Contributions to the tooth morphology in early embryos of three species of hammerhead sharks (Elasmobranchii: Sphyrnidae) and their evolutionary implications

The tooth types in the embryos of the hammerhead sharks Sphyrna tiburo, Sphyrna tudes and Eusphyra blochii are here described in labial and lingual views, and, in some cases, in additional views. The presence of cusplets was observed in the anterior teeth of S. tiburo and S. tudes, which is secondarily lost after early embryonic stages. Many aligned root foramina were detected in the sphyrnids, which, as the cusplets, are shared by many phylogenetic-related carcharhinids. Other anatomic features, related to the root and central cusp, are presented for the first time. Such characters represent the first step to compare the teeth of extant and fossil species.     

Scymnodon plunketi (Waite, 1910): a junior synonym of Scymnodon macracanthus (Regan, 1906) (Somniosidae: Elasmobranchii)

The taxonomic status and validity of Scymnodon macracanthus (Regan, 1906) and Scymnodon plunketi (Waite, 1910) are revised in light of new material from the Southern Pacific and Indian Oceans. Despite being historically accepted as distinct taxa, recent studies suggested the possibility that these species could represent a single taxon. Morphometrics, meristics and morphology of dermal denticles show that S. plunketi is indeed a junior synonym of S. macracanthus. Previous distinctive characters proved to be the result of intraspecific variation. S. macracanthus is therefore redescribed including an updated comparative diagnosis for the genus Scymnodon in the family Somniosidae.     

Comparison of teeth and dermal denticles (odontodes) in the teleost Denticeps clupeoides (Clupeomorpha)

The present work is a contribution to an extensive comparative structural and developmental study we have undertaken to understand the evolution of the dermal skeleton in osteichthyans. We have investigated the structure of developing and functional tooth-like dermal denticles located on the head of Denticeps clupeoides, a clupeomorph, and compared their features to those of oral teeth. Morphological (scanning electron microscopy) and structural (light microscopy and transmission electron microscopy) observations clearly demonstrate that these small, sharp, conical and slightly backward-oriented denticles are true odontodes, i.e., homologous to oral teeth. They are composed of a dentine cone surrounding a pulp cavity, the top being covered by a hypermineralized cap. These odontodes are attached to a circular pedicel of attachment bone by a ligament that mineralizes, and the attachment bone matrix merges with that of the bony support. The pedicel of attachment bone surrounds a vascular cavity that is connected to the pulp cavity which is devoid of blood vessels and of nerve endings. Once the odontode is functional, the deposition of collagen matrix (called circumpulpar dentine) continues against the dentine, ligament, and attachment bone surfaces, thereby provoking a narrowing of the pulp cavity. Odontodes are shed by resorption occurring at the base, but their pedicels of attachment bone persist at the bone surface and become embedded in the bone matrix, within which they are clearly visible. The oral teeth are similar in shape, size, and structure to the odontodes, and they show only small differences probably related to the different function of these elements: They are more firmly anchored to the attachment bone, and the amount of dentine is relatively smaller than in odontodes. Despite their different functions, this close structural agreement between teeth and odontodes in Denticeps suggests that 1) competent cells from the same (ecto)mesenchymal population might be involved and 2) the genetic control of the developmental processes could be identical. It is suggested that the odontode expression in extra-oral positions is a relatively late novelty in this lineage. J. Morphol. 237:237–255, 1998. © 1998 Wiley-Liss, Inc.     

