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Note on the morphology and systematic position of Alkenopterus burglahrensis (Chelicerata: Eurypterida: Eurypterina) from the Lower Devonian of Germany
Abstract
The holotype of the eurypterid Alkenopterus burglahrensis from the Lower Devonian (Siegenian) of the Westerwald area (Rhineland-Palatinate, SW Germany) is re-examined. In contrast to a previous concept, this species has flattened distal podomeres seven and eight and a movable flattened spine on the seventh podomere of the sixth prosomal appendage (podomere VI-7a). Based on the presence of such a slender paddle, A. burglahrensis has to be regarded as a basal ‘swimming eurypterid’ (Eurypterina) and is formally transferred here to the family Onychopterellidae, extending the stratigraphical range of this family into the Lower Devonian.
... Sampling of the Carcinosomatoidea is increased, with ten species included for the carcinosomatid, megalograptid, and mixopterid clades in addition to the three sampled previously. The genus Alkenopterus Størmer, 1974 is also included for the first time, as it has been shown to be a basal representative of the Eurypterina [46] rather than a stylonurine as previously interpreted [47]. Only one carcinosomatoid genus was omitted: Eocarcinosoma Caster and Kjellesvig-Waering, 1964, which is known from a single small carapace. ...
... The phylogenetic analysis, as detailed in the methods section, yielded a single most parsimonious tree (Fig. 21) with a length of 475 steps, an ensemble Consistency Index of 0.429, ensemble Retention Index of 0.796, and Rescaled Consistency Index of 0.341. The topology is predominantly congruent with that retrieved from previous analyses of Stylonurina [68][69][70] and Eurypterina [9,26,45], with the exception of the position of Alkenopterus, which is retrieved here as a basal member of the Eurypterina as suggested by Poschmann [46]. Pentecopterus decorahensis is resolved as the basalmost member of the Megalograptidae, united with Echinognathus and Megalograptus by the shared possession of two or more pairs of spines per podomere on prosomal appendage IV, a reduction of all spines of appendage V except the pair on the penultimate podomere, an ornamentation of angular scales across the posterior margin of the dorsal tergites, longitudinal rows of large scales on the tergites, and an ornamentation consisting predominantly of guttalate scales. ...
Eurypterids are a diverse group of chelicerates known from ~250 species with a sparse Ordovician record currently comprising 11 species; the oldest fully documented example is from the Sandbian of Avalonia. The Middle Ordovician (Darriwilian) fauna of the Winneshiek Lagerstätte includes a new eurypterid species represented by more than 150 specimens, including some juveniles, preserved as carbonaceous cuticular remains. This taxon represents the oldest described eurypterid, extending the documented range of the group back some 9 million years.
The new eurypterid species is described as Pentecopterus decorahensis gen. et sp. nov.. Phylogenetic analysis places Pentecopterus at the base of the Megalograptidae, united with the two genera previously assigned to this family by the shared possession of two or more pairs of spines per podomere on prosomal appendage IV, a reduction of all spines except the pair on the penultimate podomere of appendage V, and an ornamentation of guttalate scales, including angular scales along the posterior margin of the dorsal tergites and in longitudinal rows along the tergites. The morphology of Pentecopterus reveals that the Megalograptidae are representatives of the derived carcinosomatoid clade and not basal eurypterids as previously interpreted.
The relatively derived position of megalograptids within the eurypterids indicates that most eurypterid clades were present by the Middle Ordovician. Eurypterids either underwent an explosive radiation soon after their origination, or earlier representatives, perhaps Cambrian in age, remain to be discovered. The available instars of Pentecopterus decorahensis suggest that eurypterids underwent extreme appendage differentiation during development, a potentially unique condition among chelicerates. The high degree of appendage specialization in eurypterids is only matched by arachnids within chelicerates, supporting a sister taxon relationship between them.
... Lamsdell et al. 2010b Family Rhenopteridae Størmer, 1951 Remarks. This family is equivalent to Brachyopterellidae Tollerton, 1989 and Alkenopteridae Poschmann andTetlie, 2004. Lamsdell et al. (2010b) Lamsdell et al. 2010a (Figs. ...
