Petasobairdia amazonella Forel, 2020

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 : 43-44

Petasobairdia amazonella Forel sp. nov.

urn:lsid:zoobank.org:act:BC1BE3CA-3515-49D8-A4A8-8EABDD0C0EE1

Figs 9 Q–U, 10A–D

Diagnosis

A new species of Petasobairdia , short for the genus, triangular in outline with high anterior border.

Etymology

From Ἀμαζóνες/Amazónes, the legendary tribe of warrior women who, according to tradition, used to live along the Black Sea shore.

Material examined

Holotype

ROMANIA • 1 LV; Black Sea , Romanian Continental Shelf , borehole 817LV, sample CM31C; Rhaetian, Upper Triassic; MNHN.F. F63264 .

Paratype

ROMANIA • 1 complete carapace; same locality as for holotype but sample CM31B; Rhaetian, Upper Triassic; MNHN.F. F63261 .

Other material

ROMANIA • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic; MNHN.F. F63259 • 1 complete carapace; same locality as for preceding but sample CM31A; Rhaetian, Upper Triassic; MNHN.F. F63260 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63263 • 1 complete carapace; same locality as for preceding but sample CM31B; Rhaetian, Upper Triassic; MNHN.F. F63262 • 4 complete carapaces, 1 RV, 1 LV; same locality as for preceding but samples CM31A, CM31B and CM31C; Rhaetian, Upper Triassic; MNHN.F. F63356 .

Dimensions

See Fig. 3G .

Description

Carapace of medium size, sub-square in lateral view, with H max at antero-dorsal angulation and L max below mid-L; LV larger than RV, overlapping it slightly ventrally at ventral concavity and along dorsal margin with laterally compressed overreach along DB; dorsal margin tripartite with rounded angulations at both valves; PDB straight, steep (from 60° in largest specimens to 80° in smallest ones) and short (from 5% of L max in smallest specimens to 20% in larger forms); ADB and DB straight and approximately of same L (40–45% of L max); ADB slope of ±30–40°; DB sloping posteriorly from 10° to 15°; AB large, only poorly tapered ventrally, laterally compressed ventrally, with maximum of curvature slightly below mid-H; ventral margin long and straight with median concavity visible on some specimens; PB narrow, laterally compressed ventrally, with maximum of curvature located in lower ¼ of H max; surface smooth; calcified inner lamella from mid-ADB to mid-PDB, relatively wide along AVB and PVB; large vestibulum along AVB and PVB, narrow in oral area; hinge bar seemingly smooth with anterior and posterior enlarged platforms; AMS field relatively compact, somewhat hastate, located below mid-H and around mid-L, composed of anteriorly incurved row of 3 individual scars and 2 to 3 scars aligned in a short posterior row ( Fig. 10D ).

Occurrence

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

Remarks

The laterally compressed overlap of Petasobairdia amazonella sp. nov. relates it to the Permian species P. silenitiformis ( Kozur, 1985) , P. nantongensis Chen, 1982 and P. subnantongensis Chen in Shi & Chen, 1987 , for instance, but its shortness, with the posterior maximum of convexity located ventrally, providing it with a sub-square outline in lateral view, differ from conditions in all known species. Although poorly preserved, the AMS pattern on the inner surface of the paratype ( Fig. 10D ) only differs from that of P. silenitiformis , which is to our knowledge the only observation of AMS for Petasobairdia , in being more compact and less rounded. In general terms, the outline of P. amazonella sp. nov. is reminiscent of that in Bairdia donzei Herrig, 1979 from the Domerian, Early Jurassic, of Germany ( Herrig 1979a), but this Jurassic species has a longer posterior extremity and its LV is more rounded in outline and lacks the laterally compressed DB. The H/L scatter plot of all specimens of P. amazonella sp. nov. ( Fig. 3G ) records the occurrence of several ontogenetic stages, from A-4 to adult. The holotype ( Fig. 9 S–T) and paratype ( Fig. 10 B–D) are the largest known specimens, but owing to the size difference between the paratype and the LV of the holotype, we consider that the holotype is a submature stage. The development of P. amazonella sp. nov. is marked by the increasing height of the overlap as well as the elongation of the PDB, from 5% of L max in the smallest instar to 27% in the paratype, the largest known specimen to date ( Fig. 3G ).

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.

Fig. 3. Height/length scatter plots of species from borehole 817 Lebăda Vest, drill core CM31, western portion of Black Sea shelf, Rhaetian, Late Triassic. In all diagrams, the dimensions of right (stars) and left (circles) valves of complete carapaces are shown separately and circled or linked. P1 = paratype 1; P2 = paratype 2. A. Bairdiacypris multidentata Bolz, 1971. B. Bairdiacypris argonautaii Forel sp. nov. C. Carinobairdia alpina Kollmann, 1963. D. Ceratobairdia? akhilleusi Forel sp. nov. E. Histriabairdia pontuseuxinusensis Forel gen. et sp. nov. F. Isobythocypris atalantella Forel sp. nov. G. Petasobairdia amazonella Forel sp. nov. H. Paracypris ovidi Forel sp. nov.

Fig. 10 (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–D. Petasobairdia amazonella Forel sp. nov. A. Right lateral view of a carapace, sample CM31A (MNHN.F.F63263). B. Holotype, external view of a left valve, sample CM31C (MNHN.F.F63264). C. Same specimen, inner view, square indicates the area enlarged in D. D. Line drawing of the adductor muscle scar field of the paratype marked in C. E. Rectonariidae gen. 1 in Forel et al. 2019, external view of a right valve, sample CM31C (MNHN.F.F63265). F–G. “Aglaiocypris” sp. F. Right lateral view of a carapace, sample CM31A (MNHN.F.F63266). G. Right lateral view of a carapace, sample CM31C (MNHN.F.F63267). H–N. Paracypris ovidi Forel sp. nov. H. Holotype, right lateral view of a carapace, sample CM31B (MNHN.F.F63268). I. Paratype 2, right lateral view of a carapace, sample CM31B (MNHN.F.F63269). J. Right lateral view of a carapace, sample CM31B (MNHN.F.F63270). K. Paratype 1, right lateral view of a carapace, sample CM31B (MNHN.F.F63271). L. Right lateral view of a carapace, sample CM31C (MNHN.F.F63272). M. Right lateral view of a carapace, sample CM31A (MNHN.F.F63273). N. Same specimen, dorsal view. O. Paracypris cf. Paracypris sp. 1 in Lord & Lambourne 1991, right lateral view of a carapace, sample CM31A (MNHN.F.F63274). P–Q. Paracypris sp. 1. P. Right lateral view of a carapace, sample CM31B (MNHN.F.F63275). Q. Right lateral view of a carapace, sample CM31C (MNHN.F.F63276).R–U. Paracypris sp. 2. R. Right lateral view of a carapace, sample CM31B (MNHN.F.F63277). S. Right lateral view of a carapace, sample CM31C (MNHN.F.F63278). T. Right lateral view of a carapace, sample CM31A (MNHN.F.F63279). U. Right lateral view of a carapace, sample CM31B (MNHN.F.F63280). Scale bars: 100 µm.