New data on the systematics and interrelationships of sawfishes (Elasmobranchii, Batoidea, Pristiformes)

New characters based on the arrangement and morphology of dermal denticles show that sawfishes can be divided into two distinctive groups. The first group, comprising the knifetooth sawfish Anoxypristis cuspidata , is characterized by tricuspid denticles variably located on both dorsal and ventral parts of the body. The second group is represented by species of the genus Pristis , showing an uniform and homogenous dermal covering of monocuspidate denticles on both dorsal and ventral sides of the body and within the buccopharyngeal cavity. Pristis is further divided into two subgroups: the first comprises species with denticles lacking any keels and furrows (the smalltooth sawfish Pristis pectinata , the green sawfish Pristis zijsron and the dwarf sawfish Pristis clavata ); the second comprises species with denticles presenting keels and furrows well differentiated on their anterior part (the common sawfish Pristis pristis , the largetooth sawfish Pristis perotteti and the greattooth sawfish Pristis microdon ). This investigation of the dermal covering provides results which agree with studies that separate the same two species groups of Pristis on the basis of other morphological data.     

Teeth outside the mouth: The evolution and development of shark denticles

Vertebrate skin appendages are incredibly diverse. This diversity, which includes structures such as scales, feathers, and hair, likely evolved from a shared anatomical placode, suggesting broad conservation of the early development of these organs. Some of the earliest known skin appendages are dentine and enamel-rich tooth-like structures, collectively known as odontodes. These appendages evolved over 450 million years ago. Elasmobranchs (sharks, skates, and rays) have retained these ancient skin appendages in the form of both dermal denticles (scales) and oral teeth. Despite our knowledge of denticle function in adult sharks, our understanding of their development and morphogenesis is less advanced. Even though denticles in sharks appear structurally similar to oral teeth, there has been limited data directly comparing the molecular development of these distinct elements. Here, we chart the development of denticles in the embryonic small-spotted catshark (Scyliorhinus canicula) and characterize the expression of conserved genes known to mediate dental development. We find that shark denticle development shares a vast gene expression signature with developing teeth. However, denticles have restricted regenerative potential, as they lack a sox2+ stem cell niche associated with the maintenance of a dental lamina, an essential requirement for continuous tooth replacement. We compare developing denticles to other skin appendages, including both sensory skin appendages and avian feathers. This reveals that denticles are not only tooth-like in structure, but that they also share an ancient developmental gene set that is likely common to all epidermal appendages.     

Constructional morphology within the head of hammerhead sharks (sphyrnidae)

The study of functional trade‐offs is important if a structure, such as the cranium, serves multiple biological roles, and is, therefore, shaped by multiple selective pressures. The sphyrnid cephalofoil presents an excellent model for investigating potential trade‐offs among sensory, neural, and feeding structures. In this study, hammerhead shark species were chosen to represent differences in head form through phylogeny. A combination of surface‐based geometric morphometrics, computed tomography (CT) volumetric analysis, and phylogenetic analyses were utilized to investigate potential trade‐offs within the head. Hammerhead sharks display a diversity of cranial morphologies where the position of the eyes and nares vary among species, with only minor changes in shape, position, and volume of the feeding apparatus through phylogeny. The basal winghead shark, Eusphyra blochii, has small anteriorly positioned eyes. Through phylogeny, the relative size and position of the eyes change, such that derived species have larger, more medially positioned eyes. The lateral position of the external nares is highly variable, showing no phylogenetic trend. Mouth size and position are conserved, remaining relatively unchanged. Volumetric CT analyses reveal no trade‐offs between the feeding apparatus and the remaining cranial structures. The few trade‐offs were isolated to the nasal capsule volume's inverse correlation with braincase, chondrocranial, and total cephalofoil volume. Eye volume also decreased as cephalofoil width increased. These data indicate that despite considerable changes in head shape, much of the head is morphologically conserved through sphyrnid phylogeny, particularly the jaw cartilages and their associated feeding muscles, with shape change and morphological trade‐offs being primarily confined to the lateral wings of the cephalofoil and their associated sensory structures. J. Morphol. 276:526–539, 2015. © 2015 Wiley Periodicals, Inc.     

