NEW CHANCELLORIIDS FROM THE EARLY CAMBRIAN SEKWI FORMATION WITH A COMMENT ON CHANCELLORIID AFFINITIES

Journal of Paleontology, Sep 2005 by Randell, Robert D, Lieberman, Bruce S, Hasiotis, Stephen T, Pope, Michael C

The articulated material described here supports the argument of Rigby (1978) that the elongated lateral rays of Archiasterella Sdzuy, 1969 are the ascending lateral rays, as opposed to Sdzuy's (1969) interpretation that they are the descending lateral rays (see Brock and Cooper, 1993).

SYSTEMATIC PALEONTOLOGY

All material referred to is housed at the University of Kansas Natural History Museum, Division of Invertebrate Paleontology (KUMIP).

Family CHANCELLORIIDAE Walcott, 1920

Discussion.-Jiang's (in Luo et al., 1982) classification scheme for chancelloriid sclerites was based on rays-per-sclerite, which actually varies within taxa (Qian and Bengtson, 1989; Janussen et al., 2002). The sclerite characteristics significant for distinguishing and recognizing biological taxa are largely recorded in the central disc. The most informative characters appear to be: plane of symmetry; orientation of rays relative to the central disc; relative dimensions of rays (generally expressed by proximal width in the central disc); and arrangement of sutures. Strict application of this system demonstrates that Elkanospina trispinata Missarzhevsky, 1989 (pi. XXII, incorrectly given as pi. XXI in the text, fig. 17) could be conspecific with 'Onychia' tetrathallis Jiang in Luo et al., 1982 (pi. 23, fig. 2). The huge overlap in sclerite morphology between taxa is highly problematic for chancelloriid systematics. There is also a high level of inlraspecific sclerite variation. The implication is that some chancelloriid taxa in the literature may not merit true taxonomic distinction.

Genus CHANCELLORIA Walcott, 1920

CHANCELLORIA cf. EROS Walcolt, 1920

Figure 6

cf. Chancelloria eras WALCOTT. JANUSSHN, STFUNKR, AND ZHU, 2002, p. 600, figs. 3, 4, 6.1 (see for more complete synonymy).

Material examined.-KUMIP 308850.

Occurrence.-Sekwi Formation, locality 1 (see above).

Discussion.-A single incomplete scleritome has a 45 mm body twisted through 40° and lacks the apex. Central and basal parts of the scleritome show up to 8 mm relief and the apical part is flattened. The basal part narrows to a distinct root. Sclerites are poorly preserved, largely incomplete, and loosely and alternately arranged in longitudinal rows showing some spiraling. They are typically 7 1, but 6 1 may occur. The diameter of the sclerites is 3-4 mm, and averages 3.3 mm. The sclerites most closely resemble those of C. eras, but due to coarse preservation the identity of the species could not be precisely determined. The thickened basal bulb seen in some specimens of C. ems from the Middle Cambrian Wheeler Formation (Janussen et al., 2002, fig. 3.3) was not observed.

Genus ARCHIASTERELLA Sdzuy, 1969, emended

Type species.-Archiasterella pentactina Sdzuy, 1969.

Emended diagnosis.-Scleritome elongate, gently conical, sclerites arranged in roughly longitudinal rows. Sclerites bilaterally symmetrical, typically 5 or 4 O, rarely 2 0, basal ray recurved towards apex in mesial plane.

Discussion.-Morphological variation in the sclerites of A. fletchergryllus n. sp. lends support to the view of many workers (e.g., Qian and Bengtson, 1989; Janussen et al., 2002) that new chancelloriid species should not be erected solely using isolated sclerites. For example, at its basal tip A. fletchergryllus bears sclerites reduced to almost a single ray. Other species of Archiasterella are discussed below. An emended diagnosis is provided because of the additional information now available from the complete scleritome.