Phenotypic integration of the cervical vertebrae in the Hominoidea (Primates)

Phenotypic integration and modularity represent important factors influencing evolutionary change. The mammalian cervical vertebral column is particularly interesting in regards to integration and modularity because it is highly constrained to seven elements, despite widely variable morphology. Previous research has found a common pattern of integration among quadrupedal mammals, but integration patterns also evolve in response to locomotor selective pressures like those associated with hominin bipedalism. Here, I test patterns of covariation in the cervical vertebrae of three hominoid primates (Hylobates, Pan, Homo) who engage in upright postures and locomotion. Patterns of integration in the hominoid cervical vertebrae correspond generally to those previously found in other mammals, suggesting that integration in this region is highly conserved, even among taxa that engage in novel positional behaviors. These integration patterns reflect underlying developmental as well as functional modules. The strong integration between vertebrae suggests that the functional morphology of the cervical vertebral column should be considered as a whole, rather than in individual vertebrae. Taxa that display highly derived morphologies in the cervical vertebrae are likely exploiting these integration patterns, rather than reorganizing them. Future work on vertebrates without cervical vertebral number constraints will further clarify the evolution of integration in this region.     

Cercopithecoid cervical vertebral morphology and implications for the presence of Theropithecus in early Pleistocene Europe

While it is recognized that the overall configuration of the vertebral column, as well as the size and shape of individual vertebrae, differ within and between primate taxa, relatively little is known about the degree to which vertebral morphology reflects a phylogenetic signal or the degree to which vertebral elements can be used in accurate taxonomic classification. Isolated vertebrae are occasionally found in fossil assemblages, and proper taxonomic identification is necessary to make inferences about the animal's biology and place it in a broader phylogenetic and evolutionary context. Recently, three large primate cervical vertebrae (C3, C5, and C6) from Pirro Nord, Italy (early Pleistocene, late Villafranchian) were attributed to the genus Theropithecus based on size comparisons with extant cercopithecoid primates (Rook et al., 2004, J. Hum. Evol. 47, 267-277). These fossils were suggested to indicate an early dispersal of this genus out of Africa around 1.6-1.3 Ma possibly co-incident with early Pleistocene dispersals of Homo. Because of the potential importance of these fossils for interpreting Theropithecus evolution and the relatively few morphological data on primate cervical vertebral morphology, we examined the size and shape of cervical vertebrae in a large sample of extant cercopithecoid taxa (n=106). Specifically, we evaluated whether subfamily and genus level assignments can be made on the basis of isolated cervical elements. Discriminant analyses reveal that scaled shape variables are good discriminators of taxonomic affinity at the subfamily level but are poor discriminators at the genus level. Least-squares regressions show that raw linear dimensions of cervical vertebral morphology are good predictors of body mass in the extant sample. Our regression results produce a likely body mass estimate of 22-38 kg for the Pirro Nord cervical vertebrae. Based on these regression estimates, the poor ability to discriminate cervical vertebrae at the genus level, and paleoenvironmental reconstructions of Pirro Nord, it is unlikely that the Pirro Nord fossils can be confidently attributed to the genus Theropithecus. These findings have important implications for recent interpretations of the nature of Theropithecus dispersal out of Africa.     

Head posture and craniofacial morphology

The associations between craniofacial morphology and the posture of the head and the cervical column were examined in a sample of 120 Danish male students aged 22–30 years. Two head positions were recorded on lateral cephalometric radiographs, one determined by the subject's own feeling of a natural head balance (self balance position), and the other by the subject looking straight into a mirror (mirror position). Craniofacial morphology was described by 42 linear and angular variables, and postural relationships by 18 angular variables. A comprehensive set of correlations was found between craniofacial morphology and head posture. The correlations were similar for both head positions investigated. Of the postural variables, the position of the head in relation to the cervical column showed the largest set of correlations with craniofacial morphology. Extension of the head in relation to the cervical column was found in connection with large anterior and small posterior facial heights, small antero-posterior craniofacial dimensions, large inclination of the mandible to the anterior cranial base and to the nasal plane, facial retrognathism, a large cranial base angle, and a small nasopharyngeal space. The possible role of functional factors in mediating the relationship between morphology and posture was discussed.     

