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.     

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.     

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.     

Occipito-vertebral fusion in ocean sunfishes (Teleostei: Tetraodontiformes: Molidae) and its phylogenetic implications

We describe the ontogeny of the occipital skull and anterior vertebrae of the molids Ranzania laevis and Masturus lanceolatus and compare it with that of the ostraciid Lactophrys sp. The first vertebra fuses to the basioccipital in early ontogeny in the two molids and previous authors thus confused that vertebra with the back of the basioccipital, so that all previous counts of their vertebral numbers are incorrect by one vertebra. As evidenced by Lactophrys sp., ostraciids are the only other tetraodontiforms with similar occipito-vertebral fusion. In contrast to the molids, additional anterior vertebrae fuse with this complex in ostraciids. We conclude that the shared occipito-vertebral fusion in molids and ostraciids and its otherwise extremely rare occurrence among teleosts provide support for a sister-group relationship of the two families.     

Vertebral pneumatic structures in the Early Cretaceous sauropod dinosaur Pilmatueia faundezi from northwestern Patagonia,Argentina

One of the diagnostic characters of dicraeosaurid sauropods is a reduction of pneumatization of dorsal and caudal vertebrae relative to their Flagellicaudata sister taxon, Diplodocidae. Here, we analyse pneumatic structures in the dicraeosaurid sauropod Pilmatueia faundezi, compare them to those of diplodocoids and report the first record of camerate chambers in a dicraeosaurid. The pneumatic structures are in a posterior cervical centrum (MLL-Pv-002) and consist of lateral pneumatic fossae on the centrum that communicate internally with large camerae. By contrast, Pilmatueia's dorsal and caudal vertebrae (MLL-Pv-005-016) lack pneumatic fossae on the centra, which is consistent with the previously reported reduced pneumaticity in dicraeosaurids. Nevertheless, the base of the neural arch and possibly the base of the bifid neural spines of a posterior dorsal vertebra (MLL-Pv-005) show pneumatic internal chambers. The pneumatic features of the Pilmatueia cervical centrum and dorsal neural arch we describe indicate that the degree of pneumatization is variable within dicraeosaurids.     

Osteichthyan vertebrae

The earliest osteichthyan vertebrae are composed of neural and haemal arches supported by the notochord. The arches develop from one xelerotome in the position of the myosepta. Sclerotomic tissue anterior or posterior to the arch aatagen may form separate intercalaries, part of the arch bases, or, in teleosts, the zygapophyses. Centra were formed independently in a number of actinopterygian groups, in some dipnoans and in the osteolepiform rhipidistians. They ossify in the perichordal tube in either a segmentai or intersegmental position. In some teleosts, at least, perichordal ossification is preceded by calcification of the fibrous notochordal sheath. Experimentation in centrum design was greatest in actinopterygians below the teleost level. The so-called pleurocentra of some osteolepiforms may be intercalaries. Modifications in mode of development and in adult design probably reflect relatively minor changes in a fairly uniform morphogenetic pat tern that has existed throughout the history of osteichthyan vertebrae. The absence of sclerotomic resegmentation in the tetrapod sense suggests that this phenomenon arose during the rhipidistian—amphibian transition.     

Histochemical study of jaw muscle fibers in the American alligator (Alligator mississippiensis)

