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Journal of Paleontology

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Machaeridians from the Lower Silurian (Llandovery, Telychian) of Shropshire, England

¹ Department of Geology, National Museum of Wales, Cathays Park, Cardiff, CF10 3NP, UK, <lucy.mccobb@museumwales.ac.uk> and <mike.bassett@museumwales.ac.uk>

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
MACHAERIDIANS ARE marine Palaeozoic fossils, known from sediments of early Ordovician to mid Permian age (Bengtson, 1978; Cooper and Grant, 1972; Kaasa, 1992). Rare, completely articulated specimens reveal that they were long, slender, bilaterally symmetrical animals, covered by a dorsal scleritome comprising longitudinally arranged series of calcite sclerites (e.g., Adrain et al., 1991; Högström and Taylor, 2001a, 2001b). However, most known machaeridians, including those described in this paper, comprise isolated disarticulated sclerites. Until recently, the taxonomic affinities of the group were uncertain, and historically they were assigned to a number of different phyla (e.g., see Adrain, 1992). However, the recent account of an exceptionally preserved specimen with soft tissue anatomy, from the Lower Fezouata Formation (Lower Ordovician, Tremadocian) of Morocco, now indicates that machaeridians were annelid worms (Vinther et al., 2008).

Two orders of machaeridians are recognised: the Lepidocoleomorpha Schallreuter 1985, and the Turrilepadomorpha Pilsbry, 1916, essentially distinguished by the fact that the lepidocoleomorphs have two rows of sclerites, while the turrilepadomorphs have four (although rare cases of lepidocoleomorphs with two extra rows of outer sclerites are known [Dzik, 1986; Högström, 1997]).

The Silurian fossil record of machaeridians includes some relatively rare occurrences of articulated scleritomes (see Withers, 1926; Högström and Taylor, 2001a, 2001b; Högström, 1997; Adrain et al., 1991), together with more common disarticulated, isolated sclerites. Silurian occurrences are widespread globally, with reports from the British Isles (see below), North America (Hall and Whitfield, 1875; Clarke, 1896; Adrain, 1992; Högström and Taylor, 2001b), the Ukraine (Adrain et al., 1991), the Baltic region (Aurivillius, 1892; Schrank, 1978; Bengtson, 1979; Schallreuter, 1985; Högström, 1997), Bohemia (Barrande, . . . [Full Text of this Article]