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A middle Famennian shallow-water vertebrate assemblage is described from the shallow-water shelf deposits exposed in the western Mongolia Hushoot Shiveetiin gol section from the Baruunhuurai Terrane of the Central Asian Orogenic Belt (CAOB). The low diversity, yet abundant chondrichthyan fauna represents a typical shallow-water shark biofacies but lacks the expected protacrodont and phoebodont species, instead comprising almost exclusively of ctenacanthiform shark teeth and a new genus and species Junggarensis ambiguus gen. et sp. nov. This new species appears highly derived, likely occupying the shallow-water niche protacrodont and orodont sharks typically inhabit. The identification of tooth variation in Junggarensis ambiguus gen. et sp. nov. has allowed for the synonymy of previous indeterminate Famennian shark teeth and in turn confirms vertebrate faunal connections between the Central Asian Orogenic Belt and areas along the northern margins of Gondwana.

Discoveries from the Late Devonian Gogo Formation, in the Canning Basin, Western Australia have provided insights into the origin and evolution of many unique gnathostome features such as the origins of teeth, internal fertilisation, air-breathing, transitional tissues between bone and cartilage, and insights into the fin to limb transition. Although vertebrate studies have dominated evolutionary work, invertebrate studies have added important insights into the palaeoecology of the site and demonstrated close faunal affinities along the margins of northern Gondwana and China. Geochemical analyses have broadened the understanding of the pathways involved in the exceptional preservation of this Devonian Konservat-Lagerstatte. Fossils from the Gogo Formation show extensive soft tissue preservation through phosphatization recording anatomical details not normally obtained from fossil sites.

Chondrichthyes (Elasmobranchii and Holocephali) are distinguished by their largely cartilaginous endoskeleton that comprises an uncalcified core overlain by a mineralised layer; in the Elasmobranchii (sharks, skates, rays) this mineralisation takes the form of calcified polygonal tiles known as tesserae. In recent years, these skeletal tissues have been described in ever increasing detail in sharks and rays but those of Holocephali (chimaeroids) have been less well-described, with conflicting accounts as to whether or not tesserae are present. During embryonic ontogeny in holocephalans, cervical vertebrae fuse to form a structure called the synarcual. The synarcual mineralises early and progressively, anteroposteriorly and dorsoventrally, and therefore presents a good skeletal structure in which to observe mineralised tissues in this group. Here we describe the development and mineralisation of the synarcual in an adult and stage 36 elephant shark embryo (Callorhinchus milii). Small, discrete, but irregular blocks of cortical mineralisation are present in stage 36, similar to what has been described recently in embryos of other chimaeroid taxa such asHydrolagus, while inCallorhinchusadults, the blocks of mineralisation have become more irregular, but remain small. This differs from fossil members of the holocephalan crown group (Edaphodon), as well as from stem group holocephalans (e.g., Symmorida,Helodus, Iniopterygiformes), where tessellated cartilage is present, with tesserae being notably larger than inCallorhinchusand showing similarities to elasmobranch tesserae, for example with respect to polygonal shape.

Burrow, C.J., Turner, S., Trinajstic, K. & Young, G.C., 27 February 2019. Late Silurian vertebrate microfossils from the Carnarvon Basin, Western Australia. Alcheringa 43, 204–219. ISSN 0311-5518.A...

Significant new material of Late Devonian Gogo Formation fish fossils is still surfacing. Collecting in the past decade has uncovered the first Gogo shark fossils (Gogoselachusplus another new undescribed taxon), the first acanthodian (Halmacanthodes ahlbergi), the first coelacanth, as well as the first placoderm embryos. Recent studies have elucidated the nature of placoderm claspers, pelvic girdles, synarcuals and embryos, the structure of their teeth, a description of well-preserved muscles in placoderms, and how muscles attach to bones. Molecular biomarkers have also been identified in Gogo fossils. There are now five basal ray-fin fishes in the fauna, including one undescribed new taxon. The lungfish fauna from Gogo is the most diverse known for any Devonian site, with 10 genera and 12 species. The dermal skeleton and endocast of the dipteridRhinodipterus kimberleyensishave been described in detail from CT scans; and the ontogenetic stages of neurocranium formation inGriphognathus. New specimens of the tetrapodomorph fishGogonasus andrewsaehave shed further light on its endocranium, pectoral girdle and fin. Through their exceptional preservation of both hard and varied kinds of soft tissues, the Gogo fishes remain crucial for resolving key debates on the diversification, physiology, biomechanics and phylogenetic relationships of early gnathostomes.