Functional morphology and anatomy of cervical vertebrae in Nacholapithecus kerioi, a middle Miocene hominoid from Kenya

This paper describes the morphology of cervical vertebrae in Nacholapithecus kerioi, a middle Miocene primate species excavated from Nachola, Kenya in 1999-2002. The cervical vertebrae in Nacholapithecus are larger than those of Papio cynocephalus. They are more robust relative to more caudal vertebral bones. Since Nacholapithecus had large forelimbs, it is assumed that strong cervical vertebrae would have been required to resist muscle reaction forces during locomotion. On the other hand, the vertebral foramen of the lower cervical vertebrae in Nacholapithecus is almost the same size as or smaller than that of P. cynocephalus. Atlas specimens of Nacholapithecus resemble those of extant great apes with regard to the superior articular facet, and they have an anterior tubercle trait intermediate between that of extant apes and other primate species. Nacholapithecus has a relatively short and thick dens on the axis, similar to those of extant great apes and the axis body shape is intermediate between that of extant apes and other primates. Moreover, an intermediate trait between extant great apes and other primate species has been indicated with regard to the angle between the prezygapophyseal articular facets of the axis in Nacholapithecus. Although the atlas of Nacholapithecus is inferred as having a primitive morphology (i.e., possessing a lateral bridge), the shape of the atlas and axis leads to speculation that locomotion or posture in Nacholapithecus involved more orthograde behavior similar to that of extant apes, and, in so far as cervical vertebral morphology is concerned, it is thought that Nacholapithecus was incipiently specialized toward the characteristics of extant hominoids.     

Functional aspects of strepsirrhine lumbar vertebral bodies and spinous processes

The relationship between form and function in the lumbar vertebral column has been well documented among platyrrhines and especially catarrhines, while functional studies of postcranial morphology among strepsirrhines have concentrated predominantly on the limbs. This morphometric study investigates biomechanically relevant attributes of the lumbar vertebral morphology of 20 species of extant strepsirrhines. With this extensive sample, our goal is to address the influence of positional behavior on lumbar vertebral form while also assessing the effects of body size and phylogenetic history. The results reveal distinctions in lumbar vertebral morphology among strepsirrhines in functional association with their habitual postures and primary locomotor behaviors. In general, strepsirrhines that emphasize pronograde posture and quadrupedal locomotion combined with leaping (from a pronograde position) have the relatively longest lumbar regions and lumbar vertebral bodies, features promoting sagittal spinal flexibility. Indrids and galagonids that rely primarily on vertical clinging and leaping with orthograde posture share a relatively short (i.e., stable and resistant to bending) lumbar region, although the length of individual lumbar vertebral bodies varies phylogenetically and possibly allometrically. The other two vertical clingers and leapers, Hapalemur and Lepilemur, more closely resemble the pronograde, quadrupedal taxa. The specialized, suspensory lorids have relatively short lumbar regions as well, but the lengths of their lumbar regions are influenced by body size, and Arctocebus has dramatically longer vertebral bodies than do the other lorids. Lumbar morphology among galagonids appears to reflect a strong phylogenetic signal superimposed on a functional one. In general, relative length of the spinous processes follows a positively allometric trend, although lorids (especially the larger-bodied forms) have relatively short spinous processes for their body size, in accordance with their positional repertoire. The results of the study broaden our understanding of postcranial adaptation in primates, while providing an extensive comparative database for interpreting vertebral morphology in fossil primates.     

