Linear enamel hypoplasia in Homo naledi reappraised in light of new Retzius periodicities.

OBJECTIVES: Among low-latitude apes, developmental defects of enamel often recur twice yearly, linkable to environmental cycles. Surprisingly, teeth of Homo naledi from Rising Star in South Africa (241-335 kya), a higher latitude site with today a single rainy season, also exhibit bimodally distributed hypoplastic enamel defects, but with uncertain timing and etiology. Newly determined Retzius periodicities for enamel formation in this taxon enable a reconstruction of the temporal patterning of childhood stress. METHODS: Using high resolution casts of 31 isolated anterior teeth from H. naledi, 82 enamel defects (linear enamel hypoplasia [LEH]) were identified. Seventeen teeth are assigned to three individuals. Perikymata in the occlusal wall of enamel furrows and between the onsets of successive LEH were visualized with scanning electron microscopy and counted. Defects were measured with an optical scanner. Conversion of perikymata counts to estimates of LEH duration and inter-LEH interval draws upon Retzius periodicities of 9 and 11 days. RESULTS: Anterior teeth record more than a year of developmental distress, expressed as two asymmetric intervals centered on 4.5 and 7.5 months bounded by three LEH. Durations, also, show bimodal distributions, lasting 3 or 12 weeks. Short duration LEH are more severe than long duration. Relative incisor/canine rates of formation are indistinguishable from modern humans. DISCUSSION: We invoke a disease and dearth model, with short episodes of distress reflecting onset of disease in young infants, lasting about 3 weeks, followed by a season of undernutrition, possibly intensified by secondary plant compounds, spanning about 12 weeks, inferably coincident with austral winter.

Cortical bone architecture of hominid intermediate phalanges reveals functional signals of locomotion and manipulation.

OBJECTIVES: Reconstruction of fossil hominin manual behaviors often relies on comparative analyses of extant hominid hands to understand the relationship between hand use and skeletal morphology. In this context, the intermediate phalanges remain understudied. Thus, here we investigate cortical bone morphology of the intermediate phalanges of extant hominids and compare it to the cortical structure of the proximal phalanges, to investigate the relationship between cortical bone structure and inferred loading during manual behaviors. MATERIALS AND METHODS: Using micro-CT data, we analyze cortical bone structure of the intermediate phalangeal shaft of digits 2-5 in Pongo pygmaeus (n = 6 individuals), Gorilla gorilla (n = 22), Pan spp. (n = 23), and Homo sapiens (n = 23). The R package morphomap is used to study cortical bone distribution, cortical thickness and cross-sectional properties within and across taxa. RESULTS: Non-human great apes generally have thick cortical bone on the palmar shaft, with Pongo only having thick cortex on the peaks of the flexor sheath ridges, while African apes have thick cortex along the entire flexor sheath ridge and proximal to the trochlea. Humans are distinct in having thicker dorsal shaft cortex as well as thick cortex at the disto-palmar region of the shaft. DISCUSSION: Variation in cortical bone distribution and properties of the intermediate phalanges is consistent with differences in locomotor and manipulative behaviors in extant great apes. Comparisons between the intermediate and proximal phalanges reveals similar patterns of cortical bone distribution within each taxon but with potentially greater load experienced by the proximal phalanges, even in knuckle-walking African apes. This study provides a comparative context for the reconstruction of habitual hand use in fossil hominins and hominids.

Trabecular architecture of the distal femur in extant hominids.

