Alguns restos de peixes fósseis do Devoniano Médio (Eifeliano-Givetiano) da Formação Pimenteira da Bacia do Parnaíba, Nordeste do Brasil

Some Middle Devonian (late Eifelian-early Givetian) fossil fish remains are described from an outcrop of the Pimenteira Formation on the eastern border of the Parnaíba Basin (Picos area, State of Piauí, northeast Brazil). These remains include a fin spine with ribbed ornament, a bicuspid shark tooth similar to those of xenacanths and omalodontids, a badly-preserved Machaeracanthus spine, and small indeterminate scales and fragments of what may be prismatically calcified cartilage. The bicuspid tooth is the first record of its kind from the Devonian of Brazil and the first unequivocal Devonian record from South America. Its principal cusps have widely spaced cristae, like teeth of the Gondwanan Devonian elasmobranch Antarctilamna, but small intermediate cusps are absent (as in Leonodus). The fin spine has comparable ornament to those of Ctenacanthus, Antarctilamna, and Doliodus, but is too poorly preserved for accurate determination. Machaeracanthus is the most widespread Devonian vertebrate in the Malvinokaffric Realm, and its spines are also known from the Old World and Eastern Americas realms, although scales referred to the genus are reported from outside these three regions. The occurrences of Machaeracanthus spines in the Parnaíba and Amazon basins lends support to an earlier proposal based on the distribution of invertebrate fossils that these basins provided maritime connections existed between the Malvinokaffric and the Old World/Eastern Americas realms during the late Eifelian - early Givetian.Restos de peixes fósseis do Devoniano Médio (Neo-eifeliano - Eogivetiano) são descritos da Formação Pimenteira, em sua faixa aflorante na margem oriental da Bacia do Parnaíba (região de Picos, PI, nordeste do Brasil). Os fósseis incluem um espinho de nadadeira ornamentado com costelas, um dente bicúspide de tubarão similar aos dos xenacantos e omalodôntidas, e um espinho mal preservado de Machaeracanthus. Além disso, registram-se pequenas escamas indeterminadas e possíveis fragmentos de cartilagem com calcificação prismática. O dente bicúspide constitui o primeiro achado dessa natureza no Devoniano do Brasil, sendo também o primeiro com registro inequívoco no Devoniano da América do Sul. Suas cúspides principais possuem cristas bem espaçadas entre si (tal como se verifica nos dentes de Antarctilamna, um elasmobrânquio devoniano do Gondwana), porém inexistem pequenas cúspides intermediárias (como em Leonodus). O espinho da nadadeira possui ornamentação comparável à de Ctenacanthus, Antarctilamna e Doliodus, porém a sua má preservacão não permite uma determinação segura. Machaeracanthus é o vertebrado devoniano com a mais ampla distribuição no Reino Malvinocáfrico, e seus espinhos são também conhecidos nos reinos do Velho Mundo e América Oriental, embora escamas referidas ao gênero tenham sido assinaladas fora dessas três regiões. A ocorrência de espinhos de Machaeracanthus nas bacias do Parnaíba e Amazonas reforça uma proposta anterior (baseada na distribuição de certos invertebrados fósseis) de conexões marinhas entre essas duas bacias e os reinos Malvinocáfrico, do Velho Mundo e da América Oriental durante o Neo-eifeliano - Eogivetiano

Nominal species referred to Ctenacanthus

20 p. ; 26 cm.Includes bibliographical references (p. 16-20)."All known nominal species of the Paleozoic chondrichthyan genus Ctenacanthus are listed, together with information concerning provenance, whereabouts of type material (where known), important subsequent references and comments on the probable affinities of each species. Other references to undetermined Ctenacanthus spp. are listed chronologically. Of some 100 species, 10 are considered totally invalid; the holotypes of five others are known to be lost or destroyed; four others are founded on inadequate material; 10 are referred to the Acanthodii; eight are referred to another spine genus, Acondylacanthus; three are referred to Asteroptychius; nine are referred to Sphenacanthus; 20 are referred to various other genera; eight are considered close to Ctenacanthus but are excluded from it; and 23 are left in Ctenacanthus. Of the latter, however, eight are probably synonyms of the type species, C. major, and consequently only 15 species are retained. Of these, seven are from the Upper Devonian and eight are from the Lower Carboniferous; all are from marine strata. This stratigraphic range is much less than the previous records have suggested"--P. [1]

