Branchial Skeleton Research Articles

The morphology of the branchial skeleton of heterocongrines (Anguilliformes: Congridae) and its relation to their diet

Members of the subfamily Heterocongrinae (Congridae) are a peculiar group of anguilliform eels that construct sandy borrows, form large colonies, and are popularly recognized as garden eels. They live with most of their bodies inside self-constructed borrows exposing their heads and trunk to feed on zooplankton, preferably copepods, that are brought passively by currents. As plankton feeders there was a suspicion that their branchial skeleton would have structures that could aid in the filtering process, such as highly developed or modified branchial rakers, which are observed in other suspension-feeding fishes, such as anchovies and sardines. Branchial rakers, however, were considered to be absent across Anguilliformes (except for Protanguilla). Nonetheless, specimens that were examined using clearing and staining and computed tomography showed, in all cases, branchial rakers associated with their gill arches. Heterocongrines have branchial rakers across their first to fourth branchial arches. These rakers are conical and apparently unossified, but further studies are necessary to attest its degree of ossification or its complete absence. Their pharyngeal tooth plates are reduced, a condition that may reflect their preference for smaller food items. Additionally, they may use crossflow filtering to feed, although detailed studies are necessary to clarify if hydrosol sieving may also aid in food capture. Furthermore, the present study proposes that the presence of branchial rakers should be better investigated in Anguilliformes with similar feeding habits as heterocongrines, considering that these structures may be more widespread within the group than previously considered.

Large-bodied sabre-toothed anchovies reveal unanticipated ecological diversity in early Palaeogene teleosts.

Many modern groups of marine fishes first appear in the fossil record during the early Palaeogene (66–40 Ma), including iconic predatory lineages of spiny-rayed fishes that appear to have originated in response to ecological roles left empty after the Cretaceous/Palaeogene extinction. The hypothesis of extinction-mediated ecological release likewise predicts that other fish groups have adopted novel predatory ecologies. Here, we report remarkable trophic innovation in early Palaeogene clupeiforms (herrings and allies), a group whose modern representatives are generally small-bodied planktivores. Two forms, the early Eocene (Ypresian) †Clupeopsis from Belgium and a new genus from the middle Eocene (Lutetian) of Pakistan, bear conspicuous features indicative of predatory ecology, including large size, long gapes and caniniform dentition. Most remarkable is the presence of a single, massive vomerine fang offset from the midline in both. Numerous features of the neurocranium, suspensorium and branchial skeleton place these taxa on the engraulid (anchovy) stem as the earliest known representatives of the clade. The identification of large-bodied, piscivorous anchovies contributes to an emerging picture of a phylogenetically diverse guild of predatory ray-finned fishes in early Palaeogene marine settings, which include completely extinct lineages alongside members of modern marine groups and taxa that are today restricted to freshwater or deep-sea environments.

The branchial skeleton in Aptian chanid fishes (Gonorynchiformes) from the Araripe Basin (Brazil): Autecology and paleoecological implications

Gonorynchiformes are a small, but morphologically diverse group of teleost fishes with an extensive fossil record. Most extant gonorynchiforms are efficient filter feeders, bearing long gill rakers and other morphological specializations, such as microbranchiospines and an epibranchial organ. The analyses of the gill arch of the Brazilian gonorynchiform fishes Dastilbe crandalli and Tharrias araripis from the Aptian of the Araripe Basin, Northeast Brazil, demonstrate significant morphological variation suggestive of distinct feeding habitats as well as ontogenetic dietary shifts in these closely related gonorynchiforms.

