THE HETEROSTRACAN FISHES

1. The heterostracan fishes were jawless, microphagous, devoid of paired fins and encased in a bony armour. The classification is based on the arrangement of the plates of the carapace — the primitive forms possessed a tessellated armour made up of numerous small polygonal plates. Several genera had a tessellated carapace ventrally but large discrete plates dorsally. All further groups are characterized by distinct patterns of plates which remain constant within each order. The proportions in some species suggest sexual dimorphism. 2. A study of the superficial ornamentation reveals patterns of growth. From the primitive tessellated condition different evolutionary lines can be followed leading to the fusion of these small elements into large discrete plates. Among the latest group of heterostracans there was a secondary redevelopment of tesserae. 3. Impressions on the inner surface of the plates of the carapace enable certain aspects of the internal anatomy to be reconstructed. The nasal sacs were double, the acousticolateralis system was primitive. The brain was little more than the nerve cord swollen in three places, there was no cranial flexure. Impressions of two pre-otic somites were present, indicating that they had not migrated to form the extrinsic eye muscles. The branchial arches appear to have been of gnathostome type and in some genera spiracles were formed as an adaptation to a benthonic mode of life. 4. Microscopic sections of the armour demonstrate the existence of four tissues: aspidin, dentine, enameloid and calcified cartilage. Aspidin was originally acellular but later became cellular; the organic matrix was first organized like dentine, but subsequently like bone. Furthermore aspidin was capable of remodelling. Dentine appears to have acted as a skin-like tissue and was capable of regeneration. The significance of enameloid and calcified cartilage in the dermal armour is not well understood. 5. Until the end of the Silurian the heterostracans inhabited marine waters but from the beginning of the Devonian they colonized the fresh-water lakes and rivers of the Old Red Continent. One major group flourished in a large embayment on the edge of the Tungussian land mass. When the stratigraphical range and geographical distribution of the heterostracans is listed, evolutionary centres can be recognized and also migration routes: during the Upper Silurian the cyathaspids in the Canadian Arctic, the Lower Devonian pteraspids in Eastern Europe, the later Lower Devonian amphiaspids in north-west Siberia (Tungussian Realm), and the Middle and Upper Devonian psammosteids in the Baltic province. Periods of migration from the Baltic to Scotland, the Timan, Ellesmereland, the Urals and Donbas have been documented. For the illustrations the author is indebted to Miss Jennifer Middleton and Mr John Smith.     

滇东早泥盆世星骨鱼科(Asterosteidae)化石的发现

<正> 目前,泥盆纪星骨鱼科化石除非洲和南极地区尚未发现外,世界其它各地均有发现,但化石产地并不多.其时代从早泥盆世一直延续到晚泥盆世早期,多数出现在早—中泥盆世.所有化石全部产于海相地层.据现有资料统计,已经发现和描述的只有5个属,即 Asterosteus, Gemuendina, Jagorina, Ohioaspis, Bolivosteus,分布在德国(早泥盆世),美国(中泥盆世),加拿大(中泥盆世),澳大利亚(早一中泥盆世),土耳其(中泥盆世)和玻利维亚(中泥盆世).     

Structural peculiarities of the tubercles in the skin of the turbot,Scophthalmus maximus (L., 1758) (Osteichthyes,Pleuronectiformes, Scophthalmidae)

The structure of the bony tubercles of the turbot, Scophthalmus maximus (L., 1758), was examined using ground sections, microradiography, SEM, and TEM. The tubercles are small, isolated, mineralized conical plates randomly distributed in the eyed side of the body. They are composed of three layers: the outer limiting layer, the external layer, and the basal plate, which make up the thin and flat elasmoid scales of Teleostei. The main difference between regular elasmoid scales and bony tubercles lies in the organization and the growth of the basal plate. Indeed, the conical shape of the tubercle is the result of a prominent thickening of the central part of the basal plate where the collagen matrix is organized in a complicated three-dimensional network. Densely packed thick collagen fibrils form superimposed plies organized in a plywood-like structure that resembles that of the elasmoid scales but it is criss-crossed by numerous vertical sheets of thin collagen fibrils. The tubercles originate from thin and flat plates located in the skin of larvae and juveniles, whose structure is that of regular-developing elasmoid scales. Thus, the tubercles of Scophthalmus maximus could be considered as modified elasmoid scales rather than bony structures. They might be the result of specific arrangements related to the general trend of reduction of the dermal skeleton in the teleostean lineage.     