Extant great apes are characterized by a wide range of locomotor, postural and manipulative behaviours that each require the limbs to be used in different ways. In addition to external bone morphology, comparative investigation of trabecular bone, which (re-)models to reflect loads incurred during life, can provide novel insights into bone functional adaptation. Here, we use canonical holistic morphometric analysis (cHMA) to analyse the trabecular morphology in the distal femoral epiphysis of Homo sapiens (n = 26), Gorilla gorilla (n = 14), Pan troglodytes (n = 15) and Pongo sp. (n = 9). We test two predictions: (1) that differing locomotor behaviours will be reflected in differing trabecular architecture of the distal femur across Homo, Pan, Gorilla and Pongo; (2) that trabecular architecture will significantly differ between male and female Gorilla due to their different levels of arboreality but not between male and female Pan or Homo based on previous studies of locomotor behaviours. Results indicate that trabecular architecture differs among extant great apes based on their locomotor repertoires. The relative bone volume and degree of anisotropy patterns found reflect habitual use of extended knee postures during bipedalism in Homo, and habitual use of flexed knee posture during terrestrial and arboreal locomotion in Pan and Gorilla. Trabecular architecture in Pongo is consistent with a highly mobile knee joint that may vary in posture from extension to full flexion. Within Gorilla, trabecular architecture suggests a different loading of knee in extension/flexion between females and males, but no sex differences were found in Pan or Homo, supporting our predictions. Inter- and intra-specific variation in trabecular architecture of distal femur provides a comparative context to interpret knee postures and, in turn, locomotor behaviours in fossil hominins.

Human-like enamel growth in Homo naledi.

OBJECTIVES: A modern pattern (rate and duration) of dental development occurs relatively recently during human evolution. Given the temporal overlap of Homo naledi with the first appearance of fossil Homo sapiens in Africa, this small-bodied and small-brained hominin presents an opportunity to elucidate the evolution of enamel growth in the hominin clade. Here we conduct the first histological study of two permanent mandibular canines and one permanent maxillary first molar, representing three individuals attributed to H. naledi. We reconstruct the rate and duration of enamel growth and compare these findings to those reported for other fossil hominins and recent humans. MATERIALS AND METHODS: Thin sections of each tooth were produced using standard histological methods. Daily and longer period incremental markings were measured to reconstruct enamel secretion and extension rates, Retzius periodicity, canine crown and molar cusp formation time. RESULTS: Daily enamel secretion rates overlapped with those from recent hominins. Canine crown formation time is similar to that observed in recent Europeans but is longer than canine formation times reported for most other hominins including Australopithecus and H. neanderthalensis. The extended period of canine formation appears to be due to a relatively tall enamel crown and a sustained slow rate of enamel extension in the cervical portion of the crown. A Retzius periodicity of 11 days for the canines, and nine days for the molar, in H. naledi parallel results found in recent humans. An 11-day periodicity has not been reported for Late Pleistocene Homo (H. erectus, H. neanderthalensis) and is rarely found in Australopithecus and Paranthropus species. DISCUSSION: Enamel growth of H. naledi is most similar to recent humans though comparative data are limited for most fossil hominin species. The high Retzius periodicity values do not follow expectations for a small-brained hominin.

Sex-biased sampling may influence Homo naledi tooth size variation.

A frequent source of debate in paleoanthropology concerns the taxonomic unity of fossil assemblages, with many hominin samples exhibiting elevated levels of variation that can be interpreted as indicating the presence of multiple species. By contrast, the large assemblage of hominin fossils from the Rising Star cave system, assigned to Homo naledi, exhibits a remarkably low degree of variation for most skeletal elements. Many factors can contribute to low sample variation, including genetic drift, strong natural selection, biased sex ratios, and sampling of closely related individuals. In this study, we tested for potential sex-biased sampling in the Rising Star dental sample. We compared coefficients of variation for the H. naledi teeth to those for eight extant hominoid samples. We used a resampling procedure that generated samples from the extant taxa that matched the sample size of the fossil sample for each possible Rising Star dental sex ratio. We found that variation at four H. naledi tooth positions-I2, M1, P4, M1-is so low that the possibility that one sex is represented by few or no individuals in the sample cannot be excluded. Additional evidence is needed to corroborate this inference, such as ancient DNA or enamel proteome data, and our study design does not address other potential factors that would account for low sample variation. Nevertheless, our results highlight the importance of considering the taphonomic history of a hominin assemblage and suggest that sex-biased sampling is a plausible explanation for the low level of phenotypic variation found in some aspects of the current H. naledi assemblage.

Dental morphology in Homo habilis and its implications for the evolution of early Homo.

