Gondolelloid multielement conodont apparatus (Scythogondolella) from the Lower Triassic of Jiangsu,East China,revealed by high-resolution X-ray microtomography

The application of high-resolution X-ray microtomography on conodont natural assemblages has provided new information on the structure of the elements and enabled the three-dimensional reconstruction of apparatuses. We herein report four conodont natural assemblages from uppermost Lower Qinglong Formation, Longtan, Nanjing, East China. Using X-ray microtomography, we reconstructed the apparatus of the end-Smithian (Olenekian, Early Trassic) Scythogondolella milleri. Our result confirms that Scythogondolella has an octomembrate apparatus composed of 15 elements (a single S₀ element, two pairs of S_1–4, M and P_1–2 elements) like other gondolelloid apparatuses that have been tested by their corresponding natural assemblages, including Neogondolella, Novispathodus and Nicoraella. Element morphology of Scythogondolella closely resembles that of Neogondolella apparatus from the Illyrian (Anisian, Middle Triassic) of Monte San Giorgio: an alate (hibbardellan) S₀ element with two long lateral processes that meet at a denticle anterior of the cusp, a bipennate (hindeodellan) S₃ element with a bifurcated anterior process branching from the third denticle anterior of the cusp and an enantiognathiform S₂ element with two dissimilar processes of nearly equal in length. It differs from the latter in the length of the inner-lateral process of M element and the posterior process of S₀ and S_3–4 elements without considering the obvious morphological differences in P elements between them. The element positional homologues of Scythogondolella conforms to those of the standard 15-element plan shared primitively among ozarkodinin, prioniodinin and prioniodontid conodonts, and again confirms that the breviform digyrate elements of cypridodellan and enantiognathiform morphotypes occupy the S₁ and S₂ positions, respectively, within the superfamily Gondolelloidea.     

Testing hypotheses of element loss and instability in the apparatus composition of complex conodonts: articulated skeletons of Hindeodus

Knowledge of the conodont skeleton, in terms of the morphology of the elements and the positions they occupy, provides the foundation for understanding of homology, taxonomy and evolutionary relationships in conodonts. This knowledge also underpins analyses of conodont functional morphology and feeding. Direct evidence of skeletal anatomy and apparatus architecture comes from natural assemblages: fossils that preserve together the articulated remains of the conodont apparatus, either collapsed onto a bedding plane or as clusters of elements in which juxtaposed and overlapping elements have been fused together by diagenetic minerals. Here we describe six clusters of the biostratigraphically important conodont Hindeodus parvus from the Lower Triassic Shangsi section, Sichuan Province, South China. Five of these clusters represent the partial remains of articulated skeletons, providing direct evidence of the number and arrangement of elements in the apparatus. Combined with data from previously published natural assemblages this provides a test of the hypothesis that Triassic conodonts had a reduced dentition. Hindeodus parvus possessed a complete raptorial array of two M and nine S elements (unpaired S₀; symmetrically paired S₁, S₂, S₃, S₄); the paired P₁ locations were occupied by carminiscaphate elements, but the apparatus lacked P₂ elements. This is consistent with broader evidence for a particularly high degree of integration and constraint operating on the S–M array of morphologically complex conodonts, leading to conserved architecture of the array over a period of more than 250 million years. The loss of elements from the P domain implies a change in food processing ability and, given the predominance of data from P elements in conodont taxonomy and biostratigraphy, the hypothesis of element loss from the P domain has significant implications for the broader understanding of conodont diversity and evolutionary patterns.     

Natural assemblages of Hindeodus conodonts from a Permian–Triassic boundary sequence,Japan

Hindeodus parvus and Hindeodus typicalis occur in a deep‐water chert and claystone section in the Mino Terrane, Japan, which has been identified as a Jurassic accretionary complex. Conodont fossils are preserved as natural assemblages of impression fossils on bedding planes in claystone. In this study, 13 assemblages of Hindeodus species were recognized, comprising at most 13 elements which generally maintain the original composition and structure of an apparatus. We discriminated pairs of carminiscaphate P₁, angulate P₂ and makellate M elements, as well as a single alate S₀ element and two digyrate and four bipennate elements constituting the S array. Although the digyrate and bipennate elements are preserved in the S₂ and S_3–4 positions, respectively, a pair of S₁ elements was not found due to incompleteness in the natural assemblages. The conodont biostratigraphy indicates that the lithological boundary between chert and claystone units in the study section corresponds exactly to the Permian–Triassic boundary.     

