| Autor: |
Parry LA; Department of Geology and Geophysics, Yale University, Kline Geology Laboratory, 210 Whitney Avenue, New Haven, CT 06511, USA.; School of Earth Sciences, University of Bristol, Bristol BS8 1RL, UK.; Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK., Edgecombe GD; Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK., Sykes D; Henry Moseley X-ray Imaging Facility, Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK., Vinther J; School of Earth Sciences, University of Bristol, Bristol BS8 1RL, UK.; School of Biological Sciences, Life Sciences Building, University of Bristol, Bristol BS8 1TQ, UK. |
| Abstrakt: |
Machaeridians are Palaeozoic animals that are dorsally armoured with serialized, imbricating shell plates that cover or enclose the body. Prior to the discovery of an articulated plumulitid machaeridian from the Early Ordovician of Morocco that preserved unambiguous annelid characters (segmental parapodia with chaetae), machaeridians were a palaeontological mystery, having been previously linked to echinoderms, barnacles, tommotiids (putative stem-group brachiopods) or molluscs. Although the annelid affinities of machaeridians are now firmly established, their position within the phylum and relevance for understanding the early evolution of Annelida is less secure, with competing hypotheses placing Machaeridia in the stem or deeply nested within the crown group of annelids. We describe a scleritome of Plumulites bengtsoni from the Fezouata Formation of Morocco that preserves an anterior jaw apparatus consisting of at least two discrete elements that exhibit growth lines. Although jaws have multiple independent origins within the annelid crown group, comparable jaws are present only within Phyllodocida, the clade that contains modern aphroditiforms (scaleworms and relatives). Phylogenetic analysis places a monophyletic Machaeridia within the crown group of Phyllodocida in total-group Aphroditiformia, consistent with a common origin of machaeridian shell plates and scaleworm elytrae. The inclusion of machaeridians in Aphroditiformia truncates the ghost lineage of Phyllodocida by almost a hundred million years. |
