Ontogeny of 3D rib curvature and its importance for the understanding of human thorax development

Shanidar 3 'rings the bell': Virtual ribcage reconstruction and its implications for understanding the Neanderthal bauplan

The study of the ribcage is fundamental to understanding hominin evolution. However, ribs and vertebrae are scarce in the fossil record. Although Neanderthals are one of the most represented and, therefore, one of the most studied fossil Homo species, it is controversial whether there is a standardized Neanderthal ribcage morphotype that could differ from modern humans. Hence, we used three-dimensional geometric morphometrics to reconstruct and compare the Neanderthal ribcage of Shanidar 3 with another Neanderthal specimen, Kebara 2, and with 58 Homo sapiens individuals of worldwide distribution. Shape differences among the Neanderthal and H. sapiens ribcages were analyzed by a hierarchical cluster using the Euclidean distances among the permuted Procrustes distances between groups. Size differences between the Neanderthal and H. sapiens ribcages were examined using a permutation test on centroid size. To examine the potential for allometry, we performed a linear regression of Procrustes coordinates on centroid size of the sample, followed by a principal component analysis in form space. Our results show that Shanidar 3 has the 'bell-shaped' thorax typically described for Neanderthals. In fact, the shapes of both Shanidar 3 and Kebara 2 ribcages cluster apart from that of H. sapiens, being closer to cold-adapted individuals. The study of the centroid size supports similarities between Neanderthals and cold-adapted H. sapiens since significant size differences were found only between Neanderthals and temperate/tropical recent humans. The linear regression and principal component analysis showed an allometric relationship between ribcage size and shape, suggesting Neanderthals had larger and stockier ribcages than most H. sapiens, although they fall within the H. sapiens range of variation. Finally, ribcage similarities found between Shanidar 3 and Kebara 2, both inhabiting warm Levantine locations during the Upper Pleistocene, could challenge the conventional idea of a cold-adapted bauplan in Neanderthals.

The effect of Scheuermann's kyphosis on rib cage morphology: A skeletal study

BACKGROUND

Evolutionary changes in human rib cage morphology rendered it prone to pathologies like Scheuermann's kyphosis (SK). However, the impact of SK on rib cage morphology is unclear.

PURPOSE

This study aimed to examine differences in rib cage morphology (e.g., ribs and sternum) between SK patients and a control group.

METHODS

Measurements of the vertebral body, transverse process angle, sternum, and rib size were taken from the skeletons of SK patients (76) and a control group (96). Statistical tests were carried out to examine differences between the study and control groups and between the right and left sides. Correlations were obtained to examine the associations between the extent of the kyphosis (kyphosis angle) and rib cage variables.

RESULTS

The SK group yielded significantly longer and flatter ribs than the control group in both sexes. However, males had the largest differences in the 9th rib and females in the upper ribs (5-7). Inconsistency in symmetry results was found between the sexes. In summary, SK patients had a larger anteroposterior diameter in relation to the transverse diameter than the control group.

DISCUSSION AND CONCLUSIONS

SK affects the morphology of the entire thorax and changes rib proportions similarly in males and females. These changes might have a role in bipedal stability and locomotion efficiency. Moreover, understanding the unique anatomy of SK patients is essential when performing an anterior release and anterior fusion operative approach. Finally, it provides insights into respiratory complications and poor prognosis related to individuals suffering from severe hyperkyphosis.