Many species of lizard use caudal autotomy, the ability to self-amputate a portion of their tail, regenerated over time, as an effective anti-predation mechanism. The importance of this tactic for survival depends on the degree of predation risk. There are, however, negative trade-offs to losing a tail, such as loss of further autotomy opportunities with the regenerated tail vertebrae being replaced by a continuous cartilaginous rod. The common consensus has been that once a tail has been autotomised and regenerated it can only be autotomised proximal to the last vertebral autotomy point, as the cartilage rod lacks autotomy planes. However, anecdotal evidence suggests that although the regenerated portion of the tail is unable to autotomise, it can re-regenerate following a physical shearing event. We assessed re-regeneration in three populations of the King’s skink (Egernia kingii), a large lizard endemic to south-west Western Australia and surrounding islands. We show that re-regeneration is present at an average of 17.2% across the three populations, and re-regenerated tissue can comprise up to 23.3% of an individual’s total tail length. The ability to re-regenerate may minimise the costs to an individual’s fitness associated with tail loss, efficiently restoring ecological functions of the tail.

Conodont biogenic apatite has become a preferred analytical target for oxygen isotope studies investigating ocean temperature and palaeoclimate changes in the Palaeozoic. Despite the growing application in geochemically-based palaeoenvironmental reconstructions, the paucity or absence of conodont fossils in certain facies necessitates greater flexibility in selection of robust oxygen-bearing compounds for analysis. Vertebrate microfossils (teeth, dermal denticles, spines) offer a potential substitute for conodonts from the middle Palaeozoic. Vertebrate bioapatite is particularly advantageous given a fossil record extending to the present with representatives across freshwater to fully marine environments, thus widening the scope of oxygen isotope studies on bioapatite. However, significant tissue heterogeneity within vertebrates and differential susceptibility of these tissues to diagenetic alteration have been raised as potential problems affecting the reliability of the oxygen isotope ratios as palaeoclimatic proxies. Well-preserved vertebrate microfossils and co-occurring conodont fossils from the Upper Devonian and Lower Carboniferous of the Lennard Shelf, Canning Basin, Western Australia, were analysed using bulk (gas isotope ratio mass spectrometry, GIRMS) and in-situ (secondary ion mass spectrometry, SIMS) methodologies, with the latter technique allowing investigation of specific tissues within vertebrate elements. The δ18Oconodont results may be interpreted in terms of palaeolatitudinally and environmentally sensible palaeo-salinity and -temperature and provide a baseline standard for comparison against vertebrate microfossil δ18O values. Despite an absence of obvious diagenetic modification, GIRMS of vertebrate denticles yielded δ18O values depleted in 18O by 2–4‰ relative to co-occurring conodonts. SIMS analysis of dentine tissues exhibited significant heterogeneity, while hypermineralised tissues in both scales and teeth produced δ18O values comparable with those of associated conodonts. The susceptibility of permeable phosphatic fossil tissues to microbial activity, fluid interaction and introduction of mineral precipitates post-formation is demonstrated in the dentine of vertebrate microfossils, which showed significant heterogeneity and consistent depletion in 18O relative to conodonts. The hypermineralised tissues present in both teeth and scales appear resistant to many diagenetic processes and indicate potential for palaeoclimatic reconstructions and palaeoecological investigations.

The evolution of jaws marked an important transition in the evolution of vertebrates, allowing them to become successful, active predators. Some developmental events associated with this transition can be deduced from the fossil record of jawless vertebrates, with new discoveries suggesting that the separation of the nasal sacs in jawless vertebrates was a key step in the evolution of jaws. Some members of the earliest jawed vertebrates, the placoderms, have recently been shown to have teeth and hypobranchial muscles similar to those in extant chondrichthyans. Associated with the evolution of jaws was the evolution of a moveable neck, which allowed the first jawed vertebrates to raise their heads and increase the size of their mouths, making it more efficient for food and water intake. The evolution of jaws and associated musculature enabled gnathostomes to occupy new niches and to radiate, leading to the great diversity observed today. New fossil discoveries continue to populate the gnathostome stem, adding to our understanding of the early diversification of this successful group of vertebrates.

Chondrichthyans are one of two major clades of living jawed vertebrates, with a rich fossil record potentially extending back to the Late Ordovician (455 million years ago, mya). The main groups of chondrichthyans include the chimaeroids, sharks, and skates and rays. This chapter outlines the major events in chondrichthyan evolution, focusing on features of the cranium, jaw and jaw musculature, and gill arch skeleton. The “spiny sharks” (acanthodians) and other stem chondrichthyans have recently been shown to exhibit a mosaic of chondrichthyan and osteichthyan characters. Taxa such as iniopterygians and chondrenchelyiforms, resolved as stem group chimaeroids, appear in the Carboniferous and display dramatic body forms and unusual fin morphology. Chondrichthyans also show a considerable range of dentitions, both in terms of morphology and development, particularly modified in the chimaeroids. In addition to their differing tooth morphologies, chondrichthyans have several types of jaw suspensions to support a range of feeding and breathing modes. Sharks have well-developed brains that vary according to the environment rather than phylogeny. Their senses are also well-developed and finely tuned to best perform in their particular ecological niche. The long evolutionary history of chondrichthyans and their great diversity as well as the retention of some primitive characters make them good models for evolutionary and developmental studies.