RECONSTRUCTION OF AN APPARATUS OF NEOSTRACHANOGNATHUS TAHOENSIS FROM ORITATE,JAPAN AND SPECIES OF NEOSTRACHANOGNATHUS FROM OMAN

Abstract: The apparatus of an Early Triassic conodont Neostrachanognathus tahoensis Koike, 1998 from Oritate, Kumamoto Prefecture, Japan, and a species of Neostrachanognathus from Oman were reconstructed. On the basis of five natural assemblages from the Oritate area, the three‐dimensional apparatus model of N. tahoensis is interpreted as bilaterally symmetrical and composed of 14 elements consisting of pairs of P₁, P₂, P₃, S₁, S₂, S₃, and S₄ elements. The P₁ and P₂ elements are coniform elements, the P₃ elements are digyrate forms, and the S elements are bipennate ramiforms. The S elements are arranged rostrally in the apparatus and the pairs of the P₁, P₂, and P₃ elements are subvertically arranged caudally and ventrally to the S array. One of the natural assemblages was formed by rostrocaudal collapse of the apparatus on the sea floor, whereas the other assemblages indicate that conodont animals came to rest nearly parallel with the substrate prior to burial. A collection of isolated elements from Jabal Safra, Oman, includes a second species of Neostrachanognathus with a comparable apparatus.     

A 17‐element conodont apparatus from the Soom Shale Lagerstätte (Upper Ordovician), South Africa

Abstract:  Natural assemblages of a new conodont taxon, Notiodella keblon, from the Upper Ordovician Soom Shale Lagerstätte of South Africa contain 17 elements. This is the first time that a 17‐element apparatus plan has been unequivocally demonstrated in conodonts. The apparatus comprises paired P₁, P₂, P₃, M, S₁, S₂, S₃ and S₄ elements and an unpaired, axial S₀ element and provides a new template for use in the reconstruction of apparatuses from the collections of dispersed elements, particularly for those with icrion‐bearing P₁ elements and perhaps for other balognathids.     

Early Triassic conodont clusters from South China: revision of the architecture of the 15 element apparatuses of the superfamily Gondolelloidea

Abstract: Several fused clusters of conodont elements of the genera Neospathodus and Novispathodus were recovered from limestone beds at the Dienerian–Smithian and Smithian–Spathian boundaries, respectively, from several localities in Guangxi province, South China. Conodont clusters are otherwise extremely rare in the Triassic, and these are first described for the Early Triassic. The exceptional specimens partially preserve the relative three‐dimensional position and orientation of ramiform elements and are therefore extremely important for testing hypotheses on the architecture of apparatuses. These specimens partly confirm the previous reconstruction of the Novispathodus apparatus by Orchard. Within apparatuses of members of superfamily Gondolelloidea, elements previously identified as occupying the S₁ and S₂ positions instead occupy the S₂ and S₁ positions. Similarly, within apparatuses of members of the subfamily Novispathodinae, elements previously referred to S₃ and S₄ positions are reinterpreted to have occupied S₄ and S₃ positions, respectively.     

Apparatus architecture of the conodont Nicoraella kockeli (Gondolelloidea,Prioniodinina) constrains functional interpretations

We reconstruct the apparatus architecture of the gondollelid conodont Nicoraella kockeli based on fused clusters from the early Middle Triassic (middle Anisian, Pelsonian) of Luoping County, east Yunnan Province, south‐west China. This material was characterized non‐invasively using synchrotron x‐ray tomographic microscopy and the ensuing data analysed using computed tomography, allowing us to infer the composition, homologies and architectural arrangement of elements within the apparatus. Much of the original three‐dimensional architecture of the apparatus is preserved and our apparatus reconstruction is the best characterized of any taxon within the superfamily Gondolelloidea. This allows us to test architectural models for gondolelloids and prioniodinins, more generally, as well as the functional interpretations based upon them. In particular, we reject a recent functional interpretation of the conodont feeding apparatus which was based on a biomechanically‐optimized inference of apparatus architecture in a close gondolelloid relative of Nicoraella. Nevertheless, our architectural model provides a foundation for future functional interpretations of gondolleloids and prioniodinins, more generally.     

