The influence of fiber orientation on the equilibrium properties of neutral and charged biphasic tissues

Constitutive models facilitate investigation into load bearing mechanisms of biological tissues and may aid attempts to engineer tissue replacements. In soft tissue models, a commonly made assumption is that collagen fibers can only bear tensile loads. Previous computational studies have demonstrated that radially aligned fibers stiffen a material in unconfined compression most by limiting lateral expansion while vertically aligned fibers buckle under the compressive loads. In this short communication, we show that in conjunction with swelling, these intuitive statements can be violated at small strains. Under such conditions, a tissue with fibers aligned parallel to the direction of load initially provides the greatest resistance to compression. The results are further put into the context of a Benninghoff architecture for articular cartilage. The predictions of this computational study demonstrate the effects of varying fiber orientations and an initial tare strain on the apparent material parameters obtained from unconfined compression tests of charged tissues.     

Embryonic development of the axial column in the little skate,Leucoraja erinacea

The morphological patterns and molecular mechanisms of vertebral column development are well understood in bony fishes (osteichthyans). However, vertebral column morphology in elasmobranch chondrichthyans (e.g., sharks and skates) differs from that of osteichthyans, and its development has not been extensively studied. Here, we characterize vertebral development in an elasmobranch fish, the little skate, Leucoraja erinacea , using microCT, paraffin histology, and whole‐mount skeletal preparations. Vertebral development begins with the condensation of mesenchyme, first around the notochord, and subsequently around the neural tube and caudal artery and vein. Mesenchyme surrounding the notochord differentiates into a continuous sheath of spindle‐shaped cells, which forms the precursor to the mineralized areolar calcification of the centrum. Mesenchyme around the neural tube and caudal artery/vein becomes united by a population of mesenchymal cells that condenses lateral to the sheath of spindle‐shaped cells, with this mesenchymal complex eventually differentiating into the hyaline cartilage of the future neural arches, hemal arches, and outer centrum. The initially continuous layers of areolar tissue and outer hyaline cartilage eventually subdivide into discrete centra and arches, with the notochord constricted in the center of each vertebra by a late‐forming “inner layer” of hyaline cartilage, and by a ring of areolar calcification located medial to the outer vertebral cartilage. The vertebrae of elasmobranchs are distinct among vertebrates, both in terms of their composition (i.e., with centra consisting of up to three tissues layers—an inner cartilage layer, a calcified areolar ring, and an outer layer of hyaline cartilage), and their mode of development (i.e., the subdivision of arch and outer centrum cartilage from an initially continuous layer of hyaline cartilage). Given the evident variation in patterns of vertebral construction, broad taxon sampling, and comparative developmental analyses are required to understand the diversity of mechanisms at work in the developing axial skeleton of vertebrates. J. Morphol. 278:300–320, 2017. © 2017 Wiley Periodicals, Inc.     

The ontogenic development of the vertebrae in some gekkonoid lizards

The ontogeny of amphicoelous vertebrae was studied in Ptyodactylus hasselquistii and Hemidactylus turcicus, and that of procoelous vertebrae, in Sphaerodactylus argus. The embryos were assigned arbitrary stages, drawn to scale, and mostly studied in serial sections. Resegmentation occurs as in all amniotes. A sclerocoel divides each sclerotome into an anterior “presclerotomite” and a denser posterior “postsclerotomite.” Tissue surrounding the intersegmental boundary forms the centrum, which is intersegmental. Tissue around the sclerocoel builds the intervertebral structures, which are midsegmental. In the trunk and neck, postsclerotomites form neural arches, and presclerotomites build zygapophyses. The adult centrum consists of the perichordal primary centrum, plus neural arch bases (= secondary centrum). Between the latter and the arch proper, a neurocentral suture persists until obliterated in maturity. A dorso-ventral central canal persists on either side of the primary centrum, between the latter and the secondary centrum. The notochord becomes true cartilage midvertebrally in all vertebrae, and elastic cartilage intervertebrally in the posterior caudal region. Elsewhere its characteristic tissue persists. Intervertebrally, cervical hypapophyses, caudal chevrons and chevron-bases in the trunk are preformed early in cartilage. Directly ossifying median intercentra are added later in all regions. The first cervical presclerotomite is absent: the hypapophysis (= corpus) of the atlas consists exclusively of postsclerotomitic tissue, there is no proatlas, and the odontoid lacks the apical half-centrum present in other lepidosaurians. In the autotomous caudal region presclerotomites are as prominent as postsclerotomites. Both build neural arches, the two arches of each vertebra remaining distinct and ossifying separately, so that the intersegmental autotomy split persists between them. The last sclerotome is complete, its postsclerotomite forming a half centrum which ossifies. In Sphaerodactylus, while the vertebrae ossify, each intervertebral ring becomes concave anteriorly, convex posteriorly; it remains as a cushion between the condyle and a facet formed by differential growth of the centra. Thus these procoelous centra resemble the amphicoelous centra of Ptyodactylus and Hemidactylus, rather than the procoelus centra of other squamates. The vertebral column of Gekkonoidea closely resembles in its development and microscopical structure that of Sphenodon.     

