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The evolutionary transition from paired fins to limbs involved the establishment of a set of limb muscles as an evolutionary novelty. In parallel, there was a change in the topography of the spinal nerves innervating appendicular muscles, so that distinct plexuses were formed at the bases of limbs. However, the key developmental changes that brought about this evolutionary novelty have remained elusive due to a lack of data on the development of lobed fins in sarcopterygian fishes. Here, we observed the development of the pectoral fin in the Australian lungfish Neoceratodus forsteri (Sarcopterygii) through synchrotron radiation X-ray microtomography. Neoceratodus forsteri is a key taxon for understanding the fin-to-limb transition due to its close phylogenetic relationships to tetrapods and well-developed lobed fins. At the onset of the fin bud in N. forsteri, there is no mesenchyme at the junction between the axial body wall and the fin bud, which corresponds to the embryonic position of the brachial plexus formed in the mesenchyme in tetrapods. Later, concurrent with the cartilage formation in the fin skeleton, the fin adductor and abductor muscles become differentiated within the surface ectoderm of the fin bud. Subsequently, the girdle muscle, which is homologous to the tetrapod serratus muscle, newly develops at the junction between the axial body wall and the fin. Our study suggests that the acquisition of embryonic mesenchyme at the junction between the axial body wall and the appendicular bud opened the door to the formation of the brachial plexus and the specialization of individual muscles in the lineage that gave rise to tetrapods.

The earliest tetrapodomorph fishes appear in Chinese deposits of Early Devonian age, and by the Middle Devonian they were widespread globally. Evidence for the earliest digitated tetrapods comes from largely uncontested Middle Devonian trackways and Late Devonian body fossils. The East Gondwana Provence (Australasia, Antarctica) fills vital gaps in the phylogenetic and biogeographic history of the tetrapods, with the Gondwanan clade Canowindididae exhibiting a high degree of endemism within the early part of the stem tetrapod radiation. New anatomical details of Koharalepis, from the Middle Devonian Aztec Siltstone of Antarctica, are elucidated from synchrotron scan data. These include the position of the orbit, the condition of the hyomandibular, the shape of the palate and arrangement of the vomerine fangs. Biogeographical and phylogenetic models of stem tetrapod origins and radiations are discussed.

Each piece of data is valuable for unearthing the earliest history of tetrapod origin. Despite frequently incomplete preservation, each skeletal element provides important information on the morphology, phylogeny and faunistic diversity of early tetrapodomorphs. We describe here new and earlier collected material from the fossil vertebrate site Yam-Tesovo on the Oredezh River (Leningrad Region, northwestern Russia) in the deposits of the Yam-Tesovo Formation within the Amata Regional Stage (?lowermost Frasnian, Upper Devonian). Upon similarity of their dermal ornamentation, two mandibular fragments are suggested to belong to the new tetrapodomorph taxon Rubrognathuskuleshovi n. gen. et sp. This species demonstrates a general ‘elpistostegalian' morphological pattern with some early tetrapod characters. The new taxon is characterised by an almost closed intercoronoid fossa, a prearticular that is strongly convex in section and bearing small teeth along its dorsal margin, low vertical coronoid laminae and coronoid fangs that enter the coronoid tooth row. The mandibular canal runs partly in open groove or opens to the surface by a row of large pores. The dermal ornament consists of a network of small ridges forming tubercles in the nodes. The postfrontal assigned to Tetrapodomorpha shows a ‘tetrapod-like' pits-and-ridges sculpturing and a supraorbital ridge characteristic of early tetrapods as well as ‘elpistostegalians'. Its long posterolateral bone margin demonstrates a lateral projection similar to that in Tiktaalik and unknown in other ‘elpistostegalians' and early tetrapods. An unusually flattened vomer is doubtfully related to the tetrapodomorph genus Livoniana Ahlberg, Lukševičs & Mark-Kurik, 2000, based upon characteristic multiple tooth rows. Teeth in rows decrease labially and show no clearly enlarged fang pairs. New finds of the last two decades present the earliest records of some tetrapod characters in non-limbed tetrapodomorphs. This challenges previous hypotheses on the origin of tetrapods.

The Rhizodontida are a group of tetrapodomorph sarcopterygian fishes with a worldwide distribution in the Devonian and Carboniferous periods. Rhizodontids were first described in the U.K., with Carboniferous taxa such as Rhizodus, Strepsodus, and Archichthys each based on isolated teeth (probably symphysial tusks) with distinctive morphologies. Some isolated fin material has also been described, including humeri, but this material has generally been assigned to either Rhizodus or Strepsodus purely on the basis of its size (with the larger material assigned to Rhizodus) or lithology (with specimens in coalshale assigned to Strepsodus). As a first step towards resolving this situation, we have utilized micro-CT scans of U.K. rhizodontid humeri, including newly discovered specimens from Scotland, to establish four distinct humeral morphogroups. This provides a robust framework for interpreting future discoveries, with the hope that these morphogroups can ultimately be securely linked with the distinctive tooth morphologies. The histology of the endochondral bone of the rhizodontid humerus is also described for the first time. http://zoobank.org/urn:lsid:zoobank.org:pub:DABDD50C-9072-4932-BECF-2F6D2AF50C94