Evolution and function of anterior cervical vertebral fusion in tetrapods

The evolution of vertebral fusion is a poorly understood phenomenon that results in the loss of mobility between sequential vertebrae. Non‐pathological fusion of the anterior cervical vertebrae has evolved independently in numerous extant and extinct mammals and reptiles, suggesting that the formation of a ‘syncervical’ is an adaptation that arose to confer biomechanical advantage(s) in these lineages. We review syncervical anatomy and evolution in a broad phylogenetic context for the first time and provide a comprehensive summary of proposed adaptive hypotheses. The syncervical generally consists of two vertebrae (e.g. hornbills, porcupines, dolphins) but can include fusion of seven cervical vertebrae in some cetaceans. Based on the ecologies of taxa with this trait, cervical fusion most often occurs in fossorial and pelagic taxa. In fossorial taxa, the syncervical likely increases the out‐lever force during head‐lift digging. In cetaceans and ricochetal rodents, the syncervical may stabilize the head and neck during locomotion, although considerable variation exists in its composition without apparent variability in locomotion. Alternatively, the highly reduced cervical vertebral centra may require fusion to prevent mechanical failure of the vertebrae. In birds, the syncervical of hornbills may have evolved in response to their unique casque‐butting behaviour, or due to increased head mass. The general correlation between ecological traits and the presence of a syncervical in extant taxa allows more accurate interpretation of extinct animals that also exhibit this unique trait. For example, syncervicals evolved independently in several groups of marine reptiles and may have functioned to stabilize the head at the craniocervical joint during pelagic locomotion, as in cetaceans. Overall, the origin and function of fused cervical vertebrae is poorly understood, emphasizing the need for future comparative biomechanical studies interpreted in an evolutionary context.     

Tail growth tracks the ontogeny of prehensile tail use in capuchin monkeys (Cebus albifrons and C. apella)

Physical anthropologists have devoted considerable attention to the structure and function of the primate prehensile tail. Nevertheless, previous morphological studies have concentrated solely on adults, despite behavioral evidence that among many primate taxa, including capuchin monkeys, infants and juveniles use their prehensile tails during a greater number and greater variety of positional behaviors than do adults. In this study, we track caudal vertebral growth in a mixed longitudinal sample of white-fronted and brown capuchin monkeys (Cebus albifrons and Cebus apella). We hypothesized that young capuchins would have relatively robust caudal vertebrae, affording them greater tail strength for more frequent tail-suspension behaviors. Our results supported this hypothesis. Caudal vertebral bending strength (measured as polar section modulus at midshaft) scaled to body mass with negative allometry, while craniocaudal length scaled to body mass with positive allometry, indicating that infant and juvenile capuchin monkeys are characterized by particularly strong caudal vertebrae for their body size. These findings complement previous results showing that long bone strength similarly scales with negative ontogenetic allometry in capuchin monkeys and add to a growing body of literature documenting the synergy between postcranial growth and the changing locomotor demands of maturing animals. Although expanded morphometric data on tail growth and behavioral data on locomotor development are required, the results of this study suggest that the adult capuchin prehensile-tail phenotype may be attributable, at least in part, to selection on juvenile performance, a possibility that deserves further attention.     

Morphology and Function of the Vertebral Column in Remingtonocetus domandaensis (Mammalia, Cetacea) from the Middle Eocene Domanda Formation of Pakistan

The archaeocete family Remingtonocetidae is a group of early cetaceans known from the Eocene of India and Pakistan. Previous studies of remingtonocetids focused primarily on cranial anatomy due to a paucity of well-preserved postcranial material. Here we describe the morphology of the known vertebral column in Remingtonocetus domandaensis based largely on a single well-preserved partial skeleton recovered from the upper Domanda Formation of Pakistan. The specimen preserves most of the precaudal vertebral column in articulation and includes seven complete cervical vertebrae, ten partial to complete thoracic vertebrae, six complete lumbar vertebrae, and the first three sacral vertebrae. Cervical centra are long and possess robust, imbricating transverse processes that stabilized the head and neck. Lumbar vertebrae allowed for limited flexibility and probably served primarily to stabilize the lumbar column during forceful retraction of the hind limbs. Vertebral evidence, taken together with pelvic and femoral morphology, is most consistent with interpretation of Remingtonocetus domandaensis as an animal that swam primarily by powerful movement of its hind limbs rather than dorsoventral undulation of its body axis.     