The ontogenetic development of caudal vertebrae and associated skeletal elements of salmonids provides information about sequence of ossification and origin of bones that can be considered as a model for other teleosts. The ossification of elements forming the caudal skeleton follows the same sequence, independent of size and age at first appearance. Dermal bones like principal caudal rays ossify earlier than chondral bones; among dermal bones, the middle principal caudal rays ossify before the ventral and dorsal ones. Among chondral bones, the ventral hypural 1 and parhypural ossify first, followed by hypural 2 and by the ventral spine of preural centrum 2. The ossification of the dorsal chondral elements starts later than that of ventral ones. Three elements participate in the formation of a caudal vertebra: paired basidorsal and basiventral arcocentra, chordacentrum, and autocentrum; appearance of cartilaginous arcocentra precedes that of the mineralized basiventral chordacentrum, and that of the perichordal ossification of the autocentrum. Each ural centrum is mainly formed by arcocentral and chordacentrum. The autocentrum is irregularly present or absent. Some ural centra are formed only by a chordacentrum. This pattern of vertebral formation characterizes basal teleosts and primitive extant teleosts such as elopomorphs, osteoglossomorphs, and salmonids. The diural caudal skeleton is redefined as having two independent ural chordacentra plus their arcocentra, or two ural chordacentra plus their autocentra and arococentra, or only two ural chordacentra. A polyural caudal skeleton is identified by more than two ural centra, variably formed as given for the diural condition. The two ural centra of primitive teleosts may result from early fusion of ural centra 1 and 2 and of ural centra 3 and 4, or 3, 4, and 5 (e.g., elopomorphs), respectively. The two centra may corespond to ural centrum 2 and 4 only (e.g., salmonids). Additionally, ural centra 1 and 3 may be lost during the evolution of teleosts. Additional ural centra form late in ontogeny in advanced salmonids, resulting in a secondary polyural caudal skeleton. The hypural, which is a haemal spine of a ural centrum, results by growth and ossification of a single basiventral ural arococentrum and its haemal spine. The proximal part of the hypural always includes part of the ventral ural arcocentrum. The uroneural is a modification of a ural neural arch, which is demonstrated by a cartilaginous precursor. The stegural of salmonids and esocids originates from only one paired cartilaginous dorsal arcocentrum that grows anteriorly by a perichondral basal ossification and an anterodorsal membranous ossification. The true epurals of teleosts are detached neural spines of preural and ural neural arches as shown by developmental series; they are homologous to the neural spines of anterior vertebrae. Free epurals without any indication of connection with the dorsal arococentra are considered herein as an advanced state of the epural. Caudal distal radials originate from the cartilaginous distal portion of neural and haemal spines of preural and ural (epurals and hypurals) vertebrae. Therefore, they result from distal growth of the cartilaginous spines and hypurals. Cartilaginous plates that support rays are the result of modifications of the plates of connective tissue at the posterior end of hypurals (e.g., between hypurals 2 and 3 in salmonids) and first preural haemal spines, or from the distal growth of cartilaginous spines (e.g., epural plates in Thymallus). Among salmonids, conditions of the caudal skeleton such as the progressive loss of cartilaginous portions of the arcocentra, the progressive fusion between the perichondral ossification of arcocentra and autocentra, the broadening of the neural spines, the enlargement and interdigitation of the stegural, and other features provide evidence that Prosopium and Thymallus are the most primitive, and that Oncorhynchus and Salmo are the most advanced salmonids respectively. This interpretation supports the current hypothesis of phylogenetic relationships of salmonids. © 1992 Wiley-Liss, Inc.     

The composition of the caudal skeleton of teleosts (Actinopterygil: Osteichthyes)

The diural caudal skeleton of teleostean actinopterygians develops phylogeneticaily and ontogenetically from a polyural skeleton. The reduction of the polyural anlage to four, three, two or fewer centra in the adult caudal skeleton takes different pathways in different genera (e.g. compare Elops and Albula) and groups of teleosts. As a result, ural centra are not homologous throughout the teleosts. By numbering the ural centra in a homocercal tail in polyural fashion, one can demonstrate these and the following differences. The ventral elements (hypurals) always occur in sequential series, whereas the dorsal elements (epurals and uroneurals) may alter like the ural centra. The number of epurals, five or four in fossil primitive teleosts, is reduced in other primitive and advanced teleosts, but the same epurals are not always lost. The number of uroneurals, seven in fossil teleosts, is reduced in living teleosts, but it has not been demonstrated that the first uroneural is always derived from the neural arch of the same ural centrum. The landmark in the homocercal tail is the preural centrum I which can be identified by (1) bifurcation of the caudal artery and vein in its ventral element, the parhypural, (2) its position directly caudal to the preural centrum (PU2) which supports the lowermost principal caudal ray with its haemal spine, (3) carrying the third hypaxial element ventral to the course of arteria and vena pinnalis, and (4) by carrying the first haemal spine (parhypural) below the dorsal end of the ventral cartilage plate. The study of the development of the vertebral column reveals that teleosts have different patterns of centrum formation. A vertebral centrum is a complete or partial ring of mineralized, cartilaginous or bony material surrounding at least the lateral sides of the notochord. A vertebral centrum may be formed by arcocentrum alone, or arcocentral arcualia and chordacentrum, or arco-, chorda- and autocentrum, or arcocentral arcualia and autocentrum. This preliminary research demonstrates that a detailed ontogenetic interpretation of the vertebral centra and of the caudal skeleton of different teleosts may be useful tools for further interpretations of teleostean interrelationships.     

