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.     

A small ichthyosaur from the Clearwater Formation (Alberta,Canada) and a discussion of the taxonomic utility of the pectoral girdle

Albian sedimentary successions of northwestern Canada have yielded a diverse assemblage of Mesozoic marine vertebrates, and ichthyosaurs form an important component of these faunas. Here, we describe a partial postcranial skeleton of a small (estimated at less than 3 m total body length) ichthyosaur from the Wabiskaw Member of the Clearwater Formation (lowermost Albian). The semi-articulated specimen includes much of the presacral vertebral column, dorsal ribs and gastralia. Most significantly, it possesses an articulated pectoral girdle and humerus, and also preserves the pelvic girdle, allowing new insights into girdle evolution in ichthyosaurs. Whereas both sets of girdles are thought to exhibit large amounts of intraspecific variation, the pectoral girdle of ophthalmosaurids appears to evolve very slowly, remaining essentially unchanged from the Middle Jurassic onwards. In contrast, the pelvic girdle shows taxonomically informative changes within Ophthalmosauridae. The variable and poorly known nature of girdle morphology in Cretaceous ichthyosaurs precludes generic referral of the specimen.     

FUNCTIONAL AND EVOLUTIONARY ASPECTS OF THE POSTCRANIAL ANATOMY OF DICYNODONTS (SYNAPSIDA, THERAPSIDA)

Abstract:  Restoration of the major skeletal muscles and functional morphological analysis of the postcranium were carried out on two Triassic dicynodont genera, Wadiasaurus and Lystrosaurus . A phylogenetic analysis of 12 selected Permian and Triassic dicynodont taxa was conducted and the postcranial character states were then mapped onto the most parsimonious tree. The analysis revealed changes in pectoral girdle and forelimb morphology, which included reduction of the coracoid plate, increasing robustness of the deltopectoral crest, change in humeral orientation from lateral to caudolateral, increasing prominence of the humeral head, and increasing robustness of the radius. Such changes can be associated with a functional tendency to reduce the lateral component of the propulsive force while still in an abducted mode. On the other hand, changes associated with the pelvic girdle included expansion of the preacetabular iliac process, reduction of the postacetabular iliac process, craniocaudal expansion of the iliac blade, change in the shape of the pubis from flat and plate-like to small and rod-like with a cranial process, and change in acetabular orientation from lateral to caudolateral. The femoral head, starting from a cranioproximal position, progressively became dorsally pronounced and offset from the body. Other features/changes associated with the femur included increasing robustness of the trochanter major, and increasing flattening of the femoral midshaft. Changes in the axial skeleton included increasing stiffening of the trunk to reduce lateral undulations, increasing dorsoventral flexion, and increasing sacral vertebral count, which can be correlated with the preacetabular iliac expansion. These findings suggest that the dicynodont postcranial skeleton evolved towards more upright hindlimb morphology with the body held well off the ground.     

The suction mechanism of the pipid frog,Pipa pipa (Linnaeus, 1758)

Most suction‐feeding, aquatic vertebrates create suction by rapidly enlarging the oral cavity and pharynx. Forceful enlargement of the pharynx is powered by longitudinal muscles that retract skeletal elements of the hyoid, more caudal branchial arches, and, in many fish, the pectoral girdle. This arrangement was thought to characterize all suction‐feeding vertebrates. However, it does not exist in the permanently aquatic, tongueless Pipa pipa , an Amazonian frog that can catch fish. Correlating high‐speed (250 and 500 fps) video records with anatomical analysis and functional tests shows that fundamental features of tetrapod body design are altered to allow P. pipa to suction‐feed. In P. pipa , the hyoid apparatus is not connected to the skull and is enclosed by the pectoral girdle. The major retractor of the hyoid apparatus arises not from the pectoral girdle but from the femur, which lies largely within the soft tissue boundaries of the trunk. Retraction of the hyoid is coupled with expansion of the anterior trunk, which occurs when the hypertrophied ventral pectoral elements are depressed and the urostyle and sacral vertebra are protracted and slide forward on the pelvic girdle, thereby elongating the entire trunk. We suggest that a single, robust pair of muscles adduct the cleithra to depress the ventral pectoral elements with force, while modified tail muscles slide the axial skeleton cranially on the pelvic girdle. Combined hyoid retraction, axial protraction, and pectoral depression expand the buccopharyngeal cavity to a volume potentially equal to that of the entire resting body of the frog. Pipa may be the only tetrapod vertebrate clade that enlarges its entire trunk during suction‐feeding.     

