BAIRDIIDAE, Sars, 1888

Forel, Marie-Béatrice, Poulet-Crovisier, Nathalie, Korat, Lidija & Maddocks, Rosalie F., 2024, Ornate Bairdiidae (Ostracoda) in 3 dimensions: exploring carapace morphology and pore canals of Triebelina van den Bold, 1946, Nodobairdia Kollmann, 1963 and Mirabairdia Kollmann, 1963, Comptes Rendus Palevol 23 (11), pp. 137-159 : 153-154

TRIASSIC BAIRDIIDAE

The virtual cleaning of all specimens has revealed the presence of canals in different areas of the valves.In some areas, dissolution occurred and can be easily recognized as corresponding to groups of holes of different sizes underlain by disturbed sediment. The two specimens of N. mammillata are the most significant with the most abundant pores being preserved.We recognize three types of pores: NPC, pustule-related pores, and marginal pores that may have carried eyelash setae. Most of them are filled with sediment that is clearly recognizable from the valve wall by its distinct contrast ( Fig. 10B, C, F).

Normal pores

They are spread over the surface of each valve. Three main distribution zones are recognized: in association with macro-ornamentation (nodes and ridge), in association with microornamentation on the median surface (reticulation) and through nodules. They are all straight, conical with the larger opening inside. Only a few canals cross the heaviest parts of the subdorsal and subventral ornamentation of N. mammillata ( Fig. 10A). In the largest LV, they are located in the ventro-marginal region of the two median nodes, where they are aligned and organized in a radiating pattern ( Fig. 10A, C). In the carapace, they occur at all subdorsal nodes at both valves ( Fig. 10D, E).

Pore canals associated with subdorsal nodes are labelled from 1 to 6 at LV and 1’ to 6’ at RV, all being in recognizable positions regarding nodes ( Fig. 10A, D, E). The smallest specimen lacks the systems 3/3’ and 5/5’, possibly indicating that they may appear later in the ontogeny of the species. Among the few works that discussed pores in Bairdiidae, Maddocks (2013) mentions that pores of different sizes occur in adults, the largest being those that appeared earlier in the development of the species. In the present case, pore systems 4, 5 and 6 in the adult LV ( Fig. 10A) are large and roughly similar in size. Additional tiny structures are visible within the subdorsal nodes but the resolution hampers on the determination of their nature. Specimens of N. mammillata illustrated in Kristan-Tollmann (1978) show unrimmed pores of type A’ located between the subdorsal nodes ( Fig. 1M). These structures are not observed in any of the two specimens studied, most likely because of preservation and/or resolution.

In N. mammillata and M. pernodosa , pores are more densely seen in association with reticulation in the median area ( Fig. 10A, D, E, G). This pattern differs from what has been observed in Triebelina where pores appear less abundant in this area. However, in the three Triassic specimens studied, the pores appear to be intrasolar, which probably means that the supposed sola are compound with poorly developed second-order muri within. M. pernodosa displays one pore canal going through a nodule ( Fig. 10G). The study of complete and better preserved Mirabairdia specimens will be necessary for further discussion and comparison.

Nodular pores

The lateral surface of N. mammillata displays at least 14 nodules in a symmetrical pattern between RV and LV (Fig. 7). The 3D tomography reveals that these nodules are actually hollow and penetrated by tiny pore canals that can only be fully studied with higher resolution scans (Fig. 8H, I). They can easily be recognized in several of the published specimens, for instance in Dépêche & Crasquin-Soleau (1992). It is uncertain whether the pores illustrated byKristan-Tollmann (1978) from the Carnian of Italy ( Fig. 1M) correspond to these nodular pores; she illustrated such pores at the base of the two median subdorsal nodes, where they are not seen in the present analysis. This disparity needs to be verified with high resolution investigation of well-preserved specimens. The level of significance of this pattern for N. mammillata also remains to be investigated. Other species such as Nodobairdia verrucosa Kollmann, 1963 seem to also display such structures, but until type specimens are re-analysed, it is hard to determine whether the pattern of nodular pores is of specific or supra-specific significance.

Marginal pores

The largest LV of N. mammillata displays a series of narrow canals aligned along the anteroventral margin ( Fig. 11). These structures are elongate in coronal view and small round cavities in axial view. They cannot be tracked along their entire length through the valve thickness because of their small diameter that is close to the resolution limit of the CT-scan. However, their position perpendicular to the valve margin and their regularly spaced disposition reminds radial pore canals.