|Henry GEE: Foreword||7|
|Desui MIAO: Ode to an unbreakable spirit – Chang Meemann’s contributions to paleoichthyology||11-23|
|David K. ELLIOTT and Alain R. M. BLIECK: A new ctenaspid (Agnatha, Heterostraci) from the Early Devonian of Nevada, with comments on taxonomy, paleobiology and paleobiogeography||25-38|
|Marius ARSENAULT and Philippe JANVIER: Is there a spiral intestine in the anaspid-like jawless vertebrate Endeiolepis aneri Stensiö, 1939, from the Upper Devonian Escuminac Formation of Miguasha, Quebec, Canada?||39-43|
|Henning BLOM and Tiiu MÄRSS: The interrelationships and evolutionary history of anaspids||45-58|
|Carole J. BURROW, Sylvain DESBIENS, Boris EKRT and Wouter H. SÜDKAMP: A new look at Machaeracanthus||59-84|
|Gavin C. YOUNG: A new antiarch (placoderm fish: Devonian) from the south coast of New South Wales, Australia||85-100|
|Elga MARK-KURIK: Dolganosteus, a new Early Devonian rhenanid (Placodermi) from northern Siberia||101-106|
|Robert K. CARR, Hervé LELIÈVRE and Gary L. JACKSON: The ancestral morphotype for the gnathostome pectoral fin revisited and the placoderm condition||107-122|
|Carole J. BURROW and Susan TURNER: Reassessment of “Protodus” scoticus from the Early Devonian of Scotland||123-144|
|Michał GINTER: Teeth of Late Famennian ctenacanth sharks from the Cleveland Shale||145-158|
|Gavin F. HANKE and Mark V. H. WILSON: The putative stem-group chondrichthyans Kathemacanthus and Seretolepis from the Lower Devonian MOTH locality, Mackenzie Mountains, Canada||159-182|
|Marcelo R. de CARVALHO: Morphology and phylogenetic relationships of the giant electric ray from the Eocene of Monte Bolca, Italy (Chondrichthyes: Torpediniformes)||183-198|
|Min ZHU, Wei WANG and Xiaobo YU: Meemannia eos, a basal sarcopterygian fish from the Lower Devonian of China – expanded description and significance||199-214|
|Peter L. FOREY and Eric J. HILTON: Two new Tertiary osteoglossid fishes (Teleostei: Osteoglossomorpha) with notes on the history of the family||215-246|
|Gloria ARRATIA: Critical analysis of the impact of fossils on teleostean phylogenies, especially that of basal teleosts||247-274|
|John A. LONG: New holodontid lungfishes from the Upper Devonian Gogo Formation of Western Australia||275-298|
|Matt FRIEDMAN: Postcranial evolution in early lungfishes (Dipnoi: Sarcopterygii): new insights from Soederberghia groenlandica||299-324|
|K. S. W. CAMPBELL, Richard E. BARWICK and Tim J. SENDEN: Perforations and tubules in the snout region of Devonian dipnoans||325-361|
|Gaël CLÉMENT and Per E. AHLBERG: The endocranial anatomy of the early sarcopterygian Powichthys from Spitsbergen, based on CT scanning||363-377|
|Keith S. THOMSON, Xiaobo YU and Bethia THOMAS: New information on the ethmosphenoid of Eusthenopteron foordi (Devonian: Sarcopterygii, Osteolepiformes, Tristichopteridae), with special reference to the choana||379-388|
|Michael I. COATES and Matt FRIEDMAN: Litoptychus bryanti and characteristics of stem tetrapod neurocrania||389-416|
|Zhonghe ZHOU, Jiangyong ZHANG and Xiaolin WANG: The Jehol fish fauna: ecological interaction and paleogeographic distribution||417-429|
|Philippe JANVIER and John G. MAISEY: The Devonian vertebrates of South America and their biogeographical relationships||431-459|
Desui MIAO: Ode to an unbreakable spirit – Chang Meemann’s contributions to paleoichthyology
[pp. 11-23, 9 black-and-white figures]
A geologist, paleontologist, and evolutionary biologist, Professor Chang Meemann (Zhang Miman) is regarded as one of the most eminent paleoichthyologists today. She was educated in China, the former Soviet Union, and Sweden. Meemann is particularly known for her considerable breadth of knowledge of paleoichthyology, her overall impact on the study of the origin and early evolution of lower vertebrates, her integrity and exceptional intellectual prowess, her remarkable services to international paleontological community at large and the Chinese paleontology in particular, and her inspiration for young scientists in her field. Her research has taken her to many parts of the world, and she remains at the forefront of research on morphology, phylogeny, and biogeography of fossil fishes.