Histology of “placoderm” dermal skeletons: Implications for the nature of the ancestral gnathostome

The vertebrate dermal skeleton has long been interpreted to have evolved from a primitive condition exemplified by chondrichthyans. However, chondrichthyans and osteichthyans evolved from an ancestral gnathostome stem‐lineage in which the dermal skeleton was more extensively developed. To elucidate the histology and skeletal structure of the gnathostome crown‐ancestor we conducted a histological survey of the diversity of the dermal skeleton among the placoderms, a diverse clade or grade of early jawed vertebrates. The dermal skeleton of all placoderms is composed largely of a cancellar architecture of cellular dermal bone, surmounted by dermal tubercles in the most ancestral clades, including antiarchs. Acanthothoracids retain an ancestral condition for the dermal skeleton, and we record its secondary reduction in antiarchs. We also find that mechanisms for remodeling bone and facilitating different growth rates between adjoining plates are widespread throughout the placoderms. J. Morphol., 2013. © 2013 Wiley Periodicals, Inc.     

Canaliculi in the tessellated skeleton of cartilaginous fishes

The endoskeletal elements of sharks and rays are comprised of an uncalcified, hyaline cartilage‐like core overlain by a thin fibro‐ceramic layer of mineralized hexagonal tiles (tesserae) adjoined by intertesseral fibers. The basic spatial relationships of the constituent tissues (unmineralized cartilage, mineralized cartilage, fibrous tissue) are well‐known – endoskeletal tessellation is a long‐recognized synapomorphy of elasmobranch fishes – but a high‐resolution and three‐dimensional (3D) understanding of their interactions has been hampered by difficulties in sample preparation and lack of technologies adequate for visualizing microstructure and microassociations. We used cryo‐electron microscopy and synchrotron radiation tomography to investigate tessellated skeleton ultrastructure but without damage to the delicate relationships between constituent tissues or to the tesserae themselves. The combination of these techniques allowed visualization of never before appreciated internal structures, namely passages connecting the lacunar spaces within tesserae. These intratesseral ‘canaliculi’ link consecutive lacunar spaces into long lacunar strings, radiating outward from the center of tesserae. The continuity of extracellular matrix throughout the canalicular network may explain how chondrocytes in tesserae remain vital despite encasement in mineral. Extracellular fluid exchange may also permit transmission of nutrients, and mechanical and mineralization signals among chondrocytes, in a manner similar to the canalicular network in bone. These co‐adapted mechanisms for the facilitated exchange of extracellular material suggest a level of parallelism in early chondrocyte and osteocyte evolution.     

Inter‐ and intraspecific variation in the surface pattern of the dermal bones of two sturgeon species

Archaeological bone remains of sturgeon (Acipenser sturio/Acipenser oxyrinchus) from northwestern Europe are often identified to species on the basis of their surface morphology and then used to reconstruct the spatial distribution of the two species through time. The dermal bones of A. sturio are said to have an exterior surface pattern consisting of tubercles, while those of A. oxyrinchus are said to display alveoli. In the present paper, the validity of the surface pattern as a species‐specific characteristic is critically assessed. To this purpose, dermal plates from modern, genetically identified museum specimens were studied and the surface morphology observed in a series of archaeological remains was compared with the genetic identifications obtained on these same remains. The analyses show that the surface pattern of dermal bones is related to the size of the individual, with the pattern of small A. oxyrinchus being similar to that of A. sturio. In addition, variations in the surface pattern among the bones of a single individual and within the same bone have been observed. These findings explain previous conflicting results between morphological and genetic identifications and allow the formulation of some recommendations for more accurate morphological identification of isolated archaeological sturgeon dermal bones.     

