Yunnanopleura accurata ( Bokova, 1985 )
|
publication ID |
https://doi.org/ 10.4202/app.00289.2016 |
|
persistent identifier |
https://treatment.plazi.org/id/03AD87A8-FFA1-6D1D-FF06-FCAC62628727 |
|
treatment provided by |
Felipe |
|
scientific name |
Yunnanopleura accurata ( Bokova, 1985 ) |
| status |
|
Yunnanopleura accurata ( Bokova, 1985)
Fig. 36.
Material.—Several hundred internal moulds with fragments of phosphatized conchs, including figured SMNH Mo160405, 182349–182355, from samples 2A, 1282, K1a/43, K1a/47 (section 2, Fig. 1), 3/0 (section 3, Fig. 3), 4/27.5, 5/0, 5/0.25 (sections 96-4, 96-5, Fig. 2 View Fig ), Nemakit-Daldyn, Medvezhya, lower Emyaksin formations, Anabar Uplift, Siberian Platform, Russia. Correlated herein with the upper Fortunian Stage.
Description.—Low cap-shaped shells with ovoid aperture (length/width ratio ca. 1.5). Apex blunt, smooth, overhangs the apertural margin and projects slightly beyond it. Scales oriented parallel to the apertural margin appear on the shell surface distal to the apex (Fig. 36B 3) and at the subapical apertural margin (Fig. 36H 3).
Remarks.—These fossils were first described by Bokova (1985) as Stenothecoides accuratus Bokova, 1985 , and S. pandus Bokova, 1985 . The material derives from sample 1282, collected by Anatolij K. Val’kov from a section at the mouth of the Kotujkan River in the western Anabar Uplift that is equivalent to section 2 of this report. Bokova’s (1985) fossils are very similar to Yunnanopleura biformis Yu, 1987 , and Y. longidens Feng, Sun, and Qian, 2001a , from South China, which similarly co-occur with scaly shells of Purella (Qian and Bengtson 1989; Feng et al. 2001a; Parkhaev and Demidenko 2010). Yunnanopleura longidens was considered synonymous with Y. biformis by Parkhaev and Demidenko (2010). Thus, Y. accurata ( Bokova, 1985) can be considered as a senior synonym of Y. biformis . Other samples containing Purella antiqua and P. cristata also contain Yunnanopleura shells (SOM 1). Yunnanopleura sp. (Fig. 37) is generally similar to Y. accurata , but has a more extended apex which overhangs the apertural margin. The fossils occur as internal moulds with concentric folds covered with minute tubercules. Yunnanopleura sp. co-occurs with P. cristata (Fig. 35).
Given the widespread co-occurrence of generally higher Purella -like shells with more flattened Yunnanopleura - like forms in Siberia, western Mongolia, France, and South China, and including similarity in their preservation, shell structure, and textures on the surface of internal moulds, it seems likely that both form genera derive from the same, probably Halkieria -like scleritome with two terminal shells and, probably, siphogonuchitid-type sclerites ( Bengtson 1992; Yang et al. 2014).
We hypothesize herein therefore that Purella antiqua and Yunnanopleura accurata , as well as P. cristata and Yunnanopleura sp. , are components of the same scleritomes, respectively P. antiqua and P. cristata , where they represented the opposing, terminal shells/sclerites of a slug-like organism. A polyplacophoran affinity of Yunnanopleura was also discussed by Yu (2014). Without direct evidence from complete maikhanellid scleritomes, however, these forms are described in this report as form taxa under their original or revised generic names as the conchs of singleshelled organisms.
Stratigraphic and geographic range.— Fortunian Stage of Siberia and South China.
| SMNH |
Department of Paleozoology, Swedish Museum of Natural History |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.