David K. ELLIOTT and Alain R. M. BLIECK: A new ctenaspid (Agnatha, Heterostraci) from the Early Devonian of Nevada, with comments on taxonomy, paleobiology and paleobiogeography
[pp. 25-38, 3 black-and-white figures, 1 table]
Zaphoctenaspis meemannae n. gen. et sp. is described from the Lower Devonian Sevy Formation of eastern Nevada. The six previously described species of ctenaspids come from the Canadian Arctic, Spitsbergen, and Podolia, and Ctenaspis is also reported from Severnaya Zemlya. The Podolian and Spitsbergen species, here considered to comprise the genus Ctenaspis, are separated from the Canadian arctic species, which constitute the new genus Arctictenaspis and the ctenaspids are raised to family rank. The known species have a circum-Arctic distribution and the new species therefore constitutes a considerable extension in geographic range. As all the previously described species are dated to the middle or late Lochkovian and Z. meemannae n. gen. et sp. is Emsian in age there is also a considerable increase in the temporal range. Consideration of Early Devonian paleogeography suggests that dispersal took place through proximal marine environments around the Old Red Sandstone continent but the relative paucity of data makes it impossible to indicate dispersal direction. We speculate that ctenaspids were nectonic suspension feeders rather than partially buried benthic organisms.
Marius ARSENAULT and Philippe JANVIER: Is there a spiral intestine in the anaspid-like jawless vertebrate Endeiolepis aneri Stensiö, 1939, from the Upper Devonian Escuminac Formation of Miguasha, Quebec, Canada?
[pp. 39-43, 1 black-and-white figure]
A fragmentary, but exceptionally well-preserved specimen of the jawless vertebrate Endeiolepis aneri Stensiö, 1939 (a possible junior synonym of Euphanerops longaevus Woodward, 1900), displays two spirally shaped impressions, anterodorsal to the anal region. Comparison to other specimens referred to E. aneri, which distinctly show the oblong impression of the stomach contents, suggests that these spirally shaped impressions are the natural, internal cast of the intestine, which may have possessed a spiral internal fold. The structure of the impression observed in this specimen also suggests that this fold was more similar to the spiral valve of jawed vertebrates than to the spirally shaped typhlosole of lampreys.
Henning BLOM and Tiiu MÄRSS: The interrelationships and evolutionary history of anaspids
[pp. 45-58, 4 black-and-white figures, 1 appendix]
A new hypothesis for an anaspid phylogeny, including both articulated and disarticulated material, is proposed based on information from analyses using maximum parsimony. This study benefits from the opportunity to compare suggested topologies with a refined stratigraphic record, which agrees much better with the present phylogeny than previous ones. It is suggested that a large number of gill openings, fused skull bones and elongated paired fins, seen in Pharyngolepis, are derived characters among anaspids, placing forms such as Lasanius and Birkenia in a more basal position. The analysis also suggests that the birkeniid anaspids, with their scale covered body, may be a paraphyletic group since Euphanerops may be a derived and naked anaspid rather than a sister taxon.