Correlation between Hox code and vertebral morphology in archosaurs

The relationship between developmental genes and phenotypic variation is of central interest in evolutionary biology. An excellent example is the role of Hox genes in the anteroposterior regionalization of the vertebral column in vertebrates. Archosaurs (crocodiles, dinosaurs including birds) are highly variable both in vertebral morphology and number. Nevertheless, functionally equivalent Hox genes are active in the axial skeleton during embryonic development, indicating that the morphological variation across taxa is likely owing to modifications in the pattern of Hox gene expression. By using geometric morphometrics, we demonstrate a correlation between vertebral Hox code and quantifiable vertebral morphology in modern archosaurs, in which the boundaries between morphological subgroups of vertebrae can be linked to anterior Hox gene expression boundaries. Our findings reveal homologous units of cervical vertebrae in modern archosaurs, each with their specific Hox gene pattern, enabling us to trace these homologies in the extinct sauropodomorph dinosaurs, a group with highly variable vertebral counts. Based on the quantifiable vertebral morphology, this allows us to infer the underlying genetic mechanisms in vertebral evolution in fossils, which represents not only an important case study, but will lead to a better understanding of the origin of morphological disparity in recent archosaur vertebral columns.     

Craniocervical morphology and posture in Australian aboriginals

The length of the spinal column as a percentage of stature is smaller in the Australian aboriginal than in most other ethnic groups (Abbie, 1957). It is conceivable that relative lengths of the cervical column might influence population differences in craniocervical posture and craniofacial morphology. The present study aimed to elucidate this relationship by comparing head posture and craniofacial morphology in Australian aboriginals to the same features in a previously studied sample of 120 Danish students (Solow and Tallgren, 1976). The aboriginal sample consisted of 42 young male adults from the Yuendumu settlement, Northern Territory, Australia. Cephalometric films of the natural head position were taken during a field trip to the settlement. The comparison comprised 18 postural and 61 morphological variables. In the aboriginals, the cervical column was shorter and had a less pronounced lordosis. The head was held about 3° lower, and the upper cervical column was 81/2° more forward inclined. As a consequence, the craniocervical angle was about 6° larger. Comparison of the craniofacial morphology in the two groups showed in the aboriginals a shorter upper facial height, a larger anterior lower facial height, and a larger vertical jaw relationship (NL/ML). The length of the posterior cranial base, s-ba, was 4 mm shorter (P <0.001) in the aboriginals, possibly developmentally related to the generally shorter spinal column in Australian aboriginals.     

Analysis of variability in vertebral morphology and growth ring counts in two Carcharhinid sharks

Inter- and intra-regional variations in vertebrae morphology and growth increment counts (band counts) were analyzed for two carcharhinid shark species, Carcharhinus plumbeus (n = 10) and C. limbatus (n = 11). Five sequential vertebrae were removed from the cervical region, above the branchial chamber and posterior to the chondrocrainium, and thoracic region, below the first dorsal fin. Dorsal–ventral height, medial–lateral breadth, and caudal–cranial length were measured for each sampled vertebra. Results indicate no significant difference in vertebral morphology within a sampled region of the vertebral column. However, a significant difference in vertebral morphology was noted between regions for both shark species, with thoracic vertebrae consistently larger than cervical vertebrae. A sub-set of three vertebrae was taken from each sampled region of each shark for sectioning and counting of growth increments. Analyses of growth increment counts by two readers indicated no significant difference in band counts within and between sampled regions.     

Evaluation of "unique" aspects of human vertebral bodies and pedicles with a consideration of Australopithecus africanus

Recent functional studies of human vertebrae have revealed that loads borne by the axial skeleton during bipedal postures and locomotion pass through the pedicles and posterior elements as well as through the bodies and discs. Accordingly, particular morphological attributes of these vertebral elements have been linked exclusively with bipedalism. In order to test the validity of current form-function associations in human vertebral anatomy, this study considers the morphology of human thoracolumbar vertebral bodies and pedicles in the context of a wide comparative primate sample. The last lumbar vertebra of STS 14 (Australopithecus africanus) is also included in the analysis. Results indicate that certain features of human vertebrae previously thought to reflect bipedalism are characteristic of several nonhuman primates, including those whose posture is habitually pronograde. These features include the decrease in vertebral body surface area and the increase in cross-sectional area of the pedicle between the penultimate and last lumbar vertebra. In addition, although humans have relatively large and wide last lumbar pedicles, the enlargement and widening of the pedicle between the penultimate and last lumbar vertebra is not unique to humans. On the other hand, human vertebrae do exhibit several unique adaptations to bipedal posture and locomotion: (1) the vertebral body surface areas of the lower lumbar vertebrae and the cross-sectional areas of the last lumbar pedicles are large relative to body size, and (2) the last lumbar pedicles are wider relative to length and to body size than are those of nonhuman primates. The last lumbar vertebra of STS 14 does not exhibit any of these human-like vertebral features—its pedicles and body surface areas are relatively small, and its pedicles are not relatively wide, but relatively short.     