The first skeletal record of the enigmatic Cretaceous sawfish genus Ptychotrygon (Chondrichthyes, Batoidea) from the Turonian of Morocco

AbstractA new fossil batoid (ray) Ptychotrygon rostrispatula sp. nov. is described from five exceptionally well‐preserved, three‐dimensional skeletal remains from the Turonian (Late Cretaceous) of Morocco. These specimens represent the first known skeletal remains for the genus Ptychotrygon and allow an almost complete description of the genus, providing a new insight into its phylogenetic relations and validating its taxonomic status as a member of the Sclerorhynchoidei. Mechanical preparation of the fossil remains revealed a relatively large batoid species (estimated total length above 1 m). Overall the morphology resembles that of sclerorhynchoids, with a robust hypertrophied rostrum that lacks enlarged rostral denticles with enlarged paddle‐like pectoral proximal elements (propterygium, mesopterygium and metapterygium). Never before seen details of the branchial skeleton are presented (large second hypobranchial without anterior process, which was probably fused to the basibranchial and no evidence of articulation with other branchial element). To assess the phylogenetic relations of these specimens within the sclerorhynchoids a parsimonious analysis using TNT and PAUP was performed. These analyses included Asflapristis cristadentis and Ptychotrygon rostrispatula sp. nov., which were used as representatives of Ptychotrygonidae, and also includes six other genera of sclerorhynchoids with relatively good skeletal remains. Both analyses recovered two monophyletic groups within sclerorhynchoids: the first contains Ischyrhiza, Onchopristis and Schizorhiza, and a second that includes Micropristis, Sclerorhynchus, Libanopristis and Ptychotrygonidae.

Cranial osteology of the Middle Jurassic (Callovian) Martillichthys renwickae (Neopterygii, Pachycormiformes) with comments on the evolution and ecology of edentulous pachycormiforms

AbstractOur understanding of the ecology and phylogenetic relationships of Pachycormiformes, a group of Mesozoic stem teleosts including the iconic Leedsichthys, has often been hindered by a lack of comprehensive morphological information. Micro‐CT scanning of an articulated, although flattened, cranium of the edentulous Martillichthys renwickae from the Middle Jurassic (Callovian) Oxford Clay of the UK reveals previously unknown internal details of the most complete suspension‐feeding pachycormiform skull known, including the palate, braincase and branchial skeleton. The latter preserves gill rakers with elongate, pointed projections similar to those of Asthenocormus, in contrast to the finer fimbriations associated with Leedsichthys. We also reinterpret some previously described features, including dermal bone patterns of the snout, skull roof and lower jaw, and the morphology of the ventral hyoid arch. These new anatomical data reinforce the phylogenetic placement of Martillichthys as part of the Jurassic clade of edentulous pachycormiforms. The elongate skull geometry of these Jurassic taxa is strikingly similar to that of Ohmdenia, the sister taxon to edentulous pachycormiforms, but contrasts sharply with the morphology of the Late Cretaceous edentulous pachycormiform Bonnerichthys, raising questions over the phylogenetic relationships among these taxa. Most significantly, Martillichthys shows specialized characters with a restricted phylogenetic distribution among suspension‐feeding pachycormiforms, including the distinctive gill rakers and a greatly extended occipital stalk. Our analysis of Martillichthys supports past interpretations of a close relationship with Asthenocormus, and provides a model for interpreting the less complete remains of other members of this enigmatic group of fishes.

The first three-dimensional fossils of Cretaceous sclerorhynchid sawfish: Asflapristis cristadentis gen. et sp. nov., and implications for the phylogenetic relations of the Sclerorhynchoidei (Chondrichthyes)

A new fossil batoid (ray), Asflapristis cristadentis gen. et sp. nov., is described from six exceptionally well-preserved, three-dimensional skeletal remains from the Turonian (Late Cretaceous) of Morocco. Mechanical and acid preparation and computed tomographic scanning of these specimens reveal details of much of the proximal skeleton, especially the skull, synarcual and pectoral skeleton, with only the more distal parts of the skeleton missing. These fossils represent a relatively large animal (62 cm preserved length, estimated total length approximately 2 metres) possessing a robust rostrum that lacks enlarged rostral denticles. It has a narrow and small chondrocranium with jaws that are relatively large compared to the rest of the skull and robust with highly ornamented teeth that lack cusps. The branchial skeleton shows a large second hypobranchial without an anterior process, which was probably fused to the basibranchial as in other sclerorhynchoids. The synarcual is large and lacks centra through its entire length, with no direct connection to the pectoral girdle observed. Pectoral fins probably possessed enlarged proximal elements (propterygium, mesopterygium and metapterygium); the articulation facet between the coracoid and the pectoral elements was reduced. A phylogenetic analysis using both parsimony and Bayesian methods was performed incorporating this new taxon. Both analyses recovered a phylogenetic topology that places the sclerorhynchoids in a close relation to rajoids and clearly separated from the morphologically similar Pristidae within the Rhinopristiformes. With respect to the extant taxa, the phylogenies generated are similar to that obtained from molecular analysis of modern batoids. The palaeoecological implication of this discovery suggests that the Asfla assemblage was not from a ‘normal’ open carbonate shelf but rather a restricted environment favouring a low-diversity chondrichthyan fauna.http://zoobank.org/urn:lsid:zoobank.org:pub:7752385F-817D-40BF-961C-1AF7B9093E14