Applied microfacies analysis: Provenance studies of Roman mosaic stones

Summary Provenance analysis of archaeological materials is an essential tool of archaeometry but has been rarely applied to antique mosaics. Many mosaics are made of carbonate mosaic stones (tesserae). Hence, microfacies analysis offers a great potential in differentiating these limestone tesserae and provenancing their local, regional, imported or recycled origins. The methods of microfacies analysis and their prospects for studying mosaics are demonstrated by case studies of Roman mosaics from southern Germany (Kraiburg, Bavaria). Austria (Hemmaberg near Globasnitz, southern Carinthia), Italy (Asolo north of Padova) and late Punic and Roman mosaics from Tunisia (Carthage and Hergla). Microfacies-based provenance analysis comprises six stages: 1) Macroscopic assessment and definition of rock colour groups of tesserae, 2) Sampling based on rock-colour categories, 3) Definition of microfacies types and attribution to standard microfacies types based on thin-section criteria, 4) Evaluation of the mosaic site with respect to geological and paleontological data followed by comparisons of the microfacies inventory of the region with microfacies types of the tesserae, 5) Assessment of carbonate tesserae to specific geological rock/time units followed by suggestions of provenance sites. 6) Critical evaluation of provenance assessment within the archaeological context. Principal limestone colours do not necessarily coincide with specific limestone types. Uniformly coloured tesserae can represent different limestone types from different sources (cf. Kraiburg, Hemmaberg). On the other hand, a specific limestone type may be characterized by different rock colours (cf. Carthage). Provenance assessment of mosaic stones results in relatively narrow (Hemmaberg, Asolo) or only broad (Carthage, Hergla) indications of sites characterized by exposures of carbonate rocks whose microfacies criteria, geological age and rock colour correspond to those of the carbonate tesserae. The case studies argue for local and/or imported (Kraiburg) as well as regional provenances of the mosaic material (Hemmaberg, Asolo; source area within a distance between 10 and about 40 km) and indicate that off-cuts of building stones exploited within a regional frame might possibly have been used (Carthage). Differences in the composition and diversity of carbonate rocks used for the fabrication of mosaics reflect time-dependent changes in major quarrying and potential source areas (Carthage). Further provenance research of mosaics should be based on statistically representative tesserae samples, supplemented by microfacies studies of the building material used at the mosaic sites as well as investigation of nonlithic tesserae and the mortar bedding of the mosaics. The isotopic composition of limestone and dolomite tesserae also assists in the critical evaluation of microfacies categorization.     

Mineralized cartilage in the skeleton of chondrichthyan fishes

The cartilaginous endoskeleton of chondrichthyan fishes (sharks, rays, and chimaeras) exhibits complex arrangements and morphologies of calcified tissues that vary with age, species, feeding behavior, and location in the body. Understanding of the development, evolutionary history and function of these tissue types has been hampered by the lack of a unifying terminology. In order to facilitate reciprocal illumination between disparate fields with convergent interests, we present levels of organization in which crystal orientation/size delimits three calcification types (areolar, globular, and prismatic) that interact in two distinct skeletal types, vertebral and tessellated cartilage. The tessellated skeleton is composed of small blocks (tesserae) of calcified cartilage (both prismatic and globular) overlying a core of unmineralized cartilage, while vertebral cartilage usually contains all three types of calcification.     

Composition,Production and Procurement of Glass at San Vincenzo al Volturno: An Early Medieval Monastic Complex in Southern Italy

136 glasses from the ninth-century monastery of San Vincenzo and its workshops have been analysed by electron microprobe in order to situate the assemblage within the first millennium CE glass making tradition. The majority of the glass compositions can be paralleled by Roman glass from the first to third centuries, with very few samples consistent with later compositional groups. Colours for trailed decoration on vessels, for vessel bodies and for sheet glass for windows were largely produced by melting the glass tesserae from old Roman mosaics. Some weakly-coloured transparent glass was obtained by re-melting Roman window glass, while some was produced by melting and mixing of tesserae, excluding the strongly coloured cobalt blues. Our data suggest that to feed the needs of the glass workshop, the bulk of the glass was removed as tesserae and windows from a large Roman building. This is consistent with a historical account according to which the granite columns of the monastic church were spolia from a Roman temple in the region. The purported shortage of natron from Egypt does not appear to explain the dependency of San Vincenzo on old Roman glass. Rather, the absence of contemporary primary glass may reflect the downturn in long-distance trade in the later first millennium C.E., and the role of patronage in the “ritual economy” founded upon donations and gift-giving of the time.     

