1,721,146 research outputs found
Lumbar vertebral body and disc variation in modern humans with implications for reconstructing lumbar lordosis in fossil hominins
Get PDFLumbar lordosis plays a significant role in the vertebral column because it supports the weight of the torso during bipedal locomotion (Aeillo and Dean, 2002). In previous studies, vertebral body wedging (VBW) patterns (Williams et al. 2013; García-Martínez et al. 2020) and multiple linear regression formulas have been used to study lordosis in hominins (Been et al. 2010a; Been, Gómez-Olivencia and Kramer, 2012). This project evaluates the accuracy of current methods used for reconstructing lumbar lordosis in hominins through an analysis of how age, sexual dimorphism, VBW and intervertebral disc wedging (IVDW) influences lordosis. This study was the first to investigate the correlation between individual IVDW and VBW in detail and introduces the idea of reconstructing lordosis using the lumbolumbar angle. This study used a sample of modern humans, comprised of individuals between 25 and 50 years of age from the University of New Mexico Decedent Image Database (UNMDID) (n=112) and living South African adults (n=27), to study lordosis (Edgar et al. 2020). Reconstructions of lordosis were reported for fossil specimens Oberkassel 1, Oberkassel 2, Kebara 2, and StS 14. VBW, IVDW, the Cobb and lumbolumbar angle were measured digitally from CT scans. The results revealed that within the sample lordosis did not vary significantly based on age but did show signs of sexual dimorphism. Comparisons between IVDW and VBW demonstrated that IVDW contributed the most to lordotic curvature, but VBW had a stronger correlation with the Cobb and lumbolumbar angles. The relationship between VBW and IVDW was consistently negative. The reconstructed lordosis of fossil specimens was within the range of modern humans. Lordosis reconstructions varied based on methods but suggest that reconstructing the lumbolumbar angle, as opposed to the Cobb angle, could increase the accuracy of future reconstructions
A new distal fibular fragment of Homo floresiensis and the first quantitative comparative analysis of proximal and distal fibular morphology in this species
No full textThe hindlimb skeleton of the holotype (LB1) of Homo floresiensis is relatively complete and includes both fibulae, which despite being well preserved have yet to be subject to a quantitative comparative analysis with other hominids. A new distal fragment of a fibula has also been recovered from the H. floresiensis-bearing sediments at Liang Bua (Flores, Indonesia). In this study, we used 3D geometric morphometrics (3DGM) to quantify detailed aspects of the external shape and articular facet morphology of the proximal and distal ends of these H. floresiensis fibulae. The comparative sample included fibulae from 57 extant great apes (Pongo, Gorilla, and Pan), 41 recent and fossil Homo sapiens, five Australopithecus afarensis, and five Neandertals. Shape variation was analyzed using principal component analysis of Procrustes coordinates, and mean differences among taxa were tested using a Procrustes ANOVA with a randomization procedure. Size comparisons were made using centroid size and tested via correlations with principal component scores. Results demonstrate that H. floresiensis fibulae possess the absolute smallest mean linear dimensions and mean centroid sizes among our comparative sample. The proximal and distal fibular ends of H. floresiensis exhibit four key features adapted for obligate bipedalism while also displaying a suite of plesiomorphic traits shared with extant great apes and A. afarensis that, compared with that of H. sapiens and Neandertals, suggest a more versatile ankle joint with a greater range of motion and enhanced load-bearing capabilities of the fibula. Our results are consistent with other aspects of the H. floresiensis lower limb, such as long feet relative to the femur and a long forefoot relative to the hindfoot, that together suggest an australopith-like locomotor repertoire that included both obligate bipedalism and climbin
Taxonomic and functional interpretation of associated cercopithecoid carpal bones (KB 5378) from Kromdraai B, South Africa
Get PDFA partial carpus belonging to a large, South African Pliocene cercopithecoid was excavated from Kromdraai B (Gauteng, South Africa) between 1977 and 1981 alongside associated, late juvenile metacarpals 1-5 and several manual phalanges (KB 5378). Included in the KB 5378 carpus is a partial scaphoid, lunate, os centrale, trapezium, trapezoid, capitate, and hamate. Here I describe each carpal quantitatively and qualitatively in comparison to a sample of extant anthropoid primates to gain an understanding of both functional morphology and taxonomy of the KB 5378 fossils. Overall, the carpal morphology reflects that of a generalized quadruped with potential specializations for terrestrial, digitigrade locomotion. The absolute size of the carpus and metacarpals indicate that they are likely from the same individual but are more similar in size to that of Papio or Parapapio rather than the larger Gorgopithecus major, as previously suggested
A unique form of locomotion in Swartkrans hominins: An analysis of the trabecular structure of the first metatarsal