Dentition of the apron ray Discopyge tschudii (Elasmobranchii: Narcinidae)

The present study provides quantitative and qualitative analyses of the dentition of Discopyge tschudii. Overall, 193 individuals (99 males and 94 females) of D. tschudii were collected on scientific trawl surveys conducted by the National Institute for Fisheries Research and Development (INIDEP) and commercial vessels in Argentina. Discopyge tschudii has rhombic‐shaped teeth, arranged in a semipavement‐like dentition; each tooth has an erect cusp slightly inclined posteriorly and holaulachorized root. Mature males have greater tooth lengths than females and immature specimens. Discopyge tschudii exhibits dignathic homodonty and gradient monognathic heterodonty where teeth of the commissural row are shorter than those of the symphyseal and internal rows.     

The life histories of endangered hammerhead sharks (Carcharhiniformes, Sphyrnidae) from the east coast of Australia

The life histories of two globally endangered hammerhead sharks, Sphyrna lewini and Sphyrna mokarran, were examined using samples collected from a range of commercial fisheries operating along the east coast of Australia. The catch of S. lewini was heavily biased towards males, and there were significant differences in von Bertalanffy growth parameters (L(∞) and k) and maturity [stretched total length (L(ST)) and age (A) at which 50% are mature, L(ST50) and A(50)] between those caught in the tropics (L(∞) = 2119 mm, k = 0·163, L(ST50) = 1471 mm, A(50) = 5·7 years) and those caught in temperate waters (L(∞) = 3199 mm, k = 0·093, L(ST50) = 2043 mm, A(50) = 8·9 years). The best-fit estimates for a three-parameter von Bertalanffy growth curve fit to both sexes were L(∞) = 3312 mm, L(0) = 584 mm and k = 0·076. Males attained a maximum age of 21 years and grew to at least 2898 mm L(ST). The longevity, maximum length and maturity of females could not be estimated as mature animals could not be sourced from any fishery. Length at birth inferred from neonates with open umbilical scars was 465-563 mm L(ST). There was no significant difference in length and age at maturity of male and female S. mokarran, which reached 50% maturity at 2279 mm L(ST) and 8·3 years. Sphyrna mokarran grew at a similar rate to S. lewini and the best-fit estimates for a two-parameter von Bertalanffy equation fit to length-at-age data for sexes combined with an assumed mean length-at-birth of 700 mm were L(∞) = 4027 mm and k = 0·079. Females attained a maximum age of 39·1 years and grew to at least 4391 mm L(ST). The oldest male S. mokarran was 31·7 years old and 3691 mm L(ST). Validation of annual growth-band deposition in S. mokarran was achieved through a mark, tag and recapture study.     

亚洲茜草科粗叶木属及其相关属植物花粉形态研究

利用光学显微镜和扫描电镜研究了茜草科粗叶木属Lasianthus 16种2亚种、1变种及相关的5属5种的花粉形态。粗叶木属的花粉属于广孢型, 单粒。一般中等大小, 绝大多数为圆球形, 少数为近长球形或长球形。花粉形态特征, 特别是在萌发孔和外壁纹饰上表现出多样化。根据孔沟的数目或是否具有内孔, 可以将萌发孔分为(3-)4-(-5)孔沟和3孔。在所观察的这些种中, 萌发孔以3-4孔沟为主要类型, 比例为62.4%。外壁纹饰可分为细网状、粗网状和穴状。有部分种的花粉极面有穴状纹饰, 其余均为网状纹饰。网眼一般椭圆形、近圆形、三角形或者不规则形。少数外壁纹饰网脊上有颗粒状雕纹或模糊的颗粒, 网脊轮廓线呈波浪形, 一般凸出且平滑。大部分种的花粉具有沟膜, 沟膜上具有瘤状突起或小颗粒状, 沟边缘一般较平滑, 或粗糙, 有的种具有沟桥。     

Gametophyte morphology and gametangial ontogeny of Asplenium foreziense and related taxa (Aspleniaceae: Pteridophyta)

