Ecological and phylogenetic influence on mandible shape variation of South American caviomorph rodents (Rodentia: Hystricomorpha)

We analyzed mandible shape variation of 17 genera belonging to three superfamilies (Cavioidea, Chinchilloidea, and Octodontoidea) of South American caviomorph rodents using geometric morphometrics. The relative influence of phylogeny and ecology on this variation was assessed using phylogenetic comparative methods. Most morphological variation was concentrated in condylar, coronoid, and angular processes, as well as the diastema. Features potentially advantageous for digging (i.e. high coronoid and condylar processes, relatively short angular process, and diastema) were present only in octodontoids; cavioids showed opposing trends, which could represent a structural constraint for fossorial habits. Chinchilloids showed intermediate features. Genera were distributed in the morphospace according to their classification into superfamilial clades. The phylogenetic signal for shape components was significant along phylogeny, whereas the relationship between mandibular shape and ecology was nonsignificant when phylogenetic structure was taken into account. An early evolutionary divergence in the mandible shape among major caviomorph clades would explain the observed strong phylogenetic influence on the variation of this structure. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 828–837.     

Convergences in Scapula Morphology among Small Cursorial Mammals: An Osteological Correlate for Locomotory Specialization

Small cursorial mammals, such as lagomorphs, elephant shrews, and the more cursorial caviomorph rodents, share both the similar locomotor gait of rapid half-bounding and a similar scapula anatomy of a long, slender, caudally projecting metacromion process. This scapular morphology is also present in some notoungulates (extinct endemic South American ungulates), in rabbit-like taxa such as Propachyruchos. In the rabbit Oryctolagus this elongated metacromion process serves to increase the moment arm of the acromiotrapezius and levator scapulae ventralis muscles, which we propose may aid in scapula stabilization and resisting ground reaction forces during the landing phase onto a single forelimb in half-bounding. A long, slender metacromion process is thus an osteological correlate of locomotor specialization, that of rapid half-bounding in small to medium-sized mammals.     

A comparison of the ontogeny of shape variation in the anthropoid scapula: functional and phylogenetic signal

This article compares ontogenetic shape variation in the scapula of 17 anthropoid species using three-dimensional landmark-based geometric morphometrics. These data are used to investigate functional and phylogenetic signal in the major components of scapular variation and to evaluate the degree to which postnatal growth contributes to interspecific differences in shape. Results indicate that the shape of the infant and adult scapula is primarily associated with positional behavior (e.g., orthograde suspensory nonquadrupeds versus pronograde quadrupeds), but within this functional structure there is phylogenetic signal, particularly at infant stages. Growth most closely correlates with infant/adult shape and locomotor function. These results suggest that the shape of the infant scapula drives the pattern of postnatal scapular growth and adult morphology. As such, variation in postnatal growth is not the primary source of interspecific variation in adult shape. Instead, interspecific differences in scapular morphology are hypothesized to be the result of selection for variation in embryonic developmental processes that affect shape.     

Functional and historical determinants of shape in the scapula of Xenarthran mammals: Evolution of a complex morphological structure

The mammalian scapula is a complex morphological structure, composed of two ossification plates that fuse into a single structure. Most studies on morphological differentiation in the scapula have considered it to be a simple, spatially integrated structure, primarily influenced by the important locomotor function presented by this element. We used recently developed geometric morphometric techniques to test and quantify functional and phylogenetic influences on scapular shape variation in fossil and extant xenarthran mammals. The order Xenarthra is well represented in the fossil record and presents a stable phylogenetic hypothesis for its genealogical history. In addition, its species present a large variety of locomotor habits. Our results show that approximately half of the shape variation in the scapula is due to phylogenetic heritage. This is contrary to the view that the scapula is influenced only by functional demands. There are large‐scale shape transformations that provide biomechanical adaptation for the several habits (arboreality, terrestriality, and digging), and small scale‐shape transformations (mostly related to the coracoid process) that are not influenced by function. A nonlinear relationship between morphometric and phylogenetic distances indicates the presence of a complex mixture of evolutionary processes acting on shape differentiation of the scapula. J. Morphol. 241:251–263, 1999. © 1999 Wiley‐Liss, Inc.     

