Browsing by Author "Maisey, John G."

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Open Access
Anatomical revision of the fossil shark Hybodus fraasi (Chondrichthyes, Elasmobranchii). American Museum novitates ; no. 2857
(New York, N.Y. : American Museum of Natural History, 1986) Maisey, John G.
The skeletal anatomy of Hybodus fraasi, an Upper Jurassic hybodontid shark from Solnhofen, has been reinvestigated. Its cranial anatomy is very similar to that of H. basanus, a Lower Cretaceous species, and both taxa share certain features not so far identified in Lower Jurassic hybodontids. Previous interpretation of the pectoral fin morphology is shown to be incorrect, and instead the pectorals of H. fraasi conform to a pattern that is apparently conservative for hybodontids. Dermal denticles from various regions of the body, together with special lateral line scales and teeth, are subjected to SEM investigation. The shagreen consists only of nongrowing denticles"--P. [1].
Open Access
The anatomy and interrelationships of Mesozoic hybodont sharks. American Museum novitates ; no. 2724
(New York, N.Y. : American Museum of Natural History, 1982) Maisey, John G.
Open Access
The braincase in Paleozoic symmoriiform and cladoselachian sharks ; Bulletin of the American Museum of Natural History, no. 307
(New York, NY : American Museum of Natural History, 2007) Maisey, John G.
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.
Open Access
Braincase of the Upper Devonian shark Cladodoides wildungensis (Chondrichthyes, Elasmobranchii), with observations on the braincase in early chondrichthyans. Bulletin of the AMNH ; no. 288
(New York, NY : American Museum of Natural History, 2005) Maisey, John G.
The braincase of an Upper Devonian shark (Cladodoides wildungensis) is investigated using high-resolution CT scanning, and its internal and external morphology is described from three-dimensional digital reconstructions. Many features are shared with modern elasmobranchs (neoselachians); these mostly represent conserved elasmobranch, chondrichthyan, or gnathostome characters. C. wildungensis resembles neoselachians in having a closed metotic fissure defining a glossopharyngeal canal, unlike some early chondrichthyans (e.g., Pucapampella, Orthacanthus) in which an open metotic fissure extends a considerable distance beneath the otic capsule. However, the glossopharyngeal canal in C. wildungensis is connected to a persistent dorsal fissure between the occipital arch and otic capsules, whereas this fissure becomes closed during neoselachian ontogeny. The embryonic polar cartilage apparently made a much greater contribution to the basicranium than in neoselachians and gnathostomes generally. This has affected the position of the efferent pseudobranchial foramen and the location of the orbital articulation in Cladodoides (both of which are located anteriorly in the orbit), as well as the size and extent of the dorsum sellae and the hypophyseal chamber inside the braincase. Another unusual feature in Cladodoides is the postorbital position of its trigeminal and facial nerves; instead of being situated in a trigemino-facial fossa of the orbit as in neoselachians, their foramina are located behind the postorbital process, although the pituitary vein and the origin of the external rectus eye muscle (located within the trigemino-facial fossa in neoselachians) both lie in the posterior part of the orbit. The oblique orientation of the postorbital arcade (derived from the embryonic lateral commissure) may be related to the exclusion of the trigeminal and facial nerves from the orbit. A laterally oriented canal through the process probably contained the trigeminal maxillary ramus (perhaps accompanied by the buccal ramus of the anterodorsal lateral line nerve). By contrast, in neoselachians these rami pass directly into the orbit (sometimes forming a buccal-maxillary complex), but they do not pass through the postorbital process. The Cladodoides braincase probably represents a juvenile or submature individual and shows indications of incomplete development (e.g., presence of a wide buccohypophyseal fenestra and absence of a precarotid commissure; incomplete enclosure of the internal carotids and orbital arteries by basicranial cartilage; incomplete closure of the braincase roof along the dorsal midline). The braincase also lacks multiple-layered prismatic calcification, possibly representing another juvenile feature. The phylogenetic relationship of Cladodoides wildungensis is discussed. Dental, postcranial, and cranial features lend some support to the old hypothesis that cladodont sharks form a monophyletic group. While such a view is at variance with several recently published phylogenetic analyses, many of the characters noted in the present work have yet to be tested within a rigorous cladistic framework, and their phylogenetic significance is uncertain.