An enigmatic braincase from Five Points, Ohio (Westphalian D) further supports a stem tetrapod position for aïstopods

ABSTRACTWe describe a new specimen of the aïstopodOestocephalusfrom Five Points, Ohio, which preserves much of the posterior braincase. The specimen, the largest aïstopod skull described, preserves the postorbital region to the occiput. The posterior braincase has coossified the basioccipital, exoccipitals, and opisthotic. The parasphenoid is rostrally restricted, toothless, and highly vaulted along the cultriform process. The lateral walls of the cultriform process are further reinforced by large longitudinally running, ventral flanges from the parietals. Two large endochondral ventral projections from the basioccipital, previously interpreted as basal tuberosities for hypaxial muscle insertion, are here instead interpreted as articulations for the branchial skeleton. This interpretation is further supported by traces of vasculature that is consistent with what is seen in gill-bearing species. A model for the reorganisation of the basicranial region on the transition from hyomandibula to stapes is proposed, which suggests that gills, or gill-support skeletal elements, might be further distributed along the tetrapod stem than previously thought. These data further support the placement of aïstopods in the tetrapod stem group and require a reconsideration of our understanding of early tetrapod evolution.

Comparative anatomy of the gill skeleton of fossil Aulopiformes (Teleostei: Eurypterygii)

Gill skeletons provide a rich source of character information for inferring the relationships among extant fishes. However, the difficulties in accessing branchial structures in fossils have limited the use of gill-arch anatomy in phylogenetic studies of extinct fishes. Here we apply micro-computed tomography (µCT) to visualize and describe gill-arch anatomy in three-dimensionally preserved Late Cretaceous–early Palaeogene remains of seven genera attributed to the eurypterygian clade Aulopiformes (lizardfishes), a group for which detailed cladistic character sets describing patterns of variation in the branchial skeleton are available. We evaluate the placement of these fossil taxa based on characters of the gill skeleton in isolation. Our results support an alepisauroid placement for †Apateodus corneti, †Cimolichthys lewesiensis and †Halec eupterygius, and a stem synodontid affinity for †Argillichthys toombsi and †Labrophagus esocinus. These placements are broadly consistent with past hypotheses based either on formal cladistic argumentation or qualitative morphological comparison drawing on other skeletal systems. We find insufficient evidence in the branchial skeleton to place †Aulopopsis depressifrons more specifically than Aulopiformes incertae sedis. Gill-arch anatomy substantially revises past interpretations of †Sardinioides illustrans by providing clear evidence for placement within Aulopiformes generally, and as either a stem aulopid or stem paralopid more specifically. This species must therefore be removed from †Sardinioides, the type of which is a myctophiform and shows conspicuous anatomical differences from †‘S.’ illustrans. Our work provides proof-of-concept for the recovery of detailed information on gill skeleton anatomy in fossils, indicating the potential for the extraction of considerable new morphological data – and phylogenetic information – from suitably preserved fossil specimens.

Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton.