Carole J. BURROW, Sylvain DESBIENS, Boris EKRT and Wouter H. SÜDKAMP: A new look at Machaeracanthus
[pp. 59-84, 9 black-and-white figures, 1 appendix]
Machaeracanthus Newberry is a genus which was first erected in the mid-1800s for large, asymmetrical fin spines from the Eifelian (early Middle Devonian) limestones of Ohio, U.S.A. Although many Machaeracanthus spp. have been described, there are few diagnostically significant characters which are useful in separating species. The cross-sectional shape of the spines has been the main character used to diagnose the different species, but this shape varies along the length of the spine and has often been inaccurately estimated. Machaeracanthus spines differ from the ‘normal’ fin spines of acanthodians and chondrichthyans in that the central canal is totally enclosed, rather than opening out along the proximal end of the trailing edge. The affinities of Machaeracanthus have been much debated, with the genus variably assigned to the Chondrichthyes, the Acanthodii, and Gnathostomata incertae sedis. A re-examination of specimens in older U.S. collections, and evidence from newly discovered specimens from the Emsian of the Gaspé Peninsula, Québec and Bundenbach and Oberkirn, Germany, indicate that Machaeracanthus had ‘paired pairs’ of pectoral spines and a distinctive perichondrally ossified scapulocoracoid resembling those of ischnacanthiform acanthodians.
Gavin C. YOUNG: A new antiarch (placoderm fish: Devonian) from the south coast of New South Wales, Australia
[pp. 85-100, 6 black-and-white figures, 1 table]
A new asterolepidoid antiarch, Merimbulaspis meemannae gen. et sp. nov., is described from a small collection of dermal plates with distinctive ornament from the Pambula River fish assemblage of the Boyd Volcanic Complex, which has been assigned a Middle-Late Devonian (?Givetian-Frasnian) age. Similar overlap relationships between the dorsolateral plates of the trunk armour, and the location of the lateral line sensory groove on a separate posterior lateral plate, are characters only otherwise seen in the associated Pambulaspis Young, 1983, and both genera are included in a new family Pambulaspidae. New examples of the lateral plate of the skull of Sherbonaspis Young & Gorter, 1981 are illustrated, with some undescribed material from the Pambula River assemblage (acanthodians, osteichthyans).
Elga MARK-KURIK: Dolganosteus, a new Early Devonian rhenanid (Placodermi) from northern Siberia
[pp. 101-106, 4 black-and-white figures, 1 table]
The placoderm group Rhenanida is a rather poorly known placoderm group mostly of Early and Middle Devonian age. The wide geographical distribution of these placoderms is remarkable. They come from different recent continents: North and South America, Eurasia (Europe and Near East), Africa, and Australia. A new Early Devonian rhenanid, Dolganosteus remotus n. gen., n. sp. is described from the Siberian Arctic, representing the North of the Eurasian continent. Dolganosteus is, in the structure of the skull roof, closest to the Middle Devonian (Eifelian) Asterosteus.
Robert K. CARR, Hervé LELIÈVRE and Gary L. JACKSON: The ancestral morphotype for the gnathostome pectoral fin revisited and the placoderm condition
[pp. 107-122, 6 black-and-white figures, 4 tables]
A review of the proposed patterns for the ancestral morphotype in the gnathostome pectoral fin suggests that the underlying models have driven the interpretation of anatomy. Revising a previous hypothesis on the polarity of character transitions within the gnathostome pectoral fin, the current study proposes that the basal gnathostome pectoral fin consisted of a single narrow articulation between the girdle and a single basal element. This pattern is also present in the outgroup to gnathostomes (Osteostraci). Patterns among fossil and extant gnathostomes represent independent modifications of the basal element. Thus, a revised nomenclature applied to the pectoral fin includes basals as the element or elements (derived from the basal plate) articulating with the girdle and radials representing more distal and de novo endoskeletal elements. New and previously undescribed fossil material for Dunkleosteus terrelli and two selenosteid arthrodires provides the first record of ceratotrichia within recognized placoderms and for D. terrelli, the only other reported occurrence of radials outside of rhenanid placoderms.
Carole J. BURROW and Susan TURNER: Reassessment of “Protodus” scoticus from the Early Devonian of Scotland
[pp. 123-144, 8 black-and-white figures, 2 appendices]
Onychodus scoticus Newton, a taxon based originally on isolated tooth whorls from the Lower Devonian (Lochkovian) of ‘Turin Hill’, Forfar, Scotland was reassigned to the genus Protodus by Traquair in the late 1800s following discovery at the type locality of an articulated specimen comprising a head with the same kind of tooth whorls, and because of some similarity between these teeth and those of Protodus jexi Woodward. New material including tooth whorls, scales and fin spines of “Protodus” scoticus, and a re-examination of the earlier described specimens of this taxon show that “Protodus” scoticus has scales and fin spines of the Nostolepis s. s. histological and morphological type, and all should therefore be reassigned to Nostolepis scotica comb. nov. This is the first Nostolepis species known from articulated material.