Open Access
Coelacanths from the Lower Cretaceous of Brazil. American Museum novitates ; no. 2866
(New York, N.Y. : American Museum of Natural History, 1986) Maisey, John G.
"Specimens of Mawsonia sp. (possibly representing the type species, M. gigas), plus a new genus and species of fossil coelacanth, are described from the Romualdo Member of the Santana Formation, Chapada do Araripe, Ceara (Brazil). The new form, Axelrodichthys araripensis, is distinguished from other coelacanths on the basis of its cranial anatomy. The posterior moiety of the skull roof has a median dermal element plus three paired ossifications. Heavy rugose ornament of the dermal bones, the dermosphenotic morphology, and the number of paired posterior elements in the skull roof suggest that the new coelacanth is related to Mawsonia. A phylogenetic hypothesis is offered in which Mawsonia plus the new taxon represent the sister group of Macropoma and Latimeria. The new coelacanth is represented by several complete, articulated skeletons, among the first to be discovered in South America"--P. [1].
Open Access
Cranial anatomy of Hybodus basanus Egerton from the Lower Cretaceous of England. American Museum novitates ; no. 2758
(New York, N.Y. : American Museum of Natural History, 1983) Maisey, John G.
"A detailed revision of the cranial anatomy of Hybodus basanus is presented. Features of the cranial and visceral endoskeleton and associated dermal elements are described. The neurocranium differs from that of modern and other fossil sharks, notably in the ethmoid and otico-occipital regions. The ethmoid regions of Hybodus and Xenacanthus are shown to be similar in some respects. The otico-occipital regions of Hybodus and Xenacanthus differ profoundly in the topographical arrangement of the otic capsule, postorbital process, and lateral otic process. Topologically, the arrangement in Hybodus could be obtained by telescoping the otic capsules, lateral otic processes, and occiput of a Xenacanthus braincase between its postorbital processes. This imagined telescoping produces a 'short' otic region in Hybodus, but the arrangement differs from that found in modern sharks. The jaws of Hybodus basanus have a strong ethmoidal articulation but lack a postorbital one; limited protraction of the jaws seems to have been possible. There are five large labial cartilages in each cheek. In some respects these labial cartilages resemble those of chimaeras, and various theories of homology between shark and chimaeroid labial cartilages are reviewed. The hyoid arch is peculiar in that the hyomandibula passes dorsal to the otic ramus of the palatoquadrate. Five branchial arches are present, but only their epi- and ceratobranchials are described. A complete dentition is described and variation between the teeth is discussed; variation seems sufficient to include H. ensis and H. parvidens as synonyms of H. basanus. Dermal scales from various parts of the head and mouth are also described. Although the absence of critical data for most fossil sharks makes it difficult to establish a testable hypothesis of relationship, an attempt is made to compare H. basanus with other sharks. Hybodus basanus is the only Mesozoic shark in which the cranial anatomy has been studied, and the author cautions other systematists against attaching too much weight to the notion that Hybodus is closely related to modern sharks"--P. 2.
Open Access
Cranial anatomy of the Lower Jurassic shark Hybodus reticulatus (Chondrichthyes, Elasmobranchii) : with comments on hybodontid systematics / John G. Maisey. American Museum novitates ; no. 2878
(New York, N.Y. : American Museum of Natural History, 1987) Maisey, John G.
"Hybodus reticulatus Agassiz, from the Lower Jurassic of England, is considered to be the type species of Hybodus. It is founded on skeletal fragments and associated teeth. The cranial anatomy is described from several incomplete specimens, including some of the type material. Two specimens from the Upper Lias of Germany are referred to H. cf reticulatus. Comparisons are made with the Lower Cretaceous Hybodus basanus, whose cranial morphology is more completely known. The neurocranium and jaws are similar in these species, suggesting that many of the anatomical peculiarities noted in the ethmoid and otico-occipital regions of H. basanus characterize a larger group of hybodontid sharks, including the type species of Hybodus. Some differences are noted in the detailed arrangement of the lateral otic process, cephalic spines, and ethmopalatine articulation in H. reticulatus and H. basanus. These differences are considered to be of systematic importance; H. basanus and H. fraasi are placed in a new genus, Egertonodus, on the basis of several differences from H. reticulatus. The genus Hybodus remains an assemblage of nominal species, but increased anatomical data will gradually alleviate this situation. A list of genera retained within the Hybodontidae is given. Hybodontid tooth histology is reviewed, and forms the basis of a phylogenetic hypothesis which is open to falsification by other anatomical data"--P. [1].
