Caudal Skeleton Research Articles

Platydoras birindellii, new species of striped raphael catfish (Siluriformes: Doradidae) from the Xingu Basin, Brazil

A new species of Platydoras is described from the rio Xingu Basin, Brazil. Platydoras birindellii is distinguished from congeners by having gas bladder simple (vs. with posterior secondary chamber) and dorsal and caudal fins uniformly dusky (vs. with distinct marks composed of dark broad band or blotch on central portion of dorsal fin and pair of dark broad stripes on caudal fin, one central to each lobe). Platydoras birindellii shares a simple gas bladder with the sister taxon to Platydoras,Centrochir crocodili, a monotypic genus endemic to the Magdalena Basin. With respect to the caudal skeleton, the parhypural is incompletely fused to hypurals 1+2 in P. birindellii, a condition that is intermediate between those of Centrochir (parhypural typically separated from hypurals 1+2 by distinct suture) and Platydoras (parhypural typically fully fused to hypurals 1+2). Platydoras birindellii is commonly found in rocky clearwater rapids and apparently endemic to the middle and upper portions of the Xingu draining the Brazilian Shield.

Evolution of caudal fin ray development and caudal fin hypural diastema complex in spotted gar, teleosts, and other neopterygian fishes.

The caudal fin of actinopterygians transitioned from a heterocercal dorsoventrally asymmetrical fin to a homocercal externally symmetrical fin in teleosts through poorly understood evolutionary developmental mechanisms. We studied the caudal skeleton of major living actinopterygian lineages, including polypteriformes, acipenseriformes, Holostei (gars and bowfin), and teleosts, compared with reports of extinct neopterygians and basal teleosteans. We focused on the hypural diastema complex, which includes (1) a gap between hypurals 2 and 3, that (2) separates two plates of connective tissue at (3) the branching of caudal vasculature; these features had been considered as a shared, derived trait of teleosts, a synapomorphy. These studies revealed that gars and teleosts share all three features of the hypural diastema complex. Absence of a complex with these features from bowfin, fossil Holostei, and stem Teleostei argues in favor of repetitive, independent emergence in several neopterygian and basal Teleostei lineages, or less likely, many independent losses. We further observed that, in gars and teleosts, the earliest developing lepidotrichia align with the horizontal adult body axis, thus participating in external symmetry. These results suggest that the hypural diastema complex in teleosts and gars represents a homoplasy among neopterygians and that it emerged repeatedly by parallel evolution due to shared inherited underlying genetic and developmental programs (latent homology). Because the hypural diastema complex exists in gars with heterocercal tails, this complex is independent of homocercality. Developmental Dynamics 247:832-853, 2018. © 2018 Wiley Periodicals, Inc.

Effects of thyroid hormones on vertebral numbers in two cyprinid fish species:Rutilus rutilus(Linnaeus, 1758) andAbramis brama(Linnaeus, 1758)

Previous studies revealed that thyroid hormones (TH) are crucial regulators of fish development and that manipulation of the thyroid gland function can induce developmental heterochronies. These heterochronies are known to be responsible for changes in the number of serially repeating skeletal elements, such as scales, fin rays and pharyngeal teeth. The present study demonstrates that thyroid function manipulation provokes heterochronies in the development of the fish axial skeleton. We studied the variation of the total vertebral numbers as well as the vertebral numbers in different regions of axial skeleton as influenced by manipulation of level of thyroid hormone in two cyprinid species – the common roach Rutilus rutilus (Linnaeus, 1758) and bream Abramis brama (Linnaeus, 1758). As a result, the numbers of total and caudal (more rarely, abdominal) vertebrae were significantly altered. TH-treated fish demonstrated a reduced number of vertebrae at an earlier completion of calcification and at a smaller body size. This finding agrees well with the concept of pleomerism sensu C. C. Lindsey (1975). Another effect of TH on the phenotype of the axial skeleton was the frequent increase in the number of vertebrae in the caudal skeleton (four in place of the normal three) because of non-fusions in the urostyle.