Functional morphology of cercopithecoid primate metacarpals

The primate fossil record suggests that terrestriality was more common in the past than it is today, particularly among cercopithecoid primates. Whether or not a fossil primate habitually preferred terrestrial substrates has typically been inferred from its forelimb anatomy. Because extant large-bodied terrestrial cercopithecine monkeys utilize digitigrade hand postures during locomotion, being able to identify if a fossil primate habitually adopted digitigrade postures would be particularly revealing of terrestriality in this group. This paper examines the functional morphology of metacarpals in order to identify osteological correlates of digitigrade versus palmigrade hand postures. Linear measurements were obtained from 324 individuals belonging to digitigrade and palmigrade cercopithecoid species and comparisons were made between hand posture groups. Digitigrade taxa have shorter metacarpals, relative to both body mass and humerus length, than palmigrade taxa. Also, digitigrade taxa tend to have metacarpals with smaller dorsoventral diameters, relative to the product of body mass and metacarpal length, compared to palmigrade taxa. The size and shape of the metacarpal heads do not significantly differ between hand posture groups. Multivariate analyses suggest that metacarpal shape can only weakly discriminate between hand posture groups. In general, while there are some morphological differences in the metacarpals between hand posture groups, similarities also exist that are likely related to the fact that even digitigrade cercopithecoids can adopt palmigrade hand postures in different situations (e.g., terrestrial running, arboreal locomotion), and/or that the functional demands of different hand postures are not reflected in all aspects of metacarpal morphology. Therefore, the lack of identifiable adaptations for specific hand postures in extant cercopithecoids makes it difficult to determine a preference for specific habitats from fossil primate hand bones.     

Regionalization of axial skeleton in the lungfish Neoceratodus forsteri (Dipnoi)

Differentiation of the axial skeleton into distinct regions, once thought to be characteristic of the Tetrapoda, also occurs in the actinopterygian Danio rerio. In these taxa, the boundary between the cervical-thoracic regions correlates with Hoxc6 expression and morphological features such as position of the pectoral fin and associated nerves, and the absence of ribs. In the lungfish Neoceratodus, a member of the extant sister taxon to the Tetrapoda, the first vertebral element to chondrify is situated well posterior to the skull, developing from somites 6 and 7 (6/7) and associated with an enlarged cranial rib and nerves innervating the pectoral fin. Two vertebral elements develop later and more anteriorly, associated with somites 4/5 and 5/6. These three elements become incorporated into the occipital region of the skull during Neoceratodus ontogeny, until the cranial rib itself articulates to the rear of the skull. These features of early development indicate a regionalization of the Neoceratodus vertebral column: the cranial rib marks the boundary between the cervical and thoracic regions, the two more anterior vertebrae lacking ribs represent the cervical region, while somites 1-4 (cranial half), lacking any vertebral development, represent the occipital region. However, the cervical region of the vertebral column is effectively lost during ontogeny of Neoceratodus. A recognizable cervical region in the tetrapod vertebral column, as in zebrafish, suggests that cervical vertebrae are not incorporated into the skull but maintained as distinct elements of the column, representing an important shift in relative developmental timing and the influence of heterochrony in this region during the fish-tetrapod transition.     