Open Access
Cranial morphology of the fossil elasmobranch Synechodus dubrisiensis. American Museum novitates ; no. 2804
(New York, N.Y. : American Museum of Natural History, 1985) Maisey, John G.
"The neurocranium of Synechodus dubrisiensis, a late Cretaceous elasmobranch, is described for the first time. Several similarities in the ethmoidal and otico-occipital regions of Synechodus and Recent elasmobranchs contrast sharply with conditions found in other fossil sharks, including Hybodus. The neurocrania of Synechodus and Hybodus are profoundly different. Similarities between Synechodus and various groups of Recent elasmobranchs suggest two alternative hypotheses of relationship. In one, Synechodus is a sister taxon to all Recent sharks and rays. In the other, Synechodus would be closely allied to galeomorphs (orectolobids, chiloscyllids, and galeoids) and to Heterodontus. Synechodus and Heterodontus are most parsimoniously regarded as successive sister-groups to galeomorphs"--P. [1].
Open Access
An evaluation of jaw suspension in sharks. American Museum novitates ; no. 2706
(New York, N.Y. : American Museum of Natural History, 1980) Maisey, John G.
"Evidence and opinions on the nature and diversity of elasmobranch jaw suspension are discussed and the phylogenetic implications of some of these differences are considered. The hyomandibula is attached to the mandibular joint in all living elasmobranchs, and all are therefore hyostylic with respect to the hyomandibula. Amphistyly is a subset or condition of hyostyly rather than an alternative mode of jaw support. Living osteichthyans and perhaps acanthodians are similarly hyostylic, and there is no reason to suppose that this condition is anything but a primitive gnathostome character. Some elasmobranchs have an orbital process which has a consistent relationship to nerves and vessels within the orbit. It is possible to use this relationship systematically to define a group of 'orbitostylic' sharks in a novel way. The orbital process does not seem to correspond to the 'basal articulation' of acanthodians and osteichthyans"--P. [1].
Open Access
First records of fossil sergestid decapods and fossil brachyuran crab larvae (Arthropoda, Crustacea) : with remarks on some supposed palaemonid fossils, from the Santana Formation (Aptian-Albian, NE Brazil). American Museum novitates ; no. 3132
(New York, N.Y. : American Museum of Natural History, 1995) Maisey, John G.; Carvalho, Maria da Gloria Pires de.
Open Access
Freshwater stingrays of the Green River Formation of Wyoming (early Eocene), with the description of a new genus and species and an analysis of its phylogenetic relationships (Chondrichthyes, Myliobatiformes). Bulletin of the AMNH ; no. 284
(New York, NY : American Museum of Natural History, 2004) Carvalho, Marcelo R. de.; Maisey, John G.; Grande, Lance.