Revised Vertebral Count in the “Longest-Necked Vertebrate” Elasmosaurus platyurus Cope 1868, and Clarification of the Cervical-Dorsal Transition in Plesiosauria

Elasmosaurid plesiosaurians are renowned for their immensely long necks, and indeed, possessed the highest number of cervical vertebrae for any known vertebrate. Historically, the largest count has been attributed to the iconic Elasmosaurus platyurus from the Late Cretaceous of Kansas, but estimates for the total neck series in this taxon have varied between published reports. Accurately determining the number of vertebral centra vis-à-vis the maximum length of the neck in plesiosaurians has significant implications for phylogenetic character designations, as well as the inconsistent terminology applied to some osteological structures. With these issues in mind, we reassessed the holotype of E. platyurus as a model for standardizing the debated cervical-dorsal transition in plesiosaurians, and during this procedure, documented a “lost” cervical centrum. Our revision also advocates retention of the term “pectorals” to describe the usually three or more distinctive vertebrae close to the cranial margin of the forelimb girdle that bear a functional rib facet transected by the neurocentral suture, and thus conjointly formed by both the parapophysis on the centrum body and diapophysis from the neural arch (irrespective of rib length). This morphology is unambiguously distinguishable from standard cervicals, in which the functional rib facet is borne exclusively on the centrum, and dorsals in which the rib articulation is situated above the neurocentral suture and functionally borne only by the transverse process of the neural arch. Given these easily distinguishable definitions, the maximum number of neck vertebrae preserved in E. platyurus is 72; this is only three vertebrae shorter than the recently described Albertonectes, which together with E. platyurus constitute the “longest necked” animals ever to have lived.     

A central role for the notochord in vertebral patterning

The vertebrates are defined by their segmented vertebral column, and vertebral periodicity is thought to originate from embryonic segments, the somites. According to the widely accepted 'resegmentation' model, a single vertebra forms from the recombination of the anterior and posterior halves of two adjacent sclerotomes on both sides of the embryo. Although there is supporting evidence for this model in amniotes, it remains uncertain whether it applies to all vertebrates. To explore this, we have investigated vertebral patterning in the zebrafish. Surprisingly, we find that vertebral bodies (centra) arise by secretion of bone matrix from the notochord rather than somites; centra do not form via a cartilage intermediate stage, nor do they contain osteoblasts. Moreover, isolated, cultured notochords secrete bone matrix in vitro, and ablation of notochord cells at segmentally reiterated positions in vivo prevents the formation of centra. Analysis of fss mutant embryos, in which sclerotome segmentation is disrupted, shows that whereas neural arch segmentation is also disrupted, centrum development proceeds normally. These findings suggest that the notochord plays a key, perhaps ancient, role in the segmental patterning of vertebrae.     

Chirocentrids as engrauloids: evidence from suspensorium,branchial arches,and infraorbital bones (Clupeomorpha,Teleostei)