Get PDFChanges in foot bone morphology within the hominin clade are crucial for reconstructing the evolution of bipedalism and a modern human-like gait. Studies of the external morphology of the first metatarsal in humans, non-human apes and fossil hominins, have documented changes in its robusticity, epiphyseal shape and its articulation with the medial cuneiform. Trabecular bone structure has been shown to reflect habitual joint positioning, and as a result offers a promising method of interpreting first metatarsal loading in extant and fossil apes. In this study, microtomography is used to quantify the trabecular structure throughout the head and base of the first metatarsal, of a comparative sample of Homo sapiens (n=11), Pan troglodytes (n=10), Gorilla gorilla (n=10), and Pongo pygmaeus (n=6). Results from these analyses are then applied to two fossil hominin first metatarsals (SKX 5017 and SK 1813), the former being attributed to Paranthropus robustus, and the latter being of unassigned taxonomic status. Results show that within the comparative sample, bone volume fraction (BV/TV) and degree of anisotropy (DA) effectively separate bipedalism from all other forms of locomotion. Specific patterns in anisotropy and trabecular bone density distribution support the hypothesis that higher BV/TV in the dorsal regions of the bone and overall higher DA are reflective of a foot adapted for bipedalism. SKX 5017 shows patterns that are different from all modern taxa, indicating a unique form of bipedalism characterized by a habitually hyperdorsiflexing metatarsophalangeal joint and retained arboreal adaptations. SK 1813 shows a trabecular distribution in the head that is different from SKX 5017 and intermediate between modern human and non-human primates, indicating habitual but less frequent bipedalism than modern Homo sapiens and greater arboreal adaptations than SKX 5017. These results suggest that Swartkrans hominins employed habitual bipedalism, but also displayed a wider range of locomotor behaviour than modern humans
Developmental basis of primate mandibular molar crown patterning: an endostructural perspective
Get PDFAs a growing number of studies have recently implicated important developmental models and mechanisms in the cusp patterning and overall crown morphology of certain mammal taxa, it was essential to assess the relevance of these processes to the primate dentition, and their potential implications to studies of primate crown morphology. In doing so, this also allowed for the assessment of current primate crown nomenclature schemes, which growing evidence has suggested may be critically flawed. This thesis focused on an examination of the enamel-dentine junction (EDJ) of lower molars in a taxonomically broad sample of primate taxa to address these two concerns. This work represents the first attempt to gain a broad perspective of crown patterning across all primates at the EDJ surface, and from this, present a more appropriate and unified assessment of cusp patterning and nomenclature that acknowledges the important developmental processes responsible for cusp expression.
The first chapter of the thesis reviewed the literature associated with studies of EDJ morphology, the recent advances in developmental biology relevant to the mammalian dentition, and the current state of the tooth crown nomenclature. Chapter 3 assessed the multiple phylogenetic and developmental components that appear to be responsible for crown patterning in mammals, and considered their application and consequence to the study of primate crown morphology. Important examples of previously unrecognized
aspects of growth are introduced here, and considered within the context of these developmental models. Chapter 4 employed geometric morphometrics to examine the covariation between accessory cusp presence and other aspects of molar crown shape in a population of macaque lower second molars, and demonstrates that while current development models used to interpret variation in cusp patterning are broadly appropriate in macaque molars, they do not explain all manifestations of accessory cusp expression. Chapter 5 focused on the first comprehensive analysis of variation in cusp patterning on mandibular molars within the major primate clades and from this assessed the applicability of the current nomenclature schemes to each clade. Results reveal numerous new patterns of lower molar accessory cusp expression in primates, and highlight the frequent discrepancies between the expected patterns of variation inferred from the current literature and the new patterns of expected variation discovered in this study. Chapter 6 provides a discussion of the broader results of this dissertation within the context of our current understanding of primate tooth crown development
Enamel-dentine junction morphology in hominin mandibular third premolars
Get PDFIn non-human apes, as in most catarrhines, the P3 is adapted for a role in honing the large upper canine, a feature which was lost early in hominin evolution. No longer adaptively constrained to the morphology required for canine honing, the hominin P3 evolved in a variety of ways, mostly to improve its masticatory ability. This change in function makes the P3 a particularly important tooth position in hominin evolution and it has featured prominently in systematic analyses of the hominin clade. However, due to dental wear much of the original morphology of the P3 crown is lost in many hominin teeth. Analyses of other tooth positions have demonstrated that examining the enamel-dentine junction (EDJ) can improve the taxonomic signal in tooth crown morphology as well as reveal detailed insights into the presence and manifestation of discrete dental traits.
This study uses geometric morphometric techniques to analyse the shape of the P3 EDJ in a broad sample of fossil hominins, modern humans, and extant non-human apes (n = 118), aiming to characterise the major differences in P3 morphology between apes and hominins, and then within the hominin clade. The study also tests the utility of P3 EDJ shape for distinguishing among major hominin species, and addresses the affinities of a number of hominin specimens of uncertain taxonomic affiliation. Moreover, the EDJ expression of a number of P3 discrete traits are identified and investigated for the first time.
