Bairdianella cuspis Buschmina 1970

Bairdianella cuspis Buschmina, 1970

Fig. 11P

Bairdianella cuspis Buschmina, 1970: 73, pl. V fig. 2.

Bairdianella cuspis – Kotschetkova & Janbulatova 1987: pl. 24 fig. 1. — Zhuravlev & Sobolev 2019: figs 4i–j. – Sobolev 2020: figs 5–10.

CHINA • 1 complete carapace (Fig. 11P); Blue Snake section, Tangbagou Formation, sample 19BAI 03; P6M 3973 • 25 complete carapaces; Blue Snake section, Tangbagou Formation, samples 19BAI 01-03, 19BAI 05, 19BAI 37, 19BAI 39, 19BAI 44. All from the Tournaisian, early Carboniferous.

RV: L = 460–575µm, H = 188–247µm, H/L = 0.37–0.45.

LV: L = 460–587 µm, H = 201–255 µm, H/L = 0.38–0.48.

Our material is smaller than the holotype shown in Buschmina (1970: pl: 5 fig. 2) with L = 625µm, H = 325 µm, H/L = 0.52. Specimens shown in Kotschetkova & Janbulatova (1987: pl. 24 fig. 1) from Mugodzhary, Western Kazakhstan and Sobolev (2020: figs 5, 9–10)) from Pechora Uplift, Russia, have a similar size to our material with respectively L = 532µm, H = 250 µm and H/L = 0.47 and L = 580µm, H = 280 µm, H/L = 0.48. However, the specimen shown in Zhuravlev & Sobolev (2019) from North Ural is slightly larger than the present material with L = 580µm, H = 275µm and H/L = 0.47 but still smaller than the holotype in Buschmina (1970). The size variations in our material indicate that at least two stages are present and may correspond to juveniles, compare to the holotype in Buschmina (1970), but the wide distribution of the dimensions of the specimens does not allow to clearly discriminate them.

Five species have been mentioned as Bairdianella aff. cuspis in papers discussing Devonian– Carboniferous ostracod faunas, they are summarized in Table 3.

Based on specimens shown in these different contributions, the main differences between these species and Bairdianella cuspis Buschmina, 1970 seem to be weak variations of the length of the carapace, concavity at VB, degree of postero-dorsal angulation, posterior end more or less rounded and AVB sometimes truncated (visible only on Bairdianella sp. A, aff. cuspis Buschmina, 1970 in Casier et al. 2004). Specimens of Bairdianella aff. cuspis Buschmina, 1970 sensu Kotschetkova & Janbulatova 1987 in Casier et al. (2002), Bairdianella sp. A, aff. cuspis Buschmina, 1970 in Casier & Préat (2003) and Bairdianella sp. B, aff. cuspis Buschmina, 1970 in Casier et al. (2004) are also larger than the holotype but others had sizes similar to our material so may also correspond to juveniles. These differences do not seem sufficient to reasonably distinguish these forms from the species described by Buschmina (1970). However, only one specimen is shown in each of these papers with no discussion on possible other specimens, ontogenetic and intraspecific variations within the material or comparisons between these different species. Only a complete review of these taxa, based on close observations of all these specimens, can clarify this major issue. For this reason, they are kept as distinct species.

Gengis horizon, Yeltsov synclinorium, South of Occidental Siberia, early Carboniferous (Buschmina 1970). Berchogur section, Mugodzhary, Western Kazakhstan, Devonian–Carboniferous transition (Kotschetkova & Janbulatova 1987). Kamenka River section, North Urals, Russia, Famennian– Tournaisian, late Devonian–early Carboniferous (Zhuravlev & Sobolev 2019). Yjid-Kamenka river section, Pechora Uplift, Russia, Famennian–Tournaisian, late Devonian–early Carboniferous (Sobolev 2020). Samples 19BAI 01-03, 19BAI 05, 19BAI 37, 19BAI 39, 19BAI 44, Tangbagou Formation, Blue Snake section, Tournaisian, early Carboniferous (this work).