The Chirocentridae is a family of highly specialized large predatory clupeomorphs composed of two species from coastal waters of the Indian and western Pacific Oceans. Peculiarities of the anatomy of these fishes have puzzled ichthyologists who attempted to resolve their phylogenetic relationships. Despite controversy, it is currently accepted that the Chirocentridae is a family of Clupeiformes, included with the Clupeidae in the superfamily Clupeoidea. New data support an alternative hypothesis. Seven previously unreported derived character states from the suspensorium, branchial arches, and infraorbitals strongly indicate a hitherto unsuspected sister group relationship between the Chirocentridae and Engrauloidea, which comprises approximately 140 species of the commercially important fishes known as anchovies. These are character states: (1) the anterior margin of metapterygoid located anterior to the quadrate; (2) the ventral limb of hyomandibula and quadrate not separated by the metapterygoid; (3) the posterodorsal margin of metapterygoid in line with the condyle of articulation of the hyomandibula with the opercle; (4) the presence of a laminar outgrowth of the anterior margin of the quadrate; (5) the endochondral portion of the quadrate in the shape of an isosceles triangle; (6) the presence and arrangement of autogenous tooth plates on ceratobranchials 1 to 3; and (7) posterior region of infraorbital 1 well developed and extending along the ventral margin of infraorbital 2. Three of those character states are further modified and hypothesized as synapomorphies of the Engrauloidea: (1′) a substantial portion of the metapterygoid situated anterodorsal to the quadrate, (2′) articulation between the ventral limb of the hyomandibula and the quadrate, and (7′) infraorbitals 1 and 3 articulating by means of a well‐developed laminar process of the posterior region of infraorbital 1. The separation of the dorsal, paired elements of the branchial arches of the Chirocentridae and representative Engrauloidea is apomorphic within the Clupeoidei, and constitutes circumstantial evidence for the sister group relationship between those clades. Microphagy within the Engrauloidea is secondary, homoplastic to the same condition present in other clades of the Clupeiformes. The decomposition of character complexes into discrete morphological characters and its use in phylogenetic inference is discussed. The sister group relationship between the Chirocentridae and Engrauloidea renders the Clupeoidea paraphyletic. A new classification of the Clupeoidei, with the inclusion of the Chirocentridae in the Engrauloidea, is proposed. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156 , 363–383.     

Vertebral Pneumaticity in the Ornithomimosaur Archaeornithomimus (Dinosauria: Theropoda) Revealed by Computed Tomography Imaging and Reappraisal of Axial Pneumaticity in Ornithomimosauria

Among extant vertebrates, pneumatization of postcranial bones is unique to birds, with few known exceptions in other groups. Through reduction in bone mass, this feature is thought to benefit flight capacity in modern birds, but its prevalence in non-avian dinosaurs of variable sizes has generated competing hypotheses on the initial adaptive significance of postcranial pneumaticity. To better understand the evolutionary history of postcranial pneumaticity, studies have surveyed its distribution among non-avian dinosaurs. Nevertheless, the degree of pneumaticity in the basal coelurosaurian group Ornithomimosauria remains poorly known, despite their potential to greatly enhance our understanding of the early evolution of pneumatic bones along the lineage leading to birds. Historically, the identification of postcranial pneumaticity in non-avian dinosaurs has been based on examination of external morphology, and few studies thus far have focused on the internal architecture of pneumatic structures inside the bones. Here, we describe the vertebral pneumaticity of the ornithomimosaur Archaeornithomimus with the aid of X-ray computed tomography (CT) imaging. Complementary examination of external and internal osteology reveals (1) highly pneumatized cervical vertebrae with an elaborate configuration of interconnected chambers within the neural arch and the centrum; (2) anterior dorsal vertebrae with pneumatic chambers inside the neural arch; (3) apneumatic sacral vertebrae; and (4) a subset of proximal caudal vertebrae with limited pneumatic invasion into the neural arch. Comparisons with other theropod dinosaurs suggest that ornithomimosaurs primitively exhibited a plesiomorphic theropod condition for axial pneumaticity that was extended among later taxa, such as Archaeornithomimus and large bodied Deinocheirus. This finding corroborates the notion that evolutionary increases in vertebral pneumaticity occurred in parallel among independent lineages of bird-line archosaurs. Beyond providing a comprehensive view of vertebral pneumaticity in a non-avian coelurosaur, this study demonstrates the utility and need of CT imaging for further clarifying the early evolutionary history of postcranial pneumaticity.     

A pterosaurian vertebra from the Upper Cretaceous of the Saratov Region

A dorsal vertebra referred to as Azhdarchidae indet. from the Rybushka Formation (Upper Cretaceous, Lower Campanian) of the Beloe Ozero locality in the Saratov Region is described. Its vertebral centrum has a hypapophysis and, at the base of the neural arch, there is a large pneumatic foramen. The vertebra possibly belongs to Volgadraco bogolubovi Averianov, Arkhangelskii et Pervushov, 2008, described from the Rybushka Formation of the Shirokii Karamysh 2 locality in the Saratov Region.     

