Individual Skeletal Elements Research Articles

Body proportions and environmental adaptation in gorillas.

Limb length and trunk proportions are determined in a large, taxonomically and environmentally diverse sample of gorillas and related to variation in locomotion, climate, altitude, and diet. The sample includes 299 gorilla skeletons, 115 of which are infants and juveniles, distributed between western lowland (G. gorilla gorilla), low and high elevation grauer (G. beringei graueri), and Virunga mountain gorillas (G. b. beringei). Limb bone and vertebral column lengths scaled to body mass are compared between subgroups by age group. All G. beringei have relatively short 3rd metapodials and manual proximal phalanges compared to G. gorilla, and this difference is apparent in infancy. All G. beringei also have shortened total limb lengths relative to either body mass or vertebral column length, although patterns of variation in individual skeletal elements are more complex, and infants do not display the same patterns as adults. Mountain gorillas have relatively long clavicles, present in infancy, and a relatively long thoracic (but not lumbosacral) vertebral column. A variety of environmental factors likely contributed to observed patterns of morphological variation among extant gorillas. We interpret the short hand and foot bones of all G. beringei as genetic adaptations to greater terrestriality in the last common ancestor of G. beringei; variation in other limb lengths to climatic adaptation, both genetic and developmental; and the larger thorax of G. b. beringei to adaptation to reduced oxygen pressure at high altitudes, again as a product of both genetic differences and environmental influences during development.

Braincase anatomy of extant Crocodylia, with new insights into the development and evolution of the neurocranium in crocodylomorphs.

Present-day crocodylians exhibit a remarkably akinetic skull with a highly modified braincase. We present a comprehensive description of the neurocranial osteology of extant crocodylians, with notes on the development of individual skeletal elements and a discussion of the terminology used for this project. The quadrate is rigidly fixed by multiple contacts with most braincase elements. The parabasisphenoid is sutured to the pterygoids (palate) and the quadrate (suspensorium); as a result, the basipterygoid joint is completely immobilized. The prootic is reduced and externally concealed by the quadrate. It has a verticalized buttress that participates in the canal for the temporal vasculature. The ventrolateral processes of the otoccipitals completely cover the posteroventral region of the braincase, enclose the occipital nerves and blood vessels in narrow bony canals and also provide additional sutural contacts between the braincase elements and further consolidate the posterior portion of the crocodylian skull. The otic capsule of crocodylians has a characteristic cochlear prominence that corresponds to the lateral route of the perilymphatic sac. Complex internal structures of the otoccipital (extracapsular buttress) additionally arrange the neurovascular structures of the periotic space of the cranium. Most of the braincase elements of crocodylians are excavated by the paratympanic pneumatic sinuses. The braincase in various extant crocodylians has an overall similar structure with some consistent variation between taxa. Several newly observed features of the braincase are present in Gavialis gangeticus and extant members of Crocodylidae to the exclusion of alligatorids: the reduced exposure of the prootic buttress on the floor of the temporal canal, the sagittal nuchal crest of the supraoccipital projecting posteriorly beyond the postoccipital processes and the reduced paratympanic pneumaticity. The most distinctive features of the crocodylian braincase (fixed quadrate and basipterygoid joint, consolidated occiput) evolved relatively rapidly at the base of Crocodylomorpha and accompanied the initial diversification of this clade during the Late Triassic and Early Jurassic. We hypothesize that profound rearrangements in the individual development of the braincases of basal crocodylomorphs underlie these rapid evolutionary modifications. These rearrangements are likely reflected in the embryonic development of extant crocodylians and include the involvement of neomorphic dermal anlagen in different portions of the developing chondrocranium, the extensive ossification of the palatoquadrate cartilage as a single expanded quadrate and the anteromedial inclination of the quadrate.

Developmental and Evolutionary Allometry of the Mammalian Limb Skeleton.

