Notochordal Canal Research Articles

A New Genus of Late Cretaceous Angel Shark (Elasmobranchii; Squatinidae), with Comments on Squatinid Phylogeny

Three-dimensional Late Cretaceous elasmobranch endoskeletal elements (including palatoquadrates, ceratohyals, braincase fragments, and a series of anterior vertebrae) are described from the Late Cretaceous University of Alabama Harrell Station Paleontological Site (HSPS), Dallas County, Alabama. The material is referred to the extant elasmobranch Family Squatinidae on the basis of several distinctive morphological features. It also exhibits features not shared by any modern or fossil Squatina species or the extinct Late Jurassic squatinid Pseudorhina. A new genus and species is erected, despite there being some uncertainty regarding potential synonymy with existing nominal species previously founded on isolated fossil teeth (curiously, no squatinid teeth have been documented from the HSPS). A preliminary phylogenetic analysis suggests that the new genus falls on the squatinid stem, phylogenetically closer to Squatina than Pseudorhina. The craniovertebral articulation in the new genus exhibits features considered convergent with modern batomorphs (skates and rays), including absence of contact between the posterior basicranium and first vertebral centrum, and a notochordal canal which fails to reach the parachordal basicranium. Supporting evidence that similarities in the craniovertebral articulation of squatinoids and batomorphs are convergent rather than synapomorphic (as “hypnosqualeans”) is presented by an undescribed Early Jurassic batomorph, in which an occipital hemicentrum articulates with the first vertebral centrum as in all modern sharklike (selachimorph) elasmobranchs. The fossil suggests instead that the batomorph synarcual evolved by fusion of the anterior basiventral and basidorsal cartilages prior to the reduction of the anterior centra and loss of the occipital hemicentrum, not afterward as predicted by the hypnosqualean hypothesis.

On the Enigma of the Human Neurenteric Canal

Existence and biomedical relevance of the neurenteric canal, a transient midline structure during early neurulation in the human embryo, have been controversially discussed for more than a century by embryologists and clinicians alike. In this study, the authors address the long-standing enigma by high-resolution histology and three-dimensional reconstruction using new and historic histological sections of 5 human 17- to 21-day-old embryos and of 2 marmoset monkey embryos of the species Callithrix jacchus at corresponding stages. The neurenteric canal presents itself as the classical vertical connection between the amniotic cavity and the yolk sac cavity and is lined (a) craniolaterally by a horseshoe-shaped “hinge of involuting notochordal cells” within Hensen’s node and (b) caudally by the receding primitive streak epiblast dorsally and by notochordal plate epithelium ventrally, the latter of which covered the (longitudinal) notochordal canal on its ventral side at the preceding stage. Furthermore, asymmetric parachordal nodal expression in Callithrix and morphological asymmetries within the nodes of the other specimens suggest an early non-cilium-dependent left-right symmetry breaking mode previously postulated for other mammals. We conclude that structure and position of the mammalian neurenteric canal support the notion of its homology with the reptilian blastopore as a whole and with a dorsal segment of the blastopore in amphibia. These new features of the neurenteric canal may further clarify the aetiology of foetal malformations such as junctional neurulation defects, neuroendodermal cysts, and the split notochord syndrome.

Chondrocranial morphology of Carcharopsis wortheni (Chondrichthyes, Euselachii incertae sedis) based on new material from the Fayetteville Shale (upper Mississippian, middle Chesterian)

AbstractThe first known basicranium belonging to Carcharopsis wortheni is described, based on examination of endoskeletal morphology obtained from three‐dimensional reconstructions produced by high‐resolution CT scanning of a previously undescribed specimen. C. wortheni has been described from the late Mississippian (middle Chesterian) Fayetteville Shale based on jaws and teeth, but never before from its cranial anatomy. This specimen has jaw fragments and teeth, associated with the basicranium. The braincase has rounded, low extensions of the occipital region, forming a short lateral occipital shelf, the hypotic lamina is separated from the otic capsule by a continuous metotic fissure, and the postorbital flange is low. Cartilage surrounding the notochordal canal is mineralized, and broken into at least two pieces. Paired, enclosed dorsal aortae are present, which branch into orbital arteries anteriorly, with a midline pit present between the posterior openings for the aortae. Portions of the semicircular canals are visible, with associated ampullae. An improved description of C. wortheni teeth is presented based on CT scanning, including details of tooth vascularization. Carcharopsis is the first Palaeozoic chondrichthyan in which an anaulacorhize‐like vascular network has been recognized. New anatomical data presented here add considerably to our understanding of the phylogenetic relationships of Carcharopsis, and also contribute to the described diversity of Fayetteville Shale vertebrates.

