Pates et al.—Hurdiids from the middle Cambrian of Utah
coded as having straight or curved anterior ventral spines. An analysis under equal weighting recovers 70 most parsimo- nious trees of 106 steps, and in strict consensus (CI = 0.66,
111
RI = 0.85), all four Hurdia taxa and Stanleycaris are recovered in an unresolved polytomy. This is in contrast to the resolved relationships depicted in Vinther et al. (2014) and Van Roy et al. (2015), where the two H. sp. B specimens form a clade that is sister to Stanleycaris, rather than to H. victoria. From current evidence, Hurdia cannot be identified to the species level by its frontal appendages alone, and appendages fromthe Spence Shale and the Burgess Shale cannot be distinguished as KUMIP 314040 and 314178, described herein, show that Hurdia appendages from Utah do possess dorsal spines (Fig. 2.2–2.4). Hurdia can still only be separated into two distinct species by the shape of its H-element (Daley et al., 2013a).
Presence of nodes on mouthparts.—Nodes are present on the plates of Hurdia mouthparts from the Spence Shale (KUMIP 314175a/b and 314265a/b, Fig. 2.6, 2.7) and partial Peytoia mouthparts from the Marjum Formation (KUMIP 314095, Fig. 6.6, 6.7). Nodes are not often seen in Burgess Shale specimens. The nodes are similar to what is seen in Anomalocaris (e.g., Daley and Bergström, 2012, fig. 2a–d; Daley and Edgecombe, 2014, fig. 7.5). However, the plates of these mouthparts lack the subdivisions and furrowing on the outer margins that is often seen in Anomalocaris (e.g., Daley and Bergström, 2012, fig. 2g–j). The presence of nodes in the Utah specimens could be due to interspecific variation; how- ever, a more likely cause is preservational differences, which allow more 3D structure to be preserved in Utah than in Burgess Shale specimens. Similar preservational differences are seen in the oral cones of A. canadensis, where nodes are preserved in varying degrees of relief in oral cones from the Burgess Shale and the Emu Bay Shale (Daley et al., 2013b; Daley and Bergström, 2012).
Figure 8. 3D model of Hurdia appendage, with ventral spines reconstructed as being of equal thickness. (1) Lateral view, showing ventral spines appearing equally thick; (2) oblique view, showing distal ventral spines appearing thicker than proximal ones and differences in ‘hooked’ appearance at distal tip of ventral spines.
Geographical and temporal distribution of hurdiids.—Hurdia and Peytoia are distributed over a large temporal and geographic range (Table 2). Both are reported from China, the United States, and Canada. Hurdia is known additionally from the Czech Republic (Chlupáč and Kordule, 2002), and Peytoia from
Table 2. Locations from which hurdiid specimens are known. HCM = Holy Cross Mountains, Poland; Shuj. = Shuijingtuo Formation, China; Balang = Balang Formation, China; Jince = Jince Formation, Czech Republic; Spence = Langston Formation (Spence Shale Member), Utah, USA; Tulip = Tulip Beds, Mount Stephen, Yoho National Park, Canada; Burg. = Fossil Ridge, Burgess Shale, Yoho National Park, Canada; Stan. = Stanley Glacier, Kootenay National Park, Canada; Wheel. = Wheeler Formation, Utah, USA; Marj. = Marjum Formation, Utah, USA; Fez. = Fezouata Formation, Morocco. Publications: 1 = Daley and Legg (2015); 2 = Cui and Huo (1990); 3 = Liu (2013); 4 = Chlupáč and Kordule (2002); 5 = Conway Morris and Robison (1988); 6 = Briggs et al. (2008); 7 = Daley and Budd (2010); 8 = Caron et al. (2010); 9 = Robison and Richards (1981); 10 = Briggs and Robison (1984); 11 = Van Roy and Briggs (2011).
HCM Shui.
Hurdia specimens H. victoria H-elements H. triangulata H-element P-element Appendage Oral cones
App. + Oral cone assem. Body (partial/complete) Isolated flap
Peytoia specimens Appendage Oral cone
Publications Y
Body (partial/complete) Other hurdiid appendages
1 2 3 4 5, 6 Y Y Balang Jince Y
Y Y
Y Spence Y Tulip
Y Y Y Y Y
Y Y
Y 7
Burg.
Y Y Y Y Y
Stan.
Y Y
Y Y
YY Y
YY Y Y
Y Y
7
Y 8
Y 5, 6, 9 10 Y Y
Y Y
Y 11 Wheel. Y Marj. Fez.
Y Y
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