Meitanillaenus, Chang, 1974

Lee, Dong-Chan, 2013, Late Ordovician trilobites from the Xiazhen Formation in Zhuzhai, Jiangxi Province, China, Acta Palaeontologica Polonica 58 (4), pp. 855-882 : 862-864

Meitanillaenus ? sp.

Fig. 6A–E .

Material.—Seven cranidia (repository numbers: NIGP−151995–151999).

Remarks.—This species, only known from cranidial material, bears morphological features that are comparable to those of Meitanillaenus Chang, 1974 , Failleana Chatterton and Ludvigsen, 1976 , Sangzhiscutellum Lin, 1987 , and Ciliscutellum Lin, 1987 . Zhou and Zhen (2008: 271) transferred all the Chinese species that had been previously assigned to Meitanillaenus into Lamproscutellum Yin, 1980 , confining the stratigraphical occurrence of the former to the Silurian and the latter to the Ordovician. Cranidial morphology of Lamproscutellum is, however, readily distinguishable from that of Meitanillaenus by the presence of a paradoublural line, rounded antero−lateral corner of glabella, three distinct pairs of glabellar furrows, distinct fixigenal impression, and eye ridge (see Yin 1980: pl. 1: 4–6). The following species transferred to Lamproscutellum do not bear these features; Meitanillaenus luerkouensis Liu in Zhou et al. (1977: pl. 72: 1, 2; see also Liu 1982: pl. 229: 2, 7 and Tripp et al. 1989: fig. 8i); Meitanillaenus flabelliforme Liu (1982 : pl. 230: 5, 6); and Scutellum (Planiscutellum) wuxiensis Lee (1978 : pl. 107: 1, 2). From Meitanillaenus ? sp., differs M. luerkouensis in having an anterior cranidial border along the entire anterior margin and lacking a glabellar crest; M. flabelliforme in having a longer anterior branch of facial suture and more posteriorly located palpebral lobe; S. (P.) wuxiensis in having a transversely wider occipital ring and more strongly divergent axial furrows.

Tripp et al. (1989) questionably transferred Meitanillaenus luerkouensis into Failleana . Lane and Siveter (1991) treated Failleana as a junior synonym of Meitanillaenus without an explanation. Chatterton and Ludvigsen (2004, see also Adrain et al. 1995) disagreed to this synonymy because Failleana has a wider axis, distinct ventral projection of axial furrows (called “omphalus”), and a backwardly convex posterior margin of the rostral plate. Comparison of cranidia of Meitanillaenus −allied species and Failleana ( Table 3) shows that (i) Meitanillaenus has a narrower occipital ring (maximum transverse width 47% of width across cranidial antero−lateral corner versus 64% in Failleana ), (ii) an exsagittally longer palpebral lobe (31% of cranidial length versus 23% in Failleana ), and (iii) a transversely narrower glabellar constriction (39% of width across cranidial antero−lateral corner versus 50% in Failleana ). Therefore Meitanillaenus should be treated as a separate genus from Failleana .

From cranidium of Meitanillaenus binodosus Chang, 1974 , the type species from the Silurian of Guizhou (see Chang 1974: pl. 82: 12), all the Ordovician Chinese Meihttp://dx.doi.org/10.4202/app.2010.0036

tanillaenus −allied species differ in having an anterior cranidial border, much less distinct fixigenal impression, more distinctly impressed anterior course of axial furrows, and more sharply turned anterior branch of facial suture. It cannot be ruled out that all the Ordovician species may not be allied with Meitanillaenus .

Lin (1987) erected Ciliscutellum and Sangzhiscutellum from the Lower Silurian of Hunan; the type species of the latter genus is Meitanillaenus flabelliforme . Their cranidial architecture ( Lin 1987: pls. 1, 2) greatly resembles that of the Ordovician Meitanillaenus species including Meitanillaenus ? sp. described herein, except for the presence of relatively distinct eye ridge. Due to the absence of pygidial information, these Ordovician specimens from Zhuzhai cannot be confidently assigned to either genus and are questionably placed in Meitanillaenus .

Figures

Fig. 6. Late Ordovician trilobites from Xiazhen Formation near Zhuzhai, Yushan County, China. A–E. Meitanillaenus? sp. A. NIGP−151995, cranidium from locality 3; dorsal (A1) and anterior (A2) views. B. NIGP−151996, cranidium from locality 3; dorsal (B1) and lateral (B2) views. C. NIGP−151997, cranidium from locality 3, dorsal view. D. NIGP−151998, cranidium from locality 3, dorsal view. E. NIGP−151999, cranidium from locality 3, dorsal view. F. Amphilichas sp., NIGP−152000, cranidium from locality 3; dorsal (F1), oblique posterior (F2), anterior (F3), and lateral (F4) views. G. Eokosovopeltis sp., NIGP−152001, pygidium from locality 2, dorsal view. H. Eokosovopeltis cf. currajongensis (Edgecombe and Webby, 2007), NIGP− 152002, pygidium from a limestone layer overlying the mudstone at locality 1, dorsal view. I. Styginidae indet. sp. B, NIGP−152003, hypostome from locality 3, ventral view. J. Styginidae indet. sp. A, NIGP−152004, incomplete thoraco−pygidium with four thoracic segments from locality 3, dorsal view. K, M. Asaphidae indet. K. NIGP−152005, free cheek from locality 2, dorsal view. M. NIGP−152006, pygidium from locality 3, dorsal view. L. Nileus sp., NIGP−152007, articulated specimen minus free cheeks from locality 2; posterior (L1), anterior (L2), lateral (L3), and dorsal (L4) views. Scale bars 2.5 mm, except E, F, I 1 mm; G, H, K 5 mm.