Scale morphology and specialized dorsal scales of a new teleosteomorph fish from the Aptian of West Gondwana (original) (raw)
Related papers
Comptes Rendus De L Academie Des Sciences Serie Ii Fascicule A-sciences De La Terre Et Des Planetes, 2000
Scales of the lepisosteid fish †Obaichthys decoratus and †O.? laevis, from the Lower Cretaceous of the Araripe Plateau (Northeast Brazil) resemble those of palaeoniscoid-type, in which a ganoine layer overlies a dentin layer located above a basal plate composed of lamellar bone. However, the presence of canaliculi of Williamson in these scales confirms that †Obaichthys is a typical neopterygian. The scales of †Obaichthys differ from those of other gars, which do not have a dentin layer and that have ganoin tubercles with characteristic size and density. Our observations support the plesiomorphic status of †Obaichthys within the Lepisosteidae, and confirm the validity of the two species: †O. decoratus and †O.? laevis.Les écailles des deux lépisostées †Obaichthys decoratus et †O. ? laevis, du Crétacé inférieur du plateau d’Araripe (Nord-Est du Brésil) ressemblent aux écailles de type paléoniscoïde ; elles sont constituées d’une couche de ganoïne recouvrant une couche de dentine, elle-même située au-dessus d’une plaque basale d’os avasculaire. Cependant, la présence de canalicules de Williamson dans ces écailles confirme que le genre †Obaichthys est un Néoptérygien. Les écailles d’†Obaichthys diffèrent de celles des autres Lepisosteidae par la présence de dentine et par la taille et la densité des tubercules de la ganoïne. Nos résultats confirment l’état plésiomorphe d’†Obaichthys dans la famille des Lepisosteidae ainsi que la validité des deux espèces d’Obaichthys : †O. decoratus et †O. ? laevis.
The subclass Teleostei Müller was erected in 1845 to contain all fishes possessing intermuscular bones (e.g., epineurals and epipleurals) and two arterial valves (in the conus arteriosus), and that are characterized also by the absence of muscles at the basal arteria (ventral aorta). Since these characters proved difficult for diagnosing fossils, the content of Teleostei was problematic from the start. These three characters are valid and uniquely derived, but the recognition of the taxon Teleostei sensu Müller has been ignored for most of the past 150 years, and the content of the group has changed numerous times. Additionally, a polyphyletic concept of Teleostei was the predominant idea for most of the last century. It was only during the 1970s that the monophyly of Teleostei was demonstrated. Although its monophyly is accepted, its content and phylogenetic relationships have been a subject of disagreement, with only some recent consensus between morphologists and molecular biologists. Understanding the history of Teleostei requires knowledge of its fossils forms. The monophyly of the total group Teleostei, which now includes Triassic pholidophorids, is supported by numerous synapomorphies, such as autosphenotic without small dermal component; unpaired vomer (in adults); complete ring of two sclerotic bones oriented anterior and posterior to orbit; and a hypural articulating with a few caudal rays—with further transformations in more advanced teleosts. Current evidence indicates that some Late Triassic taxa ({Pholidophoretes salvus and {Knerichthys bronni) from Europe represent the oldest known {pholidophorids, and the European genus {Prohalecites from the Ladinian/Carnian (Triassic; c. 240 Ma) boundary represents the oldest stem teleost. The synapomorphies now shared by living teleosts appeared stepwise more than 100 million years ago in the common ancestors of the sequential sisters of now living groups; they did not originate in the common ancestor of the three main living teleost clades (elopomorphs, and osteoglossomorphs plus clupeocephalans), and the analyses of character distribution reflects the gradual accumulation of features that now diagnose Recent teleosts. A list of characters supporting these hierarchical phylogenetic levels is provided.