西伯利亚鲟幼鱼骨骼系统解剖研究

为了解西伯利亚鲟(Acipenser baeri)骨骼系统的形态特征, 采用传统的解剖法和透明骨法对西伯利亚鲟幼鱼进行解剖观察, 为西伯利亚鲟在形态学和分类学的研究提供基础资料。结果表明: 西伯利亚鲟幼鱼骨骼系统由主轴骨骼和附肢骨骼两部分构成, 主轴骨骼包括头骨、脊柱和肋骨, 附肢骨骼由鳍条、支鳍骨骼和带骨构成。对比分析发现, 西伯利亚鲟和施氏鲟骨骼系统的组成与构造较为相似, 其原因可能是其对高纬度低水温环境长期适应的结果。     

Study of the pectoral girdle and fins of the Late Carboniferous sibyrhynchid iniopterygians (Vertebrata,Chondrichthyes, Iniopterygia) from Kansas and Oklahoma (USA) by means of microtomography,with comments on iniopterygian relationships

The latest works on iniopterygians question their monophyly when considering only the neurocranium of the two families (Sibyrhynchidae and Iniopterygidae), which have different conditions of preservation. Some of the synapomorphies of the Iniopterygia concern the pectoral girdle and fins. However, the anatomy of these different elements is still poorly known in this taxon. Here we describe in details three dimensionally preserved cartilages of the pectoral girdle and fins of the sibyrhynchid Iniopera sp. These structures have been extracted virtually from phosphatised nodules thanks to conventional and synchrotron microtomography, using absorption and phase contrast based techniques in the later case. The pectoral girdle of Iniopera sp. consists of three elements, which are, from dorsal to ventral, a paired suprascapular cartilage, a pair of robust scapulocoracoids and an unpaired intercoracoid cartilage. The scapular part of the scapulocoracoids is extremely reduced and the suprascapular cartilages link the scapulcoracoids to the rear of the neurocranium. These characters may be iniopterygian synapomorphies. Iniopterygians, stem and crown-holocephalans share a basipterygium that articulates with the pectoral girdle and bears an enlarged first pectoral fin radial. Posteriorly, the basipterygium articulates with either a well-defined metapterygium (in crown-holocephalans) or a metapterygial axis (in stem-holocephalans).     

Early development of the postcranial skeleton of the pikeperch Sander lucioperca (Teleostei: Percidae) relating to developmental stages and growth

The early development of the postcranial skeleton (pectoral girdle, pelvic girdle, vertebral column and fins) in pikeperch (Sander lucioperca (L.)) was studied from hatching to days 47 and 43 post fertilization (dpf) at two different rearing temperatures, 15.5 and 18.0°C. Four embryonic and six larval stages were described, ranging from 3.4 ± 0.3 mm to 21.8 ± 2.1 mm in total length. The crucial point in larval development is swimbladder inflation, which enables larvae to swim energy efficiently. Until this time point, only the most essential skeletal elements to enable swimming movements have developed. As the larvae become neutrally buoyant, they grow and differentiate postcranial elements rapidly. Concurrently, swimming performance and foraging success seems to improve. A specific size is correlated with a distinct developmental stage defined by a set of traits that includes the skeletal elements. The developmental sequence of skeletal structures is temperature independent, although growth is slower and the individual developmental stages are reached later at 15.5°C than at 18.0°C. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Biomechanical evaluation of predictive parameters of progression in adolescent isthmic spondylolisthesis: a computer modeling and simulation study

Background

Pelvic incidence, sacral slope and slip percentage have been shown to be important predicting factors for assessing the risk of progression of low- and high-grade spondylolisthesis. Biomechanical factors, which affect the stress distribution and the mechanisms involved in the vertebral slippage, may also influence the risk of progression, but they are still not well known. The objective was to biomechanically evaluate how geometric sacral parameters influence shear and normal stress at the lumbosacral junction in spondylolisthesis.

Methods

A finite element model of a low-grade L5-S1 spondylolisthesis was constructed, including the morphology of the spine, pelvis and rib cage based on measurements from biplanar radiographs of a patient. Variations provided on this model aimed to study the effects on low grade spondylolisthesis as well as reproduce high grade spondylolisthesis. Normal and shear stresses at the lumbosacral junction were analyzed under various pelvic incidences, sacral slopes and slip percentages. Their influence on progression risk was statistically analyzed using a one-way analysis of variance.