Architecture and functional morphology of the skeletal apparatus of ozarkodinid conodonts

Ozarkodinid conodonts were one of the most successful groups of agnathan vertebrates. Only the oropharyngeal feeding apparatus of conodonts was mineralized, and the skeletal elements were generally disarticulated on the death and decay of the body. Occasionally, however, they were preserved in association as ''natural assemblages'', fossilized in situ after post-mortem collapse of the apparatus. From analysis of element arrangement in natural assemblages of Idiognathodus from the Pennsylvanian of Illinois we have produced a precise scale model of the feeding apparatus of ozarkodinid conodonts. At the front lay an axial Sa element, flanked by two groups of four close-set elongate Sb and Sc elements which were inclined obliquely inwards and forwards; above these elements lay a pair of arched and inward pointing M elements. Behind the S-M array lay transversely oriented and bilaterally opposed Pb and Pa elements. Our model sheds new light on food acquisition in conodonts. We propose that the anterior S and M elements of ozarkodinid conodonts were attached to cartilaginous plates. In order for the animal to feed, these plates were first everted, and then drawn back and upward over the anterior edge of an underlying cartilage. These movements produced a highly effective grasping action, the cusps and denticles of the elements converging to grab and impale any food item that lay anterior to the open array. According to this hypothesis, the anterior part of the conodont apparatus is comparable to, and possibly homologous with, the lingual apparatus of extant agnathans; the elements themselves, however, have no direct homologues. <br>     

Conodont biostratigraphy of the Early Triassic in eastern Slovenia

The Early Triassic is a critical interval for the study of recovery from the terminal Permian mass extinction, as there are small-scale extinction events, which may have contributed to the delayed recovery. The systematic measuring and sampling of a 12-m-thick section at the Mokrice locality in eastern Slovenia has resulted in the recovery of a conodont fauna from the Olenekian beds. Four conodont zones have been recognized. These zones are in ascending order as follows: the Hadrodontina aequabilis Zone, Platyvillosus corniger Zone, Platyvillosus regularis Zone, and Triassospathodus hungaricus Zone. These conodont zones confirm the proposed conodont biozonation sequence in western Slovenia and have correlation value especially for the western marginal Tethys. Multielement conodont apparatuses of Triassospathodus hungaricus and Platyvillosus regularis have been reconstructed based on conodont elements that were recently obtained from the Slovenian sections. Although the S₂element was not found, the apparatus indicates that the conodont species “Spathognathodus” hungaricus should be assigned to the genus Triassospathodus.     

Parafurnishius,an Induan (Lower Triassic) conodont new genus from northeastern Sichuan Province,southwest China and its evolutionary implications

A fundamental aspect of taxonomy at the generic level, critical to understand Early Triassic conodont evolution, is the composition of the multielement apparatus. In this paper, we document a platform-bearing new conodont genus, Parafurnishius n. gen., as well as its multielement apparatus from the Griesbachian Feixianguan Formation (Lower Triassic) in Xuanhan County, northeastern Sichuan Province, southwest China. The new conodont genus is characterized by numerous robust and irregularly distributed conical denticles with variable platform morphology that has a possible affinity with the P₁ elements of Furnishius. These genera have apparatuses similar to those of Ellisonia and are classified with the family Ellisoniidae. The strong intraspecific variation of P₁ elements and the growth series within the entire sample population suggest that Parafurnishius may have evolved from the Griesbachian Isarcicella by developing random denticle positioning away from the platform centre, and then possibly evolved into younger Triassic Furnishius by developing a stable blade configuration. This preferred interpretation implies an ellisonid apparatus for Isarcicella. Alternatively, Parafurnishius may have evolved from Ellisonia and developed a homeomorphic P₁ element with Isarcicella. This new taxon has strong intraspecific variation of denticle growth orientation during the Early Triassic.     

