Bairdiacypris argonautaii 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 : 19-22

Bairdiacypris argonautaii Forel sp. nov.

urn:lsid:zoobank.org:act:4AF32BE0-8E7A-4ABD-BCC8-42D2F99F451F

Fig. 6 F–O

Bairdiacypris? aff. Bairdiacypris sp . A Bolz – Mette & Mohtat-Aghai 1999: pl. 3, fig. 7.

Diagnosis

A new species ovoid in shape, with overlap interrupted at AVB and PVB, RV preplete and LV amplete to postplete.

Etymology

From the ancient Greek Αργοναῦται, Argonautai, referring to the mythological heroes, the argonauts, who travelled the Black Sea searching for the golden fleece.

Material examined

Holotype

AUSTRIA • 1 RV; Northern Calcareous Alps , Tyrol; Kössen Formation, Rhaetian, Upper Triassic ( Mette & Mohtat-Aghai 1999: pl. 3, fig. 7); University of Innsbruck, Austria.

Paratypes

ROMANIA • 1 RV; Black Sea , Romanian Continental Shelf , borehole 817LV, sample CM31A; Rhaetian,

Upper Triassic; MNHN.F. F63201 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63202 .

Other material

ROMANIA • 1 complete carapace; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31A; Rhaetian, Upper Triassic; MNHN.F. F63203 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63204 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63206 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63207 • 1 complete carapace; same locality as for preceding but sample CM31B; Rhaetian, Upper Triassic; MNHN.F. F63205 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F. F63208 .

Dimensions

See Fig. 3B .

Description

CARAPACE. Very large, massive, ovoid in lateral view with L max below mid-H at both valves; LV larger than RV, overlapping it all along dorsal margin with maximum at DB, and along VB, overlap interrupted along AVB and PVB; biconvex in dorsal view with W max behind L max, overlapping area seemingly flat; surface smooth.

RV. Subrectangular with H max at antero-dorsal angulation; dorsal margin tripartite with dulled angulations; PDB straight to slightly convex in young instars, short (12–21% of L max) and steeply sloping to PB (60–70°); DB straight, moderately sloping to postero-dorsal angulation (10–20°) with length increasing through ontogeny; ADB straight, long, with relatively constant length through ontogeny (37–45% of L), sloping toward AB with an angle ranging from 20° to 40°; AB large, relatively bairdiid in shape, with maximum of curvature at or slightly below mid-H; ventral margin long and sinuous; AVB steeply raised

to AB and largely convex to close to vertical in young instars; VB with tenuous oral concavity mid-L; PVB short, convex, only slightly raised to PB; PB at lower ¼ of H max, relatively narrow, gently rounded to only slightly bairdiid in shape.

LV. Ovoid with H max behind mid-H in large forms, at antero-dorsal angulation in younger instars; dorsal margin gently rounded with dulled angulations in young instars that are unrecognizable in larger instars and adults; ventral margin long and straight to gently convex.

Occurrence

Kössen Formation, Northern Calcareous Alps, Tyrol, Austria, Rhaetian, Upper Triassic (Mette & MohtatAghai 1999); Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).

Remarks

Bairdiacypris argonautaii sp. nov. is higher and shorter than “ Bairdia ” raetica Bolz, 1971 from the Rhaetian interval, Late Triassic, of Tyrol ( Bolz 1971b); it also differs by the antero-ventral and postero-ventral interruption of the overlap, dorsal margin tripartite with pronounced antero-dorsal and postero-dorsal angulations and anterior margin larger. Bairdiacypris argonautaii sp. nov. is also close to Bairdiacypris sp. in Kristan-Tollmann et al. 1979 from the Rhaetian, Late Triassic, of Iran (KristanTollmann et al. 1979) but the only illustrated Iranian specimen shows a continuous overlap along AVB and PVB and a posterior maximum of convexity located higher resulting in subsymmetric anterior and posterior borders. Bairdiacypris argonautaii sp. nov. is also morphologically close to Bairdia cf. peneovoidea Bolz, 1971 from the Rhaetian, Late Triassic, of Iran ( Kristan-Tollmann et al. 1979) but has a more rounded AVB and a larger PB. The dimensions of all specimens attributed to B. argonautaii sp. nov. are plotted in Fig. 3B . The largest specimen known to date is a right valve from the Rhaetian of Tyrol ( Mette & Mohtat-Aghai 1999). All specimens found in the present investigation are distributed across at least six successive ontogenetic stages, all smaller than the specimen from Mette & Mohtat-Aghai (1999). The ontogenetic development of B. argonautaii sp. nov. is mainly marked by an enlargement of the posterior end of the carapace.