The caudal skeleton of Arambourgthurus scombrurus (Arambourg, 1967), a Paleogene oceanic surgeonfish

Abstract A detailed description of the caudal skeleton of the Paleogene nasine surgeonfish Arambourgthurus scombrurus is provided herein. The compound (urostylar) centrum is fused with a large, nearly triangular, thick hypural plate, formed by consolidated hypurals 1–4. The compound centrum supports a large autogenous parhypural bearing a thick and blunt hypurapophysis. Hypural 5 is a small triangular bone. There is a single elongate autogenous uroneural and three epurals, the first of which is remarkably stout and elongate, with its proximal end embraced by the open neural arch of the second preural vertebra. The haemal spines of the second and third preural vertebrae are fused to their respective centra. The phylogenetic relationships of Arambourgthurus are discussed. Arambourgthurus shares some features with the Eocene Sorbinithurus and the Miocene Marosichthys, and together they constitute a monophyletic group that represents the sister group of the pair formed by the extant genus Naso and the fossil ...

Paraclupea seilacheri sp. nov., un arenque de doble armadura (Clupeomorpha, Ellimmichthyiformes) de las calizas albianas de la cantera Tlayúa, Puebla, México

Paraclupea seilacheri sp. nov. is described in this paper. This ellimmichthyiform fish from the Albian deposits of the Tlayúa quarry, near Tepexi de Rodríguez, Puebla, central Mexico, shows the diagnostic characters of the superorder Clupeomorpha (the otophysic connection, commissure of the supratemporal sensory canal passing through parietals, and the abdominal scute series), order Ellimmichthyiformes (parietals in contact to each other along the midline of the skull; a beryciform foramen in the anterior ceratohyal; three epurals in the caudal skeleton; and a series of predorsal scutes), and family Paraclupeidae (predorsal scutes with increasing sizes in anterioposterior order and postpelvic abdominal scutes with a strong ventral spine). Additionally, the characters of this new Mexican fish are distinctive and support the creation of a new species of the genus Paraclupea, these include a diamond shaped body moderately high; 18 predorsal scutes strongly ornamented with radiating ridges; most posterior predorsal scutes are subrectangular, wider than long; the abdominal scutes are spatula-like; the dorsal process of posttemporal bone is hypertrophied; and the second uroneural is short and distally reaches the end of the first uroneural. The present finding introduces the second species of the genus Paraclupea; a significative increase in the geographical distribution of this genus in the Northern Hemisphere, from eastern China to the southern North America; and the third North American Cretaceous paraclupeid after Tycheroichthys dunveganensis and Scutatoclupea applegatei.

Eurypterygii caudal skeleton

The osteology of the caudal skeleton in representatives of 41 genera in 39 families of eurypterygian fishes was studied. The caudal skeleton of eurypterygian fishes consists of five or six hypurals, a parhypural, one to three epurals, one or two pairs of uroneurals, ural centra 1 and 2, last preural centra and associated neural and haemal spines, and procurrent and principal rays. Eurypterygians like other teleosts have a diural caudal skeleton (two ural cen-tra). Primitively in basal Acanthomorpha and Acanthopterygii, the caudal elements are autog-enous and several intercaudal and postcaudal cartilages support these isolated elements. Basal groups usually have six autogenous hypurals, three epurals, two pairs of autogenous neurals, autogenous ural centrum 2, and autogenous haemal and neural spines on the last centra. In some basal groups such as Myctophidae, many of the caudal elements are fused, because of the presence of primitive conditions in related taxa, the fusion in such a groups should be re-garded as secondary and independent from that in higher taxa. In higher groups, there is a tendency for the elements to fuse together and to the centra and caudal cartilage are lost due to lack of function. In specialized groups

Comparative anatomy of the caudal skeleton of lantern fishes of the genus Triphoturus Fraser-Brunner, 1949 (Teleostei: Myctophidae)

The caudal skeleton provides important information for the study of the systematics and ecomorphology of teleostean fish. However, studies based on the analysis of osteological traits are scarce for fishes in the order Myctophiformes. This paper describes the anatomy of the caudal bones of 3 Triphoturus species: T. mexicanus (Gilbert, 1890), T. nigrescens (Brauer, 1904) and T. oculeum (Garman, 1899). A comparative analysis was performed on cleared and stained specimens to identify the differences and similarities of bony elements and the organization of the caudal skeleton among the selected species. Triphoturus mexicanus differs from T. oculeum in the presence of medial neural plates and a foramen in the parhypural, while T. nigrescens differs from their congeners in a higher number of hypurals (2 + 4 = 6) and the separation and number of cartilaginous elements. This osteological description of the caudal region allowed updates to the nomenclature of bony and cartilaginous elements in myctophids. Further, this study allows for the recognition of structural differences between T. mexicanus and T. oculeum, as well as the major morphological distinction between T. nigrescens and their sister species.

