Histriabairdia pontuseuxinusensis Forel, 2020
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publication ID |
https://doi.org/ 10.5852/ejt.2020.727.1183 |
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publication LSID |
lsid:zoobank.org:pub:85AF63D9-5E9E-4CE0-AEC6-6F7CC8C4D375 |
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DOI |
https://doi.org/10.5281/zenodo.4340708 |
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persistent identifier |
https://treatment.plazi.org/id/2A9EE0A7-227E-41AC-840C-3F3F93A26790 |
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taxon LSID |
lsid:zoobank.org:act:2A9EE0A7-227E-41AC-840C-3F3F93A26790 |
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treatment provided by |
Plazi |
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scientific name |
Histriabairdia pontuseuxinusensis Forel |
| status |
gen. et sp. nov. |
Histriabairdia pontuseuxinusensis Forel View in CoL gen. et sp. nov.
urn:lsid:zoobank.org:act:2A9EE0A7-227E-41AC-840C-3F3F93A26790
Fig. 8 View Fig G–O
Pustulobairdia subparallela – Harloff & Jäger 1994: pl. 2, figs 7–8. [not Kristan-Tollmann, 1970]
Diagnosis
Dorsal margin tripartite and lateral surface spinose except on the smooth, laterally compressed anteroventral and postero-ventral surfaces, anterior margin subvertical.
Etymology
From Pontus Euxinus , one of the Latin names for the Black Sea, where borehole 817LV was drilled.
Material examined
Holotype
ROMANIA • 1 complete carapace; Black Sea , Romanian Continental Shelf , borehole 817LV, sample CM31B; Rhaetian, Upper Triassic; MNHN.F. F63238 View Materials .
Paratype
ROMANIA • 1 LV; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63239 View Materials .
Other material
ROMANIA • 1 LV; same locality as for holotype but sample CM31C; Rhaetian, Upper Triassic; MNHN.F. F63233 View Materials • 1 LV; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63237 View Materials • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63234 View Materials • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63236 View Materials • 1 RV; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63235 View Materials • 5 complete carapaces; same locality as for preceding but samples CM31A, CM31B and CM31C; Rhaetian, Upper Triassic; MNHN.F. F63351 View Materials .
Dimensions
See Fig. 3E View Fig .
Description
Carapace subrectangular, large, inflated laterally except along compressed antero-ventral and posteroventral margins; carapace preplete with H max located at antero-dorsal angulation; L max located below mid-height; dorsal margin long and tripartite at both valves; LV larger than RV, overlapping it along dorsal margin with maximum along DB and ventral margin with maximum at oral concavity; DB long (43–55 % of L max), straight at RV and straight to slightly convex at LV, slightly inclined posteriorly (between 20° in small specimens and 5° in largest forms); ADB shorter (34–43 % of L max), concave at both valves, more strongly in adults that in younger instars; PDB short (8–20 % of L max), steeply bent posteriorly (from 60° to close to vertical in smallest instars) with terminal concavity more clearly expressed in adults; antero-dorsal and postero-dorsal angulations rounded; AB large and subvertical, with apex located in upper third of H max; AVB underlined by series of marginal denticles on both valves and bordered by a laterally compressed area; PB narrower, with maximum of convexity in lower third of H max on both valves, underlined by a narrow laterally compressed zone; 9 to 10 marginal denticles aligned along PVB, one located above PB; ventral margin long and sinuous with oral concavity located in front of mid-L, bordered by a laterally compressed zone that extends from anterior maximum of convexity to posterior one, attenuated at oral concavity; laterally inflated surface covered with spinose pustules arranged concentrically parallel to free margins except on smooth compressed zones along antero-ventral and postero-ventral margins; antero-ventral and postero-ventral margins bordered by row of sharp spines, length of which decreases ventrally, their number increasing through ontogeny; in inner view, calcified lamella large along anterior and posterior margins, weaker along oral concavity, vestibulum large; central muscle scar not visible; hinge not visible and bairdoppilate auxiliary structure absent.
Occurrence
Tyrol, Austria, Hettangian, Early Jurassic ( Harloff & Jäger 1994); Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Remarks
The short spines across the lateral surface of Histriabairdia pontuseuxinusensis gen. et sp. nov. are reminiscent of those in the Palaeozoic genus Pustulobairdia Sohn, 1960 . Pustulobairdia subparallella Kristan-Tollmann, 1970 was described from the Ladinian, Middle Triassic, of the Dolomites, Italy ( Kristan-Tollmann 1970) but lacks AD angulation, so that the DB and ADB are in line. On the contrary, specimens attributed to P. subparallella from the Hettangian, Early Jurassic, of Tyrol ( Harloff & Jäger 1994) have a well-expressed AD angulation on both valves, also expressed at young stages, similarly to in the Black Sea material. Therefore, this Jurassic material is not conspecific with P. subparallella ,which is restricted to the Ladinian of the Dolomites. Conversely, specimens from the Hettangian are attributed to Histriabairdia pontuseuxinusensis gen. et sp. nov. The surface ornamentation of H. pontuseuxinusensis gen. et sp. nov. is reminiscent of that in Anchistrocheles sp. 1 from the Carnian of Turkey ( Forel et al. 2019a), but this Carnian species is significantly smaller (L = 463 µm, H = 275 µm) and shorter (H/L = 0.6), with smaller and more abundant pustules covering the entire lateral surface. The very narrow calcified inner lamella of the only valve (LV) from the Carnian of Turkey implies that the specimen is a relatively young instar. Histriabairdia spinosa (Sheppard in Brand, 1990) gen. et comb. nov. from the Bathonian, Middle Jurassic, of France ( Brand 1990) is also defined by its pustulose surface, but it differs from H. pontuseuxinusensis gen. et sp. nov. by having much smaller spines.
The large distribution of the H and L scatter plot indicates the co-occurrence of several ontogenetic stages for Histriabairdia pontuseuxinusensis gen. et sp. nov. ( Fig. 3E View Fig ). However, the rarity of specimens of intermediate dimensions does not reasonably allow a discrimination of the stages. The holotype ( Fig. 8 View Fig L–M) and the paratype ( Fig. 8 View Fig N–O) are among the largest specimens and are thus considered as adults. The ontogenetic development of H. pontuseuxinusensis gen. et sp. nov. is marked by the progressive strengthening of the lateral spines, densification of the surface coverage, widening of the lateral compressions along AVB and PVB, an increase in the number of marginal spines and an upward migration of the PB. Jurassic specimens have a slightly higher H/L ratio for both valves ( Fig. 3E View Fig ), which may relate to distinct environmental conditions.
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