Pseudomacrocypris? kerabani Forel

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 : 50-52

Pseudomacrocypris? kerabani Forel sp. nov.

urn:lsid:zoobank.org:act:57649028-73AB-43AE-B320-0FE94576E4C3

Fig. 11 B–G

Pontocypris ? sp. pars – Kristan-Tollmann et al. 1991a: 165, pl. 2, fig. 11.

Pontocypris ? sp. – Mette & Mohtat-Aghai 1999: 53, pl. 2, fig. 8.

non Pontocypris ? sp. – Kristan-Tollmann et al. 1991a: 165, pl. 7, fig. 5.

Diagnosis

A species with truncate subtriangular outline, with low anterior and posterior maximum of curvature and offset overlap along dorsal and ventral borders.

Etymology

From the novel Kéraban-le-Têtu, by Jules Verne, that describes the adventures of a Turkish tobacco seller, Kéraban, around the Black Sea.

Material examined

Holotype

ROMANIA • 1 complete carapace; Black Sea , Romanian Continental Shelf , borehole 817LV, sample CM31C; Rhaetian, Upper Triassic; MNHN.F. F63283 .

Paratype

ROMANIA • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic; MNHN.F. F63282 .

Other material

ROMANIA • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic; MNHN.F. F63284 • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic; MNHN.F. F63285 • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic; MNHN.F. F63287 • 1 complete carapace; same locality as for preceding but sample CM31B; Rhaetian, Upper Triassic; MNHN.F. F63286 • 9 complete carapaces, 2 broken carapaces; same locality as for preceding but samples CM31A, CM31B and CM31C; Rhaetian, Upper Triassic; MNHN.F. F63359 .

Dimensions

Fig. 4A .

Description

Carapace of medium size, dorsally-truncate subtriangular in lateral view, with H max at antero-dorsal angulation, L max around lower ¼ of H max; offset overlap characterized by LV overlaping RV along DB (e.g., Fig. 11B ) and RV overlaping LV along VB ( Fig. 11E ); dorsal margin divided into three parts of similar length, with blunt antero-dorsal and postero-dorsal angulations, the latter poorly expressed in smooth juveniles; ADB gently arched inclined anteriorly with an angle of 30–35°, DB straight, slightly inclined toward PD angulation, thinly overlapped by LV at RV, PDB straight to very tenuously convex in small specimens, bent posteriorly with an angle of ± 40°; AB at the same level or slightly above PB, uniformly rounded, with relatively narrow curvature; PB narrow, rounded to bluntly angulate, with maximum close to ventral margin; ventral margin long and gently convex, with thin overlap of RV on LV in center and shallow concavity anteriorly in some specimens (e.g., Fig. 11C, G ); surface smooth; inner structures not visible.

Occurrence

Kössen Formation, Northern Calcareous Alps, Tyrol, Austria, Rhaetian, Upper Triassic (KristanTollmann et al. 1991a; Mette & Mohtat-Aghai 1999); Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).

Remarks

Pseudomacrocypris ? kerabani sp. nov. has previously been pictured from the K̂ssen Formation outcropping in Tyrol ( Kristan-Tollmann et al. 1991a; Mette & Mohtat-Aghai 1999), where it was attributed with doubt to the genus Pontocypris Sars, 1866 . One of the two specimens from the Rhaetian of Austria shown in Kristan-Tollmann et al. (1991a; pl. 7, fig. 5) is excluded because of its lateral outline and much larger dimensions. Pseudomacrocypris Michelsen, 1975 is characterized by a right over left valve overlap and a central adductorial muscle field of rosette shape made of 5–6 spots ( Michelsen 1975; Kaye 1965; Maddocks 1991). Although the dentate and tripartite hinge of Pseudomacrocypris is unusual for Pontocyprididae (Maddocks 1991) , the muscle-scar pattern as well as the nature of the overlap led Maddocks (1991) to consider that Pseudomacrocypris and Propontocypris might be synonymous, and re-attributed Pseudomacrocypris to the family Pontocyprididae . Maddocks (1991: 41) summarized the common characters between Pseudomacrocypris and Propontocypris as follows: laterally compressed carapace, subtriangular to subovate in lateral view, tiny size (L = 0.41 mm), smooth exterior with numerous tiny normal pore canals, right valve overlap, straight dorsal valve-contact line and deep vestibules. However, Pseudomacrocypris is kept as a separate genus because of its unusual hinge and age (Early Jurassic to Early Cretaceous in Maddocks 1991). Only complete carapaces have been found in the present analysis, which unfortunately precludes the close observation of hinge and AMS patterns. However, the offset overlap of RV over LV along the ventral margin and LV over RV along DB is unusual for both genera, but Pseudomacrocypris is preferred here because of the age and presence of right over left valve overlap, although partial. Pseudomacrocypris ? kerabani sp. nov. differs from P. cf. subtriangularis Michelsen, 1975 in Kristan-Tollmann et al. 1991 from the Rhaetian of Tyrol ( Kristan-Tollmann et al. 1991a) in being more slender, with narrower AB, less pointed PB and RV overlapping LV only along VB. It also differs from Pseudomacrocypris sp. from the same level by having a less rounded ADB and narrower AB with the maximum of curvature located more ventrally. Pseudomacrocypris ? kerabani sp. nov. also differs from the widespread Jurassic P. subtriangularis (e.g., Sivhed 1980; Harloff & Jäger 1994; Boomer et al. 1998; Cabral et al. 2013) by having its AB located more ventrally and LV overlapping RV along DB.

