The natomical ecord by the Numbers: Seeing Anatomy Through the Lens of Mathematics and Geometry. The scaling relationships between enamel thickness and true prism lengths are given. There is some controversy over the lumping together of material from different levels and locations in Kenya that could have confounded the description of the species’ characteristics. 2 and 3). Australopithecus anamensis is the earliest known australopith. Strength and fracture resistance are conferred to the tissue by differently oriented bundles of prisms (i.e., decussation) and by systematic differences in crystal orientation between the prism heads and the interprismatic matrix (von Koenigswald et al., 1987; Rensberger, 2000). The length of these elements was based on the local curvature of the controlling splines. Inferences about the dietary niche of A. anamensis can thus be based on more informed evidence. Consequently, the models presented here and the inferences drawn should be regarded as preliminary accounts of the strength of these different tissues (Fig. . garhi: The best-known member of Australopithecus is Au. (1998). Australopithecus anamensis is a pivotal species in human evolution. Differences in prism attitude between species, which would affect the behavior of the tissue during mastication, were not taken into account. Such internal tension arises under compressive loads that would occur during mastication and are potentially harmful to the structure of enamel (Rensberger, 2000) and the relative build‐up of these stresses is therefore reported for comparative purposes (Figs. Special Issue: Finite Element Analysis in Vertebrate Biomechanics. Australopithecus anamensis est peut-être l'ancêtre d'A. Validation of the model's predictive capabilities against measured primate specimens using controlled breaks further revealed that there are systematic differences in prism arrangements between even closely related species (Jiang et al., 2003; Macho et al., 2003). Figure 10.3 Jaw of extinct ape illustrating U-shaped dental arcade. For example, with regard to the thick enamel of hominins, both the polarity of enamel thickness (Haile‐Selassie et al., 2004) and its functional consequences remain unresolved (Macho and Spears, 1999; Ward et al., 1999, 2001; Wood and Strait. Paleoecological implications of dental mesowear and hypsodonty in fossil ungulates from Kanapoi. Molar microwear in Praeanthropus afarensis: Evidence for dietary stasis through time and under diverse paleoecological conditions. Sea otter dental enamel is highly resistant to chipping due to its microstructure. anamensis. All models are scaled to the same size and a longitudinal section through the middle of the enamel block is shown. The isotopic ecology of African mole rats informs hypotheses on the evolution of human diet. Learn about our remote access options, Hominid Palaeontology Research Group, Department of Human Anatomy and Cell Biology, University of Liverpool, Liverpool, United Kingdom, William Lee Innovation Center, University of Manchester Institute of Science and Technology (UMIST), Manchester, United Kingdom, Sport and Exercise Subject Group, School of Social Sciences and Law, University of Teesside, Middlesbrough, United Kingdom. Very little follow-up work was done until twenty-five years later, when Maeve Leakey organized digs in the … and you may need to create a new Wiley Online Library account. Additional fossil discoveries suggested that this was a new species and, in 1995, Australopithecus anamensis was proclaimed. B: The reconstructed curves of prisms are shown along the x‐z plane and the y‐z plane. Despite similarities in enamel microstructure between A. anamensis and the African great apes, the structural arrangement of prismatic enamel in A. anamensis appears to be more effective in load dissipation under these compressive loads. Dynamic Modelling of Tooth Deformation Using Occlusal Kinematics and Finite Element Analysis. By creating finite‐element models of virtual test specimens of deviating (and decussating) enamel of A. anamensis teeth and by subjecting these models to compressive stress, we inquire (nondestructively) whether the enamel of A. anamensis may have been adapted to cope with high levels of stress. afarensis derive from Hadar, a site in Ethiopia’s Afar Triangle. Interestingly, isotopic analyses of Paranthropus robustus (robust australopith from South Africa) fossil material show that while males were from the area where the fossils were found, females were not. Fossils have been found in a variety of paleoenvironmental settings, such as lakeside, woodland, and more open areas. Without appropriate structural reinforcement, these thick‐enameled teeth may be prone to failure. Cracks initiating at these sites could travel easily through the outer enamel part where prisms are relatively straight, especially in modern humans (Jiang et al., 2003). Requirements for comparing the performance of finite element models of biological structures. Despite its thick enamel, however, prism deviation in this hominin is relatively low, resulting in the scaling relationship between projected prism length (i.e., enamel thickness) and true prism length being the same as in the great apes (Fig. Unlike the parabolic tooth arrangement in the jaws of later hominins, Au. With regard to the validation process, it is noteworthy that although the overall deformation behavior of the model compares well with that in experiments, data do not exist (and cannot be obtained through traditional biomechanical testing, e.g., strain gauges) with which to compare the magnitudes of internal stress (i.e., at the ultrastructural level). Taking together, information obtained from both finite‐element analyses and dental macroanatomy leads us to suggest that A. anamensis was probably adapted for habitually consuming a hard‐tough diet. Following Spears (1997), different properties were assigned to each element to take into account