Ontogeny of the hominoid scapula: The influence of locomotion on morphology

Primate shoulder morphology has been linked with locomotor habits, oftentimes irrespective of phylogenetic heritage. Among hominoids, juvenile African apes are known to climb more frequently than adults, while orangutans and gibbons maintain an arboreal lifestyle throughout ontogeny. This study examined if these ontogenetic locomotor differences carry a morphological signal, which should be evident in the scapulae of chimpanzees and gorillas but absent in taxa that do not display ontogenetic behavioral shifts. The scapular morphology of five hominoid primates and one catarrhine outgroup was examined throughout ontogeny to evaluate if scapular traits linked with arboreal activities are modified in response to ontogenetic behavioral shifts away from climbing. Specifically, the following questions were addressed: 1) which scapular characteristics distinguish taxa with different locomotor habits; and 2) do these traits show associated changes during development in taxa known to modify their behavioral patterns? Several traits characterized suspensory taxa from nonsuspensory forms, such as cranially oriented glenohumeral joints, obliquely oriented scapular spines, relatively narrow infraspinous fossae, and inferolaterally expanded subscapularis fossae. The relative shape of the dorsal scapular fossae changed in Pan, Gorilla, and also Macaca in line with predictions based on reported ontogenetic changes in locomotor behavior. These morphological changes were mostly distinct from those seen in Pongo, Hylobates, and Homo and imply a unique developmental pattern, possibly related to ontogenetic locomotor shifts. Accordingly, features that sorted taxa by locomotor habits and changed in concert with ontogenetic behavioral patterns should be particularly useful for reconstructing the locomotor habits of fossil forms. Am J Phys Anthropol 152:239–260, 2013. © 2013 Wiley Periodicals, Inc.     

Reconciling the convergence of supraspinous fossa shape among hominoids in light of locomotor differences

Differences in scapular morphology between modern humans and the African and lesser apes are associated with the distinct locomotor habits of these groups. However, several traits, particularly aspects of the supraspinous fossa, are convergent between Homo and Pongo—an unexpected result given their divergent locomotor habits. Many morphological assessments of the scapula rely on the limited number of static landmarks available, and traditional approaches like these tend to oversimplify scapular shape. Here, we present the results of two geometric morphometric (GM) analyses of hominoid supraspinous fossa shape—one employing five homologous landmarks and another with 83 sliding semilandmarks—alongside those of traditional methods to evaluate if three-dimensional considerations of fossa shape afford more comprehensive insights into scapular shape and functional morphology. Traditional measures aligned Pongo and Homo with narrow and transversely oriented supraspinous fossae, whereas African ape and Hylobates fossae are broader and more obliquely situated. However, our GM results highlight that much of the convergence between Homo and Pongo is reflective of their more medially positioned superior angles. These approaches offered a more complete assessment of supraspinous shape and revealed that the Homo fossa, with an intermediate superior angle position and moderate superoinferior expansion, is actually reminiscent of the African ape shape. Additionally, both Pongo and Hylobates were shown to have more compressed fossae, something that has not previously been identified through traditional analyses. Thus, the total morphological pattern of the Pongo supraspinous fossa is unique among hominoids, and possibly indicative of its distinctive locomotor habits. Am J Phys Anthropol 156:498–510, 2015. © 2015 Wiley Periodicals, Inc.     

Tracking the scapula using the scapula locator with and without feedback from pressure-sensors: A comparative study

BackgroundThe scapula locator method has associated intra-observer and inter-observer errors caused by the dependency on the observer to locate the scapular landmarks. The potential effect of the pressures applied by the observer on the measured scapular kinematics when this method is used has also been overlooked so far. The aim of this study was to investigate the effect of using feedback on the pressures applied on the scapula using the locator on the intra-observer and inter-observer reliabilities of the method as well as on the kinematics obtained using this method.MethodsThree observers tracked the scapular motion of the dominant shoulder of each subject using the locator with no reference to pressure-feedback for three trials of bilateral elevation in the scapular plane and using the locator with pressure-feedback for three other trials. Variations between the measurements obtained were used to calculate the intra-observer errors and variations between the measurements obtained by the three observers for the same subject were used to calculate inter-observer errors. Repeated-measures ANOVA tests were used to look at differences between the two methods in terms of intra-observer and inter-observer errors and scapular kinematics.FindingsUsing pressure-feedback reduced the intra-observer errors but had no effect on the inter-observer errors. Different scapular kinematics was measured using the two methods.InterpretationsPressure-feedback improves the reliability of the scapula locator method. Differences in the scapular kinematics suggest that unregulated pressures have an effect on the physiological scapular motion.     