Ultrastructural features of the dogfish Scyliorhinus canicula (Pisces: Scyliorhinidae) notochordal cells and the notochordal sheath

The dogfish Scyliorhinus canicula (Linnaeus, 1758) is a primitive cartilaginous fish, evolutionary placed among cephalochordates (Cephalochordata) and teleost fish (Osteichthyes). In this study we present the ultrastructural features of the dogfish notochordal cells and the notochordal sheath, revealed by light and electron microscopy. The dogfish notochord continuously passes through notochordal canal inside the vertebral centrum. It expands in the area of the intervertebral disc placed in between two adjacent vertebrae. Two notochordal cell types could be distinguished: marginal and central ones. Due to a significant intracellular and intercellular vacuolization central notochordal cells are thin and elongated, forming a net-like structure inside the notochord. The desmosomes are the usual type of junction between notochordal cells. The notochordal sheath of dogfish vertebra is an acellular structure composed of an elastic membrane surrounded by bundles of collagen fibres arranged in different orientations and directions. The ultrastructure of the dogfish notochord revealed a similar structure to those of other vertebrates including humans.

Vertebral Development in Paleozoic and Mesozoic Tetrapods Revealed by Paleohistological Data.

Basal tetrapods display a wide spectrum of vertebral centrum morphologies that can be used to distinguish different tetrapod groups. The vertebral types range from multipartite centra in stem-tetrapods, temnospondyls, and seymouriamorphs up to monospondylous centra in lepospondyls and have been drawn upon for reconstructing major evolutionary trends in tetrapods that are now considered textbook knowledge. Two modes of vertebral formation have been postulated: the multipartite vertebrae formed first as cartilaginous elements with subsequent ossification. The monospondylous centrum, in contrast, was formed by direct ossification without a cartilaginous precursor. This study describes centrum morphogenesis in basal tetrapods for the first time, based on bone histology. Our results show that the intercentra of the investigated stem-tetrapods consist of a small band of periosteal bone and a dense network of endochondral bone. In stereospondyl temnospondyls, high amounts of calcified cartilage are preserved in the endochondral trabeculae. Notably, the periosteal region is thickened and highly vascularized in the plagiosaurid stereospondyls. Among “microsaur” lepospondyls, the thickened periosteal region is composed of compact bone and the notochordal canal is surrounded by large cell lacunae. In nectridean lepospondyls, the periosteal region has a spongy structure with large intertrabecular spaces, whereas the endochondral region has a highly cancellous structure. Our observations indicate that regardless of whether multipartite or monospondylous, the centra of basal tetrapods display first endochondral and subsequently periosteal ossification. A high interspecific variability is observed in growth rate, organization, and initiation of periosteal ossification. Moreover, vertebral development and structure reflect different lifestyles. The bottom-dwelling Plagiosauridae increase their skeletal mass by hyperplasy of the periosteal region. In nectrideans, the skeletal mass decreases, as the microstructure is spongy and lightly built. Additionally, we observed that vertebral structure is influenced by miniaturization in some groups. The phylogenetic information that can be drawn from vertebral development, however, is limited.