A diverse microvertebrate fauna is described from the Virgin Hills and Napier formations, Bugle Gap Limestone Canning Basin, Western Australia. Measured sections at Horse Spring and Casey Falls (Virgin Hills Formation) and South Oscar Range (Napier Formation) comprise proximal to distal slope carbonates ranging in age from the Late Devonian Frasnian to middle Famennian. A total of 18 chondrichthyan taxa are identified based on teeth, including the first record of Thrinacodus tranquillus, Cladoides wildungensis, Protacrodus serra and Lissodus lusavorichi from the Canning Basin. A new species, Diademodus dominicus sp. nov. is also described and provides the first record of this genus outside of Laurussia. In addition, the upper range of Australolepis seddoni has been extended to Late Devonian conodont Zone 11, making it the youngest known occurrence for this species. The Virgin Hills and Napier formations microvertebrate faunas show close affinities to faunas recovered from other areas of Gondwana, including eastern Australia, Iran, Morocco and South China, which is consistent with known conodont and trilobite faunas of the same age.

a b s t r a c t The Late Devonian was a time of major evolutionary change encompassing the fifth largest mass extinction, the Frasnian-Famennian event. In order to establish a chronological framework for global correlation before, during, and following the Frasnian-Famennian mass extinction, we carried out a coupled magnetostratigraphic and biostratigraphic study of two stratigraphic sections in the Upper Devonian carbonate reef complexes of the Lennard Shelf, in the Canning Basin, Western Australia. Magnetostratigraphy from these rocks provides the first high-resolution definition of the Late Devonian magnetic polarity timescale. A 581-m-reference section and an 82-m overlapping section through the marginal slope facies (Napier Formation) of the Oscar Range as well as a 117-m section at Horse Spring (Virgin Hills Formation) were sampled at decimeter to meter scale for magnetostratigraphy. Conodont biostratigraphy was used to correlate both sections, and link magnetostratigraphic polarity zones to a globally established biostratigraphy. As table, Characteristic Remanent Magnetization (ChRM) with dual polarities (NE, shallowly upward and SW, shallowly downward) is recovered from ∼60% of all samples, with magnetite inferred to be the chief magnetic carrier from thermal demagnetization characteristics. These directions define a geomagnetic pole at 49.5 ◦ S/285.8 ◦ E and α95 = 2. 4( n = 501), placing the Canning Basin at 9.9 ◦ S during the Late Devonian, consistent with carbonate reef development at this time. Ac onservative interpretation of the magnetostratigraphy shows the recovery of multiple reversals from both sections, not including possible cryptochrons and short duration magnetozones. Field tests for primary remanence include positive reversal tests and matching magnetozones from an overlapping section in the Oscar Range. As trong correlation was found between magnetic polarity stratigraphies of the Oscar Range and Horse Spring sections, and we correlate 12 magnetostratigraphic packages. The relative stratigraphic thicknesses of the isochronous sediments from these two sections indicate that carbonate accumulation was ∼4.5× faster in the middle slope deposits at Oscar Range than in the more distal, lower slope Horse Spring deposits for the middle Frasnian through Famennian. The magnetic field during the Late Devonian underwent a relatively high reversal frequency with good potential for regional and global correlation, and should prove useful in deciphering a high-resolution chronostratigraphy across the Lennard Shelf to enable higher confidence examination of reef development across a major biotic crisis.

Reproduction in jawed vertebrates (gnathostomes) involves either external or internal fertilization. It is commonly argued that internal fertilization can evolve from external, but not the reverse. Male copulatory claspers are present in certain placoderms, fossil jawed vertebrates retrieved as a paraphyletic segment of the gnathostome stem group in recent studies. This suggests that internal fertilization could be primitive for gnathostomes, but such a conclusion depends on demonstrating that copulation was not just a specialized feature of certain placoderm subgroups. The reproductive biology of antiarchs, consistently identified as the least crownward placoderms and thus of great interest in this context, has until now remained unknown. Here we show that certain antiarchs possessed dermal claspers in the males, while females bore paired dermal plates inferred to have facilitated copulation. These structures are not associated with pelvic fins. The clasper morphology resembles that of ptyctodonts, a more crownward placoderm group, suggesting that all placoderm claspers are homologous and that internal fertilization characterized all placoderms. This implies that external fertilization and spawning, which characterize most extant aquatic gnathostomes, must be derived from internal fertilization, even though this transformation has been thought implausible. Alternatively, the substantial morphological evidence for placoderm paraphyly must be rejected., Travel to Tallinn, London and Washington for J.A.L. to examine specimens was supported by Flinders University. G.C.Y., J.A.L. and K.T. acknowledge support from the Australian Research Council. ARC DP1092870

