Triassospathodus symmetricus ( Orchard, 1995 )

Leu, Marc, Bucher, Hugo, Vennemann, Torsten, Bagherpour, Borhan, Ji, Cheng, Brosse, Morgane & Goudemand, Nicolas, 2022, A Unitary Association-based conodont biozonation of the Smithian-Spathian boundary (Early Triassic) and associated biotic crisis from South China, Swiss Journal of Palaeontology (19) 141 (1), pp. 1-61 : 38

Triassospathodus symmetricus ( Orchard, 1995)

Figs. 19H, I–M ; 23A, B, D, E, H, I ; 24C, I–Q

1970 Neospathodus homeri Bender ; p.245, pl. 1, figs. 2, 3, 9, 10.

1970 Neospathodus triangularis Bender ; Sweet, pp. 253– 254, pl. 1, figs. 7, 8.

1973 Neospathodus homeri Bender ; Mosher, p. 171, pl. 20, fig. 14.

1977 Neospathodus homeri Bender ; Goel, p. 1097, pl. 2, figs. 10, 11.

1986 Neospathodus homeri Bender ; Durkoop et al., pl. 20, figs. 9–10.

*1995 Neospathodus symmetricus n. sp.; Orchard, p. 120, 121, figs. 2.6, 2.10–2.13, 2.18.

2004 Neospathodus symmetricus Orchard ; Koike, p. 137, figs. 35–38.

2007b Triassospathodus ex. gr. homeri (Bender) ; Orchard et al., p. 345, fig. 5.5, 5.6.

2009 Triassospathodus ex. gr. homeri (Bender) ; Orchard & Zonneveld, p. 788, fig. 15, parts 38–40.

2011 Neospathodus symmetricus Orchard ; Ji et al., p. 219, figs. 3.5a, b, c.

2014 Triassospathodus symmetricus (Orchard) ; Maekawa & Igo in Shigeta et al., p. 254, figs. 182–185, 186.1–186.3

2015 Triassospathodus symmetricus (Orchard) ; Chen et al., figs. 7.16–7.17, 8.19, 9.15.

2015 Novispathodus abruptus (Orchard) ; Chen et al., figs. 8.2, 9.13.

2018 Novispathodus abruptus (Orchard) ; Maekawa in Maekawa et al., p. 33, figs. 17.22, 17.24, 17.25, 18.4– 18.12, 18.14–18.22, 18.25, 18.28 (only).

2019 Triassospathodus symmetricus (Orchard) ; Chen et al., fig. 4, nr. 8, 1–13, fig. 5, nr. 4 (only)

Number of specimens.>50

Description. Segminate P 1 element with length/height ratio of 2.0–2.5:1 and usually 10–13 subequal, variably fused denticles that become increasingly reclined posteriorly. Straight or arcuate upper margin, subtriangular denticles edges. Te cusp is indistinct, it has as high or slightly higher than the other denticles. Te basal margin is straight anteriorly and may be downcurved posteriorly. Te margin of variably shaped basal cavity is expanded laterally and downturned posteriorly. A basal groove extends from the basal pit to the anterior end. Some specimens develop a midlateral rib.

Remarks. Te elements are similar to Tr. homeri but usually shorter and they lack a ‘true’ denticulate posterior process: in Tr. symmetricus , the basal cavity is more or less rounded posteriorly, whereas in Tr. homeri it tapers posteriorly below the inturned posterior edge of the carina ( Orchard, 1995). Some elements ( Fig. 23B, E, H ) may deserve differentiation in the future as they bear strongly reclined and gradually smaller, posteriormost denticles, as opposed to typical elements of this species.

Occurrence. Almost worldwide distribution. Nanpanjiang basin: North-eastern Vietnam, Bac Tuy Formation, Tirolites cf. cassianus beds ( Shigeta et al., 2014). South China, Luolou Formation (several sections in this paper), Qingyan section, ( Neospathodus homeri Zone, Ji et al., 2011 ); Northern Indian margin: Salt Range, Pakistan (Zone 9, Sweet, 1970). Spiti India ( Goel, 1977), Oman, Jabal Safra ( Orchard, 1995). Japan: Taho limestone (Koike, 2004). British Columbia: Canada ( Keyserlingites subrobustus Zone, Mosher, 1973 ).

Figures

Fig. 19 Novispathodinae from Qiakong,Laren and Lilong. Magnification is ×80.The scale bar is 400 μm. All elements are considered to be P1 elements if not specifically identified otherwise. A Novispathodus cf.brevissimus (Orchard); LIL515C,PIMUZ 39199. B, F Novispathodus brevissimus (Orchard); B LIL515B, PIMUZ 39200; F BAN1, PIMUZ 39201. C Triassospathodus homeri (Bender); LIL515D,PIMUZ 39317. D, H Novispathodus?brevissimus (Orchard); D LIL515D,PIMUZ 39202; H LIL514A, PIMUZ 39203. E Triassospathodus cf.homeri (Bender); LIL515C, PIMUZ 39318. G, K, O–Q Novispathodus n. sp. A; G LIL504,PIMUZ 39251; K LIL504,PIMUZ 39252; O LIL505, PIMUZ 39253; P LIL505, PIMUZ 39254;Q LIL505,PIMUZ 39255. I, L, M, Triassospathodus symmetricus (Orchard); I QIA141, PIMUZ 39336; L LIL512, PIMUZ 39337; M LIL514A, PIMUZ 39338. J Novispathodus ex gr.pingdingshanensis (Zhao & Orchard); QIA138, PIMUZ 39237. N Triassospathodus cf. symmetricus; LIL514B, PIMUZ 39339.R Novispathodus praebrevissimus n.sp; LIL505, PIMUZ 39289

Fig. 23 Novispathodinae from Qiakong,Laren, Shanggang and Lilong. Magnification is × 80.The scale bar is 400 μm. All elements are considered to be P1 elements if not specifically identified otherwise. A, B, D, E, H, I, Triassospathodus symmetricus (Orchard); A, LIL509, PIMUZ 39320; B, LIL509, PIMUZ 39321; D, QIA202,PIMUZ 39322; E,LIL509, PIMUZ 39323;H, LIL509, PIMUZ 39324; I, BAN2, PIMUZ 39325. C, F, G, Triassospathodus homeri (Bender); C, LAR231C, PIMUZ 39310; F, QIA155, PIMUZ 39311; G, SHA318,PIMUZ 39312

Fig.24 Novispathodinae and uncertain from Qiakong,Laren,Shanggang,and Lilong. Magnification is×80.The scale bar is 400 μm.All elements are considered to be P1 elements if not specifically identified otherwise.A, D, G, H Triassospathodushomeri (Bender);A LIL515C,PIMUZ 39313;D QIA155,PIMUZ 39314;G LIL513B,PIMUZ 39315;H LIL515B,PIMUZ 39316.B, E, F Triassospathodus aff.symmetricus (Orchard);B QIA138,PIMUZ 39306;E LIL505,PIMUZ 39307; F QIA136,PIMUZ 39308.C, I–Q Triassospathodussymmetricus (Orchard);C QIA140,PIMUZ 39326;I SHA313,PIMUZ 39327;J QIA143,PIMUZ 39328;K QIA144, PIMUZ 39329;L QIA141,PIMUZ 39330;M LIL515D,PIMUZ 39331;N LIL509,PIMUZ 39332;O LIL513B,PIMUZ 39333;P LIL513B,PIMUZ 39334;Q LIL513A, PIMUZ 39335.R–T Aduncodina unicosta (Ding);R BAN5,PIMUZ 39100;S SHA320,PIMUZ 39101;T SHA318,PIMUZ 39102