Ultrastructure of calcified cartilage in the endoskeletal tesserae of sharks

The tesserate pattern of endoskeletal calcification has been investigated in jaws, gill arches, vertebral arches and fins of the sharks Carcharhinus menisorrah, Triaenodon obesus and Negaprion brevirostris by techniques of light and electron microscopy. Individual tesserae develop peripherally at the boundary between cartilage and perichondrium. An inner zone, the body, is composed of calcified cartilage containing viable chondrocytes separated by basophilic contour lines which have been called Liesegang waves or rings. The outer zone of tesserae, the cap, is composed of calcified tissue which appears to be produced by perichondrial fibroblasts more directly, i.e., without first differentiating as chondroblasts. Furthermore, the cap zone is penetrated by acidophilic Sharpey fibers of collagen. It is suggested that scleroblasts of the cap zone could be classified as osteoblasts. If so, the cap could be considered a thin veneer of bone atop the calcified cartilage of the body of a tessera. By scanning electron microscopy it was observed that outer and inner surfaces of tesserae differ in appearance. Calcospherites and hydroxyapatite crystals similar to those commonly seen on the surface of bone are present on the outer surface of the tessera adjacent to the perichondrium. On the inner surface adjoining hyaline cartilage, however, calcospherites of variable size are the predominant surface feature. Transmission electron microscopy shows calcification in close association with coarse collagen fibrils on the outer side of a tessera, but such fibrils are absent from the cartilaginous matrix along the under side of tesserae. Calcified cartilage as a tissue type in the endoskeleton of sharks is a primitive vertebrate characteristic. Calcification in the tesserate pattern occurring in modern Chondrichthyes may be derived from an ancestral pattern of a continuous bed of calcified cartilage underlying a layer of perichondral bone, as theorized by Ørvig (1951); or the tesserate pattern in these fish may itself be primitive.     

Palaeohistology and external microanatomy of rauisuchian osteoderms (Archosauria: Pseudosuchia)

Abstract: The presence of postcranial dermal armour is plesiomorphic for Archosauria. Here, we survey the external microanatomy and histology of postcranial osteoderms (i.e. dorsal paramedian and caudal osteoderms) of rauisuchians, a widely distributed assemblage of extinct predatory pseudosuchians from the Triassic. The osteoderms of eight rauisuchian taxa were found to be rather compact bones, which usually lack significant bone remodelling or large areas of cancellous bone. The presence of highly vascularized woven or fibrolamellar bone tissue deposited in the core areas indicates higher growth rates during earlier life stages, whereas a more compact parallel‐fibred bone matrix indicates reduced growth rates in later development. This pattern of change corroborates earlier studies on long bone histology. With the exception of a bone tissue found in the sample of Batrachotomus kupferzellensis, which might be the result of metaplastic ossification, the general mode of skeletogenesis is comparable with intramembraneous ossification. The lack of cancellous bone tissue and remodelling processes associated with bone ornamentation, as well as the predominantly intramembraneous mode of ossification, indicates that rauisuchian osteoderm formation differs profoundly from that of the osteoderms of the only extant pseudosuchian lineage, the crocodylians.     