The phylogenetic position of Homo habilis is central to debates over the origin and early evolution of the genus Homo. A large portion of the species hypodigm consists of dental remains, but they have only been studied at the often worn enamel surface. We investigate the morphology of the H. habilis enamel-dentine junction (EDJ), which is preserved in cases of moderate tooth wear and known to carry a strong taxonomic signal. Geometric morphometrics is used to characterise dentine crown shape and size across the entire mandibular and maxillary tooth rows, compared with a broad comparative sample (n = 712). We find that EDJ morphology in H. habilis is for the most part remarkably primitive, supporting the hypothesis that the H. habilis hypodigm has more in common with Australopithecus than later Homo. Additionally, the chronologically younger specimen OH 16 displays a suite of derived features; its inclusion in H. habilis leads to excessive levels of variation.

Variation and covariation of external shape and cross-sectional geometry in the human metacarpus.

OBJECTIVES: Analyses of external bone shape using geometric morphometrics (GM) and cross-sectional geometry (CSG) are frequently employed to investigate bone structural variation and reconstruct activity in the past. However, the association between these methods has not been thoroughly investigated. Here, we analyze whole bone shape and CSG variation of metacarpals 1-5 and test covariation between them. MATERIALS AND METHODS: We analyzed external metacarpal shape using GM and CSG of the diaphysis at three locations in metacarpals 1-5. The study sample includes three modern human groups: crew from the shipwrecked Mary Rose (n = 35 metacarpals), a Pre-industrial group (n = 50), and a Post-industrial group (n = 31). We tested group differences in metacarpal shape and CSG, as well as correlations between these two aspects of metacarpal bone structure. RESULTS: GM analysis demonstrated metacarpus external shape variation is predominately related to changes in diaphyseal width and articular surface size. Differences in external shape were found between the non-pollical metacarpals of the Mary Rose and Pre-industrial groups and between the third metacarpals of the Pre- and Post-industrial groups. CSG results suggest the Mary Rose and Post-industrial groups have stronger metacarpals than the Pre-industrial group. Correlating CSG and external shape showed significant relationships between increasing external robusticity and biomechanical strength across non-pollical metacarpals (r: 0.815-0.535; p ≤ 0.05). DISCUSSION: Differences in metacarpal cortical structure and external shape between human groups suggest differences in the type and frequency of manual activities. Combining these results with studies of entheses and kinematics of the hand will improve reconstructions of manual behavior in the past.

Trabecular bone structure of the proximal capitate in extant hominids and fossil hominins with implications for midcarpal joint loading and the dart-thrower's motion.

OBJECTIVES: This research examines whether the distribution of trabecular bone in the proximal capitates of extant hominids, as well as several fossil hominin taxa, is associated with the oblique path of the midcarpal joint known as the dart-thrower's motion (DTM). MATERIALS AND METHODS: We analyzed proximal capitates from extant (Pongo n = 12; Gorilla n = 11; Pan n = 10; fossil and recent Homo sapiens n = 29) and extinct (Australopithecus sediba n = 2; Homo naledi n = 1; Homo floresiensis n = 2; Neandertals n = 3) hominids using a new canonical holistic morphometric analysis, which quantifies and visualizes the distribution of trabecular bone using relative bone volume as a fraction of total volume (rBV/TV). RESULTS: Homo sapiens and Neandertals had a continuous band of high rBV/TV that extended across the scaphoid, lunate, and hamate subarticular regions, but other fossil hominins and extant great apes did not. A. sediba expressed a distinct combination of human-like and Pan-like rBV/TV distribution. Both H. floresiensis and H. naledi had high rBV/TV on the ulnar-side of the capitate but low rBV/TV on the radial-side. CONCLUSION: The proximal capitates of H. sapiens and Neandertals share a distinctive distribution of trabecular bone that suggests that these two species of Homo regularly load(ed) their midcarpal joints along the full extent of the oblique path of the DTM. The observed pattern in A. sediba suggests that human-like stress at the capito-scaphoid articular surface was combined with Pan-like wrist postures, whereas the patterns in H. floresiensis and H. naledi suggest their midcarpal joints were loaded differently from that of H. sapiens and Neandertals.

The deep trabecular structure of first metacarpals in extant hominids.