International audience; We describe new material of the tristichopterids cf. Langlieria socqueti and cf. Eusthenodon wangsjoi and other unassignable tetrapodomorph remains from the upper Famennian locality of Strud, Belgium. Because of recent improvements in our tristichopterid knowledge, a new phylogenetic analysis is presented in addition to a paleobiogeographic analysis using the Bayesian binary Markov chain Monte Carlo (MCMC) statistical method. The origin of the whole tristichopterid clade is reconstructed with a very likely western European origin. Much of the early tristichopterid history took place in Euramerica. During the Late Devonian, tristichopterids most probably spread from Euramerica into Gondwana. The highly nested tristichopterid clade formed by Cabonnichthys burnsi, Mandageria fairfaxi, E. wangsjoi, Edenopteron keithcrooki, and Hyneria lindae most likely differentiated in Australia. Then dispersal events occurred from Australia to Euramerica with Hyneria lindae (to eastern North America) and E. wangsjoi (to Greenland/western Europe). The latter dispersal events, during the Famennian, are in agreement with the Great Devonian Interchange, which predicts dispersal events between Gondwana and Euramerica at this time.

Earliest Pennsylvanian (Bashkirian) vertebrate fossil assemblages of the Joggins Formation (Cumberland Group) of Nova Scotia, Canada, have long been noted for the unique representation of the earliest known crown amniotes, but the overall vertebrate fauna remains poorly understood. The vast majority of Joggins vertebrates have historically been assigned to the Microsauria, a group originally established by Dawson specifically to accommodate the abundant, diminutive fossils of the Joggins Formation. As the Microsauria concept has evolved, some Joggins taxa (e.g. the eureptileHylonomus lyelli) have been removed from the group, but many of the Joggins ‘microsaurs’ remain unrevised, obscuring the true diversity of the earliest Pennsylvanian tetrapod fauna. Here we amend part of this problem by revisiting the morphology of Dawson's ‘microsaur’Hylerpeton longidentatum. This taxon, represented by the anterior half of a left hemimandible, is here reinterpreted as a plesiomorphic aïstopod and assigned to a new genus,Andersonerpeton.A. longidentatumshows a surprisingly primitive anatomy of the lower jaw, retaining a parasymphyseal fang pair on the dentary, an adsymphyseal bone bearing a denticle field, fangs on all coronoids and parasymphyseal foramina, as well as a prearticular which extends far anterior along the coronoid series. However, several aïstopod characters can also be seen, including a lack of sculpturing on the dentary and a reduced number of recurved, weakly socketed teeth. The anatomy ofA. longidentatumcorroborates recent phylogenetic work which has placed the origin of aïstopods within the Devonian fin-to-limb transition but preserves a mosaic of characteristics suggesting an even earlier divergence. The presence of an aïstopod in the Joggins fauna expands the taxonomic diversity of the Joggins fauna and suggests that Joggins may preserve a more typical Carboniferous fauna than previously thought.

The Dipnomorpha include the extinct Porolepiformes, in addition to Powichthys and Youngolepis and the extant Dipnoi (lungfish). As sister group to the Tetrapodomorpha, the Dipnomorpha hold a valuable place in our understanding of early sarcopterygian evolution. With complete cranial endocasts now known from most other stem sarcopterygian groups including actinistians and tetrapodomorphs (which bracket the Dipnomorpha), a thorough understanding of the porolepiform endocranium remains one of the last pieces in the puzzle towards understanding evolution of the neurocranium in stem sarcopterygians. We present the first virtual cranial endocast of a porolepiform fish (Glyptolepis paucidens) demonstrating that it displays predominantly primitive sarcopterygian endocast characters including: lack of a bifurcation of the olfactory nerves, separate pineal and parapineal recesses, circumvention of the nasal capsule by the profundus nerve, and sessile olfactory bulbs. The union of the orbitonasal canal and the nasal capsule is consistent with that seen in Powichthys, Youngolepis and other porolepiforms, however circumvention of the nasal capsule by the profundus resembles the dipnoan Dipterus, contrasting the state observed in other porolepiforms and Powichthys. Inconsistent with the general primitive nature of the endocast seen in Glyptolepis is the large, curved hypophyseal recess, a feature shared with Powicthys but unlike Youngolepis. Furthermore, Glyptolepis displays ventral expansion of the telencephalon - a character thought to be derived within the Dipnoi. This new data enhances our understanding of brain and sensory evolution in sarcopterygians. In particular, it shows conservatism in stem Porolepiformes contrary to the disparate morphology of their sister-group the Dipnoi.