How to make a digital reconstruction of the human ribcage

Up to now, there have been no publication standardizing the digital reconstruction of the modern human ribcage from commingled costo-vertebral material. Consequently, we designed a validated protocol based on anatomical features observed in the literature and the CT scanned ribcages of 10 adult European individuals. After quantifying the shape of these ribcages using 3D geometric morphometrics, we split each vertebra and rib within their corresponding (semi)landmarks. Subsequently, individual bones + (semi)landmarks were imported to LhpFusionBox, commingled and 3D reconstructed. To validate the accuracy of the protocol, we first reconstructed a randomly chosen ribcage three times and then compared these reconstructions to the rest of the sample. Since these reconstructions were closer to their original counterpart than to the others, the remaining sample was reconstructed once. Next, we tested the intra-observer error during reconstructing using the Procrustes distances among the original ribcages and the reconstructions. We observed that first each ribcage reconstruction was clustered to its original counterpart and second there was a learning curve showing an improvement in the reconstruction process over time. Subsequently, we explored general size and shape differences among the original and reconstructed ribcages through a study of centroid size and a permutation test on the Procrustes distances (10,000 permutations), respectively. Specific shape differences between both groups were further examined through a principal component analysis in shape space. None of these analyses found statistical differences between the original and reconstructed ribcages (p > 0.05). Eventually, we extracted the mean shapes of the original ribcages and the reconstructions in order to visualize potential deviations caused by the anatomical considerations of the researcher. These results demonstrate that the protocol is accurate enough to be used when reconstructing a disarticulated human ribcage.

Sexual dimorphism in the enamel-dentine junction (EDJ) of permanent canines of European modern humans

OBJECTIVES

Dental anthropological investigations into sexual dimorphism have conventionally concentrated on evaluating the dimensions and configuration of the enamel cap of canines. However, the morphology of the crown dentine surface can be closely linked to that of the enamel surface. This link can facilitate examination of crown morphology even when the enamel surface is slightly worn. Here, we determine if the morphology of the enamel-dentine junction (EDJ) differs within (maxillary vs. mandibular) and between a sample of male (n = 26) and female (n = 21) contemporary human permanent canines from Europe.

METHODS

The morphological data of the EDJ were gathered employing a template comprising 96 landmarks and sliding semilandmarks. Subsequently, the data underwent analysis through form space principal component analysis following Procrustes registration, utilizing standard 3D geometric morphometric techniques.

RESULTS

Significant differences in the morphology of the EDJ were observed between the sexes, particularly concerning the overall shape of the crown, the symmetry of the mesial and distal edges, and the development of the distal accessory ridge.

CONCLUSIONS

Sex differences in the morphology of the EDJ could relate in part to retention of the canine-premolar honing complex in males. Our results indicate that analyses of the permanent canine EDJ may potentially provide a novel method for estimating the sex of adult and nonadult skeletons.

A preliminary study on the normal values of the thoracic Haller index in children

OBJECTIVES

The Haller index (HI) is widely utilized as a quantitative indicator to assess the extent of the pectus excavatum (PE) deformity, which is the most common chest wall abnormality in children. Both preoperative correction planning and postoperative follow-up need to be based on the standard of normal thoracic growth and development. However, there is currently no established reference range for the HI in children. Consequently, the goal of this study was to conduct a preliminary investigation of normal HI values among children to understand thoracic developmental characteristics.

METHODS

Chest computed tomography images obtained from January 2012 to March 2022 were randomly selected from the imaging system of the Children's Hospital of Chongqing Medical University. We divided the images of children into a total of 19 groups: aged 0-3 months (1 group), 4-12 months (1 group) and 1 year to 17 years (17 groups), with 50 males and 50 females, totaling 100 children in each group. HI was measured in the plane where the lowest point of the anterior thoracic wall was located and statistically analysed using SPSS 26.0 software.

RESULTS

A total of 1900 patients were included in the study. Our results showed that HI, transverse diameter and anterior-posterior diameter were positively correlated with age (P < 0.05). Using age as the independent variable and HI as the dependent variable, the best-fit regression equations were HI-male = 2.047 * Age0.054(R2 = 0.276, P<0.0001) and HI-female = 2.045 * Age0.067(R2 = 0.398, P<0.0001). Males had significantly larger thoracic diameters than females, and there was little difference in the HI between the 2 sexes.

CONCLUSIONS

The HI rapidly increases during the neonatal period, slowly increases during infancy and stops increasing during puberty, with no significant differences between the sexes.

