Columbellidae, Swainson, 1840

Harzhauser, Mathias & Landau, Bernard M., 2021, The Columbellidae (Gastropoda, Buccinoidea) in the Miocene Paratethys Sea — striking diversity of a negelected group, Zootaxa 5025 (1), pp. 1-75 : 63-66

Columbellidae diversity in the Central Paratethys Sea.

In total, 37 columbellid species from 15 genera are documented herein from the Central Paratethys Sea. Earliest occurrences are reported from the Ottnangian stage, which correlates with the middle Burdigalian. Steininger (1973) listed Auingeria bellardii and Mitrella fallax from the North Alpine Foreland Basin in Bavaria. The specimens have not been illustrated and we have not seen the material. Generally, the material from the Ottnangian of the Gernergraben and Kaltenbachgraben is poorly preserved due to deformation and aragonite leaching (own data) and therefore, these identifications are dubious. Harzhauser (2002) documented Graphicomassa polonica , Mitrella fallax and Scabrella haueri from the Karpatian stage (= upper Burdigalian). These findings derive from the Korneuburg Basin, which was a very shallow estuary ( Zuschin et al. 2014). In addition, a deep water record from the Karpatian was described by Harzhauser et al. (2011). The poor preservation, however, does not allow a clear identification. In conclusion, the early Miocene Columbellidae fauna of the Central Paratethys Sea is poorly known due to a strong preservation bias and a general lack of representative deep water faunas. This pattern changes distinctly with the early and middle Badenian (= Langhian), when up to 32 columbellid species are recorded from numerous localities in Austria, Poland, Ukraine, the Czech Republic, Slovakia, Hungary, Romania, Bulgaria, Slovenia, Bosnia and Herzegovina. This high diversity correlates with the Miocene Climatic Optimum ( Zachos et al. 2001) and was observed in numerous other Paratethyan mollusc families ( Harzhauser & Piller 2007). In modern seas, a comparable diversity of Columbellidae is recorded from the Red Sea, which harbours about 23 columbellid species ( Dekker & Orlin 2000). The same number of species is reported from tropical West Africa by Ardovini & Cossignani (2004).

Two major drops in columbellid diversity followed this Langhian optimum. The first severe decline of species diversity occurred at the middle/late Badenian boundary, which corresponds to the Langhian/Serravallian boundary. Only nine species are recorded from upper Badenian deposits. Of these, six species persisted from the early and middle Badenian into the late Badenian. The remaining three species are only known from the late Badenian. This turnover correlates strikingly with the onset of the Middle Miocene Climatic Transition, which resulted in a marked global cooling ( Westerhold et al. 2020). The diversity equals that of the modern Mediterranean Sea which harbours nine native columbellid species ( Coll et al. 2010).

The second severe drop occurred at the Badenian/Sarmatian boundary at around 12.7 Ma. None of the Badenian species crossed this boundary, which is marked by an extinction of about 97% of the marine gastropods in the Central Paratethys ( Harzhauser & Piller 2007). The driving force behind this Badenian-Sarmatian Extinction Event was the strong hydrological isolation of the Paratethys Sea due to geodynamic movements. The Columbellidae are among the few gastropod families that survived this crisis and a single species ( Astyris sarmatica ) occurs in lower Sarmatian strata. In contrast to the Sarmatian Turritellidae ( Harzhauser & Landau 2019) , this Sarmatian columbellid species has no obvious ancestor in Badenian faunas. Similarly, the occurrence of Asytris? agenta in middle Sarmatian strata is rather erratic and its roots are unknown, although a Proto-Mediterranean origin was discussed by Harzhauser & Kowalke (2002). Finally, all marine gastropods including the Columbellidae disappeared from the Central Paratethys with the establishment of Lake Pannon at 11.6 Ma ( Harzhauser & Piller 2007).