Divergence in skeletal mass and bone morphology in antarctic notothenioid fishes

Although notothenioid fishes lack swim bladders, some species live temporarily or permanently in the water column. Given its relatively high density, skeletal mass is a key determinant of buoyancy. Notothenioids have reduced skeletal ossification, but there is little quantitative data on the phylogenetic distribution of this trait. We obtained dry skeletal masses for 54 specimens representing 20 species from six notothenioid families. Although comparative data are sparse, notothenioid skeletons comprise a smaller percentage of body mass, <3.5%, than those of three non-notothenioid perciforms. With relatively high skeletal mass, the non-Antarctic Bovichtus diacanthus is similar in skeletal mass to some non-notothenioids. Eleginops maclovinus, the non-Antarctic sister group of the Antarctic clade, has a relatively light skeleton (<2% of body mass) similar to many species in the Antarctic clade. Low skeletal mass is therefore a synapomorphy shared by Eleginops plus the Antarctic clade. We provide gross, histological, and micro-CT documentation of the structure and location of bone and cartilage in skulls, pectoral girdles, and vertebrae, with emphasis on the bovichtid B. diacanthus, the eleginopsid E. maclovinus, and the channichthyid Chaenodraco wilsoni. In Eleginops and the Antarctic clade, most bone is spongy and most species have persisting cartilage in the skull and appendicular skeleton. We also measured the relative size of the notochordal canal in adult vertebral centra of 38 species representing all eight families. There is considerable interspecific variation in this pedomorphic trait and all species show an ontogenetic reduction in the relative size of the canal. However, large persisting canals are present in adults of the Antarctic clade, especially in the nototheniids Pleuragramma and Aethotaxis and in a number of bathydraconid and channichthyid genera.

Mutations in the T (brachyury) gene cause a novel syndrome consisting of sacral agenesis, abnormal ossification of the vertebral bodies and a persistent notochordal canal

BackgroundThe T gene (brachyury gene) is the founding member of the T-box family of transcription factors and is vital for the formation and differentiation of the mesoderm and the axial...

Post-metamorphic development of Early Cretaceous frogs as a tool for taxonomic comparisons

ABSTRACT Specimens of a single but currently undetermined species of the anuran genus Liaobatrachus from the Lower Cretaceous of northeast China, including four articulated skeletons preserved on a single block of sediment plus two skulls and several additional adult skeletons on other slabs, illustrate post-metamorphic developmental stages from early juvenile to fully grown adult. The relative ages of the individuals were estimated based on body size combined with degree of ossification. Post-metamorphic developmental data not only provide a basis for comparisons with other fossil and recent anuran taxa, but also help to identify both age-independent (i.e., size-independent) characters that can be used for taxonomic comparisons among individuals of various sizes (i.e., ages) and age-dependent (i.e., size-dependent, ontogenetically variable) characters that can only be used for comparisons across corresponding developmental stages. Our study revealed that the following characters are independent of size in Liaobatrachus: frontoparietals with a fontanelle between their frontal portions; quadratojugal present; vertebral centra amphicoelous and pierced by a notochordal canal; and free (not ankylosed) ribs attached to diapophyses of second to fourth vertebrae. The tibiofibula/femur and presacral vertebral column/snout-vent length ratios were also found to be size independent. In contrast, ossification of the carpus, distal tarsals, and pubis appears to be ontogenetically variable (i.e., they vary with age), and this is presumably also true of fusion between the tibiale and fibulare. These characters should only be used for comparisons among individuals at a common developmental stage.

The braincase anatomy of Lawrenciella schaefferi, actinopterygian from the Upper Carboniferous of Kansas (USA)

ABSTRACT A full description and diagnosis are given of Lawrenciella schaefferi Poplin 1984, from the Pennsylvanian (Late Carboniferous) of Kansas, U.S.A. This taxon is only known by braincases and associated parasphenoids, which are exceptionally well preserved as phosphatic nodules. The external and internal morphology of the endocrania were studied from serial sectionings which allowed detailed three-dimensional reconstructions. The study shows that, besides synapomorphies inherent to basal actinopterans, L. schaefferi displays a set of very peculiar features such as prespiracular fossae, intracranial ossicles, and paired anterior myodomes for nonocular eye muscles. Another conspicuous feature, the notochordal canal ending blindly anteriorly, has been observed until now only in more advanced Triassic actinopterans. The anatomical characters of L. schaefferi indicate, in the light of recent cladistic analyses, that this Carboniferous taxon is a relatively advanced actinopteran compared to basal forms such as Kentuckia, Mimia, or Moythomasia.

