Pates et al.—Hurdiids from the middle Cambrian of Utah
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preserved, but multiple inner rows of teeth in an approximately rectangular central opening are clearly visible. Again, there are some possible small round nodes (radius 1mm) visible on some plates.
The length:width ratio of H-elements from the carapace
of Hurdia can be used to distinguish H. victoria from H. triangulata: H. victoria has H-elements with lengths greater than 1.5 times the width (but less than 2.0 times), and H. triangulata has H-elements with lengths less than 1.5 times the width (Daley et al., 2013a). KUMIP 314039 (Fig. 4.2), KUMIP 314050 (Fig. 4.1, 4.4), and KUMIP 314056 (Fig. 4.3, 4.5), identified by height:width ratios, are the first H. victoria specimens identified from the Spence Shale; H. triangulata has not yet been identified. Reticulation polygons were observed on parts of the surface of some elements (Fig. 4.4). The specimen illustrated in Figure 4.3, 4.5 has 10 small brown patches (1–5mm in radius) and a trilobite with inferred manganese dendrites radiating from it, obscuring parts of the fossil. Similar dendrites with elevated manganese content have been reported from the Pioche Shale (Moore and Lieberman, 2009). Evidence for the two-layered H-element can be seen toward the strengthened tip (Fig. 4.5). KUMIP 314057a/b (Fig. 4.6, 4.7) is a part and counterpart
of an isolated radiodontan swim flap covered with regularly spaced, prominent transverse lines, also referred to as ‘strength- ening rays’ (Whittington and Briggs, 1985) or ‘veins’ (Chen et al., 1994; Hou et al., 1995), about 1mmwide and 2mmapart. The flap is relatively large compared to Hurdia flaps reported from the Burgess Shale (Daley et al., 2013a), measuring approximately 65mm in width and 45mm in height. This specimen is tentatively identified as Hurdia because of the presence of transverse lines across the entire surface of the flap, which is not seen in Peytoia (where the transverse lines are confined to the anterior half of the flap) or Anomalocaris (which lacks transverse lines entirely).
Sidneyia? from the Spence Shale Member.—Conway Morris and Robison (1988, fig. 26.1a, 26.1b, 26.2) identified four specimens (KUMIP 204777–204780) as broken spines of Peytoia nathorsti appendages. These are reinterpreted as distal podomeres of endopods (walking appendages) of a Sidneyia-like taxon on the basis of the rounded curvature of the overall structure, the oblique angle of the spines, the characteristic arrangement of repetitive bundles of decreasing spine size, and the presence of podomere boundaries faintly visible on some specimens (compare KUMIP 204777– 204780: Conway Morris and Robison, 1988, fig. 26.1a, 26.1b, 26.2 to Bruton, 1981, figs. 48, 53, 55, 58, 60, 88, 92 and Stein, 2013, fig. 7B–D). This therefore indicates Peytoia should no longer be reported as present in the Spence Shale. Sidneyia was previously reported from the Spence Shale (Briggs et al., 2008).
Figure 4. Hurdia carapace elements and flap from the Spence Shale Member, Langston Formation, Wellsville Mountains, Utah, USA. (1) H-element KUMIP 314050; (2) H-element KUMIP 314039; (3) H-element 314058; (4) boxed region in 1;(5) Boxed region in 3;(6) flap KUMIP 314057b; (7) KUMIP 314057a, part to 6.(1–3, 6, 7) Scale bars = 10mm; (4, 5) scale bars = 2.5mm.
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