The posterior pharyngeal segments of the vertebrate head give rise to the branchial skeleton, the primary site of food processing in fish. The morphology of the fish branchial skeleton is matched to a species' diet. Threespine stickleback fish (Gasterosteus aculeatus) have emerged as a model system to study the genetic and developmental basis of evolved differences in a variety of traits. Marine populations of sticklebacks have repeatedly colonized countless new freshwater lakes and creeks. Adaptation to the new diet in these freshwater environments likely underlies a series of craniofacial changes that have evolved repeatedly in independently derived freshwater populations. These include three major patterning changes to the branchial skeleton: reductions in the number and length of gill raker bones, increases in pharyngeal tooth number, and increased branchial bone lengths. Here we describe a detailed protocol to dissect and flat-mount the internal branchial skeleton in threespine stickleback fish. Dissection of the entire three-dimensional branchial skeleton and mounting it flat into a largely two-dimensional prep allows for the easy visualization and quantification of branchial skeleton morphology. This dissection method is inexpensive, fast, relatively easy, and applicable to a wide variety of fish species. In sticklebacks, this efficient method allows the quantification of skeletal morphology in genetic crosses to map genomic regions controlling craniofacial patterning.

Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton

Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton

First acanthodian from the Upper Devonian (Frasnian) Gogo Formation, Western Australia

A new acanthodiform acanthodian Halimacanthodes ahlbergi n. gen. n. sp., based on a single uncrushed, partial articulated specimen, represents the first acanthodian collected from the Gogo Formation, Canning Basin, Western Australia. The delicate perichondral ossifications of the lower jaws, branchial skeleton and endoskeletal shoulder girdle are preserved in 3D. H. ahlbergi n. gen. n. sp. is characterised by having a tall slender scapular shaft, paired pelvic fin spines, mineralised branchial arches and scales with an anterior median depression and a microornament of tiny smooth tubercles randomly distributed on the crown. In having paired pelvic spines and lacking prepelvic spines, it is most closely related to Howittacanthus kentoni from Frasnian lacustrine deposits of eastern Victoria. Isolated scales, here attributed to the new taxon, are found in the coeval Gneudna Formation, Carnarvon Basin, Western Australia.

A new species of Laccognathus (Sarcopterygii, Porolepiformes) from the Late Devonian of Ellesmere Island, Nunavut, Canada

ABSTRACT Recent work in the Late Devonian (Frasnian) Fram Formation of Ellesmere Island, Nunavut, Canada, has produced the first North American record of Laccognathus (Sarcopterygii, Porolepiformes), a taxon previously known only from Latvia and Russia. Represented by a large sample that includes cranial material from 22 individuals, Laccognathus embryi, sp. nov., is uniquely diagnosed by features including the absence of marginal teeth on coronoids 1 and 2, and the lack of a fifth posthyal branchial arch. The large sample allows detailed morphological description of many parts of the cranial skeleton, including the dermal skull, braincase, palatoquadrate, and branchial skeleton. Comparison of the faunas from the Fram Formation in Nunavut, the Escuminac Formation in Quebec, and the Lode and Gauja formations of Latvia confirms a Laurussian (Euramerican) biogeographic province in the late Middle/early Late Devonian and may indicate tolerance of some forms to varied salinities. A cranial reconstruction of the new taxon reveals a wide head with a width-to-length ratio of approximately 2:1, a large spiracular opening, a small orbit, and a lower jaw in which much of the labial surface faced ventrally. The cranial morphology suggests a benthic animal reliant on sit-and-wait predation.

SoxE gene duplication and development of the lamprey branchial skeleton: Insights into development and evolution of the neural crest

SoxE genes are multifunctional transcriptional regulators that play key roles in specification and differentiation of neural crest. Three members (Sox8, Sox9, Sox10) are expressed in the neural crest and are thought to modulate the expression and activity of each other. In addition to regulating the expression of other early neural crest marker genes, SoxE genes are required for development of cartilage. Here we investigated the role of SoxE genes in development of the neural crest-derived branchial skeleton in the sea lamprey. Using a morpholino knockdown approach, we show that all three SoxE genes described in lamprey are required for branchial basket development. Our results suggest that SoxE1 and SoxE2 are required for specification of the chondrogenic neural crest. SoxE3 plays a morphogenetic role in patterning of the branchial basket and may be required for the development of mucocartilage, a tissue unique to larval lampreys. While the lamprey branchial basket develops primarily from an elastin-like major extracellular matrix protein that is specific to lampreys, fibrillar collagen is also expressed in developing branchial cartilage and may be regulated by the lamprey SoxE genes. Our data suggest that the regulation of Type II collagen by Sox9 might have been co-opted by the neural crest in development of the branchial skeleton following the divergence of agnathan and gnathostome vertebrates. Finally, our results also have implications for understanding the independent evolution of duplicated SoxE genes among agnathan and gnathostome vertebrates.