Gametophytes of Asplenium foreziense and related taxa have been studied by culture of spores on mineral agar and soil. Those of A. obovatum ssp. obovatum var. protobillotii and var. deltoideum , ssp. numidicum , and of A. macedonicum are described for the first time. Gametophyte development follows the Adiantum type in the A. obovatum group, and the Aspidium type in A. fontanum . Both types of development have been found in A. foreziense , depending on the sporophytic sample. The taxa with hairy gametophytes show significant differences in hair density. As in most of the homosporous ferns, antheridia are formed first and in a high proportion of gametophytes in the A. obovatum group and in A. fontanum , except for one sample; most of these male gametophytes become bisexual. In A. foreziense and A. macedonicum archegonia are formed first or at the same time as antheridia, but the proportion of female gametophytes is higher than in the other taxa; some of the gametophytes become bisexual, most of them differentiated from the female ones. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 87–98.     

Angel sharks (Squatinidae): A review of biological knowledge and exploitation

Angel sharks (Squatina spp.) are distributed in warm temperate to tropical waters around the world. Many species occur in shelf seas and exhibit seasonal inshore–offshore migrations, moving inshore to give birth. Consequently, there can be high spatial overlap of angel shark populations with fisheries and other human activities. Their dorso-ventrally flattened body shape, large size (most species attain >100 cm total length, L_T) and demersal nature means that they may be taken in a variety of demersal fishing gears from birth. Available data indicate that angel sharks typically have a biennial reproductive cycle, with litter sizes generally <20 and the young born at c. 20–30 cm. The biological characteristics of angel sharks render them susceptible to overexploitation, as exemplified by the decline of Squatina squatina from many parts of its former range in the north-east Atlantic and Mediterranean Sea. Currently, half of the 22 recognized extant species of angel shark are classed as Threatened on the International Union for Conservation of Nature (IUCN) Red List (with a further three classified as Data Deficient). Given the biological vulnerability of angel sharks, and that many species are data-limited, the current paper provides a review of available biological information and fisheries data pertaining to this family.     

Dental homologies in lamniform sharks (Chondrichthyes: Elasmobranchii).

The dentitions of lamniform sharks are said to exhibit a unique heterodonty called the "lamnoid tooth pattern." The presence of an inflated hollow "dental bulla" on each jaw cartilage allows the recognition of homologous teeth across most modern macrophagous lamniforms based on topographic correspondence through the "similarity test." In most macrophagous lamniforms, three tooth rows are supported by the upper dental bulla: two rows of large anterior teeth followed by a row of small intermediate teeth. The lower tooth row occluding between the two rows of upper anterior teeth is the first lower anterior tooth row. Like the first and second lower anterior tooth rows, the third lower tooth row is supported by the dental bulla and may be called the first lower intermediate tooth row. The lower intermediate tooth row occludes between the first and second upper lateral tooth rows situated distal to the upper dental bulla, and the rest of the upper and lower tooth rows, all called lateral tooth rows, occlude alternately. Tooth symmetry cannot be used to identify their dental homology. The presence of dental bullae can be regarded as a synapomorphy of Lamniformes and this character is more definable than the "lamnoid tooth pattern." The formation of the tooth pattern appears to be related to the evolution of dental bullae. This study constitutes the first demonstration of supraspecific tooth-to-tooth dental homologies in nonmammalian vertebrates.     

Late Cretaceous sharks from Cuba,first record of Serratolamna serrata (Agassiz) (Lamniformes,Serratolamnidae)

Only one species of Elasmobranchii, Ptychodus cyclodontis Mutter, Iturralde-Vinent and Carmona (2005), has been reported so far from the Late Cretaceous of Cuba. Herein we describe the first record of a Maastrichtian Serratolamna serrata (Agassiz, 1843) as well as non-diagnostic remains which include a tooth referred to a lamniform shark and an isolated vertebra of an indeterminate elasmobranch. These fossils expand the temporal distribution of Cretaceous fossil sharks known from Cuba and increase our understanding of the group’s fossil diversity.     