Evidence for resegmentation in the formation of the vertebral column using the novel approach of retroviral-mediated gene transfer

We have examined the somitic cell contribution to the vertebral column of the chick by genetic labeling of sclerotomal cells in early development. Single somites of embryonic Day 2 embryos were filled with retroviral particles containing the lacZ transducing vector BAG. After a further 14 or 17 days of incubation the embryos were fixed and the vertebral column was sectioned and stained histochemically for the lacZ gene product beta-galactosidase. Cells staining for the enzyme were found exclusively on the injected side of two vertebral segments; the staining was largely restricted, however, to the caudal half of the more rostral segment and the rostral half of the next more caudal segment. No embryos were observed with labeling in less than two vertebral segments. Moreover, labeled cells were not uniformly distributed within the labeled region of each vertebra; the neural arch, for example, usually contained a higher proportion of labeled cells than did the centrum. These observations support the concept of resegmentation, whereby a vertebra forms from sclerotomal cells derived from two consecutive somites resulting in a vertebral column shifted by one half segment with respect to the segmented boundaries of the somites. The quantitative distribution of labeled cells in the vertebrae also suggests that sclerotomal cells populate the region of a future vertebral segment in an orderly fashion dependent on when the cells migrate from the somite.     

Reevaluation of the caudal skeleton of some actinopterygian fishes: II. Hiodon,Elops, and Albula

The vertebral centra of Hiodon, Elops, and Albula are direct perichordal ossifications (autocentra) which enclose the arcocentra as in Amia. An inner ring of ovoid cells forms in late ontogeny from the intervertebral space inside the autocentrum. The chordacentrum is reduced or completely absent in centra of adult Elops, whereas it forms an important portion of the centra in adult Hiodon. The posterior portion of the compound ural centrum 3+4+5 is partially (Hiodon) or fully formed by the chordacentrum (Elops, Albula). The haemal arches and hypurals are fused medially by cartilage or bone trabecles of the arcocentrum with the centra, even though they appear autogenous in lateral view in Elops and Albula. The composition of the caudal skeleton of fossil teleosts and the ontogeny of that of Hiodon, Elops, and Albula corroborate a one-to-one relationship of ural centra with these dorsal and ventral elements. The first epural (epural 1) of Elops relates to ural centrum 1, whereas the first epural (epural 2) of Hiodon and Albula relates to ural centrum 2. In Albula, the first ural centrum is formed by ural centrum 2 only. With 4 uroneurals Hiodon has the highest number within recent teleosts. Juvenile specimens of Hiodon have eight, the highest number of hypurals within recent teleosts; this is the primitive condition by comparison with other teleosts and pholidophorids. Reduction of elements in the caudal skeleton is an advanced feature as seen within elopomorphs from Elops to Albula. Such reductions and fusions occur in osteoglossomorphs also, but the lack of epurals and uroneurals separates most osteoglossomorphs (except Hiodon) from all other teleosts.     

Two series of parapophyses in neoscopelid fishes (teleostei: Myctophiformes)

Observations of the vertebrae of three genera and five species of neoscopelid fishes revealed the presence of two series of parapophyses (a ventral series and a lateral foveal series). The ventral parapophyses, situated on the ventral surface of the centra, were present on only the anterior abdominal vertebrae (AV): inScopelengys (AV1, 2),Neoscopelus (AV1–6 or 7),Solivomer (AV1–8). Parapophyses on the first vertebra were ossified, cone-shaped enlargements, the remainder being small, cartilaginous and ovalshaped. The lateral foveal parapophyses were formed from an extension of the lower edges of the foveae on the lateral surfaces of the centra, into which the ribs are set, being developed caudally to form the hemal arches: inScopelengys (AV4 posteriorly),Neoscopelus (AV6 or 7 posteriorly),Solivomer (AV8 posteriorly). The last ventral cartilaginous parapophyses and first lateral foveal parapophyses were present on the same centrum in two genera,Neoscopelus (AV6 or 7) andSolivomer (AV8). Lateral foveal parapophyses series were also found in some acanthomorphs and a ventral parapophyses series in some non-acanthomorphs. Whereas the ventral papapophyses in the non-acanthomorphs developed posteriorly to form the hemal arches, this parapophyses series in neoscopelids is incomplete, being absent on the posterior abdominal vertebrae. This suggests that the ventral parapophyses series in neoscopelids seems to be a remnant of that in the non-acanthomorphs. In myctophids, although cartilaginous ventral parapophyses were absent posteriorly from the second vertebra, enlarged ossified cone-shaped parapophyses on the first vertebra (as in neoscopelids) and lateral foveal parapophyses usually from the third vertebra were present. Accordingly, myctophids appear to be similar to neoscopelids in having two types of parapophyses.     