Conserved patterns and locomotor-related evolutionary constraints in the hominoid vertebral column

The evolution of the hominoid lineage is characterized by pervasive homoplasy, notably in regions such as the vertebral column, which plays a central role in body support and locomotion. Few isolated and fewer associated vertebrae are known for most fossil hominoid taxa, but identified specimens indicate potentially high levels of convergence in terms of both form and number. Homoplasy thus complicates attempts to identify the anatomy of the last common ancestor of hominins and other taxa and stymies reconstructions of evolutionary scenarios. One way to clarify the role of homoplasy is by investigating constraints via phenotypic integration, which assesses covariation among traits, shapes evolutionary pathways, and itself evolves in response to selection. We assessed phenotypic integration and evolvability across the subaxial (cervical, thoracic, lumbar, sacral) vertebral column of macaques (n = 96), gibbons (n = 77), chimpanzees (n = 92), and modern humans (n = 151). We found a mid-cervical cluster that may have shifted cranially in hominoids, a persistent thoracic cluster that is most marked in chimpanzees, and an expanded lumbosacral cluster in hominoids that is most expanded in gibbons. Our results highlight the highly conserved nature of the vertebral column. Taxa appear to exploit existing patterns of integration and ontogenetic processes to shift, expand, or reduce cluster boundaries. Gibbons appear to be the most highly derived taxon in our sample, possibly in response to their highly specialized locomotion.

Consideration of the thoracic phenotype of cerebro-costo-mandibular syndrome

Cerebro-costo-mandibular syndrome (CCMS) is a congenital condition with skeletal and orofacial abnormalities that often results in respiratory distress in neonates. The three main phenotypes in the thorax are posterior rib gaps, abnormal costovertebral articulation and absent ribs. Although the condition can be lethal, accurate diagnosis, and subsequent management help improve the survival rate. Mutations in the causative gene SNRPB have been identified, however, the mechanism whereby the skeletal phenotypes affect respiratory function is not well-studied due to the multiple skeletal phenotypes, lack of anatomy-based studies into the condition and rarity of CCMS cases. This review aims to clarify the extent to which the three main skeletal phenotypes in the thorax contribute to respiratory distress in neonates with CCMS. Despite the posterior rib gaps being unique to this condition and visually striking on radiographic images, anatomical consideration, and meta-analyses suggested that they might not be the significant factor in causing respiratory distress in neonates. Rather, the increase in chest wall compliance due to the rib gaps and the decrease in compliance at the costovertebral complex was considered to result in an equilibrium, minimizing the impact of these abnormalities. The absence of floating ribs is likely insignificant as seen in the general population; however, a further absence of ribs or vestigial rib formation is associated with respiratory distress and increased lethality. Based on these, we propose to evaluate the number of absent or vestigial ribs as a priority indicator to develop a personalized treatment plan based on the phenotypes exhibited.

Covariation between the shape and mineralized tissues of the rib cross section in Homo sapiens, Pan troglodytes and Sts 14

OBJECTIVES

Studying rib torsion is crucial for understanding the evolution of the hominid ribcage. Interestingly, there are variables of the rib cross section that could be associated with rib torsion and, consequently, with the morphology of the thorax. The aim of this research is to conduct a comparative study of the shape and mineralized tissues of the rib cross section in different hominids to test for significant differences and, if possible, associate them to different thoracic morphotypes.

MATERIALS AND METHODS

The sample consists of the rib cross sections at the midshaft taken from 10 Homo sapiens and 10 Pan troglodytes adult individuals, as well as from A. africanus Sts 14. The shape of these rib cross sections was quantified using geometric morphometrics, while the mineralized tissues were evaluated using the compartmentalization index. Subsequently, covariation between both parameters was tested by a Spearman's ρ test, a permutation test and a linear regression.

RESULTS

Generally, P. troglodytes individuals exhibit rib cross sections that are rounder and more mineralized compared to those of H. sapiens. However, the covariation between both parameters was only observed in typical ribs (levels 3-10). Although covariation was not found in the rib cross sections of Sts 14, their parameters are closer to P. troglodytes.

DISCUSSION

On the one hand, the differences observed in the rib cross sections between H. sapiens and P. troglodytes might be related to different degrees of rib torsion and, consequently, to different thoracic 3D configurations. These findings can be functionally explained by considering their distinct modes of breathing and locomotion. On the other hand, although the rib cross sections belonging to Sts 14 are more similar to those of P. troglodytes, previous publications determined that their overall morphology is closer to modern humans. This discrepancy could reflect a diversity of post-cranial adaptations in Australopithecus.

