A new leanchoiliid megacheiran arthropod from the lower Cambrian Emu Bay Shale, South Australia

The Leanchoiliidae is well−known from abundant material of Leanchoilia, from the Burgess Shale and Chengjiang Konservat−Lagerstätten. The first Australian member of the group is Oestokerkus megacholix gen. et sp. nov., described from the Emu Bay Shale (Cambrian Series 2, Stage 4), at Buck Quarry, Kangaroo Island, South Australia, and is intermediate in age between the well known leanchoiliid species from the Burgess Shale and Chengjiang. Phylogenetic analysis of “short great appendage” arthropods (Megacheira) in the context of the chelicerate stem group resolves the Australian species as sister to Burgess Shale, Utah, and Chengjiang Leanchoilia species, but most readily distinguished from Leanchoilia and Alalcomenaeus by a different telson shape, interpreted as being forked, widening distally, and with a few dorsally curved spines at the posterior angle. Leanchoiliid interrelationships are stable to alternative character weights, and Megacheira corresponds to a clade in most analyses

The early Cambrian Emu Bay Shale radiodonts revisited: morphology and systematics

Two species of Radiodonta (stem-group Euarthropoda) from the Emu Bay Shale (Cambrian Series 2, Stage 4), Kangaroo Island, South Australia, are revised based on new field collections and insights from recent phylogenetic analyses and advances in knowledge of radiodonts globally. Anomalocaris briggsi Nedin, 1995, the most common Emu Bay Shale radiodont, is designated the type species of a new monotypic genus of Tamisiocarididae, Echidnacaris gen. nov. The less common species, previously identified as Anomalocaris aff. canadensis Whiteaves, 1892, is formally named Anomalocaris daleyae sp. nov. Oral cones are assigned to both Echidnacaris briggsi comb. nov. and A. daleyae based on that of the latter species being found in association with pairs of frontal appendages. The Echidnacaris briggsi oral cone is the best preserved for the family Tamisiocarididae; it is triradial, with three large plates and a more pervasive ornament of nodes than in any other known radiodont. Shared characters of the Echidnacaris and Anomalocaris oral cones add support for a sister group relationship between Tamisiocarididae and Anomalocarididae. Unique eye characters documented in E. briggsi, such as being sessile and encircled by an eye sclerite, are unknown in the other tamisiocaridids, Tamisiocaris and Houcaris, and are tentatively regarded as diagnostic for Echidnacaris. An ovate head element resembling that of Tamisiocaris borealis is assigned to E. briggsi, informed by the sister group relationship between these taxa. Isolated radiodont body flaps and sets of setal blades in the Emu Bay Shale cannot be confidently assigned to a species, although relative abundance suggests that many or most are likely E. briggsi. The inner attachment margin of the body flaps is sharply defined and may represent a suture at which flaps are shed in moulting.John R. Paterson, Diego C. García-Bellidob, and Gregory D. Edgecomb

Conflict between datasets and phylogeny of centipedes: an analysis based on seven genes and morphology

Although the phylogeny of centipedes has found ample agreement based on morphology, recent analyses incorporating molecular data show major conflict at resolving the deepest nodes in the centipede tree. While some genes support the classical (morphological) hypothesis, others suggest an alternative tree in which the relictual order Craterostigmomorpha, restricted to Tasmania and New Zealand, is resolved as the sister group to all other centipedes. We combined all available data including seven genes (totalling more than 8 kb of genetic information) and 153 morphological characters for 24 centipedes, and conducted a sensitivity analysis to evaluate where the conflict resides. Our data showed that the classical hypothesis is obtained primarily when nuclear ribosomal genes exert dominance in the character data matrix (at high gap costs), while the alternative tree is obtained when protein-encoding genes account for most of the cladogram length (at low gap costs). In this particular case, the addition of genetic data does not produce a more stable hypothesis for deep centipede relationships than when analysing certain genes independently, but the overall conflict in the data can be clearly detected via a sensitivity analysis, and support and stability of shallow nodes increase as data are added

New Devonian fossil localities in Bolivia

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