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Journal of Paleontology 92(1):40–48
Figure 3. Reconstructions of the oral cones of different radiodontan taxa, not to scale. (1) Anomalocaris canadensis and A. saron, redrawn from Daley and Bergström (2012, fig. 1c); (2) the new Guanshan radiodontan oral cone reported here, based on NIGPAS 162529; (3) Peytoia nathorsti, modified from Daley and Bergström (2012, fig. 1a) and with an orbicular rather than taphonomically distorted rectangular shape (see text); (4) Hurdia victoria and H. triangulata, modified from Daley and Bergström (2012, fig. 1b) and rotated 90°. Note that the lateral large plates are wider than the anteroposterior plates in (3, 4). (5) Cladogram based on the most recent radiodontan phylogeny from Van Roy et al. (2015), showing the two main radiodontan clades Anomalocarididae+Amplectobeluidae and Hurdiidae in nodes, their representatives with oral cones known in solid lines, and three alternative positions of the Guanshan oral cone in dashed lines (A, B, and C). Two branches of Anomalocaris indicate its two species A. canadensis and A. saron. See text for discussion.
the small plates (Fig. 2.1–2.6). Similar spines are also present along the radial margins of large plates and their adjacent small plates (Fig. 2.1, 2.2, 2.5, 2.6).
Occurrence.—From the Wulongqing Formation, late period of the early Cambrian Canglangpuan Stage (Cambrian Series 2, Stage 4), at Gaoloufang, Guangwei, in Kunming, eastern Yunnan, South China.
Discussion
Taphonomic notes.—A critical assessment on potential tapho- nomic biases of radiodontan oral cones is essential given the limited characters we know from them. Doubt may be cast on the uniqueness of inner teeth in Hurdia. Intuitively, there is no good reason for the absence of a masticatory apparatus in other radiodontans, including Peytoia, Anomalocaris and the species represented by the new oral cone here, since pharyngeal teeth are present in a wide range of ecdysozoan groups (Smith & Caron, 2015). The taphonomic scenario of faster degradation of these teeth is rejected by Daley et al. (2009) because no evidence of extra inner teeth is present in any oral cones of Peytoia or Anomalocaris, and no isolated teeth are found from all Burgess Shale localities.While all radiodontan oral cones show amore or less convex shape and can potentially provide space for accom- modating inner teeth, it should be acknowledged that the inner teeth of Hurdia are closely associated or articulated with the oral cone, which is a unique case in radiodontans we know. If extra
inner teeth really exist in other radiodontans apart from Hurdia, these teeth are likely situated on the inner walls of buccal or pharyngeal cavities rather than being associated with the oral cone, and theymight be either too small to be found or concealedwithin the rockmatrix. The questionwhether extra inner teeth are present in other radiodontans can only be answered by more detailed reinvestigation or new fossil discoveries. Another question worth considering is whether the absence
of scale-like nodes in Peytoia and Hurdia oral cones is a natural feature or a taphonomic loss, as it has been suggested that surface microstructures on sclerotized plates could be effaced and that microscopic artifacts might be generated during taphonomic processes (e.g., radiodontan head sclerites; Zeng et al., 2017). In these cases, taphonomic effects act on microstructures of soft-bodied euarthropod sclerites from a specific locality or horizon of a fossil deposit and are not taxon selective. Fine scale-like nodes are well preserved in both articulated and disarticulated oral cones of A. canadensis recovered from the Burgess Shale (Daley and Bergström, 2012); thus, the possibility of a universal taphonomic efface- ment of these nodes can be eliminated. Considering the large number of oral cone specimens investigated from the Burgess Shale (Whittington and Briggs, 1985; Daley et al., 2013a), the smooth oral plates without scale-like nodes are most likely to be a natural feature of Peytoia and Hurdia.
Revision of Peytoia and Hurdia oral cones.—Before making comparisons between the new Guanshan radiodontan oral cone
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