Conodont assemblages: A new functional model

A functional model for the conodont apparatus is proposed based on Carboniferous bedding plane assemblages. It is proposed that the conodont assemblage functioned as a filter feeding and respiratory organ in organisms of unknown affinities, and that the organisation of elements in the assemblage genus Scottognathus can be used as a basic plan for interpreting the arrangement of conodont elements in other assemblages. In our model the Platform Blades opened and closed the anterior end of the system, the sieve consisted of Arched Blades, Pick-shaped Blades (assemblage genera Lewistownella and Lochriea) and the main cusps of the Elongate Blades; the denticulated bars of Elongate Blades and Pick-shaped Blades (form genera Scottognathus and Westphalicus) acted as a support for ciliated tissue. A radial and bilateral arrangement for the Elongate Blades is presented and discussed. Using this model as a guide we have reconstructed the assemblage genus Duboisella.The success of conodont organisms is attributed to the genetic plasticity of elements of the filter respiratory system, which enabled the system to adapt to evolutionary changes in the marine plankton. Ideas for further research are presented. In this account we have chosen to refer to the morphological form of conodont elements (Rhodes, 1954) rather than to the form generic and specific names assigned to them in the literature, e.g., we use the term Elongate Blades, instead of Hindeodella.     

A new Devonian species of the enigmatic Carboniferous conodont Dollymae

Arrow-shaped P₁ elements of Dollymae are characteristic for the Tournaisian conodont faunas worldwide but the phylogeny of this conodont remains obscure and its origin is cryptic. Dollymae peregrina n. sp., from the upper Famennian (upper expansa Zone) strata in the Holy Cross Mountains (central Poland), is the oldest representative of the Dollymae lineage. The morphology of the new species’ P₁ element shows primitive features in comparison to other members of this genus and is transitional in the number of element processes. Thus D. peregrina n. sp. is most probably ancestral to the remaining species. The genus appears to be monophyletic, probably rooted in Pelekysgnathus within the Icriodontidae.     

Growth and patterning in the conodont skeleton

Recent advances in our understanding of conodont palaeobiology and functional morphology have rendered established hypotheses of element growth untenable. In order to address this problem, hard tissue histology is reviewed paying particular attention to the relationships during growth of the component hard tissues comprising conodont elements, and ignoring a priori assumptions of the homologies of these tissues. Conodont element growth is considered further in terms of the pattern of formation, of which four distinct types are described, all possibly derived from a primitive condition after heterochronic changes in the timing of various developmental stages. It is hoped that this may provide further means of unravelling conodont phylogeny. The manner in which the tissues grew is considered homologous with other vertebrate hard tissues, and the elements appear to have grown in a way similar to the growing scales and growing dentition of other vertebrates.     

Cladistic tests of monophyly and relationships of biostratigraphically significant conodonts using multielement skeletal data –Lochriea homopunctatus and the genus Lochriea

Abstract: Since the 1960s, huge progress has been made in reconstructing the multielement skeletons of conodont species and developing a biologically defensible taxonomy. Nevertheless, a widespread prejudice remains that certain parts of the conodont skeleton, particularly the P₁ elements, are more informative than others with regard to taxonomy and evolutionary relationships. Here, we test these views. A new partial multielement reconstruction of the skeleton of the biostratigraphically significant conodont originally described as Gnathodus commutatus homopunctatus allows us to conduct a cladistic test of the alternative hypotheses of phylogenetic placement of this species. Our analysis also provides the first test of the hypothesis that Lochriea– species of which are markers for global correlation – is monophyletic and tests hypotheses concerning the origins of the genus. Our results demonstrate that homopunctatus is a species of Lochriea and that the genus is monophyletic. The widely held view that Lochriea arose from a species of Bispathodus is not supported. Our results show that it is difficult to predict a priori which parts of the conodont skeleton carry phylogenetic signal, and provide strong support for the hypothesis that similarity in the morphology of conodont P₁ elements alone is not a reliable guide to relationships and taxonomic groupings of conodont species. This is because P₁ elements with similar morphologies are convergently acquired in multiple conodont clades, because reliance on the characters of only one of the six or seven morphologically distinct elements of the conodont skeleton ignores phylogenetically significant data and because P₁ elements can lack characters that might seem to be diagnostic of a genus. Conodonts are no different to other organisms: ignoring data that have the potential to be phylogenetically informative is unlikely to produce the most reliable hypotheses of evolutionary relationships. We suggest that other biostratigraphically significant hypotheses of relationship between conodont taxa that are based on P₁ elements alone should be subject to cladistic testing.     