Development of the viscerocranial skeleton during embryogenesis of the sea lamprey,Petromyzon Marinus

Evolution of the skeleton was a key transition in early vertebrates. Lampreys lack a mineralized skeleton but possess cartilaginous neurocranial and viscerocranial elements. In lampreys, the visceral skeleton develops as a fused branchial basket supporting the pharynx. Here, we have adapted Alcian blue staining of lamprey cartilage and show this method results in cartilage fluorescence that we used to describe development of the branchial skeleton in Petromyzon marinus between 17 and 63 days of development. We show that skeletal rods develop from condensations of flattened discoidal chondrocytes and may involve cellular intercalation. Lamprey trabecular, parachordal, and subchordal cartilages consist of aggregations of polygonal chondrocytes positioned on the ventral and lateral surfaces of the notochord. We speculate that morphological differences relate to functional differences in the cartilage. We show that differentiated skeletal rods are derived from neural crest. Finally, we show how branchial muscles intercalate with skeletal rods of the branchial basket.

The cranial endoskeleton of Tiktaalik roseae

Among the morphological changes that occurred during the 'fish-to-tetrapod' transition was a marked reorganization of the cranial endoskeleton. Details of this transition, including the sequence of character acquisition, have not been evident from the fossil record. Here we describe the braincase, palatoquadrate and branchial skeleton of Tiktaalik roseae, the Late Devonian sarcopterygian fish most closely related to tetrapods. Although retaining a primitive configuration in many respects, the cranial endoskeleton of T. roseae shares derived features with tetrapods such as a large basal articulation and a flat, horizontally oriented entopterygoid. Other features in T. roseae, like the short, straight hyomandibula, show morphology intermediate between the condition observed in more primitive fish and that observed in tetrapods. The combination of characters in T. roseae helps to resolve the relative timing of modifications in the cranial endoskeleton. The sequence of modifications suggests changes in head mobility and intracranial kinesis that have ramifications for the origin of vertebrate terrestriality.

Ontogenetic variations in characters of Euchone analis (Krøyer, 1856) (Polychaeta, Sabellidae, Sabellinae) from Spitsbergen, and new assignments of Oriopsis ingelorae Plate, 1995 and O. liefdefjordensis Plate, 1995

Abstract Euchone analis, the type species of its genus, was collected in high densities and in different size classes from Kongsfjorden, west Spitsbergen. This material has provided the basis for an investigation of the size dependence of characters. Almost all characters used in diagnoses were highly variable, especially the number of abdominal chaetigers forming the anal depression and the shape of the depression. The only relatively constant features are the number of chaetigers anterior to the anal depression and the branchial crown‐to‐body length ratio. A branchial skeleton extension of the radiolar appendages of the dorsal lips was found for the first time within Euchone, and this character has been added to the diagnosis of Euchone. Oriopsis liefdefjordensis and small specimens of E. analis agree in all characters, and O. liefdefjordensis is proposed to be a junior synonym of E. analis. Characters found in O. ingelorae are in accordance with those described for Chone, and we propose assigning O. ingelorae to this genus. The significance of ontogenetic character variations in the Sabellidae is discussed.