differences in crystal orientation (Fig. The total number of elements for each model is thus Pan = 257,869; Gorilla = 168,784; Homo = 288,601; A. anamensis = 272,503. Molar microwear textures and the diets of Morphological comparisons were made with previously published data (Jiang et al., 2003; Macho et al., 2003) (Figs. In contrast, Pan and Homo have the highest tensile stresses away from the DEJ (i.e., in regions of lower decussation) and consequently may be more prone to fracture. Their jaws were also prognathic and their canines were larger than descendent species. Naturally broken enamel surfaces of the following A. anamensis specimens were lightly etched for 20 sec with 5% HCl and high‐resolution casts (PROVIL light, epoxy resin) were taken for SEM (backscatter) analyses. The species likely slept in trees and foraged both in trees and on the ground, as they moved bipedally around their home range in search of resources and mates. Early Humans Ardipithecus and Australopithecus. Fossils show this species was bipedal (able to walk on two legs) but still retained many ape-like features including adaptations for tree climbing, a small brain, and a long jaw. However, if we use chimps and bonobos as a model of our ancestral social organization, it was more likely a multi-male/female social organization, with males staying in their natal group (i.e. Briefly, the mathematical algorithms underlying the graphic model are based on the assumption that prism deviation (and consequently decussation) among primates is brought about by biophysical processes, i.e., the interplay of secretion of ameloblasts and the cell‐cell adhesion among them. General Principles of Evolutionary Morphology Evolutionary morphology. However, it should also be noted that by maintaining consistency in all aspects other than prism orientation, the relative magnitudes and locations of stress are suitable for comparative purposes, although caution should be adopted when making inferences about functional adaptations. A comparison of cortical elastic properties in the craniofacial skeletons of three primate species and its relevance to the study of human evolution. Functional morphology, biomechanics and the retrodiction of early hominin diets. Australopithecus anamensis is the stem species of all later hominins and exhibits the suite of characters traditionally associated with hominins, i.e., bipedal locomotion when on the ground, canine reduction, and thick‐enameled teeth. Differences in prism arrangement can thus be successfully exploited for paleobiological and functional enquiries. Although it could be argued from a phylogenetic perspective that the similarities in enamels between A. anamensis and the African apes may have been expected, such scaling relationships are surprising from a functional perspective: the results could imply only moderate crossing‐over of bundles of prisms, i.e., little decussation, and hence low resistance to crack propagation. Not all impressions revealed clear microstructures and the breaks were not always along clearly defined planes with regard to the tooth axes. In order to determine the stress concentration throughout enamel, the number of nodes exhibiting the highest stress (e.g., 20% across the entire model; darkest shading) was determined and expressed as a percentage of the total number of nodes at this cross‐section (B). Given the large degree of decussation in this region as well as the region's close proximity to the crack‐preventing mechanism of the DEJ (Marshall et al., 2001, 2003), it is improbable that any cracks initiating in this part will propagate through the enamel structure. On a microstructural level, enamel is made up of a complex arrangement of enamel prisms, whereas on an ultrastructural level, enamel is composed of differently oriented hydroxyapatite crystals held together by an inorganic matrix. As these areas of weaknesses occur on a microstructural level (Rasmussen et al., 1976), they are inaccessible to traditional stress/strain measurements (e.g., strain gauges). Therefore, the possibility that these localized cracks propagate through the structure and may threaten the integrity of the animal is based on our subjective interpretation of localized stresses. Australopithecus anamensis predates Australopithecus afarensis by 600,000 years. afarensis, may be descended from Au. We do not know nearly as much about the species as about other australopiths due to a paucity of fossil material. Mechanical Properties of Plant Underground Storage Organs and Implications for Dietary Models of Early Hominins. Ideally, in order to overcome this limitation, the whole tooth (or at least a larger piece of enamel) would have to be modeled. Australopithecus afarensis Discovered By: Peter Nzube. The Ethiopian material is close in time and geographic space to an Ardipithecus ramidus site, lending some support to the possibility of their phylogenetic relatedness. The orientation of crystals within each element was defined following Waters (1980) (Fig. Australopithecus anamensis Fossils attributed to Australopithecus anamensis (which means “southern ape of the lake” from “anam,” meaning “lake” in the Turkana language) have been recovered from sediments at Kanapoi and Allia Bay near Lake Turkana in Kenya. The findings may imply that this hominin species was well adapted to puncture crushing and are in some respects contrary to expectations based on macromorphology of teeth. Taken together, the predictions of actual values of stress, although based on well‐proven algorithms, should remain theoretical. Given the nature of the sample, error margins for the reconstructed enamel microstructures of A. anamensis are likely to be greater than they are for the extant species (Jiang et al., 2003; Macho et al., 2003). 4, Table 1). Expanded molars, low cusp relief, and thick enamel. Pliocene hominin biogeography and ecology. (1961), and (3) Xu et al. Proceedings of the Royal Society B: Biological Sciences. 