Evolution of posture in amniotes–Diving into the trabecular architecture of the femoral head

Extant amniotes show remarkable postural diversity. Broadly speaking, limbs with erect (strongly adducted, more vertically oriented) posture are found in mammals that are particularly heavy (graviportal) or show good running skills (cursorial), while crouched (highly flexed) limbs are found in taxa with more generalized locomotion. In Reptilia, crocodylians have a “semi-erect” (somewhat adducted) posture, birds have more crouched limbs and lepidosaurs have sprawling (well-abducted) limbs. Both synapsids and reptiles underwent a postural transition from sprawling to more erect limbs during the Mesozoic Era. In Reptilia, this postural change is prominent among archosauriforms in the Triassic Period. However, limb posture in many key Triassic taxa remains poorly known. In Synapsida, the chronology of this transition is less clear, and competing hypotheses exist. On land, the limb bones are subject to various stresses related to body support that partly shape their external and internal morphology. Indeed, bone trabeculae (lattice-like bony struts that form the spongy bone tissue) tend to orient themselves along lines of force. Here, we study the link between femoral posture and the femoral trabecular architecture using phylogenetic generalized least squares. We show that microanatomical parameters measured on bone cubes extracted from the femoral head of a sample of amniote femora depend strongly on body mass, but not on femoral posture or lifestyle. We reconstruct ancestral states of femoral posture and various microanatomical parameters to study the “sprawling-to-erect” transition in reptiles and synapsids, and obtain conflicting results. We tentatively infer femoral posture in several hypothetical ancestors using phylogenetic flexible discriminant analysis from maximum likelihood estimates of the microanatomical parameters. In general, the trabecular network of the femoral head is not a good indicator of femoral posture. However, ancestral state reconstruction methods hold great promise for advancing our understanding of the evolution of posture in amniotes.     

Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae)

A computer reconstruction of isolated cervical vertebrae of Azhdarcho lancicollis from the Turonian of Uzbekistan allows three-dimensional model of the cervical region of the vertebral column of this animal. The relative length of cervical vertebrae (I + II < III < IV < V > VI > VII > VIII > IX) is the same as in pterodactyloids with short cervical vertebrae. An increase in neck length is provided mostly by the middle cervical vertebrae (IV–VI). In a neutral posture, the neck of azhdarchids was not straight, as often reconstructed, but S-shaped, with the maximum angles between the V–VI (20°), VI–VII (20°), and VIII–IX (17°) vertebrae. The feeding strategy of azhdarchids was probably similar to that of pelicans. In a search for prey, azhdarchids were soaring above the water surface of large inland or nearshore marine water bodies. Their prey (predominantly fish) was captured by the widely open mouth and fell into the throat sac, the presence of which is suggested by the spiral jaw joint. Prey was swallowed during the abrupt neck flexion in the posterior segment, which brought the head in an almost horizontal position. A storklike wading ecology for azhdarchids is less probable, because these clumsy on land animals were vulnerable to terrestrial predators.     

Patterns of growth in the presacral vertebral column of the leopard gecko (Eublepharis macularius)

Postnatal growth patterns within the vertebral column may be informative about body proportions and regionalization. We measured femur length, lengths of all pre‐sacral vertebrae, and lengths of intervertebral spaces, from radiographs of a series of 21 Eublepharis macularius, raised under standard conditions and covering most of the ontogenetic body size range. Vertebrae were grouped into cervical, sternal, and dorsal compartments, and lengths of adjacent pairs of vertebrae were summed before analysis. Femur length was included as an index of body size. Principal component analysis of the variance‐covariance matrix of these data was used to investigate scaling among them. PC1 explained 94.19% of total variance, interpreted as the variance due to body size. PC1 differed significantly from the hypothetical isometric vector, indicating overall allometry. The atlas and axis vertebrae displayed strong negative allometry; the remainder of the vertebral pairs exhibited weak negative allometry, isometry or positive allometry. PC1 explained a markedly smaller amount of variance for the vertebral pairs of the cervical compartment than for the remainder of the vertebral pairs, with the exception of the final pair. The relative standard deviations of the eigenvalues from the PCAs of the three vertebral compartments indicated that the vertebrae of the cervical compartment were less strongly integrated by scaling than were the sternal or dorsal vertebrae, which did not differ greatly between themselves in their strong integration, suggesting that the growth of the cervical vertebrae is constrained by the mechanical requirements of the head. Regionalization of the remainder of the vertebral column is less clearly defined but may be associated with wave form propagation incident upon locomotion, and by locomotory changes occasioned by tail autotomy and regeneration. Femur length exhibits negative allometry relative to individual vertebral pairs and to vertebral column length, suggesting a change in locomotor requirements over the ontogenetic size range.     