Synopsis A nearly complete mandible of a large tetrapodomorph sarcopterygian from the Frasnian Alves Beds is studied with the aid of computed tomography. The absence of cosmine, a small parasymphysial dental plate bearing dentition that is discontinuous with that of the coronoids, and the presence of an elongated posterior coronoid that bears two fang pairs restrict placement of the tetrapodomorph from the Alves Beds to Tristichopteridae, and suggest that is a member of the clade that is sister to the anatomically primitive Givetian genus Tristichopterus . Taxa from this segment of tristichopterid phylogeny include the Givetian–Frasnian Eusthenopteron and Frasnian Jarvikina , but the tristichopterid from the Alves Beds is distinguished from both by the presence of an organized row of well-developed teeth on the posterior coronoid. This character has been proposed as a synapomorphy of taxa crownward of Trischopteridae, but is widely distributed among tetrapodomorph fishes. Our reinterpretation of lower jaw material of Tinirau clackae suggests this species is a member of the Tristichopteridae rather than the ‘Elpistostegalia’, and likely includes material assigned to a second species and genus of tetrapodomorph from the Red Hill site, Bruehnopteron murphyi . Proposal of a formal taxonomic name for the tristichopterid from the Alves Beds is withheld pending the discovery or analysis of further material from these deposits.

Micro computed tomography has revealed as yet undescribed internal braincase anatomy of the tetrapodomorph fishGogonasus andrewsaefrom the Frasnian Gogo Formation, Paddy's Valley, Kimberley Region, Western Australia. The complete material, including the cranial cavities and channels for blood vessels and nerves, reveals several notable features inside the endocranium. The ethmosphenoid unit includes a median capsule, which lies underneath the median postrostral and rostral series. Based on innervation and association with cutaneous vessels, potential electroreceptive function is inferred for this capsule. Several regions of poor ossification, including foramina for the glossopharyngeal and abducens nerves, as well as the apparent suture separating the ethmoid from the sphenoid portions of the braincase, are possibly indicative of early ontogenetic features. Former interpretations of the course for the superficial ophthalmic nerve inside the nasal capsule ofOsteolepisandGyroptychiusmay be incorrect, with new research supporting a path through the nasal septum, as inGogonasus.

The fin rays and two types of scales (enlarged and regular) of the Devonian sarcopterygian Eusthenopteron foordi are redescribed using light, scanning and transmission electron microscopy. The fin rays consist of lepidotrichia composed of ossified, jointed and branched segment pairs. The basal segments are cylindrical, but more distal elements are crescentic in section. The distribution of Sharpey’s fibres varies along the lepidotrichia. In the proximal segments, lateral bundles form a belt connecting adjacent hemisegments. In the distal segments, thin bundles are restricted to the area facing the fin surface. Both enlarged and regular scales have a similar spatial organisation. They are composed of a superficial highly mineralised layer covering a thick basal plate where the fibrils are distributed in superimposed strata forming a ply− wood−like structure. Nevertheless, the enlarged and regular scales differ in their shape, in the mineralised tissues of the su− perficial layer, and in the organisation of the plywood−like structure. The superficial layer of the enlarged scales is com− posed of parallel−fibered bone covering a deeper layer of woven−fibered bone. The basal plate is made of an orthogonal plywood−like structure. The thin, lamellar, imbricated regular scales display the characteristics of elasmoid scales. The mineralised tissue forming the superficial layer resembles that of extant teleost scales. In the basal plate, the twisted ply− wood−like structure is composed of closely packed fibrils that are preserved down to the ultrastructural level owing to the persistence of bridges connecting the fibrils. The enlarged and the regular scales of Eusthenopteron foordi do not present superficial odontodes, in contrast to ancestral thick rhomboid scales. The disappearance of enamel/enameloid and dentine may be related to the evolutionary trend towards a lightening of the dermal skeleton that would improve the swimming abilities of the animal. The characteristics of the dermal skeleton of Eusthenopteron foordi support the hypothesis that this process began early in osteichthyans. Key wor ds: Sarcopterygii, Tetrapodomorpha, Tristichopteridae, Eusthenopteron, fin ray, elasmoid scales, paleohisto− logy, transmission electron microscopy, Devonian.

A new cosmine-covered, tetrapodomorph fish Owensia chooi gen. et sp. nov. is described, based on a near-complete, uncrushed ethmosphenoid from the Middle Devonian sediments (Kevington Creek Formation) at Owens Creek, South Blue Range, Victoria, Australia. An anteroposteriorly directed basipterygoid process, an optic nerve foramen positioned dorsal to the basipterygoid process, and an oculomotor nerve foramen located posterodorsal to the basipterygoid process are established as autapomorphies. Owensia shares a broad ethmosphenoid shield, a lack of discernible sutures between the bones of the snout and a dorsoventrally shallow skull with cosmine-covered members of the Canowindridae. Owensia also shares the first two of these features and an occluded view of the nostrils from the dorsal surface with Gyroptychius? australis. However, the phylogenetic relationships between these taxa remain unclear. Superficial comparisons between Owensia and the Northern Hemisphere Lamprotolepis are rejected, with the positio...