The stylonurid eurypterid Leiopterella tetliei Lamsdell, Braddy, Loeffler, and Dineley, 2010 (Chelicerata: Eurypterida: Rhenopteridae) from the Early Devonian (Lochkovian) of Nunavut in Arctic Canada is redescribed. Restudy of the holotype under polarized light revealed a labrum, epistomal sutures, prosomal appendage III, and deltoid plates anterior to the genital appendage. An additional new specimen preserves the distal podomeres of appendage VI and gradually tapering opisthosomal tergites. The characters resolved here support the hypothesis that L. tetliei was relatively basal within the wider Stylonurina clade, with its tapering postabdomen supporting a more basal position within Rhenopteridae than previously suggested.
... This is especially the case when there is notable overlap in the visual field anteriorly. To expand this dataset, more basal eurypterids, such as those within Stylonurina, should be considered as these forms represent a more ancestral morphologies (Tetlie 2007;Poschmann 2014). Comparison with this group in a geometric morphometric context will allow for a more complete picture of modifications to eurypterid carapaces and lateral compound eye position. ...
Eurypterids (sea scorpions) are a group of extinct, marine euchelicerates that have an extensive Palaeozoic record. Despite lacking a biomineralised exoskeleton, eurypterids are abundantly preserved within select deposits. These collections make statistical analyses comparing the morphology of different genera possible. However, eurypterid shape has not yet been documented with modern geometric morphometric tools. Here, we summarise the previous statistical assessments of eurypterid morphology and expand this research by presenting landmark and semi-landmark analyses of 115 eurypterid specimens within the suborder Eurypterina. We illustrate that lateral compound eye morphology and position drives specimen placement in morphospace and separates proposed apex predators from more generalist forms. Additionally, evidence for size clusters in Eurypterus that may reflect ontogeny is uncovered. We highlight the use of geometric morphometric analyses in supporting the naming of new taxa and demonstrate that these shape data represent a novel means of understanding inter-generic ontogenetic trajectories and uncovering developmental changes within the diverse euarthropod group.
Stoermeropterus conicus (Eurypterida: Eurypterina), from the Telychian (Upper Llandovery, Silurian) of Pentland Hills near Edinburgh, Scotland, is described from material originally assigned to three different species (Nanahughmilleria conica, Drepanopterus bembycoides and Drepanopterus lobatus). Two other existing eurypterid species, Hughmilleria lata from the Wenlock of Norway and Drepanopterus nodosus from the Pridoli of North America are recognized as being congeneric with S. conicus, united principally by their possession of moveable mesosomal spines on the mesosoma, genital spatulae and a bulbous telson ‘boss’. Several characters support the assignment Stoermeropterus to Moselopteridae, the most basal eurypterine clade, including its possession of a pediform appendage VI with a modified ‘podomere’ 7a and the possession of a coxal ‘ear’, which may represent the remains of a much-reduced exopod. Stoermeropterus conicus resolves phylogenetically as the most basal known eurypterine, and can aid in reconstructing the eurypterid ground plan. As such an attempt is made to reconstruct the characteristics that are plesiomorphic for Eurypterida through comparison with basal Eurypterina, Stylonurina, chasmataspidids and synziphosurines. Several characteristics previously thought to be autapomorphies of Stylonurina, such as a three-segmented genital operculum, are now shown to actually be plesiomorphic conditions in respect to Eurypterida as a whole, while other apparently derived characteristics such as an epistoma and genital spatulae may be characters that are present in all eurypterids during the juvenile and are respectively either paedomorphically retained into adulthood or become hypertrophied in various species. Following the identification of a metastoma and genital appendage in some chasmataspidid species, the sole currently known eurypterid autapomorphy is identified as the fusion of the opercular plates of somites VIII and IX. Evolutionary relationships among the traditional ‘merostome’ groups are reviewed, primarily in light of segment articulations and the development of the appendage of somite VII. The concept that synziphosurines may represent a paraphyletic stem grade to a group inclusive of xiphosurids, chasmataspidids, eurypterids, and arachnids is proposed.