The anatomical growth of the thoracic cage in adolescents with specific reference to axial growth comparing the right and left hemithorax

This study has demonstrated the changing volume of both the anterior and posterior thorax in normal adolescents (without spinal or thoracic deformity), differentiating for both sex and age, to further understand how the thorax grows, along with the differences in growth between the anterior and posterior thorax. The thorax was measured on axial CT slices at every vertebral level from T3 to T12 in a series of scans previous taken for routine clinical care. Measurements taken were the anteroposterior thoracic distance and the area of the anterior and posterior rib prominences on either side of the thorax. Data was analyzed per vertebral level, differentiating for age and sex. There were 486 CT scans analyzed (257 males and 229 females) between the ages of 8 and 18 years. The analysis identified that for the anterior thorax, there are three phases of growth with an initial slow increase in volume, followed by a stabilization of little growth, followed by another phase of a more rapid increase in volume. For the posterior thorax, there was a gradual increase in area with increasing age. This study demonstrates that the shape of the thorax is age and sex dependent, with males having both a greater width and depth of thorax compared to females. Of particular note is the difference in patterns of growth between the anterior and posterior thorax. This information will add to the understanding of normal growth, which will aid in the management of conditions where that growth is disturbed.

Sexual dimorphism in the first rib of Homo sapiens

This work aimed to study sexual dimorphism in the first rib of modern humans, with a special focus on whether differences in shape are due to divergent allometric growth in males and females. Also, we compare the accuracy of sex classification using different approaches based on two methodologies, traditional morphometry based on linear measurements and geometric morphometric analysis based on 2D landmark coordinates. The sample studied here comprised 121 right and left first ribs from 65 female and male adult recent Euro-American Homo sapiens individuals. For traditional morphometrics, 12 metric variables were collected from each rib using a digital caliper, and for geometric morphometrics, six landmarks and 31 semilandmarks were captured from photographs using digital software. Both geometric morphometric and metric data were analyzed to calculate the index of sexual dimorphism, variation related to lateral asymmetry, variation in size and shape, and allometric trends between males and females. Finally, a linear discriminant analysis (LDA) was performed comparing both methodologies to test the best approach for sex classification. Results indicated that there are significant sex differences in the size and shape of the first ribs of recent Euro-American Homo sapiens. Regression analysis revealed different allometric patterns for males and females, and this could partially explain shape differences between sexes. Additionally, traditional morphometrics showed that all characteristics analyzed are significantly dimorphic, with the midshaft minimum craniocaudal diameter, the sternal end minimum diameter, and the neck minimum craniocaudal diameter displaying the most dimorphic scores. Similarly, geometric morphometrics results indicated that males have more curved and interno-exteriorly wider first ribs. Finally, analysis of sex classification using LDA yielded slightly better accuracy for traditional morphometry (83.8%) than the geometric morphometrics approach (81.3%) based on form Procrustes coordinates. This study demonstrates the usefulness of applying two different morphometric approaches to obtain more comprehensive results.

Evolutionary development of the Homo antecessor scapulae (Gran Dolina site, Atapuerca) suggests a modern-like development for Lower Pleistocene Homo

Two well-preserved, subadult 800 ky scapulae from Gran Dolina belonging to Homo antecessor, provide a unique opportunity to investigate the ontogeny of shoulder morphology in Lower Pleistocene humans. We compared the H. antecessor scapulae with a sample of 98 P. troglodytes and 108 H. sapiens representatives covering seven growth stages, as well as with the DIK-1-1 (Dikika; Australopithecus afarensis), KNM-WT 15000 (Nariokotome; H. ergaster), and MH2 (Malapa; A. sediba) specimens. We quantified 15 landmarks on each scapula and performed geometric morphometric analyses. H. sapiens scapulae are mediolaterally broader with laterally oriented glenoid fossae relative to Pan and Dikika shoulder blades. Accordingly, H. antecessor scapulae shared more morphological affinities with modern humans, KNM-WT 15000, and even MH2. Both H. antecessor and modern Homo showed significantly more positive scapular growth trajectories than Pan (slopes: P. troglodytes = 0.0012; H. sapiens = 0.0018; H. antecessor = 0.0020). Similarities in ontogenetic trajectories between the H. antecessor and modern human data suggest that Lower Pleistocene hominin scapular development was already modern human-like. At the same time, several morphological features distinguish H. antecessor scapulae from modern humans along the entire trajectory. Future studies should include additional Australopithecus specimens for further comparative assessment of scapular growth trends.