Michal GINTER: Teeth of Late Famennian ctenacanth sharks from the Cleveland Shale
[pp. 145-158, 6 black-and-white figures]
The teeth associated with articulated skeletons of Ctenacanthus compressus Newberry, 1889, from the upper Famennian (Upper Devonian) Cleveland Shale of northern Ohio, appear to be morphologically identical to those of “Cladodus” concinnus Newberry, 1875, a species based on isolated teeth from the same area and formation. Similarly to the situation in Ct. compressus, two size classes can be distinguished among the fully grown teeth of “Cl.” concinnus. Due to such resemblances, these two taxa are considered conspecific and, consequently, a new taxonomic combination, viz. Ctenacanthus concinnus (Newberry, 1875), is proposed. Two other tooth-based species from the Cleveland Shale, “Cladodus” terrelli Newberry, 1889 and “Cl.” tumidus Newberry, 1889, are also considered to represent the genus Ctenacanthus Agassiz, 1837. Close phylogenetic relationships between Ctenacanthus, the Mississippian shark Cladodus Agassiz, 1843, and the Frasnian-Famennian Cladodoides wildungensis (Jaekel 1921) are confirmed based on similarities in tooth morphology.
Gavin F. HANKE and Mark V. H. WILSON: The putative stem-group chondrichthyans Kathemacanthus and Seretolepis from the Lower Devonian MOTH locality, Mackenzie Mountains, Canada
[pp. 159-182, 14 black-and-white figures]
Mid- to Late Palaeozoic sharks and holocephalans display a wide range of armour, with bodies that range from sleek, pelagic forms to slow-swimming, chimaeroids or ray-like bottom dwellers. Despite this Late Palaeozoic diversity, there still is an expectation that early chondrichthyans will be anatomically like later species. Recent discoveries from eastern Canada (Doliodus problematicus), and several heavily spined fishes from the MOTH locality in the Northwest Territories, including Kathemacanthus and Seretolepis, described here, challenge this expectation. These fishes show scale and endoskeletal features thought to be characteristic of chondrichthyans, yet they have paired fin spines, anal fin spines, and in some cases rows of prepectoral and prepelvic spines as would be expected from primitive acanthodians. Kathemacanthus and Seretolepis do not fit neatly within the current taxonomy, demonstrating that previous distinctions between acanthodians and chondrichthyans, including scale-based criteria, fail to account for the diversity being discovered in the fossil record.
Marcelo R. de CARVALHO: Morphology and phylogenetic relationships of the giant electric ray from the Eocene of Monte Bolca, Italy (Chondrichthyes: Torpediniformes)
[pp. 183-198, 1 coloured and 8 black-and-white figures]
The giant electric ray †Narcine molini Jaekel, 1894, from the Middle Eocene (Lutetian) Monte Bolca deposits of northeastern Italy, is redescribed on the basis of three holomorphic specimens, two of which are reported for the first time. †Narcine molini is placed in a new genus, †Titanonarke, n. gen., and is compared to all living and fossil electric ray genera. It is characterized by its derived, extremely elongated tail (at least one-half of total length as measured posterior to pelvic fins), absence of dorsal fins, great size, and by other characters still of uncertain polarity within electric rays, such as absence of posterior processes at midlength of antorbital cartilages, presence of rostral fontanelle, and absence of basonasal rostral fenestrae. Some morphological features of †Titanonarke with systematic significance include its anterolaterally projecting and branched antorbital cartilages, a broad and well-developed rostrum, stout and transverse jaws with teeth arranged in tooth-bands, triangular labial cartilages, elongated and tapering hyomandibulae, and greatly elongated, lateral prepelvic process with spatulate extremities. †Titanonarke is unequivocally demonstrated to be a member of the Narcinoidea (Narcinidae + Narkidae) and of the Narcinidae, and is conservatively placed in a basal position within this family; it may eventually prove to be more closely related to the clade Narcine + Discopyge + Diplobatis, but a strict parsimony analysis is necessary to resolve this conflict. Based on the design of its mandibular and hyoid arches, it is possible to infer that †Titanonarke was a benthic, suctorial feeder, similar to living narcinoids.