Osteology of the crescent gunnel Pholis laeta and the phylogeny of the family Pholidae (Cottiformes, Zoarcoidei).

This study provides a complete description of the osteology of the crescent gunnel Pholis laeta based on cleared-and-stained specimens and X-rays to help provide sufficient morphological data to generate a robust phylogeny for the family Pholidae. Pholis laeta exhibits high variation in the structure of its caudal skeleton. The length of the preural (pu)2 neural spine is variably reduced (most common) or elongated (i.e. of similar length to that of pu3). Additionally, the neural spine of pu3 is either bifurcated or single. These results document and describe characters useful for phylogenetic inference of the family, including the insertion pattern of anal-fin pterygiophores between haemal spines. Pholidae was recovered as monophyletic (synapomorphies: ribs absent, haemonephropophyses present, gill membranes broadly joined, first neural arch fused to centrum, first anal-fin spine very robust, the dorsal fin comprises only spines and the presence of five branchiostegals), with monophyletic genera Pholis and Apodichthys (Rhodymenichthys is monotypic) and Apodichthys and Rhodymenichthys as sister taxa. The elongation of its pu2 neural spine defines Pholis and synapomorphies for Apodichthys include five infraorbital bones, no pelvic fin, a hypertrophied first anal-fin spine, the presence of two or three empty interhaemal spaces after the anteriormost anal-fin spine and having 35-46 abdominal vertebrae. Apodichthys and Rhodymenichthys are sister taxa based on the continuity of the caudal fin with the dorsal and anal fins and uniform colouration. Future study is needed to more fully resolve the interrelationships of species within Pholidae (especially the genus Pholis) and solidify the position of Pholidae within the Zoarcoidei.

Osteological development of wild-captured larvae and a juvenile Sebastes koreanus (Pisces, Scorpaenoidei) from the Yellow Sea

The osteological development in Sebastes koreanus is described and illustrated on the basis of 32 larvae [6.11–11.10 mm body length (BL)] and a single juvenile (18.60 mm BL) collected from the Yellow Sea. The first-ossified skeletal elements, which are related to feeding, swimming, and respiration, appear in larvae of 6.27 mm BL; these include the jaw bones, palatine, opercular, hyoid arch, and pectoral girdle. All skeletal elements are fully ossified in the juvenile observed in the study. Ossification of the neurocranium started in the frontal, pterotic, and parietal regions at 6.27 mm BL, and then in the parasphenoid and basioccipital regions at 8.17 mm BL. The vertebrae had started to ossify at ~7.17 mm BL, and their ossification was nearly complete at 11.10 mm BL. In the juvenile, although ossification of the pectoral girdle was fully complete, the fusion of the scapula and uppermost radial had not yet occurred. Thus, the scapula and uppermost radial fuse during or after the juvenile stage. The five hypurals in the caudal skeleton were also fused to form three hypural elements. The osteological results are discussed from a functional viewpoint and in terms of the comparative osteological development in related species.

Development of the Vertebral Column and Caudal Skeleton in Prochilodus lineatus Larvae under Laboratory Conditions