The H/L diagram of all specimens shown in Fig. 4A documents the occurrence of at least 4 ontogenetic stages, from A-3 to adult. It is noteworthy that the specimen shown in Kristan-Tollmann et al. (1991a) is much larger than all others, including those from the same locality reported by Mette & Mohtat-Aghai (1999). The holotype may be an adult ( Fig. 11C ), with a quite large dispersal of size in adult specimens, while the paratype ( Fig. 11B ) is an A-1 instar. The lateral morphology of Pseudomacrocypris ? kerabani sp. nov. is very conservative through its development, only marked by a slight enlargement of the posterior maximum of convexity and an accentuation of the tripartite division of the dorsal margin.

Figures

Fig. 11 (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. Paracypris sp. 3, right lateral view of a carapace, sample CM31A (MNHN.F.F63281). B–G. Pseudomacrocypris? kerabani Forel sp. nov. B. Paratype, right lateral view of a carapace, sample CM31C (MNHN.F.F63282). C. Holotype, right lateral view of a carapace, sample CM31C (MNHN.F.F63283). D. Right lateral view of a carapace, sample CM31C (MNHN.F.F63284). E. Left lateral view of a carapace, sample CM31C (MNHN.F.F63285). F. Right lateral view of a carapace, sample CM31B (MNHN.F.F63286). G. Right lateral view of a carapace, sample CM31C (MNHN.F.F63287). H. Pseudomacrocypris? sp., left lateral view of a carapace, sample CM31B (MNHN.F.F63288). I–J. Praebythoceratina sp. I. Right lateral view of a carapace, sample CM31B (MNHN.F.F63289). J. Same specimen, dorsal view.K. Triassocythere sp., external view of a left valve, sample CM31C (MNHN.F.F63290). L–M. Judahella andrusovi Kozur & Bolz in Bunza & Kozur, 1971. L. Right lateral view of a carapace, sample CM31C (MNHN.F.F63291). M. External view of a right valve, sample CM31A (MNHN.F.F63292). N–P. Cytheruridae gen. et sp. indet. N. Right lateral view of a carapace, sample CM31C (MNHN.F.F63293). O. Right lateral view of a carapace, sample CM31C (MNHN.F.F63294). P. Right lateral view of a carapace, sample CM31C (MNHN.F.F63295). Q. Praemacrocypris sp., external view of a right valve, sample CM31B (MNHN.F.F63296). R–S. Cardobairdia sp. 1. R. Right lateral view of a carapace, sample CM31B (MNHN.F.F63297). S. Right lateral view of a carapace, sample CM31A (MNHN.F.F63298). T–U. Cardobairdia sp. 2. T. Right lateral view of a carapace, sample CM31A (MNHN.F.F63299). U. Right lateral view of a carapace, sample CM31B (MNHN.F.F63300). Scale bars: 100 µm.

Fig. 4. 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. A. Pseudomacrocypris? kerabani Forel sp. nov. B. Hungarella koessenensis (Mette & Mohtat-Aghai, 1999).