Maneuvering in juvenile carcharhinid and sphyrnid sharks: the role of the hammerhead shark cephalofoil

The peculiar head morphology of hammerhead sharks has spawned a variety of untested functional hypotheses. One of the most intuitively appealing ideas is that the anterior foil acts, as in canard-winged aircraft, to increase maneuverability. We tested this hypothesis by determining whether juveniles of two hammerhead species (Sphyrna tiburo and S. lewini) turn more sharply, more often, and with greater velocity than a juvenile carcharhinid shark (Carcharhinus plumbeus). Although the hammerheads were more maneuverable, further investigation revealed that they do not roll their body during turns, suggesting that the cephalofoil does not act as a steering wing. We also show that hammerhead sharks demonstrate greater lateral flexure in a turn than carcharhinids, and that this flexibility may be due to cross sectional shape rather than number of vertebrae.     

Pollen morphology of Brunellia (Brunelliaceae) and related taxa in the Cunoniaceae

Pollen grains of 24 species of Brunellia were examined with LM and SEM, in order to find additional taxonomic information for phylogenetic analysis. The pollen grains were found to be 3- colporate, tectate and to have variable exine pattern. Five types of exine pattern were observed: striate-reticulate (large lumina and high muri) to finely reticulate, modified reticulate (muri and lumina irregular in shape and at various levels), modified rugulate (irregular and with protruding tectal elements) and punctate (the lumina are smaller and rounded to slit-shaped). With reference to indication of taxonomic relationships the exine pattern is not informative at all; however it is useful, for defining taxonomic species as it is correlated to vegetative, inflorescence and fruit characteristics. It seems that the punctate type could be a plesiomorphic character while modified reticulate is a synapomorphy. Relationships in the pollen morphology of Brunellia and certain genera of Cunoniaceae are discussed. El polen de 24 especies de Brunellia fue examinado en el microscopio de luz (ML) y el microscopio electrónico (MES) para encontrar información taxonómica adicional y usar esta información en el estudio de relaciones filogenéticas. El grano de polen es 3-colporado, tectado y con una alta variabile ornamentación de la exina. Se observaron cuatro categorías en la ornamentación de la exina del grano de pollen: reticulado estriado (luminas grandes y muros altos) a finamente reticulado, reticulado modificado (muros y lúminas de forma irregular y en varios niveles), rugulada modificada (irregular y proyectando elementos tectales) y la ornamentación de tipo punteado (las lúminas son pequen～as redondeadas o en forma de líneas). Desde el punto de vista de relaciones filogenéticas la ornamentación de la exina es parcialmente un carácter informativo. Sin embargo, la ornamentación es útil para definir las especies taxonomicamente por la correlacion de este carácter con caracteres vegetativos, de inflorescencia o del fruto. El tipo de ornamentación punteado parece ser el estado plesiomórfico, mientras que la ornamentación modificada reticulada es una sinapomorf´ L a. Se discuten las relaciones del grano de polen de Brunellia y ciertos géneros de Cunoniaceae.     

Comparative seed morphology and character evolution in the genus Lysimachia (Myrsinaceae) and related taxa

Summary We investigated seed morphology in 34 species of the genus Lysimachia and in 14 species and two subspecies of six additional genera (Anagallis, Ardisiandra, Asterolinon, Glaux, Pelletiera, Trientalis), which have been shown to be closely related to, or are placed within Lysimachia in previous molecular studies. We studied seed shape, seed coat structure, and seed coat surface patterns. Three major types of seed shape were identified: (1) sectoroid, (2) polyhedral, and (3) coarsely rugose with concave hilar area. In addition, seeds may be keeled or winged. The outer layer of the seed coat is either sponge-like and adhering only loosely to the inner seed coat or it is thin and tightly adhering to the underlying tissue. Seed surface patterns can be divided into six main types: (1) reticulate, (2) tuberculate, (3) vesiculose, (4) colliculate, (5) undulate, or (6) poroid-alveolate. Seed surface patterns are mostly congruent with molecular phylogenetic relationships. A reticulate surface pattern is diagnostic of, e.g. Lysimachia subgenera Palladia and Hawaiian Lysimachiopsis. Mapping seed characters onto a recent phylogenetic tree, reveals that they provide potentially synapomorphic character states for various subclades of Lysimachia. Salient examples include a rugose seed shape, which turns out to be synapomorphic for the clade comprising the genus Pelletiera plus Asterolinon linum-stellatum and a sponge-like outer seed coat layer, which characterizes a clade with Lysimachia vulgaris, L. thyrsiflora, and L. terrestris, with an analogue that apparently evolved in parallel in Trientalis europaea. We also discuss possible habitat factors that may have favored the independent evolution of particular seed types such as winged seeds in various lineages.     