OBJECTIVES: Recent studies have associated subarticular trabecular bone distribution in the extant hominid first metacarpal (Mc1) with observed thumb use, to infer fossil hominin thumb use. Here, we analyze the entire Mc1 to test for interspecific differences in: (1) the absolute volume of trabecular volume fraction, (2) the distribution of the deeper trabecular network, and (3) the distribution of trabeculae in the medullary cavity, especially beneath the Mc1 disto-radial flange. MATERIALS AND METHODS: Trabecular bone was imaged using micro-computed tomography in a sample of Homo sapiens (n = 11), Pan paniscus (n = 10), Pan troglodytes (n = 11), Gorilla gorilla (n = 10) and Pongo sp., (n = 7). Using Canonical Holistic Morphometric Analysis (cHMA), we tested for interspecific differences in the trabecular bone volume fraction (BV/TV) and its relative distribution (rBV/TV) throughout the Mc1, including within the head, medullary cavity, and base. RESULTS: P. paniscus had the highest, and H. sapiens the lowest, BV/TV relative to other species. rBV/TV distribution statistically distinguished the radial concentrations and lack of medullary trabecular bone in the H. sapiens Mc1 from all other hominids. H. sapiens and, to a lesser extent, G. gorilla also had a significantly higher trabecular volume beneath the disto-radial flange relative to other hominids. DISCUSSION: These results are consistent with differences in observed thumb use in these species and may also reflect systemic differences in bone volume fraction. The trabecular bone extension into the medullary cavity and concentrations beneath the disto-radial flange may represent crucial biomechanical signals that will aid in the inference of fossil hominin thumb use.

Early Homo erectus lived at high altitudes and produced both Oldowan and Acheulean tools.

In Africa, the scarcity of hominin remains found in direct association with stone tools has hindered attempts to link Homo habilis and Homo erectus with particular lithic industries. The infant mandible discovered in level E at Garba IV (Melka Kunture) on the highlands of Ethiopia is critical to this issue due to its direct association with an Oldowan lithic industry. Here, we use synchrotron imaging to examine the internal morphology of the unerupted permanent dentition and confirm its identification as Homo erectus. Additionally, we utilize new palaeomagnetic ages to show that (i) the mandible in level E is ca. 2 million-years-old, and represents one of the earliest Homo erectus fossils, and (ii) that overlying level D, ca. 1.95 million-years-old, contains the earliest known Acheulean assemblage.

A tooth crown morphology framework for interpreting the diversity of primate dentitions.

Variation in tooth crown morphology plays a crucial role in species diagnoses, phylogenetic inference, and the reconstruction of the evolutionary history of the primate clade. While a growing number of studies have identified developmental mechanisms linked to tooth size and cusp patterning in mammalian crown morphology, it is unclear (1) to what degree these are applicable across primates and (2) which additional developmental mechanisms should be recognized as playing important roles in odontogenesis. From detailed observations of lower molar enamel-dentine junction morphology from taxa representing the major primate clades, we outline multiple phylogenetic and developmental components responsible for crown patterning, and formulate a tooth crown morphology framework for the holistic interpretation of primate crown morphology. We suggest that adopting this framework is crucial for the characterization of tooth morphology in studies of dental development, discrete trait analysis, and systematics.

Cortical bone distribution of the proximal phalanges in great apes: implications for reconstructing manual behaviours.

Primate fingers are typically in direct contact with the environment during both locomotion and manipulation, and aspects of external phalangeal morphology are known to reflect differences in hand use. Since bone is a living tissue that can adapt in response to loading through life, the internal bone architecture of the manual phalanges should also reflect differences in manual behaviours. Here, we use the R package Morphomap to analyse high-resolution microCT scans of hominid proximal phalanges of digits 2-5 to determine whether cortical bone structure reflects variation in manual behaviours between bipedal (Homo), knuckle-walking (Gorilla, Pan) and suspensory (Pongo) taxa. We test the hypothesis that relative cortical bone distribution patterns and cross-sectional geometric properties will differ both among extant great apes and across the four digits due to locomotor and postural differences. Results indicate that cortical bone structure reflects the varied hand postures employed by each taxon. The phalangeal cortices of Pongo are significantly thinner and have weaker cross-sectional properties relative to the African apes, yet thick cortical bone under their flexor sheath ridges corresponds with predicted loading during flexed finger grips. Knuckle-walking African apes have even thicker cortical bone under the flexor sheath ridges, as well as in the region proximal to the trochlea, but Pan also has thicker diaphyseal cortices than Gorilla. Humans display a distinct pattern of distodorsal thickening, as well as relatively thin cortices, which may reflect the lack of phalangeal curvature combined with frequent use of flexed fingered hand grips during manipulation. Within each taxon, digits 2-5 have a similar cortical distribution in Pongo, Gorilla and, unexpectedly, Homo, which suggest similar loading of all fingers during habitual locomotion or hand use. In Pan, however, cortical thickness differs between the fingers, potentially reflecting differential loading during knuckle-walking. Inter- and intra-generic variation in phalangeal cortical bone structure reflects differences in manual behaviours, offering a comparative framework for reconstructing hand use in fossil hominins.

