaptations to bipedalism, suggesting that this was their predominant mode of locomotion. Here we present evidence that hominins preserved in the Sterkfontein Caves practiced two different locomotor repertoires. The trabecular structure of a proximal femur (StW 522) attributed to Australopithecus africanus exhibits a modern human-like bipedal locomotor pattern, while that of a geologically younger specimen (StW 311) attributed to either Homo sp. or Paranthropus robustus exhibits a pattern more similar to nonhuman apes, potentially suggesting regular bouts of both climbing and terrestrial bipedalism. Our results demonstrate distinct morphological differences, linked to behavioral differences between Australopithecus and later hominins in South Africa and contribute to the increasing evidence of locomotor diversity within the hominin clade.

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Tooth wear in captive rhinoceroses (Diceros, Rhinoceros, Ceratotherium: Perissodactyla) differs from that of free-ranging conspecifics

Contributions to Zoology ◽

10.1163/18759866-08302002 ◽

2014 ◽

Vol 83 (2) ◽

pp. 107-S1 ◽

Cited By ~ 11

Author(s):

Lucy A. Taylor ◽

Dennis W.H. Müller ◽

Christoph Schwitzer ◽

Thomas M. Kaiser ◽

Daryl Codron ◽

...

Keyword(s):

Life Expectancy ◽

Dental Health ◽

Tooth Wear ◽

Museum Specimens ◽

Second Molar ◽

Rhinoceros Unicornis ◽

Processing Ability ◽

Posterior Cusp ◽

Morphological Differences ◽

Free Ranging

Tooth wear can affect body condition, reproductive success and life expectancy. Poor dental health is frequently reported in the zoo literature, and abrasion-dominated tooth wear, which is typical for grazers, has been reported in captive browsing ruminants. The aim of this study was to test if a similar effect is evident in captive rhinoceros species. Dental casts of maxillary cheek teeth of museum specimens of captive black (Diceros bicornis; browser), greater one-horned (Rhinoceros unicornis; intermediate feeder) and white rhinoceroses (Ceratotherium simum; grazer) were analysed using the recently developed extended mesowear method for rhinoceroses. Captive D. bicornis exhibited significantly more abrasion-dominated tooth wear than their free-ranging conspecifics (p<0.001), whereas captive C. simum exhibited significantly less abrasion-dominated tooth wear, particularly in the posterior cusp of the second molar (p=0.005). In R. unicornis, fewer differences were exhibited between free-ranging and captive animals, but tooth wear was highly variable in this species. In both free-ranging and captive D. bicornis, anterior cusps were significantly more abrasiondominated than posterior cusps (p<0.05), which indicates morphological differences between cusps that may represent functional adaptations. By contrast, tooth wear gradients between free-ranging and captive animals differed, which indicates ingesta- specific influences responsible for inter-tooth wear differences. Captive D. bicornis exhibited more homogenous tooth wear than their free-ranging conspecifics, which may be caused by an increase in the absolute dietary abrasiveness and a decrease in relative environmental abrasiveness compared to their freeranging conspecifics. The opposite occurred in C. simum. The results of this study suggest that diets fed to captive browsers are too abrasive, which could result in the premature loss of tooth functionality, leading to reduced food acquisition and processing ability and, consequently, malnourishment.

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Tooth size and shape and their relevance to studies of hominid evolution

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1981.0014 ◽

1981 ◽

Vol 292 (1057) ◽

pp. 65-76 ◽

Cited By ~ 14

Keyword(s):

