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Journal of Paleontology 92(1):87–98
cannot mirror the original condition. Each annulus is about 30~50 μm in length. Plates are 30 μm in length and 25 μmin width. There are an estimated 50 plates in each row. Platelets are 7 μm in diameter. Microplates are 11 μm in diameter.
Genus Austroscolex Müller and Hinz-Schallreuter, 1993 Type species.—Austroscolex spatiolatus
Hinz-Schallreuter, 1993 Austroscolex sinensis new species
urn:lsid:
zoobank.org:act:F83B376E-7B04-4C32-AB76- F02456F72928 Figures 7, 8
Holotype.—Specimen NIGP160456 (Fig. 7.2), a fragment more than 3mm long.
Diagnosis.—Broad annuli with two rows of circular plates of equal size; plates sparsely distributed; median annular zone wide with densely spaced platelets; intercalary zone indistinct or narrow with densely spaced microplates.
Occurrence.—Conodonts Westergaardodina cf. calix–
Prooneotodus rotundatus Zone, Bitiao Formation, Furongian (upper Cambrian);Wangcun section, Yongshun County, western Hunan, South China.
Description.—Palaeoscolecidswith broad trunk annuli (Figs. 7, 8). Bifurcation of annuli occurs (Fig. 8.1, 8.2). Each annulus with two rows of circular plates of equal size (Figs. 7.4, 8.3, 8.7). On each annulus, the anterior and posterior rows of plates are alternately arranged (Figs. 7.4, 8.3, 8.7). Each plate has one to three central nodes and one circlet of five to eight nodes surrounding the central ones. Plates are sparsely spaced, each surrounded by 10–15 nodular platelets. Intercalary zone is indistinct. Median annular zone is wide, with densely spaced platelets. There are densely spaced microplates along the boundary between two adjacent annuli (Figs. 7.3, 8.7).
Etymology.—Species name derived from the Greek Sin-, with reference to occurrence of Austroscolex species in South China.
Measurements.—Specimen NIGP160456 (holotype; Fig. 7.2) is about 3.12mm long and 756 μm in diameter, with 36 preserved annuli. Specimen NIGP160457 (Fig. 7.1) is about 2.4mm long and 670 μm in diameter, with 22 preserved annuli. Specimen NIGP160495 (Fig. 8.1) is about 2.8mm long and 770 μmin diameter, with 27 preserved annuli. Specimen NIGP165202 (Fig. 8.4) is about 880 μm long and 700 μm in diameter, with seven preserved annuli. SpecimenNIGP165203 (Fig. 8.6) is about 1.5mm long and 800 μm in diameter, with 18 preserved annuli. Each annulus is about 100 μm long. Plates are 35μmindiameter. There are an estimated 30–40 plates in each annulus. Platelets are 6μm in diameter. Microplates are 14μmindiameter.
Comparisons.—Austroscolex was previously reported only from the middle Cambrian of Australia, including Austroscolex primitivus Müller and Hinz-Schallreuter, 1993 and Austroscolex
Müller and
spatiolatus Müller and Hinz-Schallreuter, 1993. Austroscolex primitivus has a single row of plates on each annulus, whereas A. spatiolatus has two rows of plates on each annulus, one row with smaller plates than the other. The specimens illustrated here are assigned to Austroscolex because they have broad annuli (about 100 μm), two rows of plates, narrow or indistinct intercalary zone, and broad median annular zones. They differ from A. spatiolatus in that the two rows of plates are of equal size and are thus assigned to a new species here. Austroscolex sinensis differs from Hunanscolex Duan and Dong, 2013 in that the latter has a relatively wide intercalary zone filled with densely spaced microplates.
Origin of cycloneuralians
Previously reported microscopic cycloneuralians from the Cambrian strata of South China includeMarkuelia, Eopriapulites, Eokinorhynchus, and microscopic palaeoscolecids. Eopriapulites and Eokinorhynchus were reported from the Fortunian Stage and are the oldest known cycloneuralians. Markuelia was reported fromthe middle to late Cambrian (Dong et al., 2004; Zhang et al., 2011). Three-dimensionally phosphatized and microscopic palaeoscolecids are widely distributed, from the early Cambrian (Zhang and Pratt, 1996) to late Cambrian (this paper; also see Duan et al., 2012; Duan and Dong, 2013). Microscopic cycloneuralians from the Cambrian of South
China can be divided into two groups according their trunk armor. Palaeoscolecids and Eokinorhynchus rarus have heavily armored trunk annuli, while Markuelia hunanensis and Eopriapulites sphinx have smooth trunk annuli with no armor. In general, trunk armor functions as a defense organ. The earliest animals might have been unarmored. With increasing minerals in the oceans and increasing ability to utilize these minerals, some animals evolved trunk armor, while others remained unarmored. The appearance of predators accelerated the evolution of trunk armor. With increasing predation pres- sure, those animals with trunk armor were able to protect themselves from predators and unfavorable environment, and were thus nature selected to survive. Thus, cycloneuralians with armor might be comparatively more derived than those with no armor. As to the microscopic cycloneuralians, it is proposed here that palaeoscolecids and Eokinorhynchus might be more derived than Markuelia and Eopriapulites. It has previously been proposed that ancestral cycloneur-
alians were macroscopic, priapulid-like, and introvert-bearing, and in this respect, macroscopic palaeoscolecids might represent ancestral cycloneuralians or even ancestral ecdysozoans (Budd, 2001; Harvey et al., 2010). We propose that Eopriapulites might be more suitable than palaeoscolecids to be a repre- sentative of ancestral cycloneuralians or even ancestral ecdy- sozoans, not only because Eopriapulites appears more primitive than palaeoscolecids, but also because Eopriapulites is known earlier in geological time—Eopriapulites occurred in the Cambrian Fortunian Stage, while palaeoscolecids first occurred in Cambrian Stage 3 (Liu et al., 2014). Since Eopriapulites was part of the Cambrian Fortunian small shelly faunas, it is pro- posed herein that cycloneuralians should have originated in the Cambrian Fortunian small shelly fossil faunas, or even earlier. Due to its primitive trunk armor and old geological age,
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