Cutting the first ‘teeth’: a new approach to functional analysis of conodont elements

The morphological disparity of conodont elements rivals the dentition of all other vertebrates, yet relatively little is known about their functional diversity. Nevertheless, conodonts are an invaluable resource for testing the generality of functional principles derived from vertebrate teeth, and for exploring convergence in a range of food-processing structures. In a few derived conodont taxa, occlusal patterns have been used to derive functional models. However, conodont elements commonly and primitively exhibit comparatively simple coniform morphologies, functional analysis of which has not progressed much beyond speculation based on analogy. We have generated high-resolution tomographic data for each morphotype of the coniform conodont Panderodus acostatus. Using virtual cross sections, it has been possible to characterize changes in physical properties associated with individual element morphology. Subtle changes in cross-sectional profile have profound implications for the functional performance of individual elements and the apparatus as a whole. This study has implications beyond the ecology of a single conodont taxon. It provides a basis for reinterpreting coniform conodont taxonomy (which is based heavily on cross-sectional profiles), in terms of functional performance and ecology, shedding new light on the conodont fossil record. This technique can also be applied to more derived conodont morphologies, as well as analogous dentitions in other vertebrates and invertebrates.     

Eine Conodontengruppe von Prooneotodus tenuis (MÜller, 1959) in natürlichem Zusammenhang aus dem Oberen Kambrium von schweden

A natural conodont assemblage,Prooneotodus tenuis (MÜller, 1959) was discovered in shales in Zone I of the Upper Cambrian of Hunneberg, Väastergötland, Sweden. It is composed of 12 similar single cone elements, which form 6 pairs of different size. The largest is more than twice the size of the smallest. This variation in size together with the occurrence of between 8-12 elements in conspecific assemblages recorded by Miller & Rushton (1973) makes it likely that during growth the animal added new elements to the apparatus. Should this be applicable to all conodonts, this observation would be of some relevance in the statistical reconstruction of conodont apparatusses.     

There is no general model for occlusal kinematics in conodonts

Knowledge of conodont element function is based largely on analysis of morphologically similar P₁ elements of few comparatively closely related species known from abundant articulated remains. From these, a stereotypical pattern of rotational occlusion has been inferred, leading to the suggestion that this may represent a general model for ozarkodinin P₁ elements at the very least. We test the generality of this occlusal model through functional analysis of Pseudofurnishius murcianus P₁ elements which, though superficially similar to homologous elements in gnathodids, evolved their platform morphology independently, through a different mode of morphogenesis, and in a different topological position within the element. Our integrated functional analysis of several articulated clusters of P₁ elements encompassed physical and virtual occlusal analyses, constrained by microwear and sharpness analyses. All of the evidence supports an occlusal model in which the Pseudofurnishius P₁ elements occluded with the dextral blade located between the rostral face of the sinistral blade and the first cusp of the rostral primary process. In achieving this, the dorsal and ventral blades guided the opposing elements, and the rostral processes of both elements guided the final stages of precise occlusion. Spalling and microwear on the non‐occlusal side of the element evidence malocclusion, requiring the complete separation of elements within the occlusal cycle. This occlusal cycle is entirely linear, orthogonal to the plane of attachment of the elements. Evidently, the rotational occlusal model is not general for P₁ elements, even for ozarkodinins, and it is likely that among conodonts occlusal kinematics are as disparate as element morphologies. Attempts to elucidate the diversity of occlusal kinematics and, therefore, feeding ecologies of conodonts will be repaid by an understanding of the role of this important abundant and diverse clade in Palaeozoic and Mesozoic marine ecosystems.     