Tristichopterids (Sarcopterygii, Tetrapodomorpha) form a monophyletic group of exclusively Devonian fishes. This thesis consists of descriptions of new material of tristichopterids and closely related taxa, as well as new interpretations and descriptions of previously figured material. Redescribed specimens were originally figured as far back as 1861, and publications as old as this are almost always of limited use as anatomical and systematical references, in addition to being difficult to acquire. The possibility of using new techniques and new theoretical frameworks also provides good justification for taking a second look at such specimens. In the case of this thesis, this includes the use of computed tomography scanning methods, and the cladistic approach to describing the interrelationships of taxa. The thesis includes a complete taxonomy of valid tristichopterid taxa, in addition to two new phylogenetic analyses incorporating the taxa that were described or redescribed. One of the analyses deals with the interrelationships of taxa along the entire tetrapod stem, and establishes the monophyly of the Tristichopteridae. The other analysis focuses on tristichopterid interrelationships. An account is given of evolutionary trends within Tristichopteridae, and instances of parallel evolution between tristichopterids and other tetrapodomorph groups are discussed. The biogeographical implications of tristichopterid occurences world-wide seem to corroborate the picture provided by other vertebrate groups, and give further support to one of two main hypotheses concerning the relative positions of Gondwana and Laurussia, the two major palaeocontinents during the Late Devonian. The supported hypothesis proposes a close proximity between southern Laurussia and northwestern Gondwana, as evidenced by the wide dispersal of derived tristichopterids by the Late Devonian. A Laurussian origin of tristichopterids is proposed.

The remains of Late Devonian tetrapods from the Red Hill locality in Pennsylvania help to elucidate the early stages of tetrapod evolution. Red Hill is a particularly informative site that preserves a diverse fauna and flora within a depositional setting suggesting penecontemporaneous deposition of locally derived material. Here, for the first time, we report on the full suite of early tetrapod remains from Red Hill and consider the implications for tetrapod diversity within the Red Hill ecosystem. Previously described material is reviewed and considered in relation to newly reported specimens. New material described includes isolated skull elements (two jugals, a postorbital, a lacrimal and a coronoid) and postcranial elements (a femur and a gastral scale). The characteristics of many of the Red Hill tetrapod specimens conform to the morphological expectations of Late Devonian forms. Several elements, however, illustrate more derived characteristics and strongly suggest the presence of the oldest known whatcheeriid-like tetrapod. This study demonstrates the difficulty in making taxonomic associations with isolated remains, even when found in close proximity to one another. Exploration of the characteristics of each element, however, demonstrates the presence of at least three early tetrapod taxa at the Red Hill site.

Within the Tetrapodomorpha, the Late Devonian Gogonasus andrewsae of the Gogo Formation, Gogo, Western Australia, has occupied an uncertain phylogenetic position. Following the description of several well-preserved three-dimensional skulls and pectoral girdles, the discovery of the first complete specimen (NMV P221807) made Gogonasus one of the best-known tetrapodomorph fish. Recent studies of pectoral fin structure and the spiracular opening of Gogonasus have suggested an unexpected affinity with ‘elpistostegalid’ fish such as Tiktaalik. Subsequent work has refuted characters linking these taxa, with phylogenetic analysis of the Tetrapodomorpha placing Gogonasus basal to megalichthyids and tristichopterids. In this paper we reanalyse characters linking Gogonasus with ‘elpistostegalid’ fish and those supporting the placement of Gogonasus crownward of Eusthenopteron. New phylogenetic analyses of the Tetrapodomorpha show a revised phylogenetic position of Gogonasus as being deeply nested within the Tetrapodomorpha, crownward of Osteolepis and Megalichthys, but basal to Eusthenopteron+‘elpistostegalids’. Functional consideration of the spiracular structure suggests a position of Gogonasus closer to ‘elpistostegalids’, although data is lacking from other less-well-preserved taxa to fully test the hypothesis. The humerus of the Late Devonian lungfish Chirodipterus from Gogo, Western Australia is figured for comparative purposes.

The tetrapodomorph fish Spodichthys buetleri from the Upper Devonian of East Greenland is redescribed from computed tomography scans of material originally studied by Erik Jarvik. A wealth of new a ...