Figures

Fig. 6 (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. Bairdia sp. 8, same specimen as in Fig. 5U, dorsal view. B–C. Bairdia sp. 9. B. Right lateral view of a carapace, sample CM31C (MNHN.F.F63198). C. Same specimen, dorsal view. D–E. Bairdiacypris multidentata Bolz, 1971. D. Right lateral view of a carapace, sample CM31A (MNHN.F.F63199). E. Right lateral view of a carapace, sample CM31B (MNHN.F.F63200). F–O. Bairdiacypris argonautaii Forel sp. nov. F. Paratype 2, right lateral view of a carapace, sample CM31A (MNHN.F.F63201).G. Paratype 1, external view of a right valve, sample CM31B (MNHN.F.F63202). H. Right lateral view of a carapace, sample CM31A (MNHN.F.F63203). I. Right lateral view of a carapace, sample CM31A (MNHN.F.F63204). J. Right lateral view of a carapace, sample CM31B (MNHN.F.F63205). K. Same specimen, dorsal view. L. Right lateral view of a carapace, sample CM31A (MNHN.F.F63206). M. Right lateral view of a carapace, sample CM31A (MNHN.F.F63207). N. Same specimen, dorsal view. O. Right lateral view of a carapace, sample CM31A (MNHN.F.F63208). P. Bairdiacypris sp. in Forel et al. 2018, external view of a right valve, sample CM31A (MNHN.F.F63209). Q. Bairdiacypris sp. 1, external view of a right valve, sample CM31A (MNHN.F.F63210).R. Bairdiacypris sp. 2, external view of a right valve, sample CM31C (MNHN.F.F63211). S. Bairdiacypris sp. 3, external view of a right valve, sample CM31B (MNHN.F.F63212). T–U. Bairdiacypris? sp. 4. T. Right lateral view of a carapace, sample CM31B (MNHN.F.F63213). U. Right lateral view of a carapace, sample CM31A (MNHN.F.F63214). 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. 5 (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. Acratia cf. Acratia sp. A in Bolz 1971, right lateral view of a carapace, sample CM31B (MNHN.F.F63181). B. Acratia sp. 1, external view of a right valve, sample CM31C (MNHN.F.F63182). C. Acratia sp. 2, right lateral view of a carapace, sample CM31A (MNHN.F.F63183). D–G. Bairdia sp. 7 in Mette & Mohtat-Aghai 1999. D. External view of a right valve, sample CM31B (MNHN.F.F63184). E. External view of a right valve, sample CM31A (MNHN.F.F63185). F. External view of a left valve, sample CM31B (MNHN.F.F63186). G. Same specimen, inner view. H–I. Bairdia cf. parva Ainsworth, 1987. H. Right lateral view of a carapace, sample CM31B (MNHN.F.F63187). I. Right lateral view of a carapace, sample CM31B (MNHN.F.F63188). J–K. Bairdia sp. 3. J. Right lateral view of a carapace, sample CM31A (MNHN.F.F63189). K. Right lateral view of a carapace, sample CM31C (MNHN.F.F63190). L–N. Bairdia sp. 4. L. Right lateral view of a carapace, sample CM31C (MNHN.F.F63191). M. Right lateral view of a carapace, sample CM31B (MNHN.F.F63192). N. Same specimen, dorsal view. O–Q. Bairdia sp. 5. O. Right lateral view of a carapace, sample CM31C (MNHN.F.F63193). P. Same specimen, dorsal view. Q. Right lateral view of a carapace, sample CM31B (MNHN.F.F63194). R. Bairdia sp. 6, external view of a left valve, sample CM31C (MNHN.F.F63195). S–T. Bairdia sp. 7. S. Right lateral view of a carapace, sample CM31B (MNHN.F.F63196). T. Same specimen, dorsal view. U. Bairdia sp. 8, right lateral view of a carapace, sample CM31B (MNHN.F.F63197). Scale bars: 100 µm.