Freshwater stingrays from the Fossil Butte Member of the late early Eocene Green River Formation of Wyoming are reviewed, and a new genus and species of fossil stingray is described. †Asterotrygon maloneyi, n.gen., n.sp. is remarkably well preserved and is known from articulated skeletons of juveniles and adults, both males and females. It is distinguished from all Recent and fossil stingrays, including †Heliobatis radians from the same formation, by the unique presence of a dorsal fin covered with dermal denticles directly anterior to the caudal stings. Other characters that in combination distinguish the new fossil genus from all other stingrays include: retention of separate, individual vertebrae extending to the tail extremity instead of a cartilaginous rod posterior to caudal stings; dorsal surface of disc and tail covered by numerous, closely packed, minute denticles; tail relatively stout at base; and relative proportions of disc and tail. †Asterotrygon, n.gen. shares with certain stingray genera postorbital processes of neurocranium separated from a supraorbital process by a small notch in the supraorbital shelf, presence of both dorsal and ventral tail-folds posterior to caudal stings (and internally supported by rudimentary radial elements), and hyomandibulae separated from lower jaws by a gap that originally contained the hyomandibular-Meckelian ligament. A calcified angular cartilage between the hyomandibula and Meckel's cartilage is tentatively identified in †Asterotrygon, n.gen. as well. †Asterotrygon, n.gen. is unquestionably a stingray, presenting many myliobatiform synapomorphies including caudal stings on the dorsal aspect of tail, lack of jugal arches in neurocranium, a thoracolumbar synarcual cartilage posterior to scapulocoracoid, absence of thoracic ribs, and laterally expanded, shelflike postorbital processes. †Asterotrygon, n.gen. and †Heliobatis primitively retain a narrow and slightly arched puboischiadic girdle and primitively lack calcified rostral elements in adults. A phylogenetic analysis of 23 stingray genera, two outgroups, and 44 informative morphological characters resulted in 35 equally most parsimonious trees. The strict consensus reveals the following hierarchical structure: Hexatrygon + (†Asterotrygon, n.gen., Plesiobatis, Urolophidae + (Urotrygonidae + (†Heliobatis + (Potamotrygonidae + (amphi-American Himantura, Pteroplatytrygon, Himantura, Taeniura, Dasyatis + (Gymnuridae + Myliobatidae)))))). Our resulting tree has nodes in common with previous phylogenetic analyses of stingrays (e.g., Hexatrygon is the most basal stingray genus; gymnurids and myliobatids (pelagic stingrays) are well-supported sister-groups), but includes novel components, such as a clade that includes all dasyatid genera (as a polytomy) and the component Gymnuridae + Myliobatidae. 'Dasyatidae' is not monophyletic in any of the minimum-length trees obtained; Urolophidae (Urolophus and Trygonoptera) and Urotrygonidae (Urobatis and Urotrygon) are both monophyletic, but are not sister-groups. †Asterotrygon, n.gen. forms a clade with urolophids in 21 of the 35 equally most parsimonious trees. Successive approximations weighting adds only one additional node in relation to the strict consensus, which unites Pteroplatytrygon, Dasyatis, and Himantura sensu stricto (in a polytomy) with Gymnuridae + Myliobatidae. The resulting stingray phylogeny is at odds with previous phylogenies mostly regarding the affinities of amphi-American Himantura and Taeniura, which do not form a monophyletic group with the South American freshwater stingrays (Potamotrygonidae) in any of the minimum-length trees obtained. Similar to most elasmobranch groups, stingrays display much character conflict, and cladogram topologies are very sensitive to changes in character coding. Due to a high degree of character variation present in certain generic-level terminal taxa, a more fully representative species-level phylogeny is necessary to clarify the systematic importance of tail-fold configuration, ceratobranchial fusion patterns, and other characters discussed in our study. Three additional synapomorphies of stingrays were uncovered by our study, pertaining to the configuration of the basihyal, first pair of hypobranchial cartilages, and to the forward extension of the basibranchial copula. Our phylogenetic results imply the following biogeographic patterns: the relationships of †Asterotrygon, n.gen. demonstrate a strong Indo-west Pacific historical correlation, while †Heliobatis displays an affinity with the Americas; the node containing the greatest diversity of modern stingrays ('Dasyatidae' + (Gymnuridae + Myliobatidae)) evolved only after an American stingray lineage was established sometime earlier than the early Eocene; and potamotrygonids date at least from the late early Eocene, and not the Miocene, as previous studies have implied. The mechanism responsible for the invasion of the potamotrygonid ancestor into South America could indeed have been a marine transgression as advocated by other authors, albeit a much earlier (pre-Miocene) one, during either the late Cretaceous or the late Paleocene to early Eocene.
Open Access
Hamiltonichthys mapesi, g. & sp. nov. (Chondrichthyes, Elasmobranchii), from the Upper Pennsylvanian of Kansas. American Museum novitates ; ; no. 2931.
(New York, N.Y. : American Museum of Natural History, 1989) Maisey, John G.
Open Access
Insects from the Santana Formation, Lower Cretaceous, of Brazil. Bulletin of the AMNH ; no. 195
([New York] : American Museum of Natural History, 1990) Grimaldi, David A.; Maisey, John G.; McCafferty, William P.; Carle, Frank Louis.; Wighton, Dennis C.; Popham, Edward J.; Krishna, Kumar.; Hamilton, K. G. A.; Darling, D. Christopher.; Sharkey, Michael J.; Oswald, John D.