Newly discovered pelvic and reproductive structures within placoderms, representing some of the most crownward members of the gnathostome stem group and the most basal jawed vertebrates, challenge established ideas on the origin of the pelvic girdle and reproductive complexity. Here we critically review previous descriptions of the pelvic structures in placoderms and reinterpret the morphology of the pelvic region within the arthrodires and ptyctodonts, in particular the position of the pelvic fin and the relationship of the male clasper to the pelvic girdle. Absence of clear articular surfaces on the clasper and girdle in the Arthrodira, along with evidence from the Ptyctodontida, suggest that these are separate structures along the body. We describe similarities between the pectoral and pelvic girdles and claspers, for example, all these have both dermal and perichondral (cartilaginous) components. Claspers in placoderms and chondrichthyans develop in very different ways; in sharks, claspers develop from the pelvic fin while the claspers in placoderms develop separately, suggesting that their independent development involved a posterior extension of the 'competent stripes' for fin development previously limited to the region between the paired pectoral and pelvic fins. Within this expanded zone, we suggest that clasper position relative to the pelvic fins was determined by genes responsible for limb position. Information on early gnathostome reproductive processes is preserved in both the Ptyctodontida and Arthrodira, including the presence of multiple embryos in pregnant females, embryos of differing sizes and of different sexes (e.g. male claspers preserved in some embyros). By comparison with chondrichthyans, these observations suggest more complex reproductive strategies in placoderms than previously appreciated.

Royal Society Open Science 4(7), 170214 (2017). doi:10.1098/rsos.170214, Published by Royal Soc. Publ., London

Photic zone euxinia (PZE) has proven important for elucidating biogeochemical changes that occur during oceanic anoxic events, including mass extinction and conditions associated with unique fossil preservation. Organic geochemical analyses of a 380 Ma invertebrate fossil, which included well-preserved soft tissues, from the Gogo Formation (Canning Basin, Western Australia) showed biomarkers and stable isotopic values characteristic of PZE and a consortium of sulfate-reducing bacteria, which lead to exceptional fossil and biomarker preservation. The carbonate concretion contained phytoplankton, green sulfur bacteria (Chlorobi), and sulfate-reducing bacteria biomarkers with an increasing concentration toward the nucleus where the fossil is preserved. The spatial distribution of cholestane unequivocally associated with the fossilized tissue and its high relative abundance to the total steranes suggest that the fossil is a crustacean. The presence of an active sulfur cycle in this Devonian system, including sulfate reduction and the resulting PZE, played a pivotal role in the preservation of soft tissue from the fossil and its associated low-maturity biomarker ratios.

A new acanthodiform acanthodian Halimacanthodes ahlbergi n. gen. n. sp., based on a single uncrushed, partial articulated specimen, represents the first acanthodian collected from the Gogo Formation, Canning Basin, Western Australia. The delicate perichondral ossifications of the lower jaws, branchial skeleton and endoskeletal shoulder girdle are preserved in 3D. H. ahlbergi n. gen. n. sp. is characterised by having a tall slender scapular shaft, paired pelvic fin spines, mineralised branchial arches and scales with an anterior median depression and a microornament of tiny smooth tubercles randomly distributed on the crown. In having paired pelvic spines and lacking prepelvic spines, it is most closely related to Howittacanthus kentoni from Frasnian lacustrine deposits of eastern Victoria. Isolated scales, here attributed to the new taxon, are found in the coeval Gneudna Formation, Carnarvon Basin, Western Australia.

The synarcual is a structure incorporating the anterior vertebrae of the axial skeleton and occurs in vertebrate taxa such as the fossil group Placodermi and the Chondrichthyes (Holocephali, Batoidea). Although the synarcual varies morphologically in these groups, it represents the first indication, phylogenetically, of a differentiation of the vertebral column into separate regions. Among the placoderms, the synarcual of Cowralepis mclachlani Ritchie, 2005 (Arthrodira) shows substantial changes during ontogeny to produce an elongate, spool-shaped structure with a well-developed dorsal keel. Because the placoderm synarcual is covered in perichondral bone, the ontogenetic history of this Cowralepis specimen is preserved as it developed anteroposteriorly, dorsally and ventrally. As well, in the placoderm Materpiscis attenboroughi Long et al., 2008 (Ptyctodontida), incomplete fusion at the posterior synarcual margin indicates that both neural and haemal arch vertebral elements are added to the synarcual. A survey of placoderm synarcuals shows that taxa such as Materpiscis and Cowralepis are particularly informative because perichondral ossification occurs prior to synarcual fusion such that individual vertebral elements can be identified. In other placoderm synarcuals (e.g. Nefudina qalibahensis Lelievre et al., 1995; Rhenanida), cartilaginous vertebral elements fuse prior to perichondral ossification so that individual elements are more difficult to recognize. This ontogenetic development in placoderms can be compared to synarcual development in Recent chondrichthyans; the incorporation of neural and haemal elements is more similar to the holocephalans, but differs from the batoid chondrichthyans.

A full description of a complete and articulated, three-dimensionally preserved, placoderm fish, Materpiscis attenboroughi (Ptyctodontida), from the Late Devonian Gogo Formation is presented. The jaw articulation is unique in being preserved in situ, providing new morphological information on the articulation of the quadrate, metapterygoid, and labial skeleton. In addition, separate hyoid and opercular cartilages are identified, thus confirming their presence for the first time within placoderms. Preserved orbital ossifications indicate an anteriomesial orientation of this braincase region. The complete scapulocoracoid provides additional morphological information on the pectoral fin articulation. A new specimen of Austroptyctodus gardineri preserving the anterior portion of the head and jaws allows for revised descriptions of the endocranium and visceral skeleton, including the most complete endocranial ossifications recovered to date. As well, elements of the labial skeleton not known previousl...