Minute tubercles on the skin surface of larvae in the Korean endemic bitterling, Rhodeus pseudosericeus (Pisces, Cyprinidae)

The morphology and distribution of the minute tubercles on the skin surface of larvae in Korean bitterling, Rhodeus pseudosericeus, were observed during larval development. Just after hatching, the epidermis of the larvae consists of a thin single cell layer having smaller basophilic flat or round‐flattened basal cells. As the larvae grow, the epidermis contains more small flat cells and large epidermal cells that are round or hemisphere‐shaped. These large unicellular epidermal cells, called minute tubercles, consist of more or less homogeneous cytoplasm that is PAS (Periodic acid‐Schiff method) positive. They are more densely distributed in the wing‐like yolk sac projection. Vestigial minute tubercles occur in the body region and the caudal fin‐fold region. These minute tubercles grow in number and height from 6 to 8 days after hatching onward. However, they become reduced in height and number as the larvae develop. At day 31 after hatching (i.e. free‐swimming stage), minute tubercles no longer exist on the larval skin. The sequence of occurrence and gradual disappearance of these cell structures are described and histologically documented for comparative purposes of beta, taxnomomic and environmental studies.     

江豚皮肤的超微结构及其与其它豚类的比较

江豚皮肤的超微结构与海洋豚类相同,但在各层表皮细胞中存在大量的膜被颗粒,这很可能与江豚适应从海水进入淡水的生活方式有关。大量成束的张力原纤维的存在,有利于江豚在水中深潜和快速游泳,可适应来自各方面的压力,加强细胞之间的联接。在上下颌皮肤的乳头层基部大量被囊神经末梢和有鞘神经纤维束的分布、与江豚水底觅食方式有关。白鱀豚和条纹原海豚皮肤的超微结构与江豚大致相同,但亦有其各自的特点。     

Testing models of dental development in the earliest bony vertebrates, Andreolepis and Lophosteus

Theories on the development and evolution of teeth have long been biased by the fallacy that chondrichthyans reflect the ancestral condition for jawed vertebrates. However, correctly resolving the nature of the primitive vertebrate dentition is challenged by a dearth of evidence on dental development in primitive osteichthyans. Jaw elements from the Silurian-Devonian stem-osteichthyans Lophosteus and Andreolepis have been described to bear a dentition arranged in longitudinal rows and vertical files, reminiscent of a pattern of successional development. We tested this inference, using synchrotron radiation X-ray tomographic microscopy (SRXTM) to reveal the pattern of skeletal development preserved in the sclerochronology of the mineralized tissues. The tooth-like tubercles represent focal elaborations of dentine within otherwise continuous sheets of the dermal skeleton, present in at least three stacked generations. Thus, the tubercles are not discrete modular teeth and their arrangement into rows and files is a feature of the dermal ornamentation that does not reflect a polarity of development or linear succession. These fossil remains have no bearing on the nature of the dentition in osteichthyans and, indeed, our results raise questions concerning the homologies of these bones and the phylogenetic classification of Andreolepis and Lophosteus.     

Breeding Tubercles, Papillomatosis and Dominance Behaviour of Male Roach (Rutilus rutilus) During the Spawning Period

We studied the relationship between the breeding tubercle ornamentation (i.e. skin roughness) and male pre‐spawning dominance and courtship behaviour in roach (Rutilus rutilus) within an experimental laboratory system. Sexually mature fish were caught during their migration to their spawning pond and their behaviours were studied in an artificial spawning arena. Males behaved naturally both in terms of male–male interactions and attempts to achieve spawnings. Males having many, large breeding tubercles (i.e. rough skin) were significantly more often dominant in our dyadic trials than those with smooth skin. The dominant male in the trial exhibited a more active courtship behaviour than its subordinate rival. Papilloma skin disease did not affect the dominance rank. As a result of the relationship between skin roughness and male dominance, breeding tubercles may be used by the females as a cue for choosing a high‐quality mate in a roach lek. Thus, breeding tubercles might offer a workable tool for examination of sexual selection among cyprinids.     

Le revêtement cutané des raies (Chondrichthyes,Elasmobranchii, Batoidea). II. Morphologie et arrangement des tubercules cutanés