The vascular morphology and in vivo muscle temperatures of thresher sharks (Alopiidae)

The thresher sharks comprise a single family (Alopiidae) of pelagic sharks most easily recognized by the elongate dorsal lobe of their caudal fin. Despite morphological similarities among the alopiids, the common thresher (Alopias vulpinus) is unique in that its red, aerobic myotomal muscle (RM) is medially positioned (i.e., closer to the vertebrae), its systemic blood is supplied through a lateral circulation which give rise to counter‐current heat exchanging retia, and it is capable of regional RM endothermy. Despite this information, it remains unknown if the other two alopiid species (bigeye thresher, Alopias superciliosus and pelagic thresher, Alopias pelagicus) also possess some or all of the characteristics related to regional RM endothermy. Thus, this study aimed to 1) document the presence of vascular specializations necessary for heat retention and RM endothermy and 2) measure the in vivo muscle temperatures of all three alopiid species. Laboratory dissections of the thresher species showed that only A. vulpinus possesses the lateral branching of the dorsal aorta giving rise to a lateral subcutaneous circulation and retial system, and that RM temperatures are elevated relative to ambient temperature. By contrast, both A. pelagicus and A. superciliosus have a similar systemic blood circulation pathway, in which the dorsal aorta and postcardinal vein form the basis for the central circulation and in vivo RM temperature measurements closely matched those of the ambient temperature at which the sharks were captured. Collectively, the vascular anatomy and in vivo temperature data suggest that only one species of thresher shark (A. vulpinus) possesses the requisite vascular specializations (i.e., lateral subcutaneous vessels and retia mirabilia) that facilitate RM endothermy. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Tooth development and histology patterns in lamniform sharks (Elasmobranchii,Lamniformes) revisited

The dentition of lamniforme sharks exhibits several characters that have been used extensively to resolve the phylogenetic relationships of extant taxa, yet some uncertainties remain. Also, the development of different teeth of a tooth file within the jaws of most extant lamniforms has not been documented to date. High‐resolution micro‐computed tomography is used here to re‐evaluate the importance of two dental characters within the order Lamniformes, which were considered not to be phylogenetically informative, the histotype and the number of teeth per tooth file. Additionally, the development and mineralization patterns of the teeth of the two osteodont lamniforms Lamna nasus and Alopias superciliosus were compared. We discuss the importance of these dental characters for phylogenetic interpretations to assess the quality of these characters in resolving lamniform relationships. The dental characters suggest that (1) Lamniformes are the only modern‐level sharks exhibiting the osteodont histotype, (2) the osteodont histotype in lamniform sharks is a derived state in modern‐level sharks (Elasmobranchii), (3) the osteodont type, conversely is convergently achieved when the clade Chondrichthyes is considered and thus might comprise a functional rather than a phylogenetic signal, and (4) there is an increase in the number of teeth per file throughout lamniform phylogeny. Structural development of the teeth of L. nasus and A. superciliosus is congruent with a previous investigation of the lamniform shark Carcharodon carcharias. J. Morphol. 277:1584–1598, 2016. © 2016 Wiley Periodicals, Inc.