Micro‐anatomical characterization of vertebral curvatures in Senegalese sole Solea senegalensis

The micro‐anatomical changes associated with lordotic and kyphotic vertebral curvatures (VC) in juvenile and adult Senegalese sole Solea senegalensis are described. In addition, it is demonstrated that the tissue and cellular structures of individual vertebrae can be severely affected. Two main conformations were found in deformed juvenile specimens: flattened vertebrae with dorso‐ventral compression and trapezoidal vertebrae forming concave and convex sides under compressive and tensile stresses. Histological analyses revealed the occurrence of an ectopic cartilaginous tissue within the acellular bone, both in juveniles and adults, possibly to cope with altered mechanical stress in deformed vertebrae. The results suggest that the alteration in loading to which curved vertebral columns are subjected might trigger vertebral reshaping and differentiation of cells towards this ectopic tissue. In addition, mesenchymal cells appear to play an important role in its formation. It is here proposed that the acellular bone of S. senegalensis is capable of adaptively responding to altered loading regimes at the structural level by reshaping vertebrae and at the micro‐anatomical level by recruiting chondrocyte‐like cells to areas of altered mechanical stress.     

The occipital region in the basal bony fish Erpetoichthys calabaricus (Actinopterygii: Cladistia)

Erpetoichthys calabaricus has unusual cranio‐vertebral anatomy, with an occipital centrum forming a component part of the compound basiexoccipital bone, and a ‘free‐floating’ occipital neural arch that differs from accessory arches found in some teleosts. The occipital neural arch bears autapomorphic lateral projections that articulate with small rod‐like bones resembling the spatial relationship of parapophyses and ribs, a feature normally restricted to vertebral centra. Based on analyses of cleared and stained specimens, computed tomography and histology, it is hypothesized that the lateral projections and associated rod‐shaped bones are structures that share developmental homologies to the unique ‘dorsal ribs’ of Polypteridae.     

Development of the pharyngeal arch skeleton in Catostomus commersonii (Teleostei: Cypriniformes)

Skeletal elements of the gill arches of adult cypriniform fishes vary widely in number, size, and shape and are important characters in morphologically based phylogenetic studies. Understanding the developmental basis for this variation is thus phylogenetically significant but also important in relation to the many developmental genetic and molecularly based studies of the early developing and hence experimentally tractable gill arches in the zebrafish, a cyprinid cypriniform. We describe the sequence of the chondrification and ossification of the pharyngeal arches and associated dermal bones from Catostomus commersonii (Catostomidae, Cypriniformes) and make selected comparisons to other similarly described pharyngeal arches. We noted shared spatial trends in arch development including the formation of ventral cartilages before dorsal and anterior cartilages before posterior. Qualitatively variable gill arch elements in Cypriniformes including pharyngobranchial 1, pharyngobranchial 4, and the sublingual are the last such elements to chondrify in C. commersonii. We show that the sublingual bone in C. commersonii has two cartilaginous precursors that fuse and ossify to form the single bone in adults. This indicates homology of the sublingual in catostomids to the two sublingual bones in the adults of cobitids and balitorids. Intriguing patterns of fusion and segmentation of the cartilages in the pharyngeal arches were discovered. These include the individuation of the basihyal and anterior copula through segmentation of a single cartilage rod, fusion of cartilaginous basibranchials 4 and 5, and fusion of hypobranchial 4 with ceratobranchial 4. Such “fluidity” in cartilage patterning may be widespread in fishes and requires further comparative developmental studies. J. Morphol., 2009. © 2008 Wiley‐Liss, Inc.     