Body Size ◽

Hominid Evolution ◽

Tooth Size ◽

Taxonomic Significance ◽

Early Hominid ◽

Australopithecus Africanus ◽

Preliminary Results ◽

Rate Of Increase ◽

Crown Shape ◽

Morphological Differences

Teeth have the potential to provide evidence about both the patterns of diversity of fossil hominids and the functional adaptations of early hominid taxa. Comparative studies of dental function and the direct examination of wear patterns in fossil teeth are now providing data for testing hypotheses that major differences in dietary adaptations underlie lineage diversity in the early hominids. However, this review focuses on the contributions that dental evidence can make to hominid systematic studies. Attention is drawn to the value of tooth enamel as a morphological marker and the major contribution that teeth make to the hominid fossil sample. Systematic analysis of hominid remains must start with the identification of patterns of morphological variation. Only then can the taxonomic significance of the morphological differences be assessed and attempts made to link designated taxa in a phylogenetic scheme. The preliminary results of a detailed metrical survey of early hominid premolar and molar teeth are presented. As part of this study cusp areas of first mandibular molars were measured by planimetry. Analysis of these data, without any prior assumptions about taxonomic groups, has demonstrated that the major axis of variation separates the pooled sample into morphological subgroups. These methods provide a systematic and rigorous way of identifying patterns of tooth crown morphology and will allow a more objective assessment of the affinities of individual specimens. Fossil taxa are described in terms of both absolute and relative tooth size. If canine base area and molar crown area are considered there is considerable overlap between Australopithecus africanus and Australopithecus ( paranthropus) robustus whereas there is little or no overlap between the ranges of Australopithecus africanus and Australopithecus (Parnthopus) boisei . Differences in relative tooth size among fossil taxa are taken as an example of how to attack the problem of assessing the taxonomic significance of morphological differences. Analogues from modern primates are used to derive tooth-body size relations for three relative growth models. The results suggest that increases in body size are usually accompanied by a more rapid rate of increase in canine size than in molar size. This suggests that the relatively smaller canines of the ‘robust’ australopithecines are not the result of simple scaling, but represent the result of selection against an allometric trend. Preliminary results of a survey of the subocclusal morphology of fossil teeth are presented to indicate the potential of radiographic studies and to demonstrate that changes in root morphology can be correlated with crown shape and relative size.

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New model to explain tooth wear with implications for microwear formation and diet reconstruction

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1509491112 ◽

2015 ◽

Vol 112 (34) ◽

pp. 10669-10672 ◽

Cited By ~ 75

Author(s):

Jing Xia ◽

Jing Zheng ◽

Diaodiao Huang ◽

Z. Ryan Tian ◽

Lei Chen ◽

...

Keyword(s):

Tooth Wear ◽

Dental Microwear ◽

Fossil Species ◽

Diet Reconstruction ◽

X Ray ◽

Opal Phytoliths ◽

Atomic Force ◽

Human Enamel ◽

Tissue Removal ◽

Soft Particles

Paleoanthropologists and vertebrate paleontologists have for decades debated the etiology of tooth wear and its implications for understanding the diets of human ancestors and other extinct mammals. The debate has recently taken a twist, calling into question the efficacy of dental microwear to reveal diet. Some argue that endogenous abrasives in plants (opal phytoliths) are too soft to abrade enamel, and that tooth wear is caused principally by exogenous quartz grit on food. If so, variation in microwear among fossil species may relate more to habitat than diet. This has important implications for paleobiologists because microwear is a common proxy for diets of fossil species. Here we reexamine the notion that particles softer than enamel (e.g., silica phytoliths) do not wear teeth. We scored human enamel using a microfabrication instrument fitted with soft particles (aluminum and brass spheres) and an atomic force microscope (AFM) fitted with silica particles under fixed normal loads, sliding speeds, and spans. Resulting damage was measured by AFM, and morphology and composition of debris were determined by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Enamel chips removed from the surface demonstrate that softer particles produce wear under conditions mimicking chewing. Previous models posited that such particles rub enamel and create ridges alongside indentations without tissue removal. We propose that although these models hold for deformable metal surfaces, enamel works differently. Hydroxyapatite crystallites are “glued” together by proteins, and tissue removal requires only that contact pressure be sufficient to break the bonds holding enamel together.

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