The variety of limb skeletal proportions enables a remarkable diversity of behaviors that include powered flight in bats and flipper-propelled swimming in whales using extremes of a range of homologous limb architectures. Even within human limbs, bone lengths span more than an order of magnitude from the short finger and toe bones to the long arm and leg bones. Yet all of this diversity arises from embryonic skeletal elements that are each a very similar size at formation. In this review article, I survey what is and is not yet known of the development and evolution of skeletal proportion at multiple hierarchical levels of biological organization. These include the cellular parameters of skeletal elongation in the cartilage growth plate, genes associated with differential growth, and putative gene regulatory mechanisms that would allow both covariant and independent evolution of the forelimbs and hindlimbs and of individual limb segments. Although the genetic mechanisms that shape skeletal proportion are still largely unknown, and most of what is known is limited to mammals, it is becoming increasingly apparent that the diversity of bone lengths is an emergent property of a complex system that controls elongation of individual skeletal elements using a genetic toolkit shared by all.

Contextualising the dead – Combining geoarchaeology and osteo-anthropology in a new multi-focus approach in bone histotaphonomy

Histotaphonomy has become an important area of research in funerary archaeology. It focuses on diagenetic alterations in bone microstructure and the reconstruction of post-mortem processes. Microbial bioerosion is the most common diagenetic change observed in archaeological bone, and its probable causes have been the subject of ongoing discussions.This paper presents a new integrative approach that combines methods from physical anthropology and geoarchaeology. The aim is to contextualise samples in regard to their sedimentary milieu (sediment type), the sedimentation processes they underwent, and the specific archaeological features they originate from. The analysis is based on 208 human and animal skeletal fragments from the Late La Tène site of Basel-Gasfabrik recovered from various feature types and embedded in different sediments. Both 80 μm and 30 μm thin sections were graded semi-quantitatively on a scale of 0 or 1 to 5 in regard to bacterial attack (BAI), Wedl tunnels (WTI), cyanobacterial attack (CAI), the formation of cracks (CRI), the collagen content (COI), and thermal alterations (HEI).Our results evinced no correlations between the intensity of bacterial attack and sediment types or sedimentation processes respectively. We therefore deduce that bacterial degradation of bone is mainly caused by endogenous gut bacteria. Wedl tunnels, on the other hand, are chiefly found in bones from exposed surfaces. Bone collagen content, as measured by birefringence, is dependent on a variety of factors, with thermal alteration being among the most important. Unlike the 80 μm sections used in anthropological investigations, the 30 μm thin sections typically utilized in geoarchaeological analyses permitted a reliable distinction of microbial bioerosion types. Our context-oriented histotaphonomic approach allows detailed conclusions on the causes of microbial bioerosion in bone. Moreover, it provides an important tool for reconstructing the post-mortem biographies of human and animal remains, especially in regard to (multi-stage) mortuary practices and the analysis of sedimentation processes. Thus, this novel approach generates a wealth of information from individual skeletal elements as well as from bone fragments embedded in soil samples.

Sex estimation from dimensions of the fourth lumbar vertebra in Northern Finns of 20, 30, and 46 years of age

BackgroundAccurate sex estimation (sexing) is crucial for successful forensic identification. For the cases in which only a part of the skeleton or individual skeletal elements are available, we investigated the sex estimation potential of the fourth lumbar vertebra (L4) among 20-, 30-, and 46-year-old Northern Finns. Material and methodsMagnetic resonance imaging scanned living subsamples of the Northern Finland Birth Cohort 1966 (scan at 46years, n=1363) and the Northern Finland Birth Cohort 1986 (repeated scans at 20 and 30years, n=375) provided the material for the study. After screening the scans for vertebral pathologies, we measured the maximum and minimum widths, depths, and heights of the L4 body. The mean vertebral width, depth and height were calculated together with vertebral cross-sectional area and volume. Sex estimations were performed using univariate and multivariate logistic regression analysis. ResultsWe detected marked sex discrepancy in all the studied parameters of L4 (p<0.001). In the groups aged 20, 30, and 46years, the regression models reached correct sex estimation rates of 86.4%, 87.7%, and 82.8%, respectively. At each time point, multivariate models proved more accurate than univariate models. Men showed consistently lower correct sex estimation rates than women. ConclusionAmong 20-, 30-, and 46year-old Finns, combining the measurements of width, depth, and height of the L4 body can be used to estimate sex with an accuracy of >80%. Vertebral width, depth, and height seem to yield as accurate sex estimates as more complicated vertebral parameters.