The results suggest that the morphology of the P3 EDJ is effective in distinguishing among taxa, with a very high level of classification accuracy. Further, P3 morphology is linked to previously discussed trends in hominin evolution such as the unique dental adaptations seen in Paranthropus species. The EDJ expression of discrete traits such as the transverse crest, buccal grooves and the marginal ridge are found to be variable among taxonomic groups. Potential developmental links to other features identified in molars are discussed
A non-invasive measure of bone growth in mammals: Validating urinary CTX-I as a bone resorption marker through long-bone growth velocity in bonobos
Get PDFAssessing bone growth trajectories in mammals is crucial for understanding life history dynamics, but the quantification of bone growth in natural settings can be challenging. Bone resorption markers that can be measured in urine, such as C-telopeptide of type I collagen (CTX-I), offer a non-invasive solution to assess bone growth. Although measurement of urinary CTX-I levels has been applied extensively in human studies, its use in other species is so far limited to a few clinical studies. To validate urinary CTX-I as a bone resorption marker under less controlled conditions, we investigated within-individual day-to-day variation, diurnal patterns, and sex and age-specific variation in zoo-housed bonobos (Pan paniscus). We then also correlated urinary CTX-I levels with forearm growth velocity measures. We found a day-to-day variability in urinary CTX-I levels of around 25%, comparable to human variation. Diurnally, CTX-I levels decreased, aligning with observations in humans and other species. Both sexes showed an age-related decline in urinary CTX-I levels, with a steady decrease after the age of 10 years. Additionally, we found a positive correlation between forearm growth velocity and urinary CTX-I levels across age in female, but not in male, bonobos. Our results demonstrate that urinary CTX-I levels are a meaningful measure of bone growth and highlight its potential to examine bone growth trajectories also in wild populations to investigate life history dynamics
Evolution in the palm of the human hand: Functional inferences from internal bone architecture in great apes and fossil hominins
Get PDFBiomechanics of the human hand during suspensory locomotion: a combined pressure and kinematic approach.
Get PDFThe human hand is a key anatomical area for understanding behavioural transitions in fossil hominins, particularly in relation to the evolution of human locomotion. Previous studies have examined the pressure distribution in non-human primate arboreal and terrestrial locomotion although pressure in relation to human arboreal locomotion remains unstudied. A novel combined pressure and kinematic approach is used to quantify for the first time pressure and the location of peak pressure experienced by the human hand across a range of diameters and hand postures during static and dynamic suspension activities. Significant differences were found in normalised peak pressure between the 45mm and 105mm diameters when all activity categories were combined (thumb adducted, thumb abducted, and dynamic suspension). Further analysis showed that for separate activity categories there were significant differences in normalised peak pressure between the 45mm and 105mm diameters for both the thumb adducted and abducted activities. In all cases the 45mm diameter had a greater normalised peak pressure value. The location of peak pressure has been shown to be significantly affected by diameter on the third digit and fourth proximal phalanx when the thumb is abducted. The mode locations for all activities and diameters were on the fourth-to-second digits and moved distally as the diameter increased from 45mm to 105mm. These results suggest that increasing the diameter of a superstrate [support positioned above the body: Hunt K D, Cant J G H, Gebo D L, Rose M D, Walker S E, and Youlatos D (1996) Standardized descriptions of primate locomotor and postural modes. Primates. 37: 363-387] decreases the normalised peak pressure and that diameter size affects the location of peak pressure when the thumb is abducted during suspension. There was a significant preference for the 45mm diameter out of all three diameter sizes. These results are consistent with ergonomic studies of grasping by human hand during daily manipulative activities
Trabecular Ontogeny of the Gorilla Third Metacarpal
Get PDFThe trabecular bone morphology of adult extant primates has been shown to reflect mechanical loading patterns related to locomotion. However, ontogenetic studies of humans and other mammal species has shown that there may be an adaptive lag between trabecular response and current mechanical loading patterns, which could result in adult trabecular bone morphology reflecting juvenile behaviours. This study investigated ontogenetic changes in the trabecular bone structure of the third metacarpal of mountain (n = 26) and western lowland gorillas (n = 26) and its relationship to changes in loading patterns. Results show that trabecular bone reflects mechanical loading throughout ontogeny. Bone volume fraction, trabecular thickness,and trabecular number are low at birth and increase with age. Degree of anisotropy was variable throughout ontogeny and showed no clear pattern. A high concentration of bone volume fraction can be observed on the palmar side of the third metacarpal in early life, reflecting the high frequency of climbing, suspensory, and play behaviours of young gorillas. This concentration moves to the dorsal side as terrestrial knucklewalking becomes the primary form of locomotion around 5 years of age. Fusion of the epiphysis often did not take place until 8 - 12 years of age, and overall trabecular patterning did not fully reflect adult patterns until fusion was complete, suggesting there is a lag between adult-like behaviours and adult-like trabecular morphology. No differences were found between mountain and western lowland gorillas
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