Braincase in Paleozoic sharks

122 p. : ill. (some col.) ; 26 cm.Includes bibliographical references (p. 116-122).The concepts of platytrabia/platybasia and tropibasia/tropitrabia in gnathostomes are reviewed. The terms platytrabia and tropitrabia refer to developmental states of the embryonic trabecular cartilages that can be determined only by ontogenetic studies. The terms platybasia and tropibasia originally had this meaning, but have subsequently taken on additional descriptive connotations involving morphological features in the prechordal part of the adult chondrocranium. However, platybasia and tropibasia are not synonymous with platytrabia and tropitrabia. In gnathostomes, platytrabia usually gives rise to a platybasic adult condition (but not invariably; e.g., Lepisosteus), and tropitrabia usually gives rise to the tropibasic condition (modern elasmobranchs may be an exception). Thus, ontogeny does not provide an absolute guide to the adult condition, nor does adult morphology provide an accurate means to assess the prior ontogenetic condition in gnathostomes. Platybasia and tropibasia are regarded here as useful morphological terms that can be applied to fossils or to extant forms for which ontogenetic data are not available (although it may still be possible to reach some ontogenetic conclusions, based on morphological observations). A well-preserved but disarticulated fossil symmoriiform shark braincase from the Pennsylvanian of Arkansas is described under the informal generic designation "Cobelodus", using digital reconstructions made from a high-resolution computerized-tomography (CT) scan. The braincase is morphologically tropibasic and clearly represents a departure from the common platybasic pattern found in elasmobranchs (e.g., Tamiobatis, Cladodoides, Orthacanthus). The contribution made by the embryonic polar cartilage in "Cobelodus" was probably extensive (unlike in modern gnathostomes), as in the platybasic Paleozoic shark Cladodoides. Thus, tropibasia in "Cobelodus" seems to be superimposed on an already-specialized pattern of cranial morphology found in some early platybasic elasmobranchs. The basicranial arterial circuit in "Cobelodus" was highly modified, and its internal carotids could not have communicated with the cranial cavity via the bucco-hypophyseal chamber as in other elasmobranchs. Internal carotids either were absent or met the efferent pseudobranchials within the orbit before the combined vessel entered the cranial cavity via the orbital cartilage, but the arrangement was certainly not osteichthyan-like (where the combined internal carotid/efferent pseudobranchial arteries pass through the basisphenoid pillar). "Cobelodus" and many other Paleozoic sharks possessed a postorbital palatoquadrate articulation (possibly strengthened by ligaments above the articulation in "Cobelodus"), on cartilage presumably formed in the embryonic lateral commissure. This arrangement differs from that in amphistylic hexanchiform sharks, where the lateral commissure is absent and there is no postorbital arcade; the postorbital articulation is located instead on the primary postorbital process (an outgrowth of the supraorbital shelf). Hexanchiforms are the only extant elasmobranchs with a postorbital articulation, but do not occupy a basal position in modern morphological and molecular phylogenetic analyses. Amphistyly in hexanchiforms is therefore viewed as a derived state rather than a highly conserved feature. No hyomandibular facet has been identified in "Cobelodus", suggesting that its epihyal had only a ligamentous connection to the braincase. However, previous suggestions that symmoriiforms were aphetohyoidean (with a complete hyoidean gill slit and "unmodified" hyoid arch) are not supported by morphological evidence. The systematic classification of symmoriiform sharks is in disarray. Symmoriiforms collectively are probably monophyletic, but within them only the family Falcatidae is characterized convincingly by synapomorphies. Remaining symmoriiforms have been traditionally classified as "stethacanthids" and "symmoriids", based respectively on the presence or absence of a spine-brush complex, but that distinction seems artificial because no undisputable "brushless male symmoriids" or "brushed female stethacanthids" have been documented and because sex-linked dimorphism of the spine-brush complex has been demonstrated only in falcatids. The braincase in Cladoselache shares some unusual features with "Cobelodus", suggesting that Cladoselache and symmoriiforms are closely related, but it has yet to be determined whether Cladoselache was morphologically platybasic or tropibasic

Historical review and revised diagnosis of Ctenacanthus, with a list of referred taxa

22 p. : ill. ; 26 cm.Includes bibliographical references (p. 21-22)."Ctenacanthus Agassiz is a genus of elasmobranch, originally recognized by its dorsal finspines but now known from more complete remains. However, many other fossils, including isolated spines and complete fish, have been included in Ctenacanthus, although the spines differ from those of the type species, C. major, and from other presumably related species. Earlier diagnoses of Ctenacanthus are critically reviewed and the significance of previous diagnostic changes is discussed. It is concluded that Ctenacanthus sensu lato is paraphyletic. Some spines previously assigned to this taxon resemble living elasmobranch finspines, whereas others resemble hybodontid finspines. The fish described by Dean as Ctenacanthus clarkii should be referred to C. compressus. Both C. clarkii and C. compressus finspines are sufficiently like those of C. major for these species to remain within the genus. Ctenacanthus compressus is the only articulated Paleozoic shark so far described which can be assigned to Ctenacanthus. Ctenacanthus costellatus finspines are not like those of C. major, but instead resemble Sphenacanthus spines. Goodrichthys eskdalensis may be closely related to Ctenacanthus"--P. [1]