NFIA and GATA3 are crucial regulators of embryonic articular cartilage differentiation

During appendicular skeletal development, the bi-potential cartilage anlagen gives rise to transient cartilage, which is eventually replaced by bone, and to articular cartilage that caps the ends of individual skeletal elements. While the molecular mechanism that regulates transient cartilage differentiation is relatively well understood, the mechanism of articular cartilage differentiation has only begun to be unraveled. Furthermore, the molecules that coordinate the articular and transient cartilage differentiation processes are poorly understood. Here, we have characterized in chick the regulatory roles of two transcription factors, NFIA and GATA3, in articular cartilage differentiation, maintenance and the coordinated differentiation of articular and transient cartilage. Both NFIA and GATA3 block hypertrophic differentiation. Our results suggest that NFIA is not sufficient but necessary for articular cartilage differentiation. Ectopic activation of GATA3 promotes articular cartilage differentiation, whereas inhibition of GATA3 activity promotes transient cartilage differentiation at the expense of articular cartilage. We propose a novel transcriptional circuitry involved in embryonic articular cartilage differentiation, maintenance and its crosstalk with the transient cartilage differentiation program.

Bone deep: Variation in stable isotope ratios and histomorphometric measurements of bone remodelling within adult humans

Stable carbon (δ13C) and nitrogen (δ15N) isotope studies of ancient human diet increasingly sample several skeletal elements within an individual. Such studies draw upon differences in bone turnover rates to reconstruct diet during different periods of time within an individual's lifetime. Rib and femoral bone, with their respectively fast and slow remodelling rates, are the bones most often sampled to reconstruct shorter and longer term signals of diet prior to death. It is poorly understood if δ13C and δ15N vary between bone types within a single individual, or if this variation corresponds with bone turnover rate (BTR). Here, we determined δ13C and δ15N for ten different bones from ten adult human skeletons (n = 5 males; n = 5 females). Isotope values were compared to the rate that each bone remodeled, calculated from osteon population (OPD) density. Results reveal that isotope ratios varied within each skeleton (δ13C: max = −1.58‰; δ15N: max = 3.05‰). Humeri, metacarpals, and ribs had the highest rate of bone remodelling; the occipital bone had the lowest. A regression analyses revealed that higher rates of bone remodelling are significantly and negatively correlated with lower δ15N. Our results suggest that the occipital bone, with its slow rate of bone renewal, may prove useful for isotopic studies that reconstruct diet over longer periods of time within an individual's lifetime. Isotope studies that compare individual skeletal elements between populations should standardize their methodology to bones with either a slow or fast turnover rate.

The Outstanding Applications of Skeletal Numbers to Chemical Clusters

The evolution of the use of the 14/4n series method has resulted in the discovery of skeletal numbers. The skeletal numbers have rendered the testing of the 18-and 8-electron rules much easier and faster. In the same way, they have been very useful in simplifying the categorization of clusters, the prediction of shapes, and the matching of isolobal fragments. Furthermore, the skeletal numbers have made it possible to tentatively assign ligands to individual skeletal elements in such way that the 18- or 8-electron rule is obeyed. Thus, skeletal numbers can be utilized as a simple guide in analyzing and understanding clusters.

Anatomy of the adult and the first-instar nymph of the book louse, Liposcelis bostrychophila (Psocoptera, Liposcelididae)

Anatomy of the adult and the first-instar nymph of Liposcelis bostrychophila (Psocoptera, Liposcelididae) is described in detail for the first time based on series of sections and 3D computer reconstruction. Despite its tiny size, no strong structural simplification is observed in Liposcelis. The main features of the anatomy of this species associated with miniaturization are the merging of individual skeletal elements and simplification of the endoskeleton in the nymph, lack of the midgut muscles, simplification of the tracheal and circulatory systems, oligomerization and concentration of ganglia, asymmetry of the central nervous system in the nymph, and the absence of several muscles. Changes in the relative volumes of organs during the postembryonic development of Liposcelis are analyzed and compared with other minute insects.