The dynamic flexion/extension properties of the lumbar spine in vitro using a novel pendulum system

The biomechanical properties of the ligamentous cadaver spine have been previously examined using a variety of experimental testing protocols. Ongoing technical challenges in the biomechanical testing of the spine include the application of physiologic compressive loads and the application of dynamic bending moments while allowing unconstrained three-dimensional motion. The purpose of this study was to report the development of a novel pendulum apparatus that addressed these challenges and to determine the effects of various axial compressive loads on the dynamic biomechanical properties of the lumbar functional spinal unit (FSU). Lumbar FSUs were tested in flexion and extension under five axial compressive loads chosen to represent physiologic loading conditions. After an initial rotation, the FSUs behaved as a dynamic, underdamped vibrating elastic system. Bending stiffness and coefficient of damping increased significantly as the compressive pendulum load increased. The apparatus described herein is a relatively simple approach to determining the dynamic bending properties of the FSU, and potentially disc arthroplasty devices. It is capable of applying physiologic compressive loads at dynamic rates without constraining the kinematics of the joints, crucial requirements for testing FSUs in vitro.     

Neural arch load-bearing in old and degenerated spines

We validate a technique for measuring neural arch load-bearing in cadaveric spines, and use it to test the hypothesis that such load-bearing rises to high levels in old and degenerated spines. Fifty-nine cadaveric lumbar motion segments, aged 19-92 yr, were subjected to compressive creep loading to reduce intervertebral disc water content and height to in vivo levels. The distribution of compressive "stress" within the disc was then measured by pulling a miniature pressure transducer, side-mounted in a 1.3mm-diameter needle, along its mid-sagittal diameter. During these measurements, the motion segment was subjected to a compressive load of 2 kN, and positioned in 2 degrees of extension to simulate erect standing. Measurements of compressive "stress" were integrated over disc area, and this force subtracted from the applied 2 kN to give the force resisted by the neural arch. An empirical calibration factor was applied to normalise results from each disc to values obtained under conditions when all of the compressive force could be assumed to pass through the disc. Disc degeneration was graded macroscopically on a scale of 1-4. Validation tests showed that calculated values of disc loading were proportional to actual applied load (r(2)>0.96) and predicted it with errors of 2-8%. Neural arch load-bearing in non-degenerated specimens was generally less than 20%, but averaged 49% for specimens aged over 70 yr. Multiple regression showed that neural arch load bearing (%)=14.4 x disc degeneration score+0.46 x age-35. These results indicate a substantial shift in vertebral load-bearing with increasing age and degeneration.     

The zebrafish (Danio rerio) caudal complex – a model to study vertebral body fusion

Impairment of segmentation during embryonic development leads to congenital fusion of vertebrae. Nevertheless, vertebral fusion can also occur during post‐embryonic life. Fusion can cause reduction in mobility and may be pathological, but it can also be part of normal development and mechanically required, such as in the teleost caudal skeleton, or in the tetrapod sacrum. Using a series of closely spaced ontogenetic stages of zebrafish, stained for mineralized (Alizarin red) and cartilaginous (Alcian blue) structures, we have characterized all fusions occurring during the formation of the caudal skeleton. The urostyle results from the vertebral fusion of the compound centrum preural1‐ural1 [PU1⁺+U1] and ural2 [U2⁺]. Based on developmental and morphological characters: (i) number of vestigial haemal arches, (ii) occasional presence of a haemal arch rudiment, (iii) occasional individuals with separate centra rudiments or distinct mineralization time points, and (iv) evidence for internal separation, we propose that the urostyle forms as a fusion product of five, and not three vertebral centra, as previously described. The last fusion to occur in development, between the compound centrum [PU1⁺+U1] and U2⁺, is a relatively slow process that typically occurs in Cypriniformes and Salmoniformes and is therefore considered reliable to monitor the fusion process. The vertebrae adjacent to the urostyle, preurals 2 and 3, are highly susceptible to fusion, and thus inadequate as a negative control to fusion, in contrast to trunk vertebrae, where fusion is never observed. With this we have established the basis for a new model to study vertebral fusion and to unravel cellular and molecular events underlying this process.     

Vertebral column and associated elements in dipnoans and comparison with other fishes: development and homology.