A three‐dimensional morphometric analysis of upper forelimb morphology in the enigmatic tapir (Perissodactyla: Tapirus) hints at subtle variations in locomotor ecology

Forelimb morphology is an indicator for terrestrial locomotor ecology. The limb morphology of the enigmatic tapir (Perissodactyla: Tapirus) has often been compared to that of basal perissodactyls, despite the lack of quantitative studies comparing forelimb variation in modern tapirs. Here, we present a quantitative assessment of tapir upper forelimb osteology using three‐dimensional geometric morphometrics to test whether the four modern tapir species are monomorphic in their forelimb skeleton. The shape of the upper forelimb bones across four species (T. indicus; T. bairdii; T. terrestris; T. pinchaque) was investigated. Bones were laser scanned to capture surface morphology and 3D landmark analysis was used to quantify shape. Discriminant function analyses were performed to reveal features which could be used for interspecific discrimination. Overall our results show that the appendicular skeleton contains notable interspecific differences. We demonstrate that upper forelimb bones can be used to discriminate between species (>91% accuracy), with the scapula proving the most diagnostic bone (100% accuracy). Features that most successfully discriminate between the four species include the placement of the cranial angle of the scapula, depth of the humeral condyle, and the caudal deflection of the olecranon. Previous studies comparing the limbs of T. indicus and T. terrestris are corroborated by our quantitative findings. Moreover, the mountain tapir T. pinchaque consistently exhibited the greatest divergence in morphology from the other three species. Despite previous studies describing tapirs as functionally mediportal in their locomotor style, we find osteological evidence suggesting a spectrum of locomotor adaptations in the tapirs. We conclude that modern tapir forelimbs are neither monomorphic nor are tapirs as conserved in their locomotor habits as previously described. J. Morphol. 277:1469–1485, 2016. © 2016 Wiley Periodicals, Inc.     

Scapula form and locomotion in chimpanzee evolution

A number of primatologists have followed Coolidge (Am. J. Phys. Anthropol. 18:1–57, 1933) in suggesting that 1) there are significant shape differences in scapula form between pygmy and common chimpanzees, 2) scapulae of P. paniscus resemble those of hylobatids more than do those of P. troglodytes, and 3) therefore pygmy chimpanzees may exhibit a greater component of arm-swinging and other arboreal behaviors than common chimpanzees. In this paper I utilize a comparative analysis of ontogenetic allometries of linear dimensions to determine shape differences in the scapulae of adult pygmy and common chimpanzees and to clarify size-related changes in shape resulting from ontogenetic scaling, i.e., the differential extension of common patterns of growth allometry. Results demonstrate that the scapulae of adult P. paniscus are relatively narrower (in a direction approximately perpendicular to the scapula spine) than those of P. troglodytes, supporting Coolidge's original claim. The allometric analysis further demonstrates, however, that the two chimpanzee species exhibit ontogenetic scaling for all proportions of the scapula examined. Thus, adult pygmy chimpanzees have the scapula proportions observed in small adult and subadult P. troglodytes of comparable scapula size. The implications of this finding for past claims concerning differences in locomotor behavior between the species are discussed. This work lends additional support to previous studies that have demonstrated a high frequency of ontogenetic scaling within the genus Pan and a pedomorphic or juvenilized morphology in the pygmy chimpanzee.     

A Comparison of Qualitative and Quantitative Methodological Approaches to Characterizing the Dorsal Side of the Scapula in Hominoidea and Its Relationship to Locomotion

Hominoidea have adapted to various forms of locomotion, each of which has specific requirements that are reflected in the shape of the scapula. We compared several qualitative and quantitative methods for characterizing the dorsal side of the scapula to detect morphological differences that reflect the adaptations of the scapula to locomotor behaviors. Our sample included 55 specimens of Hominoidea, representing five genera, including Homo, focusing specifically on the relative sizes of the scapular supraspinous and infranspinous fossae. In addition, we weighed the supraspinatus and infraspinatus muscles of 23 of the specimens to examine the feasibility of extrapolating muscle characteristics from osteological data. Our findings confirmed that the five genera exhibit significant differences in the relative size of the supraspinous and the infraspinous fossae that are related to their forms of locomotion. The supraspinous fossa was relatively small in Homo and Pongo but large in Pan, Gorilla, and Hylobates. The analysis of muscle weights showed that a substantial amount of information about soft tissues is lost in osteological analyses, leading us to recommend caution when drawing conclusions regarding forms of locomotion based only on osteological analyses.     

A new method for motion capture of the scapula using an optoelectronic tracking device: a feasibility study

Optoelectronic tracking systems are rarely used in 3D studies examining shoulder movements including the scapula. Among the reasons is the important slippage of skin markers with respect to scapula. Methods using electromagnetic tracking devices are validated and frequently applied. Thus, the aim of this study was to develop a new method for in vivo optoelectronic scapular capture dealing with the accepted accuracy issues of validated methods.