Se describe el desarrollo osteologico de la columna vertebral y del esqueleto caudal en larvas de sabalo (Prochilodus lineatus) bajo condiciones controladas hasta los 30 dias posteriores a la eclosion (dpe). El inicio de la formacion de la columna vertebral fue observado entre los 10-12 dpe (8,3 mm de longitud estandar, LE) con la aparicion de los primeros procesos neurales, hemales y cuerpos vertebrales pre-caudales. La osificacion de la columna vertebral ocurrio en sentido craneo-caudal y fue completa a los 28 dpe (22,6 mm LE). El esqueleto caudal inicio su desarrollo entre los 6 y 8 dpe con la formacion de los hipurales (H), parahipural (PH) y los radios caudales principales y secundarios. Los H 1 al 3 se formaron como primordios cartilaginosos en la cara ventral de la porcion distal de la notocorda, mientras que posteriormente se formaron los H 4 al 6 y el PH. Los primeros radios de la aleta caudal fueron observados en correspondencia con la formacion de los H 2 y 3, mientras que a los 28 dpe se observo la completa formacion de los mismos, existiendo 10 radios en el lobulo dorsal y 9 en el lobulo ventral. Los epurales, en numero de tres, fueron evidentes como elementos cartilaginosos en dorsal de la notocorda y distalmente a los arcos neurales, permaneciendo sin osificarse hasta los 25 dpe. El complejo centro ural se constituyo por la fusion de tres estructuras, el centro preural 1, el ural 1 y 2. El desarrollo de la columna vertebral y del esqueleto caudal muestran patrones similares a los descriptos en otros teleosteos.

Mid-Cretaceous acanthomorph fishes with the description of a new species from the Turonian of Lac des Bois, Northwest Territories, Canada

A single specimen of a new acanthomorph fish is described from a Turonian locality sampling the northern part of the Cretaceous Western Interior Seaway. This brings to three the number of acanthomorphs from Lac des Bois, Northwest Territories, Canada. The previously named acanthomorph, Boreiohydrias dayi (Boriohydriidae), was placed in the Polymixiiformes. The second, represented by a poorly preserved fish, was left unnamed and incertae sedis in Acanthomorpha. The new one described here, Cumbaaichthys oxyrhynchus gen. et sp. nov. cannot be easily placed in any previously described families. This fish is placed in the Polymixiiformes based on the caudal skeleton having 18 principal rays (16 branched), and having a full neural spine on the second preural centrum. Polymixiiform relationships are not well established but they are the subject of several current studies; therefore, the new acanthomorph is placed incertae sedis within this order but with the understanding that this placement may be refined with future work. Previous studies have suggested that acanthomorphs may have flourished with warming climates of the Cenomanian–Turonian. A comprehensive survey of named acanthomorphs from mid-Cretaceous deposits shows there are more species known from the Cenomanian rather than the Turonian, although this may be biased by the age of known fossiliferous deposits.

The evolution of sexually dimorphic tail feathers is not associated with tail skeleton dimorphism

Sexual selection can influence the evolution of sexually dimorphic exaggerated display structures. Herein, we explore whether such costly ornamental integumentary structures evolve independently or if they are correlated with phenotypic change in the associated skeletal system. In birds, elongate tail feathers have frequently evolved in males and are beneficial as intraspecific display structures but impart a locomotor/energetic cost. Using the sexually dimorphic tail feathers of several passeriform species as a model system, we test the hypothesis that taxa with sexually dimorphic tail feathers also exhibit sexual dimorphism in the caudal skeleton that supports the muscles and integument of the tail apparatus. Caudal skeletal morphology is quantified using both geometric morphometrics and linear morphometrics across four sexually dimorphic passeriform species and four closely related monomorphic species. Sexual dimorphism is assessed using permutational MANOVA. Sexual dimorphism in caudal skeletal morphology is found only in those taxa that exhibit active functional differences in tail use between males and females. Thus, dimorphism in tail feather length is not necessarily correlated with the evolution of caudal skeletal dimorphism. Sexual selection is sufficient to generate phenotypic divergence in integumentary display structures between the sexes, but these change are not reflected in the underlying caudal skeleton. This suggests that caudal feathers and bones evolve semi‐independently from one another and evolve at different rates in response to different types of selective pressures.

Chanopsis lombardi (Teleostei, Osteoglossiformes) from the continental Lower Cretaceous of the Democratic Republic of Congo. Comments on the evolution of the caudal skeleton within osteoglossiform fishes

Chanopsis lombardi (Teleostei, Osteoglossiformes) du Crétacé inférieur continental de la République Démocratique du Congo. Commentaires sur l’évolution du squelette caudal chez les poissons ostéoglossiformes. Le crâne, la ceinture pectorale, les vertèbres, le squelette caudal et les écailles du téléostéen ostéoglossiforme Chanopsis lombardi, du Crétacé inférieur continental de la République Démocratique du Congo, sont étudiés en détails. Les caractères caudaux et les écailles de Chanopsis situent ce poisson comme le membre le plus primitif de la famille des Osteoglossidae sensu lato (incluant les Pantodontidae et les Arapaimidae), ceux des Singididae (Singida et Chauliopareion) montrent que cette famille représente une lignée distincte des Osteoglossidae.