Morphological criteria for recognising homology in isolated skeletal elements: comparison of traditional and morphometric approaches in conodonts

Abstract: Accurate hypotheses of primary homology are fundamental to many aspects of the systematics and palaeobiology of fossils. They are particularly critical for conodonts: virtually all areas of conodont research are underpinned by homology, yet the majority of conodont taxa are found only as disarticulated skeletal elements, and hypotheses of element homology are inferred from morphological comparisons with complete skeletons. This can cause problems in taxa where more than one location within the conodont skeleton is occupied by elements with similar morphology. In such cases, morphological comparisons can yield equivocal or erroneous hypotheses of homology of isolated elements. The Eramosa Lagerstätte of Ontario (Silurian, Wenlock) preserves both isolated skeletal elements and articulated conodont skeletons. The latter provide a topological context within which to test hypotheses of element homology and allow blind testing of qualitative discrimination of elements. When applied to P₁ and P₂ elements of Wurmiella excavata, this revealed inaccuracy and inconsistency in distinguishing these P element types. Standardised morphometric protocols were used to further test the efficacy of those characters used in traditional qualitative identification of P element homology, revealing that, individually, none of these characters provides an effective discriminator between P element types. Principal components and discriminant function analyses of ten ‘traditional’ morphological variables combined can distinguish P₁ from P₂ elements with a similar success rate to expert identification. Eigenshape and elliptic Fourier analyses of element outlines proved less effective at capturing shape differences that allowed for discrimination between P₁ and P₂ elements. Analysis of both traditional and outline data demonstrates that in some individuals P₁ and P₂ elements are morphologically distinct from one another, while in others they are almost indistinguishable. These results demonstrate that although qualitative assessments of homology can be prone to error, especially when undertaken by inexperienced researchers, the morphometric and analytical protocols used here provide effective additional tool for discriminating morphologically similar but non‐homologous elements. These methods thus hold promise of broad application to other conodont taxa where identification of element homology in collections of isolated specimens is problematic.     

Skeletal ontogeny and feeding mechanisms in conodonts

The growth and function of the conodont skeletal apparatus have important implications for early vertebrate relationships and the evolution of vertebrate hard tissues, yet they are poorly understood. Analysis of element length, platform linear dimensions, and platform area in discrete Pa elements of Carboniferous Idiognathodus and Gnathodus bilineatus reveals that the platform increased in size at a rate significantly above that required to maintain geometric similarity. Measurements of P, M and S elements in bedding-plane assemblages of Idiognathodus and G. bilineatus indicate that relative to Pa element length, Pb and S element growth was isometric, whereas M elements grew with negative allometry. There is no evidence to support loss or resorption of S and M elements in later growth stages, or to indicate periodic shedding and replacement of elements. These results are important for understanding apparatus and element Function. The positive allometry of the Pa element platform supports interpretations of a mashing or grinding tooth-like Function for platformed Pa elements. If conodonts were active suspension-feeders, the increasing food requirements of a growing conodont would require the filter array formed by the S and M elements to have grown at a rate significantly above isometry. The lack of positive allometry of S and M elements indicates that conodonts were not suspension-feeders and supports hypotheses that conodonts fed with a raptorial apparatus and teeth. □ Conodonts, vertebrates, skeletal apparatus, ontogeny, allometry, function, suspension-feeding, teeth.     

Apparatus Composition, Growth, And Survivorship Of The Lower Ordovician Conodont paracordylodus Gracilis Lindström, 1955

Analysis of numerous conodont element clusters from the Lower Ordovician cherts of the Burubaital Formation in central Kazakhstan reveals that the apparatus of Paracordylodus gracilis Lindstro¨m, 1955 consisted of 15 elements: two M elements, nine S elements (including 1 S₀), and four P elements (2 P₁, 2 P₂). The clusters probably originated as faecal pellets, but the best preserved indicate that the architecture of the apparatus of P. gracilis was comparable to that of ozarkodinid conodonts, providing strong support for the hypothesis that the 15-element 2M-9S-4P apparatus plan was plesiomorphic for conodonts with morphologically complex elements. All the elements within the P. gracilis clusters appear to be at a similar stage of ontogeny, and there is no evidence for late addition or replacement of elements. Analysis of element growth suggests that the relative dimensions of some elements changed during ontogeny, but the available data support the hypothesis that the growth of the apparatus as a whole was isometric. The size distribution of P. gracilis in the Burubaital Formation suggests that individuals in a particular size range were preferentially selected for consumption by predators. The identity of these predators is unknown, but they may have included other P. gracilis .