Early development of the Neanderthal ribcage reveals a different body shape at birth compared to modern humans

Ontogenetic studies provide clues for understanding important paleobiological aspects of extinct species. When compared to that of modern humans, the adult Neanderthal thorax was shorter, deeper, and wider. This is related to the wide Neanderthal body and is consistent with their hypothetical large requirements for energy and oxygen. Whether these differences were already established at birth or appeared later during development is unknown. To delve into this question, we use virtual reconstruction tools and geometric morphometrics to recover the 3D morphology of the ribcages of four Neanderthal individuals from birth to around 3 years old: Mezmaiskaya 1, Le Moustier 2, Dederiyeh 1, and Roc de Marsal. Our results indicate that the comparatively deep and short ribcage of the Neanderthals was already present at birth, as were other skeletal species-specific traits. This morphology possibly represents the plesiomorphic condition shared with Homo erectus, and it is likely linked to large energetic requirements.

Late subadult ontogeny and adult aging of the human thorax reveals divergent growth trajectories between sexes

Sexual dimorphism is an important feature of adult thorax morphology, but when and how sex-related differences in the ribcage arise during ontogeny is poorly known. Previous research proposed that sex-related size differences in the nasal region arise during puberty. Therefore, we explore whether ribcage sexual dimorphism also arises at that time and whether this sexual dimorphism is maintained until old age. We measured 526 (semi)landmarks on 80 CT-based human ribcage reconstructions, on individuals ranging from 7 to 65 year-old. The 3D coordinates were submitted to the Procrustes superimposition and analyzed. Our results show that the trajectories of thorax size and shape between sexes diverge at around 12 years of age, and continue slightly diverging until old age. The differential ontogenetic trends cause adult male ribcages to become deeper, shorter, and wider than female. Our results are consistent with the evidence from the cranial respiratory system, with the development of sexual dimorphism probably related to changes in body composition during puberty combined with changes in the reproductive system.

Association between thoracic musculoskeletal abnormalities and lung function in preterm infants

INTRODUCTION

In view of the difficulties and risks of performing lung function tests in infants and the hypothesis that children with abnormal pulmonary test may exhibit thoracic musculoskeletal alterations.

OBJECTIVES

This study aimed to determine the frequency of abnormal lung function and their relationship.

MATERIALS AND METHODS

This was a cross-sectional study with children from 6 to 12 months of corrected age, born at a gestational age of <37 weeks and with a birthweight ≤1500 g, who were subjected to a lung function test and photogrammetry--an objective and non-invasive procedure. To verify the association between the thoracic musculoskeletal abnormalities and measure changes in lung function, univariate linear regression was used. The level of statistical significance was setted at P < 0.05.

RESULTS

Of the 38 infants, 12 (31.6%) exhibited abnormal lung function, including 9 (23.7%) with obstructive function and 3 (7.9%) with restrictive function. A significant association was noted between forced expiratory volume at 0.5 second <-2 z score and the acromion/xiphoid process/acromion angle (β = 4.935); forced vital capacity <-2 z score and the angle of the manubrium/left acromion/trapezium (β = 0.033) and forced expiratory volume at 0.5 second and forced vital capacity ratio <-2 z score and the inframammillary point/xiphoid process/inframammillary point angle (β = 0.043).

CONCLUSION

Preterm infants with very low birthweight presented a high frequency of abnormal lung function, particularly obstructive type and thoracic musculoskeletal abnormalities were associated with changes in lung function.