Wrists, ankles and digits distinguish tetrapod limbs from fins, but direct evidence on the origin of these features has been unavailable. Here we describe the pectoral appendage of a member of the sister group of tetrapods, Tiktaalik roseae, which is morphologically and functionally transitional between a fin and a limb. The expanded array of distal endochondral bones and synovial joints in the fin of Tiktaalik is similar to the distal limb pattern of basal tetrapods. The fin of Tiktaalik was capable of a range of postures, including a limb-like substrate-supported stance in which the shoulder and elbow were flexed and the distal skeleton extended. The origin of limbs probably involved the elaboration and proliferation of features already present in the fins of fish such as Tiktaalik.

The relationship of limbed vertebrates (tetrapods) to lobe-finned fish (sarcopterygians) is well established, but the origin of major tetrapod features has remained obscure for lack of fossils that document the sequence of evolutionary changes. Here we report the discovery of a well-preserved species of fossil sarcopterygian fish from the Late Devonian of Arctic Canada that represents an intermediate between fish with fins and tetrapods with limbs, and provides unique insights into how and in what order important tetrapod characters arose. Although the body scales, fin rays, lower jaw and palate are comparable to those in more primitive sarcopterygians, the new species also has a shortened skull roof, a modified ear region, a mobile neck, a functional wrist joint, and other features that presage tetrapod conditions. The morphological features and geological setting of this new animal are suggestive of life in shallow-water, marginal and subaerial habitats.

Letognathus gen. nov. is described from the Lower Carboniferous (Tournaisian) Horton Bluff Formation. Included in this genus is the species Letognathus hardingi (Dawson 1868), which was originally assigned toRhizodus and later toStrepsodus, but it is distinct from these genera in tooth morphology and the presence of several more primitive rhizodontid characters. By contrast with these latter more derived genera, the parasymphysial plate contacts the first coronoid; the first coronoid bears a row of lingually deflected teeth, the tooth striations occur around the entire circumference of the crown and are much finer and less regular than those ofStrepsodus, and marginal tooth row reaches anteriorly to the dentary symphysis. Phylogenetic analysis indicates that rhizodontid jaws primitively bear symphysial tusks; slender recumbent teeth; an anterior projection of the dentary over the anteromesial depression for the median symphysial plate and shows the highly derived jaws ofStrepsodus andRhizodus evolved within the Rhizodontida, rather than as primitive characters for the group. This new jaw material supports earlier models of mandibular kinesis and shows that the coronoid fangs were oriented such as to facilitate kinesis. Rhizodontid jaw evolution seems to be marked by parallelisms with tristichopterids and early tetrapods.

The lower jaw of the Devonian tetrapodAcanthostegais described for the first time. Redescriptions are provided for the lower jaws of the elpistostegidPanderichthys, the Devonian tetrapodsElginerpeton, Obruchevichthys, Metaxygnathus, VentastegaandIchthyostega, and the Carboniferous tetrapodsCrassigyrinus, MegalocephalusandGephyrostegus. The character distri- butions thus revealed differ considerably from previous accounts, particularly in the wide distribution of certain primitive characters. Meckelian ossification in the middle part of the jaw is widespread among Devonian tetrapods, being demonstrably absent only inAcanthostega.Among Carboniferous tetrapods, a tooth-bearing parasymphysial plate is shown to be present inCrassigyrinusandMegalocephalus(having already been demonstrated by other authors inWhatcheeriaandGreererpeton).A phylogenetic analysis of 26 early tetrapods including all the aforementioned genera, scored for 51 lower jaw characters, produces at least 2,500 equally parsimonious trees. However, the lack of resolution lies largely in a big top end polychotomy containing anthracosaurs, temnospondyls, seymouriamorphs, microsaurs and a nectridean-amniote clade. Below this polycho- tomy, which may correspond approximately to the tetrapod crown group, there is a well-resolved stem-group containing, in descending order,Megalocephalus, Greererpeton, Crassigyrinus, (jaws associated with)Tulerpeton, Whatcheeria, Acanthostega, Metaxygnathus, Ichthyostega, VentastegaandMetaxygnathus(unresolved), anElginerpeton-Obruchevichthysclade, andPanderichthys.This conflicts with recently published phylogenies by Coates and Lebedev & Coates, which placeTulerpetonand all post-Devonian tetrapods in the amphibian or amniote branches of the tetrapod crown group.

A new tristichopterid, Cabonnichthys burnsi gen. et sp. nov. from the Upper Devonian Mandagery Sandstone near Canowindra, New South Wales, Australia, is the second tristichopterid to be described from this locality. The first, Mandageria fairfaxi, was interpreted as the sister group of the Laurussian taxon Eusthenodon. Cabonnichthys burnsi gen. et sp. nov. is similar to these two taxa in possessing a posterior supraorbital extending ventrally behind the orbit to exclude the postorbital from the orbital margin, a posteriorly positioned pineal surrounded by kite or teardrop shaped bones, and an enlarged fang-like tooth at the anterior end of the premaxillary tooth row. Cabonnichthys burnsi differs from Mandageria and Eusthenodon in retaining a contact between the intertemporal and posterior supraorbital, and in possessing “horn-like” processes on the postparietal shield that notch into the posterior margin of the postorbital. The Tristichopteridae is a clade characterized inter alia by the possessi...