Persistent notochordal canal mimicking compression fracture: a case report

A persistent notochordal canal is a rare anomaly that is generally discovered by chance. The radiographic appearance of this entity is characteristic and usually does not require further investigation. However, in some cases plain films may fail to depict this appearance, and computed tomography or magnetic resonance imaging (MRI) is required for final diagnosis. We report the MRI findings of a young woman with persistent notochordal canal who, based on plain radiographs, had first been misdiagnosed as having a compression fracture.

The ear region of Latimeria chalumnae: functional and evolutionary implications

The anatomy of Latimeria chalumnae has figured prominently in discussions about tetrapod origins. While the gross anatomy of Latimeria is well documented, relatively little is known about its otic anatomy and ontogeny. To examine the inner ear and the otoccipital part of the cranium, a serial-sectioned juvenile coelacanth was studied in detail and a three-dimensional reconstruction was made. The ear of Latimeria shows a derived condition compared to other basal sarcopterygians in having a connection between left and right labyrinths. This canalis communicans is perilymphatic in nature and originates at the transition point of the saccule and the lagena deep in the inner ear, where a peculiar sense end organ can be found. In most gnathostomes the inner ears are clearly separated from each other. A connection occurs in some fishes, e.g. within the Ostariophysi. In the sarcopterygian lineage no connections between the inner ears are known except in the Actinistia. Some fossil actinistians show a posteriorly directed duct lying between the foramen magnum and the notochordal canal, similar to the condition in the ear of Latimeria, so this derived character complex probably developed early in actinistian history. Because some features of the inner ear of Latimeria have been described as having tetrapod affinities, the problem of hearing and the anatomy of the otical complex in the living coelacanth has been closely connected to the question of early tetrapod evolution. It was assumed in the past that the structure found in Latimeria could exemplify a transitional stage in otic evolution between the fishlike sarcopterygians and the first tetrapods in a functional or even phylogenetic way. Here the possibility is considered that the canalis communicans does not possess any auditory function but rather is involved in sensing pressure changes during movements involving the intracranial joint. Earlier hypotheses of a putative tympanic ear are refuted.

The Devonian tetrapodAcanthostega gunnariJarvik: postcranial anatomy, basal tetrapod interrelationships and patterns of skeletal evolution

ABSTRACTThe postcranial skeleton ofAcanthostega gunnarifrom the Famennian of East Greenland displays a unique, transitional, mixture of features conventionally associated with fishand tetrapod-like morphologies. The rhachitomous vertebral column has a primitive, barely differentiated atlas-axis complex, encloses an unconstricted notochordal canal, and the weakly ossified neural arches have poorly developed zygapophyses. More derived axial skeletal features include caudal vertebral proliferation and, transiently, neural radials supporting unbranched and unsegmented lepidotrichia. Sacral and post-sacral ribs reiterate uncinate cervical and anterior thoracic rib morphologies: a simple distal flange supplies a broad surface for iliac attachment. The octodactylous forelimb and hindlimb each articulate with an unsutured, foraminate endoskeletal girdle. A broad-bladed femoral shaft with extreme anterior torsion and associated flattened epipodials indicates a paddle-like hindlimb function. Phylogenetic analysis placesAcanthostegaas the sister-group ofIchthyostegaplus all more advanced tetrapods.Tulerpetonappears to be a basal stemamniote plesion, tying the amphibian-amniote split to the uppermost Devonian.Caerorhachismay represent a more derived stem-amniote plesion. Postcranial evolutionary trends spanning the taxa traditionally associated with the fish-tetrapod transition are discussed in detail. Comparison between axial skeletons of primitive tetrapods suggests that plesiomorphic fish-like morphologies were re-patterned in a cranio-caudal direction with the emergence of tetrapod vertebral regionalisation. The evolution of digited limbs lags behind the initial enlargement of endoskeletal girdles, whereas digit evolution precedes the elaboration of complex carpal and tarsal articulations. Pentadactylous limbs appear to have stabilised independently in amniote and amphibian lineages; the colosteidGreererpetonhas a pentadactylous manus, indicating that basal amphibian forelimbs may not be restricted to patterns of four digits or less.