Min ZHU, Wei WANG and Xiaobo YU: Meemannia eos, a basal sarcopterygian fish from the Lower Devonian of China – expanded description and significance
[pp. 199-214, 2 coloured and 6 black-and-white figures]
Additional morphological and histological features of a stem-group sarcopterygian fish Meemannia eos (Zhu et al. 2006) are provided, including dermal bone features, endocranial structures in the oto-occipital region, and details of the superimposed enamel + odontode layers bearing on the stepwise origin of cosmine in crown-group sarcopterygians. A lower jaw characterized by six infradentary foramina, a relatively straight dentary profile, and absence of parasymphysial tooth whorls is tentatively assigned to Meemannia. The distribution and phylogenetic significance of the lateral cranial canal, the endolymphatic duct of supraotic cavity, the horizontally-positioned coronoid-supporting face of the Meckelian bone, and the pore-canal network in dermal bone surface (integration of pore-canal network with multi-layered odontodes) are discussed in the context of the sequential acquisition of characters leading from stem-group osteichthyans to basal sarcopterygians. The histological condition in Meemannia indicates that stem-group sarcopterygians share two important histological features with stem-group osteichthyans and basal actinopterygians, i. e., the ability of an earlier generation of odontodes to induce the formation of future odontodes, and the absence of resorption. The multi-layered odontodes coexisting with the pore-canal network bring cosmine into alignment with surface covering in stem osteichthyans and actinopterygians.
Peter L. FOREY and Eric J. HILTON: Two new Tertiary osteoglossid fishes (Teleostei: Osteoglossomorpha) with notes on the history of the family
[pp. 215-246, 12 black-and-white figures, 3 appendices]
Two new fossil osteoglossids are described from marine deposits: †Magnigena arabica gen. et sp. nov. from the Palaeocene Umm Himar Formation of Saudi Arabia; Osteoglossidae indet. from the Eocene London Clay Formation of England. Additional marine occurrences of †Brychaetus are added to those already known. A review of taxa assigned to the Osteoglossidae is undertaken to establish minimum ages of the family and the crown members of the subfamilies (Arapaiminae and Osteoglossinae). Crown group arapaimines can be dated reliably to Palaeocene but the lineage must be at least as old as Campanian, the age of the oldest osteoglossine. Fossil crown group Osteoglossinae are not reliably known. There is evidence of several marine taxa belonging to the osteoglossine lineage and since these do not form a monophyletic group there is every likelihood that the distribution of Scleropages and Osteoglossum has come about by marine dispersal. The family Osteoglossidae must be at least as old as Cenomanian and there may be stem representatives known as far back as Early Cretaceous but more evidence is needed. The minimum ages calculated for the various key cladogenetic events of osteoglossid history are considerably younger than those proposed in a recent molecular study.
Gloria ARRATIA: Critical analysis of the impact of fossils on teleostean phylogenies, especially that of basal teleosts
[pp. 247-274, 2 coloured and 13 black-and-white figures, 6 tables]
Traditionally, fossils have played little role in most studies of the phylogenetic relationships of teleosts. The usual approach is to study only recent fishes and when fossils are considered their position is assumed in the cladogram. During the last few years this approach has been challenged by the inclusion of both fossil and recent species in phylogenetic studies. Some fossils and their characters play a significant role, shown in phylogenetic studies of basal teleosts, of osteoglossomorphs, and of some paracanthopterygians. An important example is studying whether elopomorphs or osteoglossomorphs are the most basal teleostean lineage. To address this problem, an analysis of the content of both groups and their fossil record is presented first. It is followed by discussion of results obtained in different phylogenetic analyses. When fossil and recent taxa are included in phylogenetic analyses, the elopomorphs stand as the most plesiomorphic group among extant teleosts. When only recent taxa are included in the analysis, the osteoglossomorphs occupy the basal position; however, this scenario is changing because recent molecular phylogenetic studies support the elopomorphs as the most plesiomorphic extant group. Some fossil taxa may present characters or a combination of characters that contradict interpretations based only on extant forms. This may be particularly important for fishes such as elopomorphs with a remarkable fossil record of more than 150 million years. Furthermore, elopiforms had greater species diversity in the Late Jurassic than they do today. The same is true of osteoglossomorphs with a slightly younger fossil record of about 140 million years and a diversity of Cretaceous forms. When studying the evolutionary history of teleosts, to exclude fossils is a mistake. This is especially true of stem members belonging to monophyletic groups with a long history. It biases interpretation of characters, their distribution, and their homology, because the characters present in the recent terminal forms may have undergone significant evolutionary transformation through time to reach their present states.