Using Digital 3D Scanning to Create “Artifictions” of the Passenger Pigeon and Harelip Sucker, Two Extinct Species in Eastern North America: The Future Examines the Past

The Virtual Curation Laboratory at Virginia Commonwealth University created 3D representations of digital morphological models, termed “artifictions,” of several bone elements from two extinct animals, the passenger pigeon (Ectopistes migratorius Linnaeus Columbidae) and the harelip sucker (Moxostoma lacerum Jordan and Brayton Catostomidae). Procuring recent comparative reference skeletons these species is extremely difficult. The creation of artifictions, 3D printed replicas of skeletal remains, aims to help researchers become familiar with the bones of harelip sucker and passenger pigeon to facilitate morphological identification of remains of these species within archaeological assemblages. Here, we discuss the two species, the techniques used to create digital topological models of individual skeletal elements, and the obstacles encountered regarding 3D printed artifictions in zooarchaeology.

Cladistic analysis of Caseidae (Caseasauria, Synapsida): using the gap‐weighting method to include taxa based on incomplete specimens

AbstractOccupying the role of primary consumer and having an early–middle Permian age range, caseids (Caseasauria, Synapsida) are fundamental to the interpretation of the early history of terrestrial vertebrate ecosystems. Despite this importance, no comprehensive, species‐level phylogenetic study of Caseidae has yet been performed. Herein, we present a phylogenetic analysis of the group, using gap weighting to include poorly known taxa. Besides the description and comments on the resultant topologies, some more general issues concerning cladistic methodologies are briefly addressed. This study highlights the importance of a total‐evidence approach, including as many within‐group taxa and characters as possible. Continuously varying characters, in the form of indices derived from measurement of individual skeletal elements, proved to be highly important, adding significantly to the resolution of, and support for, recovered trees. The utility of the postcranial skeleton in understanding relationships among basal synapsids is highlighted.

A new Devonian asteroid-like ophiuroid from Spain

A Lochkovian (Early Devonian) ophiuroid (Echinodermata), Ophiocantabria elegans n. gen. and sp., is based on a single small, well-preserved specimen collected from a shale-rich horizon of the Furada Formation, Asturias, Spain. Sedimentologic and palaeontologic data suggest its occurrence was in a near-shore setting subjected to frequent storms. Ophiocantabria is assigned to the Encrinasteridae based on the morphology of individual skeletal elements, although overall form of the new species is similar to that of approximately coeval members of the asteroid family Xenasteridae. Such homoplasy, especially among earlier members of asterozoan class-level clades, is an important but not well understood aspect of subphylum evolution.

A distinctive Late Triassic microvertebrate fissure fauna and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia) from Woodleaze Quarry, Gloucestershire, UK

During the Late Triassic and Early Jurassic, diverse terrestrial vertebrates were preserved in fissures formed in Carboniferous Limestone on an island archipelago spanning from the south of Wales to the north and south of Bristol. Here we report the faunas of two new fissures in Woodleaze quarry, near to Tytherington quarry, where the vertebrate fauna is already well known. The new site extends the lateral distribution of fissures in this vicinity to over 900m, and fissures sampled along that transect show a southerly change in the dominant species and a reduction in diversity. The Woodleaze fissure fauna is nearly monofaunal, comprising >98% of a new Clevosaurus species, as well as some Diphydontosaurus fragments, a possible undescribed lepidosaur and a few fish fossils. The new clevosaur is distinguished from the type species Clevosaurus hudsoni by its dentition, and by being smaller (average long bones are 40–80% the length of C. hudsoni). In addition, the collection also includes individual skeletal elements that were not previously well described, thus expanding our knowledge of clevosaur anatomy. The Woodleaze bones are preserved as black or dark grey, rather than white, and this preservation mode and single-species dominance occurs elsewhere only in the Windsor Hill fissure where Oligokyphus predominates. Together with Tytherington, this location offers an exceptional opportunity to study a Triassic terrestrial biota across an extended distance, and to compare near-littoral niches with more inland island habitats.

Signaling Pathways in Craniofacial Development: Insights from Rare Skeletal Disorders.