Hybodont sharks

48 p. : ill. ; 26 cm.Includes bibliographical references (p. 42-48)

Bythiacanthus St. John and Worthen, Amelacanthus, new genus, Eunemacanthus St. John and Worthen, Sphenacanthus Agassiz, and Wodnika Münster

24 p. : ill. ; 26 cm.Includes bibliographical references (p. 22-24)."Some of the finspines originally referred to Ctenacanthus are reassigned to other taxa. Several characteristically tuberculate lower Carboniferous finspines are referred to Bythiacanthus St. John and Worthen, including one of Agassiz's original species, Ctenacanthus brevis. Finspines referable to Bythiacanthus are known from western Europe, the U.S.S.R., and North America. Amelacanthus, new genus, is described on the basis of finspines from the United Kingdom. Four species are recognized, two of which were originally assigned to Onchus by Agassiz, and all four of which were referred to Ctenacanthus by Davis. Eunemacanthus St. John and Worthen is revised to include some European and North American species. Sphenacanthus Agassiz is shown to be a distinct taxon from Ctenacanthus Agassiz, on the basis of finspine morphology, and its widespread occurrence in the Carboniferous of North America is demonstrated. Similarities are noted between the finspines of Sphenacanthus and Wodnika, and both taxa are placed provisionally in the family Sphenacanthidae. A new species of Wodnika, W. borealis, is recognized on the basis of a finspine from the Permian of Alaska"--P. [1]

New genus of Late Cretaceous angel shark

29 pages : illustrations ; 26 cm.Three-dimensional Late Cretaceous elasmobranch endoskeletal elements (including palatoquadrates, ceratohyals, braincase fragments, and a series of anterior vertebrae) are described from the Late Cretaceous University of Alabama Harrell Station Paleontological Site (HSPS), Dallas County, Alabama. The material is referred to the extant elasmobranch Family Squatinidae on the basis of several distinctive morphological features. It also exhibits features not shared by any modern or fossil Squatina species or the extinct Late Jurassic squatinid Pseudorhina. A new genus and species is erected, despite there being some uncertainty regarding potential synonymy with existing nominal species previously founded on isolated fossil teeth (curiously, no squatinid teeth have been documented from the HSPS). A preliminary phylogenetic analysis suggests that the new genus falls on the squatinid stem, phylogenetically closer to Squatina than Pseudorhina. The craniovertebral articulation in the new genus exhibits features considered convergent with modern batomorphs (skates and rays), including absence of contact between the posterior basicranium and first vertebral centrum, and a notochordal canal which fails to reach the parachordal basicranium. Supporting evidence that similarities in the craniovertebral articulation of squatinoids and batomorphs are convergent rather than synapomorphic (as "hypnosqualeans") is presented by an undescribed Early Jurassic batomorph, in which an occipital hemicentrum articulates with the first vertebral centrum as in all modern sharklike (selachimorph) elasmobranchs. The fossil suggests instead that the batomorph synarcual evolved by fusion of the anterior basiventral and basidorsal cartilages prior to the reduction of the anterior centra and loss of the occipital hemicentrum, not afterward as predicted by the hypnosqualean hypothesis

A New Paleozoic Symmoriiformes (Chondrichthyes) from the Late Carboniferous of Kansas (USA) and Cladistic Analysis of Early Chondrichthyans

BACKGROUND: The relationships of cartilaginous fishes are discussed in the light of well preserved three-dimensional Paleozoic specimens. There is no consensus to date on the interrelationship of Paleozoic chondrichthyans, although three main phylogenetic hypotheses exist in the current literature: 1. the Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are grouped along with the modern sharks (neoselachians) into a clade which is sister group of holocephalans; 2. the Symmoriiformes are related to holocephalans, whereas the other Paleozoic shark-like chondrichthyans are related to neoselachians; 3. many Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are stem chondrichthyans, whereas stem and crown holocephalans are sister group to the stem and crown neoselachians in a crown-chondrichthyan clade. This third hypothesis was proposed recently, based mainly on dental characters. METHODOLOGY/PRINCIPAL FINDINGS: On the basis of two well preserved chondrichthyan neurocrania from the Late Carboniferous of Kansas, USA, we describe here a new species of Symmoriiformes, Kawichthys moodiei gen. et sp. nov., which was investigated by means of computerized X-ray synchrotron microtomography. We present a new phylogenetic analysis based on neurocranial characters, which supports the third hypothesis and corroborates the hypothesis that crown-group chondrichthyans (Holocephali+Neoselachii) form a tightly-knit group within the chondrichthyan total group, by providing additional, non dental characters. CONCLUSIONS/SIGNIFICANCE: Our results highlight the importance of new well preserved Paleozoic fossils and new techniques of observation, and suggest that a new look at the synapomorphies of the crown-group chondrichthyans would be worthwhile in terms of understanding the adaptive significance of phylogenetically important characters