John A. LONG: New holodontid lungfishes from the Upper Devonian Gogo Formation of Western Australia
[pp. 275-298, 12 black-and-white figures]
New specimens of holodontid lungfishes from the Upper Devonian (Frasnian) Gogo Formation of Western Australia allow further description of the anatomy and taxonomic clarification of two poorly known taxa. Robinsondipterus longi n. gen. is erected for Holodipterus longi Campbell & Barwick 1991 based on the holotype plus two new skulls showing that the holotype was a juvenile specimen. The adult form has a skull length close to 20 cm. It is characterised by having an elongate mandible with a symphysial length of 30 % jaw length, a palatal dentition primarily consisting of denticles with only marginal teeth of coalesced tuberosities developed, featuring two prominent tusks midway along the pterygoid margin, as seen in Griphognathus. Asthenorhynchus meemannae n. gen. is elevated to generic level for Holodipterus ‘Asthenorhynchus’ meemannae Pridmore et al. 1994, distinguished from the genus Holodipterus by having paired dentaries in the lower jaw, separated pterygoid tooth plates that fuse at maturity. Robinsondipterus n. gen. in having an elongated snout, large labial pouch and marginal dentition, is here shown by phylogenetic analysis to be the sister taxon to Griphognathus whitei.
Matt FRIEDMAN: Postcranial evolution in early lungfishes (Dipnoi: Sarcopterygii): new insights from Soederberghia groenlandica
[pp. 299-324, 12 black-and-white figures]
Median fin endoskeletons and the dermal shoulder girdle are described for the first time in the Late Devonian (Famennian) ‘rhynchodipterid’ lungfish Soederberghia groenlandica. The second dorsal fin is supported by a basal plate with a slender interneural process. Only the most anterior radials of this fin appear to be in direct articulation with the basal plate, while the most posterior radials trail behind it. The basal plate of the anal fin is similar in shape to that of the second dorsal, and bears four jointed radials. The clavicle and cleithrum of Soederberghia lack an outturned ridge that bounds the postbranchial lamina, and agree in many respects with those of other long-snouted, denticle-bearing lungfishes, including Griphognathus and Rhynchodipterus. Median fin endoskeletons are figured for the first time in Pentlandia and ‘Griphognathus’ sculpta. At least five different patterns of second dorsal fin endoskeletons can be defined for early lungfishes, highlighting postcrania as an underexploited source of characters for future systematic studies.
K. S. W. CAMPBELL, Richard E. BARWICK and Tim J. SENDEN: Perforations and tubules in the snout region of Devonian dipnoans
[pp. 325-361, 4 coloured and 28 black-and-white figures]
The dorsal snouts of most Devonian dipnoans are made of a solid piece of bone, the rostral bone, which contains no clear sutures, and therefore must have grown as an arcuate unit. The dentary is also a solid bone. Vascular supplies must have been available to resorb and redeposit these arcuate bones during growth. Interior to these bones is a set of neurocranial bones with numerous rostral tubules, said to be derived from the nerves V and VII. Many of these tubules in the neurocranium apparently terminate at the junction between the endocranium and the external bone, where a gap lies between the neurocranium and the rostrum. They subdivide into the mesh layer on the inner face of the rostral plate. Other tubules penetrate the gap and send branches to the external pores and must have supplied nerves to the rostral bone to allow it to be modified during growth. In addition, similar tubules run posteriorly from these tubes to the dorsal surface of the roof, where they anastomose with the bones. We conclude that these dorsal tubules are part of the nervous systems associated with the growth of the bones, and with the sensory systems in the rostral bones. The snouts are covered with pores, some of which are external openings of the lateral line system, and the others, which are smaller, are not dependent on the lateral line system. The anterior face of the rostrum has large pores directly connected to the rostral pores. Much smaller pores also occur on the dorsal face of the rostrum, and many of these are paired. These secondary pores are larger than those of the cosmine pores on the dorsal roofing bones. Rostral tubules provided nerves for the pores in the surface, chemosensory pores at the edge of the mouth, motor and sensory nerves for the labial cavity, and nerves to the dorsal part of the nasal capsules. Vasculature to the rostrum was provided via soft walled vessels between the rostral tubules.