Results

Stresses were mainly concentrated on the growth plate of S1, on the intervertebral disc of L5-S1, and ahead the sacral dome for low grade spondylolisthesis. For high grade spondylolisthesis, more important compression and shear stresses were seen in the anterior part of the growth plate and disc as compared to the lateral and posterior areas. Stress magnitudes over this area increased with slip percentage, sacral slope and pelvic incidence. Strong correlations were found between pelvic incidence and the resulting compression and shear stresses in the growth plate and intervertebral disc at the L5-S1 junction.

Conclusions

Progression of the slippage is mostly affected by a movement and an increase of stresses at the lumbosacral junction in accordance with spino-pelvic parameters. The statistical results provide evidence that pelvic incidence is a predictive parameter to determine progression in isthmic spondylolisthesis.     

Vertebral and rib anatomy in Caperea marginata: Implications for evolutionary patterning of the mammalian vertebral column

The pygmy right whale, Caperea marginata, is a rare mysticete cetacean with an unusual suite of axial skeletal characters. Distally expanded first ribs, a long thorax with broadly overlapping vertebral transverse processes, plate‐like posterior ribs, and a short tail contrast with other cetaceans and suggest unique developmental patterning. Twenty‐four individuals of diverse ontogenetic age were available for analysis. Multiple, variable examples of incomplete rib fusion in dependent calves indicate that the first rib of adults is an ontogenetic fusion product of ribs 1 and 2. The composite rib articulates by way of its anterior (Rib1) component to the sternum and by way of its posterior (Rib2) component with thoracic vertebra 2. Thoracic vertebra 1 lacks rib articulations. When rib fusion is taken into account, the most frequent column formulas are C7T18L1Cd16–17 = 42–43 and C7T17L1Cd16–18 = 41–43. Thoracic and lumbar series are not reciprocal in count, arguing against their developmental linkage. Instead, parallel reduction in both lumbar and caudal counts supports the existence of neocete patterning in Caperea, as in all other living cetaceans. Ontogenetic vertebral column elongation is most marked in the posterior thorax, lumbos, and anterior tail. Vertebrae in these column regions are excellent predictors of total body length.     

MSCT-3D技术在动物与人骨骼形态比较研究中的应用

目的应用MSCT-3D显示技术比较正常贵州香猪、Marshall比格犬、恒河猴与人上肢带骨及躯干骨的形态学差异。方法采用MSCT分别对贵州香猪、比格犬和恒河猴进行CT全身扫描并进行图像重建,观察其上肢带骨、躯干骨形态结构与人的异同。结果比格犬、恒河猴、贵州香猪脊椎骨和肋的基本组成与人相同,脊椎骨由椎体和附件组成,肋骨包括真肋、假肋和浮肋。而脊柱曲度、各段椎骨数目、胸骨结构、肋的数目、胸肋连接、上肢带骨的组成与人不同,恒河猴的脊柱曲度和上肢带骨连接与人相同,有颈、胸、腰、骶四个生理性弯曲并由锁骨和肩胛骨共同连接自由上肢骨,比格犬和贵州香猪只有颈、胸腰、骶三个生理性弯曲,仅由肩胛骨连接自由上肢骨。结论恒河猴躯干骨和上肢带骨与人有良好的相似性,而比格犬和贵州香猪与人差别较大。MSCT-3D技术为实验动物形态学比较研究提供了一种相对无创、快速、可以在体研究并动态连续观察的科学有效方法。     

The structure and function of the dermal pectoral girdle in bony fishes with particular reference to ostariophysines

The structure of the dermal pectoral girdle of teleostean fishes is analyzed in relation to its functions. In bony fishes the vertebral column, with a horizontal axis, and the pectoral girdle, with a basically vertical axis, form the only skeletal links between the head and the body. The individual bones of the dermal girdle are considered as supporting units joined by a series of articulations that permit differential movement between adjacent bones. The movements mediated by this linkage system are: lateral swinging of the head relative to the body, expansion of the distance between the central areas of the two pectoral girdles to permit passage of large food items, and fore-and-aft movements of the anteroventral ends of the cleithra relative to the skull. Among other factors affecting the structure of the dermal pectoral girdle are the provision for the support of the pectoral fin base and the requirement for the effective operation of a sleeve valve between the girdle and the opercular cover.
Modifications of the dermal pectoral girdle in ostariophysine fishes are discussed. A brief history of the bony fish girdle in terms of its functional components is postulated.     