This contribution comprises a review of Early Permian Sarcopterygii (Coelacanthimorpha - coelacanths; Tetrapodomorpha - Osteolepimorpha and tetrapods) of the Parana Basin in the state of Sao Paulo. The other important group of sarcopterygians - Dipnoi (lungfishes) - have still not been recorded in Sao Paulo in the Early Permian. The Coelacanthimorpha have been reported in the Itarare Group, Tatui and Irati formations. The sandstone and conglomerate at the base of the Taquaral Member of the Irati Formation are rich in icthyofossils, including labyrinthodont teeth that have been assigned to the Tetrapodomorpha. These teeth range from a few millimeters to a few centimeters in length, which makes them the largest teeth in the Permian of the State of Sao Paulo. The most frequent fish remains in the silty shale facies of the Taquaral Member are scales of Coelacanthimorpha, which may reach a few centimeters in size. Currently the coelacanths live in deep marine environments. However, during the Paleozoic they lived in waters of different salinities as well as in fresh waters. The Tetrapodomorpha were also able to live in waters of varied salinities and in continental settings. The paleoenvironmental analysis of ancient deposits with these groups of fossils thus requires a thorough survey of their sedimentary context as well as the associated paleobiota.

Four new genera of osteolepifonns and a new rhizodontifonn genus are described from the Middle-Late Devonian Aztec Siltstone (Beacon Supergroup) of Antarctica. Other indetenninate osteolepid, eusthenopterid and rhizodontid remains, and a single indetenninate porolepifonn scale, are described from the same fonnation. Koharalepis jarviki n.gen., n.sp. is a large cosmine-covered osteolepifonn with a broad flat head, two pairs of dennosphenotics, large extratemporals, a large postorbital in the cheek which does not reach the orbit, an elongate jugal, lachrymal separating the maxilla from the premaxilla at the jaw margin, and large anteriorly pointed median and triangular lateral extrascapulars. It is placed with Canowindra Thomson and Beelarongia Long in the new family Canowindridae. Platyethmoidia antarctica n.gen., n.sp. is a poorly known form with a very broad, flat fronto-ethmoidal shield with dorsomesially oriented slit-like nares, and a lower jaw with a deep articular region. It may be closely related to Gyroptychius? australis Young & Gorter. Mahalalepis resima n.gen., n.sp. is interpreted on the morphology of the frontoethmoidal shield as an early megalichthyid, and a new definition of this family is presented. Vorobjevaia dolonodon n.gen., n.sp. is a poorly known osteolepid with a distinctive jaw morphology. The rhizodontifonn Notorhizodon mackelveyi n.gen., n.sp. was the largest fish in the Aztec fauna, attaining a length of over 3 m. It is characterised by elongate frontals and small dennosphenotics in the skull, Rhizodus-type tusks, and strong tooth flanges on the coronoid and dennopalatine series bones in the jaws. The braincase in a rhizodontifonn is described for the first time, and in general morphology closely resembles that of Osteolepifonnes. Notorhizodon resembles Screbinodus Andrews in dennal ornament and Barameda Long in skull pattern. All previously described crossopterygian material from the Aztec Siltstone is revised, and Gyroptychius antarctic us (Smith Woodward) is regarded as a nomen nudum. The stratigraphic distribution of rhipidistians in the Aztec Siltstone is summarised, and the biogeography and phylogenetic relationships of the

International audience; Additional material of a large specimen of tristichopterid fish from the Upper Famennian Evieux Formation of Belgium is described. This large fish was previously assigned to Tristichopteridae gen. et sp. indet. due to the lack of diagnostic anatomical data. New available material consists of the internal surface of the parietal shield, vomers and anterior part of the parasphenoid, subopercular and submandibulo-branchiostegal bones, and an internal view of the anterior part of the mandible. A possible autapomorphy of the new form from Belgium, Langlieria socqueti gen. nov. et sp. nov., is the absence of marginal teeth on the vomer except on its most lateral part. Apart from these features, it only differs from the genus Mandageria from Australia in the absence of marginal teeth between the dentary fang and the mandibular symphysis, in the presence of a raised marginal crest lateral to the anterior coronoid fang, and in the presence of numerous small marginal teeth on the premaxilla. It differs from the cosmopolitan genus Eusthenodon in a number of respects: the supratemporal, tabular, and postparietal bones are superficially fused, as are the intertemporal and parietal bones, the dermal ornament is proportionally very fine, and the denticulated field of the parasphenoid stands proud rather than being recessed into the body of the bone.

