The distribution of Triebelina raripila and Carinocythereis carinata (Ostracoda) from the Middle Miocene of the Central Paratethys and their palaeogeographic implications

Late Middle Miocene (Upper Badenian) strata of the Fore-Carpathian Depression of Poland yield a shallow-water ostracod fauna which contains the species Triebelina raripila (G. W. Müller, 1894) and Carinocythereis carinata (Roemer, 1838). The palaeobiogeographic distribution of the two main species suggests, that in the late Middle Miocene, Central Paratethys was still connected to the Mediterranean, although still separated from the Eastern Paratethys and from southeastern Eurasia. The continuous occurrence of Triebelina raripila and Carinocythereis carinata in the Mediterranean basins, from the Early Miocene to Recent, indicates that marine conditions existed throughout, thereby allowing them to survive the Late Miocene salinity crisis.


INTRODUCTION
Triebelina van den Bold, 1946 is an ornate bairdiid genus regarded by some authors (e.g. van Morkhoven 1963; Keij 1974Keij , 1976Teeter 1975;Tabuki & Nohara 1990) as being confined to tropical and subtropical, shallow marine environments, principally associated with coral reefs. Its Recent representative which lives in the Mediterranean, Triebelina raripila (G. W . Miiller, 1894) is regarded as an endemic form. A previously unknown occurrence of this species in the Middle Miocene of the Fore-Carpathian Depression in southern Poland, once part of the Central Paratethys, provides an opportunity to verify its ecological requirements. The coexistence of Carinocythereis carinata (Roemer, 1838) with Triebelina raripila in the Middle Miocene of the Fore-Carpathian Depression, provides new data for the reconstruction of the Neogene palaeogeography of this area.
The material described here is housed at the Institute of Paleobiology of the Polish Academy of Sciences in Warszawa (abbreviated ZPAL).

MATERIAL
In the Fore-Carpathian Depression of southern Poland, which represents the northern margin of the Central Paratethys, Triebelina raripila (G. W . Muller, 1894) occurs throughout the Middle Miocene. A single specimen was found in Lower Badenian (corresponding to the Langhian) silty sediments of the Korytnica Bay, in an outcrop situated on the southern slope of the Holy Cross Mountains (Baluk & Radwanski, 1977) (Fig.  1). The Korytnica Bay Middle Miocene section consists of a variety of lithologies (e.g. sands, silts, limestones), which contain ostracods, although in variable abundance (Szczechura & Pisera, 1986). The presence of Globigerinoides, praeorbulinids and large foraminifers, present in the deposits of the Korytnica Bay, indicates an Early Badenian age for these deposits (Papp et al., 1978;Rogl & Brandstatter, 1993).
The Lower Badenian microfauna of the Central Paratethys apparently represents a tropical (or subtropical) environment, whereas the Upper Badenian portion in this area (especially its northern part) is interpreted as a temperate one. Szczechura (1982Szczechura ( , 1986Szczechura ( , 1994Szczechura ( , 1996 identified these microfaunas as belonging to the Globigerinoides and Globigerina ecozones, respectively.

RELATIONSHIP BETWEEN TRIEBELINA RARIPILA (MijLLER, 1894) AND TRIEBELINA BOLDI KEIJ, 1955
Triebelina boldi Keij, 1955, originally described from the Lower Miocene of the Aquitanian Basin, differs from Triebelina raripila (G. W . Miiller, 1894) (originally referred to as Bairdia raripila) from the Tyrrhenian Sea, mainly on outline and in the ornamentation of the left valve (Keij, 1976). The left valve of Triebelina boldi is a little higher and less elongated than in Triebelina raripila; the length/height ratio is 1.8-1.9 for Triebelina boldi while 2.0 for Triebelina raripila. Moreover, the 'carina' of the right valve of Triebelina boldi is less prominent than in Triebelina raripila. Keij (1976) also states that Triebelina boldi is the ancestor of Triebelina raripila and that both species belong to the same lineage, probably stemming from the Late Oligocene Paranesidea Maddocks, 1969. A similar view was adopted by Malz and Lord (1988).
A comparison of specimens from the Middle Miocene of the Fore-Carpathian Depression, referred here to Triebelina raripila (PI. 1, figs 1-7), as well as those Upper Miocene specimens belonging to that species from Turkey (Doruk, 1974) and its Recent representatives from the Aegean and the Adriatic Seas (see Barbeito-Gonzalez, 1971;Uffenorde, 1972; and from my own collections (PI. 1, fig. 8) provides evidence that length/height ratio does vary and even may overlap with those of Triebelina boldi. Even within Recent specimens from a single population the length/height ratio ranges between 1.6 and 2.3; at the same time, the 'carina' in the right valve is quite variable. Similar size variations may also be seen among specimens of the same sample from the Upper Badenian of Poland (PI. 1, figs 1, 3, 5 & 7). For these reasons I agree with Nascimento (1988) and Ducasse and Cahuzac (1997) and regard Triebelina boldi Keij, 1955, as a junior synonym of Triebelina raripila (G. W . Miiller, 1894). Malz and Lord (1988), on the other hand, regarded them as separate species.
Listed below is a complete synonymy of Triebelina raripila (G.