Evolution of the axial skeleton in armadillos (Mammalia,Dasypodidae)

Intraspecific and interspecific variation in cervical, thoracic, and lumbar region of the vertebral column of Dasypodidae were examined in a phylogenetic framework. The number of vertebrae for each region were recorded for 86 specimens and metric data for each vertebra (centrum length, high, and width) were recorded for 72 specimens, including eight of the nine living genera. The number of vertebrae and degree of fusion between them were used to define four characters which were plotted on two alternative phylogenies of Dasypodidae. The ratio between centrum height and width is similar across all taxa analyzed except for Chlamyphorus, which exhibits a deviation in the last two lumbars. Tolypeutes matacus is unique among the taxa examined in having a second co-osified bone called postcervical bone, which is a fusion of the seventh cervical and first thoracic vertebrae. The thoraco-lumbar numbers of dasypodids are reduced when compared with other xenarthrans and are more diverse than those of some other mammalian clades of similar geological age and higher ecomorphological diversity. Changes in size are somewhat coupled with changes in the number of body segments. Independent of the phylogenetic framework taken, changes in size are accompanied with small changes in numbers of thoracolumbar vertebrae within each genus. There are functional and phylogenetic correlates for changes in number of thoraco-lumbar vertebrae in dasypodids.     

Can habitat characteristics shape vertebral morphology in dolphins? An example of two phylogenetically related species from southern South America

Fast swimming pelagic cetacean species have osteological characteristics that promote a more stable spine in comparison to that of coastal species. The Peale's dolphin (Lagenorhynchus australis) and the hourglass dolphin (Lagenorhynchus cruciger) have a close phylogenetic relationship and are found in coastal and pelagic waters in the Southern Hemisphere, respectively. The aim of this work was to study the relationship between the vertebral column's morphology and its flexibility, across these species of contrasting habitats. Vertebral counts and multiple measurements of each vertebra were used to infer intervertebral flexibility. Bivariate plots and discriminant multivariate analyses were employed to compare each functional region along the vertebral column. Both species displayed a regionalization of the column into three stable regions and two flexible areas, which statistically differ in the proportion of the skeleton occupied in each species. While the Peale's dolphin has rounder vertebrae, associated with higher flexibility, the hourglass dolphin has disk‐shaped vertebrae and strongly inclined processes related to high stability. Although the species are closely related phylogenetically, vertebral morphology is influenced by a diverse set of ecological and behavioral factors, reflecting a high degree of vertebral plasticity within the genus.     

Pathology and the posture of the La Chapelle-aux-Saints Neandertal

The depiction of the Neandertals as incompletely erect was based primarily on Boule's (1911, 1912a, 1913) analysis of the La Chapelle-aux-Saints 1 partial skeleton. The inaccurate aspects of Boule's postural reconstruction were corrected during the 1950s. However, it has come to be believed, following Straus and Cave (1957), that Boule's errors of reconstruction were due to the diseased condition of the La Chapelle-aux-Saints 1 remains, rather than to Boule's misinterpretation of morphology. The abnormalities on the La Chapelle-aux-Saints 1 postcranium include: lower cervical, upper thoracic, and lower thoracic intervertebral degenerative joint disease (DJD), a distal fracture of a mid-thoracic rib, extensive DJD of the left hip, DJD of the right fifth proximal interphalangeal articulation, bilateral humeral head eburnation, and minor exostosis formation on the right humerus, ulna, and radius. These were associated with extensive alveolar inflammation including apical abscesses and antemortem tooth loss, some temporomandibular DJD, bilateral auditory exostoses, and minimal occipital condyle DJD. None of these abnormalities significantly affected Boule's Neandertal postural reconstruction, and a review of his analysis indicates that early twentieth century interpretations of skeletal morphology (primarily of the cranium, cervical vertebrae, lumbar and sacral vertebrae, proximal femora and tibiae, posterior tarsals, and hallucial tarsometatarsal joint), combined with Boule's evolutionary preconceptions, were responsible for his mistaken view of Neandertal posture.