A vertebral column consisting of a persistent notochord and ossified arcocentra is the primitive condition for Gnathostomata; it still persists in primitive actinopterygians and sarcopterygians. Advanced actinopterygians and sarcopterygians develop numerous types of centra that include, among others, the presence of holocentrum, chordacentrum, and autocentrum. The chordacentrum, a mineralization or calcification of the fibrous sheath of the notochord, is only found in actinopterygians, whereas an autocentrum is a synapomorphy of teleosts above Leptolepis coryphaenoides. The chordacentrum, formed by migration of cartilaginous cells from the arches into the fibrous sheath of the notochord and usually covered by a thin calcification, is a unique feature of chondrichthyans. The actinopterygian chordacentrum and the chondrichthyan chordacentrum are not homologous. The postcaudal cartilaginous centrum is only known in postcaudal vertebrae of living dipnoans. The holocentrum is present in certain fossil dipnoans and actinopterygians, where it has been independently acquired. It is formed by proliferation of cartilage cells around the elastica externa of the notochord. These cells later ossify, forming a compact centrum. A vertebral column formed by a persistent notochord without vertebral centra is the primitive pattern for all vertebrates. The formation of centra, which is not homologous among vertebrate groups, is acquired independently in some lineages of placoderms, most advanced actinopterygians, and some dipnoans and rhipidistians. Several series of structures are associated with the vertebral column such as the supraneurals, interhaemals, radials, and ribs. In living dipnoans median neural spine, "supraneural," and dorsal radial result from growth and distal differentiation of one median cartilage into two or three median bones during ontogeny. The median neural spine articulates with the neural arch and fuses with it in the caudal vertebrae early in ontogeny. Two bones differentiate in the anterior abdominal vertebrae, i.e., the proximal neural spine and the distal "supraneural." Three bones differentiate in front of the dorsal fin, i.e., the proximal neural spine, the middle "supraneural", and the distal radial; the same pattern is observed in front of the anal fin (the proximal haemal spine, the middle interhaemal, and the distal radial). Considering that the three dorsal (and also the three ventral) bones originate from growth of only one cartilage, they cannot be serial homologs of the neural spines, or "supraneural." They are linear homologs of the median neural cartilage in living dipnoans. The development of these elements differs within osteichthyans from sarcopterygians to actinopterygians, in which the neural spine originates as a continuation of the basidorsal arcualia and in which the supraneural and radial originate from independent cartilages that appear at different times during early ontogeny. The ribs of living dipnoans are unique in that they are not articulated with parapophyses, like in primitive fossil dipnoans, but a remnant of the ventral arcuale surrounded by a small arcocentrum remains at its base. A true caudal fin is absent in living dipnoans. The postcaudal cartilages extend to the caudal tip of the body separating dorsal and ventral rays (or the camptotrichia). Actinotrichia are present in young dipnoans. They are also known in extant actinistians and actinopterygians. They probably represent the primitive state for teleostomes. In contrast, the camptotrichia are unique for extant dipnoans (and probably Carboniferous and younger dipnoans). Lepidotrichia apparently developed many times among osteichthyans.     

On Polymorphism of <Emphasis Type="Italic">Protoceratops andrewsi</Emphasis> Granger et Gregory, 1923 (Protoceratopidae,Neoceratopsia)

Cervical vertebrae of six horned dinosaurs from the Upper Cretaceous of Mongolia, which are identified as Protoceratops andrewsi are examined. It is shown that vertebrae of the same serial number essentially differ in different specimens. The differences concern, for example, the shape of the vertebral centra, proportions of the centra and neurapophyses, inclination of pedicles of the neural arch and long axis of the diapophyseal base relative to the longitudinal axis of the centrum. Comparison has shown that available sample contains representatives of at less four morphotypes.     

The axial skeleton of the labyrinthodont Eogyrinus attheyi

An articulated length of vertebral column is used as a basis for the reconstruction of the salient features of the axial skeleton of the embolomerous anthracosaur Eogyrinus attheyi Watson, together with other material, including the holotype, in the Hancock Museum, Newcastle upon Tyne.
The trunk vertebrae are typically emboloinerous, with disoshaped notochordal pleuro-centra, firmly attached by broad facets to this neural arches, and much thinner intercentra. Regional variation is chiefly concerned with the span of the transverse processes, which diminishes posteriorly, and the associated separation of the two heads of each rib. A longitudinal series of trunk ribs, of diminishing length from the mid-trunk backwards, is reconstructed.
Eogyrinus has a normal tetrapod sacrum with one characteristic sacral rib. The first few caudal vertebrae bear ribs of unusual form, (of which four are preserved in sequence in the articulated specimen. The fifth caudal intercentrum bears the first and largest haemal arch and the pleurocentrum of the seventh caudal is distinguished by marked muscle origins presumably for the caudifemoral muscles.
The probability that Eogyrinus, like the few other embolomeres known, had an unusually long vertebral column for a labyrinthodont, is supported by an orthometric comparison using Romer's data on the American form Archeria.     