Descriptive catalog of Homo naledi dental remains from the 2013 to 2015 excavations of the Dinaledi Chamber, site U.W. 101, within the Rising Star cave system, South Africa.

More than 150 hominin teeth, dated to ∼330-241 thousand years ago, were recovered during the 2013-2015 excavations of the Dinaledi Chamber of the Rising Star cave system, South Africa. These fossils comprise the first large single-site sample of hominin teeth from the Middle Pleistocene of Africa. Though scattered remains attributable to Homo sapiens, or their possible lineal ancestors, are known from older and younger sites across the continent, the distinctive morphological feature set of the Dinaledi teeth supports the recognition of a novel hominin species, Homo naledi. This material provides evidence of African Homo lineage diversity that lasts until at least the Middle Pleistocene. Here, a catalog, anatomical descriptions, and details of preservation and taphonomic alteration are provided for the Dinaledi teeth. Where possible, provisional associations among teeth are also proposed. To facilitate future research, we also provide access to a catalog of surface files of the Rising Star jaws and teeth.

Primate tooth crown nomenclature revisited.

Cusp patterning on living and extinct primate molar teeth plays a crucial role in species diagnoses, phylogenetic inference, and the reconstruction of the evolutionary history of the primate clade. These studies rely on a system of nomenclature that can accurately identify and distinguish between the various structures of the crown surface. However, studies at the enamel-dentine junction (EDJ) of some primate taxa have demonstrated a greater degree of cusp variation and expression at the crown surface than current systems of nomenclature allow. In this study, we review the current nomenclature and its applicability across all the major primate clades based on investigations of mandibular crown morphology at the enamel-dentine junction revealed through microtomography. From these observations, we reveal numerous new patterns of lower molar accessory cusp expression in primates. We highlight numerous discrepancies between the expected patterns of variation inferred from the current academic literature, and the new patterns of expected variation seen in this study. Based on the current issues associated with the crown nomenclature, and an incomplete understanding of the precise developmental processes associated with each individual crown feature, we introduce these structures within a conservative, non-homologous naming scheme that focuses on simple location-based categorisations. Until there is a better insight into the developmental and phylogenetic origin of these crown features, these categorisations are the most practical way of addressing these structures. Until then, we also suggest the cautious use of accessory cusps for studies of taxonomy and phylogeny.

Dental data challenge the ubiquitous presence of Homo in the Cradle of Humankind.

The origins of Homo, as well as the diversity and biogeographic distribution of early Homo species, remain critical outstanding issues in paleoanthropology. Debates about the recognition of early Homo, first appearance dates, and taxonomic diversity within Homo are particularly important for determining the role that southern African taxa may have played in the origins of the genus. The correct identification of Homo remains also has implications for reconstructing phylogenetic relationships between species of Australopithecus and Paranthropus, and the links between early Homo species and Homo erectus. We use microcomputed tomography and landmark-free deformation-based three-dimensional geometric morphometrics to extract taxonomically informative data from the internal structure of postcanine teeth attributed to Early Pleistocene Homo in the southern African hominin-bearing sites of Sterkfontein, Swartkrans, Drimolen, and Kromdraai B. Our results indicate that, from our sample of 23 specimens, only 4 are unambiguously attributed to Homo, 3 of them coming from Swartkrans member 1 (SK 27, SK 847, and SKX 21204) and 1 from Sterkfontein (Sts 9). Three other specimens from Sterkfontein (StW 80 and 81, SE 1508, and StW 669) approximate the Homo condition in terms of overall enamel-dentine junction shape, but retain Australopithecus-like dental traits, and their generic status remains unclear. The other specimens, including SK 15, present a dominant australopith dental signature. In light of these results, previous dietary and ecological interpretations can be reevaluated, showing that the geochemical signal of one tooth from Kromdraai (KB 5223) and two from Swartkrans (SK 96 and SKX 268) is consistent with that of australopiths.

