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      The green alga Chaetocladus (Dasycladales)

      Journal of Paleontology
      Cambridge University Press (CUP)

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          Abstract

          Two species of the enigmatic alga Chaetocladus, C. ruedemanni(new species) and C. dubius(previously regarded as a graptolite incertae sedis), are described from the Silurian Lockport Group of New York and Ontario, Canada, respectively. A comprehensive investigation reveals that these and other Chaetocladustaxa occur in distinctive Konservat-Lagerstätten in association with other thallophytic algae, annelid worms, and lightly sclerotized arthropods. The sedimentology, taphonomy, and biotic composition of Chaetocladus-bearing deposits indicate that this alga thrived in shallow, stagnant, occasionally storm-agitated marine environments. In these settings, preservation of thallophytic algae and associated soft-bodied animals apparently was facilitated by a combination of obrution, anoxia, and early diagenesis of the burial muds.

          The morphology of Chaetocladuscorresponds to that characteristic of the green alga order Dasycladales, and it is herein referred to this long-ranging taxon as a representative of a new subtribe (Chaetocladinae, new subtribe) within the tribe Salpingoporelleae (emended herein), family Triploporellaceae (emended herein). This euspondyl, endosporate genus extends the range of the euspondyl dasyclads significantly, from the Early Devonian back to the Middle Ordovician, and bridges an evolutionary gap between early Paleozoic aspondyl, endosporate forms and middle Paleozoic euspondyl, cladosporate forms.

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          Most cited references6

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          The role of anoxia in the decay and mineralization of proteinaceous macro-fossils

          Actualistic experiments have quantified rate of anaerobic decay and associated mineralization around proteinaceous macro-organisms. Carcasses of the polychaete worm Nereis and the eumalacostracans Nephrops and Palaemon were buried in airtight glass jars filled with sediment and water from marine, brackish, and lacustrine environments. Over a period of 25 weeks the contents were examined to determine the state of decay and were chemically analyzed to monitor early diagenetic mineralization (two methods for such analysis are reviewed). Decay processes were active in the experimental conditions despite anoxia and had virtually destroyed the carcasses within 25 weeks. However, decay-rate in the sulfate-reducing marine system was greater than in the methanogenic freshwater environments. Petrological and geochemical analyses of the organic remains identified discrete layers of authigenic iron monosulfide (a pyrite precursor) on the surface of the decaying Nephrops cuticle within weeks of initiating the experiment. Chemical analysis of decomposing flesh showed a marked increase in pore-water calcium content with time. The results clearly show that anoxia is ineffective as a long-term conservation medium in the preservation of soft-bodied fossils. However, decay-induced mineralization can be very rapid so that even a slight reduction in decay rate can lead to improved levels of fossil preservation. Traditionally, stagnation and rapid burial are considered to be the main prerequisites for the preservation of soft-bodied fossils and the formation of Konservat-Lagerstätten . Clearly these factors are only important in that they promote early diagenetic mineralization. This is the only way to halt information loss through decay.
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            On Burrows and Tracks of Invertebrate Animals in Palæozoic Rocks, and other Markings

            J. DAWSON (1890)
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              Classification Criteria of Fossil Dasycladales

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                Author and article information

                Journal
                applab
                Journal of Paleontology
                J. Paleontol.
                Cambridge University Press (CUP)
                0022-3360
                1937-2337
                September 1997
                May 20 2016
                : 71
                : 05
                : 940-949
                Article
                10.1017/S0022336000035873
                5b3a0bae-f3e5-43f9-bbc1-86d6c3cba0d9
                © 2016
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