The Caudal Skeleton of the Zebrafish, Danio rerio, from a Phylogenetic Perspective: A Polyural Interpretation of Homologous Structures.

The structure of the caudal skeleton of extant teleost fishes has been interpreted in two different ways. In a diural interpretation, a caudal skeleton is composed of two centra articulated with one to six hypurals. Most subsequent authors have followed this interpretation. In contrast, a polyural interpretation considers the teleost fin to be derived from a fully metameristic ancestral bauplan originally composed of a one-to-one relationship between neural arches, centra (when present), and hypurals. Three different interpretations of the identity and homology of skeletal components of the caudal skeleton of the teleost fish Danio rerio have been proposed, two from a diural perspective and one from a polyural perspective. We examine each caudal skeletal component of Danio rerio from both a developmental and phylogenetic perspective. We propose that a polyural interpretation of structures is consistent with the current interpretation of the basal neopterygian caudal fin for this model organism rather than the older diural interpretation that does not take into account the metamerism observed in caudal structures during development. The polyural interpretation suggests several shared evolutionary innovations of major clades that would remain undiscovered under the older diural naming paradigm and makes the terminology of the parts of the caudal fin of Danio rerio strictly comparable to more basal fishes.

Skeletal anatomy of the early morid fish Eophycis (Gadiformes, Moridae) from an Oligocene deposit in Poland

The family Moridae (Gadiformes) is diagnosed by an otophysic connection, a horizontal gas bladder septum, unique otoliths and a specific architecture of the caudal skeleton. Their skeletal fossil record is rather scarce and uncertain: the oldest proven representatives (from Oligocene sites of the Paratethys area) are classified in the genus Eophycis. Newly collected specimens from the Hermanowa locality (Poland) allow the description of and commentary on previously unknown characters. The species Eophycis jamnensis was a typical morid fish with an elongated body, a triangular head, and single dorsal and anal fins that are not coalesced with the caudal fin. This species was most similar to the Recent species Guttigadus nana that differs from it (as from other Eophycis species) in meristic features, having two dorsal fins but lacking a vomer. A brief review of the fossil skeletal record of morid fish is presented.

Osteology and ontogeny of the wrymouths, genus Cryptacanthodes (Cottiformes: Zoarcoidei: Cryptacanthodidae)

ABSTRACTCover illustration. Cryptacanthodes maculatus (Cryptacanthodidae), caudal skeleton. Cryptacanthodidae are eel‐like, burrowing fishes distributed in the cold‐temperate coastal waters of the North Pacific and the western North Atlantic. In this issue of the Journal of Morphology, Schnell and Hilton (pp. 185–208 10.1002/jmor.20331) describe the osteology and aspects of the ontogenetic skeletal development of two Cryptacanthodes species and discuss the phylogenetic relationships of Cryptacanthodidae among other zoarcoid families.

Early Development of the Caudal Fin Skeleton of Capelin,Mallotus villosus(Osmeridae)

Development of the caudal fin skeleton of capelin, Mallotus villosus, is described based on observations of cleared-and-stained specimens from a wild caught growth series ranging in size from 4.2 mm notochord length (NL) to 144 mm standard length (SL). The sequence of chondrification and ossification for each element is described and compared with that of related salmonoid and esocoid fishes. Caudal fin elements are first chondrified in specimens that are 8.9 mm NL and all elements are ossified by 52 mm SL. In general, hypaxial elements (e.g., parhypural, hypurals, hemal arches and spines of preural vertebrae) develop before epaxial elements (e.g., epurals, uroneurals, neural arches and spines of preural vertebrae). Preural centra are among the last elements to form in the caudal skeleton of M. villosus. Interestingly, preural centrum 1 does not form. The caudal fin skeleton morphology of adult M. villosus is nearly identical to that of other osmerid species, and the developmental sequence of the caudal s...

