Tyrrhenocythere rastislavi, Pipík, 2007

Pipík, Radovan, 2007, Phylogeny, palaeoecology, and invasion of non-marine waters by the late Miocene hemicytherid ostracod Tyrrhenocythere from Lake Pannon, Acta Palaeontologica Polonica 52 (2), pp. 351-368 : 358-360

Tyrrhenocythere rastislavi sp. nov.

Figs. 4G–M, 5E, H 1 , H 2 , K, 6G .

Derivation of the name: After Rastislav (846–870), prince and sovereign of Great Morava.

Type material: Holotype: SNM RP27−9 , a complete LV ♀ and 7 paratypes: SNM RP26−16 − 1 , LV ♂; SNM RP27−10 , LV ♀; SNM RP27−11 , LV ♂; SNM RP27−12 , LV ♀; SNM RP27−13 , RV ♀; SNM RP27−14 , RV ♂; SNM RP27−15 , RV ♀.

Type locality: Pezinok, clay pit, Danube Basin; coordinates—48 ° 16’720’’ N and 017 ° 16’340’’ E.

Type horizon: Pannonian, zone E, late Miocene, Neogene.

Material.— 39 adult valves.

Diagnosis.— Tyrrhenocythere rastislavi sp. nov. differs from T. transitivum sp. nov. in having fully developed Tyrrhenocythere “brushes” on AM and PM, and by its low posterior. It differs from T. incerta Olteanu, 1989 (in Olteanu 1995: pl. 26: 2) in having posterior process on the PVM of the LV.

Description.—LV ♀ (holotype): AM symmetrically curved; ADM curved without a visible anterior angle; DM right straight and sloping toward posterior; posterior angle clearly well visible, tapered; PM curved, slightly oblique and lower than AM; strongly rounded PVM with posterior processes; VM right, slightly concave before the middle; outline rectangular; maximum height at anterior, just behind the eye tubercle.

RV ♀ : AM symmetrically curved; DM long and largely curved; only the posterior has a marked angle; PM strongly curved; PVM rounded with distinctive posterior processes; VM curved in the anterior third then straight; outline sub−rectangular; maximum height before the lengthwise mid−point.

Sexual dimorphism: obvious; males longer with elongated rectangular valves and long DM.

Muscle scars: consisting of a vertical row of five scars (the second from top divided into two), with three additional anterior scars ( Fig. 5H 1 ).

Normal pore canals: open.

Hinge (amphidont): the hinge ( Fig. 5K, H 2 ) of the LV is composed of an elongated anterior socket; a square tooth that continues into a smooth bar that is thickened slightly posteriorly; an elongated posterior socket that is dorsally crenulated, opening toward the interior; a tiny tooth in the middle of posterior socket. The hinge of the RV has a strong, elongated tooth divided into two lobes; a square socket; straight, smooth groove; an elongated, kidney−shaped posterior tooth dorsally denticulated with five elements.

Ornamentation: the ornamentation changes from outer margin to the central area; polygonal fossae on outer margin without reticulation of second order become filled with circular to semicircular pits toward the centre; the polygonal fossae disappear toward the central area becoming pits; ornamentation absent along the anterior; strong ventral rib; an anterior rib starts in ADM and extends along the entire AM; it terminates on centro−ventral margin below the ventral rib; short, weak ribs are developed on the entire AM between the anterior rib and the ordinary polygonal fossae; the ribs represent the reinforced outer lamella in the position of the main canal joining distal MPC which are visible on surface as tiny riblets between anterior rib and external AM; similar ribs and riblets are developed on PVM; one to three short spines are present on the PVM; eye tubercle smooth; weak pore conuli occur more frequently on the anterior part of the valve than on the posterior.

Marginal zone: inner lamella large with a series of parallel striae; inner margin parallel with outer margin; 9 “brushes” on AM; each “brush” is composed of 7 to 10 canals, the last “brush” on ADM with 2–3 canals; “brushes” developed on AM and PM ( Fig. 6G ); MPC short and straight on centro−ventral margin; large zone of fusion, irregularly shaped between the “brushes”; irregular, sinusoidal line of concrescence.

Discussion.— Tyrrhenocythere rastislavi sp. nov. is smaller, and lower at the posterior, than T. transitivum sp. nov. ( Fig. 7 ). The female LV of T. incerta from the Dacian of the Dacian Basin is more rectangular, elongated and without a posterior process on the PVM ( Olteanu 1995: pl. 26: 2).

Stratigraphical and geographical range.—This species was found only in the Pannonian clay deposits in Pezinok

Figures

Fig. 5. Late Miocene hemicytherid ostracods from the layer 36+37A in Pezinok, Slovakia. A–C, I, L. Tyrrhenocythere transitivum sp. nov. A. RV♂, paratype, SNM RP27−21, external lateral view. B. LV♂, paratype, SNM RP27−18, external lateral view. C. LV♀, paratype, SNM RP26−4−4, external lateral view. I. LV♀, paratype, SNM RP27−19, internal lateral view; I1, central muscle scars; I2, detail of hinge. L. RV♀, paratype, SNM RP27−22, internal lateral view, detail of hinge. D. Tyrrhenocythere sp. 1, RV, SNM RP27−2, external lateral view; D1, SEM photo; D2, valve in transparent light. F. Tyrrhenocythere sp. 2, RV♀, SNM RP28−2, external lateral view. G, J. Tyrrhenocythere pezinokensis (Jiříček, 1985). G. LV♀, SNM RP27−8, internal lateral view, G1, central muscle scars; G2, detail of hinge. J. RV♀, paratype, SNM RP27−5, internal lateral view, detail of hinge. E, H, K. Tyrrhenocythere rastislavi sp. nov. E. RV♂, paratype, SNM RP26−16−1, external lateral view. H. RV♀, paratype, SNM RP27−15, internal lateral view; H1, central muscle scars; H2, detail of hinge. K. LV♀, paratype, SNM RP27−12, internal lateral view, detail of hinge.

Fig. 1. A. Palaeogeographical map of Europe in the upper Miocene (9.5 Ma) (after Steininger and Rögl 1985). B. Lake Pannon in a time of maximum flooding surface in Pannonian zone E (Spiniferites paradoxus Biochron) (after Kováč 2000).

Fig. 2. Geographical sketch (A) and lithological col− umn (B) of Pezinok clay pit (Pipík 1998). C. Detail of the sequence with Tyrrhenocythere mirror swamps and shallow water sedimentation on the bord of freshwater− /miohaline lake (Baráth et al. 1999).

Fig. 6. Marginal pore canals on anterior margin and their transformation from straight Hemicytheria arrangement to brush−like Tyrrhenocythere one. A. Hemicytheria reniformis (Reuss, 1850), Hemicytheria folliculosa (Reuss, 1850), Hemicytheria omphalodes (Reuss, 1850), original by author. B. Hemicytheria biornata (Zalányi, 1944), original by author, Hemicytheria maeotica Olteanu 1989 after Olteanu and Vekua (1989). C. Hemicytheria major Sokač, 1972. D. Hemicytheria marginata Sokač, 1972 after Sokać (1972). E. Tyrrhenocythere transitivum sp. nov. F. Tyrrhenocythere pezinokensis (Jiříček, 1985). G. Tyrrhenocythere rastislavi sp. nov. original by author.

Fig. 7. Length (l) and height (h) ratio of early Tyrrhenocythere species from Pezinok (Danube Basin). The male valves are longer than the female ones.