Miniature armored teleosts from the Albian-Cenomanian (Cretaceous) of Mexico
Small, armoured teleosts in the Albian/Cenomanian of the Muhi Quarry near Zimapán, State of Hidalgo, Mexico, are described as "monocentrid-like" (beryciforms) and acanthomorph incertae sedis. Two new genera and species, †Handuichthys interopercularis gen. et sp. nov. and †Pseudomonocentris microspinosus gen. et sp. nov., are established. The two species are distinct from the acanthomorph incertae sedis †Dalgoichthys tropicalis gen. et sp. nov. by having a large interopercle, differences in shape of subopercle and infraorbitals 2 and 3, and arrangement of the body shields (irregular in †Handuichthys and †Pseudomonocentris, but distributed in characteristic longitudinal rows in † Dalgoichthys). †Handuichthys interopercularis gen. et sp. nov. and †Pseudomonocentris microspinosus gen. et sp. nov. are placed in a new family, †Pseudomonocentrididae. Members of the family †Pseudomonocentrididae are small fishes less than 6 cm maximum length, with large head, balloon-like body, and short and narrow caudal peduncle resembling extant pinecone fishes or monocentrids. †Pseudomonocentrids have a large opercle, a small and narrow subopercle posteroventral to the opercle, and a large interopercle, which is longer than the ventral margin of the preopercle. Strong pelvic and anal spines are present, whereas dorsal spines are absent. Head bones and body shields are ornamented with tubercles and bony ridges, and the body is covered with heavily ossified, overlapping shields, which are not arranged in well-defined horizontal or vertical rows. In contrast, the body of †Dalgoichthys gen. nov. is covered with heavily ossified, overlapping shields ordered in rows in similar fashion as extant agonids. †Dalgoichthys gen. nov. presents a curious mosaic of cottiform and scorpaeniform features such as a parietal [= postparietal] bone fused with the extrascapula that makes its identification problematic; therefore, the fish is interpreted as an acanthomorph incertae sedis, an assigment that should be revised when more specimens become available.
2004
The dorsal gill-arch musculature (DGM), aspects of the associated skeleton, the transversus ventralis 4, and the semicircular ligament are described for many species in over 200 families and over 300 genera of teleostome fishes, and the DGM musculature of over 200 taxa is illustrated. A partially new system of DGM nomenclature is used. The transversus dorsalis, is shown to be a much more complex system than has been generally recognized. DGM data are variously analyzed and shown to be of importance for defining various currently recognized suprageneric pre-acanthomorph taxa. Among the many conclusions pertaining to acanthomorphs are: monophyly of Percopsiformes is hypothesized; Icosteidae, Menidae, and Centriscidae are probably more closely related to pre-percomorph groups than to percomorph groups; there is no basis for inclusion of Amarsipidae in the Stromateoidei; monophyly of the Polycentridae (Polycentriis, Polycentropsis, Afronandus, Monocirrhus) is corroborated based on a combination of gill-arch muscle and additional characters. A new ordinal-group name, Anabantomorpha, is erected to include the seven families with parasphenoid teeth: Nandidae, Badidae, Pristolepidae, Channidae, Anabantidae, Heleostomatidae, and Osphronemidae. Anabantoidei includes the last four of these families, which have suprabranchial organs. The superfamily name Labroidea is proposed to distinguish the unequivocally monophyletic group of families, Labridae, Odacidae, Scaridae, from other families included in the suborder Labroidei. The first synapomorphy for the gobioid family Odontobutidae is hypothesized based on the position of the levator interims 2 relative to the obliquus dorsalis. Certain gill-arch skeletal characters previously unrecognized or inadequately evaluated are reported and discussed (e.g., epibranchial-ceratobranchial accessory cartilages; relationship of epibranchials 5 and 4; epibranchial 4 flange; esophageal raphe). A separately authored appendix provides a cladistic analysis of 168 taxa in 147 acanthomorph families based almost exclusively on DGM and gill-arch skeletal characters. Among the many results implied by the study are: monophyly of Percopsiformes is corroborated. Smegmamorpha Johnson and Patterson (1993) are polyphyletic, and the name is rejected for nomenclatural purposes. Its constituents comprise two or three not closely related clades: Mugilomorpha + Atherinomorpha (= Percesoces Cope, 1875), Gasterosteomorpha, and. possibly, Centrisciformes (a pre-percomorph group, comprising only Centriscidae). Gasterosteomorpha includes a monophyletic Hypoptychidae {Hypoptychus + Aulichthys), Elassomatidae, Aulorhynchidae, monophyletic Synbranchiformes (Synbranchidae + Mastacembelidae), and Gasterosteidae, thus corroborating various hypotheses of Johnson and Patterson (1993) and Johnson and Springer (1997). Labroids are monophyletic only with inclusion of Pholidichthyidae, but the group remains supported only by pharyngognath characters. Blennioidei are monophyletic and their intra-relationships resolved. Their closest relatives are, stepwise: Gobiesocidae, Draconettidae (+ Callionymidae, which were not included in the analysis), Dactylopteridae. A new ordinal-group name, Benfhomorpha, is proposed for this clade. Caproidae are polyphyletic; relationships of its two genera appear to be with tetraodontiforms on the one hand, and acanthuroids, on the other. As such, Johnson and Patterson's (1993) hypothesis that caproid relationships are among percomorphs is corroborated. Sphyraenidae and Polynemidae form a monophyletic group (first proposed by Regan, 1912).