Persistence of the notochordal canal: plain film and CT findings

Persistence of the notochordal canal: plain film and CT findings

Persistence of the notochordal canal: plain film and CT findings

We describe two cases of persistent notochordal canal documented by plain films and computed tomography as a vertical central canal surrounded by a rim of osteosclerosis extending the depth of the vertebrae involved.

Bovine notochord origin and development.

AbstractSerial sections of 60 bovine embryos (23 timed specimens) from 17 through 34 days gestation were examined to determine the processes and sequence of notochord development. Head notochord formed during days 18 through 21 as the ventral‐most layer of cells from Hensen's node became intercalated as the notochordal plate between the endodermal cells of the primitive open gut. The notochordal plate responded to contact by the neural plate during day 20 with hypertrophy of notochordal cells and a ventral curving of the notochordal plate margins to form the notochordal ridge which appeared as a dorsal evagination of the gut, but was not endodermal. Formation of the head notochord into a rod (without a notochordal canal or pit) occurred during days 20 and 21 reuniting the endodermal layer ventral to the notochord. Body notochord formed during days 21 through 32–33 caudad from the level of somite pair 6 by accumulation of notochordal cells from Hensen's node directly into a rod surrounded by a basal lamina without contact or penetration of the gut endoderm. Bovine notochord was, thus, formed by two methods. After formation by both methods, the notochord enlarged by proliferation of its own cells. Dorso‐ventral undulations of the notochord became distinct by the 27th day. The processes involved in bovine notochord development were different from descriptions published concerning other species in that 1. two methods of formation were found, and 2. notochordal plate formation preceded notochordal ridge production rather than vice versa.

Dipnoan (lungfish) skulls and the relationships of the group: a study based on new species from the Devonian of Australia

Dipnoan (lungfish) skulls and the relationships of the group: a study based on new species from the Devonian of Australia

On Anthracosaurus Russelli Huxley (Amphibia: Labyrinthodontia) and the family Anthracosauridae

A complete description is given of all the known material attributable to Anthracosaurus russelli Huxley. Apart from one skull specimen from Usworth Colliery, Washington, Tyne and Wear, England, all known specimens come, or are thought to come, from the Blackband Ironstone of Airdrie, near Glasgow, Scotland. Both horizons are of Coal Measure age, the former Westphalian A, the latter Westphalian B. Complete preparation of the holotype allows a reconstruction of the skull roof and occiput and, together with the Usworth specimen, the palate and a series of skull sections. Two lower jaw specimens are described for the first time. The cranial anatomy of Anthracosaurus is that of a massive embolomerous anthrocosaur which differs from eogyrinid embolomeres, notably Eogyrinus attheyi , in a number of important features. These include loss of the skull table/cheek kinetism and presence of an orbital lacrimal, biramous tabular horns and a wide dorsal exposure of thequadrate. Features of the palate are correlated with the distinctive dentition of relatively few very large marginal teeth and long palatal tusks: they include broad plate-like pterygoids, whose anterior rami meet in a median suture and extend laterally to the palatine tusks (thus largely concealing the palatine bones from ventral view) and whose quadrate rami lack a deep descending flange. The lower jaw is unique in having confluent meckelian fenestrae. Vertebrae attributed to A. russelli are of normal embolomerous type except that the notochordal canal is occluded by a bony plug in the centra. An interclavicle of distinctive shape is also attributed. Several North American embolomere specimens are presently placed within the family Anthracosauridae. Of these the most complete is Eobaphetes kansensis Moodie consisting of three blocks, the original holotype and paratype and a third block not before described. As was first demonstrated by Dr Donald Baird these comprise a single skull, here described in its entirety. Description of Eobaphetes is preceded by a discussion of its provenance. This was originally recorded as ‘Coal Measures’, Washington County, Kansas, which is improbable but not more so than its current attribution to the Namurian of Washington County, Arkansas. Coal and spore analysis, supported by palaeogeography, suggest a late Pennsylvanian, probably Stephanian, horizon. In most respects the anatomy of skull roof and lower jaw of Eobaphetes suggests relationships with Eogyrinus rather than Anthracosaurus . This is also the case with the closely related Leptophractus obsoletus from Linton, Ohio, to which species ‘ Anthracosaurus lancifer ' also from Linton, is referred. However, Eobaphetes and Leptophractus , together with Neopteroplax conemaughensis , share a number of distinctive features. These include a flat-topped surangular crest to the jaw and, importantly, a dentition of massive palatal tusks and anterior marginal teeth but numerous small posterior teeth in maxillary and dentary. Tooth shape is also distinctive. It is thus proposed to retain the family Anthracosauridae for A. russelli alone, while placing the American species within the Eogyrinidae, but as a new subfamily the Leptophractinae, distinct from the Eogyrinidae. A diagnosis of each of these taxa is given.