Human embryonic ribs all progress through common morphological forms irrespective of their position on the axis

BACKGROUND

We aimed to analyze the morphogenesis of all ribs from 1st to 12th rib pairs plus vertebrae to compare their differences and features according to the position along the cranial-caudal axis during the human embryonic period.

RESULTS

Rib pair formation was analyzed using high-resolution digitalized imaging data (n = 29) between Carnegie stage (CS) 18 and CS23 (corresponding to ED13-14 in mouse; HH29-35 in chick). A total of 348 rib pairs, from 1st to 12th rib pairs of each sample were subjected to Procrustes and principal component (PC) analyses. PC1 and PC2 accounted for 76.3% and 16.4% (total 92.7%) of the total variance, respectively, indicating that two components mainly accounted for the change in shape. The distribution of PC1 and PC2 values for each rib showed a "fishhook-like shape" upon fitting to a quartic equation. PC1 and PC2 value position for each rib pair moved along the fitted curve according to the development. Thus, the change in PC1 and PC2 could be expressed by a single parameter using a fitted curve as a linear scale for shape.

CONCLUSION

Human embryonic ribs all progress through common morphological forms irrespective of their position on the axis.

Ribcage measurements indicate greater lung capacity in Neanderthals and Lower Pleistocene hominins compared to modern humans

Our most recent fossil relatives, the Neanderthals, had a large brain and a very heavy body compared to modern humans. This type of body requires high levels of energetic intake. While food (meat and fat consumption) is a source of energy, oxygen via respiration is also necessary for metabolism. We would therefore expect Neanderthals to have large respiratory capacities. Here we estimate the pulmonary capacities of Neanderthals, based on costal measurements and physiological data from a modern human comparative sample. The Kebara 2 male had a lung volume of about 9.04 l; Tabun C1, a female individual, a lung volume of 5.85 l; and a Neanderthal from the El Sidrón site, a lung volume of 9.03 l. These volumes are approximately 20% greater than the corresponding volumes of modern humans of the same body size and sex. These results show that the Neanderthal body was highly sensitive to energy supply.

Daniel García-Martínez et al. report Neanderthal lung volume estimates based on measurements from rib bone fossils and lung capacity data from modern humans. They estimate that Neanderthal individuals had approximately 20% higher lung capacity than modern humans, possibly due to higher energy requirements.

Eco-geographic adaptations in the human ribcage throughout a 3D geometric morphometric approach

OBJECTIVES

According to eco-geographic rules, humans from high latitude areas present larger and wider trunks than their low-latitude areas counterparts. This issue has been traditionally addressed on the pelvis but information on the thorax is largely lacking. We test whether ribcages are larger in individuals inhabiting high latitudes than in those from low latitudes and explored the correlation of rib size with latitude. We also test whether a common morphological pattern is exhibited in the thorax of different cold-adapted populations, contributing to their hypothetical widening of the trunk.

MATERIALS AND METHODS

We used 3D geometric morphometrics to quantify rib morphology of three hypothetically cold-adapted populations, viz. Greenland (11 individuals), Alaskan Inuit (8 individuals) and people from Tierra del Fuego (8 individuals), in a comparative framework with European (Spain, Portugal and Austria; 24 individuals) and African populations (South African and sub-Saharan African; 20 individuals).

RESULTS

Populations inhabiting high latitudes present longer ribs than individuals inhabiting areas closer to the equator, but a correlation (p < 0.05) between costal size and latitude is only found in ribs 7-11. Regarding shape, the only cold adapted population that was different from the non-cold-adapted populations were the Greenland Inuit, who presented ribs with less curvature and torsion.

CONCLUSIONS

Size results from the lower ribcage are consistent with the hypothesis of larger trunks in cold-adapted populations. The fact that only Greenland Inuit present a differential morphological pattern, linked to a widening of their ribcage, could be caused by differences in latitude. However, other factors such as genetic drift or specific cultural adaptations cannot be excluded and should be tested in future studies.