Review of the osteology of the fossil fish formerly attributed to the genus †Chanoides and implications for the definition of otophysan bony characters

Three fossil species were formerly referred to the stem otophysan genus †Chanoides: †C. macropoma from the Middle Eocene of Monte Bolca, Italy, ‘†Chanoides’ chardoni from the Campano–Maastrichtian of Nardò, Italy, and †C. weberi from the Santonian of Apricena, Italy. Moreover, a monogeneric family Chanoididae was proposed as a consequence of the 40 million year range covered by this fossil record. The stem position of these species amongst otophysans, a large clade with debated interrelationships, leads us to review their anatomy with the double aim of improving their systematics and bringing new elements to understand otophysan character evolution. We clarify the anatomy of the two valid species †C. macropoma and ‘†Chanoides’ chardoni, including reinterpretation of the ethmovomerian and maxillary regions, Weberian structures and caudal skeleton; we invalidate †C. weberi nom. dub. and include ‘†C.’ chardoni in the new genus †Nardonoides; we discuss the bony apomorphies of the otophysan clade as a whole and the orders included in it and notably propose to retain only the presence of a Weberian apparatus as the apomorphy to define Otophysi.http://zoobank.org/urn:lsid:zoobank.org:pub:E82A326C-1A35-4AC7-9C7F-778C3032A309

Ecology and caudal skeletal morphology in birds: the convergent evolution of pygostyle shape in underwater foraging taxa.

Birds exhibit a specialized tail that serves as an integral part of the flight apparatus, supplementing the role of the wings in facilitating high performance aerial locomotion. The evolution of this function for the tail contributed to the diversification of birds by allowing them to utilize a wider range of flight behaviors and thus exploit a greater range of ecological niches. The shape of the wings and the tail feathers influence the aerodynamic properties of a bird. Accordingly, taxa that habitually utilize different flight behaviors are characterized by different flight apparatus morphologies. This study explores whether differences in flight behavior are also associated with variation in caudal vertebra and pygostyle morphology. Details of the tail skeleton were characterized in 51 Aequornithes and Charadriiformes species. Free caudal vertebral morphology was measured using linear metrics. Variation in pygostyle morphology was characterized using Elliptical Fourier Analysis, a geometric morphometric method for the analysis of outline shapes. Each taxon was categorized based on flight style (flap, flap-glide, dynamic soar, etc.) and foraging style (aerial, terrestrial, plunge dive, etc.). Phylogenetic MANOVAs and Flexible Discriminant Analyses were used to test whether caudal skeletal morphology can be used to predict flight behavior. Foraging style groups differ significantly in pygostyle shape, and pygostyle shape predicts foraging style with less than 4% misclassification error. Four distinct lineages of underwater foraging birds exhibit an elongate, straight pygostyle, whereas aerial and terrestrial birds are characterized by a short, dorsally deflected pygostyle. Convergent evolution of a common pygostyle phenotype in diving birds suggests that this morphology is related to the mechanical demands of using the tail as a rudder during underwater foraging. Thus, distinct locomotor behaviors influence not only feather attributes but also the underlying caudal skeleton, reinforcing the importance of the entire caudal locomotor module in avian ecological diversification.

The origin of the bifurcated axial skeletal system in the twin-tail goldfish

Twin-tail goldfish possess a bifurcated caudal axial skeleton. The scarcity of this trait in nature suggests that a rare mutation, which drastically altered the mechanisms underlying axial skeleton formation, may have occurred during goldfish domestication. However, little is known about the molecular development of twin-tail goldfish. Here we show that the bifurcated caudal skeleton arises from a mutation in the chordin gene, which affects embryonic dorsal–ventral (DV) patterning. We demonstrate that formation of the bifurcated caudal axial skeleton requires a stop-codon mutation in one of two recently duplicated chordin genes; this mutation may have occurred within approximately 600 years of domestication. We also report that the ventral tissues of the twin-tail strain are enlarged, and form the embryonic bifurcated fin fold. However, unlike previously described chordin-deficient embryos, this is not accompanied by a reduction in anterior–dorsal neural tissues. These results provide insight into large-scale evolution arising from artificial selection.