In the developing embryo, signaling pathways define how the mesenchymal precursors of bone form individual skeletal elements with the proper size, shape, orientation, and integration. Disruptions to these signaling processes lead to a large variety of congenital conditions categorized as skeletal dysplasias. While individually these skeletal disorders are rare, collectively they represent a significant cause of disability in the United States. Here, we discuss how the study of these rare events in human development reveal novel and unexpected insights into signaling mechanisms that regulate normal skeletal development and, in the process, advance novel molecular-based therapies for treatment of rare and common bone diseases alike.

Quantification of intraskeletal histovariability in Alligator mississippiensis and implications for vertebrate osteohistology.

Bone microanalyses of extant vertebrates provide a necessary framework from which to form hypotheses regarding the growth and skeletochronology of extinct taxa. Here, we describe the bone microstructure and quantify the histovariability of appendicular elements and osteoderms from three juvenile American alligators (Alligator mississippiensis) to assess growth mark and tissue organization within and amongst individuals, with the intention of validating paleohistological interpretations. Results confirm previous observations that lamellar and parallel fibered tissue organization are typical of crocodylians, and also that crocodylians are capable of forming woven tissue for brief periods. Tissue organization and growth mark count varies across individual skeletal elements and reveal that the femur, tibia, and humerus had the highest annual apposition rates in each individual. Cyclical growth mark count also varies intraskeletally, but data suggest these inconsistencies are due to differing medullary cavity expansion rates. There was no appreciable difference in either diaphyseal circumference or cyclical growth mark circumferences between left and right element pairs from an individual if diaphyses were sampled from roughly the same location. The considerable intraskeletal data obtained here provide validation for long-held paleohistology assumptions, but because medullary expansion, cyclical growth mark formation, and variable intraskeletal growth rates are skeletal features found in tetrapod taxa living or extinct, the validations presented herein should be considered during any tetrapod bone microanalysis.

Mechanoadaptation of developing limbs: shaking a leg

The proportion of total limb length taken up by the individual skeletal elements (limb proportionality), varies widely between species. These diverse skeletal forms have evolved to allow for a range of limb uses and they first emerge as the embryo develops, to achieve the characteristic skeletal architecture of each species. During this time, the developing skeleton experiences mechanical loading as a result of embryonic muscle contraction. The possibility that adaptation to such mechanical input may allow embryos to coordinate the appearance of skeletal design with their expanding range of movements has so far received little attention. This is surprising, given the critical role exerted by embryo movement in normal skeletal development; stage-specific in ovo immobilisation of embryonic chicks results in joint contractures and a reduction in longitudinal bone growth in the limbs. Epigenetic mechanisms allow for selective activation of genes in response to environmental signals, resulting in the production of phenotypic complexity in morphogenesis; mechanical loading of bone during movement appears to be one such signal. It may be that 'mechanosensitive' genes under regulation of mechanical input adjust proportionality along the bone's proximo-distal axis, introducing a level of phenotypic plasticity. If this hypothesis is upheld, species with more elongated distal limb elements will have a greater dependence on mechanical input for the differences in their growth, and mechanosensitive bone growth in the embryo may have evolved as an additional source of phenotypic diversity during skeletal development.

Skeletal Correlates for Body Mass Estimation in Modern and Fossil Flying Birds

Scaling relationships between skeletal dimensions and body mass in extant birds are often used to estimate body mass in fossil crown-group birds, as well as in stem-group avialans. However, useful statistical measurements for constraining the precision and accuracy of fossil mass estimates are rarely provided, which prevents the quantification of robust upper and lower bound body mass estimates for fossils. Here, we generate thirteen body mass correlations and associated measures of statistical robustness using a sample of 863 extant flying birds. By providing robust body mass regressions with upper- and lower-bound prediction intervals for individual skeletal elements, we address the longstanding problem of body mass estimation for highly fragmentary fossil birds. We demonstrate that the most precise proxy for estimating body mass in the overall dataset, measured both as coefficient determination of ordinary least squares regression and percent prediction error, is the maximum diameter of the coracoid’s humeral articulation facet (the glenoid). We further demonstrate that this result is consistent among the majority of investigated avian orders (10 out of 18). As a result, we suggest that, in the majority of cases, this proxy may provide the most accurate estimates of body mass for volant fossil birds. Additionally, by presenting statistical measurements of body mass prediction error for thirteen different body mass regressions, this study provides a much-needed quantitative framework for the accurate estimation of body mass and associated ecological correlates in fossil birds. The application of these regressions will enhance the precision and robustness of many mass-based inferences in future paleornithological studies.