Altered axial skeletal development

The axial skeleton is routinely examined in standard developmental toxicity bioassays and has proven to be sensitive to a wide variety of chemical agents. Dysmorphogenesis in the skull, vertebral column and ribs has been described in both human populations and in laboratory animals used to assess potential adverse developmental effects. This article emphasizes vertebrae and rib anomalies both spontaneous and agent induced. Topics discussed include the morphology of the more common effects; incidences in both human and experimental animal populations; the types of anomalies induced in the axial skeleton by methanol, boric acid, valproic acid and others; the postnatal persistence of common skeletal anomalies; and the genetic control of the development of the axial skeleton. Tables of the spontaneous incidence of axial anomalies in both humans and animals are provided.     

变色树蜥骨骼系统的解剖

用透明骨骼标本染色法制作变色树蜥的骨骼标本,并对其骨骼系统进行了全面的描述.其骨骼可分为中轴骨骼(包括头骨、脊柱、胸骨、肋骨)和附肢骨骼(包括肩带、腰带、前肢骨、后肢骨).其头骨呈梨形,眼眶完整.颈椎8枚,胸椎4枚,腰椎11枚,荐椎2枚,尾椎多于34枚.有颈肋4对,胸肋4对,腰肋11对.表现出了一系列进化特征,如前颌骨愈合成1块,额骨也愈合成1块,颧骨消失,鳞骨变小,犁骨薄弱,下颌夹板骨与齿骨、冠状骨及隅骨之间的骨缝不明显,愈合程度较高.     

Comparative morphology and osteology of pelvic fin‐derived midline suckers in lumpfishes,snailfishes and gobies

Some fishes use modified body structures – including pelvic fins – to produce suction to facilitate stability in turbulent environments. This study compares the morphology and osteology of the pelvic suckers of representative lumpfishes (Cyclopteridae), snailfishes (Liparidae) and gobies (Gobiidae). In all species studied the midline sucker (pelvic suctorial organ [PSO]) is formed from the pelvic girdle and fin rays I and 5 of the pelvic fins, comprised of similar osteological elements to those found in the pelvic girdle and pelvic fin rays although the morphology of the bony elements is species‐specific. Pelvic suctorial organs in those fishes that lack pelvic girdles are therefore homologous to pelvic girdles. The phenotypic diversity seen in so few species indicates that many sucker morphologies have arisen, origination depending on the concerted development of muscular, skeletal, nervous, and skin body tissues. The structure of the soft rays of the pelvic fins in the liparids and cyclopterids is unusual and indicative of unconventional developmental patterning of fin ray halves and of evolution in the underlying mechanisms responsible for the development of midline suckers.     

Variability and constraint in the mammalian vertebral column

Patterns of vertebral variation across mammals have seldom been quantified, making it difficult to test hypotheses of covariation within the axial skeleton and mechanisms behind the high level of vertebral conservatism among mammals. We examined variation in vertebral counts within 42 species of mammals, representing monotremes, marsupials and major clades of placentals. These data show that xenarthrans and afrotherians have, on average, a high proportion of individuals with meristic deviations from species' median series counts. Monotremes, xenarthrans, afrotherians and primates show relatively high variation in thoracolumbar vertebral count. Among the clades sampled in our dataset, rodents are the least variable, with several species not showing any deviations from median vertebral counts, or vertebral anomalies such as asymmetric ribs or transitional vertebrae. Most mammals show significant correlations between sacral position and length of the rib cage; only a few show a correlation between sacral position and number of sternebrae. The former result is consistent with the hypothesis that adult axial skeletal structures patterned by distinct mesodermal tissues are modular and covary; the latter is not. Variable levels of correlation among these structures may indicate that the boundaries of prim/abaxial mesodermal precursors of the axial skeleton are not uniform across species. We do not find evidence for a higher frequency of vertebral anomalies in our sample of embryos or neonates than in post-natal individuals of any species, contrary to the hypothesis that stabilizing selection plays a major role in vertebral patterning.