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Journal of Paleontology 92(1):40–48
PhotoshopCS6.Our use of anatomical terminology followsDaley and Bergström (2012).
Systematic paleontology
Phylum Euarthropoda Lankester, 1904 Order Radiodonta Collins, 1996
Remarks.—Monophyly of Radiodonta has been questioned recently because of the unstable phylogenetic position of Schinderhannes bartelsi Kühl et al., 2009 (Ortega-Hernández, 2016). Because Class Dinocarida Collins, 1996, comprising Opabinia regalis Walcott, 1912 as the sister taxon of Radio- donta, received no support in recent cladistic analyses (e.g., Legg et al., 2013; Van Roy et al., 2015; Yang et al., 2015), it is not used in this study.
?Family Amplectobeluidae Vinther et al., 2014
Remarks.—Only a few nearly complete isolated specimens of the new radiodontan oral cone we describe have been dis- covered during the course of long and extensive excavations of the Guanshan Lagerstätte at Gaoloufang. Conversely, more than a hundred complete radiodontan frontal appendages have been collected from this section (Wang et al., 2013; Hu et al., 2013). Within these frontal appendages, only a single specimen of Paranomalocaris multisegmentalis has been reported, and the remainder belong to Anomalocaris kunmingensis (Wang et al., 2013; Hu et al., 2013). Thus, on the basis of this large-scale fossil sampling, our new radiodontan oral cone is most likely to be A. kunmingensis, placed in the family Amplectobeluidae Vinther et al., 2014 in most recent phylogenetic analyses (Vinther et al., 2014; Van Roy et al., 2015). However, the taxonomic identity of this new cone cannot be determined with certainty currently, and it is possible that it belongs to a third radiodontan species.
Radiodontan gen. indet. sp. indet. Figures 2, 3.2
Material.—A single, isolated, nearly complete radiodontan oral cone, NIGPAS 162529, counterpart only.
Description.—Specimen NIGPAS 162529 is predominantly dorsoventrally preserved and just slightly laterally compressed, as indicated by the curved radial margins of plates and length differences between the left and right large plates (Fig. 2.1, 2.2). Minor distortion of the original symmetry, together with the imbricated arrangement of plates (Fig. 2.1, 2.2), suggests that
this oral cone was a three-dimensional structure. The orientation of this new oral cone is interpretative due to its isolated pre- servation; because three of the four large preserved plates are similar in size and wider than the other one,we tentatively orient this specimen with the narrowest large plate in a posterior position (Figs. 2.1, 2.2, 3.2; see Discussion). This orientation is supported by reference to other known oral cones; in both Peytoia and Hurdia, the lateral large plates are wider than the anterior and posterior ones (Fig. 3.3, 3.4; see Discussion), while the anterior large plate is the widest in Anomalocaris (Fig. 3.1; see Discussion). The new Guanshan oral cone is approximately circular
and ‘tetraradially’ symmetrical, with a diameter of ~7.0cm (Fig. 2.1, 2.2). The outer ring of the oral cone comprises 32 plates that surround an empty rectangular central opening (Fig. 2.1, 2.2); this central opening is ~1.5 cm long longi- tudinally and ~1.0cm wide horizontally (Fig. 2.1, 2.2). Of the 32 plates, four large ones are located 90° from one another, in anterior, posterior, left, and right positions, respectively (Fig. 2.1, 2.2), while each of the two adjacent large plates is separated by seven small ones filling in each quarter of the outer ring (Fig. 2.1, 2.2). Of these, the left, right, and anterior large plates are of similar sizes, with a maximum length of ~3.3cm and a maximum width of ~1.3 cm; the posterior one is significantly smaller, with a maximum length of ~2.0cm and a maximum width of ~0.6cm (Fig. 2.1, 2.2). The 28 small plates do not appear significantly different from one another in size, having a maximum length of ~2.7cm and a maximum width of ~0.7cm (Fig. 2.1, 2.2). Both large and small plates are overlapped adjacently by narrow lateral extensions (Fig. 2.3, 2.4). Most of the small plates as well as the anterior and posterior
large plates have furrowed folds that initiate from their outer margins (Fig. 2.1–2.4); these folds are absent from the left and right large plates (Fig. 2.1, 2.2, 2.5, 2.6). The longest of these furrowed folds reaches up to almost half the total plate length (Fig. 2.1–2.4). Clusters comprising up to 12 scale-like nodes develop on the surfaces of all large and small plates (Fig. 2.1– 2.10). Although irregularly distributed, these nodes do share regular orientation with their tips projecting inward toward the central opening (Fig. 2.7–2.10). Most of these nodes are less than 2mmin diameter, but a few reach between 3mmand 5mm (Fig. 2.2–2.7, 2.9, 2.10). Of these, smaller nodes are found on all large and small plates (Fig. 2.2–2.6, 2.8), while larger ones are only present on the anterior, left, and right large plates (Fig. 2.1– 2.3, 2.5, 2.6), absent from the posterior one (Fig. 2.1, 2.2, 2.4, 2.8). Rows of similarly sized triangular spines, less than 1mmin length, develop along the inner edges of all plates (Fig. 2.1, 2.2, 2.3–2.6); up to eight of these spines are present on the four large plates (Fig. 2.1, 2.2, 2.3–2.6), while just up to three are found on
Figure 2. The single specimen of the new radiodontan oral cone described in this paper (NIGPAS 162529), counterpart only, from the Wulongqing Formation, Cambrian Series 2, Stage 4, Gaoloufang, in Kunming, eastern Yunnan Province, South China. (1) Photograph of entire specimen; (2) interpretative drawing of entire specimen; (3) anterior large plate and small plates; (4) posterior large plate and small plates; (5) left large plate and small plates next to it; (6) right large plate and small plates next to it. (7–10) Close-ups of scale-like nodes on large plates in (3–6), respectively. al1–al7 = first to seventh small plates intercalated between the anterior large plate and the left large plate; ap = anterior large plate; ar1–ar7 = first to seventh small plates intercalated between the anterior large plate and the right large plate; co = central opening; es = lateral extensions of plates; f = furrowed folds; is = inner spines of plates; ln = large scale-like nodes; lp = left large plate; ls = lateral spines of plates; pl1–pl7 = first to seventh small plates intercalated between the posterior large plate and the left large plate; pp = posterior large plate; pr1–pr7 = first to seventh small plates intercalated between the posterior large plate and the right large plate; rp = right large plate; sn = small scale-like nodes. (1–6) Scale bars = 10mm; (7–10) scale bars = 2mm.
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