Eleven arm positions in three anatomical planes were examined using five subjects in static mode. The method was based on local optimisation, and recalculation procedures were made using a set of five scapular surface markers.

The scapular rotations derived from the recalculation-based method yielded RMS errors comparable with the frequently used electromagnetic scapular methods (RMS up to 12.6° for 150° arm elevation). The results indicate that the present method can be used under careful considerations for 3D kinematical studies examining different shoulder movements.     

Unravelling the distinctive craniomandibular morphology of the Plio-Pleistocene Eumysops in the evolutionary setting of South American octodontoid rodents (Hystricomorpha)

Echimyidae is a species-rich clade of Neotropical rodents, which diversified in association with forested biomes. Since the late Miocene, a few lineages from southern South America have been adapted to open environments. Eumysops is one of these southern echimyids, and its peculiar craniomandibular morphology has been assumed to be a result of adaptation to open environments. We performed a geometric morphometric analysis of craniomandibular shape variation to explore whether, as suspected, Eumysops is divergent from other echimyids and octodontoids. In addition, we explored whether deterministic factors driven by different ecological dimensions can explain the diversification of shape among octodontoids. We found that craniomandibular shape variation in octodontoids was related to ecological variables. Comparing competing evolutionary models suggested that the input of selective factors play a key role in octodontoid craniomandibular shape diversification; habitat and habits were found to be the most influential factors. In the analysed morphospaces, Eumysops was located distant from other echimyids due to its distinctive traits, especially wide and posteriorly displaced orbits, and related low craniomandibular joint. Divergent orbits and resulting wider panoramic vision support the interpretation of Eumysops as an open-habitat specialist echimyid. But what is more relevant, is that Eumysops occupied a sector of the octodontoid cranial morphospace not filled by living representatives; this highlights the contribution of fossils in providing key information on the specialization boundaries explored by a clade throughout its history.     

Morphology and postnatal ontogeny of the cranial endocast and paranasal sinuses of capybara (Hydrochoerus hydrochaeris), the largest living rodent

Recent studies have analyzed and described the endocranial cavities of caviomorph rodents. However, no study has documented the changes in the morphology and relative size of such cavities during ontogeny. Expecting to contribute to the discussion of the endocranial spaces of extinct caviomorphs, we aimed to characterize the cranial endocast morphology and paranasal sinuses of the largest living rodent, Hydrochoerus hydrochaeris, by focusing on its ontogenetic growth patterns. We analyzed 12 specimens of different ontogenetic stages and provided a comparison with other cavioids. Our study demonstrates that the adult cranial endocast of H. hydrochaeris is characterized by olfactory bulbs with an irregular shape, showing an elongated olfactory tract without a clear circular fissure, a marked temporal region that makes the endocast with rhombus outline, and gyrencephaly. Some of these traits change as the brain grows. The cranial pneumatization is present in the frontal and lacrimal bones. We identified two recesses (frontal and lacrimal) and one sinus (frontal). These pneumatic cavities increase their volume as the cranium grows, covering the cranial region of the cranial endocast. The encephalization quotient was calculated for each specimen, demonstrating that it decreases as the individual grows, being much higher in younger specimens than in adults. Our results show that the ontogenetic stage can be a confounding factor when it comes to the general patterns of encephalization of extinct rodents, reinforcing the need for paleobiologists to take the age of the specimens into account in future studies on this subject to avoid age-related biases.     

New rodents (Mammalia) from the late Oligocene of Cabeza Blanca (Chubut) and the first rodent radiation in Patagonia

Caviomorph rodents, the New World Hystricognathi, are one of the most characteristic groups of South American mammals. Although they have been in the continent at least since the middle Eocene, those of the Deseadan Land mammal Age (early–late Oligocene) are the best source to understanding their early history due of their good record, large geographic distribution and good temporal calibration of many of the local faunas. Here, we describe the following new taxa from the classical locality of Cabeza Blanca: Octodontoidea Acaremyidae Galileomys baiosn. sp., Octodontoidea incertae sedis Ethelomys loomisin. gen.,n. comb., Acarechimys leucotheaen. sp., Protacaremys? adilosn. sp., Chinchilloidea incertae sedis Loncolicu tretosn. gen., n. sp., Incamys menniorumn. sp., Caviomorpha incertae sedis Llitun notucan. gen., n. sp., Leucokephalos zeffiaen. gen., n. sp. and Cephalomyidae Cephalomys ceciaen. sp. The DP4 of an ‘eocardiid’, Asteromys punctus? is described for the first time. These new taxa allow us to reinterpret the relationships of some of the previously known Deseadan species and genera. They show a great early diversification at least for extra Andean Patagonia, involving at least three of the main caviomorph lineages: octodontoids, chinchilloids and cavioids.     