On the earliest Acheulean in Britain: first dates and in-situ artefacts from the MIS 15 site of Fordwich (Kent, UK).

Northern Europe experienced cycles of hominin habitation and absence during the Middle Pleistocene. Fluvial gravel terrace sites in the east of Britain and north of France provide a majority of the data contributing to this understanding, mostly through the presence or absence of stone-tool artefacts. To date, however, relatively few sites have been radiometrically dated, and many have not been excavated in modern times, leading to an over-reliance on selectively sampled and poorly dated lithic assemblages. This includes Fordwich (Kent, UK), where over 330 bifaces were discovered through industrial quarrying in the 1920s. Here, we present the first excavation and dating of artefacts discovered in situ at Fordwich, alongside their technological analysis and relationship to those previously recovered. The site is demonstrated to retain deposits of Lower Palaeolithic artefacts, with 251 flakes, scrapers and cores identified to date. Infrared-radiofluorescence (IR-RF) dating of feldspar reveals 112 artefacts to have come from levels dating to at least 570 ± 36 to 513 ± 30 thousand years ago (ka) and are most plausibly assigned to an MIS 14 deposition, with artefacts produced during MIS 15 (approx. 560-620 ka). Indeed, these IR-RF samples provide minimum ages for artefacts. Combined with evidence from exposures linked to the original quarrying activities, a similar MIS 15 age is suggested for the more than 330 handaxe artefacts discovered in the 1920s. The remaining excavated artefacts come from levels dated to between 347 ± 22 and 385 ± 21 ka (MIS 10 or 11), with this later age interpreted to reflect post-MIS 14 deposition by substrate gullying and solifluction. These data demonstrate Fordwich to be one of the earliest Palaeolithic sites in northwestern Europe, and to retain the only large Acheulean handaxe assemblage directly dated to pre-MIS 13. Thus, Fordwich is determined to be a crucial piece of the pre-Anglian Palaeolithic puzzle in northern Europe.

A Middle Pleistocene Denisovan molar from the Annamite Chain of northern Laos.

The Pleistocene presence of the genus Homo in continental Southeast Asia is primarily evidenced by a sparse stone tool record and rare human remains. Here we report a Middle Pleistocene hominin specimen from Laos, with the discovery of a molar from the Tam Ngu Hao 2 (Cobra Cave) limestone cave in the Annamite Mountains. The age of the fossil-bearing breccia ranges between 164-131 kyr, based on the Bayesian modelling of luminescence dating of the sedimentary matrix from which it was recovered, U-series dating of an overlying flowstone, and U-series-ESR dating of associated faunal teeth. Analyses of the internal structure of the molar in tandem with palaeoproteomic analyses of the enamel indicate that the tooth derives from a young, likely female, Homo individual. The close morphological affinities with the Xiahe specimen from China indicate that they belong to the same taxon and that Tam Ngu Hao 2 most likely represents a Denisovan.

Calcar femorale variation in extant and fossil hominids: Implications for identifying bipedal locomotion in fossil hominins.