The actinopterygian postcranial skeleton is not as well known as its cranial counterpart, and consequently it is less represented in phylogenetic analyses. Due to this incomplete knowledge, it is often difficult to postulate hypotheses about homologous structures. Fin rays, scutes, fulcra, and spines have been traditionally interpreted as modified scales, but their diversity has been almost ignored. The present study reveals differences in the structure and role of procurrent rays, principal rays, rudimentary rays, and spines of unpaired fins in teleosteomorphs (including †'pholidophoriforms') versus "true" teleosts and other actinopterygians. Based on results presented here, revised definitions of these elements are provided.
Lepisosteoid-type scales are described in detail for the first time from the Barremian-Aptian (Lower Cretaceous) Quiric o Formation of the Sanfranciscana Basin, Southeastern Brazil. The specimens studied herein have been recovered from a new outcrop in northern Minas Gerais state and comprise a few nearly complete posterior scales and hundreds of scale fragments extracted from the sedimentary matrix. The scales are rhombic and preserve both the ganoine and the basal plate. The ganoine layer is thin, pierced by foramina and ornamented by microtubercles, showing the typical arrangement of superimposed sheets. The basal plate is composed by lamellar and woven bone, with flattened and isodia-metric osteocytes, canaliculi of Williamson, and Sharpey's fibers. An EDS analysis suggests diagenetic alteration of the basal plate but not the ganoine layer. The morphology of the specimens is similar to that of early neopterygian fishes, including ginglymodians and aspidorhynchids. A less inclusive identification is hampered by the fragmentary condition of the material and the lack of specific diagnostic features in this type of scale. This can be also extended to some isolated scales commonly referred to Lepidotes recovered from several sedimentary basins in the Jurassic-Cretaceous of Brazil. The results add a new record of ganoid scales in the Sanfranciscana Basin, and highlight the importance of more complete specimens rather than isolated scales for a genus-level identification of early neopterygian fishes.
While a polyphyletic concept of Teleostei has prevailed during most of the 20th century, the last 30 years have only produced hypotheses supporting the monophyly of the group on the basis of synapomorphies. The concept of the taxon Teleostei sensu and , with halecomorphs as a sister-group and the Jurassic-Cretaceous †Pachycormiformes and Aspidorhynchiformes at the base, has been questioned recently. A new hypothesis has been suggested (ARRATIA, 1999) with the Early Jurassic Pholidophorus bechei as the basal taxon. The Teleostei are characterized by one uniquely derived character (presence of an elongate posteroventral process in the quadrate) and numerous homoplasies (e.g., mobile premaxilla and ural neural arches modified as uroneurals). As the fossil record reveals, the teleostean synapomorphies were acquired in the Jurassic. Although there is apparently no doubt concerning the monophyly of main teleostean lineages, e.g., the Elopomorpha, Osteoglossomorpha, and Clupeocephala, their phylogenetic relationships remain still unresolved. Four hypotheses have currently been put forward with regards to the phylogenetic position of elopomorphs vs. osteoglossomorphs and more advanced teleosts, the clupeocephalans. A similar situation concerns the sister-group of Teleostei: several taxa compete for such a role. Possible candidates are Amiiformes, Lepisosteiformes, , †Pycnodontiformes, †Pachycormiformes, and †Aspidorhynchiformes. The resolution of this sistergroup relationship requires a better knowledge of the fossil candidates; while the sister-group of teleosts remains unknown the group can only be diagnosed (character-based), but not defined (e.g., stem-based). The tremendous advance in knowledge of teleostean phylogenies in the last 30 years has been made possible by the development of new techniques, new methodologies (e.g., cladistics), and by a significant amount of new morphological and ontogenetic data which have been accumulated during the last 150 years for both fossil and living teleosts. Although many aspects of the relationships of teleosts are well known, others remain incompletely explored, e.g., those dealing with the phylogenetic relationships of many teleostean subgroups. The current state of ichthyological research is an invitation to proceed further.