An interdisciplinary approach was used to investigate the facies and paleogeography of the Lower Devonian sedimentary sequence of the Alken quarry, Mosel Valley, Germany. This 87-m-thick sequence consists of stratified sandstones and sandy shales of the Nellenkopfchen Formation (uppermost Lower Emsian). Previous interpretations of the depositional environment include terrestrial, deltaic, and shallow-marine settings. Two distinct fossiliferous units contain abundant terrestrial plant remains and a diverse mixed terrestrial to marine fauna. Physical sedimentary structures are common. throughout, whereas bioturbation is restricted mostly to the fossiliferous intervals. Erosional surfaces frequently separate the beds. Aside from ripple cross-stratification and parallel bedding, longitudinal inclined stratification is most common. Channel-fill structures are less frequent. Scour-and-fill structures exhibit marked disconformities of irregular shape on a smaller scale (din). Mud-pebble lags at the base of laterally prograding cross-bedded layers, scour-and-fill structures, and drainage rills characterize the upper part of the section. Desiccation cracks, Wind-induced striation, and water-level marks occur more sporadically in the exposure. The sedimentary structures and the paleontological information indicate a marine to brackish depositional environment that frequently was emergent. The presence of conspicuous channel-related structures reflects intertidal conditions along the coastal region of a presumed Hunsruck Island /Archipelago. Lagoons and estuaries were bordered by extended tidal flats, in which migrating channels frequently occurred. Terrestrial plant remains, however, indicate a position at the land /sea interface, which was characterized by a complex configuration of different environments. The accumulation of concentrated plant material may have been related to distinct meteorological events such as hurricanes.
Drepanopterus pentlandicus Laurie, 1892 is redescribed from the original type material along with previously unfigured specimens. A cleft metastoma is confirmed as a characteristic of the genus, along with the armature of the second and third prosomal appendages being modified into flattened blades, while the species is shown to possess a somewhat enlarged second tergite and lateral prosomal margins that overlap the first opisthosomal tergite. Different ontogenetic stages of D. pentlandicus are described, and reveal that these latter characters develop only later in ontogeny, suggesting that described specimens of Drepanopterus abonensis Simpson, 1951 may represent juveniles. Cladistic analysis of Stylonurina shows the genus Drepanopterus to be monophyletic consisting of D. pentlandicus, D. abonensis and D. odontospathus sp. nov.: it forms a basal clade of mycteropoids. Hibbertopteroidea Kjellesvig-Waering, 1959 is shown to be a junior subjective synonym of Mycteropoidea Cope, 1886, with the synonymy of many of the hibbertopterid genera hypothesised and Hibbertopterus Kjellesvig-Waering, 1959 suggested to represent juvenile specimens of Cyrtoctenus Størmer & Waterston, 1968. Hibbertopterus permianus Ponomarenko, 1985 is transferred to Campylocephalus Eichwald, 1860. The role of heterochrony in the morphological development of the mycteropoid lineage is discussed, with both hibbertopterids and mycteropids suggested to be hypertrophic and pre-displacement peramorphs respectively.
Stylonurid eurypterids (Arthropoda: Chelicerata) include some of the largest known arthropods – bizarre sweep-feeding hibbertopterids from the Carboniferous to end-Permian. New material of Drepanopterus abonensis, a stylonurid from the Late Devonian (Famennian) of Portishead, south-west England, offers key insights into this genus and its affinities. A redescription utilising the new material enables D. abonensis to be assigned as basal member of the Superfamily Hibbertopteroidea, the large-sweep-feeding forms, possessing a cleft metastoma and blades (modified blunt spines) on their anterior prosomal appendages. D. abonensis also shares characters such as a clavate telson and median ridge on the carapace with the proposed hibbertopteroid sister group the Kokomopteroidea. Hibbertopteroid eurypterids are the most long-ranging stylonurids, surviving the decline and extinction of the other eurypterid families in the Late Devonian, their survival probably because of their sweep-feeding mode of life, which was not in direct competition with their eurypterine relatives and other predators.