The calcar femorale is an internal bony structure of the proximal femur considered to be functionally related to bipedal locomotion. Among extant primates, the presence of a calcar femorale has been so far documented in extant humans and Pan and, among extinct hominins, in the Late Miocene Orrorin, in a Pliocene Australopithecus, and in a Middle Pleistocene Homo specimen. Using high-resolution microcomputed tomography, we investigated the occurrence and morphology (i.e., shape, location, and size) of the calcar femorale in an adult sample of extant humans, Pan troglodytes, Gorilla gorilla, Pongo sp., and Papio ursinus. We also investigated for the first time the occurrence and morphology of a calcar femorale in the adult proximal femoral remains of a Late Miocene great ape (Rudapithecus) and five Plio-Pleistocene hominins from Southern and Eastern Africa (Australopithecus and Paranthropus). We took four measurements: periosteal-to-tip maximum length, maximum length excluding cortical thickness, maximum vertical height, and the distance between the most anterior and posterior limits of the root. To allow for intergeneric comparisons, estimated body size was used to standardize all measurements. Nine of 10 extant humans have a well-developed calcar femorale. Among the African apes, 6 of 10 Pan and 6 of 10 Gorilla also show a distinct calcar femorale. In Pongo (n = 9), it is only present in one captive individual. None of the five investigated Papio specimens show any trace of this structure. Only calcar femorale height, which is systematically taller and extends into the lower part of the lesser trochanter, discriminates humans from extant great apes, except for one Gorilla. The calcar femorale was absent in one Paranthropus robustus and variably developed in all other investigated fossils. These results indicate that this structure cannot be considered as a diagnostic feature of habitual bipedal locomotion and emphasize the need for further investigations of its functional role.

A computational framework for canonical holistic morphometric analysis of trabecular bone.

Bone is a remarkable, living tissue that functionally adapts to external loading. Therefore, bone shape and internal structure carry information relevant to many disciplines, including medicine, forensic science, and anthropology. However, morphometric comparisons of homologous regions across different individuals or groups are still challenging. In this study, two methods were combined to quantify such differences: (1) Holistic morphometric analysis (HMA) was used to quantify morphometric values in each bone, (2) which could then be mapped to a volumetric mesh of a canonical bone created by a statistical free-form deformation model (SDM). Required parameters for this canonical holistic morphometric analysis (cHMA) method were identified and the robustness of the method was evaluated. The robustness studies showed that the SDM converged after one to two iterations, had only a marginal bias towards the chosen starting image, and could handle large shape differences seen in bones of different species. Case studies were performed on metacarpal bones and proximal femora of different primate species to confirm prior study results. The differences between species could be visualised and statistically analysed in both case studies. cHMA provides a framework for performing quantitative comparisons of different morphometric quantities across individuals or groups. These comparisons facilitate investigation of the relationship between spatial morphometric variations and function or pathology, or both.

Ontogenetic changes to metacarpal trabecular bone structure in mountain and western lowland gorillas.

The trabecular bone morphology of adult extant primates has been shown to reflect mechanical loading related to locomotion. However, ontogenetic studies of humans and other mammals suggest an adaptive lag between trabecular bone response and current mechanical loading patterns that could result in adult trabecular bone morphology reflecting juvenile behaviours. This study investigates ontogenetic changes in the trabecular bone structure of the third metacarpal of mountain gorillas (Gorilla beringei beringei; n = 26) and western lowland gorillas (Gorilla gorilla gorilla; n = 26) and its relationship to expected changes in locomotor loading patterns. Results show that trabecular bone reflects predicted mechanical loading throughout ontogeny. Bone volume fraction, trabecular thickness and trabecular number are low at birth and increase with age, although degree of anisotropy remains relatively stable throughout ontogeny. A high concentration of bone volume fraction can be observed in the distopalmar region of the third metacarpal epiphysis in early ontogeny, consistent with the high frequency of climbing, suspensory and other grasping behaviours in young gorillas. High trabecular bone concentration increases dorsally in the epiphysis during the juvenile period as terrestrial knuckle-walking becomes the primary form of locomotion. However, fusion of the epiphysis does not take place until 10-11 years of age, and overall trabecular structure does not fully reflect the adult pattern until 12 years of age, indicating a lag between adult-like behaviours and adult-like trabecular morphology. We found minimal differences in trabecular ontogeny between mountain and western lowland gorillas, despite presumed variation in the frequencies of arboreal locomotor behaviours. Altogether, ontogenetic changes in Gorilla metacarpal trabecular structure reflect overall genus-level changes in locomotor behaviours throughout development, but with some ontogenetic lag that should be considered when drawing functional conclusions from bone structure in extant or fossil adolescent specimens.