Fish-like gills and breathing in the earliest known tetrapod

THE origin of tetrapods is generally associated with the emergence of terrestrial vertebrate life. Anatomical features unique to tetrapods are usually considered to be adaptations to the terrestrial environment. Here we report the discovery of a fish-like branchial skeleton in Acanthostega gunnari, from the Upper Devonian of East Greenland, one of the earliest tetrapods known. It shows a proximally expanded ceratohyal and large, ventrally grooved ceratobranchials. Such grooves are found in the ceratobranchials of modern fishes, and house the afferent branchial aortic arches. The shoulder girdle bears a postbranchial lamina along its anterior margin. In fishes this supports the posterior wall of the opercular chamber. Acanthostega seems to have retained fish-like internal gills and an open opercular chamber for use in aquatic respiration, implying that the earliest tetrapods were not fully terrestrial. The discovery provides information on the sequence of acquisition of tetrapod characters, and supports previous suggestions that such characters as legs with digits1 evolved first for use in water.

Topography and nerve supply of the cucullaris (trapezius) of skates

Dissections of Sudan black B stained specimens reveal that, of a complex of medial, intermediate, and lateral muscles of skates, presumed homologous to the cucullaris of sharks, only the lateral muscle is innervated by a branch or branches of the vagus and is inserted, in part, to the fused pharyngobranchials of the caudal visceral arches. The medial and intermediate muscles are supplied by separate branches of rostral spinal nerves and do not attach to the branchial skeleton. The lateral muscle therefore is the most likely homologue of the cucullaris (trapezius) of sharks and perhaps other fishes and tetrapods. The medial and intermediate muscles appear to be part of the axial musculature.

Homeobox genes and models for patterning the hindbrain and branchial arches

Abstract Antennapedia class homeobox genes, which in insects are involved in regional specification of the segmented central regions of the body, have been implicated in a similar role in the vertebrate hindbrain. The development of the hindbrain involves the establishment of compartments which are subsequently made distinct from each other by Hox gene expression, implying that the lineage of neural cells may be an important factor in their development. The hindbrain produces the neural crest that gives rise to the cartilages of the branchial skeleton. Lineage also seems to be important in the neural crest, as experiments have shown that the crest will form cartilages appropriate to its level of origin when grafted to a heterotopic location. We show how the Hox genes could also be involved in patterning the mesenchymal structures of the branchial skeleton. Recently it has been proposed that the rhombomere-restricted expression pattern of Hox 2 genes is the result of a tight spatially localised induction from underlying head mesoderm, in which a prepattern of Hox expression is visible. We find no evidence for this model, our data being consistent with the idea that the spatially localised expression pattern is a result of segmentation processes whose final stages are intrinsic to the neural plate. We suggest the following model for patterning in the branchial region. At first a segment-restricted code of Hox gene expression becomes established in the neuroepithelium and adjacent presumptive neural crest. This expression is then maintained in the neural crest during migration, resulting in a Hox code in the cranial ganglia and branchial mesenchyme that reflects the crest’s rhombomere of origin. The final stage is the establishment of Hox 2 expression in the surface ectoderm which is brought into contact with neural crest-derived branchial mesenchyme. The Hox code of the branchial ectoderm is established later in development than that of the neural plate and crest, and involves the same combination of genes as the underlying crest. Experimental observations suggest the idea of an instructive interaction between branchial crest and its overlying ectoderm, which would be consistent with our observations. The distribution of clusters of Antennapedia class genes within the animal kingdom suggests that the primitive chordates ancestral to vertebrates had at least one Hox cluster. The origin of the vertebrates is thought to have been intimately linked to the appearance of the neural crest, initially in the branchial region. Our data are consistent with the idea that the branchial region of the head arose in evolution before the more anterior parts, the development of the branchial region employing the Hox genes in a more determinate patterning system. In this scenario, the anterior parts of the head arose subsequently, which may explain the greater importance of interactions in their development, and the fact that Antennapedia class Hox genes are not expressed there.

Glycolipoprotein complex in the lobster branchial skeleton

A chitin-lipoprotein complex was detected in the pre-exuvial lobster shell. The aqueous extract of this skeleton contains a lipoprotein in its highest molecular weight fraction where the phospholipids constitute the main component. Changes in the lipoprotein crystalline structure with temperature were detected, but not the formation of typical liquid crystals.