A re-examination of sarcopterygian inter-relationships, with special reference to the Porolepiformes

Tristichopterids (Sarcopterygii, Tetrapodomorpha) form a monophyletic group of exclusively Devonian fishes. This thesis consists of descriptions of new material of tristichopterids and closely related taxa, as well as new interpretations and descriptions of previously figured material. Redescribed specimens were originally figured as far back as 1861, and publications as old as this are almost always of limited use as anatomical and systematical references, in addition to being difficult to acquire. The possibility of using new techniques and new theoretical frameworks also provides good justification for taking a second look at such specimens. In the case of this thesis, this includes the use of computed tomography scanning methods, and the cladistic approach to describing the interrelationships of taxa. The thesis includes a complete taxonomy of valid tristichopterid taxa, in addition to two new phylogenetic analyses incorporating the taxa that were described or redescribed. One of the analyses deals with the interrelationships of taxa along the entire tetrapod stem, and establishes the monophyly of the Tristichopteridae. The other analysis focuses on tristichopterid interrelationships. An account is given of evolutionary trends within Tristichopteridae, and instances of parallel evolution between tristichopterids and other tetrapodomorph groups are discussed. The biogeographical implications of tristichopterid occurences world-wide seem to corroborate the picture provided by other vertebrate groups, and give further support to one of two main hypotheses concerning the relative positions of Gondwana and Laurussia, the two major palaeocontinents during the Late Devonian. The supported hypothesis proposes a close proximity between southern Laurussia and northwestern Gondwana, as evidenced by the wide dispersal of derived tristichopterids by the Late Devonian. A Laurussian origin of tristichopterids is proposed.

Fossil discoveries1,2,3,4,5,6,7 and improved phylogenies3,4,5,7 have greatly improved our understanding of the origin of tetrapods, making it possible to reconstruct sequences of character change leading to tetrapod morphologies5,7 and to tentatively identify the genetic basis for some of these changes8,9. However, progress has centred on the upper part of the Tetrapodomorpha5 which is occupied by Devonian tetrapods such as Acanthostega1,2,5 and Ichthyostega1. Few advances have been made in improving our understanding of the lower, ‘fish’ part of the group, beyond establishing Elpistostegalia, Osteolepiformes and Rhizodontida as progressively more primitive constituents10,11,12,13. It has not been convincingly confirmed or disproved that the Osteolepiformes, a diverse but structurally uniform group that is central to the debate about tetrapod origins14,15,16,17, is monophyletic relative to tetrapods (that is, a single side branch on the tetrapod lineage). The earliest steps of the fish–tetrapod transition have thus remained poorly resolved. Here we present the first detailed analysis of the lower part of the Tetrapodomorpha, based on 99 characters scored for 29 taxa. We show that both the Osteolepiformes as a whole and their constituent group Osteolepididae are paraphyletic to tetrapods (that is, each comprises a section of the tetrapod lineage with several side branches), and that their ‘uniting characters’ are attributes of the tetrapodomorph stem lineage. The supposedly discredited idea of osteolepiforms as tetrapod ancestors14,15,16,17 is, in effect, supported by our analysis. Tetrapod-like character complexes evolved three times in parallel within the Tetrapodomorpha.

The relationship of the three living groups of sarcopterygians or lobe-finned fish (tetrapods, lungfish and coelacanths) has been a matter of debate1,2,3,4,5. Although opinions still differ, most recent phylogenies suggest that tetrapods are more closely related to lungfish than to coelacanths6,7,8,9,10. However, no previously known fossil taxon exhibits a concrete character combination approximating the condition expected in the last common ancestor of tetrapods and lungfish—and it is still poorly understood how early sarcopterygians diverged into the tetrapod lineage (Tetrapodomorpha)7 and the lungfish lineage (Dipnomorpha)7. Here we describe a fossil sarcopterygian fish, Styloichthys changae gen. et sp. nov., that possesses an eyestalk and which exhibits the character combination expected in a stem group close to the last common ancestor of tetrapods and lungfish. Styloichthys from the Lower Devonian of China bridges the morphological gap between stem-group sarcopterygians (Psarolepis and Achoania)10 and basal tetrapodomorphs/basal dipnomorphs. It provides information that will help in the study of the relationship of early sarcopterygians, and which will also help to resolve the tetrapod–lungfish divergence into a documented sequence of character acquisition.

Remains of two large sarcopterygians are described from Famennian deposits in Belgium. One of them is referred to Eusthenodon wangsjoi Jarvik; it is the first occurrence of this genus in Belgium. The other, much larger one, appears to be a tristichopterid. It has a postspiracular; size and shape of the mandible similar to those of Platycephalichthys skuenicus and P. bischoffi; snout and cheek patterns close to those of Eusthenodon; unusual shape of the supratemporal resembling that of Hyneria, Mandageria and Platycephalichthys skuenicus; and tooth histology quite similar to that of Eusthenodon and Platycephalichthys.

