Ceraurinus zhuzhaiensis, Lee, 2013

Lee, Dong-Chan, 2013, Late Ordovician trilobites from the Xiazhen Formation in Zhuzhai, Jiangxi Province, China, Acta Palaeontologica Polonica 58 (4), pp. 855-882 : 876-877

Ceraurinus zhuzhaiensis sp. nov.

Figs. 3D , 10.

Etymology: After Zhuzhai village where the sampling quarries are located.

Holotype: NIGP−152016, articulated specimen from locality 2.

Type locality: Locality 2, about 60 m northwest of Zhuzhai, Yushan County. GPS coordinate is 28 ° 34’23.27” N and 118 ° 20’16.50” E .

Type horizon: Xiazhen Formation, Upper Ordovician, Dicellograptus complexus Graptolite Zone.

Material.—Three articulated exoskeletons, five cephalo−thoraces, four thoraco−pygidia, one cephalon, 12 cranidia, one thorax, one free cheek, and one hypostome (repository numbers: NIGP−152015–152028).

Diagnosis.—Species of Ceraurinus possessing three pairs of pygidial pleural ribs with free, blade−shaped antero−most pair and posterior two pairs expressed by smoothly saw−toothed pygidial margin, and pair of weakly−impressed pits on L4.

Description.—Dorsal exoskeleton elliptical in outline and covered with irregularly−distributed granules. Cephalon semi−circular in outline; transverse width 49% of sagittal length. Anterior cranidial border narrow, rimmed, and slightly indented sagittally. Anterior cranidial border furrow and preglabellar furrow merged, moderately impressed but shallower than axial furrow. Axial furrow deep and wide. Glabella sub−rectangular in outline, and slightly expands laterally or forwards in some specimens; maximum transverse width 86% of sagittal length. Central area of glabella moderately crested, which become more raised posteriorly, ending as if a large lobe is developed at posterior end; central area occupies 34% of maximum glabellar width. Three pairs of glabellar furrows present; S1, S2 and S3 equally spaced; S1 runs slightly obliquely backwards, then sharply turns posteriorly, and then merged with occipital furrow; S1 moderately deep and become shallower after turning posteriorly; S2 runs moderately obliquely and then sharply turns posteriorly, and moderately deep and become shallower after turning posteriorly; part of S2 which turns posteriorly much shallower than that of S1; S3 more obliquely directed backwards and become shallower to disappear adaxially; S3 longer than the obliquely−running part of S1 and S2. L1 and L2 sub−quadrate; pair of small pits present middle of L4. Occipital furrow curved forwards sagittally; adaxial two−thirds of the course much shallower than abaxial course. Palpebral lobe crescentic in outline and mid−point located opposite mid−point of L3; palpebral furrow moderately impressed. Preocular area of fixigenae very narrow (tr.) or nearly absent; palpebral area triangular in outline; postocular area sub−rectangular in outline, with relatively short spine at postero−lateral corner; fixigenal field covered with irregularly−dispersed pits. Posterior cranidial border straight, rimmed and obliquely directed forwards; posterior margin broadly indented at mid−length; posterior cranidial border furrow moderately deep, wide, and straight to slightly sinuous; articulating flange narrow and disappears adaxially. Anterior branch of facial suture gently curved forwards; posterior branch runs nearly transverse, and then gently turns posteriorly; facial suture of proparian type.

Librigena small, triangular in outline; librigenal lateral border furrow moderately impressed and merged with axial furrow opposite S1; librigenal field covered with irregularly−dispersed pits.

Hypostome shield−shaped. Anterior lobe of middle body sub−rectangular in outline; posterior lobe small and crescentic in outline. Anterior margin gently rounded; lateral margin strongly curved inwards at mid−point of anterior lobe, strongly projected outwards as shoulder, and then run obliquely straight backwards. Anterior border widens distally and narrows to be absent proximally; lateral border rimmed; lateral border furrows moderately deep and wide. Middle furrow shallow and disappears adaxially.

Thorax of 11 segments. Axis occupies 33% of thoracic width; axial furrow parallel−sided and then gently tapers backwards from the eighth or ninth thoracic segment. Axial ring slightly convex forwards sagittally and distal end curved forwards; axial ring furrow shallows adaxially with distinct elongated (tr.) apodemal pit at distal end. Pleura divided into anterior and posterior pleural band which are strongly convex and elongated triangular in shape, and separated from each other by deep, oblique pleural furrow; band width 37% of pleural transverse width; fulcral node moderately convex and sub−quadrate in outline. Anterior and posterior flange narrow, becoming narrower to disappear at half−way of pleura, and delineated by deep furrow. Pleural spine blade−shaped, and gently curved backwards distally; posterior spines progressively more strongly curved backwards; spine half as long as pleura.

