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  • Mimetaster hexagonalis GÜRICH, 1931


    Images:

    oilshale

    Taxonomy

    Lace Crab

    Kingdom: Animalia
    Phylum: Arthropoda
    Class: Marrellomorpha
    Order: Marrellida
    Family: Mimetasteridae
    Genus: Mimetaster
    Species: Mimetaster hexagonalis
    Author Citation GÜRICH, 1931

    Geological Time Scale

    Eon: Phanerozoic
    Era: Paleozoic
    Period: Devonian
    Sub Period: None
    Epoch: Early
    International Age: Emsian (early)

    Stratigraphy

    Hunsrück Slate Group
    Kaup Formation

    Biostratigraphy

    Bundenbach Fossil Biota

    Provenance

    Collector: T. Bastelberger
    Acquired by: Field Collection

    Dimensions

    Width: 5 cm

    Location

    heap pile "Grube Herrenberg"
    Bundenbach
    Rhineland-Palatinate
    Germany

    Comments

    This arthropod is a Marrellomorph, a clade of strange looking stem-group arthropods known from the Cambrian Burgess Shale and the slightly older Kaili Fauna in China (Marella), the Silurian Herefordshire Lagerstätte in England (Xylokorys), the Ordovician Basal Upper Fezouata Formation (lower Arenig, or lower Floian), north of Zagora in southeastern Morocco and the Caradoc (Upper Ordovician) in Bohemia (Furca) and the Devonian Bundenbach Shale in Germany (Mimetaster and Vachonisia).
    Marrellomorphs lacked mineralized hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution. 

    The head shield has two pairs of long rearward directed spikes. Marrellomorphs possessed two pairs of antennae, one long and sweeping, the second shorter and stouter. The two dozen segments each have a pair of six segmented leg / feathery gill structures. There is a tiny, button like telson at the end of the thorax. The best modern guest is that Marrellomorphs are moderately evolved primitive arthropods descended from a common ancestor of the major later arthropod groups.

    Mimetaster rekonst.jpg

    Reconstruction of Mimetaster hexagonalis

     

    MARRELLA rekonst.jpg

    Reconstruction of another Marrellomorph - Marrella splendens - from the Cambrian Burgess Shale in Canada.

     

    A thorough re-investigation of Marrella splendens based on over 1000 specimens was recently published by D. García-Bellido and D. Collins: “A new study of Marrella splendens (Arthropoda, Marrellomorpha) from the Middle Cambrian Burgess Shale, British Columbia, Canada” in Can. J. Earth Sci. 43(6): 721–742 (2006).

    The overall form of Mimetaster and other Marrellomorphs suggests that it was a soft-bottom dweller. The wide carapace border would have prevented sinking into unconsolidated sediment.

     

    Mimetaster hexagonalis is the most abundant non-trilobite arthropod from this Lagerstätte. They are considered to live in groups of several individuals; two, three or even more species on one slab are not uncommon. A thorough reinvestigation of Mimetaster based on 123 specimens was recently published by G. Kühl and J. Rust in Paläontologische Zeitschrift, volume 84, number 3, 397-411.

     



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