3D analysis of sexual dimorphism in size, shape and breathing kinematics of human lungs

Sexual dimorphism in the human respiratory system has been previously reported at the skeletal (cranial and thoracic) level, but also at the pulmonary level. Regarding lungs, foregoing studies have yielded sex-related differences in pulmonary size as well as lung shape details, but different methodological approaches have led to discrepant results on differences in respiratory patterns between males and females. The purpose of this study is to analyse sexual dimorphism in human lungs during forced respiration using 3D geometric morphometrics. Eighty computed tomographies (19 males and 21 females) were taken in maximal forced inspiration (FI) and expiration (FE), and 415 (semi)landmarks were digitized on 80 virtual lung models for the 3D quantification of pulmonary size, shape and kinematic differences. We found that males showed larger lungs than females (P < 0.05), and significantly greater size and shape differences between FI and FE. Morphologically, males have pyramidal lung geometry, with greater lower lung width when comparing with the apices, in contrast to the prismatic lung shape and similar widths at upper and lower lungs of females. Multivariate regression analyses confirmed the effect of sex on lung size (36.26%; P < 0.05) and on lung shape (7.23%; P < 0.05), and yielded two kinematic vectors with a small but statistically significant angle between them (13.22°; P < 0.05) that confirms sex-related differences in the respiratory patterns. Our 3D approach shows sexual dimorphism in human lungs likely due to a greater diaphragmatic action in males and a predominant intercostal muscle action in females during breathing. These size and shape differences would lead to different respiratory patterns between sexes, whose physiological implications need to be studied in future research.

A potential pitfall in studies of biological shape: Does size matter?

The number of published studies using geometric morphometrics (GM) for analysing biological shape has increased steadily since the beginning of the 1990s, covering multiple research areas such as ecology, evolution, development, taxonomy and palaeontology. Unfortunately, we have observed that many published studies using GM do not evaluate the potential allometric effects of size on shape, which normally require consideration or assessment. This might lead to misinterpretations and flawed conclusions in certain cases, especially when size effects explain a large part of the shape variation. We assessed, for the first time and in a systematic manner, how often published studies that have applied GM consider the potential effects of allometry on shape. We reviewed the 300 most recent published papers that used GM for studying biological shape. We also estimated how much of the shape variation was explained by allometric effects in the reviewed papers. More than one-third (38%) of the reviewed studies did not consider the allometric component of shape variation. In studies where the allometric component was taken into account, it was significant in 88% of the cases, explaining up to 87.3% of total shape variation. We believe that one reason that may cause the observed results is a misunderstanding of the process that superimposes landmark configurations, i.e. the Generalized Procrustes Analysis, which removes isometric effects of size on shape, but not allometric effects. Allometry can be a crucial component of shape variation. We urge authors to address, and report, size effects in studies of biological shape. However, we do not propose to always remove size effects, but rather to evaluate the research question with and without the allometric component of shape variation. This approach can certainly provide a thorough understanding of how much size contributes to the observed shaped variation.

The costal remains of the El Sidrón Neanderthal site (Asturias, northern Spain) and their importance for understanding Neanderthal thorax morphology

The study of the Neanderthal thorax has attracted the attention of the scientific community for more than a century. It is agreed that Neanderthals have a more capacious thorax than modern humans, but whether this was caused by a medio-lateral or an antero-posterior expansion of the thorax is still debated, and is key to understanding breathing biomechanics and body shape in Neanderthals. The fragile nature of ribs, the metameric structure of the thorax and difficulties in quantifying thorax morphology all contribute to uncertainty regarding precise aspects of Neanderthal thoracic shape. The El Sidrón site has yielded costal remains from the upper to the lower thorax, as well as several proximal rib ends (frequently missing in the Neanderthal record), which help to shed light on Neanderthal thorax shape. We compared the El Sidrón costal elements with ribs from recent modern humans as well as with fossil modern humans and other Neanderthals through traditional morphometric methods and 3D geometric morphometrics, combined with missing data estimation and virtual reconstruction (at the 1st, 5th and 11th costal levels). Our results show that Neanderthals have larger rib heads and articular tubercles than their modern human counterparts. Neanderthal 1st ribs are smaller than in modern humans, whereas 5th and 11th ribs are considerably larger. When we articulated mean ribs (size and shape) with their corresponding vertebral elements, we observed that compared to modern humans the Neanderthal thorax is medio-laterally expanded at every level, especially at T5 and T11. Therefore, in the light of evidence from the El Sidrón costal remains, we hypothesize that the volumetric expansion of the Neanderthal thorax proposed by previous authors would mainly be produced by a medio-lateral expansion of the thorax.