The Rutland Cetiosaurus: the anatomy and relationships of a Middle Jurassic British sauropod dinosaur

A relatively well–preserved specimen of Cetiosaurus oxoniensis, from the Middle Jurassic (Bajocian) of Rutland, United Kingdom, is described in detail. The material includes a nearly complete cervical series, representative dorsal vertebrae, a fragment of sacrum, anterior caudals, the right femur, and numerous rib and limb fragments. Contrary to previous suggestions that this specimen possesses 14 cervical and ten dorsal vertebrae, it seems more probable that there were at most 13 cervicals and at least 12 dorsals. The vertebral column displays several autapomorphic features which supplement the generic diagnosis of Cetiosaurus, including: (1) a stout, anteriorly directed process located at the top of the neural spine of the twelfth (?) cervical vertebra; and (2) the presence of lateral pits, separated by a thin midline septum, below the transverse processes of middle dorsal vertebrae. Cladistic analysis indicates that Cetiosaurus is probably the sister–taxon to the advanced neosauropod clade. This relationship affects the distribution of particular character states that have played an important role in determining sauropod phylogeny.     

A new candiru of the genus Paracanthopoma (Siluriformes: Trichomycteridae) from the Araguaia River basin,central Brazil

A new species of the candiru genus Paracanthopoma is described from the floodplains of the Bananal Island, a transition area between the Cerrado and Amazon, in the Araguaia River basin, central Brazil. Paracanthopoma cangussu sp. nov. is distinguished from its congeners, Paracanthopoma parva and Paracanthopoma saci, by the presence of seven opercular odontodes, five dentary teeth, five median premaxillary teeth, and first dorsal-fin pterygiophore in a vertical through the centrum of the 23th or 24th vertebra. It is further distinguished from each congener by an exclusive combination of character states, comprising the number of vertebrae, number of precaudal vertebrae, number of dorsal procurrent caudal-fin rays, number of ventral procurrent caudal-fin rays, number of dorsal-fin rays, disposition of pores on the cephalic portion of the latero-sensory system, absence of an anterior process on the anterior margin of parieto-supraoccipital, number of dorsal-fin pteryigiophores and number of interopercular odontodes. Although vandelliines are known for being exclusively hematophagous, with guts gorged with blood, two cleared and stained specimens of P. cangussu sp. nov. had Chironomidae larvae (Insecta) on their guts. Because most specimens of P. cangussu sp. nov. were collected with stomachs filled with blood, it was hypothesized that the species feeds accidentally or occasionally on insects.     

Vertebrae in compression: Mechanical behavior of arches and centra in the gray smooth‐hound shark (Mustelus californicus)

In swimming sharks, vertebrae are subjected, in part, to compressive loads as axial muscles contract. We currently have no information about which vertebral elements, centra, arch cartilages, or both, actually bear compressive loads in cartilaginous vertebrae. To address this issue, the goal of this experiment was to determine the load‐bearing ability of arch and centrum cartilages in compression, to determine the material properties of shark vertebrae, and to document fracture patterns in the centra with and without the arches. Intact vertebrae and vertebrae with the arch cartilages experimentally removed (centra alone) were subjected to compressive loading to failure at a single strain rate. The maximum compressive forces sustained by the vertebrae and the centra are statistically indistinguishable. Thus we conclude that under these testing conditions the arch does not bear appreciable loads. Independent evidence for this conclusion comes from the fact that vertebrae fail in compression at the centra, and not at the arches. Overall, the results of these mechanical tests suggest that the neural arches are not the primary load‐bearing structure during axial compression. J. Morphol. 2010. © 2009 Wiley‐Liss, Inc.