Reduced nucleus pulposus glycosaminoglycan content alters intervertebral disc dynamic viscoelastic mechanics

The intervertebral disc functions over a range of dynamic loading regimes including axial loads applied across a spectrum of frequencies at varying compressive loads. Biochemical changes occurring in early degeneration, including reduced nucleus pulposus glycosaminoglycan content, may alter disc mechanical behavior and thus may contribute to the progression of degeneration. The objective of this study was to determine disc dynamic viscoelastic properties under several equilibrium loads and loading frequencies, and further, to determine how reduced nucleus glycosaminoglycan content alters dynamic mechanics. We hypothesized that (1) dynamic stiffness would be elevated with increasing equilibrium load and increasing frequency, (2) the disc would behave more elastically at higher frequencies, and finally, (3) dynamic stiffness would be reduced at low equilibrium loads under all frequencies due to nucleus glycosaminoglycan loss. We mechanically tested control and chondroitinase ABC injected rat lumbar motion segments at several equilibrium loads using oscillatory loading at frequencies ranging from 0.05 to 5 Hz. The rat lumbar disc behaved non-linearly with higher dynamic stiffness at elevated compressive loads irrespective of frequency. Phase angle was not affected by equilibrium load, although it decreased as frequency was increased. Reduced glycosaminoglycan decreased dynamic stiffness at low loads but not at high equilibrium loads and led to increased phase angle at all loads and frequencies. The findings of this study demonstrate the effect of equilibrium load and loading frequencies on dynamic disc mechanics and indicate possible mechanical mechanisms through which disc degeneration can progress.     

Bony-tailed tadpoles: the development of supernumerary caudal vertebrae in larval megophryids (Anura)

The axial skeleton in most anuran families consists of or=7). Tadpoles from each genus are typically found in streams, where their extended caudal skeleton anchors muscles that facilitate tadpoles wiggling between plant debris and rocks or even burrowing into the stream bed. The extra centra of megophryids ossify differently in each genus. In Leptobrachella and Ophryophryne, the caudal centra ossify around the entire notochord, whereas in Megophrys and Xenophrys each develops from dorsal and ventral pairs of ossifications that expand to meet each other. The evolutionary loss of caudal centra, an apomorphic anuran trait, is reversed in larval megophryids and confirms that the machinery for caudal vertebral development has been retained in some modern anurans. A likely driving force in the reappearance of the trait in megophryids is the selective pressure associated with a riparian lifestyle.     

The line of action in the tibia during axial compression of the leg

Compression of the leg induces bending in the tibia, which can lead to tensile failure of the bone in the midshaft. The purpose of this study was to determine the orientation of the compressive load vector in the human tibia. Five cadaveric lower extremities were instrumented with in situ 6-axis tibial and fibular load cells and subjected to quasistatic axial leg compression tests in two knee positions and nine ankle positions. For each test, the location and angle of the line of action were calculated at the tibial midshaft. The line of action was extended to the bone ends in order to determine the locations of the effective centers of pressure on the tibial plafond and tibial plateau. The effective center of pressure on the tibial plafond consistently migrated anteriorly in dorsiflexion, laterally in eversion, posteriorly in plantarflexion, and medially in inversion. An opposite pattern was observed on the tibial plateau. When the knee was flexed, the effective center of pressure was generally isolated to a small area in the posterior portion of the medial tibial condyle. The percentage of the axial load borne by the fibula varied from -8% to 19%, and was related to the inversion/eversion angle of the ankle (p<0.02), as well as the distance between the fibula and the axial load path at the midshaft (p<0.001). The line of action through the tibia appeared to follow the external load path to the extent allowed by the available joint contact surfaces.     

New insights into the complex structure and ontogeny of the occipito‐vertebral gap in barbeled dragonfishes (Stomiidae,Teleostei)