In Vivo 3D Analysis of Thoracic Kinematics: Changes in Size and Shape During Breathing and Their Implications for Respiratory Function in Recent Humans and Fossil Hominins

The human ribcage expands and contracts during respiration as a result of the interaction between the morphology of the ribs, the costo-vertebral articulations and respiratory muscles. Variations in these factors are said to produce differences in the kinematics of the upper thorax and the lower thorax, but the extent and nature of any such differences and their functional implications have not yet been quantified. Applying geometric morphometrics we measured 402 three-dimensional (3D) landmarks and semilandmarks of 3D models built from computed tomographic scans of thoraces of 20 healthy adult subjects in maximal forced inspiration (FI) and expiration (FE). We addressed the hypothesis that upper and lower parts of the ribcage differ in kinematics and compared different models of functional compartmentalization. During inspiration the thorax superior to the level of the sixth ribs undergoes antero-posterior expansion that differs significantly from the medio-lateral expansion characteristic of the thorax below this level. This supports previous suggestions for dividing the thorax into a pulmonary and diaphragmatic part. While both compartments differed significantly in mean size and shape during FE and FI the size changes in the lower compartment were significantly larger. Additionally, for the same degree of kinematic shape change, the pulmonary thorax changes less in size than the diaphragmatic thorax. Therefore, variations in the form and function of the diaphragmatic thorax will have a strong impact on respiratory function. This has important implications for interpreting differences in thorax shape in terms of respiratory functional differences within and among recent humans and fossil hominins. Anat Rec, 300:255-264, 2017. © 2016 Wiley Periodicals, Inc.

In vivo measurement of vertebral endplate surface area along the whole-spine

Accurate determination of vertebral endplate surface area and diameters plays an important role in surgical procedures, spinal implant design and sizing. The objective of this study was to contribute with baseline information on the endplate geometrical parameters using subject-based 3D whole-spine computed tomography (CT) models based on myelogram CT images taken of 49 patients with spinal disorders. Superior and inferior bony endplate mesh-models were created from said 3D CT models and endplate geometrical parameters including total polygon-mesh areas, projected areas and antero posterior and transverse diameters of each endplate were measured. The position of each endplate was determined by the cumulative distance along the spinal column with respect to C2. Endplate area and diameters were analyzed by gender, spinal level, age and correlation with spinal position. Males had larger endplates than females at all levels (p < 0.05) but S1. While endplate areas and transverse diameters increased with age at C3-L5 in females, these increases were not consistent through the whole-spine and even decreases with age were found at T1-T3 in males. There was a strong linear correlation between endplate area and spinal position in males and females with correlation coefficient values of r = 0.938 and r = 0.911, respectively. However, multiple comparisons of the geometrical parameters through the whole-spine revealed localized reduction of the anteroposterior or transverse diameters at T4 and L5-S1 levels. These regional and age-related changes in endplate dimensions should be taken into account for safe interventional treatments at these sites. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1418-1430, 2016.

A hominin first rib discovered at the Sterkfontein Caves, South Africa

Abstract First ribs – the first or most superior ribs in the thorax – are rare in the hominin fossil record, and when found, have the potential to provide information regarding the upper thorax shape of extinct hominins. Here, we describe a partial first rib from Member 4 of the Sterkfontein Caves, South Africa. The rib shaft is broken away, so only the head and neck are preserved. The rib is small, falling closest to small-bodied Australopithecus first ribs (AL 288-1 and MH1). Given that it was recovered near the StW 318 femur excavation, which also represents a small individual, we suggest that the two may be associated. Three-dimensional geometric morphometric analyses were used to quantify the rib fragment morphology and compare it to extant hominoid and other fossil hominin ribs. While only the proximal end is preserved, our analyses show that South African Australopithecus share derived features of the proximal first rib more closely resembling A. afarensis and later hominins than great apes.