Two new stylonurine eurypterids are described from the Peel Sound Formation (Early Devonian, Lochkovian) of the northern coast of Prince of Wales Island, Nunavut, Arctic Canada. Associations including pteraspids and ostracodes indicate a fluvial depositional environment. An almost complete stylonurid, Pagea plotnicki sp. nov., is recognized by its large size and lack of vaulting on the carapace, and it provides evidence that Stylonurus and Pagea are sister-taxa. Also, a smaller incomplete rhenopterid assigned to Leiopterella tetliei gen. et sp. nov., is characterized by its broad turbinate carapace and lack of cuticular sculpture. This assemblage provides the first Canadian record of Pagea, and the youngest occurrence of a rhenopterid outside the Rheno-Hercynian Terrane, indicating that these taxa were more geographically widespread than previously supposed.Deux nouveaux euryptérides stylonuridés provenant de la Formation de Peel Sound (Dévonien précoce, Lochkovien) de la côte nord de l'île Prince-de-Galles, au Nunavut, dans l'Arctique canadien, sont décrits. Des associations comprenant des ptéraspides et des ostracodes indiquent un milieu de dépôt fluvial. Un stylonuride quasi complet, Pagea plotnicki sp. nov., se distinguant par sa grande taille et l'absence de structures en voûte sur sa carapace, appuie l'hypothèse selon laquelle Stylonurus et Pagea seraient des taxons frères. En outre, un rhénoptéride incomplet plus petit affecté à Leiopterella tetliei gen. et sp. nov. se distingue par sa large carapace turbinée et l'absence de sculpture cuticulaire. Cet assemblage constitue le premier exemple canadien documenté de Pagea et l'exemple le plus récent d'un rhénoptéride à l'extérieur du terrane rhéno-hercynien, ce qui élargie la distribution géographique de ces taxons.
The first well-resolved phylogeny of stylonurine eurypterids (30 taxa, 58 characters) is presented, prompting a taxonomic revision at the familial and superfamilial levels. The monophyletic suborder Stylonurina consists of four superfamilies: Rhenopteroidea, Stylonuroidea, Kokomopteroidea and Hibbertopteroidea. The enigmatic hibbertopterids – large sweep-feeding forms from the Carboniferous to end-Permian – are therefore demonstrated to be an in-group Stylonurina clade, within Eurypterida, in contrast to some earlier hypotheses. Furthermore, the genus Drepanopterus is shown to be polyphyletic: ‘Drepanopterus’ bembycoides is transferred to Moselopteridae fam. nov. along with Moselopterus and Vinetopterus at the base of the Eurypterina, defined by their possession of a pediform appendage VI bearing a modified podomere 7a. Evolution towards a sweep-feeding mode of life occurred independently in stylonuroids and hibbertopteroids, involving either multiple rows of fixed spines on the prosomal appendages (in stylonuroids) or paired movable flattened spines (‘blades’) on the prosomal appendages alongside a posteriorly cleft metastoma and coxal laden (in hibbertopteroids). The Stylonurina have a relatively poor fossil record (RCI 15%), when compared to more derived Eurypterina clades (e.g. Adelophthalmoidea RCI 66%; Pterygotoidea RCI 53%), but is relatively more complete than basal Eurypterina clades (RCI -21%). The fit between phylogeny and stratigraphical occurrences of stylonurid taxa is good (SCI 0.65 and GER 0.77, with only 0.3% of 1000 randomisation tests yielding greater congruence; GER* 0.995), and generic-level collector curves of the Stylonurina and Eurypterina show no major discrepancies in their sampling histories. These differences could be explained by geographic collection bias, taxa having different habitat preferences (and hence fossilisation potential), and ontogenetic factors: these results support previous suggestions that stylonurine eurypterids are oversplit.
Standards have been empirically developed to describe various morphological characters of eurypterids. The standards pertain to the following characters: 1) shape of the prosoma; 2) shape of the metastoma; 3) shape of the eyes; 4) position of the eyes; 5) types of prosomal appendages; 6) types of swimming leg paddles; 7) structure of the doublure; 8) differentiation of the opisthosoma; 9) structure of the genital appendages; 10) shape of the telson; and 11) types of ornamentation.
For the first time, a uniform, standardized taxonomy is proposed for classification and identification of most genera. The taxonomy is based on the observation that most higher taxonomic levels for arthropods are based on the structure and arrangement of the appendages. Details of the taxonomy rely on the morphological standards proposed here.
The order Eurypterida Burmeister, 1843, is here defined by the presence of only six pairs of prosomal appendages, the first pair being the chelicera, the next five pairs being the gnathobasic, uniramus legs. Suborders are characterized by the gross morphology of the chelicera. Superfamilies and families are characterized by the use of a single character complex, specifically the structure and arrangement of the second through sixth pairs of prosomal appendages. Genera are recognized by more specific standards.