Extinct teleost fish

27 p. : ill., 1 map ; 26 cm.Includes bibliographical references (p. 23-25).A new species of teleost, Araripichthys axelrodi, is described from the Lower Cretaceous (Aptian) Machiques Member of the Apon Formation, Venezuela. Its phylogenetic and biogeographic relationships are discussed; the new species represents both the oldest and the most primitive member of the genus. Araripichthys probably originated in the Pacific or western (Caribbean) Tethys and apparently dispersed eastward by the Albian, a pattern paralleled by Aptian and Albian foraminifers. The phylogenetic position of Araripichthys is problematic; previously it has been classified either as an advanced teleost (within acanthomorphs) or at a much more primitive level within teleosts (as an elopocephalan incertae sedis). This uncertainty is compounded further by similarity to Ferrifrons and Acanthichthys (family Ferrifronsidae), two late Cretaceous genera that have been classified as primitive acanthopterygians. Araripichthys and the Ferrifronsidae display a curious mix of characters; they share some features with higher teleosts (clupeocephalans, neoteleosts, acanthomorphs), but lack (or are unknown in) many other characters of those groups. Consequently, these extinct taxa cannot be placed satisfactorily within a current phylogenetic framework of teleost fishes, but few characters support inclusion of Araripichthys within any group of higher teleosts

Two extinct clupeomorphs

35 p. : ill. ; 26 cm.Includes bibliographical references (p. 31-34).Two extinct clupeomorphs, †Ellimma branneri from the Cretaceous of Brazil and †Diplomystus shengliensis from the Eocene of China, are redescribed. †Ellimma branneri was formerly classified within the Clupeiformes, but it lacks derived characters of clupeiforms and clupeoids. Dorsal scute 'wings' are expanded and subrectangular in †Ellimma and other members of the family †Paraclupeidae Chang and Chou (1977), approximately equal to †Ellimmichthyidae Grande (1982a). Consequently, †Ellimma branneri is classified here within the family †Paraclupeidae. †Paraclupeidae are known from the Lower Cretaceous to the middle Eocene. In the present work, two monophyletic groups are identified within the †Paraclupeidae. One group (subfamily †Paraclupeinae of Chang and Grande, 1997), known only from the Lower Cretaceous (Hauterivian-Albian), includes †Paraclupea, †Ellimmichthys, and †Ellimma. These taxa are united by strongly sculptured, skull-roofing bones with ridges radiating from the growth center, and a dorsal scute ornament of prominent ridges. †Scutatuspinosus may also belong in this group. The other group includes †Diplomystus (Upper Cretaceous-Eocene) and †Armigatus (Upper Cretaceous), which are united by a single homoplaseous character (presence of a posteriorly expanded third hypural, leaving no gap between hypurals 2 and 4): this character also occurs in pristigasteroids, †Erichalcis, osteoglossids, some elopomorphs (†Lebanichthys lewisi, and most Albula spp.), and a number of ostariophysans not included in our analysis. †Paraclupeines are customarily regarded as being more closely related to the Clupeiformes than to other teleosts (i.e., as clupeomorphs), although no derived characters are uniquely shared by †Ellimma branneri and modern Clupeiformes. The relationships of †Ellimma and certain other extinct herring-like teleosts (including other †paraclupeines) with the Clupeiformes are unclear, and they may collectively form a paraphyletic assemblage. No biogeographical hypothesis satisfactorily explains the known distribution of nonmarine †paraclupeine fishes in the Cretaceous. A substantial portion of their nonmarine fossil record is missing (as evidenced by the recent discovery of a possible †paraclupeine, †Ezkutuberezi carmeni Poyato-Ariza et al., 2000, in Spain), and some aspects of their early distribution pattern may have involved marine dispersal. Eocene †Diplomystus occurs on both sides of the Pacific Ocean, but the "Pacifica" hypothesis (which lacks empirical support) is abandoned as an explanation for such Eocene (and younger) trans-Pacific distribution patterns of nonmarine fishes. Instead, a "freshwater Arctic Ocean" hypothesis is favored. According to this hypothesis (for which there are several independent lines of geological evidence), temporary desalination of the Arctic Ocean occurred during the Paleocene and early Eocene, which may have permitted freshwater fishes to move unimpeded by salt-water barriers between Asia and North America; this temporary desalination event may eventually become recognized as a significant factor in the holarctic distribution patterns of various Tertiary-Recent freshwater fishes