Palaeobiogeography

No diversity trend is expressed in the distribution data within the Central Paratethys Sea. Twenty-one species are recorded from the North-Alpine-Carpathian Foredeep, representing the northernmost basin, 25 species are known from the Vienna Basin, which had a central position, and 23 species are described from the Făget Basin, which is a southern basin. Despite this homogeneous diversity, the species distribution indicates a paleogeographic subdivision. Only 46% of the species are found throughout the Central Paratethys. All other species have more restricted geographic occurrences. About 16% of the Badenian species are known so far only from the southern basins such as the southern Pannonian Basin, the Făget Basin and the Dacian Basin. These species are Bellacolumbella embryonalis , Clinurella sophiae, Defensina bucciniformis , Mitrella perminuta and Martaia zitteli . This “southern” group contrasts with about 14% of species, which are only known from the North-Alpine-Carpathian Foredeep and the Vienna Basin. These are Auingeria austriaca, Auingeria bellardii , Auingeria grussbachensis , Mitrella januszkiewiczi and “ Columbella ” paucicostata. Thus, Auingeria seems to have been confined to the northern basins, whereas Defensina was limited to the southern basins. The interpretation of this pattern, which has also been discussed for Turritellidae ( Harzhauser & Landau 2019) , Strombidae ( Harzhauser et al. 2003) , Mitridae ( Harzhauser & Landau 2021a) and Conidae (Harzhauser & Landau 2017) , will need detailed analyses, which are beyond the scope of this paper. Potential explanations are a N-S temperature gradient as discussed by Harzhauser et al. (2003) and/or a paleogeographic separation of these basins, which limited exchange.

The relationship of the Central Paratethyan Columbellidae with the adjacent fauna of the Proto-Mediterranean Sea is weak although open marine connections have been established ( Rögl 1998, Popov et al. 2004). Coeval faunas are known from the Langhian of the Colli Torinesi in Italy ( Sacco 1890b; Ferrero Mortara et al. 1981) and from the Serravallian of the Karaman Basin in Turkey ( Landau et al. 2013). Only 14% of the Paratethyan species are also recorded from the Proto-Mediterranean Sea ( Auingeria austriaca , Costoanachis guembeli , Mitrella complanata , Mitrella petersi , Orthurella convexula ). The faunistic relation with the Eastern Paratethys is even lower. Only Costoanachis guembeli and Mitrella viennensis occur in the Tarkhanian (= Langhian) and Konkian (= Serravallian) of the Eastern Paratethys ( Iljina 1993). There is no relation with the Miocene faunas of the northeastern Atlantic and the North Sea.

Palaeoenvironment

Paleoenvironmental preferences can be deduced for several Paratethyan columbellid species. Graphicomassa polonica , Mitrella elongatissima , Mitrella fallax , Mitrella hilberi , Mitrella complanata , Mitrella viennensis , “ Mitrella ” bittneri , Zafrona sphaerocorrugata and Scabrella haueri are recorded from localities such as Grund, Kleinebersdorf, Gainfarn and Steinebrunn, which yield shallow sublittoral faunas from sandy-silty bottoms, partly with sea grass or in neighbourhood of coastal mudflats ( Zuschin et al. 2004a, 2004b, 2014). Mitrella pseudofallax is recorded from potamidid-dominated mudflats (Kókay 1988). Similarly, the Sarmatian Asytris? agenta and Astyris sarmatica are documented only from shallow marine coastal deposits ( Harzhauser & Kowalke 2002). Therefore, these species are interpreted as inhabitants of inner neritic environments.

This group is opposed by species found exclusively in clays of the Baden Formation, which formed in about 250 m water depth ( Hohenegger et al. 2008). These species are Auingeria bellardii, Bellacolumbella karreri, Bellacolumbella katharinae , Graphicomassa korytnicensis , Mitrella demaintenonae and Orthurella convexula , which are interpreted as inhabitants of middle to outer neritic environments. Offshore environments are also likely for many species described from Coşteiu de Sus by Boettger (1902, 1906) but a sedimentological analysis of this locality is missing so far.

Concluding remark

This study adds about 20% of new species to the previously known columbellid fauna of the Paratethys Sea. This distinct increase is not based on new discoveries in the field and new collections, but results from a careful revision of museum material that has been collected already during the 19 th century. Therefore, our contribution highlightens the importance of museum collections to reconstruct past biodiversity.