Composition of fluid from the notochordal canal of the coelacanth, Latimeria chalumnae

Fluid from the notochordal canal of the coelacanth, Latimeria chalumnae, was analyzed for major inorganic and organic constituents and compared with blood serum from the same fish. Significantly or suggestively lower levels of sodium, magnesium, calcium, bicarbonate, sulfate, total carbohydrates, glucose, lactate, cholesterol, bound phosphate and total proteins were found in notochordal fluid than in serum, whereas potassium, chloride, urea, trimethylamine oxide, and total free amino acids were higher and inorganic phosphorus essentially identical. Osmolarity of notochordal fluid (1058 mOsm) exceeds that of serum (942 mOsm). A whitish precipitate in the fluid consisted of a matrix of fibers 100 A in diameter and of indefinite length. It resembled a sialoglycoprotein in composition and was stabilized by disulfide bonds. The fluid contained cellular debris.

The Neurenteric Canal in the Frog, Rana Pipiens.

Even the temporary appearance of a tubular connection in the embryo between the neurocoel and the hindgut, known as the neurenteric canal, has considerable phylogenetic significance if its presence can be demonstrated and the parts homologized in such a variety of forms as Amphioxus, Fish, Amphibia, Reptiles, Mammals and possibly even in birds (duck, goose, Sterna., Lillie). It is the purpose of this paper to add another link in the chain of evidence of the embryological existence of such a canal, using the Anuran, Rana pipiens. The neurenteric canal has been variously described as a tubular connection between the neurocoel and hindgut; the post-anal gut (Shumway and Huettner); the dorsal cavity of the closing blastopore; the short bent posterior portion of the neurocoel plus the remains of the blastopore; the notochordal canal; the anterior end of the primitive streak; and also the connection between the amniotic and yolk sacs of the mammal. Huxley and DeBeer, for instance, are very cautious in stating that with the approximation of the parallel neural ridges at that region so that “in this manner, a neurenteric canal, actual or virtual, according as to whether the blastopore is or is not still open, is formed, connecting the cavities of the neural tube and the gut.” Over 100 frog embryos (Rana pipiens) of stages 15 to 17 (Shumway and Rugh) were serially sectioned sagittally at 10 μ and examined for the possible existence of this canal. In practically every embryo the canal was either present as such (Fig. 1) or its lining of pigmented dells could be easily discerned (Fig. 2).

Early development in some sciuridae

AbstractThe early developmental history of Sciuridae (squirrel family), from the ovarian egg to the establishment of the germ layers, was studied in fixed material comprising ova and embryos from six species of five genera. No significant differences were noted in the major processes of development in the six species. Continuous diminution in the size of the ova occurs from the beginning of follicular vesiculation up to the early blastocyst stages. Corpora haemorrhagica are present in most of the recently ruptured follicles of all the species.Cleavage is regular, though adequal, up to the eight‐cell stage, the blastomeres clustering into a compact mass. There is desquamation of cellular material from the periphery of the ovum between morula and blastocyst stages. At the same time cells within the blastocyst degenerate to add to the cavity originally formed by confluence of intercellular spaces. The cavity forms among the inner cells, an inner cell mass being left at one pole and an anti‐embryonic mass at the other. The anti‐embryonic cells produce much of the yolk‐sac entoderm and contribute to the implantation mass. The latter mass forms a temporary attachment of the blastocyst to the uterine mucosa in these species. The definitive entoderm arises by migration and delamination of certain of the inner cell mass cells. A transitory notochordal canal, passing in a vertical plane through Hensen's node, is strongly suggested.