- The Paleontological Society
Palaeoscolecidans represent an extinct class of vermiform organisms with a prominent annulation ranging from the Lower Cambrian to the Upper Silurian. Since the first descriptions in the 1950s, they have been attributed to different groups, but recently they have been linked to the priapulids (Conway Morris, 1997). Palaeoscolecids are mainly considered to represent members of Ecdysozoa. Their position within this clade is still under discussion, but cladistic analyses indicate that they are either close relatives of nematomorphs (Hou and Bergström, 1994) or part of an extinct sister clade to the priapulids (Wills, 1998; Dong et al., 2004). The outer cuticle of palaeoscolecidan segments possesses microelements mineralized by calcium phosphate, which are often found isolated in the conodont collections obtained from carbonates after acid treatment. Kraft and Mergl (1989), van den Boogaard (1989b), Hinz et al. (1990), and Müller and Hinz-Schallreuter (1993) clearly showed the evidence that these isolated sclerites originate from certain palaeoscolecidan taxa. The specimens documented in this paper represent such fragmented material from the Manitou Formation of west-central Colorado. Extensive taxonomic and morphologic reviews of the palaeoscolecidans were provided by Müller and Hinz-Schallreuter (1993), Conway Morris (1997), Wrona and Hamdi (2001), and Ivantsov and Wrona (2004).
Palaeoscolecidans have been reported from different paleogeographic areas in the Ordovician (Kraft and Lehnert, 2004). In general, this group is widespread from tropical to cool water environments. Lower Ordovician whole body fossils have been published only from peri-Gondwana (e.g., Whittard, 1953; Kraft and Mergl, 1989), and there is limited information from tropical areas treating only isolated microremains (fragments and tubercles). In this time interval the data from tropical continents are restricted to Laurentia (e.g., Ethington and Clark, 1981; Repetski, 1981).
The studied material was recovered from a section at Cave of …