The dermal covering of most batoid fish is constituted by dermal denticles and by different series of tubercles or thorns. The repartition and the morphological variations of these structures can provide complementary information about the taxonomy of skates and rays. The variations in these dermal structures within Pristiforms, Rajiforms and Myliobatiforms have been studied, taking into consideration the number of tubercles, their location and their arrangement in different series. Following Hubbs and Ishiyama [30], two new terms and 15 new series are indicated. The characteristics of the arrangement and of the morphology of these structures can separate the Rajiforms, having spiny tubercles or thorns, from the Myliobatiformes, bearing lanceolate or heart-shaped tubercles. The main taxinomic characters found are: guitar fish characterized by two scapular series, one well-developed rostral series and tubercles with an anterolateral ornamentation (relief). Within this group, Rhinidae and Rhynchobatidae are set apart by the morphology of their tubercles (devoid of any anterolateral ornamentation), by the absence of a middorsal caudal series and by the presence of an outer supraspiracular series. Platyrhina and Platyrhinoidis are distinguishable by the absence of anterolateral relief and by the presence of anterolateral, lateral and parallel series. Rajoids are characterized by thorns, only one scapular series and sometimes a nucho-scapular triangle, malar and alar thorns in adults, and well-developed parallel and lateral series. Myliobatiforms are devoid of rostral, orbito-spiracular, malar, alar, anterolateral, parallel and lateral series but a caudal sting is present in most species. Sawfish are almost entirely devoid of tubercules, except for rostral ‘teeth’. The morphology and arrangement of the rostral teeth can differenciate the two genera within this family.     

Tubular phosphatic microproblematica from the Early Ordovician of China

Fenhsiangia zhangwentangi gen. et sp. nov., is named for an animal represented by a phosphatic tube-like exoskeleton with the internal walls ornamented by stellate-based rounded tubercles. As vertebrates are the only animals known to possess stellate tubercles of phosphatic material in the dermal skeleton, yet our remains do not show any morphological or histological similarity to primitive fish bone, we suggest that Fenhsiangia was an ancestral protovertebrate, possibly an ascidian or related form. A second form, here referred to as Fenhsiangia sp. differs in that the tubercles are flat-topped or concave, and the external walls are deeply pitted with lines of small pustules bordering the depressions. The Upper Cambrian and Ordovician could have been a time of great diversity and radiation for protovertebrates. with the evolution of the first true vertebrates resulting from this radiation. □ Ordovician, China, phosphatic microproblematica, protovertebrate.     

Effects of insulin on rat brain noradrenaline

A single intracardial injection of streptozotocin produced a significant increase in rat hypothalamic noradrenaline while no changes were observed in the olfactory tubercles. The parenteral administration of a single dose of insulin decreased rat hypothalamic noradrenaline; the effect had a rapid onset and lasted for at least six hours. Similar noradrenaline reductions were observed in the olfactory tubercles but in this tissue the depletion started later and recovered earlier. In addition, in olfactory tubercles after insulin injection, tyrosine level and dopamine metabolism were increased. The results show that the increases in hypothalamic NA observed in streptozotocin diabetic rats are counteracted by insulin administration and possibly the consequence of changes in noradrenaline turnover.     

Pigment cell mechanisms underlying dorsal color‐pattern polymorphism in the japanese four‐lined snake

To provide histological foundation for studying the genetic mechanisms of color‐pattern polymorphisms, we examined light reflectance profiles and cellular architectures of pigment cells that produced striped, nonstriped, and melanistic color patterns in the snake Elaphe quadrivirgata. Both, striped and nonstriped morphs, possessed the same set of epidermal melanophores and three types of dermal pigment cells (yellow xanthophores, iridescent iridophores, and black melanophores), but spatial variations in the densities of epidermal and dermal melanophores produced individual variations in stripe vividness. The densities of epidermal and dermal melanophores were two or three times higher in the dark‐brown‐stripe region than in the yellow background in the striped morph. However, the densities of epidermal and dermal melanophores between the striped and background regions were similar in the nonstriped morph. The melanistic morph had only epidermal and dermal melanophores and neither xanthophores nor iridophores were detected. Ghost stripes in the shed skin of some melanistic morphs suggested that stripe pattern formation and melanism were controlled independently. We proposed complete‐ and incomplete‐dominance heredity models for the stripe‐melanistic variation and striped, pale‐striped, and nonstriped polymorphisms, respectively, according to the differences in pigment‐cell composition and its spatial architecture. J. Morphol. 274:1353–1364, 2013. © 2013 Wiley Periodicals, Inc.