A new classification of the order Eurypterida is proposed. Three new superfamilies, Kokomopteroidea, Megalograptoidea, and Brachyopterelloidea, and five new families, Brachyopterellidae, Adelophthalmidae, Lanarkopteridae, Erieopteridae, and Hardieopteridae, are proposed.
The Upper Silurian rocks of the Gutterford Burn, in the Pentland Hills, have for some time been known to contain Eurypterid remains, but the fossils procured from these beds—chiefly owing to the exertions of Mr Hardy of Bavelaw Castle, and Mr Henderson, late Curator of the Phrenological Museum—have never been submitted to a thorough examination. When, therefore, by the kind permission of Sir R Murdoch Smith, Director, and Dr E. H. Traquair, Keeper of the Natural History Collection in the Edinburgh Museum, I was given an opportunity of examining Mr Henderson's collection, which was acquired by the Museum some years since, I entered upon the work with the expectation of finding some new and interesting forms which would repay description. My expectations in this respect have been more than fulfilled, as the collection has yielded five undoubtedly new species, one of which I have made the type of a new genus. If to these one adds at least two other new species which are in the collection of Mr Hardy of Bavelaw, and which I hope to have the pleasure of examining and describing at some future time, one is justified, I think, in saying that the Gutterford Burn is unequalled among Eurypterid localities with regard to the variety of forms it has yielded. Unfortunately the bed which has yielded these specimens is limited in extent, and further work on it would entail quarrying operations on a somewhat extensive scale.
Recently collected material of Early Devonian eurypterids (Chelicerata: Eurypterida) from the Rhenish Slate Mountains is described
and compared to the reexamined type material ofDrepanopterus struvei
Størmer, 1974 andAlkenopterus brevitelson
Størmer, 1974, both from the Emsian of Alken an der Mosel.Vinetopterus martini n. gen., n. sp., from Siegenian strata of the newly detected eurypterid localities Burglahr and Hombach in the Westerwald,
is described.D. struvei is transferred toVinetopterus n. gen.Vinetopterus n. gen. is diagnosed as having short prosomal appendage VI ofDrepanopterus-type A, and a first order opisthosomal differentiation. A second species from the Siegenian of Burglahr is described asAlkenopterus burglahrensis n. sp. The new family Alkenopteridae, diagnosed by possessing at least two pairs of non-spiniferous legs, V ofDrepanopterus-type B and VI ofAlkenopterus-type, is proposed to accomodateAlkenopterus. The palaeoecology of Burglahr and Hombach is briefly discussed and the habitat of these eurypterids is interpreted as representing
a shallow water environment in a deltaic setting with marine or brackish influence.
The phylogeny of a broad selection of taxa at the base of the monophyletic Eurypterina (swimming eurypterids) is analysed. The results suggest that Onychopterella is the most basal of these forms, in agreement with its early stratigraphic occurrence. One step up from Onychopterella is a split between the superfamily Eurypteroidea and a clade comprising the four other clades in Eurypterina: Mixopteroidea, Waeringopteroidea, Adelophthalmoidea and Pterygotoidea. Eurypteroidea is composed of two major clades; the Eurypteridae consists of most species of Eurypterus and North American representatives of Erieopterus. The Dolichopteridae, numerically less species‐rich, but more morphologically diverse, consists of Dolichopterus, Ruedemannipterus, Buffalopterus, Strobil‐opterus, Syntomopterus and most likely ’Eurypterus’ minor. Polyphyly of Eurypterus and paraphyly of Onychopterella differ from present taxonomic assignments. Not surprisingly, the fossil record of the clade is shown to be very poor as expected for animals lacking a mineralised exoskeleton. This is reflected in a low Relative Completeness Index (RCI) value of -41%.
A description is given of a nearly complete specimen of a new Ordovician eurypterid genus belonging to the family Stylonuridae. The classification of the Eurypterida is discussed; two super-families and two new families are proposed and three new names substituted for pre-occupied generic names.
Fossilium Catalogus, I: Animalia, Pars 25: Eurypterida. 28 pp
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