Pygidium sub−elliptical in outline. Three axial rings and terminal piece present; axial ring curved forwards sagittally. Three pleural ribs present; first (from the anterior) pleural rib with pleural bands and fulcral node as in thoracic segments, distally ending with free, strongly curved, blade−shaped spine; second pleural rib with pleural bands but without distinct fulcral node; third rib lacks pleural bands and fulcral node. Lateral and posterior pygidial margin smoothly saw−toothed, corresponding the second and third pleural spines.

Discussion.—The genera of the subfamily Cheirurinae are distinguished from one another chiefly upon the basis of pygidial morphology ( Ludvigsen 1977). Pygidial morphology of Ceraurinus is characterized by a pair of long, curved, carinated first pleural spines, and two pairs of relatively short posterior spines (see Ludvigsen 1977: text−fig. 1). The pygidium of Ceraurinus zhuzhaiensis sp. nov., however, has a non−carinated first spine and saw−toothed pleural margin corresponding the posterior two pleural spines ( Fig. 10B 1 , B 3 , H, N). The carination of other Ceraurinus species is also observed in genal and thoracic pleural spines as well as pygidial pleural spines (see Ludvigsen 1977: pl. 1: 7 for Ceraurinus marginatus Barton, 1913 ), while C. zhuzhaiensis lacks the feature in any of these spines. In addition, C. zhuzhaiensis is characterized by having a pair of small pits on L4. A provisionally associated hypostome ( Fig. 11F) has a shoulder that is narrower and located more posteriorly, and a border that is more narrowly rimmed, compared to those of other Ceraurinus species (see Ludvigsen 1977: text−fig. 3).

Following Ludvigsen’s (1977) treatment of Remipyga as a junior synonym of Ceraurinus, Zhou and Zhen (2008: 242 ; misspelled as C. sinensis ) transferred Remipyga chinensis Ju in Qiu et al. (1983) into Ceraurinus . It is the only Ceraurinus species listed in Zhou and Zhen, 2008 where other Chinese species previously assigned to Ceraurinus are transferred to other cheirurid genera. The sagittally−compressed, poorly−preserved cranidium ( Qiu et al. 1983: pl. 81: 9) exhibits a comparable glabellar morphology of Ceraurinus zhuzhaiensis sp. nov., but it appears to be rather oval than sub−rectangular; the more poorly−preserved pygidium ( Qiu et al. 1983: pl. 81: 10), which has three axial rings and first pleural rib with free blade−shaped spine, appears to have a much wider (tr.) pleural field posterior to the first pleura than C. zhuzhaiensis . Furthermore, C. chinensis occurs in the Wenchang Formation of the Hirnantian age, which is younger than the Xiazhen Formation.

Stratigraphic and geographic range.—Late Ordovician and Jiangxi Province, South China.

Figures

Fig. 3. Reconstruction of new species described from the Late Ordovician Xiazhen Formation; all drawings are not to scale. A. Remopleurides xiazhenensis sp. nov., dorsal view of exoskeleton (A1), and dorsal (A2) and ventral (A3) view of thoracic segments; exact extent of thoracic axial spine in A1 is not known and articulating half ring is reconstructed as if the anterior margin is broadly notched (see text for details). B. Hibbertia aodiensis sp. nov., dorsal view of exoskeleton; pits and caeca are omitted. C. Vietnamia yushanensis sp. nov., dorsal view of exoskeleton (C1) and lateral view of thoracic segments (C2); granules (see Fig. 9N) are omitted. D. Ceraurinus zhuzhaiensis sp. nov., dorsal view of exoskeleton; granules (see Fig. 10B1, B3) are omitted. E. Pliomerina tashanensis sp. nov., dorsal view of cranidium.

Fig. 1. Location of trilobite collecting localities at Zhuzhai, Jiangxi Province, China. GPS coordinate of the locality 2 is 28°34’23.27” N and 118°20’16.50” E. A. The map of China showing the sampling locality (the black rectangle). B. The magnified view of the rectangled area in A. C. Geologic map of the sampling locality.