3). The cranial features are primitive and in many respects resemble those of extant great apes (Ward et al., 1999, 2001), but preliminary analyses, primarily based on overall tooth size, enamel thickness, and mandibular corpus size, led to propositions that A. anamensis may have exploited a dietary niche different from the extant great apes as well as from later hominins (Teaford and Ungar, 2000; Ward et al., 2001). More importantly, however, enamel is particularly susceptible to fracture when internal tension develops between prisms with the stress acting across their orientation (Rasmussen et al., 1976); this would result in prisms being torn apart. “ ... Bipedal adaptations of elbow, knee, and tibia. While the postcranium clearly indicates that the species was bipedal when on the ground (Leakey et al., 1995, 1998; Ward et al., 1999, 2001), the functional consequences of the species' masticatory apparatus remain inconclusive (Ward et al., 1999, 2001). However, such inferences may be premature in light of the fact that the enamel blocks were not tested under all types of stress occurring during mastication (e.g., shear stress). Most often, they moved with the seasons in search of food. The similarities in the longitudinal plane are in part brought about by undulations of prisms in a tangential plane, i.e., in the x‐y plane close to the DEJ; this is similar between A. anamensis and gorillas. Here we present a new approach to overcome these difficulties. Australopithecus anamensis. As mentioned, it is categorized as a gracile form of australopith. 7) and they are also relatively localized close to the DEJ. The footprints demonstrate that the hominids walked upright habitually, as there are no knuckle-impressions. C gives the results of the validation procedure. Figure 10.2 Australopithecus anamensis sites. Australopithecus afarensis is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa.The first fossils were discovered in the 1930s, but major fossil finds would not take place until the 1970s. Australopithecus anamensis bone (University of Zurich), https://milnepublishing.geneseo.edu/the-history-of-our-tribe-hominini/, CC BY-NC-SA: Attribution-NonCommercial-ShareAlike. Stress is most localized in A. anamensis and least in Pan troglodytes. Each model was then expanded to create a cuboid enamel block encompassing at least one full cycle of deviating prisms in the z‐y plane for Pan (M1, 126 μm:140 μm:695 μm), Gorilla (M1, 125 μm:139.5 μm:685 μm), Homo (M3, 246 μm:270 μm:1,335 μm), and KNM‐KP 35851 (M2/3, 232.2 μm:256 μm:1,270 μm); the longest dimension of each specimen represents the respective enamel thickness from the dentinoenamel junction (DEJ) to the outer enamel surface (OES) along the long axes of the predominant direction of the prisms. 2). Genetic comparisons yield insight into the evolution of enamel thickness during human evolution. This species shows clear adaptations toward bipedalism, canine reduction, and thick‐enameled teeth (Leakey et al., 1995, 1998; Ward et al., 1999, 2001) and is generally regarded the stem species of all later hominins. The functional consequences of its thick enamel are, however, unclear. Given that the crystals are considerably stiffer than the matrix, enamel (as most biological materials) behaves in a complex manner. Each prism path was divided into 28 elements. The high degree of sexual dimorphism and the presence of the honing complex suggest a polygynous or polygynandrous mating system. Australopithecus anamensis. The dimensions of the enamel blocks were roughly proportional (i.e., Pan = 1:1.10:5.52; Gorilla = 1:1.12:5.48; Homo = 1:1.10:5.43; A. anamensis = 1:1.10:5.47). When comparing the data in Figure 4, it needs to be borne in mind that these experimental studies either did not specify the loading direction (Stanford et al., 1960) or did not test the tissue's behavior in the y‐direction. However, preliminary analyses indicate that due to the relatively low stiffness and direction of loading, detailed modeling of the structure of dentine and the DEJ does not affect stress distribution within the enamel. 2, Table 2). A: The planes are illustrated on a schematic tooth and a reconstructed enamel specimen is shown. (2005) for more details]. Australopithecine definition is - any of various extinct hominids (genera Australopithecus and Paranthropus) that existed two to four million years ago in southern and eastern Africa and include gracile and robust forms exhibiting bipedal locomotion, near-human dentition, and relatively small brains. First, the microstructural arrangement of enamel prisms in A. anamensis teeth was reconstructed using recently developed software and was compared with that of extant hominoids. Depending on the diet and stage of the chewing cycle, the direction and position of external loads on the teeth will vary. anamensis, which was discovered in northern Kenya near Lake Turkana at Kanapoi and Allia Bay. Discovery Location: Kanapoi, Kenya. 4, Table 1; see also Shimizu et al. For validation, a small piece of straight enamel was created and its biomechanical behavior (i.e., Young's moduli) was appraised against published experimental data (Craig et al., 1961; Stanford et al., 1960; Xu et al., 1998). The jaws and teeth are the most primitive of any australopith, which is not surprising since it is the oldest. Under the same applied compressive stress, the magnitudes of maximum tensile stress are comparable among species (Figs. The geometry of the three‐dimensional models, taken from the (mid)crown area of guiding cusps, was imported into MSC.Mentat, the finite‐element preprocessing software (MSC Software, 2002). With regard to the models, it is assumed that the crystal orientation between prism head and interprismatic matrix (IPM) and the chemical composition of the enamel matrix are the same for all species and throughout the tissue (Cuy et al., 2002). 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