In all stomiid genera there is an occipito‐vertebral gap between the skull and the first vertebra bridged only by the flexible notochord. Morphological studies from the early 20th century suggested that some stomiid genera have 1–10 of the anteriormost centra reduced or entire vertebrae missing in this region. Our study reviews this previous hypothesis. Using a new approach, we show that only in Chauliodus, Eustomias and Leptostomias gladiator vertebral centra are actually lost, with their respective neural arches and parapophyses persisting. We present results from a comparative analysis of the number and insertion sites of the anteriormost myosepta in 26 of the 28 stomiid genera. Generally in teleosts the first three myosepta are associated with the occiput, and the fourth is the first vertebral myoseptum. The insertion site of the fourth myoseptum plays an important role in this analysis, because it provides a landmark for the first vertebra. Lack of association of the fourth myoseptum with a vertebra is thus evidence that the first vertebra is reduced or absent. By counting the occipital and vertebral myosepta the number of reduced vertebrae in Chauliodus, Eustomias and Leptostomias gladiator can be inferred. Proper identification of the spino‐occipital nerves provides an additional source of information about vertebral reduction. In all other stomiid genera the extensive occipito‐ vertebral gap is not a consequence of the reduction of vertebrae, but of an elongation of the notochord. The complex structure and ontogeny of the anterior part of the vertebral column of stomiids are discussed comparatively. J. Morphol. 271:1006–1022, 2010. © 2010 Wiley‐Liss, Inc.     

Optimised loads for the simulation of axial rotation in the lumbar spine

Simplified loading modes (pure moment, compressive force) are usually applied in the in vitro studies to simulate flexion-extension, lateral bending and axial rotation of the spine. The load magnitudes for axial rotation vary strongly in the literature. Therefore, the results of current investigations, e.g. intervertebral rotations, are hardly comparable and may involve unrealistic values. Thus, the question 'which in vitro applicable loading mode is the most realistic' remains open. A validated finite element model of the lumbar spine was employed in two sensitivity studies to estimate the ranges of results due to published load assumptions and to determine the input parameters (e.g. torsional moment), which mostly affect the spinal load and kinematics during axial rotation. In a subsequent optimisation study, the in vitro applicable loading mode was determined, which delivers results that fit best with available in vivo measurements. The calculated results varied widely for loads used in the literature with potential high deviations from in vivo measured values. The intradiscal pressure is mainly affected by the magnitude of the compressive force, while the torsional moment influences mainly the intervertebral rotations and facet joint forces. The best agreement with results measured in vivo were found for a compressive follower force of 720N and a pure moment of 5.5Nm applied to the unconstrained vertebra L1. The results reveal that in many studies the assumed loads do not realistically simulate axial rotation. The in vitro applicable simplified loads cannot perfectly mimic the in vivo situation. However, the optimised values lead to the best agreement with in vivo measured values. Their consequent application would lead to a better comparability of different investigations.     

The lambeosaurine dinosaur Magnapaulia laticaudus from the late cretaceous of Baja California, Northwestern Mexico

The taxonomy, osteology, phylogenetic position, and historical biogeography of the lambeosaurine hadrosaurid Magnapaulia laticaudus (new combination) are revised. The diagnosis of this species is amended on the basis on two autapomorphies (i.e., longest haemal arches of proximal caudal vertebrae being at least four times longer than the height of their respective centra; base of prezygapophyses in caudal vertebrae merging to form a bowl-shaped surface) and a unique combination of characters (i.e., downturned cranioventral process of the maxilla; tear-shaped external naris with length/width ratio between 1.85 and 2.85; neural spines of dorsal, sacral, and proximal caudal vertebrae being at least four times the height of their respective centra). A maximum parsimony analysis supports a sister taxon relationship between M. laticaudus and Velafrons coahuilensis. Both taxa constitute a clade of southern North American lambeosaurines, which forms a sister relationship with the diverse clade of helmet-crested lambeosaurines from northern North America that includes well-known genera like Corythosaurus, Lambeosaurus, and Hypacrosaurus. According to the results of a Dispersal-Vicariance analysis, southern North American lambeosaurines split from the northern forms via vicariance from a common ancestor that lived in both the northern and southern regions of the continent.     

A new specimen of the thyreophoran dinosaur cf. Scelidosaurus with soft tissue preservation

A new specimen, comprising eight articulated caudal vertebrae in a cut slab of blue/grey carbonate mudstone, is comparable to the early thyreophoran dinosaur Scelidosaurus harrisonii Owen from the English Lower Jurassic. Palynological analysis indicates that the specimen is probably late Hettangian–Sinemurian (Early Jurassic), but the exact horizon and locality remain uncertain. The slab has been cut longitudinally in a parasagittal plane along the vertebral series and exposes several articulated centra, haemal arches, neural arches and osteoderms. An envelope of preserved soft tissue wraps around the vertebrae and includes osteoderms with organic material on both the upper and lower surfaces. Basal thyreophoran dinosaur osteoderms were covered by a horny sheath during life.