Scapular correlates of muscle morphology in Papio cynocephalus.

The scapula responds to the compressive states of its surrounding matrix produced by muscle functioning and weight bearing in the upper extremity with discernible structural correlates. These structural correlates can be utilized to infer locomotor behavior. After dissection and drying, the weights of several muscles of the shoulder region of 11 adult female baboons (Papio cynocephalus) were statistically compared to various dimensions of the bony scapula. A significant correlation was obtained between the weights of the individual compressive muscles, the combined weights of the compressive muscles and a scapular dimension of width. A nonsignificant correlation between these muscles and a sscapular dimension of length was also found. The results of this study were compared to those of a previous study of the scapular musculature in Macaca and opposing conclusions were obtained. The advisability of lumping macaques and baboons into a single gross locomotor category is rejected.     

An electromyographic study of serratus anterior in atelines and Alouatta: Implications for hominoid evolution

The serratus anterior pars caudalis muscle of nonhuman primates displays anatomical differences among genera that can be attributed to differences in the mechanical demands placed on these genera by their diverse locomotor: behaviors. In primates that engage extensively in climbing and suspensory behaviors, the caudal digitations of this fan-shaped muscle are aligned more nearly parallel to the long axis of the trunk. In order to clarify the selective factors promoting such a morphological change, we have conducted a telemetered electromyographic study of the caudal and middle digitations of the serratus anterior pars caudalis. During voluntary elevation of the forelimb, only the middle, more obliquely disposed digitations are powerfully recruited. The caudal digitations are either inactive or function just to initiate scapular rotation. During locomotion, the middle digitations act in the swing (recovery) phase, whereas the caudal digitations are predominatly active in the support (propulsive)These Pashe findings suggest that the caudal digitations are important in propelling the trunk past the scapula during locomotion. Evolution of a fiber orientation more parallel to the long axis of the trunk is suggested to have occurred in broad chested primates for the purpose of facilitating locomotor behaviors requiring caudal scapular retraction for propulsion, but which would be deleteriously affected if such retraction were linked to simultaneous ventral displacement of the shoulder girdle. In its current state, the human serratus anterior seems clearly adapted for arm-raising functions and indicates descent from a small ape with a thoracic shape similar to atelines.     

The Operative Treatment of Scapula Fractures: An Analysis of 10,097 Patients

BackgroundThe indications for operative treatment of scapula fractures have been debated over the past decade. Our purpose was to determine 1) the incidence and trends in the operative treatment of scapula fractures, 2) the incidence of conversion from operative fixation to total or hemi-shoulder arthroplasty (THSA) and 3) rates of associated injuries in scapula fractures. We hypothesized that the operative treatment of scapula fractures is increasing over time and that scapula fractures treated with open reduction and internal fixation (ORIF) would have increased risk for conversion to THSA.MethodsThe Humana Inc. administrative claims database was queried from 2008 to 2015. Patients with any scapular fracture, ORIF of scapula fracture, total or hemi-shoulder arthroplasty, and associated injuries were identified by ICD-9 and CPT codes. Analysis was performed for 1) all patients with a scapula fracture undergoing operative fixation (i.e. ORIF and THSA), 2) all scapular fractures treated with ORIF with subsequent conversion to ipsilateral THSA, and 3) all associated injuries.ResultsThere were 10,097 scapula fractures (28.4% glenoid, 48% female). 60% occurred in patients 65 years and older. There were 198 (1.96%) fractures (70% glenoid) treated with ORIF. There were 287 (2.84%) fractures (45% glenoid) treated with THSA (76% total shoulder). The rate of ORIF of scapular fractures did not significantly increase (RR=0.87, p=0.58). There was a significant increase in THSA as primary treatment of scapula fractures in 2015 compared to 2007 (RR=0.43, p=0.0016). Conversion from ORIF to THSA was 12.6% (25/198). Scapula fractures treated with ORIF were at significant risk for conversion to THSA (RR=4.77, p<0.0001). Associated injuries occurred in nearly 50% of scapula fractures—other fractures, lung contusion and pneumothorax/hemothorax ranking the highest, accounting for 37%, 14.5% and 8.3% of all associated injuries, respectively.ConclusionThe incidence of operative treatment of scapula fractures was 1.96% and 2.84% for ORIF and THSA, respectively. Scapular fractures previously treated with ORIF were at significant risk for conversion to THSA. Although ORIF in scapular fractures did not significantly increase over time, both THSA and overall (ORIF+THSA) operative treatment of scapula fractures increased significantly. Level of Evidence: IV