Gaël CLÉMENT and Per E. AHLBERG: The endocranial anatomy of the early sarcopterygian Powichthys from Spitsbergen, based on CT scanning
[pp. 363-377, 7 black-and-white figures]
A detailed description of the external and internal morphology of the neurocranium of the early sarcopterygian Powichthys spitsbergensis is presented. The study, which is based on high-resolution CT scanning and three-dimensional digital reconstructions, reveals a wealth of new phylogenetically informative features. Many are shared with the Porolepiformes, such as the morphology of the nasal capsules, the separate parapineal and pineal canals, and the curved shape of the hypophysial fossa. These characters therefore favour the original assignation (Jessen 1975, 1980). However, some are autapomorphies, such as the presence of two prominent ventral processes in front of the parasphenoid, while others are shared with non-porolepiform taxa such as Youngolepis. These new anatomical data have yet to be tested within a cladistic analysis, but we predict that they will affect the position of Powichthys within the Dipnomorpha, and possibly have a broader impact on sarcopterygian phylogeny and character evolution.
Keith S. THOMSON, Xiaobo YU and Bethia THOMAS: New information on the ethmosphenoid of Eusthenopteron foordi (Devonian: Sarcopterygii, Osteolepiformes, Tristichopteridae), with special reference to the choana
[pp. 379-388, 4 black-and-white figures]
New information concerning the ethmosphenoid region of the Late Devonian osteolepiform fish Eusthenopteron foordi is presented on the basis of a three-dimensionally preserved and uncrushed specimen from Miguasha, Quebec, Canada. Revised description of the exoskeletal and endoskeletal features provides evidence that Eusthenopteron has a functional choana with a choanal tube running from the nasal capsule to the buccal cavity. The fenestra exochoanalis is a slit-like opening between the premaxilla and vomer and lies directly under the narrow anteroventral extension of an un-ossified or unpreserved space (previously reconstructed as fenestra endochoanalis or fenestra ventrolateralis) where the posterolateral corner of the post-nasal wall merges with the solum nasi. Bounded by a smooth and round bony margin in the vertical wall of the premaxilla and vomer, this passageway has a size, shape, position, and orientation consistent with the function of a choana. Positional relationship to surrounding structures shows that this choana is not obstructed by any joint or the coronoid fang and that its functioning is compatible with the presence of intracranial kinesis. The specimen shows that palatal structures can be misrepresented or misinterpreted when the difference in the plane of view is overlooked. The revised morphology of the ethmosphenoid region provides data for evaluating various accounts of the snout (including the choanal region) in Eusthenopteron and other tetrapodomorphs.
Michael I. COATES and Matt FRIEDMAN: Litoptychus bryanti and characteristics of stem tetrapod neurocrania
[pp. 389-416, 10 black-and-white figures, 3 appendices]
The ethmosphenoid division of the braincase of the stem tetrapod sarcopterygian Litoptychus bryanti Denison 1951 from the Upper Devonian of Colorado is described for the first time. Of other material referred to this monotypic genus, the incomplete lower jaw (the holotype) is redescribed in the light of recent comparative studies of stem tetrapod jaw morphologies. A new set of characters describing stem tetrapod neurocrania is assembled, and when analyzed delivers a tree topology that differs significantly from the current and prevailing pectinate depiction of stem-tetrapod phylogeny. Here, we find a new clade for which we erect the name Megalichthyiformes, including L. bryanti and taxa previously identified as ‘osteolepidids’ and megalichthyids. A further group name is proposed, the Eotetrapodiformes, to include the phylogenetically stable association of tristichopterids, ‘elpistostegalids’ and limbed tetrapods. Group contents and significance are discussed, and further evidence is shown to corroborate this arrangement. Novel taxon positions include Rhizodopsis as an apical megalichthyiform, and Platycephalichthys grouped with ‘elpistostegalids’ and limbed tetrapods. By reconfiguring the stem group, clade bases are drawn closer together. Finally, Glyptopomus, previously allied with Litoptychus, is singled out as likely to be informative on conditions close to the early divergence of Eotetrapodiformes.