SPATIAL AND TEMPORAL DISTRIBUTION OF CARZ-NOCYTHEREZS CARZNA TA (ROEMER, 1838)
Carinocytherereis carinata (Pl. 1, figs 9, lo), was described by Roemer (1838) as Cytherina carinata from the Pliocene of northern Italy. According to Carbonel (1977), this species appeared first in the late Middle Miocene of northern Italy, and in Liguria and Piedmont of the Western Alps. During the Late Miocene, its range was extended to the Mediterranean, where it still lives today (Fig. 3). Carinocythereis carinata entered the Atlantic coasts of Europe during the Pliocene. In addition to the distribution mentioned by Carbonel (1977), Carinocythereis carinata is now known to occur in the Early Miocene and the late Middle Miocene of Turkey (GokGen, 1984;Safak & Nazik, 1994) as well as in the late Middle Miocene (Upper Badenian) of the Central Paratethys (Steininger, 1977;SokaE, 1979;Jii'iCek & Riha, 1991;Szczechura 1996). From the late Middle Miocene of the Central Paratethys, it occurs in the Transcarpathian Basin of the Czech Republic (Brestenska & JiiiCek, 1978;JiiiCek, 1983), in northeastern Bulgaria (Tzankov et al., 1965) and southern Poland (Fore-Carpathian Depression) (Szczechura, 1996).  (Roemer, 1838); taken from Carbonel (1977), and supplemented by my own data. Arrows indicate probable directions of species migrations.

DISCUSSION
Triebelina van den Bold, 1946 is represented by more than a dozen species, ranging from the Eocene to the Recent. The Recent forms are known mostly from shallow, tropical to subtropical waters in the Indo-Pacific and Atlantic Oceans, principally from coral-algal reefs. The distribution and the environmental preferences of Triebelina raripila, however, are different. This species prefers (today as well as in past occurrences) a rather temperate climate and a sandy marine environment with algae and/or Posidonia. Maddocks (1 969) grouped this species, together with Triebelina reticulopunctata Benson, 1959 which is described from the eastern Pacific Ocean (coasts of California), as the representatives of the genus Triebelina known from temperate latitudes. Of interest is that Valentine (1976) found Triebelina reticulopunctata (a taxon very similar to Triebelina raripila) within the Pliocene ostracod biofacies of the southwestern part of North America, which he attributed to a warm-temperate marine climate. Hartmann (1988) mentions Triebelina reticulopunctata Benson, 1959 within ostracod species which have an East Pacific-Indo-West Pacific distribution; according to Hartmann (1988) this species is also known from the Eocene of France.
Of interest is that the tropical species Triebelina serfata Triebel, 1948 invaded the eastern areas of the Mediterranean from the Indian Ocean (McKenzie, 1986;Malz & Lord, 1988), (probably) via the Suez Canal, while Triebelina raripila is still restricted to the Mediterranean. This implies particular preferences of Triebelina raripila for its environment and explains its palaeodistribution, especially its restriction to Europe.
Provincialism of Neogene faunas in Europe has been observed by a various authors. Tzankov et al. 's (1 965) examination of the Neogene microfossils (including foraminifers and ostracods) of Bulgaria allowed them to distinguish two Middle Miocene biogeographic provinces; viz. the north-western and northcentral province, which he named 'viennois', and north-eastern province, named 'crimeen-caucasien'.
Yassini's (1986) study of Neogene palaeobiogeography of the Eastern Paratethys identified different biogeographic provinces. According to this author (Yassini, 1986, fig. I), there were two provinces (i.e. western and eastern) within the Paratethys, with a boundary placed at the western margin of the Black Sea. The eastern province included the Eastern Paratethys, while the western province contained the Western Paratethys as well as the Central Paratethys. Yassini (1986), however, also suggested separating these provinces from the Mediterranean. Khalaf (1986) identified provincialism for the Middle Miocene shallow-water ostracod faunas by recognizing different biofacies in the Mediterranean and in southern Eurasia.
All these observations should help us to better understand Neogene palaeogeography, and the distribution of ostracods in the Middle Miocene in particular. As such, the differences between the southwestern European and central European forms from those of the eastern parts of Europe and southeastern Eurasia are confirmed.

CONCLUSIONS
The palaeobiogeographic distribution of Triebelina raripila (G. W. Muller) indicates that in the Neogene (including the late Middle Miocene) this species was broadly distributed in Europe, encompassing the Central Paratethys. It was restricted (as it is now) to this broad area (now forming Europe) and is thus regarded a relict rather than an endemic form in the Mediterranean Sea.
The spatial and temporal distribution of Carinocythereis carinata (Roemer) supports the above conclusions concerning the extent of the late Middle Miocene marine basins, including the Central Paratethys as well as southern Europe, thus suggesting exchange of microfauna between these areas. In addition, there is a synchronous appearance of Carinocythereis carinata in the upper part of the Middle Miocene in the Central Paratethys and in the western Alps (northern Italy), while the first appearance of both species (i.e. shallow-water ones), occurs in the Early Miocene of the Mediterranean basins.
The above conclusions, concerning the extent of the Middle Miocene marine basins in Europe, which are based on the distribution of common, shallow-water ostracod species, are in agreement with those arrived at using deep-water ostracods as recognized in the Middle Miocene of the Central Paratethys (Szczechura, 1994(Szczechura, , 1995. The separation of the Neogene, and especially of the Middle Miocene, Paratethyan basins (including both the Central Paratethys and Eastern Paratethys) from the Mediterranean, as suggested by Benson (1976), Rogl & Steininger (1984, Briggs (1995) and others, is questioned by the present study. While these authors' suggestions may be valid for Sarmatian palaeogeography, additional confirmation is required through further studies.
The continuous occurrence, from the Early Miocene to the Recent, of Triebelina raripila and Carinocythereis carinata in the Mediterranean basins, indicates that marine basins persisted thereby allowing these species to 'survive' the Late Miocene salinity crisis.