Mirabairdia, Kollmann, 1963

Forel, Marie-Béatrice & Grădinaru, Eugen, 2020, Rhaetian (Late Triassic) ostracods (Crustacea, Ostracoda) from the offshore prolongation of the North Dobrogean Orogen into the Romanian Black Sea shelf, European Journal of Taxonomy 727, pp. 1-83 : 42-43

Mirabairdia sp.

Fig. 9P

Material examined

ROMANIA • 1 LV; Black Sea , Romanian Continental Shelf , borehole 817LV, sample CM31A; Rhaetian, Upper Triassic; MNHN.F. F63258 .

Dimensions

L = 687 µm; H = 419 µm; H/L = 0.61.

Occurrence

Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).

Remarks

Only one LV of the present species was found, in sample CM31A, which hampers its attribution to any known species. It is close to Triebelina sp. F in Bolz 1971 from the Rhaetian, Late Triassic of Tyrol ( Bolz 1971a), later re-attributed to the newly erected Triebelina (Nodobairdia) nodata Bolz, 1971 ( Bolz 1971b) . However, our specimen is significantly smaller than the specimens illustrated in Bolz (1971a, 1971b), which all exceed 1 mm in length; it also differs by having a weaker marginal ridge only expressed along the ventral margin and thorns instead of knots marking the marginal ridge, some possibly being bifid (the lack of spines on the medio-lateral surface may relate to preservation). These differences may be related to ontogeny, Mirabairdia sp. possibly being a young instar of T. (Nodobairdia) nodata Bolz, 1971 as shown by its size. Although the ontogeny of T. (Nodobairdia) nodata Bolz, 1971 was not discussed in detail, this hypothesis might be substantiated by the precision made by Bolz (1971b: 224) that the marginal ridge is only expressed along the ventral margin on small specimens, where it is short and narrow; this corresponds to the type of ridge visible in Mirabairdia sp. Similarly, Bolz (1971b) indicates that in small specimens, the thorns are already strong and long, which is the case in Mirabairdia sp. However, the seemingly bifid nature of some thorns in Mirabairdia sp., as well as the specimen being slightly higher than specimens of the same length listed in Bolz (1971b), lead us to keep this species in open nomenclature until more material can resolve this doubt. Mirabairdia sp. can also be compared to M. longispinosa Kristan-Tollmann, 1978 from the Cordevolian, Early Carnian, Late Triassic of the Cassian Formation ( Kristan-Tollmann 1978) by its much thinner lateral spines.

Figures

Fig. 9 (opposite page). SEM micrographs of ostracods from borehole 817 Lebăda Vest, drill core CM31, western portion of Black Sea shelf, Rhaetian, Late Triassic. All specimens are housed in the collections of the Muséum national d’histoire naturelle, Paris, France (MNHN). A. Isobythocypris sp., right lateral view of a carapace, sample CM31C (MNHN.F.F63245). B–I. Isobythocypris atalantella Forel sp. nov. B. Holotype, right lateral view of a carapace, sample CM31B (MNHN.F.F63246). C. Same specimen, ventral view. D. Paratype, right lateral view of a carapace, sample CM31B (MNHN.F.F63247). E. Right lateral view of a carapace, sample CM31B (MNHN.F.F63248). F. Right lateral view of a carapace, sample CM31B (MNHN.F.F63249). G. Right lateral view of a carapace, sample CM31C (MNHN.F.F63250). H. Right lateral view of a carapace, sample CM31B (MNHN.F.F63251). I. Same specimen, dorsal view. J–M. Lobobairdia salinara Kollmann, 1963. J. External view of a right valve, sample CM31B (MNHN.F.F63252).K. External view of a left valve, sample CM31B (MNHN.F.F63253). L. External view of a left valve, sample CM31B (MNHN.F.F63254). M. External view of a left valve, sample CM31C (MNHN.F.F63255). N. Lobobairdia? sp. 1, right lateral view of a carapace, sample CM31B (MNHN.F.F63256). O. Lobobairdia sp. 2, right lateral view of a carapace, sample CM31C (MNHN.F.F63257). P. Mirabairdia sp., external view of a left valve, sample CM31A (MNHN.F.F63258). Q–U. Petasobairdia amazonella Forel sp. nov. Q. Right lateral view of a carapace, sample CM31C (MNHN.F.F63259). R. Right lateral view of a carapace, sample CM31A (MNHN.F.F63260).S. Paratype, right lateral view of a carapace, sample CM31B (MNHN.F.F63261). T. Same specimen, dorsal view. U. Right lateral view of a carapace, sample CM31B (MNHN.F.F63262). Scale bars: 100 µm.