Triassospathodus symmetricus ( Orchard, 1995 )
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publication ID |
https://doi.org/ 10.1186/s13358-022-00259-x |
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persistent identifier |
https://treatment.plazi.org/id/038B1D1D-644C-FF97-FF1B-EB7BD4AAF8DC |
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treatment provided by |
Felipe |
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scientific name |
Triassospathodus symmetricus ( Orchard, 1995 ) |
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Triassospathodus symmetricus ( Orchard, 1995)
Figs. 19H, I–M View Fig ; 23A, B, D, E, H, I View Fig ; 24C, I–Q View Fig
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 View Fig ) 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 ).
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