Zhonghe ZHOU, Jiangyong ZHANG and Xiaolin WANG: The Jehol fish fauna: ecological interaction and paleogeographic distribution
[pp. 417-429, 4 coloured and 1 black-and-white figures, 1 table]
The Jehol fish fauna represents an important component of the Early Cretaceous Jehol Biota (Chang et al. 2003, Zhang 2003). Three fish assemblages are recognized, corresponding to the three formations (Dabeigou, Yixian, and Jiufotang) of the Jehol Group. The paper summarizes the composition, faunal association, ecological interaction, and paleobiogeographic distributions of the Jehol fish fauna. The fish assemblages played a key role in the ecosystem of the Jehol Biota. Specifically, the Jehol fish fauna occupies an interesting position in the food web of the local ecosystem. This is evidenced not only by piscivorous and putative piscivorous diet among the early birds (e. g., Yanornis, Hongshanornis, Confuciusornis), pterosaurs (e. g., Haopterus, Chaoyangopterus, Liaoningopterus), and other reptiles (e. g., Ikechosaurus) but also by the feeding mode and possible food sources for various members of the Jehol fish fauna (e. g., Protopsephurus, Lycoptera, Coccolepis, and hybodontids). The Jehol fish fauna also has important paleobiogeographic implications, e. g., endemic forms indicating paleogeographic isolation of East and Central Asia from the rest of the Laurasia from the Middle Jurassic to the early part of the Early Cretaceous; restriction of the Jehol fish assemblages to northern China, western Mongolia, eastern Siberia, and northern Korea (Chang & Miao 2004); and hypothesized possible dispersal of fish assemblage from Eurasia to North America in the Late Cretaceous (Chang et al. 2000).
Philippe JANVIER and John G. MAISEY: The Devonian vertebrates of South America and their biogeographical relationships
[pp. 431-459, 11 black-and-white figures]
The Devonian vertebrate record from South America and the Falkland Islands is reviewed here, with special reference to the biogeographical relationships of the taxa. Although Devonian vertebrates are scarce in South America, they display two distinct faunal assemblages: a Lower Eifelian-Frasnian placoderm- and osteichthyan-dominated fauna in the northwest of the continent (Venezuela-Colombia), and a Lochkovian-Eifelian chondrichthyan- and acanthodian-dominated fauna south of the present-day equator. Approximate stratigraphical correlations with South Africa suggest that the latter faunal assemblage, notably the Emsian-Eifelian Pucapampella-Zamponiopteron community, is within the geographic bounds of the particular invertebrate communities referred to as the “Malvinokaffric Realm”. A major change seems to have occurred in South Africa by the turn of the Givetian, with the sudden predominance of osteichthyans and placoderms, but not in Bolivia and Brazil, where chondrichthyans remain unusually abundant, and placoderms or osteichthyans very rare until the Famennian. Environmental factors may be responsible for this unusual faunal composition, such as water depth, temperature, or light at the high latitude seas that occupied southern Gondwana in Early-Middle Devonian times. By contrast, the Eifelian-Frasnian vertebrate faunas of Venezuela and Colombia strikingly resemble the placoderm- and osteichthyan-dominated faunas of the Devonian tropical belt that occur widely on the northern margin of Gondwana and southern margin of Euramerica (although they also include some typically Gondwanan taxa). The presence of Asterolepis and Holoptychius in the Frasnian of Colombia suggests that an early southward dispersion of reputedly Euramerican endemics had preceded the Famennian northward dispersion of Groenlandaspis, phyllolepids, rhizodontids and megalichthyids.
|Copyright © 2015 Verlag Dr. Friedrich Pfeil|