Open Access
Morphology of the braincase in the broadnose sevengill shark Notorynchus (Elasmobranchii, Hexanchiformes), based on CT scanning. American Museum novitates ; no. 3429
(New York, NY : American Museum of Natural History, 2004) Maisey, John G.
A detailed description is presented of the neurocranium in the hexanchiform shark Notorynchus cepedianus, a primitive modern elasmobranch (neoselachian). The study is based on high-resolution CT scanning and digital imaging, which revealed both the external and internal morphology of a wax-impregnated braincase. Besides providing new data concerning Notorynchus and neoselachians generally, the investigation also provides a control for establishing the reliability of morphological observations of fossil elasmobranch braincases based on CT scans. Many of the features described here have considerable phylogenetic potential, although comparative CT scan data are still unavailable for most modern and extinct elasmobranchs.
Open Access
A new clupeomorph fish from the Santana Formation (Albian) of NE Brazil. American Museum novitates ; no. 3076
(New York, N.Y. : American Museum of Natural History, 1993) Maisey, John G.
Open Access
A new genus of Late Cretaceous angel shark (Elasmobranchii; Squatinidae), with comments on squatinid phylogeny. (American Museum novitates, no. 3954)
(New York, NY : American Museum of Natural History, 2020-06-16) Maisey, John G.; Ehret, Dana J.; Denton, John S. S.
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.
Open Access
A notopterid skull (Teleostei, Osteoglossomorpha) from the continental early Cretaceous of southern Morocco. American Museum novitates ; no. 3260
(New York, NY : American Museum of Natural History, 1999) Taverne, Louis.; Maisey, John G.
"Palaeonotopterus is an extinct osteoglossomorph and represents the oldest known fossil notopterid, coming from the continental late Albian or early Cenomanian of southern Morocco. The taxon is founded upon a single isolated braincase, and the discovery of a second braincase of Palaeonotopterus greenwoodi (described here) permits the original description to be expanded. Palaeonotopterus is more closely related to modem notopterids than to mormyrids and gymnarchids, but it is more primitive than all four modern notopterid genera, which share at least six cranial synapomorphies not observed in either of the fossil braincases"--P. [1].
Open Access
Pectoral morphology in Doliodus : bridging the 'acanthodian'-chondrichthyan divide. (American Museum novitates, no. 3875)
(American Museum of Natural History., 2017-03-10) Maisey, John G.; Miller, Randall F. (Randall Francis), 1956-; Pradel, Alan.; Denton, John S. S.; Bronson, Allison.; Janvier, Philippe.
Doliodus problematicus (NBMG 10127), from the Lower Devonian of New Brunswick, Canada (approx. 397-400 Mya) is the earliest sharklike jawed vertebrate (gnathostome) in which the pectoral girdle and fins are well preserved. Its pectoral endoskeleton included sharklike expanded paired coracoids, but Doliodus also possessed an "acanthodian-like" array of dermal spines, described here for the first time. Doliodus provides the strongest anatomical evidence to date that chondrichthyans arose from "acanthodian" fishes by exhibiting an anatomical mosaic of "acanthodian" and sharklike features.
Open Access
Redescription of Ellimma branneri and Diplomystus shengliensis : and relationships of some basal clupeomorphs. American Museum novitates ; no. 3404
(New York, NY : American Museum of Natural History, 2003) Zhang, Miman.; Maisey, John G.
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.
Open Access
Redescription of Santanichthys diasii (Otophysi, Characiformes) from the Albian of the Santana Formation and comments on its implications for otophysan relationships. American Museum novitates ; no. 3455
(New York, NY : American Museum of Natural History, 2004) Filleul, Arnaud.; Maisey, John G.
A detailed redescription of Santanichthys diasii is presented, based on several new acid-prepared and very well-preserved specimens. S. diasii has a complete Weberian apparatus and is at present the earliest otophysan fish known (early Cretaceous, Albian). In addition, this fish displays at least one synapomorphy of modern characiforms (large and globular lagenar capsules that extend well lateral to the cranium) and we consequently suggest that it is a stem characiform. If this is correct, it represents a significant temporal extension for characiforms. We discuss the phylogenetic implications of its unique combination of features in light of earlier phylogenetic hypotheses.