Tristichopterids (Sarcopterygii, Tetrapodomorpha) form a monophyletic group of exclusively Devonian fishes. This thesis consists of descriptions of new material of tristichopterids and closely related taxa, as well as new interpretations and descriptions of previously figured material. Redescribed specimens were originally figured as far back as 1861, and publications as old as this are almost always of limited use as anatomical and systematical references, in addition to being difficult to acquire. The possibility of using new techniques and new theoretical frameworks also provides good justification for taking a second look at such specimens. In the case of this thesis, this includes the use of computed tomography scanning methods, and the cladistic approach to describing the interrelationships of taxa. The thesis includes a complete taxonomy of valid tristichopterid taxa, in addition to two new phylogenetic analyses incorporating the taxa that were described or redescribed. One of the analyses deals with the interrelationships of taxa along the entire tetrapod stem, and establishes the monophyly of the Tristichopteridae. The other analysis focuses on tristichopterid interrelationships. An account is given of evolutionary trends within Tristichopteridae, and instances of parallel evolution between tristichopterids and other tetrapodomorph groups are discussed. The biogeographical implications of tristichopterid occurences world-wide seem to corroborate the picture provided by other vertebrate groups, and give further support to one of two main hypotheses concerning the relative positions of Gondwana and Laurussia, the two major palaeocontinents during the Late Devonian. The supported hypothesis proposes a close proximity between southern Laurussia and northwestern Gondwana, as evidenced by the wide dispersal of derived tristichopterids by the Late Devonian. A Laurussian origin of tristichopterids is proposed.

A new osteolepiform, Marsdenichthys longioccipitus gen. et sp. nov., is described from the Frasnian lacustrine shales (Avon River Group) near Mt Howitt, central Victoria. Because it has thin cycloidal scales with large overlap areas and lacks cosmine in the dermal skeleton Marsdenichthys gen. nov. is regarded as the sister taxon to eusthenopterids. In possessing an extratemporal bone in the skull roof, Marsdenichthys gen. nov. is more primitive than other eusthenopterids. The Osteolepiformes are assumed to be monophyletic by possession of a unique complex of cheek bones, large dermal anocleithrum, scapulocoracoid structure and basal scutes on the fins. Other characters unique to Eusthenopteron such as a long basihyal, fused first infra- and suprapharyngobranchials and large vestibular fontanelles on the braincase may be useful synapomorphies of the Osteolepiformes when more is known of the anatomy of other genera. Problems in defining osteolepidids and eusthenopterids are discussed.

Barameda decipiens, gen. nov. (Woodward, 1906) is described from the Early Carboniferous Mansfield Group, Victoria, Australia. It differs from other rhizodontiforms (Strepsodus, Rhizodus, Screbinodus, Sauripterus) by the shape of the skull roofing bones, course of the supratemporal sensory line, vertebral structure, and pectoral fin skeleton. The skull roof of Barameda, gen. nov., differs from that of Osteolepiformes in having a larger extratemporal bone that contacts the intertemporal, by the overlap areas on the intertemporal, and in having fewer snout bones. The cheek has a very large postorbital bone, and the lacrimai is narrow. There are two external nostrils, which are situated close together and differ in their position in the only other rhizodontiform for which they are known, suggesting that the group was not choanate. Rhizodontiforms are a monophyletic group characterized by specializations of the pectoral girdle and fin. They may be placed in Schultze's (1987) scheme of osteichthyan in...

SynopsisWell preserved material of the crossopterygian fishEusthenopteronenables fresh reconstructions and interpretations of its postcranial skeleton to be given. Comparisons throughout with other bony fishes show that it may be primitive in many features. Similarities with early amphibians such as the screw-shaped glenoid, the form of the humerus (on which an attempt to restore the pectoral musculature is based), the dorsal bicipital ribs and the possibility of a sacral attachment, throw much light on the origin of the tetrapod postcranial skeleton, particularly of the cheiropterygium. A functional analysis of the skeleton ofEnsthenopteronis attempted, suggesting that it resembled the pike (Esox) in its mode of life and that it may have been capable of short journeys “walking” overland. The possible selective factors stimulating the evolution of such a fish, and further evolution to the tetrapod stage are discussed.

SynopsisIn a previous paper (Andrews and Westoll 1970) the postcranial skeleton of the best known rhipidistian,Eusthenopteron, was described, and its bearing on the origin of the tetrapod postcranial skeleton discussed. The postcranial remains of other Rhipidistia are now described as far as they are known, and comparisons are made withEusthenopteronand other forms where relevant. Possible modes of function are considered in relation to the habitats in which these fishes may have lived. These studies have made it necessary to revise rhipidistian classification; the Family Rhizodontidae is re-defined and placed alone in a third Order of Rhipidistia (the Rhizodontida, alongside the better known Osteolepidida and Holoptychiida). Fresh insight has been gained into the following morphological problems: the composition of the osteolepid ring-like centrum, the origin of the tetrapod scapular blade and the diphyletic origin of the tetrapods.