Further analysis of a Late Jurassic dinosaur bone-bed from the Morrison Formation of Montana, USA, with a computed three-dimensional reconstruction

ABSTRACTA Late Jurassic sauropod bone-bed comprising thousands of individual skeletal elements in the Morrison Formation of Montana, USA, is re-analysed to further elucidate its taphonomic history. New data gained from detailed contextual sampling is assembled and presented to test the hypothesis of a drought-induced, mass-mortality assemblage, and its subsequent depositional emplacement by a debris flow. Large dinosaur bone-beds are well-known in the Morrison, yet the Mother's Day Quarry site is unique for the formation in depicting an apparent debris flow deposit. Use of a computer program tailored to the data allows three-dimensional reconstruction of the bone-bed and recreates the palaeoslope of the deposit, adding support to the debris flow hypothesis. Such digital manipulation of field data may allow a deeper understanding of other bone-bed origination events.

Hh signaling regulates patterning and morphogenesis of the pharyngeal arch-derived skeleton

The proper function of the craniofacial skeleton requires the proper shaping of many individual skeletal elements. Neural crest cells generate much of the craniofacial skeleton and morphogenesis of skeletal elements occurs in transient, reiterated structures termed pharyngeal arches. The shape of individual elements depends upon intrinsic patterning within the neural crest as well as extrinsic signals to the neural crest from adjacent tissues within the arches. Hedgehog (Hh) signaling is known to play roles in craniofacial development, yet its involvement in intrinsic and extrinsic patterning of the craniofacial skeleton is still not well understood. Here, we show that morphogenetic movements of the pharyngeal arches and patterning of the neural crest require Hh signaling. Loss of Hh signaling, in smoothened (smo) mutants, disrupts the expression of some Dlx genes as well as other markers of dorsal/ventral patterning of the neural crest. Transplantation of wild-type neural crest cells into smo mutants rescues this defect, demonstrating that the neural crest requires reception of Hh signals for proper patterning. Despite the rescue, morphogenesis of the facial skeleton is not fully recovered. Through transplant analyses, we find two additional requirements for Hh signaling. The endoderm requires the reception of Hh signals for proper morphogenetic movements of the pharyngeal arches and the neural crest require the reception of Hh signaling for the activity of a reverse signal that maintains sonic hedgehog expression in the endoderm. Collectively, these results demonstrate that Hh signaling is essential to establish intrinsic and extrinsic patterning information for the craniofacial skeleton.

The taphonomy of violence: Recognizing variation in disarticulated skeletal assemblages

The identification of violence and trauma in an archaeological context requires a nuanced and detailed analysis of material culture and human remains. This paper focuses on sharp-force trauma data from individual skeletal elements for the Ancestral Pueblo site Peñasco Blanco (n=1301) and the epiclassic site La Quemada (n=800). The material from these assemblages exhibits examples of bone damage and modification including blunt and sharp force trauma, pre- and peri-mortem modification, breakage, chopping, burning, and dismemberment. Using a methodology that combines microscopy of cutmarks (Peñasco Blanco [n=29] and La Quemada [n=623]) with taphonomic reconstruction of each category of bone damage, the combined empirical datasets suggest several of the current explanatory hypotheses cannot be accepted, e.g., cannibalism for the Ancestral Pueblo and violent trauma for all of the La Quemada remains. By examining the maximum width and depth of each cutmark in cross-section along with tool use and pattern recognition of the trauma, I suggest a series of alternative hypotheses (postmortem processing for Peñasco Blanco; ancestor veneration and mutilation at La Quemada). It is highly possible that some of the disarticulated remains have nothing to do with violence and everything to do with burial rites, veneration, or consecration.