The Gogo Formation of Western Australia preserves a unique Late Devonian (Frasnian) reef fauna. The exceptional three-dimensional preservation of macrofossils combined with unprecedented soft-tissue preservation (including muscle bundles, nerve cells, and umbilical structures) has yielded a particularly rich assemblage with almost 50 species of fishes described. The most significant discoveries have contributed to resolving placoderm phylogeny and elucidating their reproductive physiology. Specifically, these discoveries have produced data on the oldest known vertebrate embryos; the anatomy of the primitive actinopterygian neurocranium and phylogeny of the earliest actinopterygians; the histology, radiation, and plasticity of dipnoan (lungfish) dental and cranial structures; the anatomy and functional morphology of the extinct onychodonts; and the anatomy of the primitive tetrapodomorph head and pectoral fin.

An almost complete but predominantly disarticulated ptyctodont fish, Kimbryanodus williamburyensis n. gen., n.sp. from the Late Devonian Gneudna Formation, is described. The fossils occur as three-dimensionally preserved isolated plates, and this has allowed the reconstruction of the fish. A taxonomic revision of the ptyctodonts was undertaken based on recently described Australian taxa and new reconstructions of Australian, American and European specimens. The phylogenetic analysis supports a threefold division of the ptyctodonts, with Rhamphodopsis being the most basal taxon and the other ptyctodonts divided into those possessing a median dorsal spine, spinal plate and simple V-shaped overlap of the anterior lateral and anterior dorsolateral plates and those taxa which do not.

Intraspecies variation, polymorphism and asymmetric traits are observed within two families of Arthrodira, the Incisoscutidae and Camuropiscidae, from the Gogo Formation in northern Western Australia. Individual plates of the head and trunk shield show considerable variation between individuals. Plates that show the greatest degree polymorphic traits are the rostral (R), marginal (M), submarginal (SM), preorbital (PrO), anterior dorsolateral, anterior median ventral (AMV) and posterior ventrolateral (PVL) plates. The paths of the sensory line canals are the most variable feature and the dermal plates of the cheek show the greatest asymmetry. It is apparent that if anatomical data in arthrodires are to be interpreted with greater precision, detailed knowledge of intraspecies variation, polymorphic and asymmetric traits is essential. How these variables are treated in cladistic analysis is also critical. Here multistate characters were coded differently in five discrete analyses, each analysis yielding a different number of trees and relationships. It was concluded that including and coding for multistate characters gave the most robust tree. In addition, further morphological characters from a new specimen of Gogosteus sarahae Long (1994) indicates many of the characters used to separate this genus from Incisoscutum are inconsistent and so it is here considered that the genus Gogosteus is a junior synonym of Incisoscutum.

Shark teeth and scales from the Gneudna Formation type section, Carnarvon Basin are rare, but they represent a diverse fauna as well as being the first Frasnian chondrichthyan remains found in Western Australia. In contrast numerous shark teeth and scales have been obtained from coeval sections in the Canning Basin. Teeth referred to as Phoebodus bifurcatus, Phoebodus fastigatus, Phoebodus cf. fastigatus, Phoebodus latus, Phoebodus sp. C and Protacrodus sp. 1 are described from two Canning Basin localities: Horse Spring Range and McIntyre Knolls. The phoebodont species described here have a global distribution and can, therefore, be placed within the standard Frasnian phoebodont zonation. The shark remains from the Gneudna Formation type section include one new genus Emerikodus ektrapelus gen. et sp. nov., described along with Helodontidae indet and Elasmobranchii gen. et sp. indet. It is proposed that the faunal differences observed between the localities are a result of environmental differences. In addition to shark remains, scales from the thelodont Australolepis seddoni were also recovered from each locality. The well-dated Zone 6–10 conodont faunas at Horse Spring constrain the range of A. seddoni with which they occur, and importantly indicate that the Gneudna Formation type section is wholly Frasnian.

Well-preserved vertebrate microremains are abundant in the residues from a calcareous grey siltstone in thekarawakabiozone (?late Givetian) of the Aztec Siltstone at Mount Crean, Lashly Mountains, Antarctica. Acanthodians are represented by scales of acritolepidPechoralepis juozasisp. nov., climatiidNostolepissp. cf.N. gaujensisValiukevičius, diplacanthidMilesacanthus antarcticaYoung & Burrow, and an undetermined acanthodiform. The acanthodian assemblage resembles those from early Frasnian carbonates of central Iran. Chondrichthyan elements in the fauna include rare teeth ofAztecodus harmsenaeLong & Young andAntarctilamna priscaYoung, ctenacanthoid-type scales and branchial denticles which are possibly fromAntarctilamna, and scales of an indeterminate chondrichthyan. An isolated set of acanthodid acanthodiform jaws from the uppermost ‘phyllolepid’ biozone of the Aztec Siltstone at Mount Ritchie, Warren Range, Antarctica is also described.

Compagopiscis croucheri and Gogopiscis gracilis (Gardiner and Miles, 1994) were collected in high numbers and in different size classes from the Upper Devonian Gogo Formation, Western Australia. This material has provided the basis for an investigation of ontogentic and phenotypic variation of characters and their phylogenetic implications. We used the Principal Component Analysis to examine if variation between specimens assigned to C. croucheri and G. gracilis could be attributed to random variation. In our analysis we found that only the first two principal components showed any significant ability to discriminate between the specimens assigned to C. croucheri and G. gracilis. The first principal component is a measure of overall size of the specimen, so that variation in this principal component can be explained in terms of maturity and growth within a single species. Not all the anatomical variation observed in this study can be attributed to ontogeny and it is considered that the two-class ...

Here we report four high-resolution carbon isotope records in addition to trace element data for the Frasnian–Famennian (F–F) boundary interval in the Lennard Shelf carbonate system of the Canning Basin, Western Australia. This region lacks the characteristic black shale horizons associated with the global Late Devonian Kellwasser extinction events, yet still exhibits a trend in carbon isotope character similar to what has been reported from elsewhere in the world (two positive δ13C excursions with ~ 3–4‰ amplitudes). Enrichments in select trace element ratios suggest that both excursions are related to periods of oxygen deprivation and perhaps increased biological productivity. Given the continuous and stratigraphically expanded nature of Lennard Shelf sections, together with high-density sampling constrained by both conodont biostratigraphy and magnetostratigraphy, we observe that the Upper Kellwasser isotope excursion (maximum δ13C values) and associated trace element enrichments occur distinctly lower than the F–F boundary level. These results have implications for the paleoenvironmental conditions leading up to the Late Devonian Mass Extinction in terms of ocean chemistry and circulation patterns. This data set allows for a rare, detailed look at the temporal relationship between the Kellwasser events and the F–F boundary and constrains the pattern of carbon isotope perturbations at the intra-zonal scale.

This work is a contribution to IGCP 596., Here we present new data from the first well-preserved chondrichthyan fossil from the early Late Devonian (ca. 380–384 Mya) Gogo Formation Lägerstatte of Western Australia. The specimen is the first Devonian shark body fossil to be acid-prepared, revealing the endoskeletal elements as three-dimensional undistorted units: Meckel’s cartilages, nasal, ceratohyal, basibranchial and possible epibranchial cartilages, plus left and right scapulocoracoids, as well as teeth and scales. This unique specimen is assigned to Gogoselachus lynnbeazleyae n. gen. n. sp., This work was supported by grants from the Australian Research Council DP 0772138 awarded to GCY and JAL for travel and scanning of specimens at the ANU; and DP1092870 awarded to KMT for travel to collaborate. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Here we present a new species of placoderm fish, Africanaspis edmountaini sp. nov., and redescribe Africanaspis doryssa on the basis of new material collected from the type locality of Africanaspis. The new material includes the first head shields of Africanaspis doryssa in addition to soft anatomy for both taxa. Hitherto Africanaspis was entirely described from trunk armour and no record of body and fin outlines had been recorded. In addition the first record of embryonic and juvenile specimens of Africanaspis doryssa is presented and provides a growth series from presumed hatchlings to presumed adults. The presence of a greater number of juveniles compared to adults indicates that the Waterloo Farm fossil site in South Africa represents the first nursery site of arthrodire placoderms known from a cold water environment. The preservation of an ontogenetic series demonstrates that variation within the earlier known sample, initially considered to have resulted from ontogenetic change, instead indicates the presence of a second, less common species Africanaspis edmountaini sp. nov. There is some faunal overlap between the Waterloo Farm fossil site and faunas described from Strud in Belgium and Red Hill, Pennsylvania, in north America, supporting the concept of a more cosmopolitan vertebrate fauna in the Famennian than earlier in the Devonian.

The extinct placoderm fishes were the dominant group of vertebrates throughout the Middle Palaeozoic era, yet controversy about their relationships within the gnathostomes (jawed vertebrates) is partly due to different interpretations of their reproductive biology. Here we document the oldest record of a live-bearing vertebrate in a new ptyctodontid placoderm, Materpiscis attenboroughi gen. et sp. nov., from the Late Devonian Gogo Formation of Australia (approximately 380 million years ago). The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac. Another ptyctodont from the Gogo Formation, Austroptyctodus gardineri, also shows three small embryos inside it in the same position. Ptyctodontids have already provided the oldest definite evidence for vertebrate copulation, and the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to that of some modern sharks and rays. The new discovery points to internal fertilization and viviparity in vertebrates as originating earliest within placoderms.

The squamation of a complete palaeoniscoid, M. durgaringa Gardiner & Bartram, 1977, from the Frasnian Gogo Formation is described. A variety of isolated scales from the Gneudna Formation, Carnarvon Basin, are referred to M. durgaringa on the basis of comparison with the described articulated specimen. Scales of various forms are attributed to specific regions of the body.

From Jawless to Jawed The earliest vertebrates were jawless. Past reconstructions have assumed that the primitive jawed condition was much like that found in sharks. Trinajstic et al. (p. 160 , published online 13 June; see the Perspective by Kuratani ) describe fossil musculature from the early jawed placoderms (an extinct class of armored prehistoric fish) that show that the basal structure was distinct from that found in sharks, having a notable dermal joint between the skull and shoulder girdle.

International audience; Abstract Background Firm attachments binding muscles to skeleton are crucial mechanical components of the vertebrate body. These attachments (entheses) are complex three-dimensional structures, containing distinctive arrangements of cells and fibre systems embedded in the bone, which can be modified during ontogeny. Until recently it has only been possible to obtain 2D surface and thin section images of entheses, leaving their 3D histology largely unstudied except by extrapolation from 2D data. Entheses are frequently preserved in fossil bones, but sectioning is inappropriate for rare or unique fossil material. Methodology/Principal Findings Here we present the first non-destructive 3D investigation, by propagation phase contrast synchrotron microtomography (PPC-SRµCT), of enthesis histology in extant and fossil vertebrates. We are able to identify entheses in the humerus of the salamander Desmognathus from the organization of bone-cell lacunae and extrinsic fibres. Statistical analysis of the lacunae differentiates types of attachments, and the orientation of the fibres, reflect the approximate alignment of the muscle. Similar histological structures, including ontogenetically related pattern changes, are perfectly preserved in two 380 million year old fossil vertebrates, the placoderm Compagopiscis croucheri and the sarcopterygian fish Eusthenopteron foordi. Conclusions/Significance We are able to determine the position of entheses in fossil vertebrates, the approximate orientation of the attached muscles, and aspects of their ontogenetic histories, from PPC-SRµCT data. Sub-micron microtomography thus provides a powerful tool for studying the structure, development, evolution and palaeobiology of muscle attachments.

The ontogenetic trajectories of fourteen dermal plates from Compagopiscis croucheri (Placodermi, Arthrodira) and,the more derived species Incisoscutum ritchei were compared. The mechanism of allometric predisplacement occured in: the biting division of the inferognathal; the anterior ventrolateral; and the median dorsal breadth. Allometric postdisplacement occured in the postmesial breadth and the orbital diameter and allometric hypermorphosis was seen in the increases of the prepineal length and the median dorsal length. It is suggested that the lengthwise growth occurs earlier in the ontogeny than breadthways growth and that dissociated allometric heterochrony has been an important mechanism in the evolution of the arthrodires.

Teeth and jaws constitute a model of the evolutionary developmental biology concept of modularity and they have been considered the key innovations underpinning a classic example of adaptive radiation. However, their evolutionary origins are much debated. Placoderms comprise an extinct sister clade or grade to the clade containing chondrichthyans and osteichthyans, and although they clearly possess jaws, previous studies have suggested that they lack teeth, that they possess convergently evolved tooth-like structures or that they possess true teeth. Here we use synchrotron radiation X-ray tomographic microscopy (SRXTM) of a developmental series of Compagopiscis croucheri (Arthrodira) to show that placoderm jaws are composed of distinct cartilages and gnathal ossifications in both jaws, and a dermal element in the lower jaw. The gnathal ossification is a composite of distinct teeth that developed in succession, polarized along three distinct vectors, comparable to tooth families. The teeth are composed of dentine and bone, and show a distinct pulp cavity that is infilled centripetally as development proceeds. This pattern is repeated in other placoderms, but differs from the structure and development of tooth-like structures in the postbranchial lamina and dermal skeleton of Compagopiscis and other placoderms. We interpret this evidence to indicate that Compagopiscis and other arthrodires possessed teeth, but that tooth and jaw development was not developmentally or structurally integrated in placoderms. Teeth did not evolve convergently among the extant and extinct classes of early jawed vertebrates but, rather, successional teeth evolved within the gnathostome stem-lineage soon after the origin of jaws. The chimaeric developmental origin of this model of modularity reflects the distinct evolutionary origins of teeth and of component elements of the jaws.

The placoderms are a large group of primitive armoured fishes. Although wholly extinct, their enigmatic anatomy could hold clues to the evolution of the jawed vertebrates (gnathostomes), including ourselves. A new fossil discovery has clarified the mechanism of reproduction in Incisoscutum, an organism of particular interest as a member of the arthrodires, a large and important placoderm group. A well preserved fossil of an adult Incisoscutum ritcchiei female was recently found with embryos, evidence that fertilization was internal. The new fossil is of a male of the species, showing the presence of penis-like pelvic claspers similar to those found in fossil Ptyctodontida (a group of unarmoured placoderms) and in sharks. The placoderms are a large group of primitive armoured fishes, which, although now extinct, could shed light on the evolution of jawed vertebrates. Recent fossil finds have been discovered with embryos, illustrating that fertilization was internal, but direct evidence for this was missing. Here, the discovery of a completely ossified pelvic clasper in a male Incisoscutum ritchiei confirms internal fertilization in arthrodires, a large and important placoderm group. Recent finds1,2 demonstrate that internal fertilization and viviparity (live birth) were more widespread in the Placodermi, an extinct group of armoured fishes, than was previously realized. Placoderms represent the sister group of the crown group jawed vertebrates (Gnathostomata)3,4, making their mode(s) of reproduction potentially informative about primitive gnathostome conditions. An ossified pelvic fin basipterygium discovered in the arthrodire Incisoscutum ritchiei was hypothesized to be identical in males and females, with males presumed to have an additional cartilaginous element or series forming a clasper. Here we report the discovery of a completely ossified pelvic clasper in Incisoscutum ritchiei (WAM 03.3.28) which shows that this interpretation was incorrect: the basipterygium described previously1 is in fact unique to females. The male clasper is a slender rod attached to a square basal plate that articulates directly with the pelvis. It carries a small cap of dermal bone covered in denticles and small hooks that may be homologous with the much larger dermal component of the ptyctodont clasper.

The principal objective of our paper was to describe the exceptional muscle and nerve tissues occurring in the 380 Myr old placoderms from the Gogo Formation in northern Western Australia. It was never our intention to produce an in-depth discussion on early vertebrate phylogeny, but instead to

In this paper, we show exceptional three-dimensionally preserved fossilized muscle tissues in 380–384 Myr old placoderm fish (Late Devonian), offering new morphological evidence supporting the hypothesis that placoderms are the sister group to all other gnathostomes. We describe the oldest soft tissue discovered in gnathostomes, which includes striated muscle fibres, circulatory and nerve tissues, preserved as phosphatized structures precipitated by microbial infilling of small, protected areas under the headshield of the arthrodire, Eastmanosteus calliaspis . Muscle impressions have also been found in the ptyctodontid, Austroptyctodus gardineri . The specimens display primitive vertebrate muscle structures; in particular, shallow W-shaped muscle blocks such as those observed in lampreys. New information from fossilized soft tissues thus elucidates the affinities of the placoderms and provides new insights into the evolution and radiation of gnathostomes.

The synarcual is a structure incorporating multiple elements of two or more anterior vertebrae of the axial skeleton, forming immediately posterior to the cranium. It has been convergently acquired in the fossil group ‘Placodermi’, in Chondrichthyes (Holocephali, Batoidea), within the teleost group Syngnathiformes, and to varying degrees in a range of mammalian taxa. In addition, cervical vertebral fusion presents as an abnormal pathology in a variety of human disorders. Vertebrae develop from axially arranged somites, so that fusion could result from a failure of somite segmentation early in development, or from later heterotopic development of intervertebral bone or cartilage. Examination of early developmental stages indicates that in the Batoidea and the ‘Placodermi’, individual vertebrae developed normally and only later become incorporated into the synarcual, implying regular somite segmentation and vertebral development. Here we show that in the holocephalan Callorhinchus milii, uniform and regular vertebral segmentation also occurs, with anterior individual vertebra developing separately with subsequent fusion into a synarcual. Vertebral elements forming directly behind the synarcual continue to be incorporated into the synarcual through growth. This appears to be a common pattern through the Vertebrata. Research into human disorders, presenting as cervical fusion at birth, focuses on gene misexpression studies in humans and other mammals such as the mouse. However, in chondrichthyans, vertebral fusion represents the normal morphology, moreover, taxa such Leucoraja (Batoidea) and Callorhinchus (Holocephali) are increasingly used as laboratory animals, and the Callorhinchus genome has been sequenced and is available for study. Our observations on synarcual development in three major groups of early jawed vertebrates indicate that fusion involves heterotopic cartilage and perichondral bone/mineralised cartilage developing outside the regular skeleton. We suggest that chondrichthyans have potential as ideal extant models for identifying the genes involved in these processes, for application to human skeletal heterotopic disorders.

—A new genus and species of selenosteid arthrodire is described from the Late Devonian of Morocco. Driscollaspis pankowskiorum, gen. nov. sp. nov., is defined as a selenosteid with a shallow preorbital plate embayment of the central plate, a paranuchal plate embayment of the central plate as a deep embayment determined by the lateral and posterior lobe, a central plate expanded at the contact with the pineal plate as transverse anterior border, and a suborbital plate overlapping the postorbital plate. The dermal ornamentation is tubercular, forming patches of reticular ridges clustered around sensory-line canal junctions in plate centers. The sensory-line canals are distinctly raised just above the level of the dermal ornamentation, a unique character not previously recognized in any arthrodire but seen in some ptyctodontids. A new phylogenetic hypothesis supports the monophyly of the